i love the look of the 20's on my car, but whoever says that it doesnt affect the perfornace is smoking crack. My car is noticibly slower with the 20's on it then when i had the stock 18's. Handeling has improved though because of the width of the tire.

Btw i have 245's up front and 275's in the rear.

 

What type of 20" rim did you go with? Cast aluminum chrome? Lightweight Forged?

 

There's a reason why most European cars are using larger wheels... the low profiles won't flex like the taller 45 or 55s, meaning better steering response. Just sucks that you'd have to live with a wider turning radius, and slightly lower slower throttle response. But then again, with enough torque, the later shouldn't be a problem.

The weight of the wheel isn't the biggest factor here. You can get larger diameter wheels that are lighter and still find the same problem btw.

 

It would be pointless to run 275mm width tires on a 8.5" rim because it will not come close to maximizing the contact patch of the tire. If you're really stuck on running the stock rim, you'd be better off running a 255 or 265 width tire.

That said, there are a MILLION rims available in an 18" size that can fit the G. Look for something in a 18x9.5 +45 to +50 offset rim with a 5x114.3 bolt pattern for the rears and you'll be set for running 275s.

 

I thought your where seeking new tires and wheels that fit you G and were looking at many different sizes. I did not realize you where trying to fit 275's on your stock 18's. If you do that the side wall will bulge out from the wheel towards the tire tread. You will not like the look, even if it is safe.

Although it appeared you where asking about performance as opposed to cosmetics, you seem to be looking for a lower profile tire for cosmetic reasons. Let me paint a picture that might help you make up your mind. An 18 inch wheel has the same outside diameter no matter how wide it is. I know, duh, but it's an important place to start. Even if you put a 325/35 18 on your stock G Sport wheel the aspect ratio (side wall) will being just as tall as tall as a 225/50 18 tire. So for appearances the tire will look just as tall from the side as before.

A 35% aspect ration by it's self means nothing. http://www.rims-n-tires.com/rt_specs.jsp Not all 35 aspect ratios are the same either, it depend solely on the width of the tire and by a small measure from one model or brand of tire to the next. The aspect ratio of a tire is a percentage, telling you how tall the side wall is compared to the width of the tire. If you want the side wall to "appear" smaller you must buy larger wheels and a smaller aspect ratio or you must install a smaller tire witha smaler aspect ratio, i.e. -245/35 18. If you do the latter your speedometer will be off because the outside diameter of the tire is smaller. I hope that helps.

 

So for the layperson please boil it down for me....

What are the available sizes in high performance rubber that will fit on the stock 18" sport rims that will maintain the stock speedometer calibration? I am interested in performannce, not cosmetics.

 

I would say only 245-45 18!

265/40 18 may fit. Look into that size to fit the stock 8.5" G35 Sport rear wheel. All of the other tire sizes list below are probably too wide.

This info found on:

http://www.rims-n-tires.com/rt_specs.jsp

* For 245/45-18 tire comparable sizes would be:

18''
245/45-18
265/40-18
275/40-18
285/40-18


19''
245/40-19
265/35-19
275/35-19
285/35-19


20''
245/35-20
255/35-20
265/30-20
275/30-20

 

haha yea seriously..

look people its FREAKING g35 your not looking at a ferrari , porsche or lamborghini.....18'',19'',20'', we have a 4 door sedan.....dont make things so complicated..performance you will lose minimal, ride quality all depends on size and tire balance etc, looks...cants go wrong with 20''...

 

19/20's == more bling, potentially more grip if aligned correctly.
18's == more acceleration, better suspension compliance, better tire wear.

what are your priorities? that should drive your decision.

 

^^^ well put. I think 20"s look great, but you will lose a bit of throttle response and be a bit of a rougher ride. Unless the eibach's compensate a lot for this. the weight of the wheel does not matter here as much as the radius. The larger radius the more torque it takes to turn the wheel. also the added rubber on the road provides more friction to over come and your gas mileage should decrease. All of this should be very minimal and probably hardly noticable on this car. Having 18"s starting and moving up only 2"s is not that huge of a jump. If you want performance throw some 15" wheels with some skinnies up front to get your 0-60 and 60ft times lower. Oh and you will not see a difference on the dyno with changing wheels since it does not affect the engine power.

 

weight, plus radius matter in newton's law analogue for rotational acceleration; radius just has a stronger (second-order) impact.

that said, a bigger rim goes ahead and puts the most of the mass (the rim itself) farther out from the center. i posit that this change is not minor.

better springs can only do the best possible job for a suspension system of a given unsprung mass. that doesn't change the fact that the unsprung mass is still there. you can't fix wrong.

what type of dyno? if you mean an engine dyno, then you are correct. if you mean a chassis dyno then you are not.

 

^^I mean chassis dyno. If changing gears in the rear end of a car, say 2.73 to 3.73, does not effect the hp output to the dyno, then why should wheels? I understand you lose power though the drivetrain..... I guess I am confused. It would make sense that a chassis dyno would show loss of power due to the power consumption of turning the wheels but why does it not change due to different rear end gearing. I know lots of people that have done gear swaps and the only thing it changes is their acceleration not their power. Am I wrong?

 

changing parasitic losses would affect measured hp on the chassis dyno. a chassis dyno measures hp after the power has already passed through the drivetrain. that's why there are lightened driveshaft mods out there.

this is a completely different subject than loss by the way, but gearing change mean varying force multiplication, and what the dyno reads with different gearing DOES in fact change the reading, but you enter your final drive ratios into the dyno computer to back-calculate the engine output. so what you see is the same number, even though what actually occurred on the rollers is a totally differen story. but as i said, that's not the same subject that we're talking about here.

 

Ok, I was unaware they had to input the final gear ratio into the dyno. thanks for the schoolin' well then you WILL see a change on the dyno. I was in fact mistaken earlier.

 

no worries. fun topics to talk about.