1978 CB125S wheel questions

[mwyatt]

I'm bringing a 1978 CB 125s back from the dead. The rims and spokes are pretty rusty. I'd like to replace them with new aluminum rims. It looks like I can get sets from Thailand via ebay, but I'd really like to use a 17" rim I have left over from a DR650 (36 holes, angles look to be fairly close to original). It's also slightly wider so I should be able to run a 120/70 tire, possibly a 130.. The center of the rim is deeper than the OEM rim, so it looks like I might need spokes about 12mm shorter. I'd also like to lace a 17" rim to the front, but I'm having trouble figuring out what rims might work. I could probably get a Tusk rim, but which one? Spokes are a total wild card too. Has anyone converted their cb125 to 17" aluminum wheels front and back? Any ideas of rim/spoke packages that might work? I can't afford the expensive Buchanan kits.... so if I can't work it out with a Tusk rim, I may have to go with the ebay set.

BTW, this will be a track bike so keeping the OEM look isn't important.

Thanks a bunch!

 

[teazer]

I would suggest getting 18" rims no wider than one size wider than stock and then run a modern 18" tire/tyre. The problem with wider rims and rubber is that it's heavier and will never get up to operating temperature on a small bike. You probably want WM1 1.60" front and up to 1.85 (WM2) at the rear with say BT39ss race tires from your local Honda dealer.

That way, it will have all the grip you can ever use with light steering. You probably have all of 10-12 hp to play with and cannot afford to drag any more weight and rolling resistance than is absolutely necessary.

An RS125 with 17" rims and 48hp is a whole different story and runs nicely on skinny slicks. A CB125, not so much.

 

[mwyatt]

Thanks Teazer! The BT39ss look familiar. I believe a lot of vintage bikes were running those when I used to race at PIR in Portland. Are you suggesting I swap the 17 rear out for an 18" and leave the front as an 18"? Intuitively, it seems like a 17" tire would weigh less and turn in better on a small bike. I have zero experience with small bikes so I will defer to those who have some.

 

[irk miller]

The gyroscope effect of the bigger rim will certain take away from turning, but suspect it won't matter enough. You'll gain more from the skinnier 18 and lose more from the wider 17. At least that's how I am taking the suggestion from Teazer. As such, if you can buy a new front rim, then maybe a narrow 17 is the best option for front and run the wider DR 17 rim out back.