Originally Posted by
Winfried
On a Brompton folding bike, I currently use the following setup:
- Bottom-bracket: JIS square taper Shimano BB-UN55 68x118mm
- Crankset: Stronglight Impact 46/34 BCD 110 mm
- Derailleur: Shimano Tiagra
Since the 46/30T
FSA Tempo isn't available with 170mm cranks and the options mentioned above are a bit pricey, I was wondering if it'd be possible to…
1. Get a
50/40/30 triple chainset
2. Remove the 50
3. Replace the 40 with a 46
?
Are there middle 46T chairings, and do you think the whole thing will be narrow enough to fit on a Brompton?
Thank you.
The FSA tempo here only comes in 170 and 175 so perhaps your location just doesn't have them in stock. The specs say that the qfactor is around 148, while the spa cycle cranks are around 165 if you're using the triple as a double. The problem I have with the 30t on the FSA is that it's 80bcd and there are no other chainrings available. I was thinking about using a CNC machine to drill new holes on a 74bcd chainring which is limited to 26t with the 80bcd. But I ended up getting a 110/74 double.
46t middle can be found from ta zephyr, spa cycles, and sugino pe110. I have the 46t from spa cycle and it shifts really well with a 26t, but it came a little bent and bowed so I had to take a wrench and bend it back.
I might go down to 44/24
with My 20x2.10 tires and 30/11 cassette, and 46/26, I'm getting 83-17gi. With a 16 rim the equivalent inner chainring would be 30t.
i might drop the 30t cog to 32t but I'm not sure if there would be enough ground clearance for the rear derailleur for your Brompton. I have about 45mm ground clearance with the Shimano 4700gs. The sram mid cage is maybe 10-15mm shorter.