Can someone help me understand gear ratios and speed?

runnermike · Jul 1, 2014

My last gear reduction was about 12.4:1. 11t clutch, 22t input, 9t output, and 56t sprocket. My bike would cruise around 35 with no problem.

What happens if the gear ratio goes up or down? How does it affect top speed?

What will happen if I drop my rear sprocket to a 48t? I know it will drop my gear ratio from 12.4:1 to 10.667:1 how does that affect my speed?

Sry....I'm just new and a little lost with the whole gear ratio thing. Thanks!

Davezilla · Jul 1, 2014

See if this post helps... http://motorbicycling.com/showthread.php?t=54576
If the math is too confusing I think someone replied with this cool gear ratio and speed calculator app that works really good too

Davezilla · Jul 1, 2014

here's the link to the calculator app... I got it a while back when this topic was active and the app works really good... just plug in your gear ratios and rpm to get the speed...
http://jimsitton.net/ratiocalc/

The_Aleman · Jul 4, 2014

To put it all in layman's terms, the "gear ratio" is really just a reduction so that the engine's RPM can be converted to compatible wheel RPM.

The engine's crankshaft spins a _lot_ faster than the rear wheel!

More reduction = less speed (more torque multiplication).
Less reduction = more speed (less torque multiplication).

Hope this helps!

runnermike · Jul 6, 2014

Aleman....thank you! That's kind if what I thought, but wanted to be sure!

runnermike · Jul 17, 2014

My current gear ratio is 12.441:1, my new clutch has 12t instead of 11t. I can achieve this same gear ratio with my new clutch by changing my input sprocket from a 22t to a 28t.

With my new clutch and a 26t input sprocket, my gear ratio would be 11.556. I know I'll have less torque and pick up and more top end, but will the change in gear ratios be very noticeable?

The_Aleman · Jul 18, 2014

I spose whether or not it's noticeable would be up to you. You'd prolly notice it off the line, against the wind, and/or going up a hill.

12.44:1 is already a rather tall ratio for a single-speed with 26" wheel IMHO. 2K RPM = 12.5 MPH, 6K RPM = 37.5 MPH.

11.556:1 would be 13.5MPH at 2K and you'd gain 3MPH at 6K RPM. So you basically gain 1-3MPH throughout the rev range.

Of course, you can make up for the low end by pedaling harder

greaser_monkey_87 · Jul 19, 2014

So how do pedal gear ratios divide? Having trouble figuring that out. If my chainring is 36t and my rear cog is 24t, what ratio is that? 1.5:1? Or 0.66:1?

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Can someone help me understand gear ratios and speed?

runnermike

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Davezilla

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Davezilla

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The_Aleman

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runnermike

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runnermike

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The_Aleman

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greaser_monkey_87

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