changing compact chainring sizing

[rockyraccoon]

I recently replaced the double for a compact for the lower gears. I've been thinking about replacing my current 8 speed 13-36 cassette for an 11-28 one. The reason why is because I have a compact now (50/34) and with an 13-26 cassette I don't have as much gear on top end as I used to with the double. Also it'd be nice the extra gear (28T) but my concern is the gaps between them.


Here's a comparison between 11-28 and 13-26 with a compact 50/34

 

[bobones]

I don't have a problem with the gaps at all, but I'm no racer and I can't speak for everyone. The 11-28 seems to have a lot of advantages in other areas: better top and bottom gears, use of the 14 cog in small ring without cross-chaining, predictable behaviour when moving between front rings (i.e. next gear is always 2 shifts on cassette). I'm trying to get my cadence up to an average of over 90rpm so I don't mind spinning out on the small ring (e.g. 34/14 at 105rpm = 20mph). I'm using a nice and shiny PG-830 SRAM cassette that I got in a dual pack with a chain for £22 so it's not going to cost you a lot to find out if 11-28 is for you.

 

[oldcarltonfan]

Have you considered simply changing the outer chainring on a compact to reduce that horrible jump between chainrings and fitting a medium-sized cassette?

I'm riding a modified compact 34 inner 46 outer at the moment with a 9 speed ultegra 12-27 cassette. It seems to offer a fantastic compromise; I can climb almost anything and I'm only an average climber, it offers closer ratios between gears than an 11-28 a larger overlap of useful ratios between the chainrings than the 34-50 'normal' and I can still top out at nearly 30 (mph) at a cadence just below 100 (getting old, thats the limit for me). I did all of the original calculations for it on paper, but I've just run the numbers on that fantastic computer program and it seems to confirm the maths, you lose nothing but a bit of top speed.

I only had to change the outer chainring, it suits a normal short cage derailleur, normal chain length, standard front derailleur and changes gears very 'crisply' on normal Tiagra level kit.

Were I racing I would miss the top speed, but these days if I'm lucky enough to be approaching 30mph, I'm either going downhill or have a following wind therefore I just relax and enjoy a rest until the next climb!

I thoroughly recommend the set up. Should you try it and hate it then all its cost you is a cassette and a chainring. I might even buy the cassette and the 46T chainring from you (at half price obviously, used parts and all!) and keep them as spares.

I've played with all sorts of other combinations and I reckon the only way I can beat it is with a 30,39,50 triple coupled to a 12-27 cassette. Guess what I'm fitting to my new tourer?

Given that there are many people on this site with more brains and experience than me, I await the comments with interest.

Old Carlton Fan

 

[cyberknight]

Very interesting

I am about to get a new bike with sram apex and it comes specced with a 11-32 cassette, and i think a 50-34 chainring.

Rather than change the cassette i am thinking of changing the 34 to a 36 to overcome the drop at the front and raise the rear gear inches slightly.

On a 50-34 i always find i drop to the front chainring at the last moment the spin up the rest of the hill.