Gearing question

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Anonymous's picture

Gear Inches based on 700x23 tire with 700mm cranks downloaded from Sheldon Brown's web site.

A 53-23 gives me 60.6 gear inches. A 39-17 gives me 60.3 inches. For the sake of the question, lets assume that there is no cross chaining or any other friction factors. For the sake of the question lets also assume that the gear inch numbers are equal.

Which gearing is harder to turn? Or are they both the same? Does the smaller chainring in the front make it easier to turn a smaller chainring on the back. Or is it easier to turn the bigger gear option. Or do they cancel each other out and there is absolutely no difference.

I think there is no difference, but for some reason I cannot convince myself of this.

Anonymous's picture
bike man (not verified)

No friction factors, no differece.
Of course, cross chain could be good for up to a 10% loss.

Anonymous's picture
Hank Schiffman (not verified)

All other factors being equal, the higher the number of inches, the harder it is to turn the pedals. The difference you present is probably statistically insignificant. We are looking at a closed system. Whether there is a bigger chainring than a cog or the other way around will make no diffence if the number of teeth don't change.

Anonymous's picture
JP (not verified)
Larger chaining, smaller cranks.

I hope you meant 170 mm cranks! Could you imagine 700s ?

I had your exact same question a while back and while I had no scientific resolution, I did finally settle on agreeing that the larger the chain ring, the tougher the turn. So, the 53 x 23 will seem tougher than the 39 x 17 in your abstractions. I say abstraction, because you really cannot disregard chain friction. Also, I think the “toughness” may well be only off the line, on the start up where you have to mash. Once you get spinning, I can’t see that it matters.

Anonymous's picture
Christian Edstrom (not verified)

If the gearing is exactly the same, say 60.5 inches, and the chainline is perfect in both instances, a larger chainring and larger sprocket will be easier to pedal because the chain is making a less severe bend around the rear sprocket, and each link is rotating less relative to its neighbor, inducing less friction into the system. This assumes to identical new clean chains, and a new chainring and sprocket.

I'm guessing that the difference in effort is on the order of 1/10 of a percent or less (possibly far less) and would be obviously imperceptible to a rider.

The decreased chain friction could be weighed against the increased weight of the larger components, but since the question was which gearing is harder to turn, we'll ignore that.

So, in short: If the gearing is the same, they're exactly the same to you. To finely tuned laboratory testing equipment, there might be a small, but measurable difference.

Obviously, in your example, the 39-17 is easier to turn.

- Christian

Anonymous's picture
Mordecai Silver (not verified)
Larger chainring and cog = more efficient

"Assuming gear ratio and chain line are exactly the same, the larger chainring and larger cog will be more efficient. Two reasons:

1) Tension is inversely proportional to the chainwheel radius. As chainwheel size decreases, tension and the resulting frictional losses increase (frictional force is proportional to the normal force between surfaces).
2) The angle of articulation for smaller cogs is larger, meaning that the chain is bending more sharply as it goes around the cog, causing greater frictional losses.

These inefficiencies are partially offset by lower chain speed for a smaller chainring/cog combination.

Decreased efficiency causes decreased chain and sprocket longevity.

In setting the hour record, where drivechain efficiency is very important, no one except Obree has used a 12t cog. Tony Rominger set his records in 1994 on a 59x14 and 60x14."

Anonymous's picture
Christian (not verified)

Not to mention that to the casual observer, you look incredibly strong running a 60x23 fixed gear.

Hehe. Perhaps I'll build a 60x23 fixed gear.

- Christian

Anonymous's picture
a former editor (not verified)
just watch out for. . .

cement posts. ;-)

Anonymous's picture
Christian (not verified)

My new rig is here. It'll be built within the week. I went over-the-top randonneur chic this time.

- Christian

Anonymous's picture
Tony Rentschler (not verified)
Details please

Well, what'd you get? And don't leave anything out!

Anonymous's picture
Christian (not verified)

"I got a ""Joel Green"" Rivendell Rambouillet with a cream headtube and front rack braze-ons for a Nitto or supersecretcustom* front rack and direct fender mounting

Here's what I'm dressing it with:
Nitto Pearl 11 stem
Nitto 177 Noodle bars
Ultegra headset
Salsa Shaft seatpost
Brooks B.17CS (honey)
NOS Suntour Superbe Pro calipers and non-aero levers with gum hoods and cream housing
TA Zephyr 48-36 crank (may be 48-36-24, or Sugino PX 42-28)
TA Axix bottom bracket
105/MA-3 wheels (temporary)
Berthoud stainless 700x40 fenders with leather mudflap
Viva off-white cloth tape, wrapped over cork and shellaced
White Velox plugs
XT fd, Ultegra rd, 9sp DA d/t shifters
Michelin 700x25 tires and tubes
Velox rim tape

Still to come: Nitto or custom front rack, Berthoud 2886 bag, small saddle bag, and decaleur de sac, SON hub with E6, and Spanninga battery rear light or JOS CB reflector copy (secret project I am working on).

* supersecretcustom builder doesn't want it known that he'll build custom racks if you beg and plead and beg.

- Christian

Anonymous's picture
Tony Rentschler (not verified)
Just right...

and as it should be. Do you ride brevets around here much/at all? I've always liked the concept of randonneuring, and reading the ride reports, but I'm pretty sure I wouldn't like the reality - at least not for any ride over 200K!

So I took a different tack recently and built a carbon fiber frame. It has a fairly relaxed rando geometry, but there ain't no room for fenders or tires wider than 700 x 25! It's really comfortable though, and it sure is light. Here are a few pics:

Anonymous's picture
Christian (not verified)

No brevets yet, but in a fit of folly, I agreed to ride the NJ Randonneurs 200k in April with a friend of mine. Want to come along?

I love the carbon bike, but I think I admired the XO-Zip you built even more.

- Christian

Anonymous's picture
john segal (not verified)

oh oh, would that be me?

now just ignore me if i start babbling about mt. washington. registration opened yesterday.

Anonymous's picture
Christian (not verified)

I was just going to email you about that. I like hills. Shall we?

- Christian

Anonymous's picture
john segal (not verified)

no !!!!!!!!!!!

Anonymous's picture
Evan Marks (not verified)
"""randonneur chic"""


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