Formula for number of bolts/bolt-holes required on a wheel
Formula for number of bolts/bolt-holes required on a wheel
(OP)
How do you determine the optimum number of bolt holes or bolts required on an automotive wheel (like the wheels of cars or trucks), when you only have data on the tyre size, the corresponding wheel size and the load rating for the wheel? And for instance, why is it that tractor wheels have usually 6 or 8 bolt holes - while those for buses have 10 or 12 bolt holes?
I'm guessing this involves calculating of Tensile and Shear stresses on the bolts based on the wheel load, but what are the exact formulae I need to use in this regard & what are the types of forces to be considered? Is it due to tyre friction or cornering effect? Can someone help me out on this, since I haven't really worked on this type of problem before.
I'm guessing this involves calculating of Tensile and Shear stresses on the bolts based on the wheel load, but what are the exact formulae I need to use in this regard & what are the types of forces to be considered? Is it due to tyre friction or cornering effect? Can someone help me out on this, since I haven't really worked on this type of problem before.





RE: Formula for number of bolts/bolt-holes required on a wheel
The life of a wheelnut is not easy, and over the years the design of wheels and wheelstuds has converged on the sizes, and numbers, you see in use today.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Formula for number of bolts/bolt-holes required on a wheel
RE: Formula for number of bolts/bolt-holes required on a wheel
RE: Formula for number of bolts/bolt-holes required on a wheel
This issue is being addressed on Automotive Suspension Forum.
Michael
RE: Formula for number of bolts/bolt-holes required on a wheel
For my use I like the centering of the wheel to be hub center and I machine a step to engage a concentric pocket in the wheel.
I noticed a lot of late model stuff is hub center. You can tell lug center stuff, it has the tapered lug nuts.
Cheers
I don't know anything but the people that do.
RE: Formula for number of bolts/bolt-holes required on a wheel
I dont know of a modern wheel/hub that actually transfers load through the wheel center. This has been discussed heavily here.
The friction btw the hub face and its mating area with the wheel is the mechanism that transfers the load. The tension produced by the studs is what creates the normal force to produce the friction.
I napkin'd the calcs once, I'll see if I can find it.
nick
RE: Formula for number of bolts/bolt-holes required on a wheel
Nick
I love materials science!
RE: Formula for number of bolts/bolt-holes required on a wheel
Many off-road applications are hub-centric, including tractors. I have had problems with axles that were stud-centric. The wheels are stiff enough that if the studs are not perfectly centered with the holes they will eventually loosen up.
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
I think some of the lug pattern changes in modern
cars and light trucks are designed solely to give the oem an
advantage in wheel sales.
RE: Formula for number of bolts/bolt-holes required on a wheel
0.45 is a tad high for mu though, I'd have used 0.15 which is greasy steel on steel. That would drop the load to 60 kN.
A wheel only sees forces that high during events like square edge pothole, which are designed to rip the suspension apart.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Formula for number of bolts/bolt-holes required on a wheel
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
As GregLocock noted, a safe value to use for Mu with dry-metal-on-dry-metal (but not greasy)is 0.15. If there is any grease or oil present you may potentially achieve boundary conditions. So you should use a much lower Mu of around 0.06 to be safe.
I would disagree with what others said about the center pilot though. It's not there to carry loads. It's only purpose is to locate the wheel at installation.
Good luck.
RE: Formula for number of bolts/bolt-holes required on a wheel
My last employeer, which makes warehouse forklifts, previously used stud piloted wheels but switched to hub piloted in desperation over loosening wheels. They tried different approaches but none of them worked until they switched to hub centered.
My current employeer is experiencing a problem with loosening wheels on one product. They suggest checking the lug nuts every 10hrs! I haven't been privey to the details yet, but I suspect my old friend is back!
I agree that friction should be enough, but that can be tough to guarentee in my field. Many times both surfaces get thick coats of paint, well intentioned mechanics applying anti-sieze compound, almost non-existant use of torque wrenches, etc. etc. My fellow test engineers have a saying - Just because it fits on ProE doesn't mean it works in the lab (or the real world)!
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
Do you see any wear or fretting on the hub or the centre hole?
Checking whellnut torque every 10 hours is OK so long as you use a torque wrench, there was a spate of wheel stud failures in the UK because the weekly maintenance check on ambulances meant every wheelnut got 'tweaked up' every week.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Formula for number of bolts/bolt-holes required on a wheel
Regards
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RE: Formula for number of bolts/bolt-holes required on a wheel
I will also note that on the stud centered wheels we rarely noticed any movement or fastener loosening until there was permanent damage. We put on witness marks, checked the torque every 6-8hrs., etc. Once they started to move things deteriorated very quickly. On one machine the inattentive driver actually sawed the planetary housing off of the axle before he noticed anything was wrong!
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
Lug nuts (or any threaded fastener that is not self-locking) will tend to maintain its preload, and thus not loosen, if there is some elasticity in the installed joint. This can be achieved by lengthening the stud or by making the compressive spring rate of the clamped components lower. Having more elasticity in a joint will make it less likely for the fastener to lose the preload-induced thread friction that keeps it locked.
The fastener preload can be affected by thermal expansion mismatch in the clamped components, or by dynamic load variation due to vibration. If the preload strain in the fastener is very small (ie: a very rigid structure), it only takes a very small deflection in the joint to relieve the preload and allow the fastener to back off.
Good luck.
RE: Formula for number of bolts/bolt-holes required on a wheel
And as far as a rigid structure goes, most of the wheels are cut from a piece of flat steel. So fastener selection is usually very important.
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
When I bought snow tires from Sears last fall they stamped the invoice with a disclaimer saying I would have to come back within a few hundred miles to have my alloy wheel lugs re-torqued. I pointed out they had mistaken the stock 1996 Accord hub caps for alloy wheels, so I did not have to come back. Typical steel car wheels I've seen have contours around each lug hole, with the actual hub contact surfaces offset a good bit, reminding me of a stout belleville washer.
htt
here's a shot showing a steel 60s Studebaker wheel.
Stud centered, with re-entrant contours apparently designed before the days of FEA
http://i
Worked with some brother engineers, sons of the family business was making very popular handsome forged alloy wheels for tractor trailer type trucks. Flat uniform wheel centers. Lug loosening was a problem, requiring frequent maintenance.
RE: Formula for number of bolts/bolt-holes required on a wheel
If that's the case then you should only need three pegs seeing as the clamping force is coming from the nut. Most cars have 6 pegs - is this just redundency or a (poor?) assumption that they're transmitting the torque?
I have seen drive pegs ratchet back and forth and lock the wheel on. I assume this is probably due to insufficient tightening torque due to poor air pressure in the wheel guns.
Ben
RE: Formula for number of bolts/bolt-holes required on a wheel
The folks with early VW sometimes go to great lengths to augment their cranks' 4 dowels with stouter gland nuts permitting greater torque, then to 8 snugly fitting line reamed dowels as used in pre-914 4 cylindrical Porsceae. Racers then go to 8 plus a wedge fit (Gene Berg) or even to a proper crank flange (SCAT).
flywheel attachment history in pictures.
early British (MGT?)
http
Jaguar XKE
htt
Chevrolet 1955 265 CID V8 or 1968 450 HP 454 CID V8
http://images.1aauto.com/CLF/1ACLF00024.jpg
(yes there is one dowel to ensure consistent positioning, but some crankshafts come with that hole empty)
Chrysler 426 Hemi
http:
lexus V8 flywheel?
htt
Civic SI/ del sol flywheel
ht
If there's enough clamping force to keep the dowels or bolts from any real torqueage loading, there's enough. If not, there's not, and the situation gets real bad real quick.
RE: Formula for number of bolts/bolt-holes required on a wheel
A third possibility is that with only 3 pins the tire man might have to rotate the wheel 120° to hit a pin - but that doesn't prevent one from having only 3 pins but 6 holes in the wheel!? In reality the first person to do this probably figured that if the road going car needs 5 studs the race car will need at least that!
ISZ
RE: Formula for number of bolts/bolt-holes required on a wheel
RE: Formula for number of bolts/bolt-holes required on a wheel
what size thread is the center lock nut?
Dan T
RE: Formula for number of bolts/bolt-holes required on a wheel