So Im getting some custom spacers made up for my race car, and I had some questions regarding the tolerances I should use.

I am making spacers that will fit and align the cars hub with the wheels hub bore, making everything hubcentric even though it is spaced out.

Now the question is, what tolernaces should I account for with the hubs and the lugs? On one hand I would like to keep everything as tight as possible so that nothing falls out of alignement, and balance, but on the other hand Im afraid that as the wheels, hubs, lugs, brakes all heat up that if I make tolerances too tight the wheels/studs/hubs will all seize together. I would like to keep the hubcentricity as tight as possible but how tight can I go without getting into trouble due to the heat of things? Keep in mind that I have two tolerances to work with; the diameter from the hub to the spacer, and that of the spacer to the wheel.

 

by the way, Im currentlly designing everything with a .1mm fit from one part to the other

 

If you are using a 0.1 mm fit for the critical areas (hub to spacer & spacer to wheel) then I would use a tolerance of +/- 0.05 mm (that is +/- 0.002 in, for reference). I think better about tolerances and fits using english units. The tolerance specification will drive the price of the parts.

If that is too expensive, then I think if you just keep the diametrical gap to less than 0.2 mm, they should work fine. (Give them a range of fits from 0.1 mm to 0.2 mm). You can measure the hub OD and the wheel ID so you know the tolerances on those to make sure it will work with the machined spacer.

Also, don't worry about the fit for the hole for the lugs, that is not a critical interface. Make the holes large (more than 5 mm larger than the lugs) with +/- 1 mm diameter tolerance (or a standard drill size) with a +/- 2 mm position tolerance. The critical interface is with the hub, the lugs just have to pass through it. I hope that helps...maybe some one wtih actual experience with spacer tolerances can chime in.

 

about thermal effects, i would not worry about it. The coefficient of thermal expansion of steel (hubs) and spacer and wheels (aluminium) are too small with the kind of temperature changes it would see, changes in size would be on the order of 10^-2 mm, which are much smaller than the gap you will have.

Also, the aluminum spacer and aluminum wheel would expand and shrink together (because they have the same coefficient of thermal expansion) and never get appreciably closer.

 

Thanks...that was exactlly what I was looking for!

 

Wow your good!