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Tyre Clearenze


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Hokay, since the question came up, I moved one of the new 225x60x16 (26.4" tall) Michelins on 16x7 46mm offset factory wheels to the front and checked the clearance on the strut spring perch.

The answer is, about 3/8 of an inch (.375") this is roughly 10mm or Not Much (see attachment below).

I have had X-ones in that size on my 88 since 2001 with no rub but the wheel has 8mm more offset and the perch is sloped.

OTOH I had Beretta wheels on my first 86 Fiero and there was an interference (would wipe paint off) fit on the inside rear strut. I added 3mm spacers and never had a problem so .125" was "enough".

However the question remains of whether this is enough. I think so.


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Interesting - a 245x55x17 is a tall tire - 27.6" according to TireRack, an inch taller than the 225x60x16s in the picture. Do the Mustang wheels have even less offset (like 25 mm) ? Is the bottom of your front spring perch shiny ?

Looks like my 225s have about the same clearance as the tread depth - 10/32 or .3125" which is about what I thought.

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So we have Kdirk having occasional rub with 225x60x16s, Steelfoot with none on 235x60x16s, and Richard with very slight on 245x55x17s.

My experience with 225x60x16 Michelins on 16x7x38mm wheels has been very slight rub at full lock on wheel wells when new and none on the spring perch.

For one thing, we have entirely too many tire sizes available. However my experience is that a 26.5" tall tire (or less) should not be a problem. 235x60x16 at 27"-27.1" is a definite maybe. Some others: 215x60x16 (stock 91)-26", 215x65x15(stock 88-90)-25.8", 235x55x16-26.1"

The other factor is the rim width and offset. Most factory 7" wheels seem to have a 46 mm offset, aftermarket are commonly 38 mm, and I have seen reference to 25mm for Mustang wheels. (more=further in e.g. closer to the strut). A lower number could also cause rubbing of the wheel well at full lock with a large tire.

I have no experience with non-stock front struts to know if they vary dimensionally but is a possibility.

And a final one is camber. This is set with the two big bolts near the bottom of the strut. Radials seem remarkably indifferent to camber - have seen rears set from 0 to 2 degrees with no apparent effect on wear (several sets of Michelins on 3800 FWD cars).

Considering the geometry, I suspect that setting the front tires a degree or two negative (common for sporty handling) would reduce the tire clearance on the front spring perch - can anyone check ?

All that said and again in theory, the relationship between the strut and the wheel should be fixed. If hitting things hard enough to deform I suspect you would have different issues. Tires being rubber are subject to deformation and growth but again I suspect (have no proof) that the top of a radial exhibits less of this than a bias ply tire would.

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As I recall, Stangs came with different 17" wheels depending on the years. I am not sure what year these came from. Now that Padgett mentions it, I have not checked the underside of the coil spring seat on the strut because I assumed, as he does that the distance between the wheel and seat is fixed.

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Well, I will add another screwball variable to this discussion. I hadn't mentioned this before because it had already been fixed, but:

After I bought this car, one of the first things I did was a complete front suspension. I went to the dealer, bought all AC Delco parts that cross ref'd to the Reatta. Original parts no longer available, so I bought the struts, springs, end links, sway bars, bushings etc. based on the current GM/Delco part #'s.

Put this all on, took to dealer for alignment. Drove home, a few days later started to notice rub, but only on drivers side.

Went back to dealer, they tore whole drivers side apart (I had installed everything myself) and discovered that the AC Delco strut on the drivers side had the steering knuckle welded on 1/4" lower than it was supposed to be. This really inspired my confidence in the quality of the parts.

It took them a while to figure this out, and only found it after comparing measurements to another new strut. So, they replaced my new drivers side strut with another new one, and re-aligned it.

Now, I am not getting nearly the problem I had the first time, but it does still rub a bit under the circumstances I posted earlier in this thread. To this point, I have had to believe that the tires are the cause (having 225's vs. 215's). I know the strut is properly dimensioned, the dealer verified that before installing it.

I guess my question is, does anybody else think this is just a tire issue, or should I be considering other causes. If the former, I will just buy different tires, which I had planned to do anyway.

All I know is this is really screwing with me, it shouldn't be nearly this difficult.


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Well a decreased offset (tire/wheel further out) will increase the bending moment on the strut/knuckle, that is one possibility. Another is that too much offset (say 51mm - have seen wheels like that) could have the reverse effect to reduce clearance. The second is that the camber/caster adjustment could influence the clearance. Might check the steering knuckle for "slotting". Something does not sound right, how wide are your rims ?

All I know is that the 225x60x16s Michelin "X-Ones" with 12/32" tread (new) I put on in 2001 have never rubbed the spring perch (and sometimes the neighborhood speed bumps hide behind a tree and jump out at you). They are on 38 mm wheels and the "new" ones have the factory 46 mm so we will see when I can afford two more tires.

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50% worn depends on how you mean it. I consider a 10/32 tire 50% worn at 6.5/32nds and worn out at 3/32nds. That is about a tenth of an inch.

OTOH I wonder what the application of a speed wrench to the spring perch would do.

And on the gripping hand, the enterprising soul could weld/redrill the four boltholes on the strut to be a bit lower. Would need a realignment then.

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