Using a double with a greater than 16T difference.

[TheCyclingRooster]

Hi to you all out there. Has anyone experienced using a double a
as per the post title ?

I am putting the finishing touches to a totally refurbish Steve Goff frame that has a fabulous new Flamboyant Blue Jacket with new Chrome forks.

Has anyone ever tried an 18T difference - I am using Stronglight rings.

I am currently contemplating a 42/26 with a rear cassette of 12:13:14:15:16:17:19:21:23:25.

I need a quite low ratio for climbing but not such a high ratio for down-hill take-off speeds.

With the fact that I am running 140mm cranks and have been for some 8yrs since total left knee replacement they themselves are effectively increasing my chainring tooth-count by 2 teeth.

 

[Sharky]

I know its not the answer to your question, but have you considered just a single chainring? A wide cassette (11-34) with a 34 ring will give you the bottom gear you are looking for with something around an 81 at the top end. I made the switch to a single ring a few years ago. Makes gear shifts a lot less complicated.

I too ride short cranks 145 & 150mm and also pleased with this change.

 

[TheCyclingRooster]

I know its not the answer to your question, but have you considered just a single chainring? A wide cassette (11-34) with a 34 ring will give you the bottom gear you are looking for with something around an 81 at the top end. I made the switch to a single ring a few years ago. Makes gear shifts a lot less complicated.

I too ride short cranks 145 & 150mm and also pleased with this change.

Hi Sharky. I believe that if I could get an 11-34 10spd Campagnolo or even a Miche cassette I would be paying through the nose for it never mind finding a Campagnolo 10 spd rear dérailleur with a long cage.

Out of curiosity - where did you get your short cranks from ? Mine are Thorn (SJS Cycles) and actually are often used by Stoker on a tandem.

 

[Sharky]

Hi Sharky. I believe that if I could get an 11-34 10spd Campagnolo or even a Miche cassette I would be paying through the nose for it never mind finding a Campagnolo 10 spd rear dérailleur with a long cage.

Out of curiosity - where did you get your short cranks from ? Mine are Thorn (SJS Cycles) and actually are often used by Stoker on a tandem.

I've had two pairs shortened to 150mm by highpath engineering and bought two pairs of sinz cranks (145 & 150mm). One pair from Evans and can't remember the other place, but they did seem to go out of production for a while. But they seem to be back on some of the bmx websites.

 

[Ajax Bay]

OT but Crank length article by Steve Hogg

 

[TheCyclingRooster]

OT but Crank length article by Steve Hogg

Hi Ajax Bay. Having looked at the article that you you kindly flagged-up I notice that there appears to be no account of a rather short in-seam/inside leg measurement.
I myself fall into that category with a 23" (585mm) measurement - so based upon the formula given - I would be best with 126mm cranks.

What is also notable is that there is/are no suggestions as to alternative tooth count so as to compensate for the extra effort/leverage that shorter cranks demand. My need for shorter cranks was to overcome the restricted bend at the knee after total left knee replacement surgery.

Before this was carried-out I rode 170mm and 175mm cranks on my various road and Hybrid Road Bikes (Flat-bars).

 

[Ajax Bay]

Your 140s offer 17% less torque for the same force cf using 170mm cranks. This will effectively only affect your choice of lower gear (though of course you are seeking a reasonable top gear and a cassette not too widely spaced apart, hence the OP). By implication if with 170s you'd be content with a 34/28 then your selection of a 26/25 low gear with 140s is close to spot on (26/26 would be spot on).
I have never tried to run chainwheels with an 18t delta. But alternative approaches you could consider are either an 11-25 with a 39-26 or a 12-28 with a 44-28. I haven't checked BCDs: these are just examples. Finding an FD with a 42t 'curvature' and which can cope with such a low chain line (26t > 25t) which suits your new P&J will, I expect, prove challenging.

 

[KneesUp]

Would a triple mech not work better?

 

[TheCyclingRooster]

Hi again A B. I have actually stuck with Stronglight rings because of the wide range that is available in the BCD's of 74mm & 110mm - they are what Thorn Cranks/Spiders use.
Your suggerstions whilst otherwise OK for most don't offer me a low enough gear with the 44/28 + 12-28 but the high gear is otherwise OK and whilst the 39/26 does get quite close with a low gear it also produces a rather low high gear.
The Campagnolo rear cassettes in 10spd are either difficult to get as pre-owned or an arm & a leg as new or bespoke with some individual sprokets just a financial joke.

I have got my Steve Goff set-ip on a 46:36:24 with a 10spd as 12:13:14:15:16:17:19:21:23:25: but not yet taken it out for a spin/test ride.

I have located an extremely clean Campagnolo Double front derailleur that I am using as a triple - it seems OK indoors whilst running the gears but outside is often a different matter.

I had several very trying weeks with my Benotto (Avatar) and ended up putting it on an 8spd 13:14:15:17:19;21:23:25: Campagnolo with a 50:40:30 triple but the lowest gear could do with going lower

 

[TheCyclingRooster]

Would a triple mech not work better?

Hi KneesUp. Yes but the issue that I have been experiencing is gettin a triple mech without having to by a brand-new one - also triples in the pre-owned are rather scarse on the ground.
Doubles that will function as triples are few and rather far between and NOS if and when they surface are a Kings ransom.

 

[KneesUp]

What diameter is the frame? I have a triple that it too large to fit my back at home.

 

[Ajax Bay]

don't offer me a low enough gear with the 44/28 + 12-28 but the high gear is otherwise OK and whilst the 39/26 does get quite close with a low gear it also produces a rather low high gear.

Your OP question/suggestion was 42-24 with a 12-25. So a high of 42/12 = 95" (assuming 622 wheel) and low of 26". The two suggestions (a. 11-25 with a 39-26 or b. 12-28 with a 44-28) I offered give you 96" and 27"; and 99" and 27". Since these ratios/gear lengths are almost the same (as your OP) I don't recognise your assessment. I'm now unclear what top and low ratios/gear lengths you desire. Best of luck with the spreadsheet!

 

[TheCyclingRooster]

What diameter is the frame? I have a triple that it too large to fit my back at home.

Hi again KneesUp. My frame is 28.6mm.

 

[TheCyclingRooster]

Your OP question/suggestion was 42-24 with a 12-25. So a high of 42/12 = 95" (assuming 622 wheel) and low of 26". The two suggestions (a. 11-25 with a 39-26 or b. 12-28 with a 44-28) I offered give you 96" and 27"; and 99" and 27". Since these ratios/gear lengths are almost the same (as your OP) I don't recognise your assessment. I'm now unclear what top and low ratios/gear lengths you desire. Best of luck with the spreadsheet!

Hi again A B. I am not sure which calculation site you are using but the one that I use is :-- http://jbarrm.com/cycal/cycal.html

I am physically measuring the diameter of my wheels which are 700c x 23 and using the 26.5"/673mm diameter on the tables.

I am getting an 86.12 high and a 27.39 for the low on the 39/26.

I am getting a 97.17 high an a 29.68 for the low on the 44/28.

If I use another site for the calculation for the diameter it actually comes out at 667.999 but the end result is minuscule in the greater scheme of things.

 

[Sharky]

I still think in terms of 27" wheels when i calculate gear inches. So 27*50/15 =90"

Only important to compare releative set ups, so a slight discrepancy doesnt really matter.