Guest Rsand85 Posted February 12, 2012 Share Posted February 12, 2012 ok after a bit of help here this is something i can never get my head around!!and i know there's a few on here that's good at it!Trying to work out a final drive for my buggy so i can order sprockets with correct tooth numbers. The standard R1 engine runs a 16/43 sprocket set up and will do 180mph at max rpm of 11700 with a tyre diameter of 640mm. To high top end for off road im after quick acceleration not so much top end!!!. Im running 12" rear rims with kenda executioners 673mm diameter tyres and need to gear it for around 130mph max at 11700rpm. I will be running a 14T drive sprocket need to work out what size rear sprocket i need?? Quote Link to comment Share on other sites More sharing options...
CJ Posted February 12, 2012 Share Posted February 12, 2012 I would pop this up in technical my friend. More chance of people in the know replying there Quote Link to comment Share on other sites More sharing options...
garethr Posted February 12, 2012 Share Posted February 12, 2012 You'll need to know the number of teeth on the R1 gearbox sprocket (I think most bikes are 15), the red line on the tacho, and the diameter of the tyres. What does 25 x 12.50-12 mean? Is it diameter (25") x width (12.50") - rim size (12")? Quote Link to comment Share on other sites More sharing options...
Guest Rsand85 Posted February 12, 2012 Share Posted February 12, 2012 You'll need to know the number of teeth on the R1 gearbox sprocket (I think most bikes are 15), the red line on the tacho, and the diameter of the tyres. What does 25 x 12.50-12 mean? Is it diameter (25") x width (12.50") - rim size (12")? yes tyre diameter works out at 624.8mm R1 standard tyre diamiter it 640mm so not a great difference. ok standard R1 ratio is 16/43 and 180mph at max 11070 rpm im after 130mph at max 11070 this is not my strong point atall!! Quote Link to comment Share on other sites More sharing options...
garethr Posted February 12, 2012 Share Posted February 12, 2012 I reckon you'll need a 59T rear sprocket. If the R1 is geared for 180 at 11070 on 16/43: with standard 16/43 sprockets the buggy will do 180 X 624.8 / 640 mph at 11070 rpm = c. 176 with 16/59 sprockets the buggy will do 176 X (16/59) / (16/43) mph at 11070 rpm = c. 128 Quote Link to comment Share on other sites More sharing options...
Guest Rsand85 Posted February 12, 2012 Share Posted February 12, 2012 i can get a 14t drive sprocket to would i be better changing both?cheers for the reply man Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 12, 2012 Share Posted February 12, 2012 A very small sprocket will wear the chain a lot faster and create a lot more heat, and absorb a lot more power. There are plenty of gearing calculators out there. Here's the first I found.For top speed just enter the top gear ratio and the final drive (sprockets) ratio. It's dead easy with a piece of paper and a calculator, too. http://www.johnmaherracing.co.uk/gearcalc.htm Quote Link to comment Share on other sites More sharing options...
garethr Posted February 12, 2012 Share Posted February 12, 2012 IIRC 14T is about the limit. Space or availability could make 14/51 a better option than 16/59. Quote Link to comment Share on other sites More sharing options...
Guest Rsand85 Posted February 13, 2012 Share Posted February 13, 2012 IIRC 14T is about the limit. Space or availability could make 14/51 a better option than 16/59. aye space is my issue really you recon go 14/51 then? maybe this is very stupid of me to ask but if you drop the front from 16 to 14 is it not a case of dropping the back from 59 to 57? Quote Link to comment Share on other sites More sharing options...
garethr Posted February 14, 2012 Share Posted February 14, 2012 aye space is my issue really you recon go 14/51 then? maybe this is very stupid of me to ask but if you drop the front from 16 to 14 is it not a case of dropping the back from 59 to 57?No, because the ratio is important, not the number of teeth. If you change from 16 to 14. then 14 is 14/16 (14 sixteenths) of 16. This means that the new rear sprocket would have to be 14/16 of the old rear sprocket. 14/16 of 59 is 51 or 52 (actually 51.63, but you can't have .63 of a tooth ). Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 14, 2012 Share Posted February 14, 2012 Don't think of them as numbers of teeth, but as ratios. So if you found 15 teeth on the front sprocket (driving sprocket) and 26 teeth on the rear sprocket (driven sprocket) you have reduction ratio of 1.733 to 1 or commonly written 1.73 : 1 This means the driving sprocket has to turn 1.733 times for the driven sprocket to turn exactly one full turn. By dividing driven by driving teeth you can see how similar a ratio various combinations give you. Quote Link to comment Share on other sites More sharing options...
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