Gear inch crankring change question
 

Thinking of switching from a compact 50/34 crank to a 52/36. Ran the calculators at Sheldon's site and I am(and I guess always will be) confounded by gear inches and gain ratios.

The set up is front as above and 10 speed 12/27 rear cassette. I am most concerned that I will have the gearing to get up W. PA hills with a 36 front small ring.

So 34 front and 27 rear is a gear inch of 33.1 and gain ratio of 2.5
36 front and 27 rear is a gear inch of 35.0 and gain ratio of 2.6

At 80 rpm the bigger ring calculation is 8.3 mph and the smaller one is 7.9 mph. All this does not seem like much difference. Is there any real practical difference between the options?

I don't think it would be a noticeable difference. The change on top end would be a little more significant, but not a lot. Why the change?

8.3 mph compared to 7.9 mph is a big difference in power requirements when climbing. For example, a 3 mile climb of 7% average grade at 8 mph is a hard effort (for me). 7.6 mph is a lot easier.

You are on the right track when you look at climbing speed. The issue is what happens when you are putting out near max power and the speed is 6 mph or less up the hill. In the bigger gear, the cadence may be too low and your legs will tire to the point where you can no longer turn over the pedals and you have to stop and rest.

I see very little to no advantage to the 52/36 over the 50/34. I could see a 53/39 if you were looking for more top end using an 11/23 cassette. But a 50/34 with an 11/26 or 11/28 cassette will provide a bigger top end and lower gear than the 52/36 with a 12/27.

First compact I got was 50/36. After the Triple with 52/42/30----The steeper hills round here took some getting used to. Changed the 36 to a 34 and to be honest the hills I found hard in 30/26 were no harder with 34/27. Those two teeth difference made a heck of a difference----But then I have a few short sharp slopes on most rides at about 1 mile long and vary between 10 and 12 % with the few kinks at 15%.

So Look at your hills- Look at yourself and think if you can ride comfortably. But if you use the 34/27 often--Have a longer think and possibly change the cassette to give you 11t on the cassette if it is top speed you want.

Why? Tired of getting dropped off the paceline with my current setup. Don't want to scrap my ability to get up the hills however. Looking for the perfect compromise. I guess I have used the compact setup so much I am reluctant to return to a 53/39 for fear the hills will do me in again.

Just a thought--why not keep the 34 and put on a 52? If that is not enough, someone else suggested an 11-28 cassette, which with a 34/52 would give you more top end and lower climbing gears. I have found 52t 110mm rings to work well with 34t inner rings. Being an 'old f@rt', I run an 11-34 cassette. I may not be as fast up hills as the 'young fit' guys, but I do NOT have to walk my bike!

Oilman, you must hang around with a fast crowd.:D A 50 x 12 @ 90 cadence is 29.3 mph. A 50 x 11 @ 90 rpm would get you 32 mph but it may be hard to find a 11/26 or 27 cassette.

You need this. http://www.youtube.com/watch?v=8Nd13ARuvVE

I won't argue with Hermes about speed or dispute his numbers (even if I can't comprehend them), but damn if I can feel that small a difference on the low end.
But I do agree that an 11 tooth cassette cog with the 50 ring will give a faster top end than a 52/12.

36/34 is 1.059 That's about 6% harder.

On your 12-27 cog set, the jump from 24 to 27 (27/24) is 1.125, or 12.5%

So you'll lose just about half of your easiest gear, 34-27 when you go to 36-27.

It would be like having a 25.6 on your current 34 chainring, instead of a 27.

I have a 34/50 with a 13-26 or 13-29 10 speed cog set. It wouldn't slow me down in a pace line, unless they were going over 30 mph. I can get to about 34 mph on downhills with the 50-13, but I'm mostly spinning, not putting out a lot of power at that cadence.

I don't think a 52 will work on a compact crank. It has a 130 bolt pattern while the 50 has a 110.

I would think long and hard about losing the easiest gear you now have by changing the chainrings. I'd do as Hermes suggested and try a 11 cassette with your 50. I have that on one of my compact set ups and can still get some push out of the gearing at 33-35 mph with a fast cadence. If that is not enough to keep up with your group I just don't see how a larger chainring can help. Are you falling off the group on climbs and trying to catch back on descents? Surely the 50/34 with a 12/27 is sufficient for the flats??

My comment has more to do with duration of a climb. If you are near your perceived effort limit for a longer duration climb, a few % in gearing makes a difference. To say it another way, you complete the climb at 6 mph but cannot at 6.5 mph. I sounds like Oilman is getting ridden off wheels on flatter terrain. That happens to me as well. I run out of endurance at the power required to maintain speed and get dropped. Gearing is not going to help that issue.

Just make sure your shift pattern is manageable. Even with "brifters" if you have a bunch of double shifts then you may not get much use out of some of your gears and end up with big steps in bad places.

50 and 52 are available as 130 or 110.

Excellent reply. Something I can relate to and after seeing it in percentages it makes sense.

Riding in South West Pa is a conundrum. Lots of steep climbs that are not long by western US standards. Example today had one hill about 1/4 mile that has a 19% section. It is no wonder many of the early settlers took one look here and kept going to Ohio and Kentucky. Then you may get a long stretch along the valley where you can get in your highest gear and go. So my ride of 32 miles had 5 decent hills but only 2900 elevation gain. The rest being rollers or pretty flat plus decent from the hills.

And heck yes I always want to go faster.

Yes, I've even got a 56T attached to a 110 BCD crankset. And I have a 56T/130 BCD mounted on one of my bikes. And you can get an 11-27 SRAM cassette if you only need a 9-speed. I can't say about 10-speed stuff because I've been avoiding it.

Going to a 34/52? 18 teeth is a bit much for a single shift. OTOH, if the sky is the limit for differences between adjacent chainrings, then why not get a 30/53?

A 6% ratio change (36 vs 34) is noticeable -- it's about the same as the chainring shift in my 45-42 and 49-46 half-step rigs. I don't see the point in replacing the 50 with a 52, but then my top gear is 50/14 (Bianchi) or 47/13 (Capo #1) or 49/14 (Capo #2) or 45/13 (Peugeot).

FWIW, I live in the mountains and all but the Cat 1 guys use a 50/34 with an 11/28 cassette. A 50/11 gear is harder than a 52/12. 50/11 is more gear than I need on the flats in all but the fastest groups. It is also plenty of gear on the descents for me. The 34/28 lets me climb most anything. My coach used to tell me, to go faster, spin a higher cadence don't push harder.

A lot to think about. As to an 11-28 rear, a new rear der. would be required to make this work. By the time you thrown in the cassette cost it would get out of hand. There is a Dura Ace 11-27 10 speed cassette which would work with the current setup.

Thanks for all the input. I do from time to time get run off my wheels by stronger riders. I have ridden and trained about as hard as I think I can. The group I usually ride with has some pretty strong guys and if I were to give an honest evaluation I would be a mid pack rider. My discouragement comes when we get back from a brisk ride and my average is always .5 to 1 mph lower than many. Maybe there is no more gas in my tank and I should just take things the way they are?

Oilman, if you start with them and finish with them, why is your average slower? Maybe all you need is a speedo calibration! Like adding a second magnet to your wheel...

Going strictly by the book, that may be right, but many people have run 28 tooth cassette cogs on derailleurs with a stated 27 tooth maximum with no trouble.

I have two bikes with DA 7800 rear der. working just fine with SRAM 11-28 cassettes.

I'm sorry if I missed it but I don't think you said whether your issue was you were getting dropped on the hills vs unable to hang on the flats or both.

What I usually find is the problem is that I can't put out the power to stay with the stronger riders. It is much less noticable on the flats where I can stay in the draft and equalize things, I tend to be heavier than the best riders - this is not as big a deal on the flats but will kill me on the hills as I have to put out more power to hang. If I do happen to sprint out this power I am more drained and my tank is emptier when I crest the hill so with each hill I am further and further in the hole. I agree with AJ, you current drive train short allow you to hang on some pretty fast rides. If you are trying to make up your time on the down hills what I have found is that just doesn't work for long - you will find that wind resistance will eat up a lot of power needed to reach speeds capable of closing and that will take power as well.

Even though I am heavy for a climber - climbing is what I do. Hermes is spot on. If you are climbing and you can't put out enough watts to stay at you optimal cadence you will put out even less power. Eventually you will blow up, although I must admit I have gone as long as 100 minutes on a long steep climb at max power and less than optimal cadence, but it isn't pretty. But for a short 1/4 mile climb you can get away with I little higher gear, a standing climb for less than 2 or 3 minutes. even at 19%.

So I suggest you stick with your current drive train and think about a few other options.
1) Look at your tires - are they low rolling resistance. This will help you spend less energy on the flats and keep more for the hills.
2) Talk to a cycling trainer, you may find that although you are training a lot you may not be training smart and getting as much as you can out of the time you are putting in. You may be able to develope more power than you think. Since your hills are short - you need loads of power in short bursts, Hard interval training may help.
3) If you are having troubles on the hills as I suspect you may be, can you loose some weight? According to many cycling experts, good climbers are about 2 lbs/inch of body height - I am 2.5lbs/in - a tubby climber. On an uphill a 10% drop of total weight (bike + rider) on a steep slow uphill climb will give you almost a 10% speed increase maybe more if you can get to a more efficient cadence and pedal stroke.

IMHO there are a lot of other things to consider before you think about adding a faster gear.

Oh my-no wonder I'm a slug on the hills. All I need to do is drop another 25 lbs!!

Your comment about tires sparked another thought--what about wheels? That can make one whale of a difference-more so than changing gears in many cases??

I know lots of people that are running a 11-28 on a RD that says it has a limit of 27. It will work.