200 mm Road Car, Test Mule
What a delightful car this turned out to be, but it took a very long session to bring it about. I got good excercise climbing the stairs into the drivers stand numerous times. Here is the story of the track tuning session with tips on how to avoid such a long one. There is also news on the two test devices on board.
Ride Height (No inerter)
On the first few tries the car dragged the ground front and back. You could hear this. You could see the resulting scratches underneath. I ended up with a 15 lb center spring, 35 weight center shock oil. This is similar to what I have used before on our bumpy straight. I ended up with a short set of front tires in the proper compound, so I needed to modify the front lower A-arms to gain sufficient ride height. Ride Height was at 2 mm with the short tires and the A-arms all the way down. I removed .060 inch or so from the bottom of the A-arm. Note that IRS sells a set of shortened A-arms for just this purpose.
The green spring was insufficient on the sweeper. The outside edge of the chassis was rubbing. This was killing my steering. I went one up to 7# purple and brought the steering back. Yes this is backwards tuning, but note the reason. I did not have 8# blacks at the track or would have fit those.
I ran spec tires full size at first and had too much low speed steering. I switched to an almost worn out set of purple fronts and they were perfect. Note that the spec fronts are perfect on my wide pan or might be perfect with less motor on this narrow pan.
I had a little oversteer still on the very high speed turns. I increased the wing to my Favorite JConcepts 0110 and the car drifted in a neutral attitude around these turns. Perfect.
Rear Ride Height
I kept increasing this until I got good performance on the straight. I am using the 2.0 spacers placed to raise the chassis. Rear ride height is about 10 mm now. No problems in the corners with this. Full size rear tire. I was getting excellent speed on the straight. Directional stability was good. No big side dams needed.
Blowovers, Front Diffuser
I kept increasing my speed on the straight by rolling on throttle quicker and keeping throttle on longer before the sweeper. Only one time, when I held throttle way too long for a good tight sweeper turn did the car blow over. I would gauge my diffuser a great success because previously I might have had 4-5 blowovers just driving the track normally. Give this a try if you have put a powerful motor in your narrow or wide pan.
Low Roll Center Mod
The steering felt great with the low roll center mod.
I tapped a side board. This stripped the plastic nut and the car shed the wheel and bearing. I lost one bearing. The car has 5-40 spindle ends. Use a steel nylock nut here to prevent this. Associated makes one for some of their diffs. ASC 6629
The T-plate came loose
The car was equipped with a strange small size flanged 4-40 mut. I had no driver for it. They are not locknuts and need to be really tight. The car wandered back and forth aimlessly with the front t-plate screw missing. I replaced this and it was only better as the rear t-plate screws were loose. Great once these were all replaced.
The Servo came loose
I know better than to use only two screws on the servo, but my new purple hardware had not come in yet. I added two more screws. I did use locktite on the servo saver screw and it did just fine.
Finally I had a good driving car, Inerter Report
I drove about 15 laps, then I installed the inerter link. Jeff and I had pushed the rear suspension of this car and its twin down on the bench. We both decided ahead of time that the inerter suspension movement was too slow. In fact it was. On the track the rear suspension was very stiff. Speed on the straight was reduced as the car bounced more. Corner exit speed ,though, was dramatically higher as the antisquat was aided with the stiff rear end from the inerter. The center shock design actually kills most of the antisquat effect. I need to reduce the gear ratio by a factor of 10 or so. I have some ideas. The car is pretty great without it though, now that it has a full width diffuser.
This is probably the best body I have run on a narrow pan on-road. I have tried the Lola and a supercar body previously. That big rear wing is perfect yet again. Chevy Monte Carlo HD