dtm 911

I know a lot of you just rolled your eyes, but I have an honest question. I am thinking about the 964 C2 or C4 as my next car. I will show the car and I want to know what to do to accomodate 19x8 wheels all around. Obviously I need to roll the fenders, as it will be lowered, and I have heard it would need the Turbo suspension? Any ideas on the cost of all the Turbo parts that I would need? Are there other reinforcements that I could do to prevent a problem?

And an unrelated question... in your opinion, how close in reliability/problems is the '94 964 to a 993. I have heard that the 993s are pretty robust but with the 964s that was not exactly the case. What about the reliability of the C4 system?

Thanks so much for the help!!

Jay H

I can't help with the 19" wheel question.

But, the 1994 964 is probably one of the most bullet proof 911's you can buy. All the bugs were worked out by then. '95 993's seem to have a few bugs in them such as wiring harness problems on the early cars and some master/slave cylinder problems (please correct me if I'm wrong). I wouldn't be afraid of buying a 1995 993, but the '94 964 is the best of the lot.

The C4 AWD system is quite robust.

Hope this helps,
Jay
90 964

Michael W

Hi,
My friend's '95 993 had an engine wiring harness short that almost burned down the whole engine. It turned out the factory harness was wound so tight it accelerated the break down of the wire insulation. The short caused the engine to dumping fuel into the cylinders and he had 3 feet flames out the back of the pipes (so I was told). The problem was speratic and it took a while to trace down the problem.

Mike

GeoC2cab

High,
I dont think 19" wheels on the 964 is possable, what you are talking about would cost an incredible amount of $ and I doubt the car would handle that well w/ them on.
As for the reliability of a 964 any year would do, after the minor issues are taken care of u will have a car as strong as a freight train(I have a '91 and this is the case). 993's do have thier problems, I dont think the owners like to admit it, but go over to the 993 board and its loaded w/ all sorts of trouble the cars are giving their owners. A 993 owner will NEVER say/admit a 964 is better, or in that matter even close to his/her car. I'm a long time 964 owner and my car has been very "nice" to me.

MelissaM

I echo what Jay & Michael & George have already told you.

One thing about the C4 -- the system was re-designed for the 993's. I don't have the specifics, but I'm sure someone will chime in.

Good luck!

(Sorry, can't help you with the 19" wheels. You might try one of the racing forums, since they know quite a bit about suspension, etc. for fitting more rubber on the car.)

-- Melissa

Adrian

Firstly you cannot install 19 inch wheels on a 964 C4. The PDAS/ABS programming is not set up for it. You might get away with it if you ran the wheels without any tyres. The other options would be to remove the PDAS/ABS system and install some form of manual diff locking mechanism or maybe install the Paris-Dakar transmission. The C2 may be able to cope with huge modifications to take such wheels but I doubt it. The ride height would be somewhat high. Remember these 964s were designed for 16 inch wheels. For 1991 models and up the speedo will also be way out. Less of a problem on a 1989 or 1990 model but such wheels would change the effective final drive ratio as well.
The AWD system in the 964 is purely mechanical. Uses a front, centre and rear diff set up.
The 993 only uses a front and rear diff. The centre diff is replaced by a viscous coupling (invented by Subaru). The 964 uses four wheel speed sensors the 993 only three. Two at the front and one in the centre of the rear diff. I undestand that the rear sensor is a dual channel unit,
Ciao,
Adrian
911C4

John K

Dang it!
I was going to say everything Adrian just did.

Nick I

I'm not so sure that it would be as much of a problem as you suggest as far as the height of the tires. The ride height, final ratio and speedo will not be as far off as you suggest. The tire and wheel for a 235/35-19 tire is only 2.5% slower than the stock 16" tires/wheels. That means when it says 60 mph you are going 61.5. That is probably less than the error that is already in the speedometer. It is also only 0.5" taller than the 16" tires.

MikeF

One consideration that no one has mentioned....it would look ridiculous....IMHO.

Why would anyone do something to a car that clearly was not designed into its infrastructure? I sometimes wonder why we often think we are better equipped to "improve" our cars than the engineers that designed them.

The mind boggles.

Nick I

Does it really? I think it looks amazing. BTW this is a Photochop job.

Drew_K

I think it looks a little silly, BUT looks are subjective so do whatever pleases you. I believe Porsche issued a TSB stating that 18 inch or larger diameter rims should not be used on a 964 because the suspension is not designed to withstand the extra force generated. I suppose you could address that by changing out the appropriate suspension parts. However, IMO 19 inch wheels are not much of a performance gain, if any, over 18 or 17 inch wheels.

Drew
92 C2

Adrian

I want to follow up on Mr Nick Is comments about the 2.5% difference.
The 964 was designed and programmed initially for Bridgestone RE71s. I went to tire rack for the specs to compare the RE71 to the number given by Nick. He states a 2.5% difference. So I checked the rolling diameter or number of rotations per mile because this is what the PDAS/ABS unit on the C4 uses.
I also assume that the 235/35XX19 will be installed on the front. Would look a little strange on the rear.
Anyway the RE71 205/55ZR16 has 851 rotations per mile. The 235/35s offered by various manufacturers range around from 805 to 817 rotations per mile depending upon load factor. 6% of 851 is 51 rotations. These 19 inch wheels are getting very close to the limit. 817 is 4% and 805 is 5.5%. Now if the rear tyres are added into the equation, one is going to be just on or over the limit depending upon width of the tyre. According to Tire Rack the rotational speed decreases further with an increase of width in these 19 inch tyres,
Ciao,
Adrian
911C4

PS: I have seen PDAS units fail anywhere up from 4%. I have not seen one "not" fail at or over 6% differential. A couple of years ago we played around with 17 inch winter tyres and it was easy to fail the PDAS unit on the 1989 and 1990 964s. A little harder on the 1991 and up. However my research has revealed that the major change to the PDAS/ABS unit made in 1991 was not in relation to 17 inch wheels as first thought.

Nick I

I'm not sure, I might be mistaken. For my figures, I used this tire size calculator:
http://www.miata.net/garage/tirecalc.html

slant911

Adrian,

Slightly off the 19" wheel topic, but, I recently purchased a 90' C4 Cab and the previous owner had put 17" wheels on this beast. Do I need to worry about this PDAS unit failing with these tires? Tire sizes are right now 205/50/17 on front and 255/40/17 rear. On another related question - The front rubber on these tires is worn and was thinking about replacing them with 205/40/17 instead of the 50 size on the front to match the rear size. Will that work O.K.?

Thanks.

John

MikeF

John,

The "40" figure on your rear tire size refers to the percent of tire width. So, a 255-40 will have a sidewall height that is 40% of the width, in this case, 40% of 255mm. Since the fronts only have a width of 205mm, going to 205-40's would give your front tires a very short sidewall and completely screw-up the rotational diameter. Stick with 50's in front. That combination provides the appropriate rotational diameter.

Good luck,