Push bike gears (maths type question)

S@njay

S@njay

S@njay

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Honnestly did not know where this thread should go, but its all in the name of push bike gears.

Say if one mountain bike had 18 gears and one had 21 gears.

Is 5th gear the same on both bikes? (i.e. 1-5, 1 being the 1/3 cogs, 5 being 1/5 cogs, i.e 1 on the left shifter, 5 on the right shifter!)

But if this is true, then 18th gear on both bike would be 3-6, but how could that be? Becuase on the 21 speed bike, 3-7 is 21st gear, where did 19 and 20 go?!

How do you actually calculate the gears on a mountain bike, i allways presumed it was multiples, but then that dont work!

Or having 18 or 21 gears dont actually mean you have gears from 1 - 18 or 21, just means there are 18 or 21 different gear settings?!
 
It depends how large each of the wheels is, and how big the spikey circular things the chain goes on is. :)

Provided both were the same size, then yes, 3rd gear would be the same on an 18 and 1,000 gear bike.
 
S@njay said:
So a bike in 18th gear could have the same resistance of a bike in 21st gear?
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I'd say so. I'm not sure though. There could be some bicycle consortium standardizing gear rations but I doubt it as top gear is a 10 speed bike it pretty tall whilst 10th gear in a 24 speed bike is not very tall at all.
 
S@njay said:
Honnestly did not know where this thread should go, but its all in the name of push bike gears.

Say if one mountain bike had 18 gears and one had 21 gears.

Is 5th gear the same on both bikes? (i.e. 1-5, 1 being the 1/3 cogs, 5 being 1/5 cogs, i.e 1 on the left shifter, 5 on the right shifter!)

But if this is true, then 18th gear on both bike would be 3-6, but how could that be? Becuase on the 21 speed bike, 3-7 is 21st gear, where did 19 and 20 go?!

How do you actually calculate the gears on a mountain bike, i allways presumed it was multiples, but then that dont work!

Or having 18 or 21 gears dont actually mean you have gears from 1 - 18 or 21, just means there are 18 or 21 different gear settings?!
Click to expand...



No...gear ratio is what you need to find the ratio (front and rear teeth) a road bike has higher gearing compared to a mountain bike. Your shifters doesn't really matter. Also you don't use the sprocets furthest away as that stretches the chain (ie front smallest, rear smallest) you keep the chain straight.

3rd gear would not be the same on another bike with different gear ratios for that 3rd gear, unless it's the same bike or has the same gear ratio.
 
/\ ahh i see, denotes the bit i wrote in red then.

Ok, thats cleared a few things out!

But i'm not sure that the whole 1-21 gears has been cleared, from what people wrote, there is no 1,2,3,4,5,6,7,8.... sequence of gears, just a load of ratios avaliable.

My bike never came with an instruction manual on how to use the gears correctly :( (this was 5 years ago!)
 
Or having 18 or 21 gears dont actually mean you have gears from 1 - 18 or 21, just means there are 18 or 21 different gear settings?!
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You might have 21 different ratios but it's likely that some are repeated in there.

Just like Semi trucks, with 2 gearsets you can shift one without shifting the other. Some ratios might be duplicated.
 
You can have up to 3 front chainrings, these can vary dramatically by rider and by purpose. Some people like a 52 tooth big ring, but they tend to be roadies or have thighs the size of your chest.

Not many riders use all the available combinations. You would not for example often see the big ring used with the larger of the rings on the rear, so of the available 21 or 24 permutations perhaps only 50% to 65% of those combinations would be likely to be used.

So depending upon the chainset you've personally chosen will be the ratios avaialable to you. It is quite possible that some combinations of front and rear rings give identical or extremely similar ratios to others.

48:12 being the same as 36:9 for example.
 
It depends on the ratio of teeth between the chainring (front) and the cog the chain is running on at the back. Not the number of the gear.
 
PhilthyPhil said:
Slightly off topic but why do people call bicycles 'push bikes', what does pushing have to do with anything?
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I imagine that very early bikes with poor gearings or single speeds and heavy materials were pushed uphill and ridden downhill.
 
PhilthyPhil said:
Slightly off topic but why do people call bicycles 'push bikes', what does pushing have to do with anything?
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My main reason was that i cant spell bicycle :( (i just copied your spelling)

And bikes sound too much like a "motor bike".

I never knew that the whole gear thing was complex!

I couldn't use the calculator as i simply did not know what my geartrain was :(

All i have a is Raleigh Daytona (a nice simple alluminium ridged frame bike, with shimano parts).

My main reason for asking the initial question was wondering if i actually had a speed advantage of having 21 gears over a freinds 18 speed bike! (assuming the leg power was the same). Which now would mean i have to count both cogs and do some maths!
 
You probably have more ratios which, in theory, means you can keep pumping your legs at their optimal rate whilst shifting to increase speed. However, in real life there's not going to be much difference betwixt a 18 speed bike and a 21 speed bike.
 
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