sticky

I keep trying to explain to you the torque gain is 100 lb-ft at the wheels at 3000 rpm not 100 horsepower. The peak hp gain is less than the peak torque gain. That is why you see the large elapsed time gain more than the trap speed gain.

Furthermore, the entire basis for your point of the trap speed is based on a magazine trap and not a stock run from anyone on a real drag strip. GPS vs. timing beams. Your premise is flawed to begin with.

We're talking 991.1 Turbo level performance here from a flash tuned 991.2 C4S on 21's. Is that sinking it yet?

sticky

The 20's would help, yes. Especially if you put some stickier rubber on them. Didn't realize you did the run on 21's but that's a great 60 foot for street tires anyway.

Any pics of your car on 21's btw? I'm debating 20's vs. 21's here myself. Likely just going to run an 18 inch for the strip if that size clears the rear brakes.

PacificGerman

A set of lightweight 18s would be great for the strip. I have a set of 21" Vossens going on my C4 next week. Running 20" Klassens now.

PacificGerman

If anyone in SoCal is interested in going for a ride along in a tuned 991.2 let me know!

Just had my 17 C4 flashed, this thing is a monster. Low end torque pickup feels fantastic, definitely off the line faster. The traction control lights up through first gear even on 20" Pzeros. Power pulls all the way to top end, especially after 5800-6k rpm it hits hard.

I did some Vbox testing of the car stock, need to get back out there this week to compare. Will report back with data.

sticky

Someone said in another thread 18's won't work but I don't know if that is true. I was thinking of an 18 inch Hoosier radial for the strip.

Looking forward to pics of your 21's.

mac10

Sure. Here's the sizes I'm running: Pirelli P Zeros 255/30/21 on the front and 325/25/21 rear, 21x9.0 ET44 on the front and 21x12.5 ET 52.

J.Ho

So is the car with 21" on it slower than with 20"? even if the overall circumference is the same?

sticky

Thanks. I think you just settled the debate for me.

How is the ride? Lowered on which springs?

Those look like Vossens btw?

mikex25

circumference is the same but 21's in general are heavier. With drag racing you want a higher profile tire in order to induce side wall flex for better traction. Therefore with a larger wheel you have a lower profile tire with less side wall flex in conjunction with it being heavier.

J.Ho

Gotcha makes total sense.

mac10

The ride is honestly no different than stock. I did have H&R Sport Springs installed which only lowered it slightly more than the factory height. The wheels are from a Canadian company called PUR, they were a bit pricey but each wheel is forged from one piece of aluminum which makes them strong and light.

sticky

PM me what they cost if you're comfortable with that, thanks.

Dewinator

Even more impactful than the greater weight is the greater rotating moment of inertia.

sticky

We have enough torque that it isn't an issue

Dewinator

Hahaha touché.