Wheel nuts should be expensive!

[ISLAMATRON]

All this talk about wheel nuts and didnt Red Bull break one this weekend? craziness

[l.etranger]

What's this about the nut not being heavily loaded axially? Wouldn't the inside wheels of a car in the corners be loading the stub axle in tension and trying to pull the nut axially off the stub?

Figuring ~650kg with fuel at 4g in a high speed corner, 55% rear weight and maybe a 140mm center of gravity (latter two figures assumed for convenience) for the complete vehicle, I'm predicting a load of 430 kilos on the rear wheel nut.

.55 rear weight * .5 inside wheel weight * 650kg = 178.75kg rear
140mm CoG / 1400mm track * 4g accel = -.4 load transfer on inside wheel
.6*178.75kg = 107.25
107.25* 4g = 429kgf

Granted this is not high in the sense that, say, a connecting rod bolt load is high, but it's not negligible, either - for a critical safety part with just three threads, as we've seen.

(Post corrected for obvious oversight of using rear axle weight instead of corner weight.)

[PlatinumZealot]

I notice that there is a wedge surface on the nut.So there is also a radial compression to hold on the threads even tighter..

[PlatinumZealot]

Here is a nice read (Repost?)

http://www.formula1.com/news/headlines/ ... /1057.html

The humble wheel nut may not be the most glamorous of a Formula One car's components, but it still needs to be engineered perfectly if costly pit-stop errors are to be avoided.

Unlike the majority of a Formula One car's parts, the manufacture of the wheel nut does not have to be a particularly scientific process. Machined in conventional fashion from a block of steel, Jordan have used the same simple nut design since 1997.

"A lot of the other teams seem to use these new ones that don't tend to look like wheel nuts at all," explains Jordan's chief mechanic Andrew Stevenson. "They've got all these special sockets and odd-looking fins on them, and are supposed to be more efficient for pit stops. We actually tried them, but found they didn't make any difference to us at all - apart from the fact they were 10 times more expensive."

He did not say what material though or method of manufacture..

Be it Jordan's retro classics, or the more bizarre-looking high-tech designs, a set of Formula One wheel nuts weighs around a kilogram. Jordan pay around US$60 for each nut and will get through around 250 per season. Their life expectancy does, however, vary.

"We'll always start a session with a new set, but once we get back to the factory after a race all the wheel nuts that still look to be in working order are crack-tested," says Stevenson. "If nothing is wrong with one, it'll be used in testing."

Arguably the biggest enemy of the wheel nut is the pneumatic air gun used at pit stops. The gun will often bend a nut out of shape, rendering it useless. As for the dreaded prospect of cross-threading? "We have a special thread," admits Stevenson, "but it's a trade secret..."

[ced ampo]

even worse, in an open car that wheel could have hit the driver

No No!!!! Only the helmet.

[ISLAMATRON]

even worse, in an open car that wheel could have hit the driver

No No!!!! Only the helmet.

I think MAx has gotten loose and is effin with us F1tech guys.

[riff_raff]

370HSSV,

If you look closely at those pictures you posted you'll note:

A) that wheel nut is machined from an investment casting. So it is likely titanium.

B) the arrow engraved on it shows that it is a left hand thread. So I believe it goes on the right hand side of the car.

[xpensive]

Interesting interview with that Jordan's chief-mechanic, the voice of sensibility.

I believe paying 500 EUR or whatever for a nut is clearly a NASA-syndrome, decisions made be geeks, shafted by un-scrupulous companies and the whole procedure never properly overlooked by a seasoned business-person. I see it happening all the time, people paying 200 EUR for an o-ring, thinking they get a superior quality somehow.

[Jersey Tom]

No way in hell I'd use any sort of aluminum on an F1 wheel nut. Too soft, even with it coated. It would be annihilated. Too big a risk for minimal gain.

They DO see a LOT of axial load. You could work out how much, but the torque on them is in the 100-200 ft-lb range I'd imagine. Significant preload no matter how you slice it.

Personally I'd still use steel, for the surface hardness. Ti doesn't quite have it, though you may be able to get away with it if the part is disposable.

For what its worth, as someone mentioned earlier, that isn't "anodize" as a coating. Looks pretty clearly like a PVD process.

[xpensive]

Just out of curiosity JT, how do you figure that torque number (100-200 ft-lb) and resulting preload?

And could you please identify "soft" in engineering terms, and how Aluminium would be "annihilated"?

[Jersey Tom]

Just out of curiosity JT, how do you figure that torque number (100-200 ft-lb) and resulting preload?

And could you please identify "soft" in engineering terms, and how Aluminium would be "annihilated"?

Actually I take that back. 250+ ft-lbf would be my guess for wheel nut torque, based on another professional open wheel design.

Axial preload is roughly F = T/K/d (roughly since K varies so much). Let's assume T is indeed 3000 in-lbf.. K ~= 0.2, d = 2". 7500 lbf of preload. Non trivial!

Regarding aluminum, it's hardness doesn't even register on the Rockwell C scale. You can coat it with something hard, like aluminum oxide (anodize) but that doesn't change the fact that it's super soft underneath. Additionally you can get wrought alloys with ~90+ ksi tensile, but it just doesn't take abuse. I'd think the impact gun would tear those fins to pieces. Casting alloys I might add are typically much weaker than wrought.

And even if it were coated, once it starts to wear off a bit you're screwed. Aluminum galls very easily (since it is so soft) and would totally seize up the thread. Totally kill your race result. Too big of a risk.

There's a reason why aluminum threads are not popular in general. You can use them in some applications, even on some racecars, but no way I'd use it professionally or on an F1 car. Way too much risk for negligible gain. Like I said you could probably do it with Ti if its disposable, and PVD coated. Alloy Ti is I think ~40 RockC? Not terrible. But you can get alloy steel up in the 55+ range.

[xpensive]

I knew engineering with imperials was from a different universe, but I never seen an equation like that to be honest.

Where is the thread-pitch, surely you cannot exclude that, or can you?
K is the coefficient of friction I guess, but does the preload go up or down with an increase in diameter?

[Cyco]

Pre-load on a F1 wheel nut is very high, At a historic race a few weeks ago the mechanics working on one of the Ferrari F1 cars (ex-Albereto 1987) where using a torque wrench around 2m long with a decent amount of one body weight (guessing 80kgs) on it.

Didn't ask the exact setting, but did lend a hand trying to hold a wheel to crack the nuts when 2 of them didn't want to come loose. As that wheel nut would not budge the others where not removed so I couldn't judge material or mass. This was a 12 point nut, however so I'm guessing a steel one.

[xpensive]

If you had to use 1600 Nm to loosen a wheel-nut on a 1987 car, I say it had got stuck there over the 20 years.

[Jersey Tom]

I knew engineering with imperials was from a different universe, but I never seen an equation like that to be honest.

Where is the thread-pitch, surely you cannot exclude that, or can you?
K is the coefficient of friction I guess, but does the preload go up or down with an increase in diameter?

Equation is no different imperial or metric. This is basic, basic stuff that would be covered in any Mechanical Engineering curriculum.

Thread pitch is indeed excluded. Thread geometry I believe is wrapped up into "K"

There is a more accurate version of the equation that uses mean diameters of the bolt and nut (which does take into account thread pitch) but the difference is small. Given how much K varies, no point in doing it.

For a given torque, decreasing diameter increases preload.