Wheel Bolt torque settings please

I typically use 80 to 85 for my passenger cars (including F). I don't have a race car, so I don't know what I would use.

 

why would you have a higher torque requirement for the track? the car has the potential to see the same stresses on the street, well at least as far as wheel bolts go anyway.

going to 105 is a 40% increase over the spec. if the bolts were designed for that much torque, the spec would already be that high, so it may be the case that such an increase is actually compromising the bolts. it could also be the case that they decided 75 lb-ft was enough, but the bolt they sourced was much heavier duty just because of available parts supply.

hub wear due to excessive torque seems unlikely to me. if you track the car, you will have high wear. even race hubs don't last all that long.

 

Take their advice. Recommended torque is recommended torque...

 

I appreciate the kind words.

Having prepped and teched thousands of F-cars for the track over the last twenty-five years, the only variation from factory recommendations in prep for track events that I have found to be useful and prudent is raising tire pressures 4-6 psi over stock and the addition of a quart of extra oil in the wet-sump V-8 cars to reduce the tendency for starvation in long sweeping turns.

In terms of the lug bolt torque, F-cars use pretty honking big bolts in comparison to the "normal" sizes (12mm) on P-cars, BMW's and other performance cars. I'm not a trained engineer, but the clamping load required is calculated through exhaustive testing and known metallurgical standards and is well thought out and tested.

The P-cars are generally torqued to 90 lb/ft with a smaller threaded cross section, and because they're tracked often, many schools and events use that figure as gospel, so I wouldn't be concerned if the tech guys use that number. It's almost as if the F-cars are intentionally over engineered in that department.

I don't think there is damaged sustained by the F-car bolts tightened in the range of 75-105 lb/ft, but the factory setting is recommended and I know of no one who's lost a wheel by setting it at that figure. Enjoy the track! It's awesome!

 

I'm an overtorquer but the important thing is to check your torque after every session in preparation for the next session. These things come loose on track. The other thing is to make sure you mating surfaces are clean including the hub to brake rotor interface. Your clamping loads can fail due to crap in those joints. Clamping load on wheels is a more complicated issue than you can imagine.

 

FBB, did you know overtorquing can cause them to come loose?

The main reason why wheels come loose is because they've come loose ONCE and the mating surfaces between the wheel and the rotor (if clamped by the wheel to the hub) are no longer true and flat. This causes a rocking effect and the wear on the "low" side causes the clamping load to change. Once they've come loose, I never put anything back together until I've measured EVERYTHING and fixed it so it's true.

You are absolutely right. Clamping loads on wheels are more complicated than you can imagine.

 

Yes you are correct. Actually I have never had a wheel come loose because a I am paranoid sole. I even safety wire oil filters. I would love to dual use a car but because I could not stomach the safety compromises I always run a full race legal car that rides on a trailer and I have been to school to learn from Dr. Melvin and Dr. Gideon on race safety. So...what the heck since then I started racing since i had the car setup. I'm one of those HANS, full cage, full containment seat mounted to the cage kind of guys. I could never do what you brave soles do get in other people's car and instruct in the right seat often with questionable safety equipment. I am careful with my over torque to match fastner size with metalurgy and thus approximate torque. Manufacturer torque ratings need to make sense to me and then you have to factor in the application. If you really want to get into it what you need to do is confirm that the manufacturer did their homework and do a torque signature analysis and then properly set torque by angle. Sticky tires, aftermarket wheels, near boiling brake fluid, race pads, and high forces change the dynamic of what is happening at the wheel hub interface.

 

I track my dual use/street car, and what "the fat one" says is true, track stresses change things. I torque to 90 lbft and check torque between every run session. Even paint on the back of a wheel mating surface will heat up and compress and change things dramatically.

 

Torque is dependent on the material and size of the bolt.
The harder and larger the bolt size, the higher the torque setting.

I track a Porsche Boxster full race prep on a spec series (Boxsterspec under POC).
I normally torque to 90 ft-lb.
When we change set-up where a larger tire size is more optimum for the front, I need to put spacers to mount the tire.
I discovered that when I was using spacers and torquing to 90 ft-lb the wheel nuts would come loose. I then increased torque to 100 ft-lb (only when there's spacers used). The nuts didn't come loose.

For safety sake, always check toque of wheel nuts before every track session.
I haven't lost a wheel yet and don't ever want to.

 

Don't let this happen to you...

http://www.youtube.com/watch?v=jv4m41viy4I

 

In that particular incident, it wasn't improper torque that caused the problem, it was wheels that weren't the right ones for the car. The wheels weren't seated properly and the lug nuts were in bending and the failure was immediate....

 

JMF,

When we ran your car for Jim K., we torqued the wheels to 80. And he won a championship (second to his excellent driving, I'm sure the wheel torque was the reason!).

gp (former crew for that car...)

 

Nice David!!! BTW I torque to 88.