Lug Nut Torque and Tire Pressure on Custom Wheels

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The Critic

The Critic

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Without turning this into a rant post regarding my hatred of aftermarket custom wheels, how do I determine the correct lug nut torque for oversized, aftermarket custom wheels.

For example, let's say in a hypothetical situation that the factory lug nut spec was 85 ft-lbs for a 16" wheel. The owner decides to install 20" wheels and tires.

1. Do I still adhere to the factory lug nut specifications? If not, how do I determine how tight I should tighten the lug nuts?

2. What is the correct tire pressure for the vehicle now that the tire/wheel size has changed?

Thanks.
 
Regarding question 1, I believe you should use the factory lug nut specifications. I have never seen an owner's manual recommending different lug not torque depending on rim size.

Keep in mind though that aftermarket rims may require different lug nuts (length and seat).

As for question 2, I believe that depends on the load rating index of the new tires.
 
Originally Posted By: Quattro Pete
Regarding question 1, I believe you should use the factory lug nut specifications. I have never seen an owner's manual recommending different lug not torque depending on rim size.

My auto shop instructor told me that the specified lug nut torque is based on the wheel size, the wheel material and the number of lug nuts. I have no clue if this is true or not, but it sounded reasonable to me.
 
I can't believe the lug nut torque is going to need to change much at all on the same vehicle with different rim sizes.

I've also wondered what a good pressure is when changing tire/rim size. I have 245/60R17 tires on my wagon that originally had 225/75R15 tires on it. I have no idea what the correct pressure should be now but it seems to like a little more pressure than it did before. I'd like to hear an answer if somebody has one.
 
Originally Posted By: WishIhadatruck
I can't believe the lug nut torque is going to need to change much at all on the same vehicle with different rim sizes.

My dad's Previa calls for 75 ft-lbs on a 215/65R15 setup, while the Saturn requires 103 ft-lbs for a 185/65R15 setup. Both wheels are steel, but the Previa has 5 lug nuts versus 4 for the Saturn.

I'm really curious why there's such a huge difference.
 
Use the same torque specification. It's based on the stud, not the wheel.

I'd set tire pressure the same way I would any other tire; start at the manufacturer's recommended pressure and make adjustments from there.
 
any fastener/fastening is based on fastener size, not how big the object is that is being fastened.

think about it, you wouldn't torque a 1/4-20 bolt to 500 ft/lbs just because it is holding something onto the golden gate bridge.
 
Originally Posted By: The Critic
My dad's Previa calls for 75 ft-lbs on a 215/65R15 setup, while the Saturn requires 103 ft-lbs for a 185/65R15 setup. Both wheels are steel, but the Previa has 5 lug nuts versus 4 for the Saturn.

I'm really curious why there's such a huge difference.

The total clamping force is close on these two examples and is proportional to torque times number of fasteners, ASSUMING the same thread size and materials, etc.
 
If you want the tire contact patch area to be the same, then use the same pressure. This would have the effect of narrowing the contact patch shape across the width of the fatter tire to allow better cornering. But I think determining the new pressure is better done experimentally.
 
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critic,
unlike the vagaries of braking systems, requiring the rotors to be rotated three times clockwise on the vernal equinox, and a half turn anti-clockwise on the other one (reverse for Coriolis).

The clamping force on a wheel, or any other flange subject to a lot less jiggerypokery.

Consider a bolted flange/wheel to be a parallel combination of two sets of series springs.

One set is the stud, and the flex in the threads of the nut and hub. Increasing stud diameter (a) increases the stiffness. Increasing the length of the stud (b effective length) reduces the stiffness.

The other set is the the wheel. Increasing the length of the stud (i.e. b wheel material depth) reduces the stiffness, as does the amount of cutaway material.

Consider a steel wheel, where the actual wheel width at the point of clamping is only a few mm, versus a mag, which may have an inch of wheel thickness.

So to obtain the same clamping force, you need to establish the clamping force of the original wheel, which can be considered a parallel set of springs with the new set of wheels which is another set of parallel sets of springs.

I could spend all weekend doing the sums.

Or I could do them up nip tight, and add a 1/4 turn.
 
Originally Posted By: Shannow
and add a 1/4 turn.

And you were doing so well, until that last piece of "jiggerypokery."
 
Keep the lug torque the same. You don't want less, for sure. And more will stress, strip, or eventually warp things.
You may want to recheck the torque with new wheels after a week or so.
 
What Shannow said----- I think. Jiggerypokery?


Snugg'em up and add a little emfff!

Worked at a tire shop for years and years, never did torque a lug. Course we didn't use an impact wrench either. Nothing but a good old 4-way lug wrench. Never broke a stud, never had a wheel come loose.

I did one time see my working podnuh tighten the lug nut through a rim on the left hand side of an old Dodge. Forgot to tell him left hand side left hand threads on old Chrystler stuff.
 
Originally Posted By: The Critic

My auto shop instructor told me that the specified lug nut torque is based on the wheel size, the wheel material and the number of lug nuts. I have no clue if this is true or not, but it sounded reasonable to me.


I do believe he is correct as there are 3 torque specifications for my yukonxl one for 17" standard oem wheels, one for 20" oem factory wheels and one for 20"+ wheels. I do believe those specs are based on radial vs thrust loads encountered by each diameter wheel. There is also some mention of steel vs aluminum. So material strength/characteristics come into play. BTW, I noticed these at a Sears auto center spec book while getting a tire plugged. There was only a variance of about 10'lbs but there was a variance.
FWIW, the tire techs there were paying very close attention to that book and did get the torque wrench out and torque them to spec. I was impressed as I always thought those guys just stuck the impact wrench on and hammered away until it locked up then spit on the cover and slammed it on with the rubber mallet..
LOL.gif
 
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torque rating will always depend on stud/bolt diameter...

tire width also affects contact patch shape, wider tires will yeild a shorter/wider patch. Increasing the psi will just shorter the patch further.
i think it's better to base psi off cornerweight and sidewall thickness...

torque for aluminum wheels, iirc, that's less torque than steelies.

use one of those plastic sockets or wrap your regular socket w/ tape.
i lightly torque them on w/ an impact wrench then set final torque w/ torque wrench.
star pattern, of course..
 
Originally Posted By: PT1
I do believe he is correct as there are 3 torque specifications for my yukonxl one for 17" standard oem wheels, one for 20" oem factory wheels and one for 20"+ wheels.


Interesting. I had never heard of varying lug nut torque based on wheel type or diameter before this thread. My Mazda3 uses the same range - 65 to 87 lb-ft - whether it has the 15" steel wheels or the 15", 16", or 17" aluminum wheels.
 
On my VW Scirocco the wheel bolt torque was different for steel and aluminum rims: 120 Nm for the aluminum rims, the torque for steel wheels (for winter tires) I don't recall.
 
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