225/45/15 vs 255/40/17 RS for autox

[CrazyB]

I am currently running a 225 RS3 on a 15lb 15x8 wheels
For this season i was thinking of moving up to Rota Grids in 17x9 and run the 255/40/17 RS3
Anyone have experience with running the 255 tire and have any feedback.
One of the reasons i am making the jump is for next season i can run 275/49.17 r comps on this wheels also.

I know the fenders might not clear them but i am willing to add rivet on flares or custom flares to clear the rubber.

Just curious if anyone made the jump form 225 15 to a wider 17 inch tire and how the car felt.

[BlackbirdM3]

Do you have all the fender well plastic stuff removed? If not, tires will rub like crazy. Also, a bigger wheel is heavier, and will mess with your gearing as well. I thought my M3 drove better with a 225/45/15 than it did with 215/40/17s. Everything was better, the turn in was more crisp, braking was better, acceleration was better.

My vote, stay with 15s, I see no real gains being made with 17s.

Will

[2002maniac]

My only worry would be the gearing disadvantage. 255/40/17 is a lot taller than 225/45/15.

[CrazyB]

I currently have a 3.73 in the car, but I have a 4.10 seating in the garage also so that should change the gearing if that becomes an issue. As far as clearance I am fine with cutting the fenders and removing the liner, the car is not a daily driver.

I was more going to see if anyone ran this size and how the car feels on the larger tire.

[kilgojr]

My brother and I both autocross ALOT. We have run all sorts of tire combos. 15x7 with 205s with 225s, 16x8 with 225s and 245s, and 17x9 with 255. I will tell you that a 255x45x17 is WAY better then any of the other tires that we ran.

Now, we have also run 255's on a 17x8.25 front and 17x9.75 rear and it was still better then the previous 17x9 with 255 setup. This is all experience with a Kumho XS. My brother will be running a 255 Hankook RS3 this year in the 255 with 8.25 and 9.75 wheel and we only expect it to get even better because of the tire experience. The RS3's are definitely a better tire then the XS was.

As far as the gearing, we were running a 4.10 diff on the M20 with boltons. And we still had to shift into third quite a bit on the faster National Tour and Regional courses. We saw no loss of acceleration with the tires, the car was just as fast as with the smaller 23 inch tall 15 inch tires. And we carry way more speed through the turns, so all in all your times will improve.

As far as fitment, your gonna have to roll the fenders, or just pony up and get the rivet on flares. The latter is what we both did.

[CrazyB]

Great nice to hear someone who actually went in this direction.
And i do love my 225 rs3 on 15x8 best bang for the buck autox tire.

[spencers]

It's all about getting more rubber on the pavement.

Make it fit!

[BlackbirdM3]

Unsprung weight. Good luck getting a light set of wheels in a 17, and by light weight, Im talking less than 15lbs.They are out there, but be ready to drop a lot of cash for them.

I don't know that 17s are the answer. I'm sticking with 15s, I'd run 14s for autoX if I could find a set of 5x120s in an 8 inch width assuming they would clear the brakes, and I don't think they will.

Will

[bigo]

With bigger rim size and wider tire you'll get a bigger contact path so the car should be quicker on the corners but will suffer on the long straights and the fuel economy will be worse. The big wheels also kill torque of the engine on wheels. If your riding a is i wouldnt go higher than 16 in sport. I would go with the bigger rim only to fit bigger brakes.

[Jaxx_]

Running a 16x7.5 with 225/50 Advan AO48s. I would rather use a smaller wheel and slightly smaller tires and run a good tire than run a big, wide, shitty tire.

I would say steering response is another factor, but if you're doing autox you probably already have a good alignment setup, yes?

[team9]

I am currently running a 225 RS3 on a 15lb 15x8 wheels
For this season i was thinking of moving up to Rota Grids in 17x9 and run the 255/40/17 RS3
Anyone have experience with running the 255 tire and have any feedback.
One of the reasons i am making the jump is for next season i can run 275/49.17 r comps on this wheels also.

I know the fenders might not clear them but i am willing to add rivet on flares or custom flares to clear the rubber.

Just curious if anyone made the jump form 225 15 to a wider 17 inch tire and how the car felt.

DO IT!!! You won't regret it. I ran half the 2011 autox season on a 16x7 with 225 Kumho XS's and half the season on 17x8.25 front, 17x9.75 rear XXR's with 255 Kumho XS's. The difference was unbelievable! Definitely would recommend getting the rivet on fender flares from Ary at DTMfiberwerkz. Any deficit in unsprung weight is completely negated in my opinion. The first half of the season I was consistently ~2 sec slower than the other competition (modified evo's) in my local SM class. After I put on the 255's, I moved to within ~.5 secs of the leaders. Went from 4th and 5th place finishes to 2nd and 3rd. Proof speaks for itself. But this is just my opinion. I can't wait to try out the RS3's. From the articles Grassroots Motorsports has done on the latest autox tires, the RS3's far exceeded the performance of the XS's.

To give you an idea of the car setup:
Engine - cone filter, 19lbs injectors, IE shorty headers, 2.25 dual exhaust, no cat, vibrant muffler at rear
Suspension - Bilstein sports, GC coilover kit which includes GC camber plates, adjustable sleeves with Eibach race springs, 450/600 front/rear. Also have UUC Swaybarbarian sway kit 22/19mm front/rear.
Interior - removed rear seat and carpet, corbeau forza seats, corbeau harnesses, caged interior
Exterior - DTM fiberwerkz fender flares

Are you also interested in tracking the car? If so, I would still use the 255's on the track. IMO, any straight away speed is negated with the corner speed and increased corner exit speed. I say that with the exception of having a really slow corner into a really long straight. If that's the case, then you may see an advantage with a smaller tire and better gearing. But even if that's the case, you could make it all back on the rest of the track. I only have one track comparison between the 225's and 255's mentioned above. In March 2011, I ran at Talladega Gran Prix Raceway with a fastest time of 1:13.2. In November 2011, I ran again with the 255's and ran a fastest time of 1:11.2. Only differences between the two weekends was tires, and no passenger seat.

Take my experiences for what they're worth. In the end, I would do what I want to do. You'll never know if something is better or worse until YOU try it.

[BlackbirdM3]

Another factor you should think about is getting heat into the tires. The bigger the tire, the longer it takes to get heat into it. I see you are here in the Bay Area, do you ever run at Marina? The surface is fantastic, getting heat into the tires is a different story.

Unless you have some monster motor, I highly doubt you are going to run out of grip with a 225 on your car. I'm running RS3s and I don't have an issue with too little grip, especially in the rear. My car was pushing, but I also wasn't using the inside of the front tires at all. Now that I've added lots of camber and caster to the front of the car, I don't think it will be an issue. As it was at the first event I ran the car at, it was the fastest BMW at the race, race tires or not. It should be a class winner this sunday. (Maybe not, its hard to say. I think I might have too much caster at this point the steering wheel doesn't self-center well with 10.5 degrees caster. I'm hoping its just a matter of tight new parts and the issue will go away, but likely not.)

Will

[Chris916]

Bigger is always better ;) With my shitty m50 with a dragging cylinder, i was still running out of grip with 245 ra1's, 3.5 degrees of camber in the front and 2 in the rear. 255's on 17's would be magic. Most e36 guys run this setup and seems ideal as well.

[race2win]

I currently have a 3.73 in the car, but I have a 4.10 seating in the garage also so that should change the gearing if that becomes an issue. As far as clearance I am fine with cutting the fenders and removing the liner, the car is not a daily driver.

I was more going to see if anyone ran this size and how the car feels on the larger tire.

All things being equal, more tire on the ground will create more ultimate grip. The trade offs in this situation are more un-sprung weight, increase in track width, taller gearing & being able to make them fit. According to your statements above, the latter 2 trade-offs won't be an issue, but the first 2 will offset any gain at least to some extent. Plus, as was mentioned before, on colder days it will be more difficult to get heat in RS3s that large in a lighter car. Yes, the E36s run that size very effectively, but those cars are at minimum 2-300 lbs heavier. Keep in mind, CSP Miatas can run ANY wheel-tire combo...they could run 315/18s if they wanted...but they instead run 275/15s because they have proven to be the fastest package for that particular car. So bigger is not neccessarily always faster

Summing up, over-all the 17s should be faster 95% of the time, with the 15s potentially slightly better in very tight & transition heavy courses. The only way to find out for sure though is to test, back to back, on the same day & in the same conditions. I'm sorry, but to all the guys saying the 17s will for sure be faster, you will never know for sure without doing back to back testing. More to the point, even if they ARE faster, you will never know WHY or HOW they are faster. My $.02 :)

[Bimmerman325i]

For E36s, 255/40/17 on a 17x9 is the fastest street tire setup.

I can't imagine E30s being any different in that regard.