Shifting chainrings on acceleration
RutlandGav
Posts: 144
This morning I find myself with tabs for Sheldon Brown's gear calculator open, and Wiggle website.
As I twirl the allen key in my hands, my bike cowers in the corner going "Nooooo!"
Yep, it's time to replace cassette and chainrings, and i'm planning to narrow the range.
ATM, my Carrerra Subway MTB has 650b wheels, 28-38-48 chainring and 11-32 8spd cassette.
"Granny gear" is about right for the hills i face, but I can do 29mph @ 90mph in top, which is far beyond anything i'll need. I'm planning to trade some top end for a smaller step between ratios. ATM it's 15%, which makes finding a comfortable cadence/pacing sometimes difficult.
However, I'm just wondering how you commuters deal with the changeover from one chainring to the next. Invariably, it's massive , like 45% or so. You're spinning out and running out of revs, go from the inner to the middle chainring, and suddenly find yourself down at a cadence that is potentially bad for your knees.
I normally shift down one cog on the back the same time i go up one at the front, which helps. But if i put a narrower range cassette on , I'd have to shift twice to have the same effect, which is probably quite easy if you've got thumbs like Mike Lindup from Level 42.
OTOH the change i am planning to make, is to fit a road cassette to a 22-32-42 chainring. Much of the time i can avoid this by simply staying on the middle ring, provided i don't need to stop completely.
Fortunately I don't have to deal with right turns on multi lane roundabouts, where I need to go from 0 - 25mph in 6 seconds, whilst giving arm signals etc.
But no doubt, some of you do. How do you manage, stand up? Or build a super custom "narrow stepped" set of chainrings?
As I twirl the allen key in my hands, my bike cowers in the corner going "Nooooo!"
Yep, it's time to replace cassette and chainrings, and i'm planning to narrow the range.
ATM, my Carrerra Subway MTB has 650b wheels, 28-38-48 chainring and 11-32 8spd cassette.
"Granny gear" is about right for the hills i face, but I can do 29mph @ 90mph in top, which is far beyond anything i'll need. I'm planning to trade some top end for a smaller step between ratios. ATM it's 15%, which makes finding a comfortable cadence/pacing sometimes difficult.
However, I'm just wondering how you commuters deal with the changeover from one chainring to the next. Invariably, it's massive , like 45% or so. You're spinning out and running out of revs, go from the inner to the middle chainring, and suddenly find yourself down at a cadence that is potentially bad for your knees.
I normally shift down one cog on the back the same time i go up one at the front, which helps. But if i put a narrower range cassette on , I'd have to shift twice to have the same effect, which is probably quite easy if you've got thumbs like Mike Lindup from Level 42.
OTOH the change i am planning to make, is to fit a road cassette to a 22-32-42 chainring. Much of the time i can avoid this by simply staying on the middle ring, provided i don't need to stop completely.
Fortunately I don't have to deal with right turns on multi lane roundabouts, where I need to go from 0 - 25mph in 6 seconds, whilst giving arm signals etc.
But no doubt, some of you do. How do you manage, stand up? Or build a super custom "narrow stepped" set of chainrings?
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By the way, your biggest shift on the chainrings is 28->38 which is +35% not 45%!
90rpm on 48/11 with 1.9"x650b tyres is 35mph.
This.
You just need to anticipate a bit. If you are commuting then you are probably doing pretty much the same route every day. You know where all the hills, junctions and lights are you just need to think ahead and change a couple of sprockets.
I climbed the odd mountain on it and on the descents it didn't spin out until around 45mph.
At the moment I'm riding a perverse set up on my MTB 22-36-44 x 11-36 don't do this, it's horrible, confusing chews up chains and hurts derailers but I think 24-36-48 x 11-28 might just be the perfect set up for a go anywhere bike
I'm glad someone is picking up on the key issues in this thread.
Its also worth noting that Mike Lindup once came 3rd in the national Tiddlywink championships so possibly also has quite strong thumbs.
Bianchi Via Nirone 7 Ultegra
Brompton S Type
Carrera Vengeance Ultimate Ltd
Gary Fisher Aquila '98
Front half of a Viking Saratoga Tandem
The upshifts are a little slow however, particularly on the shortest chainring. I'm guessing a lack of chain tension is causing this? Only ridden it once since changing all the bits over, so possibly still need to let stuff bed in.
Shift performance was indeed awful, till i took 4 links out of the new 116 link chain.
To be honest, i'd rather the upshifts were slow on the biggest chainring, than on the smallest, since on the 22 i'm going to accelerate so fast. Perhaps remove another link or two? ATM system seems comfortable going big to big, which i'd never actually do in reality.
I have the same crank but with a 12-25 at the back and find that it's comfortable but if I push it, I end up running out of gears; doesn't happen very often as the bike's about 16kg (with pannier).
However the setup will find it's way onto another frame next year and I know the 44 will be too small, so have got a 48T ring ready for either the swap or when the ring's worn out.
Everyday Commuter
Tension doesnt change much (most if it comes from the spring preload, little is added by moving it further) so it may just be an effect of the chainline from which any tension is usually pulling the mech towards a lower gear.