2010 TireRack Solo National Championships - Sep 7th-10th

[Reijo Silvennoinen]

This got me searching last night......and found some good articles and some not so good as you can imagine. Check these out if you are inclined to do so:

http://www.pcbloadtorque.com/downloads/TITERITE.pdf" onclick="window.open(this.href);return false;

http://www.pcbloadtorque.com/TechnicalArticles.aspx" onclick="window.open(this.href);return false;

http://www.engineersedge.com/wwwboard/posts/13070.html" onclick="window.open(this.href);return false;

Gotta get ready for work - back at ya later.

Reijo

[Bill Martin]

Started reading thru that material (thanx), but got to thinking maybe we're reinventing the wheel here. So I called ARP and worked around to their tech guy, Sam Benson. We discussed AX in general and the failure at nationals specifically. But I didn't have any details, and he'd be happy to hear from you Reijo. 800 826 3045. He did indicate that there's a study going on at the factory on multiple reuse leading to galling, leading to friction, leading to underclamp. He also mentioned that racing application studs such as mine are drylubed from the factory but other applications aren't. I asked if we should be using lube such as anti-seize and he said not at the standard torque as that could lead to overstress. We agreed that using anti-seize on my lugs and torquing to 50% (75 ft-lbs on a 5/8 stud) seemed like a good idea. He said most of you guys with 1/2" studs should be using 100 ft-lbs dry, but didn't want to make a recommendation at this time on lubing the threads and dropping the torque value. Maybe the factory study will generate that data.

[KJ Christopher]

I like Marshall's idea of over-torquing the nuts which gets me thinking about what exactly would be the ideal torque for autox. The factory torque settings would be set, I would think, with the general public in mind. However I think we can all agree that we are not driving like the general public and are stressing the OEM lug nuts/studs/bolts differently. With stronger studs, we should be able to torque them more. As someone mentioned the bolts/studs stretch a little bit with every installation (that's how they work to provide friction etc.). Anyone have a handle on the torque specs and how they are arrived at?

Maybe we autoxers should be torquing our nuts to a different torque than the factory specs as a matter of habit? And perhaps a different one yet for higher strength bolts?

R

Isn't the point to put more stress (stretch) on the bolts, while remaining in the elastic range, than the bolts would see in normal use? That's Why I like Marshall's approach - he had evidence that the bolts were seeing more stretch in use than he put on with the nuts. I'm assuming he checked that the over-torquing was still within the elastic spec. Torquing to a lower spec doesn't make sense to me at all. Using autocross forces, you're lessening the margin of safety and are getting closer to having the bolts be stretched by the driving forces, which would be bad. Wouldn't this continual movement weaken the metal? Like constantly bending a paperclip till it breaks? Is the crack you saw the result of this action or the result of someone over-torquing into the plastic range?

All this talk makes me want to replace the studs on the RX8. They've seen more off and on than would be expected in a normal lifetime. Sometimes lubed with anti-seize. I've never seen any reliable data (not saying it doesn't exist) on how much decrease torque to get same amount of bolt stretch. Guess it would depend on the lube - oil might be different than anti-seize? Anybody want to guess at how much torque a stock manufacturers 12mm lug would take before you stretch into the plastic range?

Oh - I'm a CPA. Never designed spaceships, buildings, bridges, etc. But I did have the quickest STX RX8 at nationals, thanks in no small part to the help of a few engineers here who helped with me with the frequency ratios et al. I love our region - the depth of knowledge we have and the way we really work to help one-another!

[Steve Towers]

Isn't the point to put more stress (stretch) on the bolts, while remaining in the elastic range, than the bolts would see in normal use? That's Why I like Marshall's approach - he had evidence that the bolts were seeing more stretch in use than he put on with the nuts. I'm assuming he checked that the over-torquing was still within the elastic spec.

What I took away from Marshall's post was, because the aftermarket wheel did not have hub-centric rings, the studs were loaded in more in shear, not as much in tension, so sideloading caused failure. All the engineering math that goes into stress/shear calculation is WAY over my head, but I think common sense would say that if all the parts are properly fitted and you're using stock hardware, then OEM lugnut torque should work. It's a given that any type of motorsports will cause more component stress than every day driving, but to what extent, is for most of us, guesswork. My thinking is if you change the torque spec when using stock hardware, then you introduce an element that was not engineered into the OEM setup. When changing stud size and/or material, the whole game changes.

[Marshall Grice]

What I took away from Marshall's post was, because the aftermarket wheel did not have hub-centric rings, the studs were loaded in more in shear, not as much in tension, so sideloading caused failure. All the engineering math that goes into stress/shear calculation is WAY over my head, but I think common sense would say that if all the parts are properly fitted and you're using stock hardware, then OEM lugnut torque should work. It's a given that any type of motorsports will cause more component stress than every day driving, but to what extent, is for most of us, guesswork. My thinking is if you change the torque spec when using stock hardware, then you introduce an element that was not engineered into the OEM setup. When changing stud size and/or material, the whole game changes.

well actually we broke studs due to not having hub centering rings. after we put in arp studs and hub centering rings i still saw wear indicating that the wheel was slipping around the axle centerline so i increased our torque setting.

Rough guideline for torque setting is to stress the bolt to ~75% of it's yield stress. Really the only way to measure that though is with a bolt stretch gauge.

one interesting thing i've also learned is that with the longer studs and spacers on the front of the evo is after we torque the lugs and drive the car around the paddock and re check them we'll get a little more out of them do to the wheel centering up better. The rears which are on stock studs and no spacers do not do this.

[Mako Koiwai]

Should there be a difference using R tires and street tires in how much stress is produced on the studs and the required torqueing?