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Tech Tuesday: Choosing the right Karting seat

The seat and its supports are often underestimated by chassis tuners and drivers, but on the contrary such elements are a fundamental part of the chassis and determine a lot of the stiffness characteristics of karts.

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Seats come in many different brands, stiffnesses and materials, Giving each one unique characteristics

Various seats and supports

The structure of the seat and its connections to the chassis generate a system which varies sensibly the chassis stiffness. Moreover the material of the seat can vary and so also the stiffness can vary. Glass fibre, Kevlar, carbon or mixtures of these elements, with also different thicknesses of the layers, can generate variations in the torsional flexibility of the chassis in its rear part, since the seat itself will change its stiffness.

For example a carbon fibre seat is, with the same thickness, three times as stiff compared to a glass fibre one. A Kevlar seat is on the other hand much more elastic if compared to a glass fibre one. Costs are also to be considered and, as usual, carbon fibre seats cost at least double a glass fibre one.

With the use of supports it is possible to preload the chassis on one or both sides. Such load will be positioned on the rear axle bearings. Such preload will be obtained by using length of supports of just a few mm superior to the distance between the holes in the seat, where the support is screwed, and the lateral axle bearings. Supports can be bent and twisted together to obtain something very similar to a spring. Straight supports are extremely stiff. In fact a straight support works in compression on the rear axle where it is linked. Such supports are very stiff in compression. On the other hand the same support bent, works in flexion, so has a much higher elasticity and, as said before, works well as a spring, deforming when a sudden bump is hit by a rear tyre, but still creates downward force when it is needed to increase rear grip.

World's biggest kart seat T7 OMG
Proof that your dad can have a go in your kart, the “I won’t fit” excuse just wont cut it here…

Effects of supports on chassis behaviour

The stiffer the seat and its supports and the faster will be the diagonal load transfer to the wheels. In fact the weight of the driver whose effect is also increased by the centrifugal lateral force when running along a bend, is transferred to the rear tyres through the seat and its supports. If no supports are present the chassis will first bend and then only part of the weight will transfer to the rear tyres.

Usually it is best for better performance and faster reaction of the kart to have a quick weight transfer, which means good seat and supports stiffness. On the other hand a very stiff seat and supports system does not absorb any irregularity of track surface. We must not forget that if initially caster of the front internal tyre transfers load to the rear external tyre, it gives back load to front wheels as soon as it is the only rear tyre that touches the ground.

The stiffness of seat and supports permits the rear part of the chassis not to flex too much, so we will have a good lift of the internal rear tyre during a curve. If the chassis bends too much instead, both rear tyres will keep touching the ground generating great under-steer.

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Even when youve done with your seat they can be useful

On the right side of the chassis under the seat we always have two tubes, that are not only connected by the welded tubes, but also by the engine mounts. This determines the fact that the right side of the chassis is stiffer then the left one.

Acting on the seat supports we balance stiffness on the softer left side. If we use an old softened seat, with holes too big for the screws, we will have a low performance chassis. There is nothing worse then a chassis with its seat moving all around. It is also useless to try to set up the chassis with all sorts of regulations, if the area where most of the weight is concentrated deforms easily in any direction.

It is for this reason extremely important to well fix the seat to the chassis with well dimensioned holes, possibly hardened by metal rings, maybe glued to the seat with some resin.

Only when grip is extremely low (dirty or wet tracks) we can use rubber rings that absorb all the forces without loosing connection between the seat and its supports. The best solution, even though more complex, is to have the correct seat for different track conditions. Also some sponge can be used to increase comfort, but with no excess, otherwise we would loose the feeling between our body and the seat-chassis. In fact it is always with your “bottom” that you feel your chassis and understand how to drive it.

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Pistons

Tech Tuesday – Welding

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Tech Tuesday: Carbs

The purpose of a carburettor is to mix the fuel with air which it does by metering fuel through adjustable “jets” and drawing the fuel into a venturi using a vacuum effect caused by air rushing through the venturi.

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We race in X30 and so use the Tillotson HW-27A but these principles apply to other diaphragm carbs – please check your manufacturer’s instructions for specific jet settings, pop-off values and so on.

You will need:

  • A pop-off gauge – ours is from JHC – Hubchen and has a mounting point to keep the carb steady while you work on it
  • Three-in-one oil which is a useful alternative to petrol for checking the ‘wet’ performance of the pop-off needle
  • Carb cleaner
  • Something to hold the carb still if your pop-off gauge doesn’t have one
  • A 8mm socket/t-bar machined to fit in the narrow orifice where the needle seat is located. These are available from major kart shops as “Tillotson sockets”
  • Rebuild kit – for the HW-27A a DG “half” kit or RK “full” kit including inlet needle and seat

Carb 1

We rebuild carbs after every meeting as a matter of course – you will see the reason why from our photos.

To disassemble the carb, start by taking the jets out. Make a note of which jet is which, and which order everything came out. Until you’re familiar with the process you could put the parts down on a piece of plain paper and label each part.

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Despite filtering the fuel there’s still some debris on the small gauze filter, we blow that off with brake cleaner until it’s clean.

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Take the screws out and take the carb apart a bit at a time, shake the fuel out of it and clean it with brake cleaner.

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Take the pump diaphragm off, you can see a circle shape in it and that it’s slightly out of shape on the parts that do the work of pumping, so we’ll change it.

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This is the metering diaphragm – examine it and see what it looks like compared to a new one, whether it still has elasticity and integrity. This one is out of shape around the inner circumference so we’re going to change it.

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The metering needle valve needs to be checked closely, this is the valve that controls the pop-off. We fill it up with two in one oil as it has to be wet, use the pop-off gauge and see where it pops off. In this case it popped at 0.75 bar and was holding pressure at 0.5 bar as recommended by Tillotson. That tells us that the valve is in good condition. It’s doing that consistently as it was a new valve and seat at the last rebuild.

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The pop off pressure is controlled by the spring weight. There are various weight springs available however IAME UK recommends you stick with the standard spring as it gives the best performance across a wide range of conditions.

We’re going to take the needle valve assembly apart anyway to clean and check it. Remove the small screw and take the valve out. You can see the spring, valve and metering arm. Look at the end of the valve and see what kind of condition it’s in. When the pop-off pressure is tested, if the valve is holding pressure it’s safe to assume that the needle valve is in good condition.

Carb 2

Next remove the needle seat with the t-bar that has been machined down to fit in the hole.

Carb 3

Then get the small copper gasket out, this might be fiddly but often you can just tip them out.

At this point it’s completely stripped down. Spray brake cleaner into every orifice, you should be able to see fluid flowing through the high jet and the low jet. Then blow air from a compressor through the orifices.

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Check that the butterfly valve doesn’t open past the middle at full-throttle, if it does, adjust it with the screws.

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When reassembling, remember the gaskets always go beneath the diaphragms. Keep note of the order all the components must be in. If the carburettor goes back together incorrectly then the engine will most likely not start and if it does then it will not run well or in worst case scenario, it will seize!

Carb 4

Tillotson recommended jet settings are:

X30 Senior

Low: 1T

High: 1T 30-35 minutes

X30 Junior

Low: 1T

High: 1T 20-25 minutes

 

This article was originally published in Karting magazine in January 2016

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Axles

Tech Tuesday – Chassis straightening

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Tech Tuesday: Seat mounting and adjustment

The first step when using a new chassis is definitely seat choice. In terms of shape, stiffness, and positioning it is the most important set up choice you can make to a new kart, affecting both performance and comfort of the driver. With the help of one of the most experienced companies specialising in kart and car seats, Tillett, we have started to analyze the parameters that can help obtain maximum results.

History of Tillett Racing Seats

Steve Tillett, the owner of the English firm, started karting in 1978 and from his first races using high grip tyres he soon understood the need to have best possible quality seats to avoid bruised ribs and possibly to improve performance. Since then, Tillett has become synonymous with high quality kart seats growing Year after year from one man operating in a garage, to a company comprising of six factory units totalling 14,000 square feet with a current workforce of 25 and a Tillett dealer in almost countries in the World.

As well working with glass fibre, Tillett also uses exotic composites such as carbon fibre and kevlar; offering lighter, strolnger and more versaitle products. Steve wasn’t going to stop at karts though, expanding into car racing, powerboats, ski bobs. Tillett seats have even helped Mel Clarke win an Olympic Silver Medal in Archery and have featured on the silver screen, in James Bond’s ice racer in Die Another Day, the tank in Goldeneye and the attack sub in GI Joe film.

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Tillett Seats Helped Mel Clarke Win Olympic Silver in 2012

Dimension and shape
The first parameter to take care of is the correct size of the seat. The fit is all about driver preference, some drivers perffering a tighter seat while other some room to breathe. The seat should however, be supportive and a general rule of thumb with the seat is to be able to slide a finger down between the driver and the seat.from the chest down to the hip of the driver. If the seat is too large. The consequent effect will be difficulty in driving since the body is moving left and right around corners, not being able to feel the kart. Also there is the possibility of the driver hurting his or herself through movement in the seat.

A good way to fill up the area between seat and body is to use a closed cell foam until the gap has gone. Don’t over-do it though as too much foam will reduce feeling in the kart. always buy a seat with the best fit possible to reduce use of foam this will reduce the feeliling in the chassis. Of course rib protectors, such as the Tillett R4 Ribtec, as well as protecting, help reduce part of the gap, depending on how thick each protector is.

Tillett-P1-Rib-ProtectorKarol-Basz
A good Rib Protector can help secure the driver in the seat.

Seat position

Three distances need to be measured to fit a kart seat:
• Front to back in the chassis
• Angle or tilt of the seat
• Height

Most kart manufacturers will specify a reccommended seat height – measure from top edge of the seat down to rear axle surface and the distance between the extreme edge of the seat to the front (often two measures are used starting from left and then right), and the front tubing of the chassis. Tillett instead avoids this system as it is linked too much to the shape and size of the seat. Of course it can work well when measurements given by the kart manufacturer are the exact correct ones for the chassis and the seat they supply. However, depending on the driver’s weight and height such measures tend to vary.

seat fit

Tillett suggests using the shortest distance from the back of the seat, from a point 2cm to the side of the spine depression, to the front surface of the axle. The average value of such dimension is 16.5cm, but can be within the range from 13.5 to 20cm. Tilt angle is generally given by the seat itself considering that Tillett seats often have a flat base which keeps the bodyweight of the driver as low as possible within the kart. The angle of the seat can still be varied though. Tillett recommends two angles: 63° from horizontal and 58° from horizontal. 58° helps lower the centre of gravity and helps taller drivers. They a height equivalent to 5mm protruding below the level of the main chassis tubes. This value of course can increase for small drivers, very low grip or wet conditions.

To adjust front to back position keeping height and inclination fixed, Tillett suggests testing on-track chassis behaviour avoiding narrow corners, where the steering system with castor and Ackerman angles will transfer weight from one side to the other and from one end to the other of the chassis. The best thing to do is to feel the balance of the kart with a base set-up along long fast curves, understanding if the chassis oversteers or understeers.Seat stays also have an effect on set-up. One seat stay per side helps lift and unweight the inside rear wheel, whilst pushing down on the outside wheel. Adding more stays per side will stiffen the rear of the chassis keeping it flatter along corners.

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Seat stays act like Torsion Bars stiffening the rear end

Seat stiffness
Tillett has sent us different stiffness seats that we will test and write about in the next issue. Different rigidities of the seats are obtained both using different kinds of glass fibre and resin and also different thicknesses. As the seat is part of the chassis, it determines the overall rigidity, especially of the rear of the kart. Generally Tillett recommends soft seats for low power karts, as these free up the chassis, stopping the inside rear wheel from dragging on the track and absorbing power (rear internal wheel lift earlier and at lower speeds). As the power of the engine increases the additional weight transfer of a slightly stiffer seat may prove advantageous (rear wheel not lifting too early and going back into position quickly for early acceleration).

However on some track surfaces or track conditions it may be better to achieve grip by putting as much of the tyre surface as possible in contact with the track, on others it may be that the only way to get grip is to increase the downward forces that act on the outside tyres. Only Testing can give the ultimate answer!

T Board
To help us with our work we used another interesting product from Tillett, the “T Board”. This instrument is made of glass fibre and carbon fibre and is incredibly strong and light and permits to measure and set precisely three dimensions of the seat: height, inclination and distance between rear axle and back of the seat. As anticipated some chassis manufacturers also specify the two distances from front right and left edges of the seat to the front tube of the chassis, as this can also be important to determine a possible rotation of the seat around its vertical axis and offset the weight of the engine positioned on the right with the driver.

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The T Board makes seat fitting easy

The T Board must be positioned under the chassis and fastened by three clamps which are mounted on the lateral tubes and on the tube beneath the seat. This allows a plane of reference for the height of the seat. Using 2mm and 4mm spacers it is possible to set the minimum height of the seat. An additional instrument can be mounted on the T Board to set the inclination of the seat. It is a bent T shape instrument, which can be regulated in height and lateral length and has a beautiful carbon fibre protractor at its end, which gives back the measure of the angle of the seat. There are two channels for each arm of the T where the clamps can be easily mounted so that any obstruction to the clamps deriving from elements of the chassis such as tubes, brakes, engine mount, etc can be avoided.

Mounting the seat
Before starting to mount our first seat, the flexible T11VG, we measured the position of our old seat and in particular took care to write down the height, 16mm, equivalent to putting four rear sprockets beneath the seat which are each 4 mm thick. The distance between the rear axle and the back of the seat was 17cm with an angle measured by the protractor of 30°. This value must be subtracted from 90°, giving 60° of inclination of the back of the seat (driver back). What was also important to notice was that chassis was set at an average height amongst the three possibilities given on the Tony EVRR. This must be considered every time we measure the seat height, to avoid the seat touching the ground once we lower the chassis. The distance from one setting to the other on the chassis was 8mm. We set the chassis at the lower possible position. As the previous seat was already at minimum height we still needed 8mm more of height of the seat from the ground compared to before.

Since a high centre of gravity is a problem, we decided to increase the inclination to 55° as Tillett recommends. This bends the driver a little bit backward, reducing the height of his centre of gravity. The distance from the rear axle to the back of the seat was set at 15.4cm, which is a low value compared to an average of 16.5cm, but understandable considering the additional inclination given to the seat.

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Engine Cleaning

Tech Tuesday – Carbs

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Tech Tuesday: Axles

It all starts with the right preparation – checking your kart is safe and that nothing is going to impede your rapid progress to the front of the pack. Starting with the axle assembly we’ll go through each element of a well-maintained kart.

This is a key stage of kart preparation done by professional teams between races and test days, and sometimes even on a Saturday night. Mainly you’re checking that the axle assembly is safe, and it also has an effect on performance.

1. This is what the axle looks like at the end of a weekend. It’s dirty and a little bit rusty in places. The scratches are from the brake disc and sprocket carriers and also grub screws. The whole point of removing the axle is to make sure first of all there’s no cracks in it hidden inside the bearings and to clean it and check it over.

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2. The whole point of removing the axle is to make sure first of all there’s no cracks in it hidden inside the bearings and to clean it and check it over. First remove the grub screws as this image shows

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3. Zip tie the brake pedal to keep the brake disc in place while removing the axle.

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4. Removing the axle with a heavy piece of steel machined to fit inside a 50mm axle with 2mm wall thickness.

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5. The brake disc has been retained by the zip tie on the pedal as the axle is slid out. at this point you can remove the rubber bands for the water pump belt and the water pump pulley if used.

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6. Taking the brake disc and sprocket carrier and cleaning out the inside of them. This helps when you come to put them back on.

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7. Photos of the carriers before and after they’ve been cleaned up inside. It’s also a good time to check the retaining bolts are in good condition as sometimes they can be rounded off. Some people lubricate the bolts which helps them get a tighter purchase.

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8. The same process for the inside of the bearings. This is an especially good idea when it comes to reassembly and if you’re cleaning the axle you might as well do the bearings as well.

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9. This is after polishing the axle. We put the axle in a lathe and just got some 250 grit wet and dry paper to polish the axle so that rust spots and blemishes were removed. You don’t have to use a lathe, it can be done by hand quite easily but a lathe speeds it up. Some people have made clever axle polishing rigs using bearings and bearing carriers, driven by a cheap power tool.

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10. The axle, brake and sprocket carriers and the hub should all just slide back together without any undue force. The most important thing to do is to apply some medium strength or high strength threadlock onto the grub screws to make sure they don’t come loose to cause the axle to move when you’re driving around. It’s good practice to line up the original grub screw marks on the axle with the grub screw holes in the bearings. This helps to reduce the number of stress points on the axle where cracks can form. It also makes it easier to remove the axle.

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This article was originally published in Karting Magazine in December 2015

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Chassis straightening

Tech Tuesday – Top 5 setup tools

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Tech Tuesday: How to Read Your Tyres

Tyres are possibly the most important part of a go kart, or any road going vehicle really. Tyres are what connects you to the ground and for that reason it is crucial for your tyres to be at optimum performance all the time. It doesn’t matter if you’re driving a 7 year old banger with a dodgy motor. If you have new tyres working well you can be quicker than the best drivers on new chassis with bad tyres, they’re that important.

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here is blistering along the inside edge of this tyre meaning that it is overheating

Reading the Tyre

Knowing how to read the tyre properly is very important as it will tell you how the tyre is performing on track. This can be done by analysing the wear patterns on the tyres after each session. By doing so you can tell whether the tyre is at the right temperature and if all of the tyre is in contact with the tarmac. Ideally the tyre should have light graining spread evenly across the surface and be matte in colour. Any sign of blistering and the tyre is getting too hot and generating too much grip, eventually this will result in high tyre degradation and poor performance. At the other end of the spectrum, if the tyre surface is too smooth it isn’t getting up to operating temperature (you will usually encounter this when the track is damp) as a result, available grip will suffer. These problems can usually be resolved by altering the tyre pressures.

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investing in a consistent, good quality tyre pressure gauge is a must

Pressures

Tyre pressures are one of the simplest set up changes to make on a kart and are arguably some of the most important to get right as they can completely alter the way a tyre performs on track In terms of temperature and wear pattern. For example, if the tyre pressures are too high, the tyre will get too hot and blister as mentioned earlier in the article, likewise too low a pressure and the tyre will not generate enough heat and grip. Logically, the more of the tyre surface that is in contact with the tarmac, the more possible grip. This can be altered with tyre pressure as a drastically overinflated tyre will have a narrow contact patch in the middle of the tyre whereas at the other extreme an underinflated tyre will be in contact with the road near the sidewalls. When setting the pressure on cooler days, you may have to raise the pressure to get the tyre up to temperature, sacrificing contact area as a result.

Tyre care

Like every component of the kart, your tyres need caring for. It is always a good idea to brush off any excess debris from your tyres (grass, gravel etc.) after each session. This will your tyres come on quicker next session as well as prevent you working any small stones into the surface which could cause a puncture. When new, tyres come in plastic wrapping which preserves the oils in the rubber during storage, if you won’t be using your tyres again for a prolonged period of time it might be a good idea to wrap them up in cling film to help preserve them for next time. Remember when storing to keep them in a cool, dry place which has fairly consistent temperature. A garage, for example would be unsuitable during winter because the contrast between day and night temperatures is large enough to effectively put your tyres through heat cycles, hardening them up.

Saving your tyres

As we know from Formula one, it is important to save your tyres, maybe not in a clubby at shenny, but in major championships you can be using the same set of tyres for a couple of days where the warm temperatures and rubbery tracks can really take it out of your rubber. We caught up with Gary Catt who taught us the importance of saving your tyres.

“I was renowned for destroying tyres… Especially in the days when we used bridgestone special tyres for all major races. I was always good at getting the most from the tyre when it was new and managed to qualify pole in championships but tyre wear was probably the biggest reason why I didn’t actually manage to convert those poles into wins”

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Jordan Lennox-Lamb testign a historic kart in 2014

Jordan Lennox Lamb on Tyres

Unfortunately due to the tyres we are using today there is no tyre saving at all. We are literally flat out from qualifying till the final. A couple of years ago when we still used the Bridgestone special and the Vega yellow it was a key aspect. I loved having to plan your weekend and not just drive like an animal from lap 1 to lap 25. Personally, I found tyre saving relatively easy, it was one of my advantages as a driver. It is all down to feeling, the chassis must be perfectly set up for you to really make a difference.

The best way to save your tyres in in the braking zone, so that you are never forcing the front tyres. Then it is all about when you are getting on the power, especially at la Conca where the rubber can to really build up on track. On grippy surfaces such as these the trick is to be on the throttle as soon as you come off brakes, only hold off the throttle for a fraction of a second to save loading your tyres but to avoid losing too much time. Always remember to be as smooth as possible when doing so as sliding will scrub your tyres and speed.

Words by Michael Killingworth

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Kart Aerodynamics

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Be one step ahead of the competition with the TKM Carburettor Carry Case!

It is known that many kart racers will keep their carburettors in plastic bags, tupperware boxes and in the top of tools chests. Not only could this lead to irreversible damage, but the carburettor will be susceptible to the ingestion on dust and dirt leading to a loss of on track performance, numerous carburettor rebuilds, additional cost to the racing weekend along with frustrating results; the TKM carburettor case can solve all of those issues!

Weighing just 0.6Kg (1.7Kg when full) and having a compact size it is the perfect addition to your racing equipment. This robust, ergonomic and protective carry case is made from durable plastic with a tough, hard-wearing and light foam insert that is resistant to high temperatures and both oil and petrol residue. The foam insert has been designed by engineering professionals with the input from a wide audience of TKM kart racers, this has allowed for the creation of a product perfectly suited for the TKM carburettor and ancillaries.

The case stores the following:

Item Quantity Size (mm) 337 (L), 290 (W), 84 (H)
TKM Airbox Flange x1
TKM Round Gasket x20 +
TKM Carburettors x3
TKM Oval Gasket x25 +
TKM Spacer Block x1
TKM Restrictor x4
TKM Fixing Bolts x2 +
Pressure Tester x1
Carburettor Repair Kits x2 +

Key features of the case include:

  • Environmentally neutral and durable polypropylene injection moulded case
  • Features a carry handle and twin independent locking catches
  • Strong moulded hinge allows for the case to open 180 degrees
  • Protection and prolongation of your carburettors performance
  • The foam insert allows for safety, security and protection against any irreversible damage
  • Removes the storage of carburettors in dirty and potentially damaging environments
  • Uses a tough, hard-wearing, durable foam insert that has great thermal resistive properties and is also resistant to oil and petrol residue
  • Optimises the preparation of carburettors removing the chances of those poor race results
  • One stop case for your carburettor and all the ancillaries needed to race

Don’t let your race winning equipment be neglected, it can take ages to find those extra tenths of a second in motorsport. Buy a Race Tech Case today and purchase that piece of mind that your racing equipment is always in fantastic condition.

Thoughts from the Editor

They say sometimes the simplest ideas are the best and I think that’s what the carburettor case is. It’s something I’d never I thought I’d need to buy or indeed make but when it’s presented and explained to you all of a sudden it seems essential. For many drivers, mechanics, teams out there I’m sure it’s already something you may have seen kicking around at a track and the man behind it all is Will Thomas. A former racer and now mechanic at TWM, Will is someone I’ve known for many years and when he presented this to me I just had to show it to the karting community.

As well as being a simple idea there has clearly been a lot of thought put into it. Will has clearly recognised what would need to go into the case and how many of each item would need to be included to make it a product worth wile. As well as that, and perhaps most importantly, he has made sure that everything will always stay in fantastic condition and therefore proving the product does it’s job properly.

All classes being catered for

The project has moved forward drastically from just covering TKM to now covering all classes. Cases for the rest of the classes will be out shortly but at this moment in time available for sale mainly caters for TKM.

Summary

It hasn’t been made overnight, the product has been a few months in the making and Will is now ready to put it on sale. If you like what you see, or want to find out more, then click the link below to check out the RaceTechCases website!

Click here now to visit the Race Tech Case website

 

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Tech Tuesday: Chassis Straightening

Of all the components that go together to make a kart, if you had to choose a single thing that was deemed most important what would you go for?

It would be hard to pick anything other than the chassis, as all the other components rely on it in order to do their job properly. It fulfils multiple roles, everything from being a mounting point through providing the karts suspension.

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Alignment and flexing

Quite obviously a kart chassis is designed to flex, we all know that it’s by changing these flex characteristics with torsion bars etc that the chassis is tuned to work for different tracks and weather conditions. The nature of their steel tube construction means that this is possible, as it can be moved a certain distance and will then return to its original position. Watch slow-motion footage of a kart through a bend and you can see the chassis flexing this way and that as it performs.

What is straight?

Take a kart at 150kg with driver, the chassis is perfectly straight and the tyres on each ‘axle’ are of the same diameter and inflated to the same pressure. With the driver sitting in the kart at least theoretically, when put on corner weight scales they should be reading exactly 32.25kg for each of the front wheels and 42.75 kg for each of the rears 43% front 57% rear.  Measuring the distance between the centre points of the front and rear axles should reveal that it’s exactly the same left to right too. All four tyres are pressing into the track surface with an equal amount of force and the handling will be consistent.

Take the kart out for a track session and provided that the chassis isn’t flexed beyond a certain amount (the yield point) when dropped back onto the scales, the weights and measurements should remain the same.

However, abnormally high loads like an accident or constantly banging curbs can take the chassis tubes past this yield point. Once it has passed this distance it puts a set is in the tube and it won’t come back to its previous position. Bounce the kerbs hard again and if the yield point is passed once more the deformation will increase and so on.

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Bent?

Now take our 150kg kart when the chassis that has taken some hammering or a bit of a thump. Now the scales say 34kg right hand front 30.5 right front, while at the rear the figures are similarly skewed, but in the other direction. The chassis has twisted, use it like this and it will over-use (and potentially over-heat) the more heavily laden tyres and under-use those which are more lightly loaded. Take the between axle measurements once more and possibly the wheel-base will be different one side to the other. The numerical discrepancies are the least of your problems, a kart with a bent chassis won’t handle.

The good news is that provided that a tube has not buckled or creased when it has deformed there is every chance that you can bend it back. While the old trick of one wheel up on a tool box and bounce has its place but only as an emergency measure get you out for the Final, it is crude and reserved for the situations when nothing else is an option. By far the best option is to have a chassis properly jigged and set straight. The right company can deal with a surprising amount of bend and give you back a chassis that will once more perform as it should.

How bent and still be rescued?

Merely taking a nearly new chassis and jigging it would tell the whole story of what can be achieved by the proper methods. What we need was something far more difficult. Enter this poor little 1964 Tecno which had taken a heck of a thump after a steering failure; to the extent that wheel base on the left side was shorter than the right by best part of a centimetre. You didn’t need corner weight scales to tell you that it was twisted merely lifting the front wheels in turn told you all you needed to know, one side was far heavier than the other. Because of its rarity chassis replacement was not an option it needed to be rescued. Step in Adrian Beddall of B.R.T. Quietly confident that he could turn the chassis around and get rid of the woes of the last 50 years.

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Where do the experts start?

It’s little use attempting to do delicate corrections when the basics are not right, so BRT started with a simple straight-edge to determine any bend in the rear of the chassis, this is corrected by the tubes being steered this way and that using a combination of an overhead press that was part of a sort of sliding gantry affair, a ‘free’ jack that could be put anywhere and occasionally close fitting mandrels slid inside the frame tubes to allow bending moment to be applied to exactly the right area.

Only when the tubes are dead straight do they even consider taking measurements determine twist and lozenge plus measuring (and eventually correcting) in a couple of other areas which Adrian politely asked me not to mention as they are his ‘trade secrets’ and he reckons that it’s work in these areas that make the difference between a chassis that’s nearly-right and a chassis that is really-right.

Determining these values means the use of a proper surface table and dial gauges, as amateurs we don’t stand a chance without this sort of kit. Taking measurements on what even what appears to be a perfectly flat concrete floor won’t give properly accurate results.

How accurate?

What do we mean by accurate?  Well consider this…. BRT work to within 0.125 of a mm.

This level of accuracy is especially relevant for lower power classes like Cadet where having a chassis that is completely consistent in left and right hand bends it critical for finding the last few tenths or even hundredths of a second.

The correction is done by accurately packing the chassis in various positions to allow the hydraulic press to be applied to specific areas. Although the chaps are very experienced in applying just the right amount of tweak to these particular areas they are constantly looking at the heights of the chassis tubes relative to one another constantly checking that the movement has not affected other areas.

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When you get the chassis back

If you have opted for the full service not only will the chassis be straight but the back axle will be fitted in the correct position and the front stub axles will be set up for toe in and camber, All you have to do is bolt the rest of the bits back on and go racing.

How often?

Some have their chassis at least checked every meeting, others every two or three although most opt for once a season. If your driver is a habitual ‘kerb-hopper’ it is worth having it checked as often as the budget allows.

Is it worth having a new chassis trued? While Adrian admits that a chassis direct from the factory will be “pretty good” he’s prepared to say that for the ultimate performance they can often find a little improvement here and there.

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Damaging the chassis?

Occasionally owners express concerns that the correction process will mar the surface finish. I asked Adrian about this and he contests that merely correcting the sort of set that a chassis takes from day to day use rarely damages the surface finish, even accident damage which will often require more extreme measures with the common sense use of the soft pad on the hydraulic press and strategically placed blocks of soft-wood and rags wrapped around the tubes to protect them rarely does much if anything to the finish. Mind you most owners given the choice between a chassis that no longer goes around corners and one that bears a couple of scuffs from being properly straightened will opt for the latter every time!

What can’t be straightened?

Once a tube has taken a kink it is part way to collapsing and will never have the strength it once had, here you are most likely on a hiding to nothing. Depending on how far you want to go there may be ways and means of dealing with this but that, as they say, is another story.

How much does all this cost?

All kart chassis are different so it’s rather like asking how long a piece of string is. However to give you an idea a simple check and straighten of an otherwise good chassis can be achieved in an hour or so and the guys can get an awful lot achieved in three hours. Even the daunting task of taking the Tecno chassis from bent to straight only took just under five hours, considering what was achieved in that time and the fact that there were two people working on the chassis for the entire time the charge of £180 – £40 for the first hour and £30 for every hour after that seems entirely reasonable.

This article was first published in Karting magazine in August 2015 and was written by Mary-Ann Horley

 

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