Lug bolts vs studs and nuts

[Series8217]

This belongs in other cars because Fieros don't have lug bolts.

Wheel studs make it easier to take the wheel on and off and they prevent damage to the expensive part (hub) when used wrong.

Lug bolts halve the number of fasteners. What else is in favor of lug bolts?

Why do some automotive engineers choose to go with lug bolts instead of studs?

[crzyone]

Sometimes doing something different just to be different isn't a good thing. Lug bolts are annoying, and sometimes difficult to install just because it's tough to line up the holes.

[Nashco]

Why do some automotive engineers choose to go with lug bolts instead of studs?

Weight
Cost
Appearance
Corrosion

If your customer is willing to accept the risks/hassle for the above, it makes a lot of sense. Since the hub needs threaded for the lug bolts (instead of using a press in stud) there's really very little cost advantage unless a cover is required (cap on the nut, required for appearance and/or corrosion protection).

Bryce

[The Dark Side of Will]

The only cars I know that use lug bolts are German... Maybe it's just their engineering culture?

Although apparently Ferraris use or at least have used them as well: http://www.ebay.com/itm/150826635326

As mentioned above, the threads are more protected from corrosion when using bolts. If you can hold the brakes, then installing a bolted wheel is fairly easy... Hang it on the hub pilot and slowly rotate the wheel on the hub until a bolt hole lines up and you can start a bolt.

[CincinnatiFiero]

Volvos have them, but I don't think Saabs do. Porsche, VW, Audi, Mercedes, and BMWs that I've had all had them.

If you have the locating tool its easy to mount them up, or if you have a friend have them stand the brakes to make the fronts easier to put on.

I like lug bolts for changing wheels. Because you buy lug bolts matched to the thickness and offset of the wheels, so its easier to get longer studs for wider wheels, you don't have to pull the hub off and pound out studs, just spend $40 and get a new set of bolts. The Mercedes lug bolts come in like 5 different lengths so I just keep a set or two of each length on hand and I can run just about any wheels on any of my benzes or the audi.

The BMW and VW guys seem to think the studded look where the studs poke like two inches out of the open end of the lug nuts is a cool look, I don't happen to agree, I like the cleaner, flatter look of lug bolts.

[The Dark Side of Will]

NHRA has regulations for the length of stud required to protrude from a lug nut; I assume that's the genesis of the "long stud look"
Not sure what NHRA thinks of lug bolts.

[Nashco]

The only cars I know that use lug bolts are German... Maybe it's just their engineering culture?

There are non-Germans, but I can't think of any non-European from my personal experience.

Bryce

[AkursedX]

The only advantage that I see to lug-bolts is that it's much easier to add spacers to a lug-bolt car. You don't have to press out studs, just get longer bolts.

Personally, I'm not a fan of them but I have got used to them.

[Series8217]

Found some good discussion on this topic here:

http://grassrootsmotorsports.com/forum/ ... 688/page1/

User 'jstand' wrote the following:

Ignoring the effect of thread fit and wear, the material properties will determine the strength of the fastener.

Clamping force is determined by the stretch of the fastener and the modulus of the material. Theoretically a stud and a bolt of the same material should be able to achieve the same clamping force, yield strength and shear strength.

The problem is that the length of threads engaged with a lug bolt is not consistent throughout the tightening process. The more you tighten it the more threads are engaged. This produces variations in torque required to achieve the desired clamping force, more threads have more friction requiring higher tightening torque to achieve the same stretch.

When using studs, once the lug nut threads are fully engaged with the stud the length of thread engagement is the same throughout the tightening of the lug nut. This should theoretically produce more consistent results.

Here's also an explanation of why head studs are preferable to head bolts.

From: http://www.northernautoparts.com/Produc ... elId=14714

HEAD STUDS vs. BOLTS...A TECHNICAL DISCUSSION, Thanks ARP-bolts.com

ARP’s factory Tech Representatives are often asked which is better, cylinder head studs or bolts. The answer, invariably, depends on the installation. On many street-driven vehicles, where master cylinders and other items protrude into the engine compartment, it’s probably necessary to use head bolts so that the cylinder heads can be removed with the engine in the car.

For most applications, however, studs are recommended. And for good reason. Using studs will make it much easier to assemble an engine (especially a racing powerplant which must be serviced frequently and quickly!) with the cylinder head and gasket assured of proper alignment. Studs also provide more accurate and consistent torque loading.

Here’s why. When you use bolts to secure the head, the fastener is actually being “twisted” while it’s being torqued to the proper reading. Accordingly, the bolt is reacting to two different forces simultaneously. A stud should be installed in a “relaxed” mode – never crank it in tightly using a jammed nut. If everything is right, the stud should be installed finger tight. Then, when applying torque to the nut, the stud will stretch only on the vertical axis. Remember, an undercut shorter stud will have a rate similar to a longer, standard shank stud. This provides a more even clamping force on the head. Because the head gasket will compress upon initial torquing, make sure studs and bolts are re-torqued after the engine has been run.

[The Dark Side of Will]

The bit about the thread engagement for lug bolts is only true if the hub flange is so thick that the bolt doesn't reach all the way through. Because the flange is unsprung weight, no one is going to leave extra thickness and weight in it... so that argument isn't really valid.

I'm not sure I agree with the stud vs. bolt comparison in terms of loading.
There are two places where a bolt or stud sees friction as stretch is being applied: under the head and in the threads.

I think both locations affect both applications equally.
Under the head friction reduces torque applied to both studs and bolts by the magnitude of the frictional torque, via either the coefficient of static friction or the coefficient of kinetic friction, depending on whether the nut or bolt is static or being turned.

Thread friction occurs between the bolt and parent part when using bolts, or between the nut and stud when using studs.
When using a bolt, the net of indicated/applied torque and under-head frictional torque is applied to the shank of the bolt. This torque then goes to overcome the frictional torque in the threads. The frictional torque in the threads is reacted by the material of the parent part.

When using a stud, the net of indicated/applied torque and under-head frictional torque is applied to the upper threads. However, it still must be reacted by the material of the parent part. So this net torque, which is the same as the net torque of a bolt with the same diameter and pitch of the upper threads of the stud, is applied to the stud shank and the lower threads of the stud. As long as the static frictional torque of the lower threads is greater than the net torque, the stud will not turn.

That's why ARP head studs have different pitches at the top and bottom. The static and kinetic friction in the lower threads must be greater than the corresponding friction in the upper threads in order to guarantee that the nut turns on the stud and the stud doesn't turn in the hole in the block.