So I think I've decided to buy a set of the OER Ronal R-15 wheels I've always wanted instead of OER gold GTA wheels.

I have a question about the R-15 center caps though. My old 91 Firehawk had a red Firestone Firehawk logo on a round disc that was mounted into the center cap. I have even seen these sold separately over the years, the OER center caps don't even have a center cap in them, just the space for it.

As I don't have that Firehawk anymore or physical access to anyone with R-15 wheels, can someone precisely measure the diameter of this circle in the center cap? I REALLY want to use the factory center cap discs (black with the gold WS6 lettering) in the R15 center caps but I have no clue if they will fit.

Thanks! Alex

OH HEY... Does anyone know exactly what tire size I need to buy for the R15 wheels so I have the precise identical tire diameter as the factory 16x8 crosslace wheels with stock 245/50-16 tires so my speedo stays the same? Or is the Firehawks 275/4OZR-17 tire size already identical?

 

275-40-17 is the same overall diameter as the factory 245-50-16 tires (well, within 0.1"). You also have the option of using a 245-45-17 too, which is also the same diameter, but gives up 30mm of tire width.

Do keep in mind that the R-15's are 26lbs each, almost 10lbs each more than factory crosslaces - not even counting the tires.

 

Thanks for the info!

Seems like the 275/40 is a no brainer then,

I'm not too concerned with un-sprung weight. I'm more concerned with better handling from the smaller sidewall and better traction from being wider.

 

No problem.

275-40-17 is the proper size to fit the 9.5" wheel and also be the same diameter as stock.

You won't pick up any handling with a 275-40-17 over a 245-50-16 tire based on sidewall, the 245 tire won't roll over onto itself enough to really affect it. You will pick up better steering response and also turn-in with the 1" reduction in sidewall.

But another 30mm works wonders on handling - it ends up being about 5% more grip in all directions - handling, braking, and acceleration, sometimes a bit more. It might not seem like much, but 5% brings a 0.90g car up to 0.94 to .95 with just tires.

In most cases, unsprung weight on a street car doesn't hurt much. However, I had an extreme case with one of my race teams - one that was verified by lap times. The car was running 17" x 8" soft 8's and a 245-45-17 Dunlop summer tire. By swapping to CTW Motorsports 17" x 9.5" wheels, weighing 14lbs less each, the car picked up almost 3 seconds per lap at a recent race (vs last year on same tires, same track). Driver mentioned the car felt like it pickled up 25hp and was easier to drive at the limit with razor sharp turn in. Keep in mind that this was a race car, but it still surprised me when he sent me the lap time sheet.

 

I believe it. I used to be the lead tire guy for a NASCAR team back in the day, I was the guy who measured the outisde, middle, and inside temp on each tire and dictated what pressure to run based on conditions. So in race car conditions on a track, I absolutely believe that loosing the un-sprung weight made a big difference, I suspect you used different tires too?

Once I do start road racing again, I plan on a set of lightweight steel wheels with race tires for that and just swap them at the track. That's a year or more off, I haven't even started on my ProCharger yet.

I've always just loved the R15 wheels since having my Firehawk and I do allot of aggressive mountain road driving so I know my handling will improve over the stock 16x8 wheels as you mentioned even with the increase in un-sprung weight.

Anyway haha! Can anyone measure this center cap and tell me what size disc will fit? Thanks!

 

I know I am a bit late to the thread, but the Stock center caps for the 3rd gen wheels, the emblems are MUCH smaller diameter than the center of the R15 cap. I have original R15's from Ronal and my caps all say "Ronal" in the middle. I don't really care for them, but I haven't seen anything that is even close to the same size. I would consider getting custom cap emblems made, but I have been too lazy to really look into materials and pricing. I contemplated buying some self leveling clear caulk or epoxy and just painting the center, then fill the cap so it emulates the cap as it sits, but I think it wouldn't look good since the void is quite large diameter.

 

Gotcha, ok thanks for the response!

I think now that the 17" crosslace wheels are coming out I'll get those.

 

I know, I want those too, lol. The Ronals have some good tires on them and the stock 16's crosslace have some meh daily driver tires on them. I am only running the Ronals right now because I got a flat in one of the crosslace and I haven't taken it to get fixed. I think I am going to get the tire fixed and then sell the 16's to get the 17's, plus the Ronals are supposed to be on my 91 GTA but that car is apart