[patkeefe]

Hi All, and Happy Holidays!



I have the 968 up in the air, so I can fix a few nagging issues. One issue is the front tires rub on the inside at almost 100% lock, worse turning right than left. The tires and wheels are 7.5-65, with 235/45 17. This is not an M030 car. <acronym title='previous owner'>PO</acronym> did some upgrades to it. Perhaps there are some sort of M030-ish upgrades that need be done for the 17" wheels?



I am also going to fix the brakes, check the struts, and I am changing all the wheel bearings, as it has a wheel bearing noise (I hope it's it a wheel bearing noise). Brakes have been crap since the last time I took it to the track and put KFP gold pads in it. It has the stockers back in, but the car does not stop as well as it should. I guess I'll find more "while I'm in there".

Pat

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[flash]

too much negative camber? car too low? i see all sorts of weird stuff when people go too far, and many of them do.

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[patkeefe]

I don't think the car has too much negative camber, nor is it too low. I am going to do some searching here to find the specs. I don't think the rub I have is camber related. Photo attached.



   



   

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[flash]

it doesn't take much when you have a rim that far set inside. i see a lot of guys who add a lot of camber for track use (falsely thinking that is going to solve their pushing problem, when in reality it often actually slows them down, but that's a whole different topic). then camber change frequently results in rubbing. as an example, 3 degrees negative moves a 17" tire corner inward almost 1/2".



lowering exacerbates this. go too far (which is not much over 1") and you get two things. first you lower the roll center too far, which costs you speed in corners. but second it increases the amount of camber change in a corner, which can result in rubbing.



caster set at maximum, especially if the car is lowered or has a lot of camber, can do this too.



what are you alignment settings and ride height?

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[patkeefe]

Thanks Flash

I would expect the rub to be more at the top the plastic inner fenderwell with excessive negative camber. It's kind of difficult to see where exactly it is from the photos I attached; it seems more like what you would see with positive camber.



Camber effects on a 968 are probably quite a bit different than the 911...I can't get enough negative in the SC.



I am changing my wheel bearings. I definitely have the big brake setup. They appear to be the size of my S4 package I have stashed in the garage for the 911, which I have never used. I don't think these brakes were part of the factory delivered car; the only options I had are the <acronym title='Limited Slip Differential'>LSD</acronym> and power seats. Did M030 eve come on Cabs? So, now I am trying to figure out what we have here, and what the <acronym title='previous owner'>PO</acronym> modded.

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[flash]

no, M030 was not offered on cabs. that doesn't mean that somebody didn't add it, or change the brakes to bigger ones.



the SC suffers from the engine being in the wrong place, resulting in a bad F/R balance. this means that you need to make the front tires really dig in to get it to corner. the 968 is the opposite. if you make them try to dig in with camber, you overload the tire corners, resulting in roll and overheating of the tires.



the better option is to brace the underside of the suspension, thereby limiting camber change, which will inherently reduce the need for negative camber, and then reading tire temps to see where it is hot, and then altering things to accommodate that to try to achieve more even tire temps across the tire.



as for the rubbing, what it looks like is that your tire is rubbing at the rear inner corner of the left side of the car. is that correct?

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[patkeefe]

Yes, inner corner rear, in both front sides. I have a better photo.

The brakes in the front seem bigger, but I have no idea what the stock non-M030 fronts look like. The Hawk brake website shows the standard pads to be something like 3.14" wide, mine are much wider. I gave a cursory look at the rear shocks., and there are no small "helper" type springs on them. They are yellow, I'm guessing Koni.



Front left strut has a tag on it which says 951 343 031 12 Rumor has it the shocks were changed, which I got from a mechanic who worked on the car. The car was bought new by a woman, and the same people always worked on it (local PCA guys). I am guessing the shocks have about 50K on them.



Side note, whenever I had the car at DE, I always found it to oversteer a bit.



   

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[Darth Vadar]

IIRC, the offset for a 17" wheel should be about 50 to 55...

You mentioned 65? Maybe this is the culprit?

Of course, different style wheels can have different offsets and still work... I think...

Also, Factory recommends 225/40's on a 17" wheel...

Again, yours are a bit bigger... could be an issue...?

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[patkeefe]

You may be on to something, Lord Vadar. I think the wheels are the first variant of the Cup wheels. I will get the whell number tomorrow and see just what they are. Maybe some thin spacers will cure the problem, as I have room to go til I get to the fender lips.



Also narrowed down the brakes to be the M030/S4 option...36/44 mm pistons, with 304 x 32 rotors.

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[patkeefe]

Ok, so my front wheels are indeed 7-1/2J ET65. PN is 965.382.124.05. I may try and find some thin spacers.

I sent the brakes to (shameless plug) Goldline Brakes in Seattle. No one seems to have rebuild parts.

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[flash]

i hate spacers, especially on the front. unless you plan to change out to longer studs, and definitely steel lug nuts, i would not do that on any car to ever see the track. it's just asking for a failure.



it's possible that since yours is a cab, and on the track they twist a LOT, that it's just camber change during a turn that is causing a problem. that's why i came up with all of the braces. i wanted to track my cab, and the twisting was causing the geometry to go all wonky. between the lower mounting points moving 1/4" and the uppers also moving, plus all of the rubber bushings, i was getting an extra 4 degrees of negative camber exactly when i didn't want it. so, i'm still thinking your problem is alignment setting



what are your caster, camber and ride height specs?

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[patkeefe]

I hate spacers also. I really don't know any of the ride height or alignment specs, as we have never had it done. This is the wifey's car, and it hasn't been onthe track for at least 4 years, and may never see the track again. Doesn't mean I doon't drive it hard.



I am trying to figure out just what we have. I think it's stock suspension with M030 brakes and upgraded to 17" wheels. I need to measure the sway bars, but they look non-adjustable. I have to get at the power steering leaks, and pull down a rear Koni and see what kind of condition it's in.



Root cause of all this work is twofold: car makes noise, so I am changing all the wheel bearings, and the car has been neglected for years. I also feel it should ride and handle better than it does.

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[flash]

understood.



if you've never done an alignment, you're probably way overdue. that should be done at least every 2 years. you would be amazed at how much of a difference that can make.



at this point, after you change out the wheel bearings, i'd be looking closely at all bushings. the rubber is likely shot on at least the caster blocks. then get a good 4 wheel alignment, including ride height set. that will set you with a baseline. from there you can start investigating.



the only OEM swaybar that was adjustable was the rear M030. all fronts and the standard rear are not.

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[jaap]

The 7,5 with 65 offset is the correct size for the 968 however as Darth Vadar mentioned the tires should be 225/45. May be this 5mm each side is just to much with all flexing Flash has mentioned.

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[patkeefe]

Thanks again, all. I sure hate to replace those new Yokahama tires for a 5mm rub.



I have officially begun to eat and sleep 968. I can't get the hubs off the back because I don't have the horseshoe tool from SIR in my B90 kit. I am starting to doubt any maintenance was ever done on the car. CV joint grease looked like Bosco, just a little more viscous. I am still in shock after seeing the prices for power steering hoses. I am used to the Porsche tax, but evidently the 968 is in its own tax bracket.Might as well replace the stub axle seals on the transaxle while I have the shafts off. On and on. Be nice if I had a manual, but at least I have the internet and you guys on this forum!



I sure hope the noise goes away when I'm done.

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