Compact chainset vs Standard...

fingerfun · September 2009

I know this topic has been up before a while back but after doing the maths, I'll have my say:
I have been running a 53/39 up front and a 12/25 out back for ages. I have recently been thinking of changing my rear cassette to be a 12/27 to help on some of the more extreme climbs that I put myself through. My only issue with this was it would be reducing the close ratio of my rear cassette (something that already gripes me a bit with 12/25).

This got me thinking and so I did some maths...

If I used a compact 50/34 with a 11/23 cassette the resulting 50/11 combo for downhill/flats would actually give me a better gear than my current 53/12 and the 34/23 combo would be better on the hills, and let me spin more, than my current 39/25 set-up. Plus the fact it also makes it a closer ratio cassette and also a little bit lighter (albeit a very small amount!)

I worked out the above using gear inches/chain length and it worked out to be so much more logical to run a compact chainset. Why haven’t I heard of this set-up before or am I missing something!?

Cheers
Marcus

maddog 2 · September 2009

http://www.sheldonbrown.com/gears/

will tell you everything

bill57 · September 2009

I thought I'd try a compact on a winter bike, and absolutely hated it. Lasted about two days and I went back to 52/39. On paper, the theory seems sound, but one issue which is seldom, if ever mentioned, is chainline.
If you spend a lot of time in, say, 39x15 or 39x16, changing to a 34 ring will drop you down into the poor chainline zone where you would normally change up to the big ring. The result, in my experience, was continual changing between large and small rings at the front, as well as all the faffing about with the rear cogs as well. So in future, if I want a smaller gear I'll just go for a bigger sprocket on the back - or maybe just cycle harder and use the gears I've got.
It's horses for courses though, and a compact may suit many people - just be aware of the pitfalls and don't think it's the Holy Grail of cycling.

Squillinossett · September 2009

Well I have used a compact with my 1.5 since I got it. Quite like it, but find myself lacking for some grunt when I have some speed going, and the jump can be quite annoying if I hit a hill in the big chainring and suddenly its longer/harder than I thought and have to change down...end up spinning 10 to the dozen!

So just ordered one of the FSA carbon triples to try out, dont think im at the stage yet for a full double, considering I spend alot of time cycling around Huddersfield/Holmfirth!

redddraggon · September 2009

I quite like my compact, 50-11 is plenty for 40+mph, and 34-25 gets me up most things if I pace myself right.

On the flat I can sit in the middle of a 11-25 cassette on the 50t chainring, so the chainline is pretty good, I also I find I need to change less as I can stop in the 50t up less steep climbs, whereas with a traditional double I'd probably have changed to the small ring.

chriskempton · September 2009

I find 50-36 much more agreeable than 50-34, less of the "stuck between 2 chainrings", and less of a lurch when you do change.

maddog 2 · September 2009

I run 34/48 (or even 33/48, for the Marmotte)

I prefer the 48 to the 50 ring as I can stay in the big ring for most things and the chainline is better - less big-big situations. I don't miss the top end at all.

Then I only drop down to the 34 for really steep stuff, which we get quite a bit of round here - Lakes stuff and Trough of Bowland rides.

bice · September 2009

bill57 wrote:

I thought I'd try a compact on a winter bike, and absolutely hated it. Lasted about two days and I went back to 52/39. On paper, the theory seems sound, but one issue which is seldom, if ever mentioned, is chainline.
If you spend a lot of time in, say, 39x15 or 39x16, changing to a 34 ring will drop you down into the poor chainline zone where you would normally change up to the big ring. The result, in my experience, was continual changing between large and small rings at the front, as well as all the faffing about with the rear cogs as well. So in future, if I want a smaller gear I'll just go for a bigger sprocket on the back - or maybe just cycle harder and use the gears I've got.
It's horses for courses though, and a compact may suit many people - just be aware of the pitfalls and don't think it's the Holy Grail of cycling.

Ditto.

salsarider79 · September 2009

I'm trying a compact with a 11/25 cassette. Gets me up very steep climbs (25%+) but can still sit at 30mph on the flat. I don't see the point of trying 11/23 with a compact, the jumps in gears compared to 11/25 aren't small enough to worry about and are only at the top of the cassette. Try your 11/25 with a compact first... You should be able to get some cheap rings from your lbs...
Chainline wise, I don't ride small/small, or big/big, which you shouldn't anyway. I've not yet had a problem. If you get a problem, then it should be there regardless of chain ring sizes.

markos1963 · September 2009

I use a compact because my bike came with it. To be honest I would prefer a Double but cost puts me off. I find that now I'm getting stronger I can sit on the 50 ring all day and only rarely drop onto the 34. I will get a 36 ring fitted this winter for next season and probably a 11-23/25 cassette to go with it. i now ride a single speed all though the week for training and it puts it into perspective all the fuss people make about gearing as my avaerage speed is almost identical to my geared bike!

Compact chainset vs Standard...

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