genericbikedude

I've always been under the impression that any gear combination that gives the same gear inch is more or less equal. Like, a 48x16 is the same as a 51x17 is the same as a 42x14. While there may be small differences in weight and longevity due to the volumes of metal involved, different gears with the same number of inches will behave the same.

At the track, I ride a Fuji Pro, which came stock with a 53T chainring. I use a 16 cog in the back, for an 87" gear. Seems fine to me. Then one of the guys at the track tells me that having such a big chainring will slow me down. I come back and say, "well, I've got a 16 tooth cog, giveing me a gear in the mid-80s." Blah blah blah, and the guy keeps insisiting that with a big chainring, regardless of the size of the cog, it'll be harder to do sudden kicks in a sprint.

This seems like horse****, so I argued with him. Then another guy jumped in with an argument about how the greater rotational inertia, farther from the center of the axis of rotation, would make a larger chainring more difficult...

OK, so you've got a bit of unimpeachable physics there, but the scale is all wrong. going from a 53T to a 47T is a 3-inch change in circumference. Divide this by pi and you get about a 1 inch change in diameter. This cannot possibly be enough to matter in terms of rotational inertia.

Looked at another way, if I took the chain off and put the bike on a trainer, a crank with a 53 would spin about as easy as a crank with a 42. And not a lot different from a crank with no chainring.

Am I wrong here? Somebody please let me know if I'm missing anything, or if this guy was smoking the ready rock.

11.4

At Elite or World Cup levels, most track racers when queried will tell you that there's a difference in the responsiveness between these equivalent-geared cog and chainring combinations. It's not necessarily an obvious issue, but some riders will ride like a 54x18 in training to get an 81 inch gear, simply because they want to keep the feel of the 54 for when they're riding a 54x15 in the pursuit. I hear it too much not to believe it, and from my own experience I definitely turn in slightly faster 200 meter times on a smaller chainring than on a bigger one (compensating in the cog teeth, of course). Angular inertia isn't really the point necessarily, nor is overall weight or anything like that. I've heard a lot of arguments, but top riders who don't even know the gears they're riding and rely on a mechanic and coach to set them up will consistently do better on short power events on smaller chainrings and on longer events on bigger chainrings. This was what Sarah Ulmer discovered when she broke all the records in the women's pursuit, for example. And Theo Bos is pushing some mighty gears and trying to use a 13 in the rear to keep his chainring smaller, especially on tracks like Moscow where speeds get so high.

If I ride with a powermeter on the bike on an indoor track and ride the same interval in different chainrings (I'm riding intervals from 200 to 800 m), and ride right to a consistent wattage level, I feel better on the smaller chainring. If I ride to maximum speed, I do slightly better on the smaller chainring. So go figure. Even with someone else choosing the tooth combinations so I'm not anticipating the difference, I get this result.

So .... for most purposes I wouldn't worry about it. Do worry about gear inches overall -- on the track a couple inches' difference is a LOT in a race, so one tooth difference in the front can really change your performance. And changing wind on the track is really critical for tracks where this is an issue -- I can change gearing all the time if the wind is erratic or the workout or event is changing. But ultimately there does seem to be a difference and most top riders will observe it. I'd also like a better explanation.

genericbikedude

Thanks 11.4. I don't have much experience so I'm inclined to believe you, but I too would like an explanation of why this would be. The guy who originally told this to me had no good explanation, and no real anecdotes either.

Looked at from the other side however, if one wants an 87" gear, would it not then be inadvisable for one to run something like a 39x12? One could do it with an older road chainring (no pins and ramps) and a suntour 12T cog, on a 130BCD crank such as a stronglight. What is the drawback of going too small, or is there one?

11.4

At a certain point (like a 39/12) you start getting more chain noise, which probably means more chain friction, from the tighter turns. Also, since most track equipment is traditionally 144 BCD and since many track hubs have one kind of problem or another with 12 tooth cogs, you have a bottom limit that these days is usually at a 46x13 anyway.

But the real point is that there's a difference in how the setups feel and respond. It's like many madison racers who like to use 3/32" chains because they feel they are more supple and make their legs feel better after long hot nights of indoor racing. I'm not sure how to explain that one either, but every sport has this awareness among top athletes -- pole vaulting, javelin, etc. I wouldn't get torqued about it -- if you can't feel the difference, just ride what you want.

circles

You can get an idea of the difference on a road bike. Most road cranksets/clusters have gearing overlap. Take a 39-53 double and a 13-24 cassette for instance:
39 x 14 = 75.2 gear inches and 53 x 19 = 75.3 gear inches.
Try it with a Powertap on a trainer if you've got access to one.

Six jours

I think it's pretty much been said already: pursuiters tend to like big/big and sprinters tend to like small/small. Anyone who gets too loud about their preference is probably full of shyte, as far as I'm concerned.

My preference was always for big/big. I used an 88 most of the time and prefered a 52x16 to the classic 49x15. I doubt I went any better with it, I just liked the way it felt -- especially with the 3/32", as mentioned. I do believe it's about not bending the chain too tightly around the cog, and if you think about it, it makes a bit of sense: if bending the chain causes a trace of friction, bending it more should cause a bit more friction. In the big picture, though, I'm sure it's meaningless.

The sprinters, OTOH, tended to prefer small/small, and always explained it to me as a "more direct connection", "better jump", etc. which definitely struck me as nonsense. But again, whatever works for you. Heck, I knew a fellow who stuck with inch pitch stuff forever because he felt it gave him better torque!

Bottom line? Men have gone faster than you and me with just about any combination you can install on a bike. I'd find something else to worry about!

Scott H

The world of track cycling is rife with widely held, but wholly BS, myths. The effect of moment of inertia changes between various chainring sizes is one of them. Anyone, and I mean anyone, who claims he can tell a difference between two chain ring/cog combos which result in the same gear ratio is delusional. The relative differences between the weight of one chain ring vs another is so small, and the effect on acceleration even smaller, that it would be hard to measure with technical instruments and virtually impossible to detect by the seat of your pants.

The only possible difference anyone can feel is the effect attributed to the fact that the gear ratios are likely not exactly equal.

Six jours

I can feel a difference between drastically different combos. The 16 cog absolutely feels smoother and runs more quietly than the 12, all other things being equal. And the 53 ring of the road bike definitely feels different than the 39 ring, as just about anyone who's ridden one can attest.

I guess I could say something about anyone not being able to feel the difference is a moron or somesuch, but that wouldn't be very nice, now would it?

ultraman6970

I think the key point in here is to tell genericbikedude why eventhough gears are giving you the same ammount of distance per pedaling, the sensation when riding such combinations is so different.

People forgot to mention something that really basic in here... TORQUE... a BIG COG will have/generate a big TORQUE. This is physics 101, so wont explain this very and important phenomena. Is for many of you known that as bigger the cog the lighter it is. Again physics 101 aka torque.

The rule of thumb is this one "the cog is the one that will command and tell you how hard to move the gear it will become." For example... 47x14 and 50x15 are almost the same... depending on how strong u r or the effect u want to acchieve sometimes is better use the 14 instead of the 15.

I read about sprinters and persuit people, well both races are so different that I doubt a persuit person will even try to run using 47x14 because after the second KM i bet he might feel just like the bike became a panzer tank (i'll talk about the chainwheels later). Lets comeback to physics 101... 15 has more torque than 14, in consequence it is easy to move than 14. Somebody was talking about 39x12? u can't do anything with that in track racing. It will be hard to move or sprint with it, besides try to keep a pace with it? forget about it. (quite bad choice)

Ok... the reality in track is that the chainwheel will give you the hability to do changes in the racing pace, or the chance to give that extra punch in a sprint (forget all about road ok?). In my previous example... 47x14 and 50x15... both are technicaly the same. 47 gives you and extra punch when sprinting, you can accelerate more because it drags more (physics 101)... usually sprinters have somebody who can do race pacing for them (real track team work racing)... in the case of 50x15 thats is just in the midle... not light, not heavy, u can do pacing with it or sprint with it... is like the ideal gear (51x15 is nice also)

Now I'll take 52/53x16... is like the same as 50x15 or 47x14 to start with but... yes again physics 101, 16 has more torque right? is easier to move right? but u need to compensate the lack of inches puting a larger wheelchain right? Well 52/52x16 is quite nice gear but u can't sprint with it. At least in the track u can't sprint because you will feel as pedaling in the air and other guys passing you just like nothing.

Scott H is claiming that is imposible to feel the difference between 2 gear combos if they give you the same ammount of meters (inches) per pedaling. Well you can tell right away that it feels different, is not a thing of being delusional, it is how it is. In the road isnt that big deal after all, but is a mere thing of start playing with the gears in the road bike to feel the difference. An example... is easier to ride with 53x18 than with 39x14/13? lets face it, nobody in his sane judgement will do 100 kms using 39x14 ever. Well i know a moron but he is an special case hehehe...

For those starting in this thing of track racing.. my advice is to start with 48x15 or something like that... for sure at the end of the season all the guys will be using 50x15 anyways.52x16 is justified if you arent that strong and you are strugling while using the 15 t cog. One thing for another... it will be easier to ride but in the sprints you will suffer. One thing for another one.

I won a sprint qualification match in a panamerican in Mar del Plata argentina when junior back in the day using 49x15 and the other guy was using 47x13 i believe (he changed from 47x14 to 13 because i won the 1st match)... it was windy that day I needed to be fast so I move from 51x15 to 49x15. Well ... second match.. he needed to win so I tricked the colombian to start a long sprint (this is when scott H talks about momentum/inertia and stuff) like 400 meters sprint... he bite it! It was too energy consuming for him to use 47x13 and move it fast in a fraction of a second... so I got him tired when we got to the curve... the rest is history for him. This is tactics.... I'm fast but not that fast but i won the match because of his lack of knowledge of "physics 101" and desperation. Usually desparation makes paople do wierd stuff in track but well have a good nite u all



ps: please dont give me the s****T about world cups ok? those guys are not HUMAN!

Scott H

I hear you saying you can tell a difference, and you can say it's physics 101, but you haven't provided any empirical evidence that there is a difference. I still whole heartedly contend that while you may think you can feel a difference (and if you think you do, then it may as well be true since that's all that really matters. Perception is reality, you know) there is no measurable difference.

You feel a difference because you expect to feel a difference because you believe you are going to feel a difference. The laws of physics don't give a damn about how you came about achieving a certain gear ratio... if you are talking about comparing two different ring/cog combos that come to EXACTLY the same gear ratio, then your performance will be the same.

As for previous posters who've stated that they can tell the difference between a 16 and a 12, or a 53 and a 39, well, d'uh... I'd hope you could. But, what you can not do is prove a difference between the affect on your performance by using any ring/cog combo over another combo, assuming identical gear ratios.

I know you can 'feel' the difference. But to say that your 'feeling' has any bearing on things is like saying that wearing a green jersey makes you faster or a red jersey makes you climb better.

Six jours

Oh, I doubt there's any real performance difference. And I don't mean that I can feel the difference in development between a 12 and a 16, I mean I can feel the difference between near-identical developments gotten with different combinations.

Probably true. I was merely responding to the assertion that "Anyone, and I mean anyone, who claims he can tell a difference between two chain ring/cog combos which result in the same gear ratio is delusional."

Perhaps less inflammatory language would catch you less flak.

Yoshi

I would not be surprised if you can feel a difference between identical gear ratios with different sized gears. The more teeth engaged on the chain the more efficient the drive train (well, too a point I'd assume). Overall this will probably have a miniscule effect on performance, but I bet it would change the "feel" to a noticeable degree.

There are more things involved than just the gear ratio. The friction on the chain, the angle the chain forms at the contact point with the gear, the angle between the links on the circumference of the gear, etc. will all effect the efficiency of the drive train.

ultraman6970

Yoshi is right and six jours also, the point is at least for me... yes u can feel the difference... and yes, depends a lot of the person what is the best to use and in what situations. Some people cant use small cogs because they are simply not that strong, solution use another combination more suitable to your conditions, if you have more performance with large cogs than with small cogs, go ahead. Say that people is delusional because they can feel the difference is totally out of context i believe. But well is his oppinion and I dont agree at all because is not a psicological thing, the cruel reality is that u can feel the difference, wonder if somebody have done a test not in the street but in a real track. Because so far I havent heard anybody stating that actually did the test of going to the track and rode with different combos.

Well i havent seen any tracker or ex tracker even say something but people saying "this guy is crazy" but nothing to back up their words more over than the keyboard. I say "try it, ride in a track and then share your experience." I started this thing when i was 12 y/o and ended at 25 y/o because I had to decide between school or the track. I was good but not that good I need to admit that. But well I saw Obree, I ran against the Curuchet brothers back in the day... but well... no i have no clue... too late.. better go sleep...

nites y'all....

Six jours

Oh, I've ridden the track once or twice...

Honestly, I never did any timed tests with the intent of verifying whether one combination was faster than the other. I figured both the "small/small is faster" match race guys AND the "big/big is faster" pursuit guys were full of beans. I do know that I switched from "standard" gears most often based on a 15 cog to "big/big" gears based on the 16 cog simply because I liked the way big/big sounded and felt. It was quieter and smoother. I don't believe it made the slightest difference in times and results. What I had for breakfast, how I trained last week, how well my gut was working at the moment, that puff of wind coming out of turn three... All completely overwhelm any foolishness about big/big small/small.

Somebody put a fork in this thread.

11.4

This is at least somewhat quantitative. When I've ridden with World Cup riders they all see the same -- in fact, some riders will test out tracks for the best ring/cog combination. A very fast track like Manchester can suit a slightly larger chainring but the same final gear ratio, while a slower track will suit a slightly smaller one. Steeper tighter tracks tend to favor smaller chainrings for sprint events. And everyone is on powermeters so their data are based on speed and power output.

CafeRacer

So far the best comment in there is in referance to World Cup riders not being human!

I work with a bunch of old geezers who all raced in their day. All of them tend to enforce the idea of running big and big is smoother on your legs but small and small is better for sprinting. I dont buy into it 100% but theres 2 other things to consider.

-With smaller chain rings and cogs its easier to have a couple warm up gears and not have to have a massivly long chain or extra links.

-small cogs generate more noise witch is friction. Anyones bike gets louder as they go from their warm up gear to race gear. Espessialy a 13 tooth. I know a guy who does over gear work on a 12 and its the loudest thing Ive ever heard! There is a point where cog size isnt efficient any more, but on the same note Top level sprinters are such perfect pedalers that effeciency isnt such an issue.

I agree that itsa bit of Bullchit but then again when I get preached too I dont hide the fact Im on a 45/13

Keith99

Of course there are differences. A simple mental excercise will confirm it. Imagine you are running with an 8 tooth in the back. Good chance it will actually fail. The larger the chain rings the smoother and the chain has to chance angles when going over the gear less.

Now how noticable it is is a different question, but it would not be that difficult to cover the drivetrain and test if someone can tell the difference.

tuz

If the angle at which the chain bends around the cog/chainring is the cause of friction, noise, etc... (personally I can't comment on the feel) then yes there is a difference between equal gearings but with different ring/cog combination.

A chain around a sprocket will form a polygon with T sides where T is the tooth count. The angle is then (T-2)*180/T degrees (check wikipedia).

Changing from 40 to 52 T changes the angle by 2 deg (2% diff). Keeping the gearing around 83", we have a 13 or 17 T cog at the rear. The angle difference is 6.5 deg (4% diff).

Having larger rings will require more chain (more weight) and increase slightly frontal area. I'm no track rider so wouldn't know if those make a difference.

I'm wondering... Is the torque on the hub threads under pedalling only a function of gear ratio, or does it increase with a bigger ring/cog combo?

Boss Moniker

Torque is only dependant upon gear ratio, not just your cog (well, assuming constant crank length and wheel diameter, which everyone seems to be sticking to so far). Ultraman doesn't seem to understand this.

I do believe there is a very, very slight difference that is the result of many factors, including small changes in gear inches (because with integer tooth counts, the diameters of the chainring/cog are restricted to specific values, and these can be close but rarely line up perfectly unless they are whole number multiples), small changes in friction, and small changes in weight. The rest is strictly psychological placebo and tradition.

Statements like "you can't sprint on X*Y gear ratio" are abolutely 100% erroneous, though. For a good 99% of track riders out there the difference is so negligable so as to be unnoticable.

This is an interesting discussion, though.

tuz

Thats what I though: torque creates angular acceleration, which is constant at a given gear ratio and, like you said, crank/wheel size. Intuitively I though that a bigger rear cog would have more torque somehow...

Good point btw. Minute gear changes could probably be felt.

11.4

All this assumes 100% efficiency in power transmission. While I don't have a really good explanation for why there seems to be a difference, when you go to small cogs you are losing transmission efficiency. That's part of what a lever arm contributes in real life, and a bigger cog is a lever arm as well. I only mention this not as an answer but to dispel absolute belief in the point made above, since it's a theoretical argument that is impaired by real life efficiencies. Good thinking, though.

CafeRacer

Why doesnt everone just relax....sip some tea.....and then agree that weather or not it is phyicaly faster or not its not worth debating for another 100 years No socks and small cogs is just how sprinters do it.......

obstacle

Very nice post. Great information here!

Pista Largo

I suspect the difference is that a larger chainring will flex more under load than a smaller one. For ordinary mortals this isn't much of an issue, but for elite riders it well may be. It strikes me that improved chainring rigidity is the main reason to ride 1/8" equipment rather than 3/32"

ultraman6970

?? if it was like that all the sprinters in the tour the france would be using 1/8 chainrings my friend. They sprint using 53x11 or 10 with a super narrow chain but who knows at this point

Can u imagine a campy 10 sp using a 1/8 chainring? darn... well its too late and im drunk!

cya!