Sheldon's 'Gain Ratio' versus effort (compact/double)

bbolger

Hi, I'm considering upgrading from a compact 50/34 to a standard double 53/39.

This is for two reasons

spinning out on some descents (e.g. turning left at the top of Nag's head...)

but more importantly the teeth on the large ring are looking pretty worn out (no pic handy)

I've got a 12/27 cassette on the back.
I could throw an 11-25 cassette on the back, but stilll have the problem of the worn teeth.

For this I could replace the chainring or just go for it & upgrade to a double.
I wouldn't use the 34 front ring very often, need it in Wicklow 200 though obviously, and Bellewstown, others etc.
Did the Swords CC Ardgillan climb in the 50 ring.

Looking at Sheldon's gearing calculator

and calculating for both 50/34 & 53/39
for 700 X 23 / 23-622 tire with 170 mm cranks
with 10-speed 12-13-14-15-16-17-19-21-24-27 Cassette

it looks like the gain ratio for

34 front, 27 back is 2.5
34 front, 24 back is 2.8


39 front, 27 back is 2.8
39 front, 24 back is 3.2

So (long winded way to get to my question...), is the effort involved in turning 39/27 equivalent to 34/24, as they both have the same gain ratio?

If so, then I know what my easiest gear will feel like if I upgrade.

Thanks.

Lumen

bbolger wrote: »

is the effort involved in turning 39/27 equivalent to 34/24, as they both have the same gain ratio?

Yes, although the ratio isn't exactly the same.

cdaly_

Yep.

bbolger

Lumen wrote: »

Yes, although the ratio isn't exactly the same.

Great - I basically wanted to confirm if they would 'feel' the same once I upgraded.
Guess I'll need to train myself not to use the 34/27 anymore until then...

That Kippure climb to the mast is going to be even tougher next time around

Thanks

nomdeboardie

Yes (almost).

Don't have to use Sheldon's calculator or think in terms of "gain" as such, as your wheel size is constant - just divide teeth numbers for gear ratio, i.e. 39/27 = 1.444 vs. 34/24 = 1.416.

I think you may have meant 34/25 though, which would be 1.360 (so 1.444/1.36 = 1.06, or 6% more torque needed, I think)

greenmat

Doing exactly the same as you for the same reasons, Standard double ready to be installed. Have 12-27 and 11-23 casette's so can play around with them. I was wondering would my climbing suffer by upgrading to the Standard Double but this thread has answered my doubts. Roll on next wednesday, I'll be the one with the shiny cranks.:)

bbolger

nomdeboardie wrote: »

I think you may have meant 34/25 though, which would be 1.360 (so 1.444/1.36 = 1.06, or 6% more torque needed, I think)

24 it is as cassette is 10 speed Shimano 105:
12-13-14-15-16-17-19-21-24-27

bbolger

greenmat wrote: »

Doing exactly the same as you for the same reasons, Standard double ready to be installed. Have 12-27 and 11-23 casette's so can play around with them. I was wondering would my climbing suffer by upgrading to the Standard Double but this thread has answered my doubts. Roll on next wednesday, I'll be the one with the shiny cranks.:)

I'll be upgrading in the next few weeks.
Be interested to see how you find the new setup on Wednesday (Swords CC?) - good luck.

greenmat

bbolger wrote: »

I'll be upgrading in the next few weeks.
Be interested to see how you find the new setup on Wednesday (Swords CC?) - good luck.

It will also be interesting to see if my mechanical skills are any good . Should have done it a few weeks ago, jumping in at the deep end in a way.

bbolger

greenmat wrote: »

It will also be interesting to see if my mechanical skills are any good . Should have done it a few weeks ago, jumping in at the deep end in a way.

As long as you have one of these by your side you'll be fine




Got a quote from Cycleways & Humprhies to do it, about €170 for parts & €30 for labour. Might need new chain too (if current one stretched).

TheBlaaMan

Yeah, good post..........thinking something similar myself. I do think you'll need extra links in the chain however (or perhaps a new one is due if your chainrings are kaput) and will require to move the FD up the seat-tube to cater for the larger (inner esp) chainring.

greenmat

bbolger wrote: »

As long as you have one of these by your side you'll be fine




Got a quote from Cycleways & Humprhies to do it, about €170 for parts & €30 for labour. Might need new chain too (if current one stretched).

Have a new chain, chainset and cassette, should have got a new RD too to complete it. Got the 53/39 Ultegra Chainset brand new on here for €110.

bbolger

Finally took a few pics of the components...
Both front & rear have about 5,500 km, chain has been replaced a couple times.

Front chainring looking pretty worn (at least I assume it is?):






Rear cassette (does it look ok or should I replace too?):




How often do you need to replace jockey wheels?


Thanks in advance for any advice!

smacl

bbolger wrote: »

How often do you need to replace jockey wheels?

Been wondering that myself, having recently taken off and regreased mine.

Mycroft H

bbolger wrote: »

Finally took a few pics of the components...
Both front & rear have about 5,500 km, chain has been replaced a couple times.

Front chainring looking pretty worn (at least I assume it is?):






Rear cassette (does it look ok or should I replace too?):




How often do you need to replace jockey wheels?


Thanks in advance for any advice!

I'd be replacing the front chainring, rear cassette and chain on that. (unless you have replaced the chain very recently)

Jockey wheel looks find. There not under any load so they last ages. I've only replaced one, but that was on a 30 year old derailleur.

letape

I wouldn't assume the chain is worn - you should use one of those tools to measure chain wear (cheap to buy on-line). You say that you hae changed your chain a couple of times in 5,500 kms - that seems very often.

I would also be surprised if your chaintings and cassette wear in 5,500 kms, especially when you have replaced your chain during this time. Mine certainly don't!

bbolger

BX 19 wrote: »

I'd be replacing the front chainring, rear cassette and chain on that. (unless you have replaced the chain very recently)

Jockey wheel looks find. There not under any load so they last ages. I've only replaced one, but that was on a 30 year old derailleur.

Planning on replacing front & chain (as per original post) so will add the cassette to that list too - thanks.

This raises another question - how long do these components typically last?
I know it probably depends on a few factors, road conditions, frequent care & maintenance, regular chain replacement, cross-chaining etc.

I heard Beasty mention in another thread that you should expect to replace a cassette about every 3,000km or so.

TheBlaaMan

That cassette is fine IMHO. I dont think I'd be replacing it....

Strangely, the chainring teeth appear to be worn on the opposite side to what I would expect.....but I'm no bike mechanic.