Silvertarga

I was considering 18 inch wheels on a 964 C2, and remember reading (I think it was Streather) that you should never put 18s on a 964

I am running 17 inch turbo twists and have a set of 18 inch as well

Is there a suspension modification for 18s / some advantage to 18s or will I die in a horrible ball of fire as a result of putting 18s on my 964

mwneedham

With respect to running 18's on a 964, my car came with 18 inch wheels and I have tracked the car for the last 4 years in these RH replica wheels. In fact this past week-end at Sebring, I was on Toyo R-888's because of several recommendations on this forums....and they were right....I had a BLAST on the new tires. I have had no issues with 18's other than the additional cost.

MWN

swftiii

Same here - I run 18s on the track with MPSCs and Hoosiers. My street wheels are the 17s with street rubber. No issues from me.

Skip

frankvan

AFAIK,
as long as diameter of TIRE is roughly same as stock and you don't rub the tires anywhere you can use any size rim you want. Otherwise those lowered Neon's with 22's and big exhausts would be bursting into flames.

However, others may correct me.

( I run 18s in the summer time with no apparent problems)

Silvertarga

Sounds like the 18s are the wheel of choice on the track...I dont track the car ..only reason I changed wheels was those dreadful "style" 90 Phone dial wheels

So there is no real advantage to going with 18 inch (I am happy with the 17 inchers) unless I want to compete with the hondas and neons .. still wonder why Streather warned against 18 inch wheels on a 964

crg53

I think it is a bit like your mom saying "don't go swimming for at least 1 hour after you have eaten". One of the advantages of 18" wheels are your increase in tire choices; the only disadvantage I have heard of is a bit rougher ride on the road, i.e. lower aspect ratio. You may also have rubbing issues depending of offset, tire choice and camber settings.

Wikkid911

I think he said 'don't put 18"s on but you can put 19"s on, providing you buy them from me'.

LastMezger

Interestingly the ride on my car improved significantly over the standard 16-inch wheels and old (probably hard) Michelin Sports. The 18s with H&R Greens and Michelin PS2 provide better ride quality than any 997 I've been in. I'm genuinely comfortable...and impressed.

Porsche964FP

I have 18s the only issues are with clearances especially if you are lowering the car... but then for lowering camber adjustments and rolled arches cure those problems.

My question however is doesn't running bigger wheels affect the speedometer and gears? Or is this negligible?

August West

Only if the rolling circumference changes. I think you'll notice when 18's are put on, the tires tend to be lower profile, meaning less sidewall, and if the circumference stays the same, it won't affect the speedometer. It's that 2 digit number (like 35, 45, etc.) in the tire nomenclature, which means the sidewall is 35% or 45% of the width of the tread. Forgive me if I'm stating the obvious.

I've heard somewhere that the 18's stress the undercarriage more...I think it was mentioned pertaining to 993s.

crg53

As an example: 255/40ZR 17 does 828 revs per mile, a 265/35ZR 18 does 824, so the difference is really nil.

altarchsa

"..........only reason I changed wheels was those dreadful "style" 90 Phone dial wheels............."

Heyyyyyy... (see the avatar) You can see I have no experience with this, but you might want to at least look at:

http://www.pcarworkshop.com/images/d...0593geolab.pdf

This PCNA Technical Bulletin says "Retrofitting 18" wheels on Porsche vehicles which do not have 18" wheels as original equipment is NOT ALLOWED." While this was a technical issue back in 1993, everyone with 18" wheels here yells BS every time it's brought up. You might want to consider following the guidelines for upgrading to 17" wheels by fitting the improved caster mounts.

Now, everyone can restate, "Don't worry, it'll be fine...........

LastMezger

Here's a neat calculator:

http://www.rimsntires.com/specs.jsp

frankvan

There's alot of us that better call Porsche NA immediately. Of course this only applies to the second rate bodies they shipped across the pond, all the euro cars are fine!
And now that these cars are 20+ years old we should probably be fitting 15's on so as to stress the frames and bolts less. (Obviously those Neons are much better built to handle the stresses of the big wheels)

LastMezger

Bah! I'm not worried at all. I can imagine that if you're going 150 mph into a bend that the forces transferred by an 18-inch wheel and tire combo are great than 16 or 17 but at North American speeds...hardly an issue. Now if you track you car...