ExMB

So in essence 5 1/2 month between tests. Mile high race track weather would affect performance of the vehicle as well. I think there are several of you that go out there for open track days as well. That brings up the question with all those additional runs between those dates have you become more comfortable in the car and could that be a contributing factor?

Eric5280

No, Sir. Most of summer is spent in E36. My last RE71 2:03 lap was a couple weeks before the RE71 2 min lap with TPC links and springs. Same tires, two weeks apart.

bhk1004

is here a ride height difference between this and stock? I don't want to drop ride height and want to see if this will affect rake.

Eric5280

Stock ride height. Did Joe's recommended alignment of 0 toe front, .25 toe rear/side. Camber for me is -2.5 f, -2 r.

orthojoe

Yargk

Lap time improvements due to modifications are difficult to quantify. I have a feeling springs or the DSC module make little difference on the absolute best possible lap time. However, I would guess that they help with predictability and consistency.

Personally, I'm interested in whether wider front wheels and tires lower lap times. I'd guess that this modification would enable later braking and more trail braking, increasing the speeds in the first half of the corner, if it helps at all. Here's video of an S2000 that had a min speed of 75 mph in turn 2 at thunderhill, which is comparable to GT4 min speeds in that corner, however, in turn 1 the S2000 is going 100 mph at the third brake marker and only slows to 89 just before the apex of the turn. I haven't seen GT4s entering 1 that quick, but that may just be because the S2000 driver is superhuman. Still I wonder if there's something to be gained with front grip.


On another note, I think dive planes and a gurney flap would net 0.5 mph in turn 8. A different S2000 than the car mentioned above rolled through 8 with a min speed of 105.5 mph(!) with about 2-2.5x the downforce of the GT4. By my calculations the downforce on this S2000 (again not the one above) is worth about 3-3.5 mph over the GT4, so the GT4 should be able to do 102 mph or 102.5 with dive planes and a gurney flap through 8.

orthojoe

FWIW, I'm not convinced that 265 up front does anything and might actually be slower. Here is why:

1) Potter's first day at thill he ran 1:58 on oem tires. After he switched to 265, he was no faster.
2) Potter's best time at Sonoma is 1:48.2 on 265, which matches my best time there of 1:48.2 on 245s. Potter is a better driver than me.
3) A pro driver (hartanto) bought a GT4 with 265s and is planning on downsizing because he thinks the tires are too wide for 9" wheels and didn't like the way they performed.

laranja

So we can say that 265s "might be" slower, but
we really don't know. It's more of a feeling.

It'd be nice to test, same driver, same day.

Yargk

Thanks for the data points, I was aware of 1 and 2, but 3 is new to me. Makes sense though, 265 is a bit wide for 9s. 9s were fitted by many people without camber plates (that actually bring the tire in.) I always thought that 9.5s could fit with the perfect offset, trimming of the brake duct, and camber plates, and perhaps 265s on 9.5s would be optimal, but this is just a guess and doesn't follow from point 1 and 2 above. (heck maybe they won't fit and if they do 9.5s wouldn't be faster either )

245 is a tad wide for 8.5s too actually. Probably wouldn't change much against the stopwatch, but stock tires with 9X20 in the front might feel a bit better...

RDCR

Joe, for some reason I thought you went with the 265s because they were lasting longer? (or you thought they would).

orthojoe

Nope. Never did 265 because both sets of wheels are 8.5" and too narrow.

orthojoe

Based on my convo with Andrie, I think you are right that 9" with 245 would be better.

991RS runs 265 with 9.5", fwiw

ExMB

Porsche had to do something to slow the GT4 down. GT3 wheels are 20x9 with 245 tire.

Shockwave

Andrie bought a GT4! Thats amazing. He is well known in the S2000 community. Very fast!

orthojoe

Yeah, I'm waiting for him to put down some benchmark times!