I am currently running 53/39 130BCD on a GXP BB, always feel i am working to hard on the 53 so want to size down, I cant go 50/34, is it worthwhile going 50/38 will 1 tooth in the inner really make that much difference or should i bite the bullet and buy a whole new 50/34 crankset.
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Hugh Manatee
Veteran
I have two main bikes. One has 39/53 with a 12-23 cassette. After a ride where I physically couldn't turn the pedals up one admittedly very steep hill I decided to go compact with a larger spread at the back.
After a bit of fiddling, I have ended up on the other bike with 38/50 and a 13-26 cassette.
I have found myself in the big ring more often but can also spend time in the small ring without spinning madly. This was important to me as I have a self imposed embargo on the big ring in Winter.
I don't seem to ever go lower than forth or occasionally third on the cassette. The big geared bike is still quicker. I should point out it is pretty flat here. What climbs there are tend to be long and dragging.
I found it cheap to change the 130 BCD ring getting a reasonable quality ring from ebay.
After a bit of fiddling, I have ended up on the other bike with 38/50 and a 13-26 cassette.
I have found myself in the big ring more often but can also spend time in the small ring without spinning madly. This was important to me as I have a self imposed embargo on the big ring in Winter.
I don't seem to ever go lower than forth or occasionally third on the cassette. The big geared bike is still quicker. I should point out it is pretty flat here. What climbs there are tend to be long and dragging.
I found it cheap to change the 130 BCD ring getting a reasonable quality ring from ebay.
Ajax Bay
Guru
- Location
- East Devon
A 38 instead of a 39 will gain you 2.6%. A 28 instead of a 27 will gain you 3.7%. I had a 52/42 (SR Apex) and changed to a 54/40. The FD coped and the 40 made it a bit easier (circa 5%). But the bigger gain was moving from a 14-25 block to a 14-28 (6sp) block: that gained me 12% for the hard (Devon) hills.
So before you swap the 39 for a 38, make sure you're running the largest large sprocket your RD can handle. There are recent threads on here discussing the options - even for a 30.
So before you swap the 39 for a 38, make sure you're running the largest large sprocket your RD can handle. There are recent threads on here discussing the options - even for a 30.
Thanks Alex. sure my RD can take a 30 but i have already bought the 28, so i'll maybe run that up a couple of our most horrid hills before deciding changing the inner, was out on a particularly hilly run on Sunday and spent most of the day looking for gears i didnt have
Spiderweb
Not So Special One
- Location
- North Yorkshire
The lowest gear on my bike was a 25 on the back and I was struggling with some hills. The local bike shop fit a new cassette with a 30 tooth which is a massive improvement. They did this without changing the rear mech, if I required a larger sprocket then the rear mech would need to be changed for a longer caged one.
It is likely you will need a new longer chain too as I did.
It is likely you will need a new longer chain too as I did.
Ajax Bay
Guru
- Location
- East Devon
If you are just making the change for your hillier than hilly 5 days (and then expect to change back), then a cassette with a 30 can be fitted without changing (lengthening) the chain provided you promise yourself that you will never go large/large or even large second large. To help the RD cope, the B screw may need adjustment. If this wider cassette becomes a 'permanent' then heed @Spiderweb 's experience ref chain length.
