GTM roll cage modifications and race car build log

[kabacj]

It's Thompson Raceways inaugural race weekend. An exciting day for track lovers in the north east where we needed some variety. I had a host of changes to test on the GTM including stiffer rear toe link mounts.

Lucky for me I was pitted with the factory five brain trust. . Mark Dougherty (aka the traveling builder) ,John George( FFR challenge series national champion) , Jim Schenck (engineer responsible for the GTM), Pat Maddigan who runs a heavily modified challenge car, Brendan Dougherty who has been working on factory five cars his whole life and Chris Allen who owns a factory five coupe and is racing the spec e-30 class. Talk about a crew of guys who know what they are doing.

Friday am we had a drivers meeting and track walk. The first session was a bit hairy as nobody knew the racing line. The pace of the lap is relatively slow. The track is tight. Several turns where the camber falls off as you exit and and six pavement transitions as we enter and exit the oval.

Friday practice the verdict was good. The car was stable when transitioning from hard G turns to full throttle and off throttle. Seems like I fixed that problem.

Next step was to start tuning the car. I really should have aligned the car after all my welding, but I had marked all the suspension points and mounts to put it all back together with the same settings I started with. I know it was low probability, but work and travel ate up all my garage time in the past two weeks. It's all I had time for.

I had some instability around 120 as I went over some big dips in the front straight.

Thompson has many places where it cycles the suspension through its travel top to bottom. Our theory is that was cycling the rear toe through changes due to bump steer and getting the car into a setting range it did not like.

A toe change and addition of more shock damping and we got the car to settle down over the high speed dips on the front straight.


One thing I learned this weekend is that if you mess up the rear toe/ bump steer on this car you completely change how it handles. It's been said before but it's worth repeating. The car even turns differently when the rear toe is wrong.

The few people who have complained about stability of the car most likely had their rear toe incorrectly setup.

By mid day Saturday I had the car working well enough that I was comfortable pushing. We all had found the fast line around the track and learned where we could pass. The only bad thing was we also started ripping up the new pavement. This made passing a real challenge. Off line was covered with the small stones that make up the track surface. Marbles in the true sense. I think everyone in our group went off the track at least once on Saturday.

I spun for the first time in the GTM and the second time and drove the car sideways like a drifter countless times. One time the car swapped from left to right 5 or 6 times before I caught it. I'll have a hi-lights video soon.


Skip to my rookie race on Saturday afternoon.

Ill admit it was a little scary. Its been 10 years since I have raced anything. I don’t really know the racing protocol. Sure I learned it in the racing school but that’s not the same. We never did rolling starts or standing double yellow restarts on motorcycles… ah hell how hard could it be?

Since the track was super slick. Off line was basically unusable in many corners and nobody wanted to wreck their car on lap one. The first turn was very reasonable. HUGE difference from motorcycles. Turn one is a hairball every time, every race, regardless. You have a bunch of kids 20-30 and a few adults from 40-60 fighting to win the race in turn 1 going 5-10 wide from a standing start. Bumping is normal.

Not so with cars. Much higher dollar investment in the equipment and cooler heads prevailed. . I was the only guy out there on full tread DOT tires. That was not ideal but I did not let that stop me from trying to match corner speed with cars on full slicks. That usually worked. One lap I tried to make a pass in an off camber turn off line. Note to self, don’t do that. I instantly spun on the marbles but luckily was able to get the clutch in and lock the tires and release when I was going forward again. I didn’t need to restart the car. I don’t think I even stopped moving, just down two gears and I was off again. No flat spots . Cool! Dodged that bullet.

I only had one other close call during the race. After I was out of traffic I kept pushing my lines wider to try to carry the most speed through the corners. Of course that got me very close to the slick line. Acutally into it a few times. Its possible to drift a GTM! Not the fast line, but its fun.

I ended my rookie race without further incident. To my surprise I got 3rd place in SU.

The two winners were driving 850+ hp TA1 Trans Am cars. Im not in their league yet, but ill get there Lots of folks driving the high horsepower cars spun off including me. I was just lucky enough to limit the time penalty .

My first car racing trophy.



John