What's your favourite gear ratio?

Get with the program, everyone knows 23T are too heavy. Bin it. Climb like an angel.

Luis Herrera?

considering 52-16 on my new bike or is this a bad idea?

Too high for the street for most people. What are you riding now, can't you try it out?

considering 52-16 on my new bike or is this a bad idea?

It's an excellent idea if you're going to average about 22mph, which means even in flat open country with no stops at junctions you'll be doing about 25mph on the level sections.

It's an excellent idea if you're going to average about 22mph, which means even in flat open country with no stops at junctions you'll be doing about 25mph on the level sections.

Agreed, that's much too low to go under an hour for a 25. I'd suggest a 14T sprocket would be better.

Depends on your preferred cadence, I've been using 53/15 this year and it didn't seem too spinny at 23:31 for 10 miles, but I know I can also stay on top of 53/14 at that speed. OTOH, one of my friends was knocking out long 21s consistently on 53/15, while another was usually a few seconds behind me on 60/15. As I've said many times, the right gear is the one that gets you to the timekeeper in the shortest time, not the one that makes you look good in the car park.

Doing 53/11, but SS and with brakes and fat 20" tyres. And Tramadol.

The HHSB I'm building will be 48/17, only because of undrilled fork, so I need some reasonable amount of skid patches. Not sure if I can actually stop it - the last breakless FGFS was running 44/17.

Fuu! It's 97GI! That's why my knees hurt.

Calling Tester, calling Tester...... Do you have a mathematical formula for calculating RPM from mph by gear ratio? Initially, I'm interested in 48:18 with 21mm tyres, but if there's an adaptable formula for different ratios it would be very welcome!

^ I think you can work it out here, pretty detailed info.
No 21mm tyre choice though, 20 is the closest.

I created a Track Gear calculator . Give it a try. https://www.dropbox.com/s/ll3sn1vwfhw8clh/Track%20Calculator%20Complete.xlsx

This is really very useful, can't remember if you can change tyre size or not, but good nonetheless.

I use a spreadsheet (attached), but the formula is
Speed/mph = (Chainring/Sprocket) × wheel diameter/mm × cadence/rpm × 1.171e-4
The units are the common ones, which is why the conversion factor is a funny number (including the pi).
The sheet is approximately correct for 700C tyres not too much wider than the rims they are on, it doesn't do a fully rigorous calculation of tyre rolling diameter from cross section and rim width, and it takes no account of tyre drop under load because gear roll out is measured with no load for MG gear check, the only time when that degree of precision is of interest.

The science nut in my house wants the units to be m/s, m and rad/s, in which case
v = gear ratio × wheel radius × crank angular velocity

1 Attachment

• gear_to_speed.zip

It's all about pi(e)...

Bristol being a city of hills and living at the top..46 x18 is the middle way! Enough on the ups and spinning the downs. It was actually the ratio of the Buddha.

The quick and dirty method you can use while you're riding is that 100rpm on 100" gear is 30mph, it's pretty simple from that to work out the unknown from speed/gear/cadence if you know the other two.

Bristol being a city of hills and living at the top..46 x18 is the middle way! Enough on the ups and spinning the downs. It was actually the ratio of the Buddha.

not much good for skids. 47/18 or 48/19 would be much more appropriate.

Calling Tester, calling Tester...... Do you have a mathematical formula for calculating RPM from mph by gear ratio? Initially, I'm interested in 48:18 with 21mm tyres, but if there's an adaptable formula for different ratios it would be very welcome!

Ca. 96 rpm @20 mph

Oh, a "Bike Gears" app has all the calculations - you just move the slider.

Thank you Tester and EEI from the bottom of my heart, or at least the heart of my bottom! Now at last I will know how fast my legs are revolving when I reach my max speed of 35.2mph (downhill, obviously!) on 48:18, it feels like 3,000 RPM....

not much good for skids. 47/18 or 48/19 would be much more appropriate.

Ah but the numerical balance, I got a thing about numbers...and I'm not so bothered for skidding these days, it cost me a fortune in underpants.

Luis Herrera?

42/23 up mountains and stuff

thank you tester and eei from the bottom of my heart, or at least the heart of my bottom! Now at last i will know how fast my legs are revolving when i reach my max speed of 35.2mph (downhill, obviously!) on 48:18, it feels like 3,000 rpm....

170 rpm?

not much good for skids. 46/18 or 48/19 would be much more appropriate.

ftfy.

Still not much good for skids though Ed.

9 patches?