School me on Gearing

[jambee]

I have been riding a my 650B Elephant NFE with Compass 42mm tires for almost two years now. I love that ride.

I set up the bike with 1x11. The crank is setup with 44.

I noticed that I ride in the smallest cassette rings pretty much 95% of the time.

Now looking at my 700C bike (with 44mm compass tires), I managed to trash my big ring (compact crank) of 50 teeth while mostly riding in the middle of the cassette.

Now here is the schooling point: I am looking to migrate the Elephant NFE to 2x11 setup. Looking at the other 2x11 setup, do I keep the rings the same? Is the wheel diameter going to influence the size of the rings?

School is in session!

[jemdet]

A smaller wheel size will reduce the gear-inches for a given gear combination and tire size. In other words, a 50-11 on 700c wheels will be a taller gear than 50-11 on 26" MTB wheels if tire size remains the same.

Case in point - this vintage hill-climb bike. Stuck with road freewheel and crankset options? Make the rear wheel smaller.

EDITS in italics as per posts below.

[jambee]

Thanks @Jamdet

so am i to understand that if i want to ride in the middle of a cassette on a 650B wheel, I will need a larger chainring on the front?

[jemdet]

Originally Posted by jambee

Thanks @Jamdet

so am i to understand that if i want to ride in the middle of a cassette on a 650B wheel, I will need a larger chainring on the front?

If you are currently riding in the small cogs, then yes.

[jambee]

Great to know!

I guess the benefits of riding in an area that's flat as a pancake...

[Mark McM]

Originally Posted by jemdet

A smaller wheel size will reduce the gear-inches for a given gear combination. In other words, a 50-11 on 700c wheels will be a taller gear than 50-11 on 26" MTB wheels.

That depends on the tires mounted. 26" wheels with MTB tires have a remarkably similar circumference to 700c wheels with road tires, so the same chainring/sprocket combinations will give very similar final gear ratios.

Here's a cycle computer calibration chart that shows circumference values:



Different width tires can have a significant affect on final wheel diameter/circumference, so when comparing gear ratios, you'll have to use the tire size, not the wheel size. (Note: One of the features of 650b wheels is that a 650b wheel with a fat tire has a similar diameter as a 700c wheel with a narrow tire, although in this case, the 700c wheel will have an equally fat tire, so the 700c wheel will act to increase the final gear ratio.)

[jemdet]

Originally Posted by Mark McM

That depends on the tires mounted.

You are right - the salient measurement is the total circumference of the part making contact with the road. I should have said "for a given gear and tire size."

[Ralph]

I came up from an era when everyone knew their exact gearing on a ride. Would know what inch gear they were in when riding. I would mark the valve stem on my driveway, roll the bike down the driveway 2-3 times, measure distance, and divide that by number of times wheel rolled over. That gave circumference, then use simple formula (pi D) to solve for diameter. Not have much air in tire, etc....figure tire diameter pretty close.

Then divide the front chain ring teeth by number of rear cog teeth, and multiply that times the wheel diameter. Got a gear inch number. (multiply the gear inch by 3.1415 and you knew how far bike moved in one revolution of the cranks)

So when us guys rode along, (back in the 5 and 6 speed rear days), we always talked about what inch gear we were in. Or what gear we used to climb a steep hill, or go down the other side. Or if someone said he was in a 52X17, everyone knew what inch gear that was. Also everyone understood the concept that 44x11, 48x12, 52x13 was same inch gear. Or that there were a bunch of ways to make same low climbing gear. We just understood those concepts.

Basically, 6th or seventh grade math. But also seem to remember this explanation of gearing was in the owners manual of my first Schwinn Paramount in 73.

[Mark McM]

Originally Posted by Ralph

I came up from an era when everyone knew their exact gearing on a ride.

Knowing your gear options is far more important when you have few options to select from. With modern 10 & 11 (& 12) speed systems, the intermediate gears are so close together, that you don't really need to know their individual sizes - if the gear you're in seems a bit too small or large, then you just shift to the next one.

There is one group of riders that continue to obsess more over exact gear sizes more than even those with 5spd freewheels, and that group is fixed gear riders. When you've only got one gear, you have to make sure that single gear will work in all situations. If you hung around the pits during a Red Hook Crit (fixed gear road criteriums), you'd witness endless debates about exactly what gear ratio to use for the specific conditions of the race (sharp or wide corners, wet roads, field size, winds, etc.), with racers often make last minute changes.

[nooneline]

You can figure this out by following the logic through the drivetrain: a bigger chainring is "more gear" because it pulls more chain each revolution; a smaller cog is more gear because, for a given amount of chain pull (say, 1 revolution of the cranks), it turns the wheel more times (if you have a 48t chainring and a 12t cog, the 12 turns the rear wheel 4 times). and, a big wheel is "more gear" all else the same, because more rear wheel spins means more distance covered.

[cp43]

I like to use this website to pick my gears:

http://gear-calculator.com/

It lets you compare two setups. So, you can put in your current gearing, and note the gear inches of the gears you use most.
Then, make the second setup the new gearing. Play with the cassette size and chainring sizes until you get the gear inches you want on the cogs you want.

Chris

[pdmtong]

Originally Posted by cp43

I like to use this website to pick my gears:



http://gear-calculator.com/



It lets you compare two setups. So, you can put in your current gearing, and note the gear inches of the gears you use most.

Then, make the second setup the new gearing. Play with the cassette size and chainring sizes until you get the gear inches you want on the cogs you want.



Chris

This one. It’s incredibly flexible and very insightful.


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[Gummee]

Phooey on it!

Ride ONE geared bikes and be done with all the silly equations and stuff

M