Road Cycling - Gears

My bike has chainrings of 53/39 and a 9 speed cluster of 12/13/14/15/16/17/19/21/23 (Ultegra).

I'm finding that on a fast descent I cannot pedal fast enough to keep up, so would rather a cluster that started with an 11. At the other end, there are some hills I regularly climb, and others I plan to (eg, Alpe d'Huez) that would be very tough using the 39-23 combination. I'd like to go to a 25 at least or maybe even a 27.

How practical or desirable or possible would it be to get a cluster of 11/13/15/17/19/21/23/25/27.

I have used a 53x12 @ 80kmh (50mph) and still had spin left in the legs.... what sort of speeds are you trying to kill yourself at?

I find a 39x25 a good climbing gear, but I wouldnt think twice about chucking a 27 on and a 38 chainring (smallest you can fit) for the hills you mentioned.

Or you could get a MTB cassette that goes from 11t through to 32T or something, and a long cage deraileur, and chuck that cassette on just for the Alpe dhuez. Remember to reguarly replace the chain if swapping cassettes.

Brendon

Or you could get a different crank that would allow for a much smaller chainring.....some others here on the board will know more.

Brendon

Specialities-TA make a crank that takes 110mm bolt circle, so you can fit a smaller small ring, but still use big rings. They are expensive, but very good quality, and many pros use TA rings on their Shimano and Campy cranks.
If you spin out on 53/12, maybe you should practice high cadence pedalling. Use a low gear, dont apply much force, or try to go fast, just spin those pedals as fast as you can for 1 min.

You can calculate the additional gorund you would cover with a change:

wheel diameter x 3.14 x chainring teeth / sprocket teeth

to do what you suggest, you'd pick up about a little more than two feet per revolution...

normally 11's are used by the big sprinters for flat riding, guys like Zabel and Chipo, and Petacchi. Heck, in training Armstrong uses a 12 as his smallest gear (rides a 12-25 in training). For descending the Tourmalet, the Galibier....

if you are riding through that, you need to give Bruyneel a call...quickly

or buy the new Dura Ace with the tenth gear

"Gear Calc is a free cyclists gear calculator. The output can display the gear inches, rollout or metric values together with the speed attained for a specified cadence. The gear table is also charted to provide a visual representation of your gear ratios."

I live in a hilly area and used the calculator to help configure a cassette change. Really good tool.

Joe
Techmarc Gear Inch Calculator (http://www.techmarc.co.uk/gearcalc.htm)

Robert,

My Ultegra cassette is set-up like this:

12/13/14/15/17/19/21/24/27

Some of the cogs are combined (to rings attached to one another); some are separate, 'individual', rings.

I like this combination, because it gives me both 'sprinting' power (not to be overrated, in my case...) and climbing possibilities. On a very long, steep, safe downhill ride, the 11 will probably not make a huge difference vis-a-vis the 12.

How practical or desirable or possible would it be to get a cluster of 11/13/15/17/19/21/23/25/27.

With Shimano Dura-ace and Ultegra 9-speed cassettes, the largest 4 or 5 cogs are linked together in spider modules (each module has 2 or 3 cogs) making it more difficult to fully customize gearing. The 105 9-speed stuff may still be separate cogs, though.

What you could do is buy two cassettes, a 12-27 and an 11-21 or 11-23, use the 11-12-13-15 from the smaller cassette and the 17-19-21-24-27 from the 12-27 and you'd have 11-12-13-15-17-19-21-24-27.

Thanks to all for your advise. It is most appreciated.

To NZLCyclist who said 'I have used a 53x12 @ 80kmh (50mph) and still had spin left in the legs' - 53x12 with a 2.1 metre circumference wheel gives a distance of 9.275 metres per pedal revolution. Therefore you would need 8625 pedal revolutions to cover 80kms. To do this in an hour you would need a cadence of 143 pedal revolutions per minute, or 2.4 per second. I think that is pretty fast!!

My riding partner just put the new FSA Compact crank set up an his main bike. This is a 52/34 front set up. He combines that with his 12/25 rear cassette and loves the versatility (flats and climbing). Something to consider.
Some of the combinations that are mentioned here have gear jumps that are too big for me, especially in the lower (12, 13, 14, 15) groupings. I tend to stick to my 11/21 cassette. Sounds radical, but I am older and slower so I use it with a DA 53/39/30 triple ring group.
I also "spin out" down hills, but I figure that is common. 34-38 mph seems to be terminal spin velocity for me, after that it is aero-tuck time.