Torque for Wheel Lugnuts

[David T]

60 is great for sitting in the garage. Ergo 60 is great for most cars.

Overtorqueing can have bad results. On alloy wheels it can crack the rims. You can distort the rotors. You can fatigue the studs and lugnuts. On the shell type lugnuts you will spin the covers, especially when you try to remove them. Do yourself and your car a favor and get a torque wrench. They aren't expensive and it makes you more professional. 60 is NOT "great" for most cars. Always look up the manufacturer's recommended torque and use it. It is usually listed with tire pressures in the owner's manual. The ONLY time you tighten lugnuts by feel is if you have to change a tire on the side of the road.

[Michael]

Sometimes my sarcasm is lost on those that need it most.

[David T]

Hard to convey subtle emotions like sarcasm over the Internet. Sorry if I missed it.

[DMC-81]

Interesting. I always thought it was 60 ft/lbs as well. As mentioned, wheel nuts are listed on L:12:1 at 70 ft/lbs, but "wheels" are listed on A:03:01 at 60 ft/lbs. I have always used the "wheels" spec, but now it looks like that might not be right.

If "wheels" isn't the lug nuts, what is it?

Hmm, it seems there is a discrepancy in the manual/ documentation. Who knew! I agree that 60 seems low, especially where other cars are 80-100. I think I'll still stick with 70, as it works for me.

[Jonathan]

So I really thought I had a legitimate chance of making a single, concise post in a thread and leaving it so, but alas, that's not meant to be...

I was away for a week or so and wanted to look some things up before replying.

I had thought the confusion was between 55 and 60 ft lb and not 60 and 70. I had never seen the 70 and had always thought the other reference was 55, but for the life of me I can't find where that was.

What I did find were six torque references to the "wheels." Two for 70 ft lb, two for 60 ft lb and two for 59 ft lb (which is really just four references for 60 ft lb).

Here they are:

Lug nut torque 59 reference 2.JPGLug nut torque 59 reference.jpgLug nut torque 60 reference 2.JPGLug nut torque 60 reference.JPGLug nut torque 70 reference 2.JPGLug nut torque 70 reference.jpg

I've personally used 60 ft lb for the majority of the ten years I have had the car and not had any issues. My lug nut covers are also all in good shape coincidentally.

I would be inclined to believe the 70 ft lb reference though as it is in the Owners Manual as well as the workshop manual (the L section already mentioned). The 60 ft lb reference is in the A section of the workshop manual, but also makes a couple of appearances in the technical bulletins, specifically the one for the suspension recall.

I will likely stick with 60 ft lb until told otherwise. 70 ft lb may be correct though and I'd love to hear from a DMCX guy with their thoughts on the matter.

Interesting how a couple of you guys mentioned how 60 ft lb "seems" low compared to new cars. It does seem low, but so does putting 23 psi of air pressure in the front tires. That's what is required though and I would be inclined to trust it. I won't try and tell you that the entire car and documentation was put together without a single engineering calculation mistake, but going with what seems right for a new car in your old car isn't right to me either. Similar with the discussion on what octane for the fuel to put in. I'd rather go with what was originally intended until you know for certain you'll have problems continuing to do so.

Now that was anything but concise, but there you go...

[DMC5180]

Kind of an interesting topic of discussion. Just for curiosity, I looked up the wheel nut/ lug nut torque specs for our 2 current daily drivers and 2 previously owned DD's.

3 are GM vehicles (Cadillac,Pontiac,Chevrolet) with Alloy wheels ALL spec'd at 100 ft lb. Tapered seat lug nuts
1 Toyota with Alloy wheels spec 76 ft lb. Flange type lug nut with integral centering bushing.

1 DMC with 2 conflicting spec listings of 60 or 70. In this case, I shoot for the middle at 65 ft lb tapered seat lug nut

[Jonathan]

Interesting discussion indeed.

Something else came to mind and that is about the conversion from ft-lb to N-m or vice versa. I have seen in other areas where the conversions aren't consistent. And this is not something exclusive to DeLoreans either. You can find it occasionally in today's products too.

The conversion as I understand it is:

1 N-m = 0.7376 ft-lb

or

1 ft-lb = 1.3558 N-m

So, with the different references we've seen in the DMC documentation, I get this for the accurate conversions:

59 ft-lb = 79.99 N-m
60 ft-lb = 81.35 N-m
70 ft-lb = 94.91 N-m

80 N-m = 59 ft-lb
100 N-m = 73.76 ft-lb

So, often when it quotes both sets of units in the spec, one of them isn't right anyway, because they are all rounded one way or another. I think the one that might have been originally intended is the 80 N-m, because you see how this is exactly 59 ft-lb. That might not have looked quite clean enough in the manuals though for someone that was doing the review and it then became the 60 ft-lb we see.

And perhaps enough problems had arose and people got nervous and made a poor decision to go on top of a previous poor decision and someone, JZD perhaps, might have called over and said, "60 ft-lb??!! That seems too low! Make it higher!" And we got the 70 ft-lb.

Just a guess of course. None of those guys back then had the Internet to look things up. Nor did many of them use the US system of measurement, so they might not have been very familiar with it. We still see inconsistencies with how many litres are in a US gallon versus an Imperial gallon. Or confusion between pounds (or ounces) of force versus pounds mass. Someone in the UK trying to figure it all out at the time might have just said the heck with all these fractions of ounces and inches and pints and picked something that ended with a zero and that was that.

[Dangermouse]

So me standing on the end of my lug nut wrench and thinking "meh, good enough" is not scientific enough?

[Jonathan]

So me standing on the end of my lug nut wrench and thinking "meh, good enough" is not scientific enough?

<SARCASM FONT>Oh, that's plenty good enough. Just make sure you do your torquing before having lunch as that excess weight might throw off the calculation.<SARCASM FONT>

[Dangermouse]

Good tip.