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When should I shift my front derailleur?

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When should I shift my front derailleur?

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flag garrett22
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Posted: Jan 5, 2022 at 8:41 Quote
I’m a mtb'r who’s had a single front chainring for a while now. However, I recently bought a Giant Defy with a 2 x 10 drivetrain.

While on my normal road ride (a river bed bike path with no interruptions), I found my self asking, 'when should I be going between the 2 front chainrings?' I mainly ask this due to not wanting to cross chain too much.

The riverbed ride is relatively flat and can usually ride it in the larger chainring. Occasionally, though, I need to downshift the rear (left half of the cog set) for a mild climb or to go from a stop if needed.

Should I stay in the large front and just cross chain occasionally? Or should I downshift the front whenever I’m in the left half of the cog set?

Thx
flag BenLow2019
Posted: Jan 5, 2022 at 9:10 Quote
You will have some ratio overlap with your 2x setup which is normal so you have to keep it in mind when shifting - there are some "useless" gear combinations, but generally you want to:
1) keep the chain straight while you...
2) maintain your optimal cadence while...
3) keeping the power to your legs nominal in order to sustain the effort.

First off you should never hear/feel the chain dragging on the front derailleur. If you do then you're cross chaining too much.
Second, in general, stay off your smallest 3 cogs while on the small ring up front and stay off the biggest 3 cogs while on the big ring up front.

My normal mode in road riding is to usually stay on the big ring up front and only move the rear as necessary for the slight changes in grade. When I approach a short climb then I'll stand up and power up the hill - most often not shifting or only shift one or two cogs easier. If I am on a long climb and I find that I've shifted to an easier gear about 3 times then and I want to go even easier then I'll move front and the rear - drop to the smaller ring up front and double-click back down to a smaller cog in back. This usually puts me in the ratio to cadence area that feels about right.

This website lets you mess around with gear combinations for speed, cadence etc. A fun thing to mess with that shows interesting information: https://www.bikecalc.com/speed_at_cadence

This site has a nice discussion on the topic: https://wickwerks.com/support/crosschaining/

Hope that helps.
Good luck.
flag garrett22
O+
Posted: Jan 5, 2022 at 11:18 Quote
Thx sir, that does help alot
flag dirttorpedo
Posted: Jan 24, 2022 at 15:36 Quote
BenLow2019 has an interesting take on the question. Personally I will use all of the gears in my rear cluster except the largest (easist) on my big ring without issue or the smallest (hardest) in my little ring. When it comes to when to shift I try to avoid making a front derailleur shift during a hard climb and will try to plan ahead to get into the small ring well before the climb (I find I can cruise around 28kmh in my little ring/little gear combination). Otherwise I try and do the rest of my riding in the big ring.
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