[Stef Marazzi]

Need some clever science/physics person to explain this to me. Or at least someone with a power meter.

Our cycle group is doing a silly hilly bike ride up Crowcombe Combe and Draycott steep.

Everybody is panicking and swapping cassettes and chainrings over before Sunday.

I have a 30 tooth chainring with a 27 toothed cassette on 105 Chainset (Triple)

My mate has a SRAM 1x Chainset

He has a 40 toothed chainring with a 36 toothed cassette.

So our gearing is 30/27 or 40/36 – both at 1.11 ratio.

Both ratios are therefore exactly the same.

I know from by gear calculator app, that in theory, if we were going up a hill at 90RPM, we would both go along at 7.9 Miles per hour.

In my opinion, it would “feel” exactly the same to ride up a hill. (assuming both bikes weighed the same, our bodyweights were the same, crankarms the same etc)

Another friend says that the Triple, with the 30 tooth Chainring would actually still feel easier to turn the cranks round, because of Torque.

But, due to my lack of physics understanding, I dont understand why this would be the case. and if it was true, How much easier would it be?

So my  question is which is easier to turn? Is one easier than the other? Would one method use less watts than the other?

If there some kind of calculation that could be worked out?

And if the triple is easier to turn, and uses less watts, why isnt everybody riding triples? (Hey I know I should drink Triples and not ride triples, but it came with the bike and at the time I hadnt read the velominati! :-p  )

I guess this question could be applied to any single bike, where the ratios overlap, e.g. is the smaller chainring version of a gear ratio always actually easier to turn the pedals, and uses less watts, than the big chainring version of that ratio?

I found this article, but never really had a definite answer.

Sur la Plaque: Mechanics of the Big Ring

I’m hoping some of you guys with experiences of power meters will have tried “overlapping” gear ratios and have noticed a measureable effect.

Comments please!

 

 

 

 

 

 

 

Topic

[CXR94Di2]

Carton wrote:

CXR94Di2 wrote:

Ratios are the same, it will come down to weight and power applied who gets up quickest/easiest.  Weight being the important factor.  A 100kg rider with 300-325watts climbing will get beaten by a 75KG rider producing 235-250Watts on a longish climb

They’d actually get there pretty close. With W/Kg within the same range, aero comes into play. Push comes to shove I’d put my money on the heavier guy on flatter climbs and the lighter guy on steeper climbs.

 

Gravity will eventually tire the bigger rider first on steeper climbs.  I agree that less steep power wins most times.  I have seen this when racing against lighter riders on Bkool, I can power away on slopes but then get pulled back on steeper hills

[P3t3]

Darren C wrote:

Actually, I disagree because if you think of the crank arm as a lever with the chainring being the load partway up the arm, then physics shows that the further the distance between the place where the force is applied and the load the greater the torque. So the smaller chainring will require less force as its load is closer to the fulcrum, making the crank arm a longer lever, think of how you use a crowbar, that can lift a much higher load than say a screwdriver even though you are applying the same force or why using a wheelbarrow you can lift much higher loads than just by carrying it by yourself (the load is close to the fulcrum with a long lever, the handles), that’s my theory anyway!

 

 

The crank length and the wheel circumfirence remain constant though.  These are your inputs/outputs.  What the gearbox does in between isn’t governed by its physical size, but by its gear ratio, which is ultimately the equivalent of your lever length.  

Basically your nonsenese needs a re-think! 

As an aside, and on your average wheelbarrow the fulcrum isn’t right at the front of the barrow so if you load the front of the barrow properly it doesn’t take much lifting.  

 

[fukawitribe]

BBB wrote:

BBB wrote:

It’s been established that larger chainrings/cogs combos have higher mechanical efficiency due to lower chain friction (see the huge jockey wheels that some pros use).

The diffrences are probably marginal.

 

Friction Facts did a test on this a wee bit ago, quite interesting and along the lines of what you might suspect regarding radius of curvature and chain line effecting friction.. was slightly surprised at the magnitude actually.

http://www.bikeradar.com/road/gear/article/friction-facts-free-speed-from-proper-shifting-44016/

[BBB]

It’s been established that

It’s been established that larger chainrings/cogs combos have higher mechanical efficiency due to lower chain friction (see the huge jockey wheels that some pros use).

The diffrences are probably marginal.

 

[wycombewheeler]

Same ratio means sane pedals
Same ratio means sane pedals turns per metre and same force multipliers. But the chain will move further on larger rings. Does your mate have an old rusty chain that results in significant extra friction? Fit a new chain or lube it. Or maybe larger rings and cassette weigh more. Maybe if you carry his spare tube for him it will balance up.

[Stef Marazzi]

What this debate needs, is
What this debate needs, is someone with a power meter to go and overlap some identical gear ratios and test it.

[Darren C]

Paul J wrote:

Paul J wrote:

Assuming other factors are the same (e.g. chain line), the larger ring should be slightly easier. Because the chain follows a longer circumference around, and hence the links have to turn less, which should mean slightly lower chain friction losses.

Actually, I disagree because if you think of the crank arm as a lever with the chainring being the load partway up the arm, then physics shows that the further the distance between the place where the force is applied and the load the greater the torque. So the smaller chainring will require less force as its load is closer to the fulcrum, making the crank arm a longer lever, think of how you use a crowbar, that can lift a much higher load than say a screwdriver even though you are applying the same force or why using a wheelbarrow you can lift much higher loads than just by carrying it by yourself (the load is close to the fulcrum with a long lever, the handles), that’s my theory anyway!

 

[Carton]

CXR94Di2 wrote:

Ratios are the same, it will come down to weight and power applied who gets up quickest/easiest.  Weight being the important factor.  A 100kg rider with 300-325watts climbing will get beaten by a 75KG rider producing 235-250Watts on a longish climb

They’d actually get there pretty close. With W/Kg within the same range, aero comes into play. Push comes to shove I’d put my money on the heavier guy on flatter climbs and the lighter guy on steeper climbs.

[Paul J]

Assuming other factors are
Assuming other factors are the same (e.g. chain line), the larger ring should be slightly easier. Because the chain follows a longer circumference around, and hence the links have to turn less, which should mean slightly lower chain friction losses.

[kungdog]

I cycled up Draycott Steep a

I cycled up Draycott Steep a couple of weeks ago. Just past the hardest part, I passed a woman parked up. Out the window she said “well done” and offered me an orange!

[The Gavalier]

Welsh boy wrote:

Welsh boy wrote:

giff77 wrote:

rather than looking to the velomati,  I would refer to sheldon brown in regards to the physics and mechanics of the bicycle for a greater insight of all things velo. 

I would not trust Sheldon Brown as a source for reliable physics, last time I looked he was talking rubbish about the length of crank altering gear ratios.

Is that why giff77 seems to think a 175mm crank will give a 3% lower ratio than a 170mm on the same gearing? I’m surprised nobody has picked up in this.

[CXR94Di2]

Ratios are the same, it will

Ratios are the same, it will come down to weight and power applied who gets up quickest/easiest.  Weight being the important factor.  A 100kg rider with 300-325watts climbing will get beaten by a 75KG rider producing 235-250Watts on a longish climb

[pruaga]

Imagine a two different see

Imagine a two different see-saws*, on with a 10 kg weight half way along one end and the other with a 5kg weight at the end.  Which would be easier to lift?

 

*weightless, frictionless, in a vacuum, perfect.

[Welsh boy]

giff77 wrote:

rather than looking to the velomati,  I would refer to sheldon brown in regards to the physics and mechanics of the bicycle for a greater insight of all things velo. 

I would not trust Sheldon Brown as a source for reliable physics, last time I looked he was talking rubbish about the length of crank altering gear ratios.

[Judge dreadful]

If I’m going for hills, I use

If I’m going for hills, I use a triple up front ( 50:39:30 )and a 9 speed 12-27 cassette. I’ve not found a climb that I can’t get up with the 30 / 27. I find the triple gives me a lot of flexibility.

[Author]

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