Hi y'all. I'm looking at switching out my SRAM Rival standard crankset to the new 2010 SRAM Force 172.5mm compact crankset.

Two questions:
1. I'm planning on riding mountains more often and I consider myself a decent climber. What kind of improvements would I see when it comes to climbing? I'm sure it would be easier but how much? I can't help to think that easier also means slower... Any thoughts?

2. Will I be able to use my existing SRAM GXP bottom bracket from my Rival to the Force crankset? Are there any differences? I wasn't able to determine that there were.

Thanks!

1. You should match your gearing to your ability and pedaling style, and perhaps carry a bailout gear or two. What gearing that entails is a mystery to us. Do you currently ride the same mountains you plan on riding more? If so, has your gearing been sufficient or could you use an extra gear or two to help keep your cadence up? The only way lower gears won't have you going slower is if you up your cadence. If a too low cadence is tiring you out prematurely, lower gearing might even be faster assuming you can more efficiently spin at a higher cadence. If you are walking up hills because you are over-geared, lower gearing will, in most cases, be faster.

2. AFAIK, yes. The only issue you may have installing a compact is getting the front derailler low enough for the 50T ring if you have a braze-on mount. Most will allow it but some need the slot lengthened or won't work at all.

How much easier? Simple math. 39/34 = 1.15 or 15% easier. A typical 1-cog change is in the 8-11% range. If you need more help, then a cassette with the next larger cog size is needed.

How much slower - same answer. 15% in the same cog at the same cadence, but the easier part may allow cadence to increase.

FWIW, I'm 57 years old and can handle most Colorado mountain climbs with a 34/25. There are a few where a 34/27 would be handy. I usually shift 2-cogs smaller when I get out of the saddle. If my 34/25 isn't comfortable when seated, I'd drop to the 21T and stand.

How much easier? Try using an online gear calculator to find gear inches of your existing climbing gear and gear inches for the new climbing gear. The differences can be expressed in % which may help you get a feel for how much easier the gearing will feel.
In reality you will be doing the same amount of work with either gear set. But a lower gear will work your heart and lungs more, the higher gear will work your leg muscles more. There's always a trade-off.
A cadence meter and heart rate meter can help you find your ideal climbing gear.

Yeah, I do like the idea of having a bailout gear (or two). I'll be riding the same mountains and actually going beyond my usual rides. So endurance will be a factor. I try to maintain a cadence between 70-85 rpm. I'm currently riding with a 53/38 and an 11/25 cassette. It seems that my other partners slowly start to outpace me but then again they regularly ride the mountains whereas I have been doing streets and hills. So it may be more of a fitness factor but then again, they're all riding compacts...

Go compact. I just made the switch myself (all Shimano in my case).

Same age, went to compact 50-34 5 years ago and never looked back. I started with 12-25 (9) and now ride 11-23. Plenty of low gears for steep hills. Flats and downhill, large ring.......hills ...small ring. Simple, effective and great at the end of a long day.
Hockey

Does your current gearing allow you to maintain that cadence? If so, changing to a compact won't do anything to help you. If your current gearing has you pedaling slower than you'd prefer, input your speed and revised gearing numbers into a gear calculator and see how things will look. You may need a crankset and cassette change to get your desired cadence.

Personally I don't think hills ever get easier, because at the same time it "seems easier" you will get a little faster so it still hurts the same
But compact did help my old legs in taking some time off my climbing, but like I said it still hurts I just get their a little faster.

I can maintain it varies within that range. I would like to remain on the top half of that range for longer so I'm thinking compact will help me there.

Seems like everyone here is pro-compact!

Check out the SRAM Apex. Compact crank with a very wide cassette. Gives you gearing like a triple. Don't know if it is really what you want, but your high gear is 50/11 and your low gear is 34/32. Compared to a 12-27 cassette on a 30/42/50 triple, the Apex is 3% lower and 9% higher.

Anyway it's another option for you. More options = better most of the time.

A higher cadence should help. That's a really low cadence on a flat ride, not too bad for climbing but higher would be better, in my opinion.

As noted, it's simple arithmetic. As DaveSSS calculated, 39/34 = 1.15 so switching to the compact will make the pedals 15% easier to push. You said you have a 53/38. Is that a typo or miscount? 38T chainrings are available but they aren't standard on any OEM road crank I know of but if it's correct the compact will lower you low gear by only 11%.

You also said you have a 12x25 cassette. Going to a 12x27 will lower the low gear by another 8% and the only cogs that differ are the largest two. A 12x25 is 12......23,25 and a 12x27 is 12......24,27. All the other cogs are identical.

I'm far from pro-compact actually but I do think that people should gear their bikes for their intended usage and pedaling style. Personally, my feeling is that if a standard double isn't working for you then you'd be better off with a triple. Compact doubles are, in my opinion, a poor compromise all around. Whatever can be done with a compact can be done better with a triple. High gear, low gear, gear spread, and gear spacing are all better with a triple than a compact. The only reason I'll ever recommend a compact to someone is if their current bike has a standard double and their shifters are not triple compatible (which is where you are).

Yeah, I switched out my 39T with an FSA 38T from Aebike.com I also made a typo above. My cassette is an 11/28 instead of 11/25. Never said 12 though.

Joejack: I'm not a big fan of the triple unless it's a mountain bike. Here in LA, I'd get my butt kicked for riding a triple. LOL

Grow some

except for when you have a compact double at least as wide - if not wider - than a triple. You also minimize duplicate or very similar gear ratios with the double. I have 20 gear combos now, and my friend with a triple has 24 - but our high gear is the same. His low may be lower but who cares. I am a flatlander. We probably have identical "useful" gears, but my crank weighs less and my chain is not as long.

It will be interesting to see how the new Apex group holds up against a triple. At least it will be to me, for some reason I like to follow some marketing campaigns to see what passes and whY fails the marketplace test.

Compacts and triples both have their place. Reducing duplicate gears is a bad thing, not a good one. A lot of people find that out when they are constantly shifting back and forth between their compact chainrings because their most-used ratios are between the big and small chainring limits. You also have to shift one more cog after every chainring shift - there is no free lunch.

A compact would need a wide spaced 11-28 to match the low gearing of a triple with a much closer spaced 12-25. With that 11-28, you lose the 16T cog and get large jumps, starting right after the 19T cog. A triple can also provide another ratio lower just by substituting a 28T chainring for the common 30T and another with a 12-27 cassette.

I've used both for climbing the Colorado mountains. I did my best time on the Mt. Evans hillclimb route using a 53/39/28 triple with a 12-25. A time of 2:35 will usually get you into the top 10 in my 50-59 age group.

I now use a compact 50/34 with an 11-25 (11 speed). I've lost my two lowest gear ratios with this setup, but I get by with it. I still might switch to a 12-27 or 12-29 for Mt. Evans, since top gearing makes no difference.

Thanks, Dave, for replying with pretty much the same reply I would have if I had beat you to it.

Another nice setup is the compact double up front with a MTB derailleur and cassette in back. You get the increased range of the road triple but you have more overlap so you don't shift the front as much. Bigger gear jumps but honestly gear jumps are small enough these days. SRAM is doing this for the Apex group they announced (and SRAM and Shimano are starting to move MTB stuff to 10 speed).