Just was talking to a friend of mine at the track the other night and the following came up. on a stock ITR that's trapping 97mph how much of a difference would the switch from:

1. 40 pound 205 40 17
2. 35 pound 205 45 16
3. 31 pound 205 50 15

also that 97mph trap was on a GSR tranmission. the correct J4D gears and LSD are going in soon. on a very slick track the car was running 14.9s with wretched 2.6 60ft times on the 205 40 17. with that trap i know the transmission change will help the 60ft. how about the wheels and tires? i did ask this same ? over in drag racing. later had the thought it may get some well deserved replies here as well since some of you have personally tried these combos.

 

I've also wondered about this in the past but thought I'd get flamed just for asking. I always thought the larger wheels on the same car would slow it down in the 1320.

 

use the 205/50/15 i ran 14.4@98 with a 2.0 60ft with some chepo tires on my 98R

 

oh i would be cool with that. i also bet i'll click 98mph when i install the real ITR transmission this weekend. the GSR trans i was using to hit 97 falls out of vtec on the 1-2 shift, not to mention the gearing isn't as good. maybe i'll order up some of those tire rack specials, the TR motorsports c1 15x7 wheels. 12.8lbs and only 99 bucks a pop. talk about a deal.

 

The biggest difference is the kind (make/model) of tires you use, not the wheel diameter or wheel/tire weight. Stickier tires will give you better times than larger/smaller wheels or tires. For maximum acceleration at the dragstrip, get a pair of drag radials, take out some air and warm 'em up.

Also, you sound confused when you say that the "GS-R trans falls out of VTEC on the 1-2 shift". VTEC doesn't add power; rather, it keeps the power from dropping when revs rise, so there isn't less acceleration below the VTEC crossover point than above it; look at the torque curve and you'll see it's basically very flat. You CAN lose acceleration with a transmission when upshifting with a wider gap between two gears, but the reason you do so is because of the gearing difference, and NOT because of a lower amount of torque in the higher gear before you hit VTEC. Remember, acceleration depends on torque at the wheels, and torque at the wheels is torque at the crank times gearing (less any drivetrain losses). When you talk about being below the VTEC crossover point after the upshift, you sound like you're blaming the amount of torque in the higher gear for the lower rate of acceleration, and it's not because of that, it's because of the large difference in gear ratios.

You may want to read this article to better understand the effect of horsepower, torque, and gearing on your rate of acceleration.

 

it could just be the drop in rpm that's to blame since a gsr trans will go from 8500 in first and put you at roughly 5500 in second. the j4d gearset with it's closer ratios should keep the rpms up and thus the power. i guess my paragraph did sound like i was blaming vtec which is a little annoying that it drops out on the 1-2 shift. i do completely agree about what you wrote on vtec simply allowing the rpms to keep rising with the larger cam profile. as for the tires and traction. on a strip that was not prepared, the BFG KD while being a great handling tire, has such a stiff sidewall that it was hard to get any traction when i mixed in the 45deg air and lack of an LSD. the ITR transmission is going in soon, with both tires going i'm sure the 60ft time will come down.

 

didnt your old gsr run 14.9 with bolt ons? you should be mid 14s now...

 

actually it did, it's the mph that's telling of the ARRRRR's power. the gsr engine tweaked with bolt ons barely broke 93mph, the R is clicking 97. i used a 205 40 16 to run that 14.9 as a GSR which in effect geared my car lower. the track was also better prepared that day which allowed a 2.25 second 60ft.

 

Yeah, the KD is not a drag radial; it's a very sticky street tire, like the Falken Azenis and the newer, stickier tires that have come out in the past few years, so it's designed more for sharp cornering than for acceleration, and also it needs to be warmed up to be effective. Drag radials are designed not to need so much warmup, and also designed to allow their sidewalls to deform when you reduce the air pressure in them to increase the size of the area of the tire in contact with the ground ("contact patch"). Different tires for different purposes.