Sputnik

Hello there,
Just a quick question..really..what is the difference between 17" and 18" wheels (aside from the fact that one is 1" smaller <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" /> )
To say true I still don't know what dimension of the wheel that number describes...I assume it is the distance between metal ring of the rim and the point on the tire where it "touches" the road...
I 've built an imression (while reading some other posts) that "bigger IS better" But how the bigger wheel would effect the performance of the car? My car currently has 17" cup wheels. What kind of "gain" in performace I would expect in case if I decide to upgrade to 18"? How much ussualy this kinf of upgrade my cost?
Thanks!

Glen

Hello, the main difference is a shorter tire sidewall equalling less sidewall flex. You will notice a sharper turn in and the car will feel more responsive. the downside is the 18's are less forgiving on bumps and potholes as a result. 17's make a great street wheel because of that reason, conversely 18's make a great track wheel for the other reasons. Hope that helps....

Robert Henriksen

I hear what you're saying about 18" on the track; I'll chip in, though, that if you're not racing, the 17" still let you drive very quickly, and the 17" rubber is significantly cheaper!

fbfisher

I have driven 993's with 17 and 18 inch wheels - at high speed on very twisty canyon roads - never on the track. I notice little if any difference in handeling. Ride is noticably better on 17 all other things being equal. Was has yet to be mentioned is that 18s look way better and are worth the extra price and added discomfort for that reason alone.

Skytop

The popular trend now is definitely toward big, bigger, biggest wheels!

I attended the Miami Int'l Auto Show in late November and was amazed to see 25" wheels being sold. I can only wonder what the rubber to shod those tractor like wheels would cost. However, the young'uns seem to have the scratch to invest 10-12K into fancy wheels to impress the female of the species and intimidate the male wannabees.
Many of the high line sports cars were sporting 20 and 21" wheels so that indicates where size is trending. I feel my 18's are humongus enough and the cost of each rear tire causes you to swallow hard when you multiply by two! <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

There are Rennlist threads that discuss the performance difference between 17 and 18's if you wish to get the techno side of the question answered.
Skytop

<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Robert Henriksen

I guess I should also throw in the usual 'track snob' perspective as well . If you can take your car out on the track and drive it to within 85% of the car's ability on 17" wheels, well, then you may be able to really take advantage of 18" rims. I've not yet met the track newbie who can use 60-70% of their car on the first outing. If you've got 17" rims, enjoy the ride. When you outgrow them, then consider the cost/benefit tradeoff before taking the plunge.

Like I said, I may not be a hard-core, flea-bitten squinty-eyed racer dude w. HUGE brass *****, but I've got plenty of track miles under my belt. And these days people who spend huge wads of money on kit for their cars & then turn 3:00 laps times just embarrass the hell out of me.

Now, if all you're interested in is bling, then disregard the above!

Can you tell I've got a few glasses of wine under that same belt tonight? <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />

fbfisher

Define "Bling" : Noun, 993 <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Allen

[quote]Originally posted by Robert Henriksen:
<strong>the 17" rubber is significantly cheaper!</strong><hr></blockquote>
Not to mention how cheaper the wheels themselves are...if you ding one up and have to replace it.

[quote]Originally posted by Glen:
<strong>17's make a great street wheel because of that reason, conversely 18's make a great track wheel for the other reasons. </strong><hr></blockquote>
On this note...I replaced my 17" with 18" and was gonna sell my 17". Everybody told me that I should keep the 17" for track tires
I guess the reasoning is that if the 17" were dedicated for the track, then it wouldn't be a big deal if they get dinged up some. But on the other hand, one of the reasons I got the 18" was for the added performance...so if I change wheels fr track use, I'm kinda defeating the purpose. Anybody else thought about this?

Skytop

Thinking about the fact that as the wheel gets taller, the tire ratio gets shorter.
Now......
How much shorter can the darn tire get as wheels get larger? My 30 section rear tires are only about 1 3/4" tall. Where does the law of diminishing returns start to take become too severe? How much shorter/rigid can a tire become by going to (gulp!) a 20 series tire??? How much gain will realized in enhanced handling?

How much more compliant will a suspension be so that the driver's fillings don't fall out?

Say, I'm working up a perspiration thinking about this!~

os993

Don't forget the weight penalty you get when you go to 18". I was very pleasantly surprised how light my 17" cup wheels are - very impressive for factory..

The only justification I would use to upgrade to 18's is for looks, but frankly, I think the 993 looks just great with factory 17" and a ROW M030 suspension setup! Not to mention, 17" do just great on the track with some decent track tires...

maurice97C2S

Let's not forget 18s are mandatory for some of the brakes we have or can fit. Brakes have been the real driver of wheel sizes in racing over the last 15 years, although carbon disk systems on F1 seem to be a bit smaller.

As always, it is a tradeoff of pros and cons -
18s - crisper turn in, harder ride, potential big brakes, expensive tyres that stick like s**t.
17s - better ride, cheaper tyres, more forgiving?

Me, I just love my hollow spokes!

Cheers, Maurice

Bins

Does this mean that there is actually no difference in terms of overall "wheel and tyre" size between the 17" and 18", ie, The space between the tyre and the body is the same for both.
Its just that it seems like the space between my tyre and the body is less than other 993s and yet I thought I had stock suspension.

maurice97C2S

[quote]Originally posted by Bins:
<strong>Does this mean that there is actually no difference in terms of overall "wheel and tyre" size between the 17" and 18", ie, The space between the tyre and the body is the same for both.
Its just that it seems like the space between my tyre and the body is less than other 993s and yet I thought I had stock suspension. </strong><hr></blockquote>

Hi Bins

The fronts are within 0.5 mm in rolling diameter on my quick calculator - rears however, 17s are 635.8mm for 255/40/17 vs 642.7 for 265/35/18 and 628.2 for 285/30/18. Calculated on width x section x 2 + wheel diam, so not exact for all tyres.

So depends what you have, as always!

Cheers, Maurice

JohnM

Hi Bins,

With OEM rim and tyre sizes 17" and 18" have the same outer diameter, within a couple of mm (the 285/30/18 rears are slightly smaller than 255/40/17, the 265/35/18 slightly larger, but in both cases can depend on tyre manufacturer).

I have found the change to 18" wheels (225/40 & 285/30) to be a huge improvement, the front end response and grip are much better than the 17" Targa wheels I did have, and the 18" wheels+tyres (Pzero Rosso) are lighter than the 17" Targa wheels+tyres (S02 N3). In fairness, the S02's had endured 2 track days adding up to about 250 track miles, and that left them a tad knackered. I won't get to a track with the 18" wheels until Spring. My car is on the firm side anyway, with PSS-9, monoballs and nylon front bushes, but I like it that way

tom97c4s

[QUOTE]Originally posted by maurice97C2S:
[QB]Let's not forget 18s are mandatory for some of the brakes we have or can fit.

My car has the big reds and I have no problem putting 17" winter wheels on.