The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Minimum Sidewall/Wheel to Strut Clearance?

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Hey guys, new member here, although I've lurked for a couple months now. Seems like an awesome forum! My question is pretty much as the title says. I recently bought 18x10 SVE drifts and although they clear, they are close to the strut (maybe a quarter inch). I plan to run 275/35/18 Hankook RS4 but wanted to get your take on how much room is enough in there. Thanks!
 
Welcome to TMO. I would say 3mm so at 6mm you should be fine. I personally like 5-10 mm but I'm over cautious. If needed you can always throw a 5mm spacer in there.
 
Ok thanks! To clarify that’s ~5mm between strut and tire (not wheel) correct? I figured there can’t be nearly as much tire deflection at the top of the tire compared to the bottom which contacts the ground.
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
A quarter inch is already way more clearance than you actually need. An eighth of an inch is enough, and depending on your wheel and tire combination you don't even need that much.

This measured about 1.2mm at both the wheel and the tire (nothing rubbed until just before a couple of OE wheel studs started to let go - they might have been overtorqued once). Datalogs show peak lateral g's a bit north of 1.3.

DSC03378-web.jpgDSC03379-web.jpg

I've worked with slightly smaller clearances before (15" wheels on a different car, about 1/32" to the tierod end).


Norm
 
898
544
I don't like to run less than 3mm in tire clearance, but have on occasion run them as tight as Norm describes above. Some tire, like hoosiers, have a little bit of run out, so I am generally more concerned with tire sidewall clearance than rim clearance. 3mm of strut to rim clearance is more than enough, and you can get by with less.
 

Grant 302

basic and well known psychic
I ran the same size R-s3 on SVE drifts in the past. Clearance to the sway bar link bolt is what you should check. Never had contact with the stock Boss strut.

The top of the tire can move quite a bit if contact with the ground near perpendicular. Like that, the whole carcass shifts over when cornering. I'll try to dig up some old pics later.

Welcome to TMO!
 
898
544
My guess is that tires mounted on rims narrower than "measuring width" do exhibit more deflection toward the strut than tire mounted on rims out toward "max recommended".
Norm

That has been my observation. With a 315 Hoosier's on a 10'5 rim I can sometimes see a bit of side to side wobble if I spin the wheel when checking clearance. 305 Pirellis don't seem to have any noticeable run out on the same wheel.
 

Grant 302

basic and well known psychic
My guess is that tires mounted on rims narrower than "measuring width" do exhibit more deflection toward the strut than tire mounted on rims out toward "max recommended".


Norm

Certainly, but my example and the OP's setup in question are 275/35-18s on 18x10 rims. Hardly the case there, as the wheel is 1/2" wider than the measuring rim size at 9.5".

R-s3 on the drifts back in 2014:
11259654073_4dea089f25.jpg

There's still a fair amount of deflection with 275 Rivals on 11" wide rims (11/2017).

38625389206_bccc01eabb.jpg
 

Grant 302

basic and well known psychic
Lol. 75 series/aspect ratio? I don't see that it's 'died out' by axle height.

What I'm talking about happens at near 0º dynamic camber. Specific tire construction will certainly make a difference, and I don't mean truck tires.
 

Grant 302

basic and well known psychic
Not the best example of what I'm talking about, but you can see how the rear tires are deflecting quite a bit at the top even when compared to the bottom.

f1-japanese-gp-2016-nico-rosberg-mercedes-f1-amg.jpg

The 275 in question is also an SL construction. Mine made contact with the OEM sway bar link bolt with this wheel/tire combo. Though I'm sure there will still be those who doubt. ;)
 
Thanks for all the input guys! A lot of great information in this thread. Norm, I feel like I have a mile of room in there now lol. I’ll have to monitor the tires to see if there’s any rubbing but I feel better now than before. I wouldn’t be surprised if I have to trim that sway bar endlink bolt. By the way, all your guys cars are beautiful!
 

Grant 302

basic and well known psychic
I wouldn’t be surprised if I have to trim that sway bar endlink bolt.

Easiest way to fix it is to shim it back with some washers. Leaving the hex end of the bolt makes it much easier to remove when needed.

By the way, all your guys cars are beautiful!
Thanks, but just don't look too closely at my blue one! :D
 

Grant 302

basic and well known psychic
Can't find the pictures, but I'm sure you could see the light contact I was making on that bolt. I had no rubbing on the strut body, and I think the zinc coating would survive light contact. At least the hex end is relatively smooth.
 

Grant 302

basic and well known psychic
Of course, after I post that I can't find it... I found it!
Something wrong? Knowing how to drive? ;)

While I am not 100% certain it *is* contact with the bolt...well, you tell me what you think...

These are from last year when I first installed the R-s3s on SVE drifts:
15678786415_d35898ba41.jpg

15058840644_b7e8a62e45.jpg



Took these yesterday for you:
15680358822_61c3107630.jpg

15678766715_31014fdcc7.jpg



Well, if you want something *new* to discuss or argue about, I think it's more like up to 1" or maybe more travel at the bottom...

And apparently, people didn't believe me in 2014 either! :rolleyes: ;) :D
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Lol. 75 series/aspect ratio? I don't see that it's 'died out' by axle height.
I did say "mostly died out". The picture was more for illustrating the concept than something you'd work up any low-profile tire behavior directly from. Even 285/35's on 11" wide wheels deflect a tiny bit at the strut, but it's less than 1.0 mm at >1g with any reasonable-for-tracking inflation pressure.

I do have got a more directly applicable picture somewhere . . . OK, found it

Cornering distortion.jpg


With respect to that formula car - there's at least three hints suggesting that the left rear is flat or well on its way to being flat, so it's not going to have much lateral stiffness anywhere around its circumference.


Norm
 

Grant 302

basic and well known psychic
Might be a better example where the camera isn't tilted over 12º... but I still see inboard movement at the top. And yes, I know those tires are relatively 'stretched' on.

Super sports definitely move over 1mm at the top. This is my car with Super Sports 295/30-19 on 19x10 and 265/35-19 on 19x9 in front. The rear side walls at rest are very close to 'square' the fronts have just a hint of curvature inboard. My estimate for the rear travel is just shy of 1/4" at the top. More than that for the fronts. Easily 1/2". Super Sports can have an XL rating, but easily have SL or LL like sidewall stiffness. I think that's why they grip better than other tires with similar (inner) compounds/treadwear ratings.

15619943066_f4d6f7f4c8_c.jpg

I've never had a problem with under-inflated tires on track. Before I learned about mapping pressures from Rob, I was always incrementally bleeding pressure through the day.
 

TMO Supporting Vendors

Top