1988 CORVETTE WHEEL LUG TORQUE

The owners manual for my 1988 Vette w/ 17" wheels shows lug torque of 80 ft. lbs. My local shop insists the torque should be 100 ft. lbs. Which is
correct. Will the 100 ft. lbs. do any damage to the wheels/lugs/rotor? Thanks.
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Go 90 and sleep better.
-W

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I'd go with the manual. Excessive tightening can warp the rotors. My son bought new tires earlier this year and had a flat. He couldn't get the wheel off. I brought tools to help him get going. Torque wrench showed over 130 ft lbs. All four wheels. I reset them all to 80 per the manual. Brakes seem fine - no warp to rotors apparent when driving.
Who knows
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Thanks. I have to re-torque them anyway, after driving about 50-100 miles. Then I will reset them to 80 ft. lbs. Thanks for the input.

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PHIL wrote:

Might be a good idea check the '88 shop manual. Section 3E of the '89 manual shows a drawing of the '88 wheel (without the vent vanes). and indicates 100ft-lb for the 17" aluminum wheel and 80ft-lb for the compact spare.
The '89 owner's manual gets tangled up in a discussion of changing wheels on the road, temporary tightening, going to where there's a torque wrench etc. etc. then adjusting to 80 ft-lb (the correct torque for the steel compact spare). It then specifies and 100ft lb for the 17" alloy wheel and 80 for the (steel) spare.
I if the car isn't getting much maneuvering stress, 80 is probably an OK number.
*Perhaps Dad might offer something here ----------->* An issue to consider is that, if these wheels were run overtorqued I'm hesitant to work them heavily with under-torqued lug nuts. Seems like a good way to stress crack some aluminum.
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I think that what is most important is that all lugs have about the same torque to avoid warpage. I cannot believe that the difference between 80 and 100 is enough to make the wheel fall off at 80. I would say that 80 is the minimum for ANY car. I would go by your owners manual. Just be sure the manual is correct.
Vito

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Agree, RTFB -- look in the shop manual and find out what the designed torque is for the '88 alloy wheel.
Since all this will be an educated guess, talk with a mechanic with some racing or autocross experience (Dad's probably the best we got.)
Here we go: Torque & Pre-load 101...
Now, assume that 100 ft-lb was the original designed lug torque to accommodate the max anticipated operating loadings for infinite life of the wheel, studs, nuts etc.
If you torque the lugs to 130 ft-lb and apply working loads, the total of pre-load + working loads may fall outside the infinite life estimates. You are then introducing some stress and perhaps metal deformation (wheel, stud threads etc.) Now, you no longer have a system that will provide infinite life using 100 ft-lb of torque.
If you then remove the wheel and re-install it, the optimum torque for some maximum life may be something like 105 or 110 ft-lb. Definitely not some value at or below the original design torque (unless the parts are made of some magic metal that has "healing" properties).
Think of the difference between 80 and 130, not the difference between 100 and 130.
So if the original spec torque was 80, the optimal torque might now be 85 or 90.
If it was 100, the new torque for optimal life might now be 105.
In both cases, the working life of the system will be shorter than was was intended in the original design.
We have no clue as to how much abuse the system got when it was over torqued so it's one big crapshoot -- but it isn't 80 ft-lb. At 80, the wheel will experience more damage.
CAPISCE ??
Hey Dad --- educated guess??
Uncle_vito wrote:

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It all comes down to what the wheel manufacture says to use on their wheel. Most times you can't find that for used wheels and due to our "sue for anything society" I can see why. Your car model dealer would be the best information source for stock wheels but as these cars get older that gets harder to get from a dealer. As a guide line I have followed these simple rules from steel to aluminum based on stud size. Notice that I did not include magnesium as I have no knowledge of that material and its failure rate due to age.
For smaller wheels and smaller studs 7/16, 1/2 & 12 M/M torque to 70 to 85 ft/LB, larger studs and wheels 85 to 100 with some small truck rims using 130 to 145 with 9/16 studs. All are done with the star pattern for 5 bolt and a crossing pattern for 4 and 6 stud wheels. NEVER lubricate the stud threads for any reason and a clean thread will give you the most reliable torque reading. Good NASCAR teams hand tap every lug nut before a race. Re-torque after driving 100 miles should always be done on new wheels and a good safety check for older wheels if you have any doubts.
Now the disclaimer, those are target figures and do not allow for ignorance of your thread condition, thread engagement, or how sound your wheel is when you put it on. It also does not cover non stock wheels and/or spacers. In other words if you reach your torque and your wheel is still loose you got problems going soon.
Personally I use 100 ft/LB. on my factory wheels and 110 when I autocross. All aluminum wheel failures I've seen are due to loose lug nuts and cracks from tire change machines. That 100 ft/LB. torque figure is stated on page 81 section 3 of my service manual that is 5" thick. Two inches of which is CYA and duplication of redundancy just like this post. Redundancy for tight lug nuts is a good thing.
Be safe.
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