[mofoSTI]

The more I look at it the less I like it. I think money was wasted putting it in the wrong places like the paint, NAV and wheels to start with. I am sure those rims weigh more than the stock BBS's robbing power from that 425 horse monster. I am sure you could build an STI like the lynchfield t25 for the same money. Then you would have people lined up and camping at the doors of the dealership for one.

[WipeOutXXL]

Anyone race one at the track?
I want one to come to the Grove in WI to see it stand it's ground....

[donmei]

mofo,
thats a great point. there are plenty of monster STi's on stock wheels. For the most part, a wheel "upgrade" to an STi is purely cosmetic. Its tough to beat the stock forged BBS wheels. Particularly the 05 on, which have 8" wheels.

Don

p.s. I'm not saying that wider rubber wont help. But its certainly not low hanging fruit as far as upgrades go. Also, anyone with even a slight understanding of physics should understand that going to a larger wheel HURTS performance. Purely on the basis of performance, your wheels should be only large enough to clear your brakes.

[nonissan]

Originally Posted by donmei

Purely on the basis of performance, your wheels should be only large enough to clear your brakes.

don,

you seem like a smart guy, and i'm not doubting this statement, but.... could you please expand on it a little? wouldn't a larger diameter wheel/tire setup still put more rubber on the ground? all other things being equal (wheel weight) wouldn't larger diameter be better?

edit: for road race, not drag where small diameter allows larger sidewall for more flex.

[Rmiller]

Originally Posted by nonissan

don,

you seem like a smart guy, and i'm not doubting this statement, but.... could you please expand on it a little? wouldn't a larger diameter wheel/tire setup still put more rubber on the ground? all other things being equal (wheel weight) wouldn't larger diameter be better?

edit: for road race, not drag where small diameter allows larger sidewall for more flex.

I guess a large diameter tire would appear to put more tread on the ground, as the curvature is less angled, if that makes sense. I couldn't think of anything else you could be referring to, but it doesn't matter anyhow because overall diameter of the outside of the tire shouldn't change when changing wheel size.

[mofoSTI]

19" rims will robb power down low and take a little out of the brakes with the extra rotating mass, but they will carry themselves better through high speed corners than a smaller 17" rim. The 17" will accelerate and brake better ( less rotating mass ).

[nonissan]

Originally Posted by Rmiller

I guess a large diameter tire would appear to put more tread on the ground, as the curvature is less angled, if that makes sense. I couldn't think of anything else you could be referring to, but it doesn't matter anyhow because overall diameter of the outside of the tire shouldn't change when changing wheel size.

well, then if you're not changing the outside diameter with a larger wheel, then you'd be running smaller/stiffer sidewalls which would be of benefit, no?

[nonissan]

Originally Posted by mofoSTI

19" rims will robb power down low and take a little out of the brakes with the extra rotating mass, but they will carry themselves better through high speed corners than a smaller 17" rim. The 17" will accelerate and brake better ( less rotating mass ).

yes, with an increase in rotating mass, you're going to be robbed of power. i am asking about if you were able to get a larger wheel but in the same weight (actually i'm thinking about gramlights which are 18's and lighter than our stockers)

as for the esx sti....

[bickford]

wow, no thanks.

[donmei]

Nonnissan,
what if you got gram lights in 17s, they would be lighter still.

And the weight would be concentrated closer to the axis of rotation which would reduce the polar moment of the innertia.

Botom line, lighter is better, smaller is lighter (for a given wheel/tire combo).

On a wrx, best performance would be achieved with a 14" wheel if you are using stock brakes. I know this is heresy, but the physics is physics.

Re contact patch size, the amazing thing is that contact patch size is more a function of the amount of air in the tire than the size of the tire itself. Y
There are multiple engineering compromises that must be addressed, but maybe I can give an idea. If a tire is flat, it has a huge contact area, but it is so flexible, that it is useless. Conversely, if a tire has 80 psi in it, it will be very stiff and responsive, but ultimate grip would suffer because of the tiny contact patch.

So we strike a compromise. Someone mentioned that a larger diameter wheel will have a larger contact patch than a smaller diameter wheel. For a given psi, this is not true. It will have a longer contact patch. Conversely, a wider wheel will have a wider, shorter contact patch but not a larger one.

This is where we get back to tire pressure. A larger wheel can be run with a bit less pressure so the patch is bigger.

but why would anyone go bigger in diameter when more width offers the same thing, with less increase in weight and less increase in polar moment of inertia (google it). There is only one reason: APPEARANCE

I laugh when I see hondas with 9 inch rotors enveloped by 18 inch 25# wheels.

Big wheels look sexy. yes. But they make the car slower. Period.

One other interesting thing to note is that the subaru rally car, when competing on dirt, where traction and braking is decreased runs smaller diameter brakes and smaller wheels than when on tarmac stages. The tires have taller sidewalls, so total rolling height is the same, but if there was a benefit to running bigger wheels, don't you think they would?

Big brakes require big wheels.

Another interesting thing has to do with the development of open wheeled racing cars. When they went to inboard brakes, amazingly the wheel diameters started to shrink. This is now governed by rules, but it is for other reasons. (all else being equal, a larger diameter tire will last longer)

Hope this helps.

Don

nonissan - your assumption that rolling diameter is not changed is not realistic. Yes, it is a goal when going +1 or +2 on tires. This works when you are going from a 55 series tire to a .45 series tire. But our car already comes with 45 series tires. I doubt that people going from 17s to 18s or 19s actually install 35 or 25 series tires on them. btw, I'm winging it on the math a bit. but you can figure out the total rolling difference by just using the total tires height. which is wheel height + (2 x sidewall height)

OK, I'm getting sucked into doing the math for you. so here it goes

Sidewall height is measured by multiplying the tire width by the aspect ratio. For our stock cars it'd look like this: 225mm x .45 = 101mm sidewall height
Next convert mm to inches (google) 101 mm = 4.37 inches
17+ (2*4.37) inches = 25.74" tall
x 3.14 = 80.8" diameter

Now lets look at superricer +1 combo
18" wheels with 235/35 tires
82.25mm sidewall
3.24"
18+(3.24*2)=24.48

So you see, if you do the most likely superricer upgrade. you actually decrease the rolling size of the tire. But the heaviest part, the rim is actually farther out.

What do you gain and what do you lose. Well you have a heavier wheel tire combo. You gain responsiveness, and you may gain some grip with the ability to run lower pressures.

But - and this is a huge BUT, how much of this gain is from the larger diameter and how much if from the wider tire.

So lets try a 17" tire/wheel combo, but bump up to 235 width like above

sidewall height is still 3.24 inches
17+(3.24*2) = 23.48 inches

So if instead of putting bigger wheels on the car, you just put wider tires(and/or wheels) on your car, you get less rolling mass and better performance.

I've taken some liberties as far as assumptions not mentioned here in the interest of brevity (!!!??!!). but go ahead flame away.

Don

[snorky]

^^^well put. CN: a stiffer sidewall with wider tires is the way to go for increased lateral grip.

[Fierysun]

The interior of the ESX STI is so hideous, that the first time I sat in it, I was surprised this crap was ever approved for sale. They would have been better off with an all black interior and ESX logo's.

In addition, the mod's done to the car, looks more like corner gas station mechanic then factory. A bit too hack and slash.

[donmei]

I was behind an STI LTD tonight on the highway. Grey. It looked nice. I would have prefered a sleeper if it was available when I bought my car in 04. The big brembos peeking through the wheels and the spec V type lip kinda give it awaythough.

If you want a limited edition STi, the factory LTD is the one to have.

[mofoSTI]

If I dont go with the evo X I would concider a white wingless 07 STI and go for the sleeper look.

[nonissan]

Originally Posted by donmei

Nonnissan,
what if you got gram lights in 17s, they would be lighter still.

And the weight would be concentrated closer to the axis of rotation which would reduce the polar moment of the innertia.

Botom line, lighter is better, smaller is lighter (for a given wheel/tire combo).

On a wrx, best performance would be achieved with a 14" wheel if you are using stock brakes. I know this is heresy, but the physics is physics.

Re contact patch size, the amazing thing is that contact patch size is more a function of the amount of air in the tire than the size of the tire itself. Y
There are multiple engineering compromises that must be addressed, but maybe I can give an idea. If a tire is flat, it has a huge contact area, but it is so flexible, that it is useless. Conversely, if a tire has 80 psi in it, it will be very stiff and responsive, but ultimate grip would suffer because of the tiny contact patch.

So we strike a compromise. Someone mentioned that a larger diameter wheel will have a larger contact patch than a smaller diameter wheel. For a given psi, this is not true. It will have a longer contact patch. Conversely, a wider wheel will have a wider, shorter contact patch but not a larger one.

This is where we get back to tire pressure. A larger wheel can be run with a bit less pressure so the patch is bigger.

but why would anyone go bigger in diameter when more width offers the same thing, with less increase in weight and less increase in polar moment of inertia (google it). There is only one reason: APPEARANCE

I laugh when I see hondas with 9 inch rotors enveloped by 18 inch 25# wheels.

Big wheels look sexy. yes. But they make the car slower. Period.

One other interesting thing to note is that the subaru rally car, when competing on dirt, where traction and braking is decreased runs smaller diameter brakes and smaller wheels than when on tarmac stages. The tires have taller sidewalls, so total rolling height is the same, but if there was a benefit to running bigger wheels, don't you think they would?

Big brakes require big wheels.

Another interesting thing has to do with the development of open wheeled racing cars. When they went to inboard brakes, amazingly the wheel diameters started to shrink. This is now governed by rules, but it is for other reasons. (all else being equal, a larger diameter tire will last longer)

Hope this helps.

Don

nonissan - your assumption that rolling diameter is not changed is not realistic. Yes, it is a goal when going +1 or +2 on tires. This works when you are going from a 55 series tire to a .45 series tire. But our car already comes with 45 series tires. I doubt that people going from 17s to 18s or 19s actually install 35 or 25 series tires on them. btw, I'm winging it on the math a bit. but you can figure out the total rolling difference by just using the total tires height. which is wheel height + (2 x sidewall height)

OK, I'm getting sucked into doing the math for you. so here it goes

Sidewall height is measured by multiplying the tire width by the aspect ratio. For our stock cars it'd look like this: 225mm x .45 = 101mm sidewall height
Next convert mm to inches (google) 101 mm = 4.37 inches
17+ (2*4.37) inches = 25.74" tall
x 3.14 = 80.8" diameter

Now lets look at superricer +1 combo
18" wheels with 235/35 tires
82.25mm sidewall
3.24"
18+(3.24*2)=24.48

So you see, if you do the most likely superricer upgrade. you actually decrease the rolling size of the tire. But the heaviest part, the rim is actually farther out.

What do you gain and what do you lose. Well you have a heavier wheel tire combo. You gain responsiveness, and you may gain some grip with the ability to run lower pressures.

But - and this is a huge BUT, how much of this gain is from the larger diameter and how much if from the wider tire.

So lets try a 17" tire/wheel combo, but bump up to 235 width like above

sidewall height is still 3.24 inches
17+(3.24*2) = 23.48 inches

So if instead of putting bigger wheels on the car, you just put wider tires(and/or wheels) on your car, you get less rolling mass and better performance.

I've taken some liberties as far as assumptions not mentioned here in the interest of brevity (!!!??!!). but go ahead flame away.

Don

no flames. kudos on taking the time for explanation. so bigger wheels on (non-open wheeled) racecars are ONLY to accomodate bigger brakes?

still may go with the 18 gramlights because they are re-donk-ulously cheap and still lighter than the stockers.