I’m trying out a new tire/wheel setup for the track and need some feedback about the minimum clearance between the tire sidewall and strut. With a 25mm spacer I have 2mm clearance. I have driven on the street with them and there is no rubbing, but I don’t know if there could be any deflection on the track which could cause rubbing. Is 2mm sufficient clearance for track use?

definitely tight. but deflection shouldnt cause an issue since it'll be back on the right part of the rim by the time it rotates up there. I've run with a couple of mm clearance. It could become a problem with taller tires that flex more, tho. FWIW - I ran 31mm spacers and found them to be the sweet spot

honeybadger said:

definitely tight. but deflection shouldnt cause an issue since it'll be back on the right part of the rim by the time it rotates up there. I've run with a couple of mm clearance. It could become a problem with taller tires that flex more, tho. FWIW - I ran 31mm spacers and found them to be the sweet spot

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Thank you! The 2mm clearance is with Apex 19x11 ET52 and Continental ECF 315/30/19. I first fit them with a 28mm spacer, and running -3.4 camber they seemed really close to the fender so I was worried they would rub under compression while turning. I switched to a 25mm spacer and the fender fit is still tight, but at least gives a little more space.

The 2mm clearance might be tight for the track depending on your tire selection. I've experienced some strut rubbing on the track with 25mm spacers, Apex 19 x 11 ET52 wheels and 305/30-19 Goodyear 3R's. I did not experience any rubbing with the same tire and wheel combo and 28mm Apex spacers or 30mm MMR spacers. I also used Falken 660's and Hoosier TrackAttackPro's with the 28mm and 30mm spacer combination without experiencing any strut rubbing. The car is a mostly stock 2021 Mach1 that's only used for track days and time trial/time attack at BRP Classic, CVR, ORC-LVMS, Spring Mountain, and WSIR.

krisk said:

I’m trying out a new tire/wheel setup for the track and need some feedback about the minimum clearance between the tire sidewall and strut. With a 25mm spacer I have 2mm clearance. I have driven on the street with them and there is no rubbing, but I don’t know if there could be any deflection on the track which could cause rubbing. Is 2mm sufficient clearance for track use?

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I've always considered 5mm the minimum gap sidewall to anything.

JAJ said:

I've always considered 5mm the minimum gap sidewall to anything.

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Thank you for the feedback. Is your 5mm guideline based on known issues with running less than that amount or some other reason?

Is this the same size tire, or were you running the 295 previously?

Junkyard Dog said:

Is this the same size tire, or were you running the 295 previously?

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I was running 295/30 previously.

krisk said:

Thank you for the feedback. Is your 5mm guideline based on known issues with running less than that amount or some other reason?

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I've had rubbing and that spacing fixed it.

Really helpful info on this thread, and good timing since I'm experiencing an interesting dilemma myself after mounting 305 wide tires today.

I'm doing the tried and true setup: 2018 Mustang GT PP1 with magride, -2.77 front camber, 1 inch lowered on FP springs, 19x11 ET50 wheels on 305/30r19 tires, with extended studs and 1 inch spacer. This should be a perfect setup without any issues...

But unfortunately I'm getting rubbing on my front left tire, at the transition between edge of tread and tire sidewall. Front-right side tire is perfectly fine despite having the same alignment, camber and tire poke as left side. As far as I can tell, I only rub on a straight line going over mild or harsher bumps or road imperfections. The sound is like a screechy "SCRRRP" for half a second or less immediately during the bump only.

Not sure how, but my left side outer fender tire clearance must not be enough...so I want to move from a 25mm spacer to a 19mm spacer and get 6mm extra outer clearance, and lose 6mm inner clearance. I measured inner clearance using the drill bit method and with wheel turned full lock pointing away from the car. A 1/2 inch thick drill bit just barely gets stuck at the tighest point between the strut and inner tire. Thats about 12.7mm of clearance, rounding down to 12mm to be cautious, if I moved to a 19mm cortex spacer, I would theoretically be at 6mm inner clearance and gain the 6mm outer clearance. I am not sure if this would be enough

I could also cut my strut towers to get more negative camber since the alignment tech yesterday told me I was maxed out at -2.77. I think -3.2 or more negative camber if I can get it would help with the tire rubbing too.

Crazy the variation of how some people are running 28mm spacers and I'm looking at 19mm because 25mm is too much.

What do you guys think?


Here are some pics below:

Rubbing marks on edge of tread


Other side tire looks perfect



Camber plates are at the same level both sides.

I think I would go with more camber - I keep reading that S550s love -3.0° or more. Fix your clearance issue and get higher mid-corner speeds due to more front outside tire grip at the same time. 2 birds with 1 stone and all that.

Working on getting the strut cutting tool as we speak - hopefully will be able to cut them out next week and get another alignment. Aiming for -3.2 degrees negative front camber.

Junkyard Dog said:

I think I would go with more camber - I keep reading that S550s love -3.0° or more. Fix your clearance issue and get higher mid-corner speeds due to more front outside tire grip at the same time. 2 birds with 1 stone and all that.

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Really, it's any McPherson strut car. It's the nature of the beast. It's also tire dependent, but you basically go more negative until you start to degrade braking. That can be -4.5* or higher on some cars.