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Discussion Starter #1
I haven't found a way to put the front end up on jack stands that I'm comfortable with. So I went with hub stands. While attaching them, I noticed that all of the car's weight is on the bolts. Can the bolts take this? I considered getting hub centric rings to fill in the gap but from what I've read this is probably not necessary.

Good news is that after 10 hours my car has not hit the floor. ;)
 

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Discussion Starter #3
Yeah, but some say that since the wheels are hub centric that the center of the hub takes the weight. Others state that that's not true and say that there's still a tiny gap between the wheel and that area.
 

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Should be no problem at all, as long as you torque the lug nuts properly.

Digs up from the brain old engineering calculations from long ago...

Lets assume (for easy calculation) that the weight of the car is 2000lbs, and the weight is distributed 50/50 front to back. That puts 500lbs on each wheel. Now lets add a typical engineer fudge factor of 20%, which gets us to 600lbs per wheel. Divide by 4 lugs per stand, and you are putting approximately 150lbs of shear force on each lug.

Now, consider that even without the hub support, with a properly torqued lug, roughly (from a calculation I recall long ago) 80% of the shear force when static, is taken by the friction between the hub surface and wheel surface, and only 20% is taken by the lugs. Lets be conservative again, and say that it is 60/40 instead of 80/20.. thus 40% of that 150lbs is taken by each lug, or 60lbs of shear force per lug.

The cross sectional area of a lug is about 0.175 in^2, thus the lug experiences a shear of 342psi. The shear strength of an SAE80 steel lug is in the neighborhood of 90000 psi (150000psi tensile strength * 60%)

342psi is much smaller than the 90000psi strength.. so.. you should be OK ;)


Edit: feel free to rip this calculation to shreds..
 

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Discussion Starter #5
Wow, thanks for the calculations.

I found someone's post (may have been for an Elise) that said the front corners were in the low 300 lbs range and the rears were around 650ish. I guess the main test will be the rear end.

The OEM bolt are conical. Where can I find flat ones to better mate with the front face of the hub stand?
 

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Should be no problem at all, as long as you torque the lug nuts properly.

Digs up from the brain old engineering calculations from long ago...

Lets assume (for easy calculation) that the weight of the car is 2000lbs, and the weight is distributed 50/50 front to back. That puts 500lbs on each wheel. Now lets add a typical engineer fudge factor of 20%, which gets us to 600lbs per wheel. Divide by 4 lugs per stand, and you are putting approximately 150lbs of shear force on each lug.

Now, consider that even without the hub support, with a properly torqued lug, roughly (from a calculation I recall long ago) 80% of the shear force when static, is taken by the friction between the hub surface and wheel surface, and only 20% is taken by the lugs. Lets be conservative again, and say that it is 60/40 instead of 80/20.. thus 40% of that 150lbs is taken by each lug, or 60lbs of shear force per lug.

The cross sectional area of a lug is about 0.175 in^2, thus the lug experiences a shear of 342psi. The shear strength of an SAE80 steel lug is in the neighborhood of 90000 psi (150000psi tensile strength * 60%)

342psi is much smaller than the 90000psi strength.. so.. you should be OK ;)


Edit: feel free to rip this calculation to shreds..
Always appreciate someone that gives a technically correct answer and backs it up with at least back of the envelope calculations... but have to agree with your assessment...
 

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Wow, thanks for the calculations.

I found someone's post (may have been for an Elise) that said the front corners were in the low 300 lbs range and the rears were around 650ish. I guess the main test will be the rear end.

The OEM bolt are conical. Where can I find flat ones to better mate with the front face of the hub stand?
No problem.

Conical should be fine. The surface contact that generates the friction and the bulk of the shear strength is the contact between the hub face, and the back side of your stand. One way to think of it- the lug bolt's job is not to provide shear strength.. it is to provide the tensile force that creates the friction between the wheel and the hub, and that friction is what provides the shear strength (this is why it is very important to make sure your lugs are not just torqued up tight, but have the specific torque value required for the particular hub you are using)

BTW: even at 650lbs per wheel in the back, you are still several orders of magnitude in the safe zone for your lugs.. :)
 

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Always appreciate someone that gives a technically correct answer and backs it up with at least back of the envelope calculations... but have to agree with your assessment...
The 5-years of structural engineering graduate school and 4 years of post-docs/research that followed, pretty much made it impossible for me to make such a post without providing the mathematics :D
 

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Thanks again!

I wish I went into engineering. It's more interesting to me than medicine. :(
Yeah.. but look who owns the Exige on hub stands, and who is longingly looking at said Exige while calculating the capacity of hub stands saying "Some day..." rotfl
 

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Nice Color! (Where did you grab the stands?)
 

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Discussion Starter #12 (Edited)
Looking at your car, Benjamin, tells me I really need to get my car detailed!

Got the hub stands from Techno Toy Tuning. $90 for a pair in red or black. I think they are based in Sacramento, CA. So you won't have to pay sales tax. But shipping is the killer. $45 to ship them to me. They're heavy.

https://technotoytuning.com/universal/parts/techno-toy-tuning-hub-stands

There's a picture of an Exige on one of these hub stands on their website so it must work, right? ;)

These should make painting my calipers much easier.
 

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Hi.

Great info. I have had my car on 4 stands like that for a week with no issue. Some on LT store their cars all winter on the same type of stands too. Just some practical examples.

-Alex
 

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Discussion Starter #16
Thanks. That's actually the thread that got me started into looking for hub stands. Until I came across these from TTT, I only saw the expensive ones by BBX. I don't need those (yet?) since I'm not interested in doing my own alignment.

My main concern was whether the hub stand needed to rest on that nubbin (not sure what to call that part that protrudes from the center of the hub) to take up some of the car's weight. But now looking at the plans for the stands in that thread, it looks like those center holes are oversized as well (60 mm hole in stands vs 56.6 mm hole in wheels).
 

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One single M12 grade 8 bolt can support nearly 7x the weight of an Elise in shear.
Theoretically.. Though I wouldn't recommend testing it (as the Mr. Hyde Crazy Engineer side of me starts designing a contraption to hang 7 Elises from a single lug in shear).
 

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Since I am not a mechanical engineer or the medical profession, I am not clear on the aversion to jack stands;). They seem well engineered for the purpose and I use them to hold up my Elise almost every week for pad swaps, fluid changes, suspension torquing, etc. It takes about 5 minutes to get all 4 wheels off the ground.

It does look cool on those hub stands though, like a really nice hover car. Beautiful Exige BTW.
 
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