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Author Topic: Aftermarket hoops?  (Read 463 times)

Offline redrover

  • Posts: 192
Aftermarket hoops?
« on: Mar 31, 2018, 12:39:11 »
Can I lace any hoops onto Honda hubs?

I found these BMW Airhead aluminum rims (Front 19x1.85 and Rear 18x2.5) and wondering if there would be any problem with lacing a CB450 hub into them??


Offline jpmobius

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Re: Aftermarket hoops?
« Reply #1 on: Mar 31, 2018, 16:10:45 »
Speaking of the most common style rim spoke pattern, which these are, and of course the hub and rim use the same number of spokes, generally, hubs and rims can be broken down into 2 groups:  drum brake and disc brake, or if you like, large and small hub diameters.  This is because the holes drilled in the rim are at an angle that aims fairly far away from the axle centerline for large drum brakes, and closer to the axle for small disc brake hubs or spools.  As a rule, the fit for spoke nipples in the rim is fairly sloppy, so there is some leeway in fitting hub diameters, i.e. a rim drilled for a drum brake hub can usually be used for a different size drum brake hub as long as the right spoke length is used.  Likewise for small diameter hubs, but generally the spoke angle for a large hub will be too extreme for a small hub and vice-versa.  With care, a rim can be re-drilled to accommodate a different diameter hub, but attention must be paid to ensure the nipples are adequately supported in the rim.  If the rims are not correctly drilled for the hub diameter, the nipples will be held at the incorrect angle and the spokes will curve when laced.  This places a very large bending moment on the spoke wire where it leaves the nipple, and severely loads the nipple flange mostly on one side (as well as the nipples pocket in the rim) instead of evenly all the way around, so it is important the angle is close.

This rim is for a much smaller hub than it is currently laced to.  All the spokes are very loose, so they look ok.  If I were to tighten them, they would all bend as the nipples align with their drillings.  I'm holding a free nipple in the position it will take when tight.  I eventually used this rim with this hub, but I had to re-drill the holes to the correct angle, and also re-machine the pockets to center up over the new holes.

 
« Last Edit: Mar 31, 2018, 16:27:03 by jpmobius »
Mobius


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Offline redrover

  • Posts: 192
Re: Aftermarket hoops?
« Reply #2 on: Apr 02, 2018, 02:20:34 »
Wow ok... thanks, that is some seriously useful info!

So theoretically, if the BMW Airhead donor bike used a front disc and rear drum brake (like my CB450), chances are that the hole angles could potentially accommodate the CB hub and drum, correct?

Offline redrover

  • Posts: 192
Re: Aftermarket hoops?
« Reply #3 on: Apr 09, 2018, 02:46:57 »
So if the BMW donor bike had a disc front brake and rear drum brake (just like the CB450), the angles on the rims should be ideal to fit the CB450 front disc and rear drum hub... Correct??