In addition to NASA TT6 (in which I’ll be running completely separate wheels/tires), I'm also building my Integra GS-R to run in a local Power-to-Weight based autoX class next year. The car weighs around 2600 lbs, is making 160whp (corrected for altitude of ~5000 ft above sea level, so probably closer to ~130whp uncorrected) and is using a B16b Type R gearbox. I'm limited to 200tw tires that are no wider than 225.
Note: I am not running with the SCCA; SCCA classes are irrelevant for my purposes.
I'll be running 15x9 wheels up front and 15x8 wheels in the rear.
I've decided I want to run A052's, but am torn between 205/50's and 225/50's up front (A052's don't come in 225/45's unfortunately). With the 205's I think I hit the rev limiter in 2nd gear around 59-60mph, with the 225's I think that would go up to 62-63mph. Is it worth the extra tire height and weight to run the wider 225/50's on a 9 inch wheel?
I've also considered running RE71RS tires, but its a moot point, as they also only come in 205/50 and 225/50 (no 225/45 available), leaving me in the exact same predicament.
I know Andy Hollis ran 205/50’s A052's on a 9 inch wheel on his One Lap CRX, but he was running on track and I think that had more to do with not wanting to lose gearing- I’m not sure how applicable that is to autoX?
Any suggestions?
No direct experience but I would think the extra lateral grip would make up for the change in gearing?
I have 255/??-17 on a 17x9 and they fit perfect so I can't imagine that 225 is too wide. Seems like a good idea to me
z31maniac said:
No direct experience but I would think the extra lateral grip would make up for the change in gearing?
That was my general thinking as well.
I pulled out the gearing calculator, to see exactly how much gearing I would be giving up. I input the B16b transmissions gear ratios, combined with the GS-R's OEM fuel cut RPM of 8200rpm.
On a 205/50/15, the tire diameter should be 23.1", which should give me the following speeds per gear:
If I went to a 225/50/15, the tire diameter grows by 0.8", up to 23.9", giving me the following speeds per gear:
^^^^^It looks like the difference in 1st and 2nd would be around ~2mph higher per gear. If my math serves me correctly, I think that would mean around a ~3% reduction in total gearing/acceleration. I'm assuming the increase in lateral grip would more than make up for the loss of acceleration?
Just for giggles, I input the car's stock tire size (195/55/15, 23.4" diameter) to see how much gearing I'm losing vs stock tires:
205 A052 is optimal on an 8.5" wheel, though many folks (like me) put them on 9's cuz 8.5's kinda don't exist.
A 225 will be a great fit on a 9.
As for the gearing deficit for autocross, the extra 2mph may actually be a benefit to avoid shifting to 3rd.
As for me, I can't run the taller 225/50-15 because it hits the upper inner fender unless I raise the ride height a bunch. Not worth it, Need a 225/45-15 for EF's. Might not be an issue for Integra.
In reply to Andy Hollis :
Thank you, Andy! I appreciate it!
After doing some searching, it appears that the DC2 also has a tough time running that tall of a tire (23.9" diameter- 225/50/15), requiring some extra height and internal fender work. It might not be a terrible idea to just stretch the 205 to avoid the hassle...
Andy Hollis said:
205 A052 is optimal on an 8.5" wheel, though many folks (like me) put them on 9's cuz 8.5's kinda don't exist.
A 225 will be a great fit on a 9.
As for the gearing deficit for autocross, the extra 2mph may actually be a benefit to avoid shifting to 3rd.
As for me, I can't run the taller 225/50-15 because it hits the upper inner fender unless I raise the ride height a bunch. Not worth it, Need a 225/45-15 for EF's. Might not be an issue for Integra.
Andy, I think you just saved me some money, sir!
I didn't realize an 8.5" wheel would be optimal for an A052 205/50... Goodwin Racing just so happens to sell 8.5" wheels:
https://www.good-win-racing.com/Mazda-Performance-Part/61-1924.html
Coincidentally, I just so happen to have the EXACT same style 8" wheels (Konig Hypergrams) already. Instead of stretching a 205 over a 9" wheel, I think I'll just pick up 2 8.5" wheels that I'll use in the front. Cheaper than picking up a set of 4 like I was planning on doing!
A +25 offset on an 8.5" wheel (vs +35 on current 8" setup) means a bit more poke (83mm vs 66.6mm- just a bit higher than I would be with the 15x9 +33 I was planning on running at 81.3mm).
I think that's the route I'm going to go to avoid overstretching the 205 A052. Saves me money in the process! Thanks again, Andy! After all the tech articles I've read of yours, I think I owe you a beer, brother haha!
