Jimcee

Thanks for the info.I recently moved from NYC to Milford Ct.When I lived in the city I rode a mountain bike & because of heavy traffic had to be vigilant.In the past year I bought a Raleigh road bike.In addition to type 2 diabetes,I have lower back pain & a touch of arthritis in my left knee.I'm 5'7" 200lbs & the only exercise I can do is biking.I was a long distance runner,but back problems ended that.I try to bike 4-5 times a week for 1hr to 1 1/2hrs.It's when I bike 2hrs plus that I start having pain in the lower regions.I've found a small bike shop nearby where I'll ask about the seat & shorts.Thanks again

Jimcee

Thanks for the info.I wrote a reply,but it didn't post

hefeweizen

You guys are great!

McBTC

Put these two gear ratios into BikeCalc.com and both are 2.2 gear inches. Facts are facts.

rawly old

Correct, absolutely correct. However one offers considerably more leverage against the pedal
being more distant from the fulcrum.

Archimedes once said," Give me a place to stand, and I shall move the world," He was referring to leverage.
Think of your 170mm crank as the lever & the chainring as the fulcrum. Your pedal will be closer to a 39T
ring than a 24t ring. the further from that ring, (fulcrum), the more leverage you can exert. Basic physics.

McBTC

I'm no expert but I don't believe you have a proper handle on the physics. The crank arm is the lever; and, the bottom bracket is the fulcrum (axis or pivot). Your leg of course provides the turning force. Gearing does not change the length the lever arm, nor the amount of force (or power) that a cyclist is capable of generating.

When looking at bicycle gearing, calculating the inches of travel makes sense because it takes into consideration the circumference of the wheel that is being turned-- all else being equal, just going to a smaller wheel will increase torque...

rawly old

[QUOTE=McBTC;19158682]I'm no expert but I don't believe you have a proper handle on the physics. The crank arm is the lever; and, the bottom bracket is the fulcrum

The 'Fulcrum' changes every time you move from one chain ring to the next. That's
what gears do. I'm sorry you don't grasp the concept. Probably diminished blood
flow to the brain. you should ride more & post less. It will improve function.

DougG

The force applied by the tire to the tarmac is determined by the ratio of the crank arm length to the radius of the rear tire, multiplied by the gear ratio. Period. All of this analysis of intermediate forces and torques gets canceled out. Yes, it is true that you are applying more torque to a smaller chainring than to a larger one, but this is exactly canceled out at the rear wheel as the smaller cassette cog applies less torque to the wheel than does the larger one!

One can try this out on a typical road bike by comparing the effort of pedaling a 50/25 gear combo to 34/17 (or something similar depending on your gearing).

McBTC

[QUOTE=rawly old;19158851]I doubt it but thanks for making me feel so much smarter than I really am...

McBTC

All fine up to here-- in this instance a call out to subjective reasoning can only perpetuate scientific ignorance. Old Rawly already informed us about what he knows, "for a fact & utterly without a doubt that it is easier to pedal a 24/11 that it is to pedal 39/18. I have bikes on which I can use both arrangements, and I have tried both! there is significantly less resistance with the 24/11. I am not imagining it."

rawly old

[QUOTE=McBTC;19159333]Perhaps you think this is just something I made up of the top of my head, But I
can assure you it has been tried, tested, & proven. Though the ratio is the same
24/11 is easier to pedal than 39/18. I'm glad you feel so much smarter than
you really are. And Doug, No it's not. All either of you need do is try it, but
your stubborn mind set & ego will never let that happen.

It's really extremely simple, 24/11 has a mechanical advantage due to increased leverage!

McBTC

... by the seat of your pants.

Speedskater

If the ratios are the same then the resistance should be the same. If it's not, then there is a problem in your drive-train.
If anything, because the chain has to wrap around a smaller radius with the 24/11 the drag might be higher.

McBTC

It could be that a combination of smaller rings means there will be less friction (fewer teeth) so perhaps less resistance (except that there might be a lot more friction between the links of the chain because the chain is wrapping around a smaller radius as you mentioned) but then, the smaller rings would result in a slower moving chain so maybe there would be less rotating mass to deal with, but... irrespective of what Old Seat of the Pants may believe, none of this has anything to do with a change in leverage since the length of the crank does not change and the fulcrum would still be the center of the bottom bracket.

Speedskater

Small chain-rings have more friction than large ones. But it would take some good equipment to measure the difference.

10speedBill

First, the arithmetic in Spoke Calc is rounded off. Let's get it right.
The 24:11 ratio = 2.181818....
The 38:18 Ratio = 2.11111.....
So, the 24:11 is about 3% lower than the 38:18, and therefore is in fact easier.
Now with that said, if the real ratios were identical, there would be no difference in pedal force. The longer chainring lever length on the 24:11 is offset by the shorter lever length on the 11 tooth cassette gear. The analysis that the true measure is the wheel inchs per pedal revolution is the correct analysis. In the real world, there is a tint difference in the force required caused by friction differences between the two different combinations.
There, now go ride your bike and pedal however feels best to you.

McBTC

And, a 39:18 ratio is...?

peterws

Is this STILL raging? I`m surprised that somebody`s mother hasn`t yet been brought into the fray . . . .Curmudgeons Rule!

Don`t ask . . .

For the record, when I (rarely) use the small chainwheel in anticipation, I invariable change up on the gears so the ole legs rotate at the same liesurely pace . . . never noticed any change in effort needed.

So there you are! End of.

tsurr

come on admit it, you can't agree to disagree********************?? so what, move on

Wildwood 

Repeat an inaccurate statement often enough and someone besides yourself will likely believe it.

Ronno6

During the mindless seemingly unending miles of distance riding (long,long ago) I used to amuse my mind wondering this very conundrum.
It had been precipitated by reading that at Indy in 1967, the Granatelly #40 Turbine car, which was 4 wheel drive, somehow divided the applied power 60% to the rear wheels and 40% to the front (or, something along those lines.) The only way I could figure that was by differing gear combinations arriving at the same ratio, assuming front and rear tires were the same size (also unknown.)
I had posed this question some time ago on the Bike Mechanics thread, and as I recall, the determination was that the large/large combination was potentially easier due to the larger diameters resulting in more chain wrap at reduced deflection angles between links. But, I would have to revisit that thread to be sure.
Anyway, I thought I was looking forward to joining this group in 3 months or so, but now I'm not sure. Y'all are far too cerebral for my capabilities.........

McBTC

Each wheel travels a different distance when cornering so a fixed split between front and rear is no long good enough (except on wet and slippery surfaces)-- we also need a differentials between the axles of 4x4s...

Ronno6

Ummmmm....what??

I'm sure that the STP #40 Turbine Racer had front and rear differentials to handle the distance difference between inside tire and outside tire arcs...........that is not the point of my ponderance...

The issue is: how did the designers achieve a power differential between front and rear wheels?
For example, say the turbine generated 500HP. (actual HP was 550)
How did the Ferguson 4 wheel drive system transmit 40%, or 200HP to the front wheels, and
60%, or 300HP to the rear wheels??

McBTC

Viscous couplers?

Ronno6

It didn'
t even have a CV joint in the driveline....if it had, it probably would have won..............