Monday, January 17, 2011

Foam Tire Week 2

I'll probably have a video later, but for now I'll detail what happened at the track.  I cut some new tires, both A & B compound for the day to see what was what.  The layout was new, so the track was somewhat green.  I left the car basically as it was from the last practice day.

B compound tires worked very well on the green track.  I ran them several times until the car wanted to traction roll a bit.  I thought maybe the tires were a bit much as the traction was coming up, so I switched to A tires.  The A tires still wanted to traction roll as well.  This is where I save some time by telling you that I forgot to change the axle cams when I went from 55.5mm rears to 59mm rears.  I was probably at about 5-5.5mm ride height in the back, wondering why my car was traction rolling.  The front was 4mm, but the rear was just too high, not to mention the rake was not helping.  Anyway, while not paying attention to this, I did have a chance to try a bunch of stuff on the front end to tame it.

I kept the lowered position of the front camber plate.  However, I began to raise the ballstud to take away a bit of the active caster.  I also moved the ride height shims around on the outer part of the arm to change the camber gain as well.  Just dropping the plate gives a steeply angled front arm that gives a lot of camber change, and excess static camber as well. Moving ride height spacers from between the top of the sterring knuckle and the bottom of the upper arm, to the top of the upper arm changes the angle of the upper arm.  You can put the spacers on top of the arm to kill some of the camber and maintain a similar active caster angle.  This was helpful in reducing the traction roll.  You could see it was excessive front bite by the way the chassis would overpower the t bar/damper plate, and make it lift a front tire before the inside rear followed. 

I wound up trying a "soft" t bar vs. the "flex" t bar with the u cut out, just to keep the twisting down.  This did help, but it killed the rotation as I figured it would.  Not that the car didn't turn, but it was very flat, and slid the rears vs. letting the chassis roll and rotate the car.  This felt a bit bound up mid corner.

Around that time I remembered I had never changed the axle cam, and once I got my rear ride height to 4mm, the car had not the slightest tendency to traction roll.  What did happen was the front end of the car did feel a bit dead.  It actually turned fairly well, and was very nice off center, but didn't have quite enough steering.  By this point I had spaced the ballstud on the camber plate up 3mm, I reduced this to 2mm, and got back some steering.  I didn't change the ride height spacers at all. 

I had a chance to run most of the day with my buddy Jimmy's 21.5/no timing esc equipped 104, which had the front end set up normally, but was pretty dialed in.  It was nice to see what lap times he had as a baseline.  I either matched or was off his hotlap by .1, but he had more hotlaps and a better average.  He did have more rip out of the hole, so that was to be expected a bit.  I gave the radio to my friend Kevin for some laps, and he could hang with Jimmy no problem as well, and with a car he never drove before.  That does seem like a good thing.  The car is definitely good, but I need to re evaluate the front end again, since I wasted a bunch of time with the traction roll problem that probably is not a problem.  I think that I will be able to go back to a more aggressive front end setting and have additional steering without lifting tires.  The nice part is that I know what to do to keep the car feeling very neutral and easy to drive and still have steering.  It should not be hard to balance that with the amount of steering needed on a small carpet track.

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