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Sprocket Ratios

Started by teeds, November 06, 2018, 06:58:30 PM

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teeds

November 06, 2018, 06:58:30 PM Last Edit: November 08, 2018, 09:41:58 AM by teeds
Can someone clarify if the GPB gear ratio settings represent the number of sprocket teeth?

Manu

It's Easier to Fool People Than It Is to Convince Them That They Have Been Fooled.

teeds

Thanks Manu.

So based on that is there a bug where, I think with all bikes, 1 tooth change on the rear incorrectly makes more difference in speed than 1 tooth change on the front?

My understanding is that 1 tooth change on the front equates to a 3 tooth change on the rear.

Manu

November 06, 2018, 11:08:06 PM #3 Last Edit: November 07, 2018, 12:00:35 AM by Manu
Supposedly the front sprocket (driver) has a shorter diameter (less teeth) therefore it rotates faster than the rear one (more teeth) when they are connected by a chain. Therefore the change of one teeth in the front sprocket makes more difference in speed than changing one in the rear.

If front sprocket is changed with less teeth = Less bike speed
If front sprocket is changed with more teeth = More bike speed

If rear sprocket is changed with less teeth = More bike speed
If rear sprocket is changed with more teeth = Less bike speed
It's Easier to Fool People Than It Is to Convince Them That They Have Been Fooled.

HornetMaX

Quote from: teeds on November 06, 2018, 09:46:19 PM
My understanding is that 1 tooth change on the front equates to a 3 tooth change on the rear.
Depends on the number of teeth.

Starting from 2 front and 4 rear, ratio is 1/2. If you have -1 front you get 1/4. To get the same 1/4 adding to the rear, you have to do +4 (2/8).

There's no absolutely correct rule like "-1 front = +3 rear" (even if it may be a decent approximation in some usual ranges).

teeds

Fair comment Max, I'm going by my MX experience so probably not ideal for GPB comparison. But regardless of exact ratios I think it still remains that 1 tooth change on the rear will never affect speed more than 1 tooth change on the front as I've never seen a bike with more teeth on the front sprocket than the rear.


HornetMaX

Give a concrete example (numbers) and we can sort this out in no time.

I remember a long time ago I checked GPB calculation of top speed (shown in the garage) and I got the same exact results.

teeds

My logic doesn't seem to have been shot down so i'll get some examples  :)

Only seen this in non stock bikes, stock bikes seem fine.