Standard double to Compact or semi compact

[adyc]

Hi, my current bike is fitted with a "double" chainset (53/39). If I wanted to change to a compact or semi, is it a straight swap or would I need to change any other parts, eg chain etc?
Also is it worth the bother? My usual riding is 90% on flat terrain with the occasional venture into hilly lands but not very often.
Thanks

 

[mrbikerboy73]

Might not be worth the expense if you ride mainly on flat stuff. A new cassette with different gearing would be a cheaper and easier option.

 

[Doyleyburger]

I wouldn't have anything other than a compact on my bikes, but I live in hilly country. I had a standard 53/39 on a winter bike last year and really noticed the speed difference on the flats but found it difficult to get on with when climbing.
Stick with the standard if I were you if you mainly stick on flat roads

 

[Nigelnaturist]

Stick a triple on, then you have your normal double and a lower range if needed, plus you can keep a close grouped cassette, I ride a 12-23 rear (12-13-14-15-16-17-18-19-21-23) and a 50-38-28, but I could change any of the ring, i.e. the 28 to 26 (not particularly nice combo due to having to go back quite a few gears, but gives a low 30" gear) or swap the 50 to a 52 (though I would need to move the FD up) or a 38-39-40 middle ring, or change the rear to a 12-27 (12-13-14-15-16-17-19-21-24-27) I think you can see why I changed to the 12-23, however the 50-38-26 12-27 worked pretty well apart from missing the 18th giving a range from I think it was 25" or so to 110",

However as you were asking about doubles, if changing to a compact (apart from the new 4 arm cranks) its the BCD (bolt circle diameter) of the chain rings that determine if its a normal or a compact a 39/53 is normally a 130mm BCD on a shimano, the compact is usually 110mm so the cranks have the holes in a different place, so going from a normal double or triple to a compact double or triple you most likely need new crank arms and chain rings the smallest inner ring on a 130mm BCD is 38th you can now see why I opted for a compact triple, I know the
FD can cope with a 24th large to small and does up to 12th inner to middle, middle to outer.

People tell me its not a proper bike, now I admit i am not fast average 15-16mph with an average 37-40ft/mile climb rate and round here I am never wanting for another gear (well apart from one hill where I nearly wished I had left the 26th inner on)

 

[Nigelnaturist]

I wouldn't have anything other than a compact on my bikes, but I live in hilly country. I had a standard 53/39 on a winter bike last year and really noticed the speed difference on the flats but found it difficult to get on with when climbing.
Stick with the standard if I were you if you mainly stick on flat roads

I don't see why its any quicker on the flat unless spining out on your 50x12 or 11 even on my 38x12 to spin out on the flat on that I have to be doing more than 24-25 mph, though when i had it set up with a 52x12 it was quicker downhill, but like I said I am not very fast.

 

[Sharky]

An interesting topic. A few weeks ago, there was an article in Cycling, that 50 x 34 is now being super ceded with a 52 x 36 combination on some new bikes. I find it hard to believe that such a small change would make much difference. Probably a marketing ploy to appeal to new cyclists who are told that it is a "faster" option.

However, on my training/winter bike i got a it fed up with my 50/34 combination. I was finding the ideal gear was either on a little/little combination or a big/big combination. I was for ever changing up from the 34 to the 50 and at the same time changing down at the rear etc. All made worse when riding in the dark and can't see which cog you are in, so can do a simultaneous front / rear change, only to find your are in almost the same gear and then you lose a it of momentum trying to find the gear you really wanted.

So in a mad phase, I swapped the 34 for a 40 and removed the front changer and cut the front cable. This now gives me 7 out of 9 very usable gears all on the 40 ring. I have kept the 50 ring on, to stop the chain derailing, but now never use it. This new set up is like riding a single speed, but with an option to fing a higher/ lower gear when you need it. No more messing about with double gear shifts. Just a single click takes you to the next gear and no more trimming on the front gear at the cross over point. Not being able to go onto the big ring, makes you spin more and improves cadence ability and stops me from over gearing. On the fast sections, I can still get up to 25 mph still peddling and any faster, I am probably freewheeling down hill. On the hills I have lower gears available than my single speed bike, so again happy.

I will probably refit the front at some point, but at the moment finding the restriction to just a 40 front ring quite beneficial to my training workouts.

Keith

 

[Nigelnaturist]

@Sharky This is what I find with my middle 38, on which I reckon 85-90% of my riding is done even a couple of the short 1/10 we have, the change at the front is good between the rings and choice is important, my average gear is around 61-61" or a 38x17 (you see why that 18th is so important to me) and like you I would either be either side of the cassette, a 40th ( I have run one and I quite liked it on the set up a 12x27 with a 30-40-52) but on the 12-23 it would leave the centre ring gearing just a tad to high for me.

 

[cyberknight]

Just to be different i use a 50/36 which fits me just fine as i always felt the jump form 50 to 34 was to much .

 

[T.M.H.N.E.T]

An interesting topic. A few weeks ago, there was an article in Cycling, that 50 x 34 is now being super ceded with a 52 x 36 combination on some new bikes. I find it hard to believe that such a small change would make much difference. Probably a marketing ploy to appeal to new cyclists who are told that it is a "faster" option.

Try one.

 

[Citius]

Newsflash: simply adjusting the gearing won't make you instantly faster.

 

[bpsmith]

Newsflash: some people love stating the obvious...

 

[Nigelnaturist]

Newsflash: simply adjusting the gearing won't make you instantly faster.

I don't know, I certainly ride better on my 12-23 than the 12-27 and I think on the whole a bit quicker, but a lot of the rides I have done since the change have been pretty small around the 2.5-3.5 miles, I think as @cyberknight points out that 16th gap is a big one, as I mentioned earlier I did have the bike set up with a 26th inner which worked well on the 12-27 cassette but it was awful on the 12-23, the biggest thing I have found since the change, I don't go less than the 38x23 which is 44" (or a 34x21) unless it is a really demanding hill, which there are not to many around here, but whilst I don't use the inner ring much its not there as a last resort its used to have better cadence up those tougher hills, my lowest gear is the same as a 34x28 so I don't view it as a granny gear as such.

 

[Citius]

I don't know, I certainly ride better on my 12-23 than the 12-27 and I think on the whole a bit quicker,

Your ability to turn a certain gear inch at a certain cadence is dictated by your fitness. So if you can turn a 23 comfortably up a hill then it won't be a suprise that it is faster than turning a 27.

 

[bpsmith]

Your ability to turn a certain gear inch at a certain cadence is dictated by your fitness. So if you can turn a 23 comfortably up a hill then it won't be a suprise that it is faster than turning a 27.

I think the point was that having less jumps in gear changes is faster overall than having bigger gaps. Hence an 11-23 is faster than an 11-27.

 

[Nigelnaturist]

Your ability to turn a certain gear inch at a certain cadence is dictated by your fitness. So if you can turn a 23 comfortably up a hill then it won't be a suprise that it is faster than turning a 27.

Depends if you can spin the 27 quick enough for it to be quicker, the point I am trying to make is that compacts leave you wanting in gear ratios between having a low enough gear to get up the most difficult hill you have to do and a high enough gear to maintain a good speed, my average non zero cad is about 86rpm and my average gear at that is 61" (said I wasn't fast) but having a close grouped cassette coupled with three front rings is far better for many than a compact 34-50, I know as @cyberknight said I would be toward either end of the cassette, as it is these days I am tending toward the higher gears on the cassette on 38th front, simple because I changed from the 12-27 to 12-23 and whilst on the 12-27 I would climb mainly on the 38x24, I have had to up it a little on the 12-23 which as you say has made me fitter, not by fitting ever bigger cassettes but by fit a smaller one.

The other advantage is you will always have the right gear, sometimes you find one gear is to high one is too low, especially when its windy.