mornview

If I have a hub (say, in this case, a 110mm coaster brake hub) and I want to throw a few spacers on there to increase the spacing (to put it on a 120mm or 130mm frame), how many more millimeters of spacers can I add on until the hub is no longer safe?

hueyhoolihan

I don't have any idea what would or wouldn't be safe for you, but one problem, among many, with over spacing a hub is that the length of the axle between the bearings and the attachment points on the frame can become too long to support the rider and bike weight without causing a bent or broken axle. an example is the demise (and recent resurrection by Sun) of the 8 speed freewheel/hub.

all in all i believe that putting a 120mm hub on a 130mm frame is less likely to be hazardous to my health than the 30 mile ride around the suburbs/urban area that i take on a daily basis.

and i'm pretty sure that the two coaster brake hubs that i have used over the past few years were originally designed for 120mm spacing. and that neither has be re-engineered for at least 50 years.

BTW both are now are sold with spacing for 130mm's and have solid steel axles, i'm guessin mostly to withstand the abuse caused by the coaster brake.

mornview

Yeah, I'm guessing you're referring to the Velosteel coaster hubs. I'm glad that they're available as a ready-made option, but I have quite a few 110mm coaster hubs just sitting around, so I'd prefer to put them to work if possible.

And yeah, it is primarily that stress on the axle that I'm concerned about. I'm not a big guy by any means at 5'8, 180lbs., but you never know when I might find the perfect cargo-hauling frame, and what it might be spaced at .

FBinNY 

There's no real limit, but you'll run out of axle so don;t forget to allow for the thickness of the dropouts, and leave enough room for 10mm of nut plus a washer.

Also keep in mind that you want to preserve some semblance of chain line.

Andrew R Stewart 

+1 I'll add that having the frame fit the hub/axle width well is more important the wider everything gets. There's more leverage acting on the axle the longer it gets so if you also have to spread the frame and the drop outs aren't parallel you'll end up with some axle bowing. While this isn't the focus that the OP seemed to have I thought it is worth mentioning.

I've respaced a tandem frame from 120mm to 140mm then built up two rear wheels for it. One was a 120 double threaded steel one that allowed me to use a Shimano disk brake (this was in the mid 1970s, the hub and brake came off a JC Penneys bike). the other was a Normandy Sport hub, also originally a 120 width. Both wheels/hubs preformed well w/o issues. I wish I could say the same for that version of my tandem riding life. Not having a steady partner proved to be a real problem. Andy.

mornview

Thanks guys; chain line was an element I was totally overlooking.

fietsbob

IDK how much bending you are willing to do to the coaster brake arm so it is still able to be under the left chainstay when you finish the job.