Tyre pressures and wheel nuts

[Petrolthreads]

I'm back on track on Monday and wanted to ask the more experienced among you what tyre pressures you run on track days, and also last time out I noticed guys checking wheel bolts after every run, is that really necessary?

[rix313]

IMO it's good practice to check the wheel bolts, gives you piece of mind when driving that the wheels wont fall off.

[Petrolthreads]

Does that happen often then?

[Black_Potato]

lots of heat expansion on track, so do wheels fall off often, no, but thats because we check them after each session ;)

Have I seen it happen, yes on a lotus at bedford autodrome.. have people in PBMW had problems yes but I think they have noticed befor they actually came off.

Tyre pressures depends on the tyre, but for say a R888 you want to run at aprox 30PSI, now when you go on track the pressure goes up so most folks set them to around 23-24psi cold so that when hot they are around 30PSI.

[MillRat]

On this topic, I have replace the wheel bolts with studs (Turner Motorsport) on my track car, and yes it is good practice to check them before every run (it is better to use a torque wrench as well). I have competed at 2 events where a tyre has separated from a car due to incorrectly tightened wheel bolts/nuts.

My question is, what torque should the wheel nuts (not the factory bolts) be tensioned to? I ask because wheel studs/nuts do not require the same tension as bolts to provide the same clamping force. I am worried that by using the wheel bolt torque, I will over tension the nuts, and that could end in a sad day at the track if the studs snap.

EDIT: Like said above, a starting pressure of 23-24psi is a very good start. I typically run my front tyres 1-2 psi higher as my rear tyres tend to heat up more.

[Black_Potato]

I'm cant comment specifically on your E30 setup but I have had various cars with studs and bolts and the torque settings have all been in the same range. i.e. around 100nm

I think the Lotus was the lowest at 84nm, the Jags the highest at 115nm...

Personally I'd be happy at around 100/110nm.

[GeoffBob]

So long as the thread on the stud has the same pitch as the bolt it replaced then it will have the same torque value. The finer the thread the lower the torque required to achieve the same clamping force.

[Screacher]

First time I used my car on track, I had all four wheel studs on two corners come loose This was the session immediately after lunch. Car had been on track for much of the morning session but had stood cooling for an hour or more at lunchtime. Second lap out, I felt a very parculiar vibrartio0n but managed to limp back to the pits to check.

I think the main problem is due to wheels heating and then cooling. Had they been hot all the time, I don't think it would have been such a problem. Also, I think it is more likely on cars with painted wheels. Consequently, if the car is off track for any length of time, I always check them before going out again.

[GeoffBob]

Torqueing wheel nuts/bolts is an exceptionally important practice. It is a common misconception that it is by virtue of the shear strength (strength of the bolt/stud perpendicular to its axis) that the wheel is held intact. It is, in fact, due to the friction between the inside face of the wheel and outside face of the hub, that the wheel is held in place, and it is by virtue of the clamping force (in reponse to the tensile force exerted upon the bolt/nut as it is tightened) that this friction is created. In the absence of this friction, and due to the fact that the shear strength of a bolt/stud is typically half its tensile strength, it is possible to shear improperly tightened bolts/studs under heavy braking or acceleration. This is also the reason why five is better than four, and six better than five etc. since more bolts/studs results in an overall better shear strength. The moral of the story, however, is to keep those suckers correctly torqued.

[UweM3]

Most of the time I have seen bolts/nuts coming loose on track days is due to freshly sprayed or powder coated wheels with the mating faces not masked up before painting.
The extra heat generated on a track day burns the paintlayer away on the mating faces and presto, you nuts/bolts are loose!

Or simply forgotten to torque them up after swapping wheels. I ALWAYS torque my wheels up, even if I only roll it on the trailer. Better safe than sorry. As soon as I fit a wheel to my car, I torque it up.

I also check them in the morning before a track day (together with tyre pressure) and after lunch break.

And I have said it more than once, I disagree with all of you running R888 at low pressure I run them 38-40 psi HOT on the M3. Give it a try, you may be in for a surprise

[Petrolthreads]

Thanks guys quite an education this thread so what torque should mine be at 15inch bbs four studs, standard set up I think

[MillRat]

Thanks guys quite an education this thread so what torque should mine be at 15inch bbs four studs, standard set up I think

Do you have an E30 repair manual? If so, it is stated in there the correct torque settings for the wheel bolts.

Also, thanks Geoff for clearing that up for me. I always knew it was the frictional force between the wheel and the hub that stopped the wheels falling off, but always thought that the torque required for a bolt was higher than a nut.

Uwe, good call about the powder coating. I never considered it being a problem before. Thankfully, I haven't been caught out before.

[Petrolthreads]

No I don't have a manual can you buy a PDF?

[Black_Potato]

You can get haynes manual or even better the Bentley service manual.

110nm from memory.

Lots of Torque settings here...
http://www.e30zone.net/modules.php?name ... c&t=134960