135mm hub motor on 130mm frame

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 like and 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!

I decided to go with just fitting the wheel on. It was pretty easy to do it just by hands and although the dropouts look quite beefy there was no need for any real force. 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.

Now on both sides the motor has M10 nuts (on the inside of the dropouts). Around 8mm thickness each of em. I was thnking of removing the left one and replacing it with a couple of washers 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. 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?

(photos will come)

7mm seems like a lot, but since the 5mm went without much effort, the extra 2 mm may work. How's the other side look? Maybe you can take some of the shoulder off of the axle on the non-drive side to compensate

thats exactly my thought. I was thinking of taking out the nut from the non drive side (it is there to give space for disc brakes also which i dont have) and replace it with some plain spacers. Or grind the nut by 3mm to make it thinner..

Did it have a rear wheel?
I mean, are you the one who did take off the rear wheel, and/or do you have it.

That is because many FS alu frames are made to compress the hub. So your 130 mm dropout width might be purposely designed for a 135 mm hub. Easy to measure the original hub to know, or check the parallel alignment of the dropouts to see if they need to be pulled apart in order to be perfectly aligned.

it did have a rear wheel yes, its a 130mm the one it came with, but i am pretty sure it is not the original one since i bought the bike second hand. I assumed that since the bike had 7 gears it would be 135mm dropouts. such a fail.

I bet that since it is a genesis vapour (uk cx frame) it would come with 130mm dropouts originally like most of cx frames. I tried to look at older versions of the frame it looks like a genesis of 2013 but with cantilever brakes.. I measured the distance of seatstays/chainstays to the rim. It stays aligned. then i measured the dropouts again after removing the wheel, at 132,5 mm. That was either their original distance, or they accomodated some as a result of the stretching.

http://www.thebikelist.co.uk/genesis/vapour-10-2012

here is how it should have been originally

Distance of the rim from the chainstay won’t tell anything. It is the distance between dropouts that is required to make them perfectly parallel, that will tell you the hub width that it’s made to fit.

MadRhino said:

Distance of the rim from the chainstay won’t tell anything. It is the distance between dropouts that is required to make them perfectly parallel, that will tell you the hub width that it’s made to fit.

Click to expand...

measuring the distance of the seatstays and chainstays to the rim will tell if one side of the bike was stretched more than the other and will show if the wheel sits centered. since the dropouts are moved outwards hopefully by the same distance, 2,5mm each, they cannot be parallel, provided they were perfectly parallel when the distance was 130mm. Now they should have an angle...but my question is different and is about experiences of stretching an aluminium frame by 5mm to fit a motor hub...

If they were parallel with 130 mm spacing, as you said yourself they aren’t when spread to fit 135 mm.

That is the only problem that you will experience. It is not important if you are not using the disc brake, and as long as the wheel sits straight.

Should be within safe limits to do 6 mm each side of flex. I suspect those nuts are needed on the motor, part of what holds it together. But if a 1 mm washer on one side will help, try it and see.

Main thing is don't bend it out wider than it can go and spring back. Or so wide it leave the dropouts noticeably not parallel anymore. Any bend out will do some angle, but if small enough, like 3 mm per side, it should still fly.

Don't start a crack by bending it too far.