Marc Shaw

I just finished another day at RaceCity here in Calgary -- went well.

Problem is, my Pilot Sports rubbed so hard on the oil line and secondary muffler that I got a slow leak that then allowed the tire and bead to separate around turn 4-5 (a fast left-hand sweeper) so I lost ALL tire pressure and almost went agricultural. After I pumped the tire back up, a slow leak was confirmed so I rushed out to buy new tires so as to not lose the rest of the day (I bought MPSC's as that was all I could find locally in a hurry)

but....

When I went back on track, I could tell immediately the right rear tire was still rubbing on hard left cornering.

So, how do I fix it or where is the problem??

The specs:
1. I just got an alignment (RS spec with -2.5 and - 2 camber) with a CB.
2. I have MPSC's 255/40/17's on the rear
3. I run 17" Boxster Twist wheels as track rims (8.5" with ET 50 rear)
4. I have the H&R street performance coilover setup (with spring rates of 250-285 front and 265-285 rear).
5. I also have TRG sways -- 21 mm (I think) rear set at medium.

I run with the red group (fastest students) so I drive pretty hard and fast.

Any ideas??

Are the offsets too low and would a spacer help (but the fenders are not rolled and I suspect the tire would rub on the fender)?

Are the rear tires too wide or do I need stiffer springs that are not progressive??

I need to fix this before the end of June (next track day) so any help appreciated.

Marc

YYC930

Call me Monday Marc.......our shop just dealt with this problem on a 964.......exact same thing......but I can't remember the cure.

garrett376

You're sure they're ET50???
On my narrow body C4 I ran 255/40 17's on 9" ET55 rears with a 3mm spacer (so ET52) with no issues - overhanging tire boogers would make the oil line shiny, but the tire never hit.

garrett376

Stick your hand in there to see how much static space there is between the tire and the line. I had enough room to squeeze my index finger in there - maybe 7-8mm or so... and that was with 3 degrees negative rear and a little extra toe-in...

Do you have a flattened oil line? Mine are later model cars (92 and 94) which have a flat oil line.

Marc Shaw

Hi Garrett - I was hoping you'd be around.

I just walked out to the car sitting on the trailer in the parking lot to check (I am still at the hotel by the track - 8 hour drive back tomorrow).

Yes, it is an 8.5 with ET 50.

I have about two stacked fingers (1.8 cm) between the tire and the secondary, about 3/4 of a finger (7 - 8 mm) between the tire and the oil line, and just over 1 finger (1.3 cm) between the tire and the trailing arm.

I cross posted this problem to the racing forum and it was suggested that deflection in the trailing arm rubber bushings allows the trailing arm to move in under load so the oil line/secondary gets rubbed but that does not explain why the trailing arm itself gets VERY rubbed (when I removed the dead wheel, there was a small pile of rubber shavings on the trailing arm).

The oil line is factory flattened. I have 0.16 toe both left and right rear.

Keith, I'll give you a call at your shop Monday - thanks.

Marc

garrett376

If your trailing arm was getting rubbed, then you may be looking at a bum wheel bearing, or some really flexible wheels! When you jack up the rear, can you wiggle the wheel when it's mounted? A really slack wheel bearing will permit the wheel to go off center. Worn out bushings will not have anything to do with the tire rubbing the trailing arm! That's either too wide of a tire for the rim, or too low of tire pressure permitting roll-over of the tire sidewall. Have you ruled out those things?

When you're driving on track, how can you tell it is rubbing? What do you hear? How can you tell it's rubbing badly? Are you sure you didn't just have a cracked rim causing a flat?

Marc Shaw

When I got the alignment and CB done last week, I had the Stealer check all wheel bearings. All were okay except the left front which I had them replace (I did not have time to do it myself).

The tire pressures were at 36 cold and got up to about 42 hot. The new tire is holding air so I don't think the rim is cracked.

When turning hard left, I (and the instructor) could hear rubbing at the right rear which was made worse when we went over small undulations or irregularities in the pavement. The secondary has a 4 cm wide streak of rubber on it, the oil line has a 3 cm polished area, and the trailing arm has a 3 cm wide rubber smear on it - plus the pile of rubber shavings.

As soon as I got back out with the new tires on, I could hear the same rubbing so I cut short my last session so I would not toast another tire (MP$C!).

I went for a casual street drive this evening and did not hear anything so I am not sure if I can replicate the rubbing away from the track. I guess I'll have to clean all the rubber smears off and pull some hard corners in a deserted parking lot then pull the wheel off again to see where it is rubbing. I'll also try to wiggle the wheel on the car to see it anything there is loose or wobbly.

I don't know - is 255 too wide for a 8.5" rim?

Marc
ps. on a positive note, I did get signed off to drive solo so my car weight loss program just improved by 180 - 200 lbs!

garrett376

I don't think 255 is too wide - I ran that size on my race car for half of a season on an 8" rim! And that was again with 255/40 17 VictoRacer V700 tires. Now I have never run MPSC's - do they make a lot of tire boogers? The tire boogers may be wiping off the inside of the tire and making the appearance of the line being rubbed and the trailing arm. Does the tire show a certain rub - as in the letters, etc. are worn flat? That is what I'd look for - the tire will certainly wear out faster than the metal of the trailing arm or muffler!

With VictoRacer tires when they start to wear down, two turns at Willow Springs - both hard and fast right turns, make an odd noise that I initially thought was a rubbing tire. At first it sounded like rubbing, but it wasn't a sound I noticed, it was vibration that I could feel in my butt. The tires just made a strange vibration-type "noise" I could feel. I found my oil line would get a 1cm shiny spot but from tire boogers - not the tire actually rubbing. Maybe MPSC's do this also?

I find it hard to believe those tires could rub that badly if your rear bearing is sound (go jack it up and see if you can wiggle it - maybe you had a 400lb passenger in the car that toasted the rear bearing!!!). When I had a cracked rim, and I've had two of them!!!, it took about 8 hours for the air to run down to close to nothing with the car just sitting still. I still wonder if your rim is cracked!!!

RSAErick

Hi Marc,

I solved a rubbing issue with 255/50-17 MPSC's by installing 6mm spacers, which I received from Jeff Curtis.

Here is the link that discussed my problems and eventual solution. Lot of great info:
https://rennlist.com/forums/showthre...rubbing+spacer

Note that I did NOT replace the wheel studs when going to the 6mm spacers. However, if I was going to space any further I definitely would.

Good luck!

Marc Shaw

Erick - thanks, very informative thread and your picture looks exactly like my problem!

So, you went with the 6 mm studs, not 9 mm as you were debating over. Stock studs?

I also noted a little rub on the oil lines at the inside top of the wheel well in the right rear side -- I think that is a problem of too low a ride height for the springs I have.....or else I am just too fast.

I think I will check the wheel bearing and recheck the tire pressures. I'll try a spacer (I think I have a 5 or 6 mm at home) and will likely end up putting in 52 mm studs with 6 - 9 mm spacer and rolling the fenders.

Marc

Chris M.

How did you not have to replace the studs? I just put on open steel lug nuts and the studs don't even come out past the top of the nuts. I have the same rubbing issue as Marc with 9" et55 Cup IIs and 255 MPSCs and was going to add 6mm spacers but after I installed the new nuts I realized I was going to need new lugs too.
I never had a rub with the exact same wheels and Pirellis Pzeros but after my first event with the MPSCs I got rubbing on both passenger and driver side control arms but no rubbing on the oil line (car is a 92). I can wedge a piece of cardboard between the tire and control arm, let go of it, and it stays in place. Pretty tight.

garrett376

It sounds like you guys need to ditch the MPSC's.... something is fishy with them. Either they're wider than they say or they're really flexible. Everyone on here I believe has trouble with the MPSC's. Get RA-1's!!!

tonytaylor

My C2 used to run with the H+R coilovers with MPSC 255/17 on 8.5 or 9 inch (can't rember exactly ) RUF wheels with 47 offset at RS ride height and had exactly the same problems as Marc.

I think the H+R street coilovers are too soft for spirited track driving at RS ride height.

Solved the problem by fitting H+R supercup coilovers, 22mm spacers and having the rear fenders streched out ( not simply rolled ). It doesn't rub anywhere at the rear now even with 265/18 on 10 inch wheels.

ThomasC2

I have the same rubbing with MPSC and 6 mm spacer. I think the side wall of the tire is more round than on many of the other brands like myt set of Toyo 888.

YYC930

Marc......we used a 3mm spacer........and the car had 255's.......problem solved.