Gear Chart For The Track

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Derny Driver
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Re: Gear Chart For The Track

Postby Derny Driver » Sun Aug 25, 2013 4:29 pm

briztoon wrote:So if I am riding my road bike in it's 53 chain ring, with an 11 cog, I'll roll 130.1 inches or 3.3 meters with one revolution of the pedals. :?:

No.
130 is just a number. Big number = hard gear to pedal. Small number = easy to pedal.

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Alex Simmons/RST
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Re: Gear Chart For The Track

Postby Alex Simmons/RST » Sun Aug 25, 2013 6:12 pm

foo on patrol wrote:Not a hope in hell that a 130" gear will roll out to 10.38 metres. :?

Foo


That's exactly the rollout it will have.

Rollout = gear x Pi

gear = wheel diameter x chainring teeth / cog teeth

In this case a 27" wheel x 53 chainring / 11 cog = 130.1" gear

The rollout of such a gear would then be 130.1" x Pi = 408.7" = 10.38m

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Alex Simmons/RST
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Re: Gear Chart For The Track

Postby Alex Simmons/RST » Sun Aug 25, 2013 6:23 pm

briztoon wrote:Can you explain why different figures are in different colours please.

It's gearism, and shoud be banned. :)

Really though, someone has simply chosen to aribtrarily colour code the gears according to three size categories. Small, medium and large, with gear sizes of 65" and 80" being the artitrary cut over points for each category. As DD says, it's a guide to gears suitable for a road fixed gear bike.

The skid patches is a bit different, and just a way to then not only choose the gear you like using the upper half of the chart, but one that will also over time more evenly wear the rear tyre out should you choose the skid the bike for braking.

The higher the skid patch number, the more evenly you'll wear the rear tyre if you brake that way. A low number will see skids wear the same patch of tyre out and the useful life of the tyre will be much shorter*.

Of course just using brakes would be much better, but we are not talking about sensible cycling here.


* It should come as no surprise that the chain rings with consistently highest numbers of skid patches are prime numbers.

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foo on patrol
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Re: Gear Chart For The Track

Postby foo on patrol » Sun Aug 25, 2013 6:30 pm

Alex Simmons/RST wrote:
foo on patrol wrote:Not a hope in hell that a 130" gear will roll out to 10.38 metres. :?

Foo


That's exactly the rollout it will have.

Rollout = gear x Pi

gear = wheel diameter x chainring teeth / cog teeth

In this case a 27" wheel x 53 chainring / 11 cog = 130.1" gear

The rollout of such a gear would then be 130.1" x Pi = 408.7" = 10.38m


Ok I'm confused now. I have always been of the belief that it was one full 360 revolution of the pedals! :?

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jaffaman
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Re: Gear Chart For The Track

Postby jaffaman » Sun Aug 25, 2013 7:30 pm

foo on patrol wrote:
Ok I'm confused now. I have always been of the belief that it was one full 360 revolution of the pedals! :?

Foo


It is. Lets simplify it for ease of working. Say your front crank is a 55 and the rear is on an 11. Every time you turn the pedals 360 degrees, you move 55 chain links. At the back, the 55 links will spin the rear 11 tooth cog around exactly 5 times. So, one turn of the pedal, the wheel goes around 5 times.

If the wheel is 27" then In gear inches we would call this case as being 5x27 = 135 gear inches.

In terms of distance travelled, each time the wheel goes around it will go 27" x pi on the ground which is 84.8" or 2.15 metres. Try it. Roll your wheel around and see how far it is.

So then. One turn of the pedals is 5 turns of the wheel and in this hypothetical case rollout is 5x27" x pi (135 x pi) inches which in this case works out to 424.1 inches or 10.75 metres.

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Re: Gear Chart For The Track

Postby bigfriendlyvegan » Sun Aug 25, 2013 9:31 pm

foo on patrol wrote:Ok I'm confused now. I have always been of the belief that it was one full 360 revolution of the pedals! :?

Foo


The gear ratio gives you the number of times the cog will rotate for one revolution of the chainring. If you were running a 100 tooth chainring and a 25 tooth cog (for the sake of simplifying numbers), then one revolution of the chainring will give you 4 revolutions of the cog (100/25). If you had 20 teeth on the back, you would get 5 revolutions of the cog for one of the chainring, and so on.

To get the distance that represents you need to know the circumference of the wheel, since each time the cog turns the wheel will turn as well. The circumference is Pi times the diameter. So we have Alex's equation of:

Rollout = wheel diameter x Pi x chainring teeth / cog teeth

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HLC
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Re: Gear Chart For The Track

Postby HLC » Sun Aug 25, 2013 9:34 pm

50x15 = 90 inches.

Therefore, 1 chainring tooth = ~2 inches, and one sprocket tooth = ~6 inches.

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foo on patrol
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Re: Gear Chart For The Track

Postby foo on patrol » Mon Aug 26, 2013 6:42 am

Yep ok, just goes to show you're never to old too learn! :mrgreen:

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Re: Gear Chart For The Track

Postby ldrcycles » Mon Aug 26, 2013 7:07 am

Derny Driver wrote: cadence 110


Ahh that's why. My preferred cadence is significantly slower, more around 90rpm, entering that into Sheldon's calc for my 52-14 gives 43.3kmh, which is exactly where I feel most comfortable on that bike. Out of interest, I changed the cadence to 120 and got a figure of 57.8kmh, definitely getting pretty quick there!
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Derny Driver
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Re: Gear Chart For The Track

Postby Derny Driver » Mon Aug 26, 2013 5:10 pm

ldrcycles wrote:
Derny Driver wrote: cadence 110


Ahh that's why. My preferred cadence is significantly slower, more around 90rpm, entering that into Sheldon's calc for my 52-14 gives 43.3kmh, which is exactly where I feel most comfortable on that bike. Out of interest, I changed the cadence to 120 and got a figure of 57.8kmh, definitely getting pretty quick there!

90 is about right for road riding. In an individual pursuit on the track the optimal cadence is around 106-108. From a standing start getting a 100 inch gear up to around 56kph in half a lap takes a big effort. Then the rider settles back to around 52 kph at that cadence around 105-110 and has to do 11 and a half more laps without losing any speed at all. For me, I find individual pursuits and points races the most fascinating to watch.

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Re: Gear Chart For The Track

Postby dalai47 » Mon Aug 26, 2013 5:53 pm

Derny Driver wrote:For me, I find individual pursuits and points races the most fascinating to watch.


Great to watch, hard to race well... :wink:

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