Lotus Elan

Bolt on wheel lug nut torque specs

PostPost by: rgh0 » Sun Jul 08, 2018 1:01 pm

Craven wrote:I think the speculation that someone has had purpose made studs ( see pic ) to a different lower steel grade is taking thing just too far. With the cost regime of Lotus at the time they specified and had fitted to a bought in mass produced item a different grade stud is risible.
Past unknown history of stress undergone by these studs even in normal roadside spare wheel change, is more than likely a reason for breakage later in its service life.


I dont know what grade the wheel studs were originally made to do you ? i would be surprised if they were Grade 8. They appear softer to me than a typical modern Grade 8 stud. Maybe i should do some hardness and tensile testing on one

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PostPost by: Craven » Sun Jul 08, 2018 3:06 pm

What I do know is the hubs and studs were a Standard Triumph production item, they gave a torque figure of 48 ft lbs. these are purpose designed and manufactured as wheel retaining studs their actual specification is irrelevant.
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PostPost by: rgh0 » Tue Jul 10, 2018 12:20 pm

I presume your Triumph data is accurate - what was posted was not original Triumph manual information as far as I could see . However assuming it is accurate it means either a grade 8 stud within the normal range of friction assumptions or a very high friction level and a grade 5 stud.

Thus you need to determine what studs are fitted to your hubs and what friction levels are happening on your hubs and wheels to nut interface. Get the assumption wrong and you maybe break the studs. Then you say the studs are to small and you fit larger one as others do.

All I am trying to highlight is that the 3/8 studs in either grade 5 or grade 8 are plenty big enough to hold your wheels on provide you don't over torque them..... The challenge is to find a torque that holds them on and does not over stress the studs. For me 25 ft -lbs works on alloy wheels with hardened washers and smooth studs and nut thread ( unlubricated) in full race conditions for 40 years with sticky tyres. Depending on the wheel / nut / stud combination and usage you have you may need more than I do. Going to 45 ft-lbs risks stretching breaking a grade 5 stud in average friction level situations and it failing.

Just my simplistic engineering approach, your mileage may vary.

In the end do up the wheel nuts as hard as you like as its your decision and I hope you have 40 years of engineering bolting analysis to back up that decision as the wheels may fall off if you get it wrong. Relying on a listing from a Triumph manual from 50 years ago based on bolting assumptions that may not apply to your situation is just guessing.

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PostPost by: Craven » Tue Jul 10, 2018 12:45 pm

One has to believe the design engineers knew what they were doing, it?s quite possible their practical figures took into consideration the very high friction ( surface area ) of the dry cup and cone of wheel and nut.
Past history of any critical fastener on a 50 year old car is of concern, your solution don?t use recommended torque settings.
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PostPost by: rgh0 » Tue Jul 10, 2018 12:52 pm

Craven wrote:One has to believe the design engineers knew what they were doing, it?s quite possible their practical figures took into consideration the very high friction ( surface area ) of the dry cup and cone of wheel and nut.
Past history of any critical fastener on a 50 year old car is of concern, your solution don?t use recommended torque settings.


My solution is based on my wheels, nuts, hubs and my engineering analysis as I have highlighted. Anyone else solution's needs to be based on their current set up of wheels, nuts, studs. If its close to the original triumph one then maybe the original triumph torque spec is maybe OK - If its wrong you will know eventually

Personally I would start low at maybe 30 to 35 ft lbs for a standard steel wheel and nut combination and check often and increase it if it comes loose.

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PostPost by: Craven » Tue Jul 10, 2018 2:08 pm

Couple of further references to wheel nut torque, both 3/8 unf studs.
BMC Mini.
MG Midget.
Official publications.
p1030364.jpg and

mini-wheelnuts.jpg and
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