Wheel Nuts - Right Hand and Left Hand Thread

[balangproject]

There's an excellent thread already on the fsae forums about single wheel nuts: http://fsae.com/eve/forums/a/tpc/f/1256 ... 4610603711

How are you justifying the need for a single wheel nut and the risk it brings in a series where there are no pit stops to reap the benefit of a fast wheel change?

A very fair question. You're right, there are no pit stops and a quick wheel change isn't necessarily required, but there are moments when you need to change wheels quickly due to weather changes, but a single nut won't benefit that much.
We've always had a single nut on our cars, so its easier to improve on a design which we have and I think its beneficial for me to design a feature used on high end racing cars. Even though aesthetics shouldnt be important, a single nut is visually better I find and it brings the car closer to a professional formula car which might help on the marketing and sponsorship side of things.

I'd be interested to find out why Porsche have fitted one to their GT3 RS aswell.

Race Tech no.115, p.34-38.

http://issuu.com/thisisnotadrill/docs/rceteh115webpub

Thanks great article.

[SpookTheHamster]

Porsche's reasoning will be entirely commercial/aesthetic. They're selling the idea of a race car for rich people to use on the road, so it has to look racey.

[PlatinumZealot]

When you torque the wheel nuts and send the car on it's way, there will be a fair amount of contact force between the nut and wheel. My understanding of the concept is that under braking, if there's any slop between the wheel and the drive studs that allow the wheel to rotate a bit... there is enough friction between wheel and nut to drag the nut in the direction of rotation and self-tighten it.

Either way, the amount of slop there is likely going to be small and the effect probably isn't huge. And in any event, I know that current era pro open wheel cars have positive locking mechanisms on the hub & nut to prevent any rotation and all. That is still the most effective fail safe, and the mechanism only unlocks when the impact gun goes over the nut.

Memories from reading my machine design book, small vibrations during the period you describe above causes threads to lift and the nut/bolt to spin. So having the tighten rotation the same as the forward rotation of the wheel actually causes the nut to tighten when the nut starts to move.

I don't know how many of you guys have ever used an angle grinder before, but you can slip the holding nut on the spindle and turn the grinder on and the nut will tighten. The same goes for hole saw mandrels, and the engine fan on my BMW. I only need to tighten the fan nut with my hand, and when I turn on the engine the rotation does the rest.

[strad]

Memories from reading my machine design book, small vibrations during the period you describe above causes threads to lift and the nut/bolt to spin. So having the tighten rotation the same as the forward rotation of the wheel actually causes the nut to tighten when the nut starts to move.

.
And that explains why them old Plymouth lug nuts on that side were so hard to get off.

[riff_raff]

I read the article where Symonds describes the theory, but I don't know if I entirely believe it. Most of the mechanism Symonds describes for a pin-drive, centerlock wheel nut coming loose seems plausible, with the exception of one variable. And that variable is the prevailing clamped friction force between the wheel and axle flange face.

Proper design would seem to dictate that the prevailing clamping friction at the wheel/axle flange interface due to the installed nut preload should always be adequate to resist the shear forces applied, due to braking/driving torques or wheel bump forces. As Symonds noted, there will always be some small clearance between the drive pins and the mating holes in the wheel. So unless the wheel is tightly clamped against the axle flange, there will be a small, constant, relative sliding motion between the two. This would produce fretting, which is normally a condition to be avoided.

If there were indeed any relative sliding between the wheel and axle, the nut would loosen very quickly, due to the high cyclic load frequency rate that exists here. As a matter of interest, production car wheel fastenings (lugs) are designed to transfer forces solely via clamped friction between the wheel and axle.

[hardingfv32]

And that variable is the prevailing clamped friction force between the wheel and axle flange face.

Symonds says in the last sentences of the article that a wheel nut tightened properly is not going to come loose. He acknowledges the importance of the clamping force earlier in the article.

Brian

[Davey1000]

Regarding left handed and right handed threads, bicycle pedals have opposite handed threads on opposite sides. This is so that precession does not make one of the pedals unscrew.

In the good old days cars used opposite handed threads too. Of course a lot of the old cars used the lug-centric wheels which carry the weight of the car on the wheel nuts. Modern cars tend to use hub-centric wheels. With this type of wheel and hub there is a central spigot to carry the weight. In fact the spigot and the wheel are such a good fit that if rusting occurs one may need a hydraulic puller to remove the wheel (been there done that!)

Some classic cars such as the Leyland Mini used lug-centric wheels. Quite frequently, deceased Minis become parts donors and live again as trailers however there is a snag. The snag is the loosening of the wheel nuts on the left hand side (never on the right hand side) If the single axle trailer is loaded to about half a ton and if potholes and roadworks are traversed, nut loosening is quite likely to occur because of precession (trailers up to 750 kilos are not required to have brakes so it cannot be the braking that does it) Unfortunately left handed studs are not available but in this case slightly longer studs are available. If these are fitted it is possible to fit 3/8" UNF Nylock nuts on top of the wheel nuts. Problem solved! Empirical results show that this remedy is only needed on the left hand side. Of course if the axle load is so low and the roads are so smooth that fretting is never going to occur one can get away without using lock nuts.

[bigpat]

I read the article where Symonds describes the theory, but I don't know if I entirely believe it. Most of the mechanism Symonds describes for a pin-drive, centerlock wheel nut coming loose seems plausible, with the exception of one variable. And that variable is the prevailing clamped friction force between the wheel and axle flange face.

Proper design would seem to dictate that the prevailing clamping friction at the wheel/axle flange interface due to the installed nut preload should always be adequate to resist the shear forces applied, due to braking/driving torques or wheel bump forces. As Symonds noted, there will always be some small clearance between the drive pins and the mating holes in the wheel. So unless the wheel is tightly clamped against the axle flange, there will be a small, constant, relative sliding motion between the two. This would produce fretting, which is normally a condition to be avoided.

If there were indeed any relative sliding between the wheel and axle, the nut would loosen very quickly, due to the high cyclic load frequency rate that exists here. As a matter of interest, production car wheel fastenings (lugs) are designed to transfer forces solely via clamped friction between the wheel and axle.

Not quite.....
The taper on each lug nut engages with a similar taper on the wheel. The torque loadings from the wheels are still transferred through the wheel studs back to axle assembly.

I believe different handed nuts on each side are a waste of time. As mentioned earlier with the large contact where between nut and wheel, with the correct torque on the nut it shouldn't 't loosen.

Another major point that is forgotten is that all wheels are located on drive pegs, and THESE are what transfer torque loadings, not the wheelnut. The tight fit of the pegs the wheels ensure that there is no slip between the wheel and the nut. In this case, direction of thread makes NO difference!

I know the TWR Jaguar XJ-S, and the Le Mans XJ-R's, and Lola open wheelers used directional nuts, yet all a Reynard race cars used conventional thread on all wheel nuts, so even the best can't make their minds up!

[riff_raff]

bigpat-

I would disagree with you comment about it being possible to produce a precise enough fit between the 4 or 5 pins on the hub and the holes in the wheels to create a shear fit capable of sharing the load between the pins, and without allowing even the slightest amount of relative motion at the wheel/hub face that would result in fretting damage. It's not possible for several reasons. First, since there must be some clearance between the pins and holes to allow the wheel to be installed, in theory only two of the pins will initially take the shear loads. Second, due to the large thermal CTE mismatch between the hub and wheel materials, it is not possible to get a net fit between the pins and holes without creating excessive stress in the hub and wheel as they change temperature.

Clamped friction from the nut is the primary means of transferring torque between the wheel and hub. The pins are only a back-up measure if the nut becomes loose.