My daughter has been riding a Redline Expert LE BMX for about two years now and has recently been really enjoying riding the local single track. I have geared it down so she handle most of the gnarly climbs but then its too slow for normal riding around...
It was obviously time to fire up the lathe and get creative.
In a nutshell, I took an XT M760 11-32T cassette with its aluminum spider and machined it down to fit on the single speed freehub that came with the redline hub/rear wheel on the BMX.
Here's a pic of the freehub:
Here's the machined cluster (or at least 5 gears of the cluster):
Much more info in my article "Adding gears to a single speed BMX" if anyone's interested.
Over the next couple of days I'll put the bike together and I'll update with some more info and pics. I'm pretty happy that things worked out dimension wise - BMX's use 110mm rear dropouts so there is not a lot of room to play with but the 5 cogs fit perfectly.
At present, to get a 1 x 5 setup going I'm adding the following weight:
- modified XT cluster with only 5 cogs - 185g
- shifter+cables - ~100g (haven't decided on grip shift or trigger type at the moment)
- extra chain links - ~50g
- XT derailleur - 230g (maybe less, with the limited range of gears I may be able to get away with using a spare road rear derailleur ).
If I was buying a cluster to modify I might start with a PG990 XRAM cluster. The spider arms on the XT cluster stick out a long way past the last cog and at the moment they are coming within about 1mm of the spokes when fitted to the wheel. I'm worried about them catching if the spokes flex a lot. I am going to investigate machining a bit of that material away tomorrow just to be on the safe side.
Phase 2 of the project will be adding a front derailleur, an extra chain ring and shifter for 2 x 5.
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Thread: Sub 8kg 20" 10 speed kids bike