Any advantage to bigger ring and cog?- Mtbr.com
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  1. #1
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    Any advantage to bigger ring and cog?

    Anyone tried using a 36 or 38 ring with corresponding larger rear cog? Does it run smoother or last longer?

    Conversely, anyone found the lower limit of durability for rear cogs? i.e. a 13T wear out really quick but a 15T is ok...

    Thoughts welcome. Got a 32 ring wearing out and trying to decide if I should go up to a 36.

  2. #2
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    For a given gear ratio, bigger ring and cog simply translates to lower chain tension and subsequently lower cog/chainring wear. I've been running 32's on front and have had no problem getting a several thousand miles out of them. I do rotate and flip them every 500-1000 though which helps. I think the downside of going to larger cog/chainrings is worse than replacement costs every year to 2 years.

  3. #3
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    I guess downsides would be chainring clearance and weight? Anything else?

  4. #4
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    You'll run into ground clearance issues as well. There's nothing wrong with a larger drivetrain, but I would imagine the larger chainrings would be prone to bending easier. You're also going to have just that many more chain links that may break.

  5. #5
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    Depending on what cogs you buy, some aren't available larger than 20t (ie, King). Plus, some larger cogs are more expensive in larger sizes(ie HBC).

    WIth such great availability and low price of 32t rings, it just seems like the best compromise. Salsa 32t rings are a smidge over $30. If you go HBC, they are not much more either (but you'll wait a while).

    However, there may be some advantage in certain circles to saying, "I have a big cog"....
    Last edited by Raybum; 06-28-2012 at 11:28 AM.

  6. #6
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    I have been running 36x20 or 36x22 depending on the conditions. Using the 36 makes everything smoother and means I can go a bit longer between tension adjustments.

  7. #7
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    I went from a 32-16 to a 36-18. It allowed me to run a magic gear type setup with no tensioner..... Also the benefit of longer wear life and lower tension is always a plus......

  8. #8
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    The system is operates more efficiently. The chain does not have move as much to get around the cog, while the friction of the chain going through this motion is small it will be less. The force is spread over more teeth with gives better purchase it is less likely to slip, this will be a key advantage to some riders. Keep in mind there is less torque on the system with a larger front chainring, so even with the same gear ratio the system transmit power differently. This could be a major disadvantage depending on your riding style as with larger rings it will be harder to get up something steep than with smaller rings because of torque even with the same gear inches, but you will be less likely to loose traction due to spinning the tire on the dirt. In theory there should be less bending of chain rings that was mentioned above due to these factors. Everything will wear longer than with smaller rings, and should be easier to maintain.

    As far as clearance I think we are talking about the differnce between a 32 and 36 tooth cog, not necessarly a 32 and a 44 tooth cog, so there is still greatly improved clearance from a set us with a big chainring. I do enjoy the larger clearance that running a single speed offers but chances are in the situation where you are hitting a ring that small there are larger issues at stake, like if you need a 32 tooth chainring to clear something it might be something that you should probably be walking. So I am not sure this is a disadvantage.

    Running this set up is not for everyone. I think it has much greater advantages for the stonger riders and should be avoided by the weaker ones. If you are pushing easier than 2 to 1 then dont waste your time with this. On the other hand if you push big boy gears and can clear your chainring over the rocks you ride over then this could solve many of the problems that you have had with equipment failing in the field. Less chains breaking, less cogs or rings bending, chain tension needing to be adjusted too often. Plus all these parts will wear longer.

  9. #9
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    Quote Originally Posted by cpeterson View Post
    Keep in mind there is less torque on the system with a larger front chainring, so even with the same gear ratio the system transmit power differently. This could be a major disadvantage depending on your riding style as with larger rings it will be harder to get up something steep than with smaller rings because of torque even with the same gear inches, but you will be less likely to loose traction due to spinning the tire on the dirt. In theory there should be less bending of chain rings that was mentioned above due to these factors.
    I call BS on the torque theory...

    If gear inches are the same then the torque transmission is also the same.

  10. #10
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    Quote Originally Posted by febikes View Post
    I call BS on the torque theory...

    If gear inches are the same then the torque transmission is also the same.
    I agree.

    Here is how I see it, comparing large and small gears of the same ratio:

    1. With larger gears, the chain travels a longer distance for each crank revolution

    2. With the same gear ratio, the rider is doing the same amount of work. Work on the chain is chain tension x distance of the chain traveled. So the chain that has more distance traveled has lower tension.

    3. The torque applied to the rear wheel in either case is the same. Torque = r x F, r is the radius of the rear cog and F is the chain tension. The big system has lower chain tension but more leverage (bigger r), while the small system has higher chain tension but lower leverage.

  11. #11
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    There are benefits to using a larger chainring and cog. It is correct that the torque is equal with the same gear ratios, but the tension on the chain and the load on the teeth can vary a lot with different diameter cogs.
    Example:
    F = 50 lbs force at tire contact patch (assuming equal traction)
    D = 27 tire diameter
    T = Torque = F*(D/2) = 675 in/lbs
    16T cog = 2.563 pitch diameter
    22T cog = 3.513 pitch diameter
    16T Chain tension = T/(PD/2) = 527 lbs
    22T Chain tension = T/(PD/2) = 384 lbs
    Now assuming the chain wraps around 180 degrees with equal load on each tooth
    16T tooth load = 527/8= 66 lbs force per tooth
    22T tooth load = 384/11= 35 lbs force per tooth
    A larger cog will put less load on the chain and cog which will make parts last longer and reduce breakage

  12. #12
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    Quote Originally Posted by cpeterson View Post
    The system is operates more efficiently. The chain does not have move as much to get around the cog, while the friction of the chain going through this motion is small it will be less. The force is spread over more teeth with gives better purchase it is less likely to slip, this will be a key advantage to some riders. Keep in mind there is less torque on the system with a larger front chainring, so even with the same gear ratio the system transmit power differently. This could be a major disadvantage depending on your riding style as with larger rings it will be harder to get up something steep than with smaller rings because of torque even with the same gear inches, but you will be less likely to loose traction due to spinning the tire on the dirt. In theory there should be less bending of chain rings that was mentioned above due to these factors. Everything will wear longer than with smaller rings, and should be easier to maintain.

    As far as clearance I think we are talking about the differnce between a 32 and 36 tooth cog, not necessarly a 32 and a 44 tooth cog, so there is still greatly improved clearance from a set us with a big chainring. I do enjoy the larger clearance that running a single speed offers but chances are in the situation where you are hitting a ring that small there are larger issues at stake, like if you need a 32 tooth chainring to clear something it might be something that you should probably be walking. So I am not sure this is a disadvantage.

    Running this set up is not for everyone. I think it has much greater advantages for the stonger riders and should be avoided by the weaker ones. If you are pushing easier than 2 to 1 then dont waste your time with this. On the other hand if you push big boy gears and can clear your chainring over the rocks you ride over then this could solve many of the problems that you have had with equipment failing in the field. Less chains breaking, less cogs or rings bending, chain tension needing to be adjusted too often. Plus all these parts will wear longer.
    Quote Originally Posted by febikes View Post
    I call BS on the torque theory...

    If gear inches are the same then the torque transmission is also the same.
    Quote Originally Posted by smilinsteve View Post
    I agree.

    Here is how I see it, comparing large and small gears of the same ratio:

    1. With larger gears, the chain travels a longer distance for each crank revolution

    2. With the same gear ratio, the rider is doing the same amount of work. Work on the chain is chain tension x distance of the chain traveled. So the chain that has more distance traveled has lower tension.

    3. The torque applied to the rear wheel in either case is the same. Torque = r x F, r is the radius of the rear cog and F is the chain tension. The big system has lower chain tension but more leverage (bigger r), while the small system has higher chain tension but lower leverage.
    Quote Originally Posted by TacoMan View Post
    There are benefits to using a larger chainring and cog. It is correct that the torque is equal with the same gear ratios, but the tension on the chain and the load on the teeth can vary a lot with different diameter cogs.
    Example:
    F = 50 lbs force at tire contact patch (assuming equal traction)
    D = 27 tire diameter
    T = Torque = F*(D/2) = 675 in/lbs
    16T cog = 2.563 pitch diameter
    22T cog = 3.513 pitch diameter
    16T Chain tension = T/(PD/2) = 527 lbs
    22T Chain tension = T/(PD/2) = 384 lbs
    Now assuming the chain wraps around 180 degrees with equal load on each tooth
    16T tooth load = 527/8= 66 lbs force per tooth
    22T tooth load = 384/11= 35 lbs force per tooth
    A larger cog will put less load on the chain and cog which will make parts last longer and reduce breakage
    DANG! THIS IS EXCITING!
    I love watching a Battle Royale like this.... reminds me of the old days when Gladiators battled it out....

    Sorry for interrupting, I just got all excited... Please continue!

    You guys are seriously talking way beyond where my interest in bikes takes me... but I still enjoy reading this stuff...

  13. #13
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    Chainring cogs are like screw threads - the "first tooth" or "first thread" takes almost the entire load - but if there are more teeth, that load gets there less frequently for each revolution, and therefore less cog/ring wear. While I will also call BS on cpeterson's torque philosophy, he is right on about the chain bending less traveling around larger cogs. Virtually all the resistance in a chain-drive system is due to the chain links moving against each other at the side plates "bending". Less bending = less friction/resistance. Of course, this comes at the expense of heavier rings and cogs. It'd be interesting if someone had the time and resources to measure the watts saved (or increased) spinning these systems at RPMs that are in the ranges we SS riders tend to spend our time at, and see if there is a "sweet spot" that would benefit a rider looking for the greatest efficiency.
    R.I.P. Corky 10/97-4/09
    Disclaimer: I sell and repair bikes for a living


  14. #14
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    Quote Originally Posted by Raybum View Post
    For a given gear ratio, bigger ring and cog simply translates to lower chain tension and subsequently lower cog/chainring wear. I've been running 32's on front and have had no problem getting a several thousand miles out of them. I do rotate and flip them every 500-1000 though which helps. I think the downside of going to larger cog/chainrings is worse than replacement costs every year to 2 years.
    But your adding more:

    Chain Links = more moving parts = more wearing parts!

  15. #15
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    Quote Originally Posted by NEPMTBA View Post
    But your adding more:

    Chain Links = more moving parts = more wearing parts!
    But each link in the chain is under stress less frequently, so a longer chain should last longer I would think.

  16. #16
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    Awesome thread! Great topic.

    One thing not mentioned here is that with larger cog/chainring combo, you are much less likely to drop your chain. To me that's the greatest advantage.

    In fact, all the folks that are trying to solve their chain slack problems, should move to larger rings/cogs.

  17. #17
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    Ok boys, girls, and aliens...
    ...It's about to get a lot more convoluted and even a way back in the day story!

    So, back in the day I raced Motos and still do, but that's not what I was getting at...
    ...I ran one of my Moto's a 125cc in a stock class and were not allowed to do any mods like changing pipes and carbs, but we could do as we wish with gearing. Chain size was 520 pretty much standard, but using a smaller, lighter and different pitch 428 yielded results as to quicker accelration, but it had more links, so it wore at more places (aka stretching) and wore quicker, of course I was racing, so it didn't matter as replacing was racing if ya wanted to run up front of the pack!

    I always run a wider chain on my singlespeeds, no matter what the size of the cogs, and since they don't have to deal with shifting and ramps on cogs!

  18. #18
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    Shimano promoted less chain tension (lower torque in the system? Not totally sure that's the same thing..) when launching dynasis gearing. Larger cogs have less chain tensionand wear for a given input torque/power. I was puzzled when I read that but apparently it's true. Whether going from a 32 to a 36 makes a big difference I have no experience, but in general I use the largest combo I can on the SS, oval 34 is the current frame's limit tho.
    Larger rings are also more efficient, but that only varies 3-4% max from extremes of gear. Still, a % or 2 here and there adds up. There's a HPV journal report on all this I found from a link in the IGH form.

    It'd be interesting to ride a 44/22 and a 32/16 back to back to see if it actually feels any different. Smoother maybe, but actually more effective?

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