7 replies to this topic

[TecnoRacing]

Just a question regaurding the physics/design of racing wheels...

Obviously with the tire revolution in the sixties we saw racecars moving towards increased wheel widths but also a deeper dish effect (the mounting points being further inward from the outer edge of the wheel rim.) F1 has never really moved away from this, while most modern sportscars (Prototypes, GTS), running much larger wheels diameters, are using wheels with the mounting surface (and the 'load') much closer to the outer edge...

I was just hoping someone might reflect on the issue of wheel offset and whether it has been dictated by specific performance concerns or rules requirements etc...Obviously this is all inter-related with suspension layout, track, brake placement etc.

Incidently I've always thought racing wheels with a greater negative offset, are vastly more attractive from an aesthetic point of view... And I really bemoan the use of new convex (ugh!) wheel extractors on modern Formula 1 cars, which are covering these up...

[fastcarl]

F1 cars must use 13" wheels , so i suspect the the offsets used are dictated by what brakes they need to fit in there,, whereas the sportscar types can use much bigger wheels therefore the big brakes can fit inside the backface .but from what ive seen they still have a big proportion of possitive offset,.maybe just dont look it ast a glance.and whilst im thinking about it, i'm sure the KPI will be exactly where it needs to be in relation to the contact patch,

carl


carl

[Peter Leversedge]

I don't know much about F1 but in sprintcar racing we used wheels of different off set to adjust the cars handling to suit the track conditions. We also uesd spacers for the wheels and hubs

[Greg Locock]

I was about to say that you can design a lighter wheel for a given stiffness (which is one of teh crieterion used for production cars) if the negative offset is increased.

BUT I think that confounds the issue - production wheels are the stylist's playground, and they'll always want a lot of metal at the outer face of the wheel to make them blingy. SO you end up having to run heaps of materal to get from the mounting face to the outer face.

I think in an unconstrained design you would get the lightest system by using slight positive offset - that would shorten the length of the stub axle, albeit at the cost of your brake package, although I suppose there is no real reason not to move the rotors inboard and expose them to the elements.

[Goran Malmberg]

Wheel offset is a complex issue to give an straight answer on. Myself I am very much in to that geometry design should be very much zero as a starting point. This means zero scrub, sai etc. The wheel must have pretty much positive offset then. The wheel itself may become weaker but we got less spindle and steering componet stress, so we are moving forces from on place to another. From what I have experienced a good design A-arm layout will not take so much possitive offset from the wheel that problems should arises. However, F1 is a phenomenon of its own, and I dont think we should look to close to what tey are doing to draw any conclusion of what is beeing best in more general termes or not. It is advanced to extent of xxxx,
and to sort out why thing are the way they are, takes a book at least. And I guess the questioner is more interested in the wheel centre line in relation to SA effect here.
Regards.
Goran Malmberg

[Ben]

Originally posted by Goran Malmberg
Wheel offset is a complex issue to give an straight answer on. Myself I am very much in to that geometry design should be very much zero as a starting point. This means zero scrub, sai etc. The wheel must have pretty much positive offset then. The wheel itself may become weaker but we got less spindle and steering componet stress, so we are moving forces from on place to another. From what I have experienced a good design A-arm layout will not take so much possitive offset from the wheel that problems should arises. However, F1 is a phenomenon of its own, and I dont think we should look to close to what tey are doing to draw any conclusion of what is beeing best in more general termes or not. It is advanced to extent of xxxx,
and to sort out why thing are the way they are, takes a book at least. And I guess the questioner is more interested in the wheel centre line in relation to SA effect here.
Regards.
Goran Malmberg

You may have vaguely convince me on your "zero car" philosophy with regard to roll centre heights, but zero scrub radius? It will always become negative scrub once the tyre deflects - surely not a good thing?

Ben

[Goran Malmberg]

Ben, I see your point here. My zero philosophy is that it is a starting point from where to add what is needed. So, the final car build up will not become a "zerocar". Now in this particular case the questioner asked for wheel offset, and I think I should not get to fare in explaining my zero philosophy. Depending on tire sidewall heights, the tire will be more or less sideway flexible. In the case of large diameter wheels that will house deepley mounted spindles-upprights, the tire in use will also become a lower profile, thereby more stable. If using for example 1-2 dgr sai , the wheel need to have quite a lot positive offset even if using 1-2" of scrub. When looking at F1 tires we are not exactley lookong at a low profile tire, and who knows about its technology? We are more close to what I am talking about by looking at LMP cars and their wheel offsets.
Regards.
Goran

[murpia]

F1 rims have greater offset on the front than the rear. The front's need to package the brakes outboard of the kingpin axis, the rears don't, so the rears can be closer to Greg's lighter / stiffer wheel.

Regards, Ian