When Do You Shift Chainring?

[snailracer]

I asked the qn on the forum about 18 months ago and was told that double shifting increased the probability of de-chaining. No explanation was forthcoming.
My own experience refutes the assertion but nonetheless I try to avoid doubleshifting. If the episode is unplanned then probably a lot of power is going through the system and so double shifting may not be the best option.

When you double-shift down, the number of teeth the chain engages suddenly reduces, because you are shifting to a smaller cog and smaller chainring at the same time. This suddenly introduces slack in the chain, that must be taken up by the derailleur and the rider's pedalling. The derailleur (and chain) has mass and limited spring pressure, and the rider's legs cannot "catch up " instantly, so cannot take up the chain slack instantly. The resulting short period of slack in the chain is when it may de-chain. How often you actually de-chain then depends on lots of other factors (spring tension, derailleur design, gear tooth design, chainstay length, etc.)

Double-shifting up is less likely to de-chain because the chain does not go slack - tension increases, and this increase is much more gradual because the gear cable action is slower changing up, compared to when changing down.

 

[ColinJ]

I was on a Spring training camp on the Costa Blanca about 10 years ago and Robert Millar was staying in the same hotel so he came out on several of our rides. I watched as he rode at the back chatting to the people around me, and then powered effortlessly up through the group to the front. We were going up a significant climb at the time but he stayed comfortably in the 53 ring the whole time. He was obviously strong enough to do it, but I couldn't help thinking that our slow climbing speed was imposing a really low cadence on him. I suppose that fixed gear riders are used to that, but I can't get my head round choosing it when more optimal ratios are available at your fingertips.

PS I should add that he wasn't averse to cross-chaining - he used the full range of his cassette. He was riding top-of-the-range bikes with Dura Ace/Record fitted and he didn't have to pay for them so he probably wasn't too concerned about wearing transmissions out

 

[snailracer]

...

PS I should add that he wasn't averse to cross-chaining - he used the full range of his cassette. He was riding top-of-the-range bikes with Dura Ace/Record fitted and he didn't have to pay for them so he probably wasn't too concerned about wearing transmissions out

According to one MIT study I read, cross-chaining doesn't reduce efficiency much (neither did a dry chain, surprisingly). Therefore, IME, it should follow that cross-chaining won't cause excessive wear.

The factor that did reduce efficiency measurably was riding on small cogs (e.g. 11-tooth), which makes sense because there is a larger chain force on each tooth for a given power. As there is overlap in gearing between the chainrings, it would seem more efficient to drop into the smaller chainring/bigger cog combination earlier as one approaches a climb.

 

[ColinJ]

According to one MIT study I read, cross-chaining doesn't reduce efficiency much (neither did a dry chain, surprisingly). Therefore, IME, it should follow that cross-chaining won't cause excessive wear.

TBH - I've never really questioned the conventional thinking on that. It seemed to make sense so I believed it.

The factor that did reduce efficiency measurably was riding on small cogs (e.g. 11-tooth), which makes sense because there is a larger chain force on each tooth for a given power. As there is overlap in gearing between the chainrings, it would seem more efficient to drop into the smaller chainring/bigger cog combination earlier as one approaches a climb.

I've wondered about that question, but I think you've got it the wrong way round! If bigger is better, then climbing in big ring/big sprocket would be better than small ring/smaller sprocket (both with the same ratio).

 

[snailracer]

... I think you've got it the wrong way round! If bigger is better, then climbing in big ring/big sprocket would be better than small ring/smaller sprocket (both with the same ratio).

Aaaargh you're right, I got that backwards

 

[Camrider]

'When Do You Shift Chainring?'
I try not to shoot to often between them and incur the possible chain derailment

Never mind derailment what about the cleaning

 

[SoloCyclist]

Plenty of info for me to consider here. Thanks.

I think what I really need to start giving more thought to what lies ahead. If I'm fairly confident of reaching the top without the need to go on to the 39 then I don't think I should change down even if there is an identical ratio.
If however, I do think the need to use the 39 is going to be unavoidable then I should change down earlier before I run out of cogs at the rear.

On the other hand if I do try and stay on the 53 and get caught out by gradient or conditions I can double shift after easing off the power slightly.

Sounds like I need to get some lumpy miles in. I think I might find it more strange jumping from my compact commuter to standard weekend bike than I first imagined.

Edit: Not long in from doing a 30mls loop that I sometimes use. Took in a few hills and must say that I think I have been being silly in the past.

Because when I'm going well, I am used to being able to power up certain climbs, when I'm not going well I have had a tendancy to punish myself and seen it as defeat if I had to drop down. I would grind and get out the saddle and have to recover more at the top. This has worked for me in the past and I have made good progress and gained the fitness I needed to get beack to where I was.

Now I suppose I'm getting older and need to start using my energies better, and today was the start of that I hope. I'm using the gears a lot better and even felt that a dull ache that I had been experiencing at the back of my left knee wasn't there. I was on the smaller chain ring more today than the whole of last year I think (The front derailleur needed a service last time as it was basically seized) Double shifting down is no problem at all though.

My ride today, I felt, was more consistant cadence wise. At the top of climbs no real recovery was needed and I just rolled on. As I get fitter and stronger again this season I assume I will be strong enough to push on in larger gears, but no more stupidity of feeling I'm not trying hard enough if I need the lower gears. :-).

p.s I was still on my compact chainset.