Hubcentric Wheel Center Bore Clearance 2

[mattstr]

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?

 

[evelrod]

I have used many wheels that do not fit the center hub snuggly. Indeed, my race wheels clear by INCHES! Total allighment and centering is done by the lug bolts/nuts. Tapered nuts on my GM motothome (no centering hub on the front), sleeve nuts on the race cars and, extremely tight fit on the lug bolts of my Budd wheels on the Dodge/Cummins. Perhaps I am missing something? I do check the runnout on new race wheels , but no problems of late.

Rod

 

[Joest]

I would use just enough clearance to allow the wheels to be easily installed (0.0005 - 0.002"). Remember that tire temperatures can be above 200F. This will quickly transfer to the aluminum wheel causing it to expand. Assuming you have a steel hub, the clearances will increase as temperature goes up since the aluminum expands more than the steel. Wheel spacer such as H&R use tolerance in line with those that I mentioned

 

[GregLocock]

Rod - there's two different philosophies when mounting disc wheels to the hub. You either locate off the centre, or use lugnuts or bolts with tapered faces. I've only ever used the second approach.

Cheers

Greg Locock

 

[evelrod]

Me too, Greg. In my experience the only wheels that did not use the lug bolt/nut to center were the 'knockons' with Rudge splines and the pin drive centerlocks in racing applications. They are a 'taper fit' anyway.
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

 

[GregLocock]

Dunno.

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

 

[mattstr]

Thanks to everyone for helping answer my question.

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

 

[Joest]

Greg's calc is a very good approach. Mind you, it is based on about 55 mph. If you plan to drive over 100 mph (e.g. racing), I would go tighter, like half or a third of that.

-Joest

 

[JakubMech]

Force arising from out of balance wheels has a squared relationship to speed. So if your doubling speed, should reduce eccentricity by 4 for the same force.

Jakub

 

[GregLocock]

Hmm.

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