Rear hub adapter confusion.

[TheMightyGoat]

I'm building a couple bikes after the ones my girlfriend and I bought got stolen. I'm trying to do them right so rather than use the sprocket that clamps to the spokes, I researched and ordered two of the hub adapter style sprockets for her bicycle and mine. However, they're the wrong size. I ordered two 1.5" hub adapters. After looking at the bicycles more carefully, it looks like the hub on mine (the part in between the spokes) measures about 1.25" diameter, while hers measures about 7/8" diameter. Those sizes don't seem to correlate to hub adapters I see online. I see 1", 1.5", and 1.8". I already have the 1.5 and it's too big for both bikes. So the 1.8 would be too big as well. That leaves only the 1". Not sure if that fits one of the bikes, but regardless, I must not be understanding something as that still leaves one other different size hub.

I've seen some hub adapters listed as 32mm, which translates roughly to 1.25". Do I need a 1" and a 32mm? I have not found both of those sizes listed from any one vendor. There's a 32mm listing on Amazon but shipping ETA is next month.

What am I missing?

 

[Chainlube]

Try to find a spacer for the adapter to make up the difference between hub and adapter.

 

[TheMightyGoat]

Try to find a spacer for the adapter to make up the difference between hub and adapter.

I have seen a few listings for aluminum spacers/bushings for these hub adapters. Just like the hub adapters themselves, I haven't found any spacers listed for 7/8" or 1.25". Short of getting someone to make one on a lathe out of a piece of aluminum I'm not sure how I could make my own spacer that would be precise enough to keep the hub adapter/sprocket properly centered. If it isn't properly centered and solid on the hub, then it isn't an improvement over the thing that clamps on to the spokes.

Maybe I'll just use the crappy spoke clamp thing even though I didn't want to....

 

[GreasyChris]

I have a 1.25 hub I'm using as well I ordered the 1.8 adapter and a pack of adapter pieces that do the 1.25 hub. Not sure what you can do with your other wheel. I got my adapters from gasbike.net
I didnt want to order from them cause i have heard of horror stories but it fit and they speed it out right away. I believe kingsmotorbike has the same thing as they are the same company. Mbrebel also sells the 1.8 and adapters but they dont ship to Canada so I had to go gasbike

 

[TheMightyGoat]

I have a 1.25 hub I'm using as well I ordered the 1.8 adapter and a pack of adapter pieces that do the 1.25 hub. Not sure what you can do with your other wheel. I got my adapters from gasbike.net
I didnt want to order from them cause i have heard of horror stories but it fit and they speed it out right away. I believe kingsmotorbike has the same thing as they are the same company. Mbrebel also sells the 1.8 and adapters but they dont ship to Canada so I had to go gasbike

Oh you're right, I didn't see the 1.8 to 1.25! That might be just what I need. Thanks. And if the 1" doesn't fit the smaller bike.... that would be a pretty thin shim..... guess I'll have to down a few beer cans that day.

Of course now I need to order two 1.8 hub adapters as well. This hobby is getting expensive!

 

[FurryOnTheInside]

hers measures about 7/8" diameter

There's obviously going to be a lot of leverage on that round smooth cylinder with radius of only 7/16" or 11.1mm
I can imagine why they can slip, being so tiny in diameter and totally smooth and circular without any splines or keyway at all. It just isn't the normal accepted way to ensure torque is transferred safely between a sprocket and its shaft.
When it slips there are only the three bolts to catch on the spokes and stop the slip. Only three spokes now taking all the torque as a side load part-way along their length. No wonder that many people have lost even more spokes when the "clamshell" adapter slipped than they were losing to the 9 bolt rag joint from the kit. I hope yours works better. Be careful how you put it together.

Ime, the 6 bolt disc brake mount is the best place to bolt a sprocket adapter to. You just need to get the right bike at the beginning and find or make the right adapter plate yourself, I think. Sorry.

 

[TheMightyGoat]

...a lot of leverage on that round smooth cylinder with radius of only 7/16" ..totally smooth and circular without any splines or keyway at all...
...When it slips there are only the three bolts to catch on the spokes and stop the slip

I had these same two thoughts, myself, while test fitting the hub adapter. I was considering gouging the hub up a bit with a file to give the adapter a little more tooth and resist slipping. Regardless, everything I've read or heard prior to now says that the hub adapter is an improvement over the one that clamps on to the spokes, and I've already said I'm trying to do this on the cheap with the bikes I have, so I'm not sure how your advice is in any way helpful. I'm not going to be getting different bikes or having any custom parts fabricated. Thanks.

 

[TheMightyGoat]

Actually, given another moment's thought, it would be very easy to drill and tap your own set screws into the hub adapter. I would say 3 around it. Maybe not a keyway, but that would be a vast improvement over clamping two smooth surfaces together, and a lot easier to do at home than fabricate a spoke/adapter plate.