Gears: how low can I go with a Shimano Sora 9-spd rear mech?
HighlandBimbler
Posts: 6
My shiny, but eclectically furnished, new road bike has a Shimano Sora 9-spd rear mech (long cage), and a close-spread cassette with 11-23 teeth .
It also has a Shimano Tiagra front mech and a Truvativ Isoflow Road 72.5mm crankset with 30.42.52 teeth.
The shifters are Shimano Tiagra 9-spd.
While a dream on the flat, frankly this set-up is killing me on my long, steep local hills!
My questions:
1) I've been told I can't simply swap out the inner chainring on the crankset for something smaller, as 30T is as small as I can go without getting a whole new crankset - is this right? If not, how small could I go?
2) I've also been told the largest sprocket the Sora rear mech could handle is 25 teeth - is this right? If not, any suggestions for a compatible 9-spd cassette that would give a good spread of gears for both hill-climbing and cruising on the flat?
Grateful for any helpful response. Cheers.
PS. My first post - be gentle!
PPS. I'm also on a budget
It also has a Shimano Tiagra front mech and a Truvativ Isoflow Road 72.5mm crankset with 30.42.52 teeth.
The shifters are Shimano Tiagra 9-spd.
While a dream on the flat, frankly this set-up is killing me on my long, steep local hills!
My questions:
1) I've been told I can't simply swap out the inner chainring on the crankset for something smaller, as 30T is as small as I can go without getting a whole new crankset - is this right? If not, how small could I go?
2) I've also been told the largest sprocket the Sora rear mech could handle is 25 teeth - is this right? If not, any suggestions for a compatible 9-spd cassette that would give a good spread of gears for both hill-climbing and cruising on the flat?
Grateful for any helpful response. Cheers.
PS. My first post - be gentle!
PPS. I'm also on a budget
0
Comments
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It may be difficult to find smaller chainrings in the BCD (bolt circle diameter) that you require.
The Sora should be fine up to 27 teeth.0 -
All of Shimano's mountain bike rear mechs are compatible with 9 speed Tiagra, this would allow a largest cog on the cassette of 34 teeth.0
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@ Supersonic & Whyamihere
Thank you both; I very much appreciate you taking time to answer.
Just to clarify:-
Supersonic says my existing Sora mech can handle up to 27T.
Whyamihere seems to be saying I could could go up to 34T if I swapped my Sora mech for some other Shimano MTB mech.
With either option, am I likely to need to alter my chain length?
Cheers guys,
HighlandBimbler0 -
30 x 27 is what I run (it is hilly round here...); on the steep stuff it's noticeably easier than the 23 cassette and I can't imagine needing lower gearing. And your chain will be OK too.0
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Mr_Si
Thanks very much indeed. Just googlemapped your location and you do indeed have hills . . . very reassuring!
Moving from 23 to 27 teeth is about a 17% increase in mechanical advantage, which sounds like more than enough to me.
Thanks again to you and to Supersonic & Whyamihere - I think I've got the answers I need now.
Cheers guys
HighlandBimbler0 -
You'll need a longer chain with the new cassette. In theory, you could be ok, as long as you didn't go to the bigger cogs on the cassette while in the big chainring, but if you forget and accidentally shift to those gears, things are going to break.
Chains are pretty much a standard length before being shortened to fit the bike though, so if you buy a new one with your cassette, you'll be fine.0
