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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:16 - 23 Sep 2012    Post subject: Sprocket ratios Reply with quote
Quick question.


Previous track bike was on a 12" rear wheel.

120/80-12 (1515mm rolling radius)
37t rear sprocket
16t front sprocket


Current track bike, is on a 10" rear wheel.

90/90-10 (1269mm rolling radius)
37t rear sprocket

What size front sprocket would I need to keep the ratio the same?

The biggest I have is an 18t (And that's the biggest that will fit).

Please dont post a link to the gear commander website, as it asks the box ratios which I dont know.

I'm not good enough at maths to work it out easily.
Can anybody else?
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WannaBeDude
World Chat Champion



Joined: 05 Jul 2011
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PostPosted: 21:21 - 23 Sep 2012    Post subject: Reply with quote
This chart allows you to get a VERY close same percentage afaik Idea

https://i37.photobucket.com/albums/e53/covdude/2012/GearRatios_zps928832b7.jpg
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Frost
World Chat Champion



Joined: 26 May 2004
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PostPosted: 21:32 - 23 Sep 2012    Post subject: Reply with quote
19.1T Laughing

or if you can stick a 35 on the back the front would need to be 18.069132963T, so an 18T front would basically be exactly what you'd want.
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:33 - 23 Sep 2012    Post subject: Reply with quote
But you're not taking into account the SMALLER rear wheel with that chart.
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WannaBeDude
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PostPosted: 21:42 - 23 Sep 2012    Post subject: Reply with quote
Forgive my thickness, but the chart figures will put out that percentage to whatever wheel or tyre Confused

Knowing you work with cars and shiz, im waiting to be corrected tbf.
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Frost
World Chat Champion



Joined: 26 May 2004
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PostPosted: 21:45 - 23 Sep 2012    Post subject: Re: Sprocket ratios Reply with quote
binge wrote:

Previous track bike was on a 12" rear wheel.

120/80-12 (1515mm rolling radius)
37t rear sprocket
16t front sprocket


Current track bike, is on a 10" rear wheel.

90/90-10 (1269mm rolling radius)
37t rear sprocket


I assume you mean 'Circumference' by rolling radius.
16/37 = 0.432432432 rear sprocket rotations to 1 at the front. 0.432432432 * 1515mm = 655.135135135mm travelled per front sprocket rotation.
Aiming to keep that the same on the new setup:
655.135135135 / 1269mm = 0.516260942 rear wheel rotations
0.516260942 * 37 = 18.069132963 front sprocket tooth count to maintain the same ratio between engine rotation and distance travelled.
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:47 - 23 Sep 2012    Post subject: Reply with quote
covdude wrote:
Forgive my thickness, but the chart figures will put out that percentage to whatever wheel or tyre Confused

Knowing you work with cars and shiz, im waiting to be corrected tbf.



Well the sprockets are your "final drive ratio".
But the rear wheel it's self, is like the final final drive.
Adjusting tyre/wheel size adjusts the acceleration or top speed.


Frost has hit the nail on the head. Thats what I needed to know, thanks mate.
The reason I wanted to go with this option, is because I run wet and dry wheels, with a sprocket on each wheel.
Talon rear sprockets are £25 a pop, where as a front sprocket is under a tenner (And I'd only need one).
I'll go with the 18t, and see how I get on. 19t sprockets dont exist, and simply wouldnt fit anyway. Sad




Ben
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:48 - 23 Sep 2012    Post subject: Re: Sprocket ratios Reply with quote
Frost wrote:

I assume you mean 'Circumference' by rolling radius.
16/37 = 0.432432432 rear sprocket rotations to 1 at the front. 0.432432432 * 1515mm = 655.135135135mm travelled per front sprocket rotation.
Aiming to keep that the same on the new setup:
655.135135135 / 1269mm = 0.516260942 rear wheel rotations
0.516260942 * 37 = 18.069132963 front sprocket tooth count to maintain the same ratio between engine rotation and distance travelled.



Erm, you've just fried my brain mate. Laughing
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WannaBeDude
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Joined: 05 Jul 2011
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PostPosted: 21:50 - 23 Sep 2012    Post subject: Reply with quote
Ok - your sorted, lets hijack =

I went from 150 / 60 to 160 / 60 / on the rear -

Is not that difference negible - or is it noticable . Smile Confused Karma
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:53 - 23 Sep 2012    Post subject: Reply with quote
I did a similar thing on the R1. From 190/50, to 180/55 (I prefer the narrower tyre).
Technically, the profile is different, but it's too small to even notice, plus, I've fucked around with the sprocket on the R1 anyway.

Think you'd need to drastically change tyre sizes to notice anything.





Ben
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WannaBeDude
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PostPosted: 21:57 - 23 Sep 2012    Post subject: Reply with quote
I changed caus -

Size not avail in 150
Larger for surface and looks
Better with pot holes

Ta Thumbs Up
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 22:01 - 23 Sep 2012    Post subject: Reply with quote
Did exactly the same thing on my NC29.

Ran a 150/60-17 standard, and I went up to a 160/60-17 because of choice of tyre.
Same with the front, they run a 120/60 standard, and I upped to a 120/70.

All the 400 club racers run them sizes too, so scrubs (YUCK!) were readily available for me at the time. I opt for new tyres now though.
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Pete.
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Joined: 22 Aug 2006
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PostPosted: 22:05 - 23 Sep 2012    Post subject: Reply with quote
Frost wrote:
19.1T Laughing

or if you can stick a 35 on the back the front would need to be 18.069132963T, so an 18T front would basically be exactly what you'd want.


This, 19T. It's close too - you'll lose about 0.5mph off the top speed.
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