Wasted Potential Posted January 16, 2018 Share Posted January 16, 2018 I am contemplating the necessity of 18" over 17" (or the reverse of that...) The same size tire say 245/35, on a 17" VS. 18" rim will have the SAME or MORE sidewall flexing amid corner? Is there any performance benefit to a larger rim if the larger rim weight is proportional to that of a smaller rim and the weight is located in proportional distances from dead center of hub? A smaller total diameter will result in more torque output (whether marginal or not) but a larger total diameter will allow for better high rpm boost building? This importance becomes at what gear/speed does one spend most of their driving... More interested in some mechanics of this, as well as if most autoX folks are prefer 17" or 18". Link to comment Share on other sites More sharing options...
jrho Posted January 17, 2018 Share Posted January 17, 2018 If you're after performance, I would recommend going with a 17" wheel set up. Same sidewall heights on a 17" wheel or an 18" wheel should in theory have the same sidewall flex. However usually people will run a shorter sidewall tire on an 18" wheel set up to keep the rolling diameter the same and will claim that shorter sidewalls are stiffer. In reality due to most high performance tires having quite stiff sidewalls in the first place, I doubt that the minimal sidewall difference will contribute to less sidewall flex. There isn't any performance benefit to a larger wheel with a larger wheel weight. Wheels are rotating masses so the more you can reduce it, the more drastic the difference in feel and also the amount of effort required to turn said wheel and tire combo. I went from a relatively heavy 18" 3 piece wheel to 17" Enkei RPF1s and the difference was very apparent. Link to comment Share on other sites More sharing options...
Wasted Potential Posted January 17, 2018 Author Share Posted January 17, 2018 I contribute my question to... Having a turbo car with 3.73 gears, versus 2.73 gears. The 2.73 felt like the top end load allowed for the vehicle to be "stronger". Obviously the gear could allow for more velocity, but the "pull" felt stronger. It was also quicker in the quarter mile with the 2.73s, but that coupe be due to the 3.73s spinning in through third and needing to shift into fifth right at the end. On a non high end performance tire I would presume they all have horrid roll, so I guess would a high performance on 18s be better than a low performance 17? What is deemed a "notable" difference in rim weight? I know factory is 17x7 around 19.5 to 20.5 lbs on assumption. Majority of fair price aftermarket are 21-24lbs it seems. Link to comment Share on other sites More sharing options...
2_Liter_Turbo Posted January 17, 2018 Share Posted January 17, 2018 The only reason why you'd want to go to a larger wheel for performance, is if you were trying to fit larger brakes than the smaller wheels could fit as well as available tire sizing (18" offers more choices for some tire classes). Otherwise, the smaller wheel is better! Link to comment Share on other sites More sharing options...
Wasted Potential Posted January 17, 2018 Author Share Posted January 17, 2018 Do larger rims allow for a notable caliper breathing and air fishing? I'm sure rim design plays a more important role, but I'd assume rim size being larger creates more total flow Link to comment Share on other sites More sharing options...
jrho Posted January 17, 2018 Share Posted January 17, 2018 I contribute my question to... Having a turbo car with 3.73 gears, versus 2.73 gears. The 2.73 felt like the top end load allowed for the vehicle to be "stronger". Obviously the gear could allow for more velocity, but the "pull" felt stronger. It was also quicker in the quarter mile with the 2.73s, but that coupe be due to the 3.73s spinning in through third and needing to shift into fifth right at the end. On a non high end performance tire I would presume they all have horrid roll, so I guess would a high performance on 18s be better than a low performance 17? What is deemed a "notable" difference in rim weight? I know factory is 17x7 around 19.5 to 20.5 lbs on assumption. Majority of fair price aftermarket are 21-24lbs it seems. Comparing a high performance tire on an 18" with a low performance tire on a 17" isn't really a fair comparison but yes the 18" would be better in that case. I went from a 19 lb wheel to a 15 lb wheel and noticed a pretty solid difference. Everyone has their own definition of fair pricing, but the flow formed offerings from Enkei and Konig are what I would recommend for best bang for your buck. There's a reason why so many people run RPF1s on this forum and a lot of other platforms too. As for cooling the brakes, I doubt most wheel manufacturers are taking this into consideration. The only things I can think of are the turbo fan coverings on race wheels that draw in fresh air but most people depend on air ducts to the brakes for cooling. Link to comment Share on other sites More sharing options...
Wasted Potential Posted January 17, 2018 Author Share Posted January 17, 2018 I think of the foxbody "turbine" rims, supposed to cool the brakes better. Never saw that one tested... Link to comment Share on other sites More sharing options...
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