New Viper has 6 lugs, that many on a sports car has to be a first.

 

Given that spacers aren't used...and sticky tires aren't used...are the 8.8 Ford 4-lug rears at any disadvantage over a street-driven 5 or 6-lug design? I figure with autocrossing, an advantage may exist (side-force)...but I haven't (in my experience) noticed a lot of lug failures due to "shearing" forces. How much torque does it take to "snap" a set of 4, 5 or even 6 -lugs of the same dia.? (engineering question)...assuming that no spacers are used, that lug nuts are torqued properly...and that the rear rims would be "locked-down". Also, increasing tire height and rim size has to have a negative influence on lug integrety...but is there a formula for this?...
Sorry to be so long-winded, but I'm curious how this all ties in together....

 

The studs only get as much torque load as the tire grip allows. That's the thing that saves parts and allows OEM 7.5 rear ends, etc. Remember that every extra pound of mass, say in a larger axle, needs to be shlepped around by the car it's whole life. That slows it down and uses more fuel throughout the life of the car. When you put sticky tires on it, and increase the power, you can expect to overstress some parts. Obviously the weakest link should fail first.

5 or 6 studs spreads out the load (vs. 4) so they could be smaller. If one fails say due to overtorqing during installation, you lose a greater percentage with four than 5 or 6. This could lead to heavily overloading the other 3 and subsequent catastrophic failure.

OEM designs are usually overkill for normally driven cars. You rarely hear of a wheel shearing off the studs in a production car that's never raced with sticky tires.

Cornering loads put tension loads on the studs which is what they are good at resisting. Tire traction still determines the max loads the studs receive.

 

Look closely at the rear of some of those 8/9 sec stangs, a few of them still sport a 4 lug 8.8 rear, I could see where they would live in a non transbrake or manual trans car with 4 lug.


David

 

Good info. so far. I'm still curious about rim dia./tire height. Seems more leverage would occur b/c of increased rim/tire size. Comments?...

 

The shear forces in the wheel studs are determined from the torque at the axle divided by the distance from the center of the axle to the stud, or 2.25 inches on a 4.5 bolt circle. This doesn't change with tire diameter, but it changes with overall gear ratio. Tires are "gears" too, as we know, so shorter tires generally mean lower numerical gears in the rear to get the same carspeed for a given engine rpm. That means less axle torque but the same driving force at the wheels at a given rpm. Of course that's power, which we know doesn't change with gears (except for friction and inertia losses).

Cornering loads are a little more complex, but they are tension/compression loads where the studs are very strong.

Anytime the bolted wheel connecton is not tight, and anything can move, it gets to be a real problem.

 

A buddy has a 5.0 that runs high 8's at >150mph. He is using the 8.8 with 4 lugs (aftermarket axles and studs though). However, he changes the studs every season and is thinking about upgrading to a 5 lug setup.

Rich Krause

 

Did he ever have any failures durning the season? Does he magnaflux to see if stress cracks are developing? I'm starting to think that maybe an upgraded onstuds on a 4-lug set-up is all one would require. I was wondering what IHRA or NHRA rules say about axle/no. of studs requirements...if any. Any thoughts...

 

Something I have seen, Shearing off the lugs. I dont know the story but this video fits this topic perfect!
http://www.smallblockposse.com/image..._SalemNSCA.wmv

 

Vega / Monza came with V8, no?

What I wanna see is a wheel that's installed on the hub like a balancer. Keyed. Now that would be a strong setup.

 

Well, maybe not. Keys generally are for location, not for taking shear loads. If they are used for that in high torque or cyclic loads they often fail either by shearing or wearing out the keyway when they move slightly as loads are applied and released. Balancers are often pressed on. That press fit takes the loads. Some balancers don't even have locating keys. Not trying to rag on you, jmd. I've just seen too many keys fail due to folks trying to use them to drive not locate.

Perhaps the best way we have for wheels is the pin drive with one center nut. Open wheel cars like F1, IRL, CART and most sports racing cars use this. The 4-6 pins don't clamp and are used only for location and to take shear loads, and the center nut does all the clamping but doesn't take any shear loads from driving or braking. Eureka! What a smart design! Of course the center nut needs a couple hundred lb-ft of torque, so it's not very practical for a normal OEM street car.

My $.02

 

That's a really good point.