Testing, testing 123

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Ginetta Super One MSA Series

By Jerry Thurston

“We are going testing this Thursday “, it’s a snatch of conversation often heard in Karting circles.

Although many use the words testing and practice in an interchangeable manner, if you want to be pedantic (and in this case we do) we need to realise that they are two different things. Practice is about refining the driver, testing is about refining the kart

Where do you test?
On the face if it this is a no brainer, but it isn’t… Because we want to achieve two different things.

Practice on the circuit you know least, this will help to bring the driver on allowing them to experiment with lines, looking for the grippy and slippery spots. Everything from the day goes together to teach them the subtleties of a really quick lap.

Test on the circuit you know the best. It is important that the driver knows the test circuit well enough to put in consistently quick laps with the kart as near the ‘limit’ as possible. It is only when the machine is being pushed as hard as it can go that any meaningful data can be gleaned from really subtle changes.

Budget for testing
In order to achieve consistently good results top teams treat test and practice days as a fundamental part of their racing operation, they’ll be scheduling sessions at their ‘home’ circuit to experiment with differing products or set-up changes that they want to try and planning days at circuits that drivers are unfamiliar with to coach them in the subtleties of that track. It’s going to cost money but you should be budgeting to test too, why spend thousands on a seasons racing to achieve mediocre results when a couple of hundred extra could make all the difference to your places.

Measurement
Because it’s going to cost you time and money, it’s no good at all turning up at a circuit for a test day without having a clear idea of what you wish to achieve and a way of measuring this. If you have been dogged by understeer all season a test session designed to cure or at least reduce this will be worth every penny spent if you get a result.

The base measurement is nearly always lap times but this is dependent on a clear lap time after time, on those frustrating days when the driver is continually baulked other measurements might be more useful, revs down the straight will give an indication of an increase or decrease in top speed, a change in steering angle through the bends when compared to previous traces will give you a good idea about oversteer and understeer issues. It all depends upon how much you want to spend, the more test gear you have on the kart the more you can measure, but the cost spirals too!

Although kart changes following testing should be results-driven, don’t dismiss things that for instance make the driver more comfortable, a tweak that has no effect on lap times but makes the kart fractionally easier to drive could pay back handsomely at the end of a long hot race when the driver is fresher than their competition.

It is no use trying to refine a single component or setting when the handling of the kart is changing all the time. It doesn’t really matter if the kart is not yet handling at its optimum, although somewhere near would be nice. What is most important is that the kart is smooth and consistent throughout the lap allowing the driver to get the maximum from it, this way when a change works it will be shown in the lap times. Fundamentally it comes down to establishing an even base-line. This means always running the same fuel, tyres, engine chassis set-up etc.

How to test
As we alluded to earlier, ideally you should test on a clear track; this means that you can put in lap after lap without being slowed by ‘traffic’. Favour going out at times when few people are about or looking to rent track time either on your own or to reduce the costs perhaps share the expense with couple of mates.

Try to do all your testing in one concentrated session. The vagaries of British climate means that track conditions can change hour by hour, even subtle changes in the temperature or weather are enough to upset performance in a positive or negative manner. If you start tyre pressure testing, for instance at midday on a hot track, then go away and come back at 5pm when the track temperature is still high but the air has cooled a bit your lap times are probably going to be different, any data that you collect is going to be skewed.

Remember too that it is very unlikely that you will be able to do any meaningful comparative testing on two different days.

The tyres will be one of the biggest factors that are subject to change; ideally you would use rubber that is new each time. However most of us don’t have that sort of money, so we will be going for tyres that are within a use-window. If you choose to use tyres that have done between 25 and 75 laps, you wouldn’t test on rubber that has done more or less work.

More sophisticated still is to forget the number of laps and monitor the heat-cycles that the tyres have been through, the more times a tyre has been cycled the more it’s performance will drop off. You might therefore chose to use tyres that have not endured more than say, five or six cycles.

If you can change a setting ‘on the fly’ by bringing the kart in doing a quick change without the driver even getting out and then sending it straight back out again without the tyres cooling so much the better.

Test engine?
Unless you are specifically developing engine mods, rather than hacking around wearing out your race unit, it can be prudent to have a motor that is just for test purposes, for many this could be an unsealed version of the motor used for your class of racing as these can be bought cheaply and refreshed from time to time without the expense of going to an authorised rebuilder. Using the same motor every time you test is one more step towards a level playing-field.

Test chassis?
All chassis are equal, but some chassis are more equal than others. While it should follow that chassis A and chassis B which left the factory a week apart after being made on the same jig should handle the same, they often don’t. However, if you are running a brand of chassis that is consistent from one to another a test chassis is a definite consideration. Remember though to get proper results everything needs to be exactly the same as your race chassis from the make and type of seat and its position to the brand of wheels and accessories fitted.

Do one thing at once
This adage is age old and quoted ad infinitum. We all know it so how come when we get to the circuit we all break the rules and do a couple of little tweaks together? The trouble is that it’s so tempting; you notice a couple of things that you consider aren’t quite right, so sort them both out together. Often this doesn’t matter but sometimes it makes a huge difference. So, which tweak did the job, or was it a combination of both? You can find out provided that you have written everything down, this gives you the opportunity to return the kart to its previous specification and then test each little modification separately.

The rule is, once you start collecting data and recording don’t fiddle with anything but the area you are working on. If you are experimenting with axle width don’t muck about with chassis settings, gearing, tyre pressures or anything else.

Money no object?
Won the lottery? Here’s what we would do. We would definitely visit every circuit that we race at several times, firstly to get the driver totally familiar with their complexities then once this was done to experience these circuits under different conditions. Be it wet, dry, hot or cold. Each time we visited the object would be to refine the set-up of the kart to best suit those conditions, building up a picture of what needed doing to go the quickest ‘out of the box’. Eventually we would have an invaluable set of data, Whilton Mill on a hot day? Look in the book; we need to set the Kart up like this…

Back in the real world!
Assuming that like us your budge it limited, it is almost guaranteed that your testing will be done on a convenient ‘home’ circuit. Don’t worry; you can still get meaningful results that will translate to the other circuits that you race on.

What you are looking for is a designated set of base line settings. Once these have been found, after every meeting or test the kart will be re-set to these. However, the base-line figures are never totally immovable. It is very likely that you will come across a tweak that improves the kart generally. Quite obviously it would be daft to re-set the kart to its old, poor-handling self so this tweak will re-establish the base line and in future you will start from there.

You are aiming to reach a stage where the kart is ‘happy’ or has reached it’s’ sweet-spot’ if these terms are a little too touchy-feely for you, call it a mid-point. All the major stuff has fallen into place, the seat position is OK, and any ballast is in the correct place, even the basic axle width and torsion bar settings are about right. This mid-point setting will give you the consistent base you need to experiment with other things.

Experiment improves the breed
Don’t be afraid to try radical ideas… We once had a rear hub come loose and migrate inwards towards the chassis, instead of the kart immediately starting to handle like a pig on casters the lap times showed an improvement before dropping off as you would expect. This gave us the confidence to try re-setting the rear track width to narrower than we had previously dared. The result was that we found a consistent three tenths of a second per lap. Why hadn’t we tried this before? Simply because nobody else ran their rear track that narrow!

Book a test day and get working, move things this way and that, stiffen, soften, try all those mods that are rumoured to be the hot things in the paddock. Write everything down along with the resulting lap times. Record down the settings where the kart hops, this means that you have too much grip for today, but these could come in useful on a cold April morning. Similarly record what you have done to make the kart slide (front and or rear), good to know for those days where there is too much grip.

Refinements
Once the kart is ‘happy’ you will usually find that almost no matter what the circuit or time of year your final race setting will be this mid-point, plus a few tweaks here or there.
Refinement testing is all about modifying the settings on the kart little-by-little in order to get the maximum out of it for any particular circuit. The good thing about returning to the mid-point (base-line) settings each time you get the kart home is that this, plus the notes from your more radical experimentation should make it far easier to work out what you have to do on the next race day.

If it’s a blazing hot day only a week after a round of an international championship has visited the circuit you can be pretty sure that there is still be loads of sticky rubber down in the corners so you’ll working from the previously established mid-point accordingly. Conversely if it’s shivering day on a circuit that hasn’t been used for weeks you’ll know that you’ll need to go the other way to find some grip.

And finally…
To corrupt the meaning of Newton’s third law… Every action has an equal and opposite reaction. Modifications that make a kart better through fast bends often corrupt the handling in slower corners and vice versa. Compromise is the name of the game, if getting the kart flying through the sweepers gives the most opportunity for quick lap times and overtaking take the hit in the slower corners or the opposite for a tight circuit.

Time spent on a circuit is never wasted, but how much use it is? That’s down to you.