[ggggbmw]

I just put a set of wheel studs on my car. One thing that surprised me is that the recommended torque for the wheel nuts on the studs is only 75 ft-lbs.

That is way less than than the 103 ft-lbs that we use for the standard wheel bolts. Why the difference? Why 30% less torque required when using the stud nuts? 75 ft-lb is the lowest torque I've ever used on any car for nuts or bolts, and they felt barely tight (comparatively) when torquing to that level. Seems weird to be using a lower torque for track oriented studs.

Anyone have a good explanation?

Googling around I found a vague reference to clamping vs. twisting forces, but nothing authoritative, and didn't make much sense to me.

Note, this is different than the torque used to seat the studs in the hubs. Vendor said 50-80 ft-lbs for that (I used 65), and to let the thread-locker take care of holding them in place.

[dradernh]

Originally Posted by ggggbmw

I just put a set of wheel studs on my car. One thing that surprised me is that the recommended torque for the wheel nuts on the studs is only 75 ft-lbs.

What was the source of this recommendation?

Wherever it originated, it's wrong. The correct torque is 140 nm / 103 ft. lbs. for dry threads (i.e. stud/bolt threads that are not lubricated).

[ggggbmw]

The recommendation is from Bimmerworld. I'm using their 'Premium' studs. Their install doc is here: https://www.bimmerworld.com/core/med...t=.pdf&whence= (Yeah, likely overkill for my use, and pricey, but their strength explanation is persuasive, and I liked the aesthetic of the round tip.)

I would think that an outfit like Bimmerworld would provide the correct information. But I can ask them specifically. They were very helpful answering questions on the size of the stud shoulder during the purchase.

[jb-slow]

Probably just the material used in the studs themselves. My 360 has a spec of 73, seems super low but engineers do know some things.

[aerobod]

Standard BMW M14 wheel bolts are grade 12.9 that is good for 190Nm or 141lbft of torque, so well within the 140Nm specified torque. Limiting the torque to 75lbft on an M14 stud implies it is likely grade 8.8 which would be good for 110Nm or 81lbft.

[dradernh]

Originally Posted by ggggbmw

The recommendation is from Bimmerworld. I'm using their 'Premium' studs. Their install doc is here: https://www.bimmerworld.com/core/med...t=.pdf&whence= (Yeah, likely overkill for my use, and pricey, but their strength explanation is persuasive, and I liked the aesthetic of the round tip.)

I would think that an outfit like Bimmerworld would provide the correct information. But I can ask them specifically. They were very helpful answering questions on the size of the stud shoulder during the purchase.

Well, I certainly won't argue that I know more than Bimmerworld!

Between aerobod's comment and your reference, it sounds like wheel nuts on a BMW can indeed be properly torqued-down at what seems like a remarkably low value (at least to this long-time owner).

If it was me, I'd still call Bimmerworld to hear their reason for this spec, and I'd do it in the spirit of learning more about this topic. If you do that, it would be great if you shared with us in this thread what they have to say.

[cooolone2]

You adhere to the torque spec of the stud/bolt manufacturer, or you risk failure! Studs can stretch threads if too much torque is applied! Don't just go gutten teit...

And if you want to be sure, don't trust the reseller, etc., then contact the manufacturer yourself! This will provide you the information you need!

[ggggbmw]

I received an answer from Bimmerworld, and they confirmed that 75 ft-lbs is the correct value. (Got an answer on 4th of July. Wow, that is amazing service.)

This is the verbatim quote: "Seventy-five ft-lb is correct. Using more torque puts the steel into plastic deformation, leading to fewer cycles before failure."

However, linking that with the comment from aerobod, I'm still left wondering. Their Premium studs are listed as being 12.9 grade. Which should be good for 141 ft-lb. So even the usual 103 ft-lb should be well below the plastic range. Then again, no specs on the nuts, so maybe are the weaker wear item.

Apex lists the torque on their studs at 90 ft-lbs, so again, another manufacturer that lists a lower value than the equivalent bolt torque. Their explanation is more extensive: "Studs experience different loads than OEM bolts during installation. The difference is that a bolt is rotated into its threads in order to engage and secure it into place while torquing the wheel to the hub. This process creates both a twisting force and vertical clamping force. On the other hand, studs are already engaged into the hub and therefore do not require the same torque to compensate for friction while threading into the hub. Final torque on your wrench is achieve with less resistance and, therefore less torque is required to achieve the same clamping load." This is found in their FAQ here: https://www.apexraceparts.com/media/...structions.pdf
Not sure that's any more clear, but it's another data point.

In the end, cooolone2 may have the best advice to adhere to the manufacturer recommendation. And then again, maybe I'll just bump the torque to 80. But I don't think I will be going all the way to 103.

[Polo08816]

I use the same wheel studs and 75 ft-lbs of torque. No issues here even with tracking the car a lot. Wheel studs are one of the best mods I made as far as convenience of maintenance. No more needing to stabilize/hold the wheel/tire while changing them.