UKC

Getting jealous of my mate's low gears on his MTB compared to my cyclo-cross bike when he cycles and I walk.

9 speed cassette 11-34 I think. The bike is ridden pretty much exclusively off-road, top gear is nice for bouncing at speed on good gravel but rarely used.

I have FSA Vero (road?) with 48 and 32 teeth chainrings and FSA bottom bracket.

Shimano Altus FC-MT101 (MTB?) chainset 36/22T looks like a reasonable option for significantly lower gears. Is this a dumb idea?

Anybody know if bottom bracket compatible between Vero and Altus?

Is there a chainline issue (length of bottom bracket axle?) or some road Vs MTB issue?

Would Shimano Sora front mech need changing or just lowered on down tube?

Any impact in rear mech?

Lots of questions as I have no idea!

I was hoping you'd get some replies as I'm interested in something similar. I have Shimano Altus (I think), it's 46/30 and I'd like a lower gear or two but without losing the top gear. So a 46/26 or something, but it doesn't appear to exist.

The best thing I've found so far, which might help you a bit, is a 9 speed 11-40 cassette. Should be a bit easier and cheaper than a new chainset, but I'm not sure if the derailleur can cope with the range so I haven't tried it yet.

Shark tooth gear hanger extender to accommodate 11-40 on current rear mech?

That's a possibility.

Really I should have triple chainrings at my age!

Use one of the on-line 'gear size' calculators ( or one of the tables in an old fashion book) to work out the 'size' of lowest gear your friend has so you have a reference. In the 'old system' (now back in favour by Boris), where the gear is compared to the diameter of the big wheel of a penny farthing, the lowest useable gear on a mountainbike was traditionally about 16 or 17 inches.

At the other end, 95 or 100 inches is generally considered the 'easist' top gear that allows you to pedal at a reasonable speed, but you would 'spin out' fairly soon on a steep-ish descent. Down to 80 inches and you could pootle along the flat quite happily but have to freewheel down nearly every incline. But you can find what's the lowest top gear you would personally could accept by riding your current bike in a variety of intermediate gears and note which combination is as low as you are happy to go. Then note the number of teeth front and back on that combination and convert that to a gear size in inches.

Now you have the 'size' of he lowest gear you require and the 'size' of the lowest high gear you're prepared to accept. You can achieve that in any number of ways, but at least you'll know for certain that any combination of bits you find available / workable / affordable will give you the range you require.

The fact that you even know what a triple chainring is shows your age! 😂

Oi! I resent that!

46 & 26 - different bolt circle diameters and you only have two BCDs on triple crankset?

Due to bolt circle diameters, perhaps only to get 46/26 is to put 2 chainrings on middle (46) and inner (26) positions of triple crankset but that is an ugly bodge* and I've no idea if is compatible with crankset or front mech.  

*file/round off protuberances for unused big chain ring position?

Looking at triple on my wife's hybrid it's riveted rather than bolted anyway.

Entering to the 21st century and getting a cassette with some dinner plate sprockets may be the answer. Pity I can't get a cassette 15-50.

My reckoning for highest gear is 46->36 on chaining ring is equivalent of going from 11->15 or a couple of gear changes on rear of current setup. Highest 2 or 3 gears used almost only on tarmac which I don't do much of on this bike.

And for the lowest my reckoning for 32->22 on chainring is equivalent of 34->50 on cassette so equivalent to another 2 or 3 rear gear changes with my current crankset.    

Using a calculator my current gears (48/32 & 11-34) range from 25 to 110 inches.

And 36/22 & 11-34 gives 17 to 86 inches.

I probably should just buy an MTB!

nice idea and cheap. both square taper? should work fine. as well as larger rear sprocket (although with only 9 speeds the gaps could become too big)

https://road.cc/content/feature/how-get-ultra-low-gearing-gravel-bike-adven...

i'd take the 48/32 off your hands -my gravel bike was from the early days when they thought 50/34 was a good idea- not much difference tho..

Yes fitting lower gears is a good idea.

Yes chain-line will be an issue trying to fit a MTB crankset to  a drop bar bikes bottom bracket because drop bar cranksets typically use much shorter axles  as they don't have to clear fat tyres. I've found that inner ring of an MTB chainset can foul against the chainstays if you fit them on very short bottom bracket axles.

Both cranksets use JIS square taper so you may be able to use your original bottom bracket.

According to FSA the Vero uses a 110.5mm axle bottom bracket for a 44mm chainline

Shimano recommend a 123mm axle length for the Altus FC-MT101  for a 50mm chainline.

Fitting the altus chainset to your bottom bracket will move it in towards the bike 6.25mm, keeping the same chainline theoretically, but the inner ring might foul on the chainstay. But as the calculate chainline is the same it should be fine.

You'll need to replace you front derailleur as well as the Sora cage won't be shaped right for the much smaller rings of your new crankset. Its only rated down to a 46T big ring

Rear mech will be fine, you'll just have to shorten your chain.

You can get 11-40's in 9 speed, this is what I use on mine. I've just got a cheap Acera rear mech with an extender.

https://www.highonbikes.com/products/sunrace-csm980-cassette-9-speed-black?...

ahh, didn't know about that. so would need eg Shimano Alivio M3120 available for £11.99

So I need a bottom* pull (road) front mech suitable for small (MTB or hybrid) chainrings.

Thanks for info, it's complicated!

magma - £11.99 - that's my kind of pricing

*it seems dual pull (top and bottom) exists

i'm thinking the same. how wide can your tyres go? my old gt grade 9 speed has very little tyre clearance- 37mm limit- not idea for steep gravel and low gears..

As an aside, I remember once rejecting a Felt bike in a local shop because it had a triple crankset and they wouldn't change it for a double.

Shame, as otherwise I really liked it (yes, I know it's not just the crankset...).

After lots of useful* advice on UKC and from the email when I bought them

Schwalbe Addix Smart Sam Plus GreenGuard SnakeSkin Tyre Wired - 700 C · Size: 700 x 40 C

https://fawkes-cycles.co.uk//schwalbe-tyres-schwalbe-addix-smart-sam-plus-g...

The bike originally came with something supple and knobbly which were useless because they punctured a couple of times in the first week of commuting so were replaced with Schwalbe Marathon Plus slicks. Then lockdown & WFM came along and I became a leisure only cyclist - off-road and near zero traffic. Still with a bit of road, canal path & broken glass to get off-road so still Schwalbe.

I expect I'll be commuting through the rain and darkness again this winter on my other commuter (touring bike).

*best useful UKC advice was - for judging bigger tyres, check width clearance for current tyres at chainstays (as well as clearance at seat tube, seat stays and front forks). Chainstays likley to be the narrowest limit & front forks the widest.

yes, dual pull front mechs are a great invention, one of those why didn't they think of it before things.

It looks like the following should be compatible with existing square taper bottom bracket, current 11-34 cassette, rear mech capacity, frame geometry(?)...

Shimano Altus FC-MT101 chainset 36/22T

SHIMANO ALTUS TOP SWING Front Derailleur (Clamp Band Mount) 2x9-speed 

https://bike.shimano.com/en-EU/product/component/shimano/FC-MT101-2.html

https://bike.shimano.com/en-EU/product/component/altus-m2000/FD-M2020-TS.ht...