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Change cassette/rear derailleur or go sub-compact?

by darrenleroy
Wed, Jul 04, 2018 17:17
37

Has anyone ever decided to go sub compact, say 48/30, rather than change the rear cassette? 

I have moved to hill country. My rear cassette is 12-25 and I struggle on some of the steeper ascents. I have a compact on the front.

I have a Record rear derailleur (short) that won't cope with a larger ranging cassette. Instead of changing the rear derailleur and cassette I wondered if going to a sub compact would give me the equivalent of being in the 32 teeth sprocket?

I am crap at maths and struggled to grasp the tables that work it out for you.

 

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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37 comments

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madcarew replied to darrenleroy | 6 years ago
2 likes

darrenleroy wrote:

herrkaa wrote:

I have a Chorus with a short cage and I've been running a 12-29 Miche cassette for years without any issues. Are you quite sure that your Record won't cope?

 

I'm not 100 per cent sure but my LBS has said it won't. It's quite a jump from 25 to 29. My rear derailleur is already pretty stretched out in the 25 cog.

I'm thinking I will have to replace the rear derailleur and cassette. Bummer. I might just go the whole hog and change up for an 11 speed Potenza. I hate wasting equipment that works perfectly but I suppose I could try and flog it on eBay. 

It would be a rare derailleur that can't cope with an 18 tooth difference in the back. If your derailleur is already stretched out on the 25, it may be that your chain is too short.

Going from Standard to sub compact will give the equivalent of a 27 on the back (1 more gear) and going to a full compact will give the equivalent of  a 29 on the back ( 2 more gears). TBH, going full compact at 34/50 would be a good result, but for an awful lot cheaper, a 12 - 29 cassette would achieve a better result (you'd lose 1 top gear, but it doesn't sound like you're bothered by that having suggested a 48 would be ok). Get another opinion from a different LBS before taking the plunge on a new chainset. You can probably find the capacity of a record derailleur on line.

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alexb replied to darrenleroy | 6 years ago
1 like

darrenleroy wrote:

herrkaa wrote:

I have a Chorus with a short cage and I've been running a 12-29 Miche cassette for years without any issues. Are you quite sure that your Record won't cope?

 

I'm not 100 per cent sure but my LBS has said it won't. It's quite a jump from 25 to 29. My rear derailleur is already pretty stretched out in the 25 cog.

I'm thinking I will have to replace the rear derailleur and cassette. Bummer. I might just go the whole hog and change up for an 11 speed Potenza. I hate wasting equipment that works perfectly but I suppose I could try and flog it on eBay. 

If you are using Campag 10 speed (which I guess you are), and a 53/39 then the 11-25 gives you the following gear range:

127.1"-41.2"

Compared to:

115.1" to 31.7" using the 48/30

Using a 13-29t 10 speed cassette on a standard 53/39 gives you 

107.5" - 35.5

Using a 50/34 combination with the 13-29t cassette will give you

101.5" - 30.9" - so lower than the sub-compact with a slight loss at the top end

So I'd suggest first trying a new chain and cassette (13-29), then maybe fitting smaller chainrings.

There's quite a lot of gear duplification, but this seems normal for compact doubles.

Unless you are completely spinning out the 53 on the flat, I'd suggest trying the larger casette first (a Veloce cassette and KMC chain are going to cost you less than £50).

The smart way to use a double is with an ultrawide cassette and a very narrow double - it's possible to find gear combinations that allow the  front chainring to fill the gap between ratios in the rear cassette with no duplications at all. 

 

Avatar
darrenleroy replied to alexb | 6 years ago
0 likes

alexb wrote:

darrenleroy wrote:

herrkaa wrote:

I have a Chorus with a short cage and I've been running a 12-29 Miche cassette for years without any issues. Are you quite sure that your Record won't cope?

 

I'm not 100 per cent sure but my LBS has said it won't. It's quite a jump from 25 to 29. My rear derailleur is already pretty stretched out in the 25 cog.

I'm thinking I will have to replace the rear derailleur and cassette. Bummer. I might just go the whole hog and change up for an 11 speed Potenza. I hate wasting equipment that works perfectly but I suppose I could try and flog it on eBay. 

If you are using Campag 10 speed (which I guess you are), and a 53/39 then the 11-25 gives you the following gear range:

127.1"-41.2"

Compared to:

115.1" to 31.7" using the 48/30

Using a 13-29t 10 speed cassette on a standard 53/39 gives you 

107.5" - 35.5

Using a 50/34 combination with the 13-29t cassette will give you

101.5" - 30.9" - so lower than the sub-compact with a slight loss at the top end

So I'd suggest first trying a new chain and cassette (13-29), then maybe fitting smaller chainrings.

There's quite a lot of gear duplification, but this seems normal for compact doubles.

Unless you are completely spinning out the 53 on the flat, I'd suggest trying the larger casette first (a Veloce cassette and KMC chain are going to cost you less than £50).

The smart way to use a double is with an ultrawide cassette and a very narrow double - it's possible to find gear combinations that allow the  front chainring to fill the gap between ratios in the rear cassette with no duplications at all. 

 

I'd happily just change my rear cassette for something ultrawide but my 10 speed Record rear derailleur won't allow much past a 12-25. According to my LBS anyway. 

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Dnnnnnn replied to herrkaa | 6 years ago
0 likes

herrkaa wrote:

I have a Chorus with a short cage and I've been running a 12-29 Miche cassette for years without any issues. Are you quite sure that your Record won't cope?

Bit late to the party but this is very close to my set-up (short cage Chorus on a 28t (available singly from acycles)) and no problems.

Just back from the Pyrenees myself and wish I'd invested in a 30t. I'm sure the mech would have coped fine (whereas - on a 28t - I only just about did).

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darrenleroy replied to Dnnnnnn | 6 years ago
0 likes

Duncann wrote:

herrkaa wrote:

I have a Chorus with a short cage and I've been running a 12-29 Miche cassette for years without any issues. Are you quite sure that your Record won't cope?

Bit late to the party but this is very close to my set-up (short cage Chorus on a 28t (available singly from acycles)) and no problems.

Just back from the Pyrenees myself and wish I'd invested in a 30t. I'm sure the mech would have coped fine (whereas - on a 28t - I only just about did).

 

For me it's a question of being able to spin freely. The lower the gear the easier this is. Having a 30 or 32 on the back (or even lower) allows one to spin which puts less pressure on knee joints and muscles in general. I found the 10 per cent and above sections, especially further into the ride, had me struggling to spin freely. But I also accept with time and training this will become less of an issue. But, hey, if Chris Froome uses a compact chainring and 32 on the back sometimes that would suggest riding with a 32 isn't a silly idea. It would even suggest, given Froome is an elite athlete, an even lower gear on the back wouldn't be a bad idea.

Last year in the Alps I met a Belgian chap who was supremely fit. He smashed it up Alpe d'Huez and swore by his triple, claiming it was the most efficient spread of gears for how he cycled up big hills. It just isn't considered 'cool' I guess, otherwise we'd all be doing it.

Avatar
Canyon48 | 6 years ago
2 likes

Short answer; no, a subcompact would not give you an equivalent gearing as a larger cassette.

A subcompact 48/30 with an 11-25 would give you a much smaller range than a 50/34 with an 11-32.

In addition, 50/34 with 11-32 gives you a greater gear range, a lower low gear and a higher high gear.

 

Avatar
rdmp2 | 6 years ago
0 likes

I have a sub compact but on a heavy touring bike so not really a comparison. Would slightly reduce your gearing but at greater expense than changing cassette. If you can’t do the maths this website lets you compare 2 setups side by side

 

http://ritzelrechner.de/

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