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Old 05-20-2002, 02:22 PM   #1
gnildronde
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Default 16" vs 17" wheels?

Everyone says 17" wheels are superior for handling and braking. I know it's supposed to be because of the lower aspect ratio. However, if you have a 205 16" wheel, doesn't the 205 stand for 20.5 cm? So, the 205 16" would be the same as the 205 17"? I've always been told that there are more options with the 17" wheel but if you're not going with mega wide tires, what's the advantage? Wouldn't a high quality 16" be just as good as a similar quality 17"?

I know the aspect ratio (or think I know) has to do with the percentage of height to width but if both tires are 50's or 45's, doesn't it equal out?

Ultimately, I want to know if a 225 16" 45 series would give roughly equivalent performance of a 225 17" 45 series. And if not, why?

I understand physics fairly well and this doesn't make much sense to me.

I also believe the smaller rim would create quicker 0-60 and probably 1/4 mile times. Is this true?
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Old 05-20-2002, 03:39 PM   #2
Bottom Feeder
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Default Re: 16" vs 17" wheels?

Quote:
Originally posted by gnildronde
Ultimately, I want to know if a 225 16" 45 series would give roughly equivalent performance of a 225 17" 45 series. And if not, why?
It would, but your tire would be a whole inch shorter, which is a lot.
What you need to do is find out what the ideal tire height of a particular car is (usually what came stock, obviously), decide what tire width you're looking for, decide what wheel diameter you want, then play with the aspect ratio to find a size that's close, and hope that someone makes a tire in that size.
General rule of thumb:
For tires, every 10mm you want to go wider, go down 5% in profile.
For wheels, every inch you want to go taller, go down 5% in profile.
For example, a stock 205/55-16 translates pretty darn close to the popular 215/45-17 that most people put on their Subarus. It ain't perfect, but it'll get you in the ballpark.
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Old 05-21-2002, 01:50 AM   #3
Nordstone
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Default

Can someone please explain the science relevant to this question or does everyone just take the popular opinion for granted?
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Old 05-21-2002, 02:16 AM   #4
Concillian
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Popular opinion?

As I understand it there are 2 sides:

Side 1) smaller wheel = lighter and less inertia

Benefit here is quicker acceleration and deceleration through decreased inertia from the smaller wheel. Even at similar weights a smaller wheel (where the majority of the mass, the rim, will be significantly closer to the center of the wheel) the inertia will be much smaller on a smaller wheel. Lighter weight is also a benefit in the ability of the suspension to react.

Side 2) smaller sidewall = less suspension flex

Benefit here is less sidewall flex and better suspension feel. Obvious benefits in less things moving around when the car si shifting it's weight.

As far as which side you're on it depends on what you do. Personally, I feel that sidewall flex between high performance tires is going to be negligible for 1" of additional sidewall, at least compared to the rest of the stock suspension. If you go and add stiffer bushings everywhere, and are racing, maybe a different story.

Typically racing teams will use the smallest rim that fits over their brakes, and I believe for good reason.

That being said, I have 17" rims, not because of the technical reasons, but because the Subzeros are CHEAP, cheaper than any reasonably light 16" alternative that I could get at the time (read: nobody was selling 98-00 RS rims)

I firmly believe that if a rim company wants to ensure a Subaru fitment will make money that they strive to make a wheel that is:
- small (15x7/7.5 or 16x7/7.5)
- Fits over WRX brakes and 4 pots
- inexpensive (like the Rotas, under $150 each)
- reasonably light (15 pounds or so)

Because besides 98-00 RS rims, there is nothing that fits that category, and 98-00 RS rims are getting fewer and further between.

Either that, or I hope subaru starts giving the WRX and/or the RS 16x7 wheels in the near future.

There was a time where I would have bought 2 to 3 sets of wheels that fit those criteria, and I can forsee a time in the future where I'd still want 1 set, 2 if they were 15s.

Seems every week a new design for Subaru fitment is avaiable in 17 and/or 18" sizes, yet still no 15s or 16s aside from crazy expensive forged rims or heavy rally wheels.
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Old 05-21-2002, 09:33 AM   #5
LordBass
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I just went with lightly-used 16" '00 RS rims for my TS because:

1. They are half the cost of used 17s + tires, and half the cost of new 16s & new tires.
B. New England roads are typically less than ideal. I don't want to worry about bending a nice, big, fancy 17" rim on some Massachusetts pothole.
3. See point #1.

I would guess that for everyday driving, you won't notice much handling difference between 16s + 17s as long as the tire is good.

lb
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Old 05-21-2002, 10:34 AM   #6
Jon Bogert
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Quote:
Ultimately, I want to know if a 225 16" 45 series would give roughly equivalent performance of a 225 17" 45 series. And if not, why?
The same model tire on the same width wheel, yes, they will give roughly equivalent performance. As others have mentioned, the 16s will be 1" shorter so your gearing will be 4.3% lower. Also, the moment will likely be a bit less, unless you get incredibly light 17s.

A 205/55 will have a narrower footprint and a significantly taller sidewall. Again, keeping the model of tire the same, the 205/55 will have somewhat larger slip angles.

There is also the bounciness issue. With a firm suspension, all but the stiffest 205/55s will feel a little bouncy as the tire's spring frequency will be lower compared to the suspension spring's.

Jon (forever in search of the stiffest 205/55 tires )
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Old 05-21-2002, 02:56 PM   #7
mtb_dude
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Default Re: 16" vs 17" wheels?

Quote:
Originally posted by gnildronde
Everyone says 17" wheels are superior for handling and braking.
That's a big maybe (see below)
Quote:

I know the aspect ratio (or think I know) has to do with the percentage of height to width but if both tires are 50's or 45's, doesn't it equal out?
Yup! There is no difference in tire height, and therefore will have very similiar slip angles in a corner.
Quote:

Ultimately, I want to know if a 225 16" 45 series would give roughly equivalent performance of a 225 17" 45 series. And if not, why?
The only reason to go to 17" is if you meet any of these requirements:

- You're brake mod won't fit on a 16" wheel
- You'll be racing on smooth pavement and need every 0.01 second to win
- You've found 11 lbs 17" rims for less than $3k (not gonna happen)

17" are almost always heavier. That means acceleration and braking will be worse. Some would argue that braking control would be better, but at the same A/R, I totally disagree. Also not only are they heavier, but they are also have more mass further away from the axle, meaning a larger moment of inertia, or rotational "mass".

If you were to go 17" you should drop the A/R until you have the same total height as with the 16" wheels. I calculated an ideal A/R of 38.8 assuming 205 tires and 45 A/R in the 16" wheels. So either 40's or 35's. Now with this setup, you have a shorter, stiffer tire (lighter too but a larger moment of inertia so really a stalemate in terms of "mass"). This WILL give you better handling if your suspension is also stiffer. If not, the suspension will give more and produce more body roll. This stuff is not simple at all.
Quote:
I also believe the smaller rim would create quicker 0-60 and probably 1/4 mile times. Is this true?
Yes! Lighter and less moment of inertia. There's just a lot of people who don't think it through like you have. 17" wheels do LOOK cooler though.
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Old 05-21-2002, 11:58 PM   #8
Nordstone
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mtb_dude and Jon Bogart,

Thanks for the helpful info. Those are the types of answers I was seeking. I think I'll save some dough and just get some good tires for my 16" wheels.
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