Hubcentric Wheel Center Bore Clearance
Hubcentric Wheel Center Bore Clearance
(OP)
I would like to custom machine 15x7 Kossei K-1 wheels for my '80 Triumph TR7/8. However, I cannot find reliable information on the required clearance between the hub and wheel center bore. The design is hubcentric on a 2.225" hub / 3.750" bolt circle, with ~500 lbs per wheel.
If the centerbore has no clearance to the hub, I am concerned that the aluminum wheel may freeze onto the steel hub. If there is too much clearance then the wheel will not be centered, and the forces will be on the lug bolts rather than the hub.
Should I just have the centerbore machined based on machining tollerance so that there is no interference with the hub, or do I need to add a few thousandths?
If the centerbore has no clearance to the hub, I am concerned that the aluminum wheel may freeze onto the steel hub. If there is too much clearance then the wheel will not be centered, and the forces will be on the lug bolts rather than the hub.
Should I just have the centerbore machined based on machining tollerance so that there is no interference with the hub, or do I need to add a few thousandths?





RE: Hubcentric Wheel Center Bore Clearance
Rod
RE: Hubcentric Wheel Center Bore Clearance
RE: Hubcentric Wheel Center Bore Clearance
Cheers
Greg Locock
RE: Hubcentric Wheel Center Bore Clearance
What automotive applications would require a machined center fit for allignment? In heavy duty trucks, Budd wheels use a very tight fit on the duel wheel setups but the same wheel is mounted reverse on the front with NO centering aside the lugs.
I still feel like I am missing something. I was at the Lincoln dealer yesterday and checked out a couple of 18" and 20" custom wheels setups on F-150 "Lightning" trucks. Nothing exotic there. If we were talking about brake drums or such I could see the need, but not wheels.
Rod
RE: Hubcentric Wheel Center Bore Clearance
OK, in the absence of other info, we could reverse engineer a solution.
Say the acceptable out of balance is 10g at 300 mm
At a rotational speed of say 12 Hz that will generate a force of 12*6*12*6*.01*.3 N, 15 N
Tyre radial rate is 200 N/mm, so we would want to set it central within 15/200 mm, call it 3 thou, to minimise tyre force variation.
Also, to minimise out of balance, say tyre and wheel are 20 kg, maximum allowable eccentricity is 10*300/20000
or 0.15 mm, 6 thou
So, dynamic considerations say the maximum radial clearance should be less than 3 thou.
Cheers
Greg Locock
RE: Hubcentric Wheel Center Bore Clearance
I can understand the confusion about not using the lugs to center the wheel. The Triumph TR7/8 hub is not designed to use the lug bolts for centering the wheel. The OEM steel wheels have untapered holes and the lug nuts just hold the wheel on to the hub. The wheel center bore has a number of spots pushed inward along the stamped taper so that it will center around the machined steel hub (makes it difficult to measure clearance).
Some articles I have read indicate that if the hub was designed for a 'hub'-centric wheel, then there may be problems using a 'lug'-centric wheel. This may be due to loose tollerances on the lug placement, or due to how the loads are distributed. (only the design engineer would know for sure)
It looks like the safe bet will be to keep clearance between 0.0005-0.0020". I'll have one wheel machined and if it looks good, have a set of four done and post the results.
Thanks Again
-Matt
RE: Hubcentric Wheel Center Bore Clearance
-Joest
RE: Hubcentric Wheel Center Bore Clearance
Jakub
RE: Hubcentric Wheel Center Bore Clearance
Perhaps one should bear in mind that the wheelhop frequency is about 12 Hz, typically, and the response will fall at - 6 dB / octave thereafter.
I didn't choose that frequency at random.
Cheers
Greg Locock