More on gearing.

[jimboalee]

More on gearing. ( not 'moron gearing' ).

Many of you will now be familiar with the little equation to determine the gear required to perform a sustained climb of a 10% gradient.
For those who aren't, it is ( 1 / (Bike + luggage) weight lb ) x 1000 = gear inches.

Eg 25 lb of bike and luggage. ( 1 / 25 ) x 1000 = 40.

When this was explained to me, it was assumed the rider was of moderate to advanced physical ability.
Many members of this forum have queried the formula for a 'stout' individual.

I have devised an enhancement.

The United States Navy have a grading for BodyFat% in 'twenty something' men. A guy who is 22% fat is classified as "Acceptable". This will be the threshold for leniency.

My suggestion is :- reduce the gear by 1 inch for every 1 % fat OVER 22%.

Eg. The rider has measured 28% bodyfat. 28 minus 22 is 6, so on the aforementioned bike, the 10% gradient gear would be 40 minus 6 = 34.

The normal reduction of 1 inch per 1 % steeper gradient still applies. If it is a 14% gradient, the 28% fat guy would need a 30 inch gear, or 30T ring to 27T sprocket to make sure.

It would be a very slow climb and no shame would be attributed if the guy got off and walked.

 

[Downward]

I tell you what we give you our data and you can do the sums ?

 

[jimboalee]

I tell you what we give you our data and you can do the sums ?

I'm giving you the methodology for FREE!

If you want me to do the workings, send your details with a ten quid note enclosed

 

[SimonC]

Length of climb and how much power a rider can put out must also be relevant here.

I can power up 10% on big ring - I'm sure many can - and sustain that for about a minute, but if it was a long climb of similar gradient, then I would ride at a sustainable power output, at a decent cadence between spinning and grinding.

So what sort of sustainable power output is used in your calcs, to determine gear ratios.

 

[jimboalee]

Length of climb and how much power a rider can put out must also be relevant here.

I can power up 10% on big ring - I'm sure many can - and sustain that for about a minute, but if it was a long climb of similar gradient, then I would ride at a sustainable power output, at a decent cadence between spinning and grinding.

So what sort of sustainable power output is used in your calcs, to determine gear ratios.

How about working it out for yourself.


Do my sums and find the 10% gear that is correct for you.

You should know your 'natural' cadence, which you ride at to complete a 100 km pop.

What speed is that in the 10% gear?

Go up your gear chart to the gear you are comfortable cruising at your 'natural' cadence and derive the speed. ( I wouldn't be surprised if its 2 x 10% climbing speed )

Cross reference this on your Roadload curve to see the power.


Simples


I presume from the low response to this post, you are all happy with your gearing, so any more moaning "my gears are too high" will not get any free help.

 

[SimonC]

How about working it out for yourself.


Do my sums and find the 10% gear that is correct for you.

You should know your 'natural' cadence, which you ride at to complete a 100 km pop.

What speed is that in the 10% gear?

Go up your gear chart to the gear you are comfortable cruising at your 'natural' cadence and derive the speed. ( I wouldn't be surprised if its 2 x 10% climbing speed )

Cross reference this on your Roadload curve to see the power.


Simples


I presume from the low response to this post, you are all happy with your gearing, so any more moaning "my gears are too high" will not get any free help.

Unfortunately I dont have a roadload curve - presume this comes from powertap or SRM or similar.

 

[MacB]

well my commuter stripped down is 36lbs, so add in pannier etc probably runs around 42lbs, this means a bottom gear around 23 inches needed.

Best I stay away from 10% hills on my commuter

 

[threebikesmcginty]

Blimey - there's a lot to think about isn't there, I usually just get on my bike and ride it!!

 

[Downward]

Blimey - there's a lot to think about isn't there, I usually just get on my bike and ride it!!

Really you should be asking yourself "Can I get up this Hill" and if you can that's fine. If not Ride more.

Maybe this could be moved to Know how cause any beginnner will be losing the will to live.

 

[yello]

Maybe this could be moved to Know how cause any beginnner will be losing the will to live.

Agreed. With all due respect to jimbo this is not really a beginner's topic.

 

[HJ]

Oh no not more about gearing...

I also feel this would be more appropriate to Know How than Beginners, jimboalee knowledge of the subject is rather advanced...

 

[Randochap]

Blimey - there's a lot to think about isn't there, I usually just get on my bike and ride it!!

But some people like to spend more time talking about it.

 

[Breedon]

So when i come to a hill i should now use a calculator+slide ruler and a laptop to see if i can climb it, instead of just chucking it in a high gear and spin

 

[jimboalee]

This SHOULD be in 'Beginners', because as we have witnessed, Newbies go out and buy a roadrace bike without the thought or knowledge of gearing, then come on this chatboard and cry 'HELP!'

With these SIMPLE tools, a newbie can assess if the bike he/she desires has LOW enough gearing to climb the hills in his/her locale.

Experienced and stronger riders like you lot will no doubt find the gearing I prescribe a bit on the LOW side, but to a freshman, they are suitable.

IF,, the newbie takes time to do some homework, choose a bike with his/her new found knowledge and rides out in the satisfaction he/she has a little bit more than a basic idea of how that new bike works, he/she will arrive home PLEASED, not disenchanted because the bike didn't perform as the sales literature said.

Two and a half thousand quids worth of Roadrace bike will not necessarily have gearing to climb up a 20% all afternoon. Is it better the newbie KNOWS this BEFORE he/she shells out their loot?

Tom Crowther explained the 'gear thing' to me and put me in the correct frame of mind to expect the worst when climbing a hill. It did me no harm.

Does it harm you?

 

[Panter]

Hmmmmmm.

Well, as a fat bloke who climbs hills, albeit in a slow, breathless way I have to admit that I just stick it in the small, spikey ring at the front and the big spikey one at the back and just hope for the best

Works for me........