unravelling Gearing theory and formulae

[jimboalee]

As I have mentioned before on other threads, my uncle rode competitively for the Royal Air Force at the same time Charlie 'Dancing uphills' Holland was riding.
Charlie was a member of the Midland Cycling and Athletic Club and Charlie's brother ran a newsagent in Sheldon, East Birmingham through the seventies.
Crowthers Cycles ( Tom Crowther of Mercian Cycles fame ) had his shop about two miles from Sheldon at Hobs Moat, Olton, Solihull.

Janet Crowther was a member of Beacon RRC with June Pitchford in the seventies, just as I was a nuisance young lad whole had his beady eye on a Peugeot 531 race bike.

When the time came for the purchase, I slipped out about my uncle John and Charlie.

The original equipment Pug was too high geared for a half fit junior, so Tom and his wife Ethel ?? can't remember, suggested a re-gear to a funny little 'reciprocal of what??'.

I then learned about the witchcraft.

 

[earth]

Ok,

I followed your calculation and plugged in the following values:

Fat 21%
BMI 23.1
Height 170cm
Weight 67Kgs
BMR 1609
Bike + Kit 9.5Kgs


I calculated the BMI and fat using measurements and web calculators then used my WW scales and found they both came up with the same result - remarkable!

Body Fat < 22% therefore no reduction in gear inches.
Bike = 1/(9.5*2.2)=47 gear inches

Drive Wheel Diameter = 26.3

47/26.3 = 1.78

Ratio of 1.78 required (for 10% hill at what speed cadence? - this bit I don't understand)

My small front chainring is 39

So 39/1.78 = 21.9 ... 22

So all that worked out to 39/22.

Well thats interesting but I dont think I would like to go up a 10% hill in 39/22.

Can you explain further?

 

[Sittingduck]

I dread to think what the calculations would say about my required shortest gear length. It's currently 34.5 but I know I need something a tad less to haul my lardy ass up big hills

Anyway - thanks to Peanut and Jimbo for this thread... very interesting stuff all this...

 

[peanut]

well just in case everyone now has a mental picture of a deformed fat git with arms like a urangatan on a bike I'd better post a picture

see i'm not that deformed am I ?

 

[garrilla]

Great thread guys.

Will a helmet help?

 

[MacB]

Great thread guys.

Will a helmet help?

yes, as you labour up a sharp incline, in too large a gear, the helmet will save your bonce as you fall from the bike in exhaustion

 

[Speck]

well just in case everyone now has a mental picture of a deformed fat git with arms like a urangatan on a bike I'd better post a picture

see i'm not that deformed am I ?

Two horsepower Peanut

 

[jimboalee]

Two horsepower Peanut

Rumour has it Orangutan muscle is four times as strong as human muscle.

If Peanut can manage 385 Watts up his stairs, 4 x that is OVER 2 hp

Fancy a transplant ?

 

[Davidc]

Just worked through the same calculation for getting me up Blagdon hill, and it says I need 22"

 

[jimboalee]

Rumour has it Orangutan muscle is four times as strong as human muscle.

If Peanut can manage 385 Watts up his stairs, 4 x that is OVER 2 hp

Fancy a transplant ?

Fancy a chat about Genetically Modified Peanuts ?

 

[Scoosh]

Two horsepower Peanut

Which one are you ?

 

[jimboalee]

It would be interesting to see if, in a month or two, some young upstart publishes an article in Cycling Plus Magazine about an easy way to decide what gears to fit on your bike.

My solicitors hold a hand written explanation of the technique, dated and sealed YEARS ago.

So abandon all plans to take credit for something you read here.

 

[jimboalee]

It would be interesting to see if, in a month or two, some young upstart publishes an article in Cycling Plus Magazine about an easy way to decide what gears to fit on your bike.

My solicitors hold a hand written explanation of the technique, dated and sealed YEARS ago.

So abandon all plans to take credit for something you read here.

I say this because I have just been reading BikeRadar's "Myths Busted" feature.
The myths busted were predominantly subjects discussed on this chatboard over the last three or four months.

I am wondering who ( because there is always a University professor casting judgment ) is going to bust my myth?

 

[peanut]

It would be interesting to see if, in a month or two, some young upstart publishes an article in Cycling Plus Magazine about an easy way to decide what gears to fit on your bike.

My solicitors hold a hand written explanation of the technique, dated and sealed YEARS ago.

So abandon all plans to take credit for something you read here.

ok Jimbo don't get carried away mate

I thought that the results were quite interesting but wouldn't say a single test had proved anything.
Someone else pointed out that if you reduced my bike weight by 5lbs to 20lbs the result was nothing like the gearing I have on my bike.

I'm far from convinced that lightening my bike by 5lbs would reduce my gearing needs by 10" + or 6x sprocket teeth, ie 32" to 42" which is what your formula would suggest.

 

[jimboalee]

ok Jimbo don't get carried away mate

I thought that the results were quite interesting but wouldn't say a single test had proved anything.
Someone else pointed out that if you reduced my bike weight by 5lbs to 20lbs the result was nothing like the gearing I have on my bike.

I'm far from convinced that lightening my bike by 5lbs would reduce my gearing needs by 8" + or 4x sprocket teeth, which is what your formula would suggest.

You'll be surprised.

When you get to a hill and lift your backside off the saddle, you will notice that missing 5lb.

I've got a 24lb Dawes and a 17lb SWorks. 7lb difference. I climb up the 10% in Tanworth in Arden in 42 x 19 on my Dawes, but 53 x 21 on the Spesh.
A 15" difference.

The difference is 7lb reduction in total weight. A 30% reduction in the 'dead weight' I am heaving.

Now for more fireworks.

This is 'Technical - Know How'.

Imagine a hod carrier on a building site reducing his brick count by 30%, he'd think Christmas had come early

Imagine 'Donkey calf' raising. Load up the stack until you can only rep 10 in a set. Now reduce the stack by 30%. How many reps can you do now? Its a damned sight more than 15 !!
The 'dead weight' has reduced by 30% and your bodyweight stays the same. ??? Very strange.

The normal method of deciding where to start on a weighs stack is to do 1 rep to failure. Note down that weight.
Reduce it by 25%. Now that is a 8 - 10 rep set. How does that compute

The 'Donkey Calf' raise includes most of your bodyweight in the lift, but it still follows the same deduction methods as the bench press and side lateral raise.

So why is a bicycle different?