[OldKawaFan]

Hi all. Just joined and I can't seem to find an answer for my question. I have a 1972 G4TR (bought from original owner, 781 original miles!) that I recently got running. I want to use it as a learning platform for my grandkids, but I'd like to update it a bit. The one thing I want to do is switch to a 21" front wheel. I know it's a 36 spoke wheel, but I'm trying to determine what length spokes I'd need to lace up a new 21" rim. Most everything I find online is for more modern bikes that have a disc brake and use 2 different length spokes. Does someone know what length spokes I'd need or how I can go about determining this? Thanks!

 

[WFO-KZ]

Welcome and congrats on a rare find. The G4TR is a classic little workhorse and loads of fun to ride.

May I ask why you want to change the stock 18" front wheel to a 21"? Doing so will alter various aspects of steering geometry, possibly with detrimental results.

 

[OldKawaFan]

Thanks for the welcome. The bike holds a bit of nostalgia for me. In 1970, two adult friends of ours moved up from Honda Mini-Trails to the Kawasaki Trailboss. I got to ride them quite a lot and when I saw this one a few months back, I made an offer. As for changing the wheel, I realize it will impact the steering geometry some, but I feel for the type of riding this bike will be used for, (trails, off road only) the benefits of a 21" wheel to traverse some obstacles would be an advantage. I have been very conscientious in getting the bike running again to not destroy the bikes originality and I plan to do the same with this "mod". I'll retain the old wheel, spokes and tire, knowing that with a little labor, I can return it to stock.

 

[WFO-KZ]

3" is a big change. Have you found anyone else who has done this who could advise on the effects on handling?
It might be a big improvement or it might be terrible. But a lot of work and $$ to find out.

Can you adapt a 21" wheel so you don't have to re-spoke the original? Even if it is just for a trial run?

 

[OldKawaFan]

The actual change is 1.5". I've blocked the bike up and that changes the head angle only by a degree or two, as I replaced the rear tire with a slightly larger outside diameter tire. That can be compensated for by simply sliding the forks up in the triple tree a bit, if there were handling issues. Probably the worst is that I'd have to lengthen the kick stand.

 

[WFO-KZ]

Height wise yes. I was speaking in terms of wheel diameter.

Increasing the rake angle by a degree or two without compensating elsewhere has the effect of increasing high speed stability at the expense of low speed stability. If you slide the fork tubes up to compensate, you may find that the fender will now hit the tire long before the suspension bottoms out.

But to answer your original question, I believe there are companies that will respoke just about anything you desire and they make or purchase spokes at whatever length is needed. I don't think it will be cheap though. Best of luck and post back here with the results for the benefit of others who might consider doing the same.

 

[OldKawaFan]

LOL, I don't think this thing has more than about 4" of travel, but as I said, this will be for low-speed trail riding and learning. If one of the grandkids takes it over about 30 mph, hope they have their helmet on tight! I'll let you know how things progress.

 

[WFO-KZ]

It has 4.5" of travel. The wheel takes up 1.5" of the available space and if you slide the forks to compensate you will have to slide by more than 1.5" due to the angle so let's say 2". So you have lost a total of 3.5" of the space between the fender and the tire assuming that your 21" tire has the same height profile as the 18". So 3.5" plus 4.5" of fork travel = 8".

Was the original space between the fender and the stock tire 8"? Seems excessive for a bike with only 4.5" of travel. In any case it may clear but I think it will be close