Bicycle Mechanics - 50/34 compact dbl w/11-27 10sp doable?

I'm having my local bike shop build me a new bike. I currently ride a 52/39/30 triple 9 sp with a 12-27. I'm concerned about running out of RPM at the top end with the 50 tooth chain ring. Is a 11-27 doable with a Dura Ace rear deraillure and shifters? I'm not a bike mechanic but looking at the Shimano CS-6600 10 sp cassette sprocket teeth combinations it could look like 11-13-14-15-16-17-19-[21-24-27] Is there any drawbacks? How would you do it?

TIA,
jw

Personally, I would scrap the 16 and put a 12 on it just to make it fairly even, because the intervals get more drastic the smaller the cog goes (11-13 is a bigger jump than 15-16). Anyway, I have a similar setup on my bike with a 34/50 and 13, 14, 15, 17, 19, 21, 23, 26, 29 (9 spd) cassette. I love it because it allows me to climb pretty well. I do miss the 12 sometimes, but I'm not a racer so I can stay under 40 mph.

The only drawback I can think of is the gears being spread apart a bit, so sometimes I can't seem to find the "perfect" cadence and have to go with "close enough", which might mean choosing to spin 88 or 98 instead of 90-95 like I prefer. All in all, I'd rather have the climbing gears than closer spacing considering the hills and mountains around here. I do think I should have gone with a triple, though.

How often do you use the 12T cog now? The drop from 52 to 50 T will reduce your top gear by only 4% which is a pretty small increment. Unless the current 52/12 is marginally too low, I'd keep the 12T.

A 50/11 is a tremendously tall high gear for all but the strongest riders and if you only use it downhill, you would probably go just as fast by tucking in out of the wind and coasting.

I'm with Hillrider. Unless you can average above 26mph on a century (sub 4hr)
and ride with the semipro group all the time you won't miss the 11t sprocket.
50x12 at 100rpm cadence is over 32mph. If you are cadence challenged then
50x11 at 90 rpm is about the same. This is 350watts power output at the
minimum. If it fits, then go for the 11t, but you will be in the top 0.5% of
cyclists.

Agree with Hillrider, keep the 12, 50/12 is plenty high enough.

Al

I pretty much concur with the above posters.
When the 11 tooth is too tall and you're spinning out on the 13, you'll hate yourself for not having the 12.

I have a 50/36 with a 12-27

I am using a FSA 50/34 compact and Shimano Ultegra parts with a SRAM 11-26 cassette. I rode a triple with 12-27 for 3 years prior. I find I use the 50x11 a lot. I also find I do better on grades over 12% with the 34x26 than the original 34x25. A 34x27 would give you even more of a lower gear.

I've got a 50/36 with 12-23 on my main road bike. Riding in Spain with a fast group ride the last couple of weeks, I found that I was spun out often on long downhill grades while trying to keep up with the group (yes, at about 35 mph or so, but there were usually ample downhills for this since we did a lot of climbing). I'm planning to put an 11-26 or 11-27 on for these sort of occasions.

IRD makes a shimano 11-28 cassette you might look into.

Personally, I would scrap the 16 and put a 12 on it just to make it fairly even, because the intervals get more drastic the smaller the cog goes ....

+1

You also need a lockring for an 11t. I run the 11-27 as urbanknight describes.


The only drawback I can think of is the gears being spread apart a bit, so sometimes I can't seem to find the "perfect" cadence and have to go with "close enough"...

True, but the rest of the cassette is the same as a 12-27 9-spd, so it has the same spacing that was perfectly fine a few years ago.


Unless you can average above 26mph on a century (sub 4hr) and ride with the semipro group all the time you won't miss the 11t sprocket."

Yes and no. It's all up and down where I live and I missed the extra top end when I went to the compact. I'm no semipro. What is not obvious and can come in handy is that you get a 34-12 option without a full cross-chain.

I'm in a similar fix. I got a 50-36 and dropped it to a 50-34. Then I realized i was never in the 50/11 or 50/12 unless I was going downhill. Tonight I installed a 13-25 (replacing a 11-23) that has lots of steps.

Agree with Hillrider, keep the 12, 50/12 is plenty high enough.

Al

I'm going to buck the trend here and suggest you stick with the 11. In Pennsylvania, Alabama and Oklahoma, you might not use the 11 much but Alameda, Cal. is probably more like my back yard than those other places. You'll have ample opportunity to use an 50/11 (122 gear in.) on long downhills long after you'd be spun out on a 50/12 (112 gear") or 50/13 (103 gear"). The speed difference is 38 mph to 27 mph at 90 rpm.

Lower top gears make sense in flatter areas or in areas with shorter hills but in the mountain west, downhills can go on for miles. Coasting gets boring and spinning at 120 rpm is hard;)

One more thing...

I don't think an 11t will "mesh / stack" properly with a 13t anyhow. Could be wrong...

Shimano has some guides online showing what cassette parts work with what. It's more complex than I thought
9 speed hubs at
http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/CS/EV-CS-6500-1680A_v1_m56577569830611831.pdf
10 speed at
http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/CS/EV-CS-6600-2370_v1_m56577569830608752.pdf
as you can see, you often need to buy a cassette instead of just swapping some cogs. Different combinations have differing requirements. For exapmle, a 13 tooth cog isn't the same as all other 13 tooth cogs.

One more thing...

I don't think an 11t will "mesh / stack" properly with a 13t anyhow. Could be wrong...

I don't see why not. It fits on the splines the same way a 12 would and a 13 to 11 jump isn't that big. It should work.

You'll have ample opportunity to use an 50/11 (122 gear in.) on long downhills long after you'd be spun out on a 50/12 (112 gear") or 50/13 (103 gear"). The speed difference is 38 mph to 27 mph at 90 rpm.


Actually 50-11 at 90 rpm = 32mph
50-12 90 = 29
50-13 90 = 27
Assuming a 700 X 23 tire size. And 90 is a pretty mild spin.

The jump from a 13 to an 11 is the largest possible two cog gap. If you've got to have an 11 it would make more sense to sacrifice the largest single cog, probably the 16, not a good choice in my opinion. A good aero position will give you more speed than the 11.

I have a 50x13t top-gear and I have no problems spinning it up to 150rpms. After that speed, it'd be faster to get into a tight tuck rather than keep on trying to pedal...

Actually 50-11 at 90 rpm = 32mph
50-12 90 = 29
50-13 90 = 27
Assuming a 700 X 23 tire size. And 90 is a pretty mild spin.

The jump from a 13 to an 11 is the largest possible two cog gap. If you've got to have an 11 it would make more sense to sacrifice the largest single cog, probably the 16, not a good choice in my opinion. A good aero position will give you more speed than the 11.

You are correct about the speeds. I misread a number. I will also agree that 90 rpm is pretty mild. On a long steep downhill you would probably be spinning more in the 100-120 range.

How ever I'd have to disagree on the cassette. What jwill911 is trying to do similar to what has already been done by IRD (http://www.interlocracing.com/cassettes_steel.html). I think they've even done more elegantly by eliminating the 14 and 16 tooth cog and adding a 28 at the end. Their cassette is a 11/12/13/15/17/19/21/23/25/28 compared to jwill911's 11-13-14-15-16-17-19-[21-24-27]. I'd be tempted to take his set and get rid of the 14 or 16 and graft a 29 (9spd) to the back. It'd give him a fair low, a good high and a pretty progressive middle.

For the speed thing, it's not just about speed. If you have a downhill that can last for 15 to 20 minutes or even much longer, the 11 is nice to at least be able to run your legs around once in a while. On a low high geared bike here in the west, you could be coasting for a very long time. Your muscles get pretty stiff after 10 minutes of no pedaling. When you come to that inevitable up hill, your legs will kill you. Trust me, I've been there;)

I don't see why not. It fits on the splines the same way a 12 would and a 13 to 11 jump isn't that big. It should work.


FWIW, I've been running an 11-27 (11-12-13-14-15-17-19-21-24-27) cassette on two wheelsets since early last year.

On my cassettes (one 6600, one 7800) if you stack the 11t into the 13t the spacing between them is slightly less than the spacing between the 11t and 12t, or between any other two gears for that matter. I confirmed this just a few minutes ago. The difference is small, maybe 0.1mm-0.2mm, and I don't know if there would be any issues because of it, but it is definately smaller.

I don't see why not. It fits on the splines the same way a 12 would and a 13 to 11 jump isn't that big. It should work.The other criteria is the location of the chain-ramps on the side of the cog. They are designed for a specific progression of one cog to the next. That's why you have the "series" marking on the cog like S, T, U, V, etc. that shows which cogs work best with each other. If you want a 11->13t jump, you need to select a cogset that uses that particular combination. Mixing & matching individual cogs into your own custom cluster doesn't work well when you don't have a matching series.

The other criteria is the location of the chain-ramps on the side of the cog. They are designed for a specific progression of one cog to the next. That's why you have the "series" marking on the cog like S, T, U, V, etc. that shows which cogs work best with each other. If you want a 11->13t jump, you need to select a cogset that uses that particular combination. Mixing & matching individual cogs into your own custom cluster doesn't work well when you don't have a matching series.

According to Sheldon Brown's site, for the 11-15, it's a nonissue.

I am using Campagnolo but did something similar to what you are looking at. I have a 50/34 compact in front with a 11-29 cassette. I like riding hills and hilly centuries and at 50 want to preserve my knees.
I had a triple (53-42-30) and wanted something less bothersome in the front. Yet I wanted the same climbing gears so I went from an 13-26 to a 13-29 in the rear. With the 53/13 combo I was overspinning on downhills so I figure the 50/13 would be even worse, a 12 in the back would have provided about the same ratio but I wanted something that allowed me to spin while descending to keep the legs warm without overspinning thus the idea of the 11. I do not race so I would never use the 50/13 combo on the flat. I bought a used 11-23 cassette took the 11 out and used it to replace the 13 on the 13-29 cassette. The end result is 11-14-15-16-17-19-21-23-26-29.
After a year of usage I am pretty please, the shifting works fine and the big jump from 14 to 11 only happens on steep downhills so it has never been an issue. Moving back from from 11 to 14 is not an issue either.
I know it's not a very conventional cassette but if it's what you are looking for, why not! It can work.

FWIW, I've been running an 11-27 (11-12-13-14-15-17-19-21-24-27) cassette on two wheelsets since early last year.

On my cassettes (one 6600, one 7800) if you stack the 11t into the 13t the spacing between them is slightly less than the spacing between the 11t and 12t, or between any other two gears for that matter. I confirmed this just a few minutes ago. The difference is small, maybe 0.1mm-0.2mm, and I don't know if there would be any issues because of it, but it is definately smaller.

I appreciate all the feedback, now I understand the reasoning for have closer gear ratios in the smaller cogs and making a larger jump in the middle range. I'm going to take the bike with the 12-27 10sp and just feel it out. If I feel like I'm over spinning on long down hills I'll look into the 11-27 change sam83 suggests. I know I won't be pushing the 12/50 too hard in the flats unless I have a big tail wind.

Thanks,
jw

True, but the rest of the cassette is the same as a 12-27 9-spd, so it has the same spacing that was perfectly fine a few years ago.

Actually, I am on a 9 spd, but yeah it's not that bad. 20 years ago, I believe my 7x2 bike had something like a 14-25 and a 53/42, and I don't even know what traditional 10 speeds had, so we're in luxury now.

I appreciate all the feedback, now I understand the reasoning for have closer gear ratios in the smaller cogs and making a larger jump in the middle range. I'm going to take the bike with the 12-27 10sp and just feel it out. If I feel like I'm over spinning on long down hills I'll look into the 11-27 change sam83 suggests. I know I won't be pushing the 12/50 too hard in the flats unless I have a big tail wind.

Thanks,
jw

Probably the best decision because it won't cost any more to change it later since you have to buy a 12-27 plus the 11t and a lockring anyhow.

But for around my neck of the woods it seems like the middle of the cassette is just a place I'm passing through a lot of the time. It's all up and down so the jumps rarely catch me out.

As I said before, the thing that surprised me - and I found very useful (more than the 50-11) was the 34-12 option without a full cross-chain. On occasion I'll find myself in the 34-13 and then needing one more gear, but just for a bit before having to go back up the cassette. To avoid cross chaining in the 12-27, it's a shift to the big ring and multiple shifts in the rear to get to the 19. In the 11-27, it's just a shift to the 12t. You may find that helpful in your situation. Or not.