SolarRoller

Hello,

I am building a custom bicycle and am thinking of putting a 50/34 compact crank with an 11/25 cassette.

Does anybody have any experience with this combination?

Is there any risk of spinning out on flats or when riding down hills?

I have only ever built/ridden classic bikes...

Thanks!

rm -rf

A 50/11 is 119 gear inches.
What did you have on your classic bike?
A 53/13 is 107 gear inches,
A 53/12 is 116 gear inches.

At 110 rpm, the 50/11 is 39 mph. You won't spin out.

Do you have hills? That 34/25 low gear isn't very low compared to the typical 34/28 or even 34/32 low.

DrIsotope

34/25, you say? Hope you don't happen upon too many hills.

SolarRoller

The classic has 52/40 + 14/29.

Yeah, I see your point about 34/25 not being low enough... I mostly ride on flat and mild inclines, but would like to have the option to ride steeper inclines with this new bike. The reason I was thinking 11/25 was because I have read complaints about unsmooth shifting jumping up to a 28 ring, not sure how valid that is.

HTupolev

As far as not spinning out on downhills, your new configuration will be much more capable than the old; its top gear is 22% above the 52-14, sort of like like being able to shift a couple steps higher.

The issue, if you want to be able to ride steeper inclines, is that your low gear is barely lower than your old low gear; the difference is only a small fraction of a gear step.

Many derailleur systems today can shift up into 40+ tooth cogs in back. 28 is nothing.

By the way, it's confusing to call the rear sprockets "rings." "Chainring" refers to the sprockets in front.

bikeme

I'm running a 50/34 with an 11 spd. 11-28 and never spin out. Now, in a hammering pace line on a downhill, my cadence is way up there but I'm still not "spun out". I might be turning 120+ but am fine with that.

supton

I've spun out on 52x12, but it was a pretty big hill. I don't do that very often.

Personally I'd prefer to optimize gearing in the range I use the most. I've got no sense of pride so I'm ok with walking the occasional hill; but sometimes I have a sense of mortality and will back off when going down it.

Kopsis

SRAM offers an 11-26 cassette if you want just a little more low-end but don't want to go all the way to an 11-28. SRAM and Shimano 11-speed road cassettes are fully interchangeable.

Note that the Shimano 11-28 shifts fine into the 28t (even though it's a 3t jump), but it loses the 16t so you have four 1t jumps, five 2t jumps and one 3t jump (going to the 28). The SRAM 11-28 retains the 16t but pays for it with 3t jumps in the last three downshifts so you have six 1t, one 2t, and three 3t jumps. For relatively flat riding, I prefer the SRAM spacing since the few climbs I do have are short and optimizing cadence for them really isn't important. If you do long climbs, the Shimano spacing might be preferable.

cny-bikeman

If one is going both up and downhill on a ride, which is almost always the case, pushing a high gear when going downhill is mostly just wasteful, especially if you do not have very low gears for the uphill. Whatever energy you use on the downhill will primarily go to overcoming wind resistance, while going uphill it almost all goes into helping you get up the hill. In any case if you spin out going downhill you should be tucked down and coasting anyway. Finally, a 3 tooth jump is neither large nor difficult, and as it's for your lowest gear it is not encountered very often.

DrIsotope

Unless you're at the front, if you stopped pedaling and got into a tuck, you'd likely go faster. Whirling legs create significant drag. Remember the guy going superman on the fixie, and just blowing past everyone?

Man, do I ever agree with this. I've pretty much given up pedaling down grades steeper than say 3%, and it hasn't affected my overall speeds one way or the other. Much more important to have the gears to go up the hill-- gravity does a pretty good job helping you down.

TimothyH

Keeping a little power applied can help maintain stability and control on fast descents over loose surfaces.

Gravel roads near me tend to have steep and long downhills and it is nice to be able to keep a little power on using the higher gear combo.

Coasting in a tuck on gravel or dirt descent isn't going to work generally.


-Tim-

superdex

Rode a 50/34 and 12-25 around the Colorado Front Range for the last few years. The 34/25 is low enough for me for climbs like Deer Creek/High Grade/Lookout etc. (Lookout Mtn is 4.5mi of 5-6%) When I tackle bigger climbs like Vail Pass or Mt Evans, I put on a 12-28.

all depends on your fitness and goals. to wit, I just put on a 52/36 to go with an 11-25, having finally gotten strong enough.

MRT2

You need to know your body and abilities, and gear inches is one area where you don't have to guess. Use an online gear inch calculator to calculate the range of your current setup, then do the same for your proposed compact double.

I currently run a touring triple with a 12 - 27 road cassette. My easiest gear is a 26 - 27, or just a bit smaller than a 1:1 ratio, or 26 gear inches, and a big gear of 4:1, or 108 gear inches. If I were to switch to a compact double, I would have to go with a 12 - 36 to get the same low gear, but i would also have a bigger high gear.

SolarRoller

Ah so true, the classic I'm riding tends to spin out on mild inclines! The low gears work well where I ride though.

How large of a cassette can you use with a Shimano Ultegra SS cage?

*noted: sprockets not rings

SolarRoller

Fair point. Perhaps optimizing gearing for the everyday ride, while also having a second rear wheel with a larger cassette for special occasions.

SolarRoller

Great info! The SRAM sounds more suitable for the type of riding I do i.e. mostly flat & mild incline, with the rare steeper climb.

supton

Eh, it's not that hard to swap cassettes. If you've got spare wheels then sure, it saves a minute.

As long as the RD and chain are sized to deal with the change in cassette sizes.

*

I actually ditched 12-25 for 12-23 on my road bike, as I felt (at the time) that I could feel the lack of the 17T cog (? could be wrong, maybe it was 18T). Now that bike is set the way I want it. I only use the 52T ring on some downhills (for fun) and pretty much stay in the 42T the rest of the time. Personal preference but that's me. On occasion I find flat ground, and it's nice to use close steps.

Trying out a 50/34 x 12-25 at work, on group rides. I don't think I'd like it for my solo bike. I guess strong riders would only use the 34 for rough hills, but since I'm not a strong rider I find myself shifting the FD "a lot". Feels like the FD shifting is right in the middle of where I normally ride--on my other bike, I only need the FD on descents, and not always. But I guess that's how I'd set up a double.

MRT2

There is a forum member who asks, how finely do you want to slice the bologna? IMO, sweating the difference between the SRAM 11 - 28 and the Shimano 11 - 28 is among them. How much will you miss the 17 tooth cog, vs. how much will 3 tooth jumps for the last 2 or 3 cogs bother you? If you are competing professionally, then maybe you, and your coach, trainer, and team director can get together and figure out which cassette to use. I think you are probably fine with either option.

HillRider

I'm currently running 12x27 10-speed cassettes with a Shimano road triples geared 50/39/26. I substituted the 26T for the stock 30T. The overall range is 112 gear-inches to 26 gear-inches and I have the all-important to me 16T cog. There is no double crank/cassette combination that could give me that range with the same small intermediate steps I have now.

MRT2

I am a fan of the 26 tooth chainring as well. I don't need the small chainring for anything except climbing. And when I need it, I need it for the 3 bailout gears which are 33, 29, and 26 gear inches. If my small chainring were a 30 tooth, I lose the 26 gear inch gear, and my smallest gear is just a hair over 29 gear inches. It might not seem like much, but sometimes that is the difference between making it up the hill and walking. The middle chainring covers everything up to about 75 gear inches, and I only shift to the big chainring when I am over 18 mph, which is maybe only 5 to 10% of the time.

Kopsis

Probably. But if one must make a choice, what's the harm in making it an informed one? I'd argue that what, on the surface, seem like small gearing changes are far more noticeable to the recreational rider than most of the other minutia that gets debated on BF.

FrenchFit 

Your title doesn't match your post. I've run a 48/34 crank with more of corn cob freewheel, like 11-21, and like it a lot. But, I am talking pure recreational riding, not blasting down hills 40+ mph. i can't imagine why anyone would want to ride a bicycle over 25 mph, but that's me. I'm hearing they have this new fangled invention that allows you to ride a bicycle 60mph, I think it's called a motorcycle....

supton

It's a bit of a blast (literally) once past 30mph.

Personally, I won't ride a motorcycle. Too dangerous.

nillevang

I hate compacts. Somehow the sweet spot is always somewhere between the big and the small ring, and I find myself either x-chaining or shifting constantly at the front.

What I've done is a 1x9 setup with a 46 tooth narrow wide chainring up front and a 12-36 mtb cassette at the back. Perfect setup for flats, rolling hills and moderate inclines. If I were cycling in the mountains it would probably be a different deal, but i never pedal uphill for more than a couple a minutes before its flat or downhill again. Thus I'm saving a ton of annoying 34-50 up- and downshifts at the front.

Retro Grouch 

Yup. Everybody wants to talk about their easiest hill climb gear or their fastest gear. I think that on a compact double equally important is the favorite flat road gear. You'd like that to fall right in the middle of the cassette so that you have a couple of trim gears going each way.