Why do tourers have a smaller big chainring?
 

Why have a crank set like 24-34-44? Why not have something like 24-36-50? It gives you the low gears and the high gears. Nothing is gained by having a 44 big ring rather than a 50. You use low gears in the little rings and high gears in the big ring. So why this choice?

Some of them have 50/39/30. I have one.

Because some people don't like to go beyond the derailer's stated capacity.

probably because most experienced tourists realize that they're not going to go fast enough enough of the time to make use of the large ring/small cog very often if they use that large of a ring...and even then it would only be going downhill, when they would probably be better off resting and coasting.

How often do you go 25+mph on flat ground when your bike is loaded down with 50 pounds of gear?

Why do tourers have a smaller big chainring? So they can handle a variety of terrain with a heavily laden bicycle. A 50T on a loaded touring bicycle is next to useless.

Think gear inches. I never use anything much over 90 except down hill. I would rather have low gears than high. If you have ever gone 30 mph with 50 pounds of stuff strapped to your bike, you would probably avoid doing it twice.

Ok, so derailer issues.

And a 44 tooth is worthless too. Changing a 44T into a 50T adds more gears and doesn't get rid of any.

Let's say you are using a Shimano mtn RD;
Typically it has a maximum wrap of 45T.
And you are using an 11-34 9s cassette;
You just used up 23T on the rear.
That leaves 22T difference *maximum* between the large and small chainrings.
So if you want a 24T small ring, the large ring cannot exceed 46T.

That's the stated capacity, but you can get more out of it. The capacity is listed for cyclists that might use the small/small combination. The chain will rub front derailer in this situation, but if you only use the bigger cogs in the rear with the smaller chainring, you can push the limit a bit farther. Also, by using a shorter chain and not using the big/big you can push the rear derailer capacity.

But you risk the chance of using the wrong combination and bad things can happen.

I know you *can* exceed that;
Here is my cyclo-touring bike with an 11-34 and 22/32/48: http://www.dim.com/~ryoder/SomaPhotos/IMGP0014.jpg
Note how close the lower chain is to the upper idler pulley; There is about 3/16" clearance with a *new* chain.
With some stretch, the chain rubs the pulley.

I have to disagree with you Machka. If I am using an evenly stepped crankset, then I like the 48 tooth front ring. But on my Miyata, I have a 50 tooth big ring with half stepping and a granny gear and I love it. With half step gearing it is awesome at finding the right gear.

All of the above + My bike geared with 44/32/22 cranks and an 11-34 cassette spins out at 90 rpm and 26 MPH. There are not too many of us that can do that for any amount of time with a loaded bike even when being chased by a big dog!

10 Wheels commented in another thread about the challenge of keeping up (going uphill) with lower geared bikes on a cross country ride. I still don't understand why Cannondale geared their more expensive "touring" bike with 50/42/30 and an 11-32, while gearing their T2 with something more tour friendly, 48/36/26 and an 11-34. IMO that is still a little high for loaded touring in hilly country. My wife and I did our X-country ride with a 26 small rings and changed to a 22's soon after the trip. I also changed my wife's Cannondale T800 (similar to the T2) to a 44/32/22, which really made her happy on the Pacific Coast route last summer.

This is what happened to me when I was riding slower that I could walk! sustained +12% grade in NY.
[IMG]http://i783.photobucket.com/albums/y.../toughhill.jpg[/IMG]

Well yeah, you are using the small/small there. That's why I said if you don't cross chain and use a shorter chain, you can push the limits.

Doug, I agree with you. I like real low gearing. I am a spinner, usually around 110 rpm cadence. So, I like using smaller gears and spinning faster than a lot of people. There is no way I would want a 30 small ring and a 26 is not the best for me.

http://www.crazyguyonabike.com/pics/...ivetrainv2.jpg

I run 22, 36, and 48 tooth chainrings in the front and a custom 13-34 9-speed cluster in the back. Out of the 27 possible gear combinations, I get 22 usable, evenly spaced gears with a range from 17.6 to 100.3 gear inches.

Below 17 gear inches, I'm moving too slow to stay upright. If I spin out at 100 gear inches when loaded, it means I'm either going downhill or I have a huge tailwind. Either way, I'll coast and enjoy the ride.

My gear spacing (in gear inches):

22x34 = 17.6
22x30 = 19.9
22x27 = 22.1
22x24 = 24.9
36x34 = 28.8
36x30 = 32.6
36x27 = 36.2
48x34 = 38.4
36x24 = 40.8
48x30 = 43.5
36x21 = 46.6
48x27 = 48.3
36x19 = 51.5
48x24 = 54.3
36x17 = 57.5
48x21 = 62.1
36x15 = 65.2
48x19 = 68.6
36x13 = 75.2
48x17 = 76.7
48x15 = 86.9
48x13 = 100.3

Moving up to a 50-tooth chainring gets me a couple more gear inches on the tall end (104.5) where I really don't need them at the expense of screwing up the gear spacing where I do care with more duplicated ratios.

I set the chain as short as possible on the big-big combo.
I have no interest in running a chain short enough that things break if you accidentally shift into that.
In general, I avoid the small-ring + 2 smallest cogs, and big-ring + 2 largest cogs.

Oh, I agree with you. I wouldn't do it either, it isn't worth it to me. I'm just saying it is possible.

The question should be "why do most cyclist have such large rings". Most road bikes are seriously over geared for the average rider. They have the same gearing as professional cyclists and, let's be honest, not many weekend cyclists can average 27mph. If you want to do 60mph plus on downhills, or a 50mph sprint, then there is an argument for big rings, but most non competition cyclists would do well to adopt the gearing used by tourists. As an example I run 42/26 rings with an 11/34 cassette giving me 21" to 103" gearing. I can climb anything in the 21" gear and 103" lets me sustain 24.5mph at 80rpm.

Also when designing gearing it's important to minimize replication of gear ratios and to get suitable step sizes. Of course rear and front derailleur capacity limitations must also be met (within reason), hence my use of 42/26 instead of 42/24 to stay within the 16t range of a compact FD.

http://wheelsofchance.org/2009/08/28...-the-question/

Surprisingly, a lot of cyclists coast down hills and don't need the big gears. I don't get it myself. I almost always pedal down hills. I like to keep spinning, and it also helps me burn more calories. I've got 53-39 chain rings on 3 of my road bikes, and I often use the 12-53 combination going down hills where I ride. Of course, if there aren't many hills where you ride, there's not much need for big gears either. My commuter bike has a 50-34 compact crank, and I often spin out going down hills, but I can live with the smaller big ring because the compact crank is great for cycling with more gear.

+1

I don't like to go fast down hills.

I once had a blowout on the front tire at 17 mph on a flat road.

Thought the bike would crash before it finally stopped.

Tarwheel... If your running an 50/11 you have taller gearing than your 53/12. Are you running a 12?

Occasionally you can get up to 25+ on the flats. I've ridden several really good tailwinds at that speed...or better:thumb:

But it's the downhill that really need that kind of gearing. You ain't lived until you've hit 50 mph on the west side of Trail Ridge Road on a loaded bike. Of course the bike started a death wobble at that speed but that's just part of the thrill:D

++

I recently changed out my road triple for a mountain bike triple (not just for touring) because the 50 was way too much for me. I like to ride at 90-100rpm which means I won't need anything more than a 44/12 until I can ride >48kph/30mph on a regular basis. I also find the harder I'm working the higher my cadence, I often ride at >110 if I'm working really hard so I really don't think I'll ever need more than a 44.

Or why not 24-36-46?
because the high gears aren't needed when the average speed of a touring cyclist is slower than the average speed of a road rider/racer. There isn't much use having a 50/11-13 when the speeds at which you can utilize that gear with the power output used in touring is no different than getting into an aerodynamic tuck and coasting.

This is a time worn issue for bike shops when beginning cyclists would come in asking "I need a bigger gear, I'm pedaling down hill and can't pedal any faster" and that was with a 52/14, 100" top gear. The facts were the same then with a 100" gear as now with a 122" gear. The hp required to ride at 24mph with the windage of touring gear on the flats is totally outside of normal strength, obviously it'll be used on descents but the same argument holds that the hp required to utilize a speed increase at 24mph downhill is still outside the steady aerobic hp used in touring.