pcar964

I incorrectly assumed the 964T had enough room in the back to fit just about anything, like the earlier 930s. I'm assuming it's a huge ordeal and very expensive to go to N/A rear trailing arms, and not worth the hassle. I'd be happy with 10s back there anyway - does anyone know if 10s with 295s in the rear would fit without rubbing? Or are we limited to 285s?

cobalt

I run the speedlines with PS2's in 295. They clear but barely. I have about .400 clearance both inside and out. The biggest issue is the trailing arm. I see minor rubbing probably from occasional hard cornering and sidewall flex but nothing that would be of concern.

Don't know the cost to install n/a control arms but I am sure it is not cheap.

jeff91C2T

Are these /30 or /35? 18" or 19" rims??

If you're rubbing on the trailing arm...are you sure you want to consider this minor???

cobalt

30's on 18" speedlines. All there is to indicate rubbing is a little black (very little) and it is just on the parting line of the casting which could be cleaned a little better. The parting line sits about .150" further out than the rest of the casting and could be tooled down. It is probably just from extreme cornering and only touches an area about .5" where the parting line is and looks like a little dirt more than rubber, it is also only on the drivers side. There is absolutely no signs of any rubbing on the tire itself. I have run 275's on my C2 and had far worse rubbing before using spacers and it was still safe. there is no concern for damaging the tire.

jeff91C2T

Dang...any rubbing on the rear wheels to the trailing arm sends shivers down my back. The power these cars put out and the consiquences of failure (ie...at the track at speed) is significant. Calling this safe is a bit of a stretch I think.

With that said I'm pushing the envelope myself :-) I'm going to look at fitting 305's on the rear instead of the current 285's. I've see two 965's with them installed (one car has been posted here a few times...the purple Turbo at Park Place). The trick...as the shops have explained it is the right spacing to the trailing arm, "plenty" of negative camber, and stretching the rear fender a bit.

pcar964

Cobalt, how low is your suspension set? I have Bilstein HDs and H&R red springs, not too low but lower than stock - I wonder if the 295s rubbing is affected by ride height?

cobalt

Not by any means is it unsafe. As I mentioned it is almost nonexistent and probably shouldn't have mentioned it. I would take a pic and you would see what I am saying but the car is asleep for the winter. I have nearly 30 years experience with Porsche's and I know if something is safe or not. I think you would be surprised how many people at the track have minor rubbing they don't even know is occurring.

My car is as low as it can go with the Bilstein HD's and H&R reds. There is absolutely nothing unsafe about the minute rub that occurred once or twice and I can assure you running a 295 is quite safe. Although each car is different as is with my car one side the casting is cleaned differently than the other which caused this conversation. I can easily blend in the parting line but I see no reason to.

You mentioned running 305's I don't see how it can be done safely. If my 295's barely fit I highly doubt a 305 would. The tire would have to rub with a far more dangerous amount than my 295's and running 305's on anything less than a 10.5 is more dangerous with far more sidewall flex that would almost guaranty tire rubbing.

jeff91C2T

Hey Anthony...just a heads up. Your 295's don't fit, they're rubbing remember :-)

Ya...305's are pushing the limit for sure, which is why stretching the fenders are part of the process. That purple 91 at Barrier w/ 700+ rwhp (posted earlier on this board) is running 305's. As I mentioned, this fit requires attention to detail.

Regarding rubbing....to each his own. I could accept rubbing on something sacrificial such as plastic, but on a structural item such as the trailing arm? Even with your 30 years of experience I'll stay clear of that advice ;-)

cobalt

Hate to say it but you are being an ***. We are talking an amount I shouldn't have even mentioned it is so minute. But I figured in fairness to the OP I would point it out to show how insignificant it is. Sand paper would be enough to remove the .030 of added parting line that the grinder didn't clean on the one trailing arm. You can easily take the parting line down to flush on the casting without impacting the structural integrity of the casting. It is only at the parting line that it rubbed and it was just enough to leave a faint line of black but no visible wear on the tire itself. I am sure i mentioned this before.

If you want to make something out of nothing you are doing your job quite successfully. I have no problems with 99% of your posts but you are pushing this way too far out of perspective here. I manufacture aluminum and magnesium sand castings that would make the best part on any Porsche look like crap and believe you me I have no doubts of what I am saying regarding material removal and I have no doubts that the once or twice off chance that the one side rubbed has any impact on the integrity of the tire or casting. I was trying to make the point that each casting and car is different and that special attention should be made when mounting any tire wider than the factory 265. Hell if you fit a 285 and under inflate it or one brand v another might create a situation that would be unsafe. I can assure you what I am trying to describe is far from any concern. As far as what you are attempting IMO As I mentioned, this fit requires attention to detail. I think it needs more observation than attention to detail and sounds dangerous at best.

jeff91C2T

Good point Anthony (which I haven't considered), if your tire were to go into an under inflated condition, this so called "minor" rubbing might be just a bit more of an issue for you. Is that safe?

I left out the tire diameter just for the sake of keeping this simple, but since we're splitting hares (both literally and figuratively) the tire dia plays a measurable role in the fit due to the geometry effect. Get into how you drive your car...street vs track vs auto x...and all this factors in to the descision making when pushing the limits. As I like to drive 10/10'ths and turn my own wrench, I appreciate pushing the limits. However seeing so many track incidents makes me risk adverse I guess...

And as for me being an *** stand point...no worries. Just calling you out on something you probably should not be giving advice on. Case in point you mentioning that a tire being under infated is going to have an impact on tire rubbing where the Turbo's have issues (ie...at the trailing arm). Toe-in and suspension under load (at the 9 o'clock position) might be a better place to look eh?

I guess after 30 years of experience it's hard to look at things in a different way ;-)

cobalt

Jeff WTF?

I hate to see something like this get blown so far out of proportion. My advice is sound and I will continue to stand behind it 100000000000%. There is absolutely nothing unsafe about my car and I drive it 10/10ths (most likely the cause of the minute rub) I drive my C2 the same way 10/10ths I would continue to drive it this way without worries. I know the differences between a dangerous rub and what I have been trying to describe without pics. Several top mechanics agree with me on this too. My wife drives my cars and I would never allow her to drive anything unsafe. I will more than likely sand down the casting in the future to eliminate the poor cleaning job done by the foundry and it will no longer be an issue under the most extreme conditions.


As I tried to explain we are talking less than a credit card thickness of area and any 964 turbo may encounter these differences in the manufacturing process. Hell these are sand castings not investment castings and a standard tolerance of +/- .030" plus whatever they didn't clean properly could impact the wheel fitment. It doesn't matter if you are running a 285 or 295 there is only about .100" difference in clearance between the two tires and the trailing arm. This is why I see this ever so slight rub on one trailing arm vs the other.

BTW rolling Dia of a 295/30 is 25" I have turned my own wrench too restored numerous cars and have seen occasional tire failure at the track from rubbing, I can assure there is no way this condition can be the cause of a tire failure. Even if the tire were under inflated and pushed hard.

I don't have any pictures of a rear trailing arm but if you look at yours you will see there is an area (parting line) that is cleaned but not flush with the casting. It is done by hand and varies from casting to casting. A properly made casting should have had this cleaned flush. If it were we wouldn't be having this discussion.

So you are saying my info is dangerously incorrect because of some additional material that should have been removed from the factory that has no sharp edges and does not rub constantly not even occasionally but once or twice in 4k miles of driving hard?

Do I understand you correctly?

jeff91C2T

Dang! WTF is right!! I can almost picture you beating on the key board!!!

Again no worries. I think with your 10/10'ths driving you feel more then safe with your rubbing. For my 10/10's....I'll stay away. Based on what I've read I question your level of competence for giving such (free) safety advice, even when it's minor rubbing as you say.

Do you understand me now?

cobalt

Alas I am beginning to see the light.

I am not banging my keyboard I am busy and shouldn't be wasting time defending something so inane. Although I think the people reading this should understand that differences do exist on pre 94 MY cars and it can vary more so from car to car and should be considered when fitting larger rubber. In the case of my car one trailing arm is slightly different shape than the other because of improper cleaning and can be easily remedied without concern. Although I do admit your comments are unfounded and therefore have become somewhat infuriating. I am assuming you are going to preach to me on structural integrity of sand castings next and how you shouldn't touch the factory parting line? Maybe you will try to convince me this will create a stress riser and lead to failure of the casting next? The fact that you can make a judgment about what I am saying with such authority and so few facts is beyond me.

I will take a picture when I get a chance I am sure once you see what I have been attempting to describe is pointless to argue about but for some reason you feel compelled to call me on something you have not seen or observed and deemed it unsafe.

You must be the worlds greatest mechanic or should I call you Carnac?

It might put it to rest but in this case I doubt it. I showed this to not only my mechanic but a current PCA national technical chair and they came to the same conclusion as I did. These are people that takes safety to a level that is unsurpassed.

I will leave it at this for now and wish you happy holidays.

jeff91C2T

Your passion for these cars, your opinion, and especially sand castings is admirable! Good stuff...

Happy holidays to you as well!!

pcar964

So back to my question then, anyone else running 295s on 10s in the rear? Pictures?