Lower gearing for Specialized Sirrus

RobinB2

My Dad has a Specialized Sirrus and is looking to lower the gearing in order to be able to ride up some of the forestry tracks near where he lives. The types of gradient and road surface are probably more appropriate for a mountain bike, so not sure which forum to post this in

The bike currently has a 11 speed Shimano 105 rear mech with the cassette having a 32 tooth largest cog. Front chainset is a FSA Gossamer Pro, alloy, MegaEVO BB, sub compact, 48/32T, 110mm BCD spider

I'm wondering what would be the cheapest way to lower the gearing? I think the 32 tooth option at the front is the smallest possible with the 110 bcd chainset and not sure a 105 GS rear mech would work with anything larger than a 32 cassette. If going for a new chainset, would one of the FSA mountain bike chainsets fit the same bottom bracket, for example? I asume that going to a 86 BCD chainset would give some smaller chainring options

Any feedback on the cheapest and most practical way to lower the gearing would be appreciated

defycomp2

11 or 12-34 rear cassette with some twiddling of the B screw will probably work; it does with SRAM.

RobinB2

Thanks DefyComp2 - however I was hoping that by going to a 28 tooth or smaller chainring, this would give a greater gearing change than the rear cog going from 32-34. I've also not had particularly good experiences in the past with trying to make Shimano rear derailleurs work with larger than recommended cassettes

mercia_man

https://www.spacycles.co.uk/m2b17s109p3 ... cral-Rings

You can get these in 44/28, 42/26 and even 40/24. You would need new square taper BB also sold by Spa.

Nick Payne

Easiest change would be different cranks, assuming that the front derailleur can be lowered enough to accommodate the smaller large chainring. E.G. something like this, which has 38/24 chainrings (it's nominally a 10-speed crank, but will work perfectly well with an 11-speed chain and derailleur: https://cycle.shimano-eu.com/content/seh-bike/en/home/mtb/drivetrain/crankset/fc-m625.html

RobinB2

Thanks Mercia man, Nick Payne - looks like a different chainset is the way to go - if I could do this without changing the bottom bracket, that would be ideal. Even though bottom brackets don't cost that much, by the time you've paid a LBS to swap them, the bottom bracket costs will be in the same ballpark as a new crank

RobinB2

Turns out that lowering the gearing below what is already on the bike is a non-trivial exercise! I was going to go down the smaller chainset route but having had a closer look at the current front derailleur bracket, I'm not sure it'll drop any lower to work with anything much smaller than the current 48/32 setup

I ended up using a Wolf tooth roadlink to run a 11-40 cassette but still retaining the standard 105 gs derailleur. This seems to work but have to be careful using the larger chainring in any of the larger cassette options. I'm now on the lookout for a smaller 110 bcd, 4 bolt chainring to bring the full gearing range back within the rear derailleur tooth capacity