I agree 67; we took it far...

And wheels are based on appearances... And I do agree with the rotational mass... However the larger Diameter rim adds quite a bit top speed numbers... And todays wheels are made really light weight...

In all honesty I was Surprised that Porsche uses 285/30/18 in the rear thats really wide... I would agree though from a racing on the track and most likely due to the rules of whatever class you race in that 17"s would be ideal...

 

One reason racers like 17s are because the tires are cheaper, as are the wheels. Bigger = more expensive. The tire selection for 17s is much larger than for 16s too, so it makes sense to go to 17s. And, the sidewall is nice on 17s.

Larger diameter tire=higher top speed. The wheel doesnt have much to do with it. Plus, most 944s, especially NAs, cant go fast enough to justify a larger diameter tire... I would assume unless you are running out of gear it wont make any difference.

285 isnt that wide when you consider some of the other tires Porsche uses on their cars. I think a gt3 has 305s in back? A gt2 must use massive rears as well.

 

I use a 285 on the rear of my turbo. I can tell you that on the track, I like 18"s more than 17"s. Less sidewall flex.

 

In PCA, diamter is open, but width is width of the widest available factory wheel for that model +1". So, an S2 with an M030 option had 7.5's and 9's, meaning you can run 8.5's, and 10's. A standard turbo had 7's/8's, so can only run 8's/9's. Turbo S was 7's/9's, so can run 8's/10's.

FWIW, I'm trying to put together a set of four 17X9's to run 255/40R17's. Toyo RA1's run only $175 a tire. I only do DE's, so I don't have to worry about rules.

 

Dannie thanks for posting..very interesting

 

Again if anyone wants the PDF file just shoot me a PM w/ your email and I will send it to you...

The File covers; 911's 959's 924's 928's & 914's model Cars...

 

DANNiE - I am buying new rims for my 89 944 Turbo S. I see you have 19" rims. I'm looking at a set of RUF RG5's 19" on ebay. I know they will fit. I currently have RUF 8x17 & 10x17 which fit perfect. My problem is that I'm not sure if 19" look too big for the car. Is it possible you can send me pictures of your car with the 19's so I can judge?. How do you like 19's on the car?

Thanks,
Fernando

 

Sorry to jump on this thread late, but did everyone notice this "approved" list is for TIRE recommendations? We've all read the warning about larger diameter wheels. This list is for tires and tires only. I think most of us can figure out what tire we'd prefer if we know our rim size and have internet access.

 

Its been awhile; I saw a few request for the PDF file here it is...
File is about a 1.5mb pdf any way it can be uploaded..?

Lets see if this works...

Try link:
https://drive.google.com/file/d/0B_r...ew?usp=sharing

UPDATE: sent you the file anyways but the link should work now I changed the settings on the file; should be viewable & downloadable no login now...

 

Link is bunk.. edit: works now..
PM sent..

 

.pdf

 

There is a TSB that states exactly why Porsche do not permit 18" wheels on the 944/968, but I guess you haven't read it. It should be around if you search.

The 968 Turbo S is permitted to run 18" wheels because of all the other mods.

Cheers,
Mike

 

TECHNICAL SERVICE BULLETIN

INSTALLATION OF 18" WHEELS NOT APPROVED

Model All Porsche Models
Group 4
Bulletin No. 9305
Date April 15, 1993

Concern:

Retrofitting 18" wheels on Porsche vehicles which do not have 18" wheels as original equipment is NOT ALLOWED.

General Information:

Endurance tests have shown that equipping certain Porsche vehicles with 18" wheels in an application not already approved by Porsche Cars, N.A. may result in loosened bolts and/or threaded connections on the front wheel carriers. This, in turn, may cause fractures in these components. Fractures may also occur in the front strut mounts and in the body in the area of the rear suspension as a result of the installation of 18" wheels not already approved for installation for this specific application.
Such damage can occur without warning and the vehicle may become very hard to control/steer as a result of the improper installation.
Porsche dealer personnel coming in contact with a vehicle that has been retrofitted with 18" wheels in an application not approved by Porsche, should inform the owner of the potential for damage to their vehicle and loss of steering control. Porsche Cars, N.A. should also be notified of any vehicles retrofitted with 18" wheels.

 

That .pdf just confuses me more about offsets..