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I'm working on a custom build based on a '78 CM185. I'd like to go up to 18" tires front and back while retaining the original hubs. Never attempted this before, but I know it's possible (see Classified Moto's Tiny Moto - https://www.classifiedmoto.com/motor...85t-tiny-moto/).

Does anyone know if there are specific limitations? What should I be looking for when purchasing rims and spokes? Are lacing patterns standard or will they vary between rims? How should I determine correct spoke length?

Any help is much appreciated.
 

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I would start by doing measurements to the hub width and diameter and then post those here and let's see what model with 18" wheels comes close to the similar size hubs.I think spoke pattern is very similar to many different wheels.
 

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Sure its possible. Specific limitations must exist but I'm unclear what they are, you do see 300 series tires on WIDE rims spoked to stock Harley hubs, so maybe its all limited by the depth of one's pockets and one's imagination, and I suppose what physically fits your specific bike.

Here are a few of my past posts on the subject, some of it may help.
http://www.hondatwins.net/forums/44-tires-wheels-brakes/107882-re-using-46-y-o-spokes.html

http://www.hondatwins.net/forums/52-tires-wheels-brakes/106593-71-sl-350-rims.html#post893577

Spoke pattern will wind up being similar to stock, just make sure to match the rim to the hub, 36 or 40 spokes depending on the bike. Take lots of photos before disassembly and watch lots of YouTube videos on how to lace wheels, you can do it.
 

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The width of the 18" rims you use should be close to stock or up to one size wider to maintain the same predictable feel/handling to match what that bike was designed to do.What size rims and tires are stock for that bike ?
 

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Rim width will need to remain the same as stock if you're retaining the stock swing arm and front end. Same goes for the tires. Alan listed the stock rim widths, looks like they are 36 spoke wheels. So now you need the rims, David Silver Spares has them for the CB350 which uses the same diameter (18") and widths.
Spoke calculator here Spoke length calculator, it's possible the CB350 spokes will work, really depends on hub diameters
 

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Rim width will need to remain the same as stock if you're retaining the stock swing arm and front end. Same goes for the tires. Alan listed the stock rim widths, looks like they are 36 spoke wheels. So now you need the rims, David Silver Spares has them for the CB350 which uses the same diameter (18") and widths.
Spoke calculator here Spoke length calculator, it's possible the CB350 spokes will work, really depends on hub diameters
Is this specific to the cm185 ?

It's quite common to run 2.15 rims on most of this era of bikes with no modifications

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Is this specific to the cm185 ?

It's quite common to run 2.15 rims on most of this era of bikes with no modifications

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It's really dependent on the available clearance. IE; a CL350 runs a 90/90 tire on a 1.60 rim and there just enough clearance. A 100/90 is a very close fit if at all and that's still on a 1.60 rim, should be 1.85. A 2.15 rim would run a 120/90 and it would by rubbing the fork sliders if you got it in w/o bending the forks some.
 

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It's really dependent on the available clearance. IE; a CL350 runs a 90/90 tire on a 1.60 rim and there just enough clearance. A 100/90 is a very close fit if at all and that's still on a 1.60 rim, should be 1.85. A 2.15 rim would run a 120/90 and it would by rubbing the fork sliders if you got it in w/o bending the forks some.
DOT recommends a 2.15 (WM3) rim for tire sizes of 3.25 to 3.60 and 90/90. Wity acceptable sizes on a 2.15 rim ranging from 3.00 to 4.00... and 90/90, through 110/90 ... 110/80 also being acceptable.


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