Lower gearing on cyclocross bike for hilly road use

cps26

Hi there,

Was wondering if anyone had any advice on the following: I've got a Cannondale CAADX 6 Tiagra (http://thebicyclebuyer.com/bikes/cannondale-caadx-6-tiagra-89999.html) which I bought to commute on; however recently I've been starting to get into some longer road rides.

I find that when the gradient of a hill reaches a certain point, the lowest gear is a bit 'chewy' for me, and while this is obviously partly due to my strength / fitness (or lack thereof!), I wonder if having a lower bottom gear would help. Specifically, the bike has a FSA Omega MegaExo 46-36T chainset, while I understand that a more standard road set up would be a 50-34T chainset.

So... my question is: is there any way of relatively cheaply swapping the inner chainring on that chainset from 36T to 34T? So far I as I can tell, both chainrings could be removed by undoing the 5 allen bolts holding them in place, but would something like this (http://www.chainreactioncycles.com/Models.aspx?ModelID=35783) fit, or would I need a specific FSA MegaExo chainring to fit? I can only find the whole MegaExo chainset for sale (http://www.chainreactioncycles.com/Models.aspx?ModelID=35734).

Any thoughts/advice gratefully received!

cougie

I'd either hang in there or maybe look at a block with bigger sprockets. Cyclocross bikes have lower gearing already.

Monty Dog

Yes, swapping the inner chainring to a 34 is straight-forward. Release / remove the 5 chainring bolts and swap the ring over. You'll also need to adjust the position of your front mech by lowering it a bit - check out www.parktool.com for all the details. If that isn't enough, then you could fit a 13-28 cassette which is the biggest rear sprocket you can fit on your transmission.

cps26

Thanks Monty Dog - very helpful. Do you (or anyone else) happen to know if any FSA chaninring (for example, this one: http://www.chainreactioncycles.com/Models.aspx?ModelID=35783) will fit on that chainset, or do I need to find a MegaExo-specific one (which I can't seem to do at the moment?)


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night_porter

Any 110bcd ring will fit if your current setup is 110bcd.

I am not sure I agree about dropping the front mech though. The height of the front mech is determined by the big chainring not the bottom one and if you lower it you will remove the 2-3mm gap you need (unless it is too high already).

I would just change the inner ring for a smaller one and to be honest if you are struggling with a 36 you might want to consider something smaller than 34 too.

Assuming you have a 12-25 cassette the 34/23 (the 2nd smallest gear) will still be harder than your current 36/25 so you will only be gaining 1 slightly easier gear at most.

Maybe a smaller inner ring would be better, just make sure that the number of bolts/bcd is the same as you currently have?

tim_wand

Night porter is right no need to lower the front mech its clearance (2-3MM) is dependent on the outer chain ring.

Mega Exo is Fsa's proprietry name for external bearing double brackets and has no effect on the type of chain rings you need.

Most (Compact chain rings 34 / 36 teeth ) shimano or Fsa have a 110 BCD (Bolt circle diameter) as does yours. Bigger chainsets such as standard 53/39 combinations tend to be 130 BCD but you need the 110.

You can find 110 BCD chain rings with 34 teeth quite easily. You may need a bolt ring tool though to disassemble your spider.

A 34 tooth inner front chain ring will not really extend your gearing that much compared to your current 36 tooth set up.

Personally I would buy the same chainset you have in a compact 50/34 combination I picked one up last week on flea bay for 45 quid including the B/B (Which you shouldnt need)

For my alps tour bike I went with this compact chainset front and a long cage rear mech at the back with a 32/12 HG 50 shimano mtb cassette this combination could get me up a brick wall.

Remember the maximum differential a short cage rear mech can handle if you change the rear cassette is around 26 teeth total between top and bottom cog rear plus difference in teeth between front chain rings.

I.E on mine 32-12 (20) plus 50-34 (16) total 36 teeth hence the need for a long cage rear mech.

Sheldon Browns really is the best website for any advice on changing gear set ups

cps26

Thanks for all the helpful advice on here - apologies for the lack of response till today - have been away.

So it sounds like I could either move to a 34t lower chainring, or get a 27t cassette, but not both if I stick with the short cage differential (as the chain differential would then be too great). As set out in the previous v helpful post, the difference in these gearings is not great - using SB's gear calculator, based on 60rpm, the speeds in the lowest gear would be as follows:

Current setup (36 - 25): 6.8mph
New chainring (34 - 25): 6.4mph
New cassette (66 - 27): 6.3mph

So the new cassette option gives a (very slight) further advantage - can you get a nine-speed Shimano HG50 (or something that would be compatible) with 27t?

night_porter

Yes, anywhere.

£15 @ CRC cheap as chips