How bad did I mess up? Advice please!

I accidentally ordered a 20t freewheel for my single speed (profile pic) and run a 46t crank in the front. Apparently I wasn't reading clearly when I ordered this. Will I be spinning out like crazy? Should I return it and order the 17t or 18t like I originally planned?? Is it worth trying first then ordering? My other single speed runs a 16t freewheel and a 30 something crank, I'm constantly spinning out/over spinning on that. I was trying to avoid repeating this with this build.

I don't understand how to interpret the gear ratio calculators available on most sites. Math is NOT my strong point!!

HELP!!

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Permalink Reply by Lanterne Rouge on April 2, 2014 at 2:24pm

How strong are your legs, and how fast do you like to go?

My personal sweet spot was between 70-75 inches when I was riding FG/SS. This would make sense since a common setup for factory FG/SS street bikes is usually 48/18 or 47/17. If you've got a 46T crank, you really want a 17 or 16T cog. 

Permalink Reply by millenial removing Bernie tattoo on April 2, 2014 at 2:26pm

http://sheldonbrown.com/gears/

Put your gears in, then for "Gear Units" select "MPH @ 90 RPM."   This will tell you how fast you are riding at a typical cadence for road riders. So for example the 46-20 will go around 16 mph @ 90 rpm and yes you'll be spinning out a lot.

Permalink Reply by Skip Montanaro 0mi on April 2, 2014 at 2:28pm

Unless you're planning to change the length of your crank arms or put on significantly different wheels, the only thing that matters (relatively speaking) is the ratio of the charinring teeth to the cog teeth. 44/17 seems to be a pretty popular combination. That's a 2.59:1 ratio. 46/20 is 2.3, so yeah, you might find yourself spinning a bit. A 46/18 will give you a 2.56 ratio. A 51/20 chainring would give you roughly the same ratio. I ride a 46/17 which I find too high much of the time. I'm probably going to move toward 45/17 or 46/18, either of which get me into that 2.5:1 area.

Permalink Reply by Hey! Bike Shop Guy on April 2, 2014 at 4:07pm

46-20 is 60.7 gear inches and 36-16 is 56.4 so they are going to ride very close to the same cadence at any given speed so if you spin out close to as easy as your current set up unless it is like a 32 or smaller.

I think both of your ratios are way to light for average riding in this area, go back and return the 20t one you got and get something like a 16 or 17 and you'll probably be a lot happier in the long run.

Permalink Reply by Amanda on April 2, 2014 at 4:41pm

Thanks All! I should have paid closer attention when I ordered the freewheel. Oh well, live and learn I guess. Luckily I ordered it from Amazon, and am able to exchange it for the 16T option. I currently have a 16T fixed set up on the bike and I like to feel as far as cadence is concerned. I'd say its my sweet spot. So I made the exchange and all should be well as of Wednesday next week. I'll be riding 46 16 from here on out! Thanks for the input! My other bike is used for hauling, so that ratio (30 something by 16)works much better for hauling a heavy load. When the new freewheel comes in, this bike will be my fun all around bike. Looking forward to increasing temps and spring like weather once again! 

Amanda 

Permalink Reply by Alex James on April 4, 2014 at 4:11am

I just saw this thread! I've got a 16t Dicta freewheel that I would happily give you, FO FREE. It came uninstalled and unused with a project bike I've got going on. You could cancel your amazon order if you want it. Just throwing it out there. 

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