ktmrfs wrote:
jus2shy wrote:
Is this different from Hub-piloted versus Stud-piloted rims? I thought all passenger vehicles were stud-piloted rims and that hub-piloted rims were found on vehicles usually in commercial service?
maybe in days gone by, but currently the vast majority of passenger cars and light trucks are hub centric not lug centric. Among other things, it has way less stress on the studs/bolts since with hub centric wheels, the flange/hub takes the vertical load and the studs take the horizontal load. In lug centric, the stud must take vertical and horizontal loads. Or, maybe more correctly radial and axial loads. One issue in going from hub to lug centric rims is that now the lugs must take all the loads, which may or may not be a issue with the loads the studs are designed to take.
TT seem to be another story, most of them are lug centric.
I'll take that a tad bit further and say for years or at least decades ALL motorized vehicles from the factory use the Hub Centric method of centering the wheel even if they have the conical lug nuts and seats. The conical lug nuts and seats are actually just a different method of fastening wheels onto the studs ... a secondary benefit is that they will somewhat (albiet poorly) center a wheel on the studs. As mentioned in another post many aftermarket wheels have a larger hub pilot so one wheel can fit a variety of vehicles, but you run the risk of encountering NVH issues. As mentioned TTs might actually depend more on what is called a Lug Centric system mainly because there you are not so concerned with introducing minor NVH issues since those are not manned or are steerable like a vehicle is so some vibration/harshness will not be evident or observable for the most part.
The reason that OEM/factory wheels use the hub centric system is that it is much easier to cast/machine one hole in the center of something that to get 5, 6, or 8 holes accurately placed around a central position. There are some aftermarket wheels that are still hub centric and you can generally tell that in that they will use the flat washer type fastening system. A word of caution is that the conical fastening system is a lot more forgiving in the range of torque values than the more demanding flat washer system and if you have the latter proper torquing using a good torque wrench and doing the follow up torque checks are critical from a safety standpoint. This is because if a wheel is allowed to slip with the flat washer system it can put a shear stress on the wheel studs something less likely with the conical fastening system since the lug nut has to ride up out of the conical seat to bind against the wheel stud. This hub centric factory design is also why some times factory steel wheels will get "stuck" because any slight corrosion in the incredibly close tolerances between the hub and wheel pilot can basically "weld" the wheel to the hub. IIRC factory specs are somewhere in either the several thousandths of an inch.
Your point about the loads on the wheel studs in a true lug centric system is in theory true, but even in a lug centric system the hub will be carrying part of the load because in the natural torquing of the lug nuts more than likely you will "FORCE" the wheel up against the hub at some point or multiple points so as the wheel turns the load can shift from the hub to the hub studs depending on the orientation of the wheel to the ground. Generally even true lug centric wheels the wheel pilot is not so large that the entire load is only carried by the hub studs, but that is a consideration if you are dealing is very high loads like we are concerned with when towing such heavy trailers.
WHEW ... off the soap box and if you're wondering where I got all this it was from some extensive "schooling" by a gent who has decades of experience in actually designing wheels for a major vehicle manufacturer (one of the old big threes).
Larry
