Can someone explain gear ratios to me?

[5v3d3b0]

Please can someone explain how gear ratios are calculated and what significance they have... Maybe this should be in the workshop, so sorry if that's the case.

[bazza]

It's a long shot, but it might just work...

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____________________
"That's it. You people have stood in my way long enough. I'm going to clown college."
'98 Ducati 750SS, '08 Suzuki GSX650F ©2004-2014, Bazza's Harmless Banter

[gavin]

gears multiply torque. the lower the gearing, the more torque, or rather thrust, you will have at the rear wheel. accereration will be higher, top speed will be lower ( though this isnt always the case - see below)

overall gear reduction is three parts:

primary reduction ( crank shaft to gearbox) is usually quoted as driven (gearbox) over drive (crank) this might be 68/19 or 3.587

gear ratios are usually quotes as driven gear over drive gear, first might be 39/12 or 3.250, sixth might be 24/26 or 0.923 etc

final drive ( chain and sprockets) is also quoted as driven over drive, this might be 48/14 or 3.428

you can usually only alter the final drive, smaller at the front and/or bigger at the back lowers gearing, and vice verca.

this is one of my bikes on standard gearing

https://homepage.ntlworld.com/gavin.prior/dynabike/lomas/through%20gears.jpg

and this is it on lower gearing

https://homepage.ntlworld.com/gavin.prior/dynabike/lomas-opt/through%20gears.jpg

note that in this case the top two gears are redundant on standard gearing ( brown line is as fast as it can go due to drag) but lowering the gearing increases the thrust in 5th and 6th and allows it to pull slightly higher top speed, as well as accelerate better through the gears.
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1988 TZR125 : 1990 RD350YPVS/ RGV250 HYBRID : 1982 RD80LC : 1983 RD80LC : 1994 RGV250 : 1991 TZR125 / CR500R HYBRID : 1976 BENELLI 500 QUATTRO : 2006 TRIUMPH 675

[5v3d3b0]

Gearbox
6 speed.
1st 10/30 (0.33)
2nd 14/29 (0.48)
3rd 17/27 (0.63)
4th 19/25 (0.76)
5th 21/24 (0.87)
6th 22/23 (0.67)

Thats's the gear ratios for the Rs 125. What can I find out looking at that. It still just looks like numbers... First gear is 0.33...Right. 0.33 WHAT?
Thanks for your patience

[gavin]

0.33 to 1 or 0.33:1.

drive gear pinion from clutch has 10 teeth, first gear cog has 30 teeth. one complete revolution of drive gear pinion = 0.33 of one full revolution of the first gear cog.
____________________
1988 TZR125 : 1990 RD350YPVS/ RGV250 HYBRID : 1982 RD80LC : 1983 RD80LC : 1994 RGV250 : 1991 TZR125 / CR500R HYBRID : 1976 BENELLI 500 QUATTRO : 2006 TRIUMPH 675