Tire to frame clearance

[Rayk]

I just had a pair of Cooper Cobras installed on the rear of my ‘87 TR 295/50x15. They’re on a pair of the Alloy 15x8 GN wheels. When I got home I measured the clearance between the frame the the tires and got concerned. On each side there is just barely 0.2 in. At the front of the tires and only about 0.1 (the width of a thin piece of cardboard) at the rear.

I took the car back to Discount Tire this morning to have 1/4 in. Spacers installed they refuses to install them. The tech said their spec said there had to be at lease 7 full turns to tight and there were only about 4 1/2. Without the spacers there is about 8 turns.

So, should i have these tires taken off? Or, maybe just install the spacers at home and not worry about it. I originally wanted the Coopers or whatever street radial available in 275/50 x 15 but only drag radials are available in that size. Opinions requested from guys who have been there.

 

[626gn]

I just had a pair of Cooper Cobras installed on the rear of my ‘87 TR 295/50x15. They’re on a pair of the Alloy 15x8 GN wheels. When I got home I measured the clearance between the frame the the tires and got concerned. On each side there is just barely 0.2 in. At the front of the tires and only about 0.1 (the width of a thin piece of cardboard) at the rear.

I took the car back to Discount Tire this morning to have 1/4 in. Spacers installed they refuses to install them. The tech said their spec said there had to be at lease 7 full turns to tight and there were only about 4 1/2. Without the spacers there is about 8 turns.

So, should i have these tires taken off? Or, maybe just install the spacers at home and not worry about it. I originally wanted the Coopers or whatever street radial available in 275/50 x 15 but only drag radials are available in that size. Opinions requested from guys who have been there.

Personally, I would not be comfortable with only 4-1/2 turns to tight. You may be able to swap your current lug nuts with "extended thread lug nuts", that may give you the added thread engagement needed to safely run the 1/4" spacers. Pretty sure those aluminum GN wheels use a conical seat lug nut but you need to verify to be sure. The other option is swap out your wheel studs for longer ones. A 295 is a large tire and using a spacer will push it out even further. Do you have the rear end jacked up or fender lip rolled so it clears without tearing up your tires?

 

[Turbo6inKY]

Discount Tire is correct in not installing with that little thread engagement.

The rear studs are M12x1.50 thread. 4.5 turns is only 3mm of thread engagement. That's not enough thread engagement to even calculate the stripping force, which means it may as well be zero. You could strip the studs or the lugs of threads just torquing it.

At 4mm, the stripping force (amount of force required to rip the threads out and separate the parts) is only ~6732.3 newtons. That's only 1513 pounds. Sure, you have five of them, but that's not a lot of margin, and if one breaks the failure will quickly process through the other four. That's so close of a margin that taking a corner sort of fast and managing to just tag a curb and that wheel is coming off. Let's not do that.

At 8mm of engagement, the stripping force skyrockets to 60591 newtons, or 13,621 pounds. Enough to hang the car sideways by the wheel with three more cars tied to it... from just one lug.

Get longer studs.

 

[1986 Buick GX1]

1/2” longer studs.
They can be had at local auto parts stores as well.

Dorman 610-323 Dorman Wheel Studs | Summit Racing

Free Shipping - Dorman Wheel Studs with qualifying orders of $109. Shop Wheel Studs at Summit Racing.

www.summitracing.com

 

[GNVYUS 1]

Options...

Ditch 295 tires...
275/60/15 Nitto if you want more rain safety but better dry traction. MT SS or ET Street Tires for even better dry traction.

3" Studs like mentioned
And the tires still if you want to dump the radials.

 

[Rayk]

Discount Tire is correct in not installing with that little thread engagement.

The rear studs are M12x1.50 thread. 4.5 turns is only 3mm of thread engagement. That's not enough thread engagement to even calculate the stripping force, which means it may as well be zero. You could strip the studs or the lugs of threads just torquing it.

At 4mm, the stripping force (amount of force required to rip the threads out and separate the parts) is only ~6732.3 newtons. That's only 1513 pounds. Sure, you have five of them, but that's not a lot of margin, and if one breaks the failure will quickly process through the other four. That's so close of a margin that taking a corner sort of fast and managing to just tag a curb and that wheel is coming off. Let's not do that.

At 8mm of engagement, the stripping force skyrockets to 60591 newtons, or 13,621 pounds. Enough to hang the car sideways by the wheel with three more cars tied to it... from just one lug.

Get longer studs.

I don’t want to get studs so long that I have to use open ended lug nuts. So, where can I buy lugs just long enough to to make up for the spacer I use?

 

[Turbo6inKY]

I don’t want to get studs so long that I have to use open ended lug nuts. So, where can I buy lugs just long enough to to make up for the spacer I use?

Then you don't want to run a 295 with a spacer.

Open lugs are the only way tech can tell you have enough thread engagement. If you want to go fast, you want open lugs and longer studs. If you want to just have fatty rear tires at the car show, screw them on yourself. But don't drive anywhere because if something comes apart and you hit somebody, your insurance company will throw you under the bus.

 

[Rayk]

I don’t want to get studs so long that I have to use open ended lug nuts. So, where can I buy lugs just long enough to to make up for the spacer I use?

Then you don't want to run a 295 with a spacer.

Open lugs are the only way tech can tell you have enough thread engagement. If you want to go fast, you want open lugs and longer studs. If you want to just have fatty rear tires at the car show, screw them on yourself. But don't drive anywhere because if something comes apart and you hit somebody, your insurance company will throw you under the bus.

First of all, I understand and appreciate the recommendations to get longer studs. And, I believe the advice given so far. But, I'm not new to TRs or racing them at the track. But, I only race on occasion and when i do, I have a pair of 15 x 10 wheels with MT 275/50x15 drag radials on them. They fit fine with plenty of frame clearance and lug engagement with the closed-end lugs that came with the wheels.

I merely want to buy longer studs that will allow the 295 street tires to clear the frame with whatever spacer is required. My calculations tell me that the 6mm spacers will give me about 1/2 inch frame clearance. So, I merely want to buy new lugs that are 6mm longer than the stock lugs. That will allow me to use the same lug nuts I use now which have about 9 turns to 100 ft lbs tightness. This doesn't sound difficult but, I don't know where to obtain custom length M12 studs.

 

[1986 Buick GX1]

First of all, I understand and appreciate the recommendations to get longer studs. And, I believe the advice given so far. But, I'm not new to TRs or racing them at the track. But, I only race on occasion and when i do, I have a pair of 15 x 10 wheels with MT 275/50x15 drag radials on them. They fit fine with plenty of frame clearance and lug engagement with the closed-end lugs that came with the wheels.

I merely want to buy longer studs that will allow the 295 street tires to clear the frame with whatever spacer is required. My calculations tell me that the 6mm spacers will give me about 1/2 inch frame clearance. So, I merely want to buy new lugs that are 6mm longer than the stock lugs. That will allow me to use the same lug nuts I use now which have about 9 turns to 100 ft lbs tightness. This doesn't sound difficult but, I don't know where to obtain custom length M12 studs.

As mentioned in post #4 these are 1/2” longer than stock and can be purchased at local auto parts stores. They may have to be ordered.

Dorman 610-323 Dorman Wheel Studs | Summit Racing

Free Shipping - Dorman Wheel Studs with qualifying orders of $109. Shop Wheel Studs at Summit Racing.

www.summitracing.com

 

[mblum]

By pushing this 295 out towards the fender lip, you don't foresee rubbing issues there unless you already have a trimmed fender lip or rolled fenders?

Unless your car is the stock ride height or higher I would think there would be clearance issues around the fender lip, at least I did with my 275/65R15 Nittos and MT ET Streets. I'm running the G-Body 15x8 rear GM re-pops and they do fit well. I have about 3/8" of an inch of clearance between the frame and the inside of the tire, so is about as tight as I'm willing to accept. My 86 has GM springs, so I assume they are stock, but at that ride height I did rub the inside of the rear fender lip when backing up on a not so perfectly level surface, like an inclined driveway. I had to roll my fender lips just slightly and now I have about 1/4" clearance. Again this is with 275" that fit perfectly in the fender well. I know a 295 wouldn't fit on my car without other body modifications, or raising it up 3".

Summit racing does sell a ton of wheel stud, but you have to search by size, not by vehicle type. On my 72 Chevelle which is lowered 3" I went with 1/2-20 ARP wheel studs and cut them to my preferred length. I run three different types of wheels on that car and I wanted the option of using wheel spacers, but didn't want to risk compromising the strength, so I went 1/2-20 and purchased deep style lugs. This has worked out well for me, but took a bit of planning and part searching.

 

[Rayk]

By pushing this 295 out towards the fender lip, you don't foresee rubbing issues there unless you already have a trimmed fender lip or rolled fenders?

Unless your car is the stock ride height or higher I would think there would be clearance issues around the fender lip, at least I did with my 275/65R15 Nittos and MT ET Streets. I'm running the G-Body 15x8 rear GM re-pops and they do fit well. I have about 3/8" of an inch of clearance between the frame and the inside of the tire, so is about as tight as I'm willing to accept. My 86 has GM springs, so I assume they are stock, but at that ride height I did rub the inside of the rear fender lip when backing up on a not so perfectly level surface, like an inclined driveway. I had to roll my fender lips just slightly and now I have about 1/4" clearance. Again this is with 275" that fit perfectly in the fender well. I know a 295 wouldn't fit on my car without other body modifications, or raising it up 3".

Summit racing does sell a ton of wheel stud, but you have to search by size, not by vehicle type. On my 72 Chevelle which is lowered 3" I went with 1/2-20 ARP wheel studs and cut them to my preferred length. I run three different types of wheels on that car and I wanted the option of using wheel spacers, but didn't want to risk compromising the strength, so I went 1/2-20 and purchased deep style lugs. This has worked out well for me, but took a bit of planning and part searching.

Appreciate the info in such detail. The 295/50s are now sitting on the GN after-market 15 x 8 wheels with no spacers. My ride height is with Bilstein Shocks all around and airbags in the rear at 10 psi. On the street, it doesn't squat much on take-off with those Cooper Cobras so, I don't foresee any rub with 1/4 inch spacers. I'm not sure about hard turns but, so far no rub. I'll look into the longer studs mentioned and, if I need a custom length, I have a local machine shop that can probably fix me up.