I've always had a very slight side to side swaying sensation in certain conditions that I was not able to pinpoint. It was especially bad back when I had a trunk/top case on the back of my bike. An old timer on a forum noted that the tall rear tire mounted on a 16" wheel can get a little wobbly (concerning a top case causing 'sidewall flex, by increasing the leverage on the vertical axial moment of the bike') and that pretty much got the thought in my head to swap the rear wheel to a 17" or 18" at some point.
the 1979 cb650 would have been an easy and cheap path forward since it's pretty much a direct swap to a 17" wheel with the advantage of the wheel design matching my front tire. Unfortunately, those wheels were not cheap and getting more expensive by the day.
I found 2 or 3 listings on ebay and was looking at a minimum of about $90 to get one shipped to my house and then I would still need to clean it and swap out the bearings. Since I'm a glutton for punishment, I felt it might be more fun to attempt to swap the rear wheel from a 91-2003 Nighthawk CB750. It was not a direct swap, and I would ultimately need more parts to buy even if the wheel itself was a little cheaper.
For $65.62 (including the $34.52 shipping cost) I got my project started by ordering just the wheel. I reasoned that the newer wheel (would be lighter than the reverse comstar) and after I paint it, it wouldn't be really obvious that it's a different design from the front which will remain a reverse comstar until I figure out how to mount a nighthawk wheel in the front. (apparently, the triple tree doesn't fit the cb750c, I would need to mill out a different triple tree to be able to use the much larger Nighthawk forks). I'll need the brake panel for this wheel since I don't expect the old drum brake parts to fit.
I suspect the boxed Nighthawk swingarm is lighter than the current tube swingarm and decreasing some of that weight could improve ride and handling although I'm not sure I'm a skilled enough a rider to tell the difference.
Nevertheless, I will need to figure out if I'm going to be able to easily swap the 17mm Nighthawk Axle to to use the original 20mm CB750c Axle and original swingarm, or if it would be easier to get a Nighthawk swingarm and use the 17mm axle and NH OEM wheel mounting components. There could be a fair amount of leg work to figure out the correct bearings, collars and spacers for this application but that's where the fun will be if I can ever figure it out. I know it's been done before, there's just not a lot of knowledge floating on the Internet on such a swap. I think bike builders don't share this kind of knowledge so their custom bikes don't get diluted once everyone else starts reproducing their work. Unfortunately, I've yet to locate an early 80s cb750 with late 90s Nighthawk wheels doing many nights of image searching. Not enough of an updgrade or not possible?
honestly, if someone is going to go through all the trouble, why not go all the way and mount up a single sided swing arm? For me, an old bike should have old bike aesthetics.
Moving from 2.5"X 16" wheel to 4" X 17" wheel should also give me more tire options including the availability of radial tires (unfortunately, only for the back tire. Apparently, Harley does mix radial and bias ply tires for some bikes, so it's not too weird). I guess I should have done a bit more research since there are not many tire options available for the Nighthawk rear wheel. I think there might still be more options than the cb750c though.
I'm going to take my time to measure and order stuff a little at a time so I don't have a big hit to my cash flow. Money is tight as always.
some measurements that I will add as I progress through various stages of dismantling:
I was originally intending to sleeve the hole in the frame for the smaller diameter Nighthawk pivot bolt before I knew the size of the cb750c bolt. Without taking everything apart, I loosened the pivot bolt and tapped it out a little so I could measure the bolt diameter. Unfortunately a .5mm thick sleeve is a little hard to find especially in steel or aluminum but I did find some carbon fiber tubing on ebay with the proper dimensions for sleeving. 16mm OD X 15mm ID. Apparently, the strength of carbon fiber tubing is pretty good, but since it's only acting as a sleeve, there shouldn't be any issue with using it for this application. This also means I don't need to worry about galvanic corrosion from using incompatible metals between the frame, sleeve and pivot bolt.
Edit:
I found this link to a cross reference chart that looks like it will come in very handy to someone so I decided to post a link to it and save the data offline, just in case.
the 1979 cb650 would have been an easy and cheap path forward since it's pretty much a direct swap to a 17" wheel with the advantage of the wheel design matching my front tire. Unfortunately, those wheels were not cheap and getting more expensive by the day.
I found 2 or 3 listings on ebay and was looking at a minimum of about $90 to get one shipped to my house and then I would still need to clean it and swap out the bearings. Since I'm a glutton for punishment, I felt it might be more fun to attempt to swap the rear wheel from a 91-2003 Nighthawk CB750. It was not a direct swap, and I would ultimately need more parts to buy even if the wheel itself was a little cheaper.
For $65.62 (including the $34.52 shipping cost) I got my project started by ordering just the wheel. I reasoned that the newer wheel (would be lighter than the reverse comstar) and after I paint it, it wouldn't be really obvious that it's a different design from the front which will remain a reverse comstar until I figure out how to mount a nighthawk wheel in the front. (apparently, the triple tree doesn't fit the cb750c, I would need to mill out a different triple tree to be able to use the much larger Nighthawk forks). I'll need the brake panel for this wheel since I don't expect the old drum brake parts to fit.
I suspect the boxed Nighthawk swingarm is lighter than the current tube swingarm and decreasing some of that weight could improve ride and handling although I'm not sure I'm a skilled enough a rider to tell the difference.
Nevertheless, I will need to figure out if I'm going to be able to easily swap the 17mm Nighthawk Axle to to use the original 20mm CB750c Axle and original swingarm, or if it would be easier to get a Nighthawk swingarm and use the 17mm axle and NH OEM wheel mounting components. There could be a fair amount of leg work to figure out the correct bearings, collars and spacers for this application but that's where the fun will be if I can ever figure it out. I know it's been done before, there's just not a lot of knowledge floating on the Internet on such a swap. I think bike builders don't share this kind of knowledge so their custom bikes don't get diluted once everyone else starts reproducing their work. Unfortunately, I've yet to locate an early 80s cb750 with late 90s Nighthawk wheels doing many nights of image searching. Not enough of an updgrade or not possible?
honestly, if someone is going to go through all the trouble, why not go all the way and mount up a single sided swing arm? For me, an old bike should have old bike aesthetics.
Moving from 2.5"X 16" wheel to 4" X 17" wheel should also give me more tire options including the availability of radial tires (unfortunately, only for the back tire. Apparently, Harley does mix radial and bias ply tires for some bikes, so it's not too weird). I guess I should have done a bit more research since there are not many tire options available for the Nighthawk rear wheel. I think there might still be more options than the cb750c though.
I'm going to take my time to measure and order stuff a little at a time so I don't have a big hit to my cash flow. Money is tight as always.
some measurements that I will add as I progress through various stages of dismantling:
| Rear Axle | pivot bolt | wheel bearing kit | wheel weight w/tire (excl drum, cush) |
|
| cb750c | 20mm | 16mm | 25-1362 | 35 lbs |
| Nighthawk 750 | 17mm | 15mm | 25-1258 | 32.5lbs |
 |
| 1999 Honda Nighthawk 750 swing arm dimensions |
I was originally intending to sleeve the hole in the frame for the smaller diameter Nighthawk pivot bolt before I knew the size of the cb750c bolt. Without taking everything apart, I loosened the pivot bolt and tapped it out a little so I could measure the bolt diameter. Unfortunately a .5mm thick sleeve is a little hard to find especially in steel or aluminum but I did find some carbon fiber tubing on ebay with the proper dimensions for sleeving. 16mm OD X 15mm ID. Apparently, the strength of carbon fiber tubing is pretty good, but since it's only acting as a sleeve, there shouldn't be any issue with using it for this application. This also means I don't need to worry about galvanic corrosion from using incompatible metals between the frame, sleeve and pivot bolt.
Edit:
I found this link to a cross reference chart that looks like it will come in very handy to someone so I decided to post a link to it and save the data offline, just in case.
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