The Compact Gap......gearing

Unknown

Thanks to many on this forum I have been able to get my compact chainset and bb changed and working. I have noticed that I have a difficulty when I am going approx 17 mph in that I am caught between my 50 and 34 front chainrings. If I shift onto the big chainring then i will have to put a little bit of extra effort in to get it up to 20ish mph (when my cadence is good and the chain is not too offline).

I have a 13-26 (8 speed) at the back and I suspect that I may need a 13-23 ( http://sheldonbrown.com/k7.html#8cassettes ) which will ensure that i have more options at the 18mph area?????

I am a good climber so am willing to sacrifice lowest gear.

I am doing Lejog in 7 days in August and am pretty sure that alot of my downhill/flat cycling will be around the 17-19mph mark (any more than 20mph and I will be freewheeling!). Hills I will take slowly and steadily.


Have people had the same problem? What would you recommend?

P.S. Pearsons were great and the FSA cheapo compact feels lovely!!!

alan_sherman

A closer ratio cassette at the back will make it worse! I had teh same issue and changed to a 36 tooth inner ring which enables me to stay on the inner ring up to 20 mph before switching to the big ring.

use sheldons gear calculator which you can set to show MPH at 90 rpm:

Gear chart using MPH @ 90 RPM
For 700 X 23 / 23-622 tire with 175 mm cranks
With 8-speed "V" 13-14-15-17-19-21-23-26 Cassette
50 36 34
13 27.1 19.5 18.4
14 25.1 18.1 17.1
15 23.5 16.9 15.9
17 20.7 14.9 14.1
19 18.5 13.3 12.6
21 16.8 12.1 11.4
23 15.3 11.0 10.4
26 13.5 9.7 9.2

So you get a little USABLE duplication on the 36x 14/15 and 50 x 21/23.

(I have an 11-2310 speed cassette hence I can go faster on the inner ring)


Cyclist, public transport passenger, pedestrian, driver, motorcyclist.
I get on OK with myself, so why can't we all get on with each other?

alan_sherman

Forgot link:
http://sheldonbrown.com/gears/

Cyclist, public transport passenger, pedestrian, driver, motorcyclist.
I get on OK with myself, so why can't we all get on with each other?

Two sheds

Swapping to 13-23 won't help much on it's own because you add a 16 tooth cog at the expense of your 26. And presumably you are hunting between 50/21, 34/15 and 34/14 (64, 66 and 61 inches).

How about swapping the inner ring for a 36? 36/15 = 65 in., 36/14 =

Put a hump in your back
Shake your sacroiliac
And ride on

Two sheds

... 69 in.

(Ooops, pressed reply too soon, then found AS has made the same suggestion!)

Put a hump in your back
Shake your sacroiliac
And ride on

Unknown

Thaks I will look into buying one.

Do I need an FSA???

Steve I

Surely, the whole point of a compact is to allow lower gears for easier climbing while still using a double chainset. 34-23 gives you a 39.9" bottom gear, 39-26 gives you a 40.5" bottom gear, virtually the same. It strikes me you'd have been better off retaining a non-compact chainset of 39-52 with your 13-26 cassette. Having said that, there's an ex-racer guy in our club who runs a compact in order to run a very close ratio block at the back with a largest sprocket size of 21t and still retain climbing ability.

nick hanson

As i've said on other similar threads,just get a smaller outer ring.Think about it,the compacts are for touring,& how many tours require you to sit on a 108 inch gear for any length of time?
I run a 48 outer on mine & manage to rev out in the mid 40 mph's,which,i'm sure is fast enough to adopt an aerodynamic tuck position

so many cols,so little time!

mdg1157

just change onto the big ring sooner!!

piedwagtail91

a few clubmates have had the same problem and have fitted a 48 outer ring.i looked at the gear charts ,decided i'd miss the 39,40 or 42 ring and got a triple in the sale to keep my 40 ring together with the 50 for flat work and 30 for long climbs.