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Tech Bulletin 9604 says that 18" wheels cannot be fitted on 993's before VIN 323614, even with the rack brace fitted. Does anyone know why?
My car is pre-323614 and came with 18" wheels, I fitted the brace shortly thereafter based on recommendations here. Recently, I was denied a wheel alignment because the steering rack bushings were worn causing a shift in rack position with right vs left lock. I had noticed a little squirly action during weight transfer in corners but thought it was the alignment. As the rack bushings only had 40,000 miles/6 years vs the originals which went more than twice that, I started looking into what could have cause the expedited wear of these bushings.
The only two factors I can think of are wheel weight and lateral force; 18" wheels should be heavier than 17"s and the wider contact patch provides more grip in corners. Well, I just weighed my Allegherita 18's with RE71-Rs and they are a couple of pounds each lighter than the Cup II 17's with Michelin AS4'sso that doesn't seem to be the factor. I may occasionally test the lateral grip of the front tires but it's not a sustained condition for the street so that doesn't seem likely either.
I do like the positive turn-in you get with 18"s due to low sidewall flex but need to understand why Porsche says no.
Any ideas?
Tech Bulletin 9604 says that 18" wheels cannot be fitted on 993's before VIN 323614, even with the rack brace fitted. Does anyone know why?
My car is pre-323614 and came with 18" wheels, I fitted the brace shortly thereafter based on recommendations here. Recently, I was denied a wheel alignment because the steering rack bushings were worn causing a shift in rack position with right vs left lock. I had noticed a little squirly action during weight transfer in corners but thought it was the alignment. As the rack bushings only had 40,000 miles/6 years vs the originals which went more than twice that, I started looking into what could have cause the expedited wear of these bushings.
The only two factors I can think of are wheel weight and lateral force; 18" wheels should be heavier than 17"s and the wider contact patch provides more grip in corners. Well, I just weighed my Allegherita 18's with RE71-Rs and they are a couple of pounds each lighter than the Cup II 17's with Michelin AS4'sso that doesn't seem to be the factor. I may occasionally test the lateral grip of the front tires but it's not a sustained condition for the street so that doesn't seem likely either.
I do like the positive turn-in you get with 18"s due to low sidewall flex but need to understand why Porsche says no.
Any ideas?
The steering rack just needs to be reinforced, as was standard from '96 on
I think that the part # is 993 347 130 02 which may be NLA
this thread reads a little funny because detail seems to have been added to the original question after the first responses.
as an early '95 owner (vin prior to one in TSB) i'm also interested in this more nuanced version of the question.
presumably, you just need new bushings and then the alignment and you're good to go.
im just wondering if the premature failure of my rack bushings is related to running 18s on an early VIN 95 car.
if the rack bushings are the only negative effect of running18s then I’ll just buy a dozen. However, the engineer in me says Porsche had a reason to not allow it. Distorting the front chassis or stripping rack mounting points would make me run 17s exclusively.
So the change occurred April 1995. From then on, you could bolt on the brace and use 18” wheels.
anyone know of any changes to front tub around that time.
next time I’m under there I’ll take some pics of mine, maybe someone with an older car could post some pics of the body under the rack?
Very early 95 here, 320225. I have been running 18" MY02's since 2006 after installing the steering rack brace. No problems in 15 years!
It is the burocracy inside a Company that works like a credit collection agency.
The Limonengelb (Or Lime Yellow, or for the most susceptible Summer Yellow) 993, it is from March 1995 and it is supposed to be rebuilt as a tribute of a 993 CUP, chassis related.
It took time and asking several times, in the end they called me from a Porsche customer service located in Portugal and they told me the chassis number doesn't allow to fit the 18" wheels.
But I also got to know that if one takes the car to Germany the TÜV would allow to install 18" wheels.
So there is no technical impediment: what i think is that there must be involved some kind of commercial agreement that Porsche has to obey.
Noone of the Porsche technical customer care so far has been able to tell me what is the impediment, so it must be everything but something technically related.
Last edited by nothingbutgt3; 12-03-2021 at 07:51 PM.
Hmmm, Jan. 95 build for me, 323188. I installed new bushings and the brace and have been running 18"'s for maybe 2 years and ~ 12,000 miles. No issues so far...
Before brace install Installing bushings and brace
I came across this thread when ordering new rear arms for my 97.
Some very interesting conversations by knowledgeable people in the 993 world.
While we stare at the front I wonder if you should not look at the rear?
That said you'all might want to read this:
Racing & Drivers Education Forum
Post "
95 993 DE Car
https://rennlist.com/forums/racing-and-drivers-education-forum/334546-95-993-de-car.html
There were a number of changes made by Porsche to the 96 - 993 suspension which are recomendations going forward that 95 car owners may want to be aware of, depending how you use or drive your car. The suspension geometry was changed, possibly bushings as well.
Enjoy
TJ
11-30-2021, 04:24 PM
Why are 18" wheels not allowed on early '95 cars?
