Gear selection question

curium

I have a tricross with an 11-12-14-16-18-21-24-28-32 cassette at the rear and a 50-39-30 (or is it 34? - doesn't matter for my question).

I normally pootle along on the flat in the 50x16 or 50x18 and move up and down the rear cassette as needed.

At what point when using the 50 chainring and moving up the cassette would I be better off moving to the 39 chainring instead of moving up the rear cassette?

The assumption I make when asking this question is that at some point there is crossover between the 50 and 39 chainrings.

I'll look into this properly when I get home from work this evening.

Cheers for any help

hopper1

You should change to the 39 (middle ring) to avoid your chain going to extremes... ie; Big ring to 32 at the back...

curium

hopper1 wrote:

You should change to the 39 (middle ring) to avoid your chain going to extremes... ie; Big ring to 32 at the back...

I know this. My question was hypothetical. e.g. instead of going from 50x21 to 50x24 would I be better off going to 39x21. This is the sort of thing I was asking.

RonB

Try this...

http://www.sheldonbrown.com/gears/

careful

I can only speak for myself but when I get close to an undesirable combination (chain angle) its a matter of anticipating whether the the next change is likely to be up or down. For example, if approaching a longish ascent I would change to a smaller sprocket, but then drop to the smaller ring well before the climb starts. Similarly when approaching congested traffic & lights etc where you may need a lower gear for acceleration.
Conversely, when the going is getting easier, it seems a good idea to get on the big ring in readiness for a series of up changes as you accelerate.

boneyjoe

I used to try keeping a good chain line (staying in higher gears in big chainring, full range on middle chainring (usually on climbs or off-road) and lower gears for granny ring (seldom used) - only to find my casette needed replacing, as I'd worn a couple of the mid to high gears.

However, to answer the OP, I think a lot is down to feel and individual preference, regardless of the actual ratios. Personally, I find a much better rythm on climbs and off-road in the middle chain ring, compared to low gears in the big chainring, even though ratios are similar. Best to experiment a bit, and see what works best for you.

rake

keep the straightest chainline. but generally bigger chainring = less wear.

keef66

I tend to use big chainring for downhill, middle chainring for flat or short / gentle gradients, and small for longer, steeper hills.

I don't worry too much about chainline