XRAY - Model racing cars

Tony, looking at your last setup posted you raised the rear roll centre when most people seem to go the other way. I wondered if you would care to share your thoughts with us as to how you came to this conclusion (what was the car doing) and what the improvement was when you had changed?
As this is a new chassis it would be nice if one of the team drivers would go through a days racing with thoughts on what needed changing and why and what improvements it had. Not looking for a bible on setup changes just an insight into how the team drivers think and setup their cars.

Are you really sure you want me to get into a days racing with you?

As to your first question, most of the reports people have made have been about oversteer especially on corner exit. However some, like me, have had the opposite challenge on their hometracks, i.e. mid-corner understeer and understeer on corner exit.

Raising the rear roll center in my case served two purposes. First it increased the steering and allowed me to hold the corners better. Second it helped increase the corner speed as it reduces rear chassis roll resulting in a more responsive car, especially at higher speeds.

With regards to a days racing, well that entirely depends on the race and what the car is doing.

For me the race begins (if I can find enough time) a couple of days before the event. I allways look through my old setups for the track I am about to race at and evaluate the last time I ran the car (i.e. evaluate the setup that is currently on the car). First I put the springs I want to run on the car, refill the shocks if needed (e.g. to get more rebound) and attach the shocks to the car at the angle I want to run. Then I set the ride height, the front/rear camber and the front/rear toe angles. Next I set the downstops and check the uptravel (i.e. how far the chassis can move upwards before the tyres lose contact).

In the first practice run at the track I usually take it somewhat slow and concentrate on what the car is doing in each corner. How is it handling in the fast corners and how in the slow corners. How is it handling in each section of the corner (entry off-power, middle on/off power, exit on-power). At this stage my first focus is to get the tyres to work. If the tyres (additive, tyre treatment) are not working any changes to the setup will in general be useless. This is because the changes won't be very noticeable without grip and also because if the track is still getting grippier you may be changing a good setup that just looks bad at the moment...

Once I get the tyres sorted the next thing is to find balance. A car with neutral steering through all corners and all sections of a corner is the ideal, but this is usually impossible. The next best thing for me is neutral in most corners and slight oversteer in the rest as this will be fast, if potentially difficult to drive. Assuming the car is close to a good setup at this point I will choose to focus on only a couple of setup options. The first choice I make is the body I want to run. I only use two types: Protoform Stratus 3 and Mazda 6. If the car is tending towards understeer I will go with the Mazda 6, otherwise I will go with the Stratus 3.

With the body choice done I start focussing on damper angles and spring choices. I usually start soft and try harder settings if the track is smooth, grip is good and temperatures are not too high. I also consider anti-roll bars at this stage if I feel the car has too much chassis roll. However, I prefer to run harder springs and more downstop (less uptravel) to reduce chassis roll if I can. If these don't get me the handling I need I start looking at the suspension geometry. I.e. roll center position for the suspension arms, top link length and angle, castor, anti-dive, anti-squat etc. These tend to be bigger changes with the really big ones being chassis flex, track width and wheel base.

Sometimes I decide to go for the big changes fairly soon if I find that the car's handling is way off and radical changes are needed. This is more or less a hit and miss approach because the problem then is with either the starting setup or the tyres (often the latter...). Only in this case (or when I know exactly what I can expect) do I make multiple changes at the same time. In all other cases I try to do a single change at a time so I know whether the change helped, made things worse, or had no influence.

By making only a single change at a time I can use specific changes to help analyse why the car is handling the way it is. There are so many reasons WHY a car will understeer that it is sometimes not so easy to decide what change is needed. For instance the front springs of the car can be too hard, but they can also be too soft. Front tyres maybe overheating, or not getting hot enough. Through selected changes to the setup you can analyse the problem and be more effective in resolving it. For instance if the front tyres are not getting hot enough and the car is understeering as a result, going to harder springs will usually give more steering as this will make the tyres heat up more. So if I try harder springs and the car actually understeers more this could be an indication that the front tyres are actually overheating instead!

Hope this gives you some ideas...

Thanks for that Tony, the insight into setup also helps. How about getting a few of the Team drivers to do the same based on an actual Weekend/days racing, I am sure it would benefit all of us.
Thanks again
JohnT

I'll see what can be done about that. Like the rest of us the team drivers also have day jobs or are still in school, so time is limited to write such stories. When push comes to shove car preparation, practice and racing tends to get the priority over writing reports