Sprockets

[That_Hornet]

What is the normal increase in top speed in changing the amount of teeth on the sprockets.

And on the other hand what sort of increase in acceleration for adding some on the rear?

Ta

[Kickstart]

Hi

Totally depends on the bike. Some bikes are low geared and will rev well out in top, others are high geared and are possibly faster in 5th rather than 6th.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Wafer_Thin_Ham]

The hornet 6 is geared really high as standard. It'll just about rev out in sixth downhill, but you have to take it right to the limiter in fifth to ensure you're still in the power when you change up.

You can go up 3 on the rear and not lose a great deal, but remember you'll be using more fuel for a given road speed, and the Hornet's tank isn't the biggest to start with.
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[That_Hornet]

Not for the hornet, looking for some winter hack. 350 maybe. Wanted to know if I could sacrifice top end form some more acceleration

[Kickstart]

Hi

You can sacrifice top speed for 1st gear acceleration. Rest of the time you have the option of being in a lower gear for much the same effect.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Wafer_Thin_Ham]

[Blue_SV650S]

If you look up the internal 'reductions', measure the rear wheel circumference and ascertain the sort of revs you would want to sustain, add on your chosen sprocket combo, then its just down to maths!

Here you go, I wrote this up a while ago when I wrote some software to automate the process and handed it out, people were interested in how it worked.

So here is the backbone algorithm in pseudo code, comments (depicted by/started with a ‘ ) ... you can look up your specs and plug in your numbers in Excel, then it is just a case of changing the sprocket values and you can see the changes on final speed.

‘If wheel was turning at engine speed, with wheel circumference in cm; work out distance that would be travelled in miles per hour
SpeedCalculationWithoutReduction = ((WheelCircumfarance/100000) * (RPM * 60)) * 0.621371) 'Circumferance in KM, Revvs per hour, KM to Miles

‘ now work out reductions:-

Reductions = primaryreduction * gearratio * (rearsprocket / frontsprocket) ‘gearratio is the gearbox reduction e.g. from the specs, 6th is 23/27 (0.851), primaryreduction is also from specs

‘ Now reduce the wheel speed using the calculated overall reductions:-

SpeedInGearAtRPM = SpeedCalculationWithoutReduction / Reductions


‘ Here are the gear ratios for SV650:-
‘Pimary - 2.088 (71/34)
‘1st - 2.461 (32/13)
‘2nd - 1.777 (32/18 )
‘3rd - 1.380 (29/21)
‘4th - 1.125 (27/24)
‘5th - 0.961 (25/26)
‘6th - 0.851 (23/27)

‘Standard sprockets for an SVS 44rear 15front

So a worked example:-
Input:-
200cm circumference, 10500rpm, 6th gear, 15t Front, 44t Rear.

SpeedCalculationWithoutReduction = ((200/100000) * (10500 * 60)) * 0.621371) = 782.9275
Reductions = (71/34) * (23/27) * (44 / 15) = 5.21801
SpeedInGearAtRPM = 782.9275/5.21801 = 150.0433

i.e. at 10500 in top with a 2m circumference rear tyre, you would theoretically be doing 150.0433mph!!!


So there you go ... aren't I kind!?!

Oh and its also a good one if someone tells you what speed they got out of their bike and you think it is suspect ... if you know their sprockets and rear tyre, then you can PROVE they are full of sh1te!!
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[Kickstart]

Hi

Or if you have a dyno chart and want a bit more detail (such as when you will have stuff all go) then try:-

https://www.bikegraph.co.uk

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Wafer_Thin_Ham]

Prove's the speedo's full of shit.
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[That_Hornet]

Chears. Im now going to sit down and try and make out what that all means....