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Discussion Starter #1
I'm brand new to the 9-2X (as in haven't even taken possesion yet).
We want to put some new wheels and tires on it.
It's an Aero w/ the 16s and 50 series.

Doing some looking, 18s and tires will be about the same cost as 17s.
I was looking at the Konig Reasons w/ a 215-40R18 Yokohama or G-Force BFG.

Are there any recommendations to stay at a 17 or are 18s fine?
 

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Just realize you'll be sacrificing acceleration and braking, and probably handling to a degree. As well as ride quality.

You are adding substantial weight further away from the hub, thereby slowing you down accelerating and making it harder to stop....and you are increasing your "gearing" as your wheel/tire height is increasing.

Your suspension isn't made to handle the extra unsprung weight and aspects, so those won't work the way they were supposed too....

And, your sacrificing ride quality due to very thin stiff rubber. Also, your wheels will be more likely to get bent up over 30-50k...

All this for what, looks?

Why not save yourself some money and just go with 17" wheels and tires. Plus one tire sizing typically gets you the best of all worlds, and we already know the 9-2x was built for the 17" 215/45 tire/wheel combo.

Good luck in your choices.
 

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I know how added unsprung weight and rotational mass affects accelaration, and braking. But seriously...an 18" wheel and tire combo is NOT a bad thing on this car. Particularly with 225/40-18 tires.

Overall diameter of the wheel/tire will not change. Gearing will be unaffected.

A larger contact patch is never a bad thing. A shorter/stiffer sidewall is GOOD for handling. It's better, not worse. If you get good quality wheels you'll have to do do some serious curb bashing to bend them. And, also, if you get a good quality wheel it will be lighter in 18" than the stock 16" wheels.

My Superleggeras weigh about 18lbs each and they're 18x8. That's lighter than just about any factory 16" wheel. The wheel/tire combo is lighter than stock. They're super strong (shot peened, actually) and they're not likely to bend or break during normal street or track use. I do race and there was an immediate improvement over the stock wheels and tires.

I think maybe you need to reasses your stance on upsizing wheels and tires. With modern technology making quality wheels more affordable, the whole weight issue and bent-rim issue is becoming less of a consideration.

The only thing that remains unchanged is the degredation in ride quality with larger wheels & shorter sidewalls. High performance always comes with a comprimise of comfort and economy. It's unavoidable and should be considered a prerequisite idea when modifiying your car.
 

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Discussion Starter #5
joefrompa said:
Just realize you'll be sacrificing acceleration and braking, and probably handling to a degree. As well as ride quality.

You are adding substantial weight further away from the hub, thereby slowing you down accelerating and making it harder to stop....and you are increasing your "gearing" as your wheel/tire height is increasing.

Your suspension isn't made to handle the extra unsprung weight and aspects, so those won't work the way they were supposed too....

And, your sacrificing ride quality due to very thin stiff rubber. Also, your wheels will be more likely to get bent up over 30-50k...

All this for what, looks?

Why not save yourself some money and just go with 17" wheels and tires. Plus one tire sizing typically gets you the best of all worlds, and we already know the 9-2x was built for the 17" 215/45 tire/wheel combo.

Good luck in your choices.
By my calc, using stated sidewall tire dimensions, the overall OD change is less than 4mm. I don't think you could even calculate an overall final drive gear reduction with that small of a difference; let alone actually realize one while driving.

My concern was more with the tire/rim combo mass difference. I didn't think it could be that significant but wanted to check here. You lose an inch of sidewall but gain an inch of spoke.

The answer is though, yes this would be for looks. It's actually my wife's car and I doubt she'll ever be racing it. Appearance is the goal. I personally don't see anything wrong with that so long as there is no significant compromise to the vehicle.
If it's ok to consider 18s, we will. But if she likes the looks of the 17s better, we'll go with those.

Thanks all for the input.
 

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well, I posted a long, detailed explanation of my thoughts on this...but it got erased, lol, when I accidentally hit the backspace button on the laptop in the dark.

So, anyway, he's going to gain about .8" of tire/wheel height with what he's going at, which is about 20mm.

Some math...an inch is 25.4mm. So he's increasing 50.8mm in wheel height...he's decreasing 30mm in sidewall height by going from a 55 series to a 40 series.

Net increase: ~20.8mm of sidewall height. Plus the weight is further out from the hub.

And, as a side note to something you said earlier, having a larger contact patch is not always a good thing, except in straight line acceleration on the drive wheels. That being said, a 225 would be a great tire for this car IMHO....a 255 would not :p

Let me know your thoughts.
 

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As a site note, and you seem to be well aware of this already (but for those who are not).


Most of the negatives I'm pointing out can be rectified by a properly made lightweight wheel and correct tire.
 

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Discussion Starter #8
joefrompa said:
So, anyway, he's going to gain about .8" of tire/wheel height with what he's going at, which is about 20mm.

Some math...an inch is 25.4mm. So he's increasing 50.8mm in wheel height...he's decreasing 30mm in sidewall height by going from a 55 series to a 40 series.

Net increase: ~20.8mm of sidewall height. Plus the weight is further out from the hub.

And, as a side note to something you said earlier, having a larger contact patch is not always a good thing, except in straight line acceleration on the drive wheels. That being said, a 225 would be a great tire for this car IMHO....a 255 would not :p

Let me know your thoughts.
As compared to a 215-45R17, which was your recommendation, and, as you mentioned, a factory available size, and the 215-40R18; the overall diameter delta is 3.9mm. Hardly a significant enough deviation from "factory" conditions to measurabley deteriorate performance.

215*0.45*2 + 17*25.4 = 625.3mm
215*0.40*2 + 18*25.4 = 629.2mm

Compared to the 225, the delta is close to a 1/2".
I don't believe anyone suggested running a 255???

According to jdmpart, it's quite likely that the 18 and tire combo is lighter than the 16 and tire which would allieviate the weight concern.
 

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jdmpartstx said:
My Superleggeras weigh about 18lbs each and they're 18x8. That's lighter than just about any factory 16" wheel. The wheel/tire combo is lighter than stock. They're super strong (shot peened, actually) and they're not likely to bend or break during normal street or track use. I do race and there was an immediate improvement over the stock wheels and tires.
Just keep in mind that generally OEM wheels are heavy for a reason- to make sure they can handle the abuse. While Superleggeras are well beloved, an Audi forum I read has seen a fair number of cracks running perpendicular to the spokes (usually on just one or two spokes). I know of no significant issues occurring before each crack was discovered, and OZ was apparently very good at rectifying the situation. Other aftermarket companies might not be as good, should a problem arise.
 

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joefrompa said:
-------snippage to save bandwidth--------

And, as a side note to something you said earlier, having a larger contact patch is not always a good thing, except in straight line acceleration on the drive wheels. That being said, a 225 would be a great tire for this car IMHO....a 255 would not :p

Let me know your thoughts.
Little noticed by all, the wider tire does NOT have a larger contact patch than a narrower tire (not notably anyway) it just has a different shape. The wider tire will have a wider (lateral) but shorter (longtitudinal) shaped patch, at least when the tire is static. Dynamic loading alters the shape some, but that's another LONG topic. Contact patch size has only to due with the weight of the car at each corner, AND the pressure in the tire. (again, ignoring dynamics). All said, what this means is that under cornering, the wider patch is more effective at generating forces, and since slip angles are reduced, quicker to respond to steering inputs. I didn't bother to figure out the rolling radii of each package, but if it's properly +2 sized, the difference in diameters will be negligible, hence gearing is uneffected. If the wheel is lighter than stock, it'll still MARGINALLY effect acceleration and braking (due to, as you called it, the weight (really mass) being further from the hub, known as rotational inertia). As other's called it, IF the weight of the wheel tire combo is about the same as stock, the biggest drawback is the smaller sidewalls having a stiffer spring rate, so the absorption of high frequency road bumps will suffer, and the rims will have more chance of damage from both bumps and curbing. The poster should try a set on a similar car on the roads that they drive to see, if possible, but I actually see little difference in ride quality between my 16" snows and my 17" summer tires on my 3800 lb Audi. Both suck on the stutter bumps on the dirt roads of my area. Unfortunately, my new job has me driving up one of these roads. Bummer. BTW, I don't expect my Saabaru to do much better, which I'll find out this weekend when I take delivery.
 
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