Continuing on with setup issues for the Tamiya track, one thing which I may have overlooked in the past was the tightness of the diff. I generally set my diff tight enough that it will not slip, but still has good diff action. I was told that the best way to run the diff is as tight as possible, but still having smooth action. This was something I never tried since I subscribed to a "1/12" theory of setting a diff, which is to have it just about as loose as it can be without slipping, and then leave it alone.
Well, I tried the tight diff, and I think that it's more an arrow to keep in the quiver when you need it than a hard and fast rule. What it seemed to do for my car was to make corner entry very stable. This came at the cost of mid corner rotation, and maybe some corner speed, at least for my setup. There is a 180* at the end of the big sweeper at the Tamiya track, and at that 180* with the tight diff the car gets into the corner with a lot of control and stability. The down side is that if you don't enter the right way, or have the brakes right, the car may push some here. I also felt like it was not quite as fast through the carousel type corners. It appears that locking up the rear end is creating stability. On my car, this may not have been the way to go for a couple reasons. I run a full size pack unlike most guys who run shorties. My car tends to be more stable in the first place, but with a short pack the car is a lot more lively especially in terms of the rear. I would imagine if you run a short pack, this would be something that would help calm the car down. The other issue is that I tend to like to drive the car on throttle as much as possible. I'm not much of a point a shoot driver, and having a car that will turn on power is key. Locking up the diff is going to make the car steer less on power, so it hindered my setup. There is a place for it as an adjustment, however. I do remember some of the guys from the UF1 MIDWEST series who had just clamped down their diffs. They ran on the ultra high bite Toledo track, and having a car that was not twitchy on corner entry would make a big difference. Their line of thinking makes a lot more sense now.
In the end, I was very happy with the car. It would drive very well over the whole run, and I felt like I could push it as much as I needed to without it wanting to spin or roast the rears off. A second place finish was not bad at all, and I felt good about that considering I get about 2 weekends at the Tamiya track to try to dial the car in versus the untold laps guys who live locally can get in. A few people told me I could have used some more motor, and that probably was true. I don't worry about motor most of the time, since I feel like you can't launch a cannon from a canoe, as the saying goes. Better to have a good car, motor is way easier to get a hold of in most instances. That being said, I am putting more time into making sure that I have a better motor program.
To sum it up:
-Make the car work in the heat of the day, over the whole run
-The car needs to be able to rotate in the 180* and carousel turns
-Your best results occur at any race when you are only making minimal adjustments...tire prep, adding or reducing a small shim, etc. Ripping the car down to the chassis is a last ditch effort.
(photos from Tamiya USA web site)