I am a newer rider that need to work on hills and take some weight off. Is a 30/27 low gear much better than a 34/27 gear? I amtrying to decide if I should get a triple or compact cranks on my new Talon SL…
I have a road bike with a triple and cassette’s with large cogs of 23 or 25. I have a tri bike with a compact (50-34) with large cogs of 21 to 25.
If you want to calculate speeds at different rpms with different gears (i.e. 30-27 vs. 34-27) then there are a couple calculators on the web - I believe analyticcycling.com and kruetzotter (? sp) has some and you can print spread sheets…
The compact set-up shifts a bit nicer and is less likely to drop a chain in my experience. Although at typical triathlete flat land speeds (18-20 mph) you often are running a poor chain line with either the 50-20ish or 34-13/14. Also less chance someone will call you a wimp with a triple…
Triple - only the biggest 4 or 5 cogs usable for the 30 and the smallest with the 52. I’ll occasionally drop a chain if I don’t shift carefully from 42 to 30. A 30-27 is a pretty easy gear but a lot depends on what hills you are climbing and what cadence you like to climb…
If I was going to do some of the extended climbs around me (3000-5000 foot climbs often with some 10-15% sections) or some really steep stuff - 12% plus - I’d want my triple with a 25 or 27…but I’ve yet to do a triathlon where a 34-23 or 34-25 wouldn’t do the trick but so much depends on your strength/speed , the course/hills, and how you like to ride (cadence).
Dave
If you plan on doing a lot of riding, I would recommend the compacts with 34/25. You’ll be surprised how quickly your strength will increase with a lot of riding. You might not be able to do the steepest hills right away, but 30/27 seems a little over-kill. My first bike was a triple with 30/25 gearing, and after a few weeks of riding I never used the 30 again. It is a road bike and not a mountain bike 
Thanks, I live in Oregon near some big grade hills… Also need to work on leg strength. Is there much of a difference between a 34/25 and a 30/25
Thanks…
I ride in hilly areas and have used both. Would recommend the compact 50/34. When I had my triple way back when I barely ever used the 30 and tall rear gears. Plus the compacts are a little neater and lighter.
Good question. I’d suggest compact cranks. My wife is in your situation and currently has a triple that usually does not shift crisply. Here’s what I found:
30x27=30.67 gear inches (how far you go in one revolution, small # is easy for hills, bigger # tougher for speed)
34x27=34.76 gear inches
Fairly close and both in the serious granny gear category. As a comparsion, a traditional 39x23=46 gi, while a 39x27=39.87. On the fast end:
50x11=125 gi
53x11=132 gi
Good luck
go here to work out your options, note on 3rd screen you can see cadence v gear comb v speed http://www.panix.com/~jbarrm/cycal/cycal.30f.html
I had a 34/50 - 12/25 lasted 7 rides then changed to 36/52. I would prefer a triple 30/42/52 - 23/12. Chain line would be better, less cross over on the inner ring (36) The 34 was basically useless for most applications other than going up hill. I dont climb well but ride flats and rollers much better. Caveat is I road race as well.
gear inches is not how far you go in one revolution. you have to multiply by pi to get that.
.0767*(frontgear/backgear)crank rpm=speed in mph
at 60 rpm a 30-27 is 5 mph, a 34-27 is 5.8 mph.
A while back I stole some chainrings off an old mountain bike crankset and put them on my road bike for a 46-36 for a while with a 12-21 cassette. I learned a couple of interesting things from this. Number one, you really don’t need a huge top end gear unless you ride with a group or you like to see how fast you can go on downhills. If neither of those is an issue then get a compact with 34-46 or 44 and ride that for a while until you are stronger. You may scoff at a high end of 44-12, but in truth I spent most of hilly race last week in the 44 using the whole range from about the 13 to the 25 (It was the smaller ring in my case).
Number two, a 10-tooth front jump is much more smooth (quicker) than larger 14-16 tooth jumps. In Virginia I was continually doing the double shift because of the rolling terrain.
The main problem I see with compacts stems from the really big jump from the 34 to the 50. It just won’t be as snappy. If you have a lot of rolling hills you won’t like that; if most of your hills are really long then it might not be a major issue.
I haven’t used a triple for a long time, nor on anything but a mountain bike. You may like it since you will likely spend the large percentage of your time in the 42, plus you have a low-low and a higher high.
Chad