135mm hub motor on 130mm frame

[erian]

Hi everyone,

so here's the thing.

I have ended up with a problem i did everything to avoid, but my memory failed me miserably. i bought an mxus 135mm rear hub motor 250watts to fit on a frame i bought and have used as a city bike (130mm rear dropouts, 6061 triple butted aluminium). Before i put the motor on i would swear that the frame had 135 mm dropouts, it doesnt! the bike is an old Genesis vapour British cx which was turned to a city commuter by the previous owner/s (upright riding position, mudguards, racks, baskets).

I decided to go with just fitting the motor wheel on. It was pretty easy to do it just by hands and although the dropouts look beefy there was no need for any real force whatsoever. Luckily everything fits well enough, there is no touching between the motor and the frame, but i cannot use the smallest cog of the cassette (the chain will grind both frame and derailleur hanger), so i adjusted the gears to move only from 2nd to 8th.

What do you think? has anyone tried it? what about the stretched aluminium frame? Its a UK genesis, and although 5mm (2,5mm on each side) is not a lot, would it compromise the structure?

Now on both sides the motor has nuts (they go on the inside of the dropouts). Around 6mm thickness each of em. I was thnking of removing the left one and replacing it with a couple of washers (there is some space on the non drive side since im not using disc brakes) just to move the wheel a bit to the left. 2mm will do the trick , then redishing and I will be able to use the smallest gear. Opinions ideas? should i ride it like that?

(photos will come)

 

[SHAN]

Opinions

You've got 5mm of difference. I had a similar problem, but with a steel frame. My preference is to have the dropouts running parallel. So as I have access to the equipment I removed 2.5 mm from (in your case) each of the 6mm nuts, and this has survived fine. Regarding your sprocket clearance, the simplest way for me, assuming its a cassette, would be to run with 7 cogs instead of 8, spaced to suit your requirements, and replace the offending cog with a spacer which can be obtained from the likes of "Velosolo". No doubt you're going to get a lot of opinions, good luck.

 

[Deleted member 4366]

The frame is no problem at all. I've stretched them 25mm or more before. The gears are easy to sort out too. Just add a 12mm washer to the axle. You'll need a narrow one, like 18x12mm (standard is 24 x 12mm). You can sometimes remove a washer that's already there, then switch the anti-rotation washer inboard instead of outboard to get the spacing.

 

[SHAN]

Opinions

If you do a google search "spreading an aluminium bicycle frame" you will get some useful information. I have seen the result of a destroyed 8 speed hub, as a result of a badly spread frame (I.e forcing the hub in), caused by the dropouts not running parallel, putting undue torsional stress on the center axle and bearings over a period of time. Obviously, this is not a powered hub, but the same stresses apply. There are various YouTube tutorials showing how to spread a frame that are worth viewing. Simply pulling the rear dropouts apart to accept a wider hub may well work, but its rough enough for me, but then again, there are those with more experience in such matters on here than my mere 3 plus decades. ​

 

[Deleted member 4366]

I have seen the result of a destroyed 8 speed hub, as a result of a badly spread frame (I.e forcing the hub in), caused by the dropouts not running parallel, putting undue torsional stress on the center axle and bearings over a period of time.​

That sounds like somebody jumping to incorrect conclusions to me: Owner stretched frame by 10mm. Hub self destructed. Someone assumes that they're related. Someone forgot to mention that the adjuster wasn't properly set.

Just about every frame has to be stretched a bit to fit a rear hub-motor. Any problems with hub-motors are now pretty rare, let alone bearings failing. OP has nothing to worry about.

 

[SHAN]

That sounds like somebody jumping to incorrect conclusions to me: Owner stretched frame by 10mm. Hub self destructed. Someone assumes that they're related. Someone forgot to mention that the adjuster wasn't properly set.
.

Interesting and anticipated reply. Don't worry, I won't bang my head on the way out. Bye.