29er Gearing Chainset/Cassette Advice

TheJackal

Just ordered an SC Highball Carbon 29er frame from the US and am getting around to speccing it out.

I currently ride my featherweight Scott Scale 26" on a 44-30 and 11-28 2X10 combination and can get up most things as I'm a much, much better climber than descender.

All the talk is of how a 29er takes more effort to get going but once you're going you go quicker, so given that I'd like to use a spare Ultegra 11-28 cassette I've got kicking around, on what I hope to be another relatively light build, should I drop to a 40-28 chainset to compensate for those bigger wheels?

I know it's not going to give me loads but whilst I'd love to just splash out on that insanely light XX 12-36 cassette, is the 29er going to be really that different?

Onions and experiences anyone?

supersonic

Momentum of wheels aside, the gearing is higher on a 29er: usually around 10%

See here:

http://sheldonbrown.com/gears/internal.html

TheJackal

Yes, thanks for that. I had used the tables before but thought that there might be a bit more to it!

My lowest current combination of 30 on the front and 28 on the back gives me a gear ratio of 2.0, so I've erred on the side of caution and gone for a 38/26 combination which gives me a 2.1 ratio, admittedly with a shorter crank arm of 165mm as opposed to my usual 175mm.

Of course, I could always slap a dinner plate on the back if I really can't turn the 26 to 28 combo but I'll give it a go.

supersonic

Larger heavier wheels take more effort to gain a certain speed. At a constant speed they take the same effort to keep that speed. To slow down they take more braking - again, is all around 10%.

The advent of 10 speed has been a lot about a wider rnage of gearing in the cassette, especially to combat the 29er higher low gear.

The Rookie

supersonic wrote:

At a constant speed they take the same effort to keep that speed. .

On a smooth surface I agree, but anything with some 'lumpiness' will distort a 29er less due to its longer ramp length and should leave it with a slightly lower net rolling resistance, although the make model of tyre is likley to have as much effect as the 26-29 change.

Simon