Cyclists - Gearing, what's more efficient?

thescouselander

Something I've been wondering about for a while - whats more efficient when it comes to selecting a gear?

I can select very similar gears on my road bike by using either the big ring at the front and a larger ring at the back or I could use the small ring at the front and a smaller ring at the back.


In both instances I keep about the same cadence for a given speed but is there any difference in efficiency between the two selections? I always seem to go faster using the big ring at the front but I cant really explain why.

johnfarquhar74

thescouselander wrote: »

I can select very similar gears on my road bike by using either the big ring at the front and a larger ring at the back or I could use the small ring at the front and a smaller ring at the back.

If you love your bike, don't do this, the chain should be parallel with the bike, not crossing over from big sprocket to big sprocket or small to small.

thescouselander wrote: »

In both instances I keep about the same cadence for a given speed but is there any difference in efficiency between the two selections? I always seem to go faster using the big ring at the front but I cant really explain why.

Mmmm? Are you saying you're feet go round the same RPM and the speed of your bike is the same when your big2big/small2small. If so, the work rate is the same and you shouldn't be going faster.

Either way, on my 21 or 24 speed bikes, I like to pick up a healthy cadence and maintain that regardless of hill or flat through using the gears. Obviously the road speed is the variable here! I usually start off on middle front sprocket and middle rear, this is normally a decent gear to move off from on the flat. I then move to larger front gear and build up my speed by going down the rear, always remembering to change back down when coming to a stop.

I'm sure I seen an illustration online for bike gears. For the average 21/24 speed bike there only is about 10/12 useable gears!

thescouselander

Just to clarify - if I'm using the larger ring at the front I seem to go faster because I can maintain a higher average speed than when I'm using an equivalent combination on the small front ring - this is more noticeable when going up a slight incline.

Maybe you bring up a good point though - perhaps a more parallel chain should be more efficient.

johnfarquhar74

thescouselander wrote: »

Just to clarify - if I'm using the larger ring at the front I seem to go faster because I can maintain a higher average speed than when I'm using an equivalent combination on the small front ring - this is more noticeable when going up a slight incline.

Maybe you bring up a good point though - perhaps a more parallel chain should be more efficient.

You can count the teeth on the rings and work out the ratio of pedal turns to wheel turns, if the number is the same then any feeling of ease/speed is exactly that, just a sensation.
The parallel chain thing is just good practice for a derailleur system, if you go big2big your putting the mechanism under a lot of strain, also small2small would mean a lot of slack in the chain, which equally, isn't that good!

thescouselander

Having had a look round on the net I haven't found much on the subject but this study on motorbikes seems to suggest using bigger sprockets is more efficient.


http://www.springerlink.com/content/bj274q1060h31xn3/fulltext.pdf

andygb

thescouselander wrote: »

Having had a look round on the net I haven't found much on the subject but this study on motorbikes seems to suggest using bigger sprockets is more efficient.


http://www.springerlink.com/content/bj274q1060h31xn3/fulltext.pdf

A motorbike is a bit different to a human powered machine. You should always try to use a gear which will allow you to pedal comfortably (90 to 100 RPM), whilst making good progress. Try to keep the chain as in line as possible most of the time, avoiding the very large or very small sprockets.
Tell me what size chainrings and sprockets you have, and what speed you want to travel at, and I will try to suggest a decent gear combination.

Pew_Pew_Pew_Lasers!

The simple answer is that its most efficient to select the gear that maintains your cadence. Don't use the big ring in combination with the lowest gear on the back though. That just increases wear.

MX5huggy

thescouselander wrote: »

Having had a look round on the net I haven't found much on the subject but this study on motorbikes seems to suggest using bigger sprockets is more efficient.


http://www.springerlink.com/content/bj274q1060h31xn3/fulltext.pdf

Sheldon Brown covers just about everything about bikes in far too much detail!

http://www.sheldonbrown.com/gearing/index.html