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Different cog numbers - speed difference?

Old 05-03-20, 05:35 AM
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Sergio_CH
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Different cog numbers - speed difference?

I am new to all this, just got my first bike with Di2 Ultegra, but I already know, that next bike will have wireless shifting, which is currently SRAM.

I was looking around and I wonder the following:

I have Ultegra with 50/34 and 11/32

SRAM Force eTap has 48/35 and 10/33.

I have questions:
1. 50-11 is faster at same cadence than 48-10?
2. 34-32 makes climbing easier than 35-33?

Cheers!
S.
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Old 05-03-20, 05:43 AM
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Ah, just read somewhere else:

"It’s done that by offering cassettes which start with a 10-tooth smallest sprocket. Coupled with SRAM’s 48 tooth large chainring, that gives you a top gear ratio just smaller than a 53◊11, but with a smaller, lighter front plate. At the back, there are options up to 33 teeth which, coupled to a 35 tooth inner chainring give exactly the same low ratio as a 34◊32."

So, I interpret it in the following manner: 50-11 will make me move slower than 48-10 at same cadence and 34-32 will be as easy when climbing as 35-33.
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Old 05-03-20, 06:43 AM
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Originally Posted by Sergio_CH View Post
So, I interpret it in the following manner: 50-11 will make me move slower than 48-10 at same cadence and 34-32 will be as easy when climbing as 35-33.
The 34x32 and 35x33 work out to the same 28 gear inches, so no difference. On the high end the 48x10 is a slightly taller gear than the 50x11 at 126 inches vs. 120. But this only matters if you are regularly spinning out either gear, which is unlikely!

Go here to enter and compare chainring and cassette combos, have fun!: https://www.sheldonbrown.com/gear-calc.html
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Old 05-03-20, 07:07 AM
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Gear inches is nothing but a meaningless number. It a gear ratio like 53/11=4.8 times 27. 50/10 =5, so it will produce more speed at a given cadence.

Larger ratios will produce higher speeds at a given cadence, but only if you have the power to spin a high cadence.

The thing that makes no sense with SRAM AXS is gaining range with a 10T sprocket and 12 speeds, the giving up range by only offering a 13T chainring.
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Old 05-03-20, 07:14 AM
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Originally Posted by DaveSSS View Post
Gear inches is nothing but a meaningless number. It a gear ratio like 53/11=4.8 times 27. 50/10 =5, so it will produce more speed at a given cadence.
Gear inches is just another unit of measurement that many cyclists find quite handy. A scale of 28-100 (or so) can be more relatable when comparing gears than 1.06 - 4.8.
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Old 05-03-20, 11:17 PM
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Originally Posted by DaveSSS View Post
Gear inches is nothing but a meaningless number. It a gear ratio like 53/11=4.8 times 27. 50/10 =5, so it will produce more speed at a given cadence.



Originally Posted by AlmostTrick View Post
Gear inches is just another unit of measurement that many cyclists find quite handy. A scale of 28-100 (or so) can be more relatable when comparing gears than 1.06 - 4.8.
Most gear inch calculators also take into account wheel and tire size, so it can be used to compare equivalent Ďgearsí between bikes, especially if you have different size wheels, like a 26Ē/650 -v- a 700c wheel bike
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Old 05-04-20, 08:18 AM
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https://www.bikecalc.com/speed_at_cadence

Here you go. Put in your info, take a look. I like it better than the Sheldon page linked.
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Old 05-04-20, 09:44 AM
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Originally Posted by burnthesheep View Post
https://www.bikecalc.com/speed_at_cadence

Here you go. Put in your info, take a look. I like it better than the Sheldon page linked.
My critique of that calculator is it doesn't allow any fine tuning of tire size. For example, it calculates ALL 700c/29er tires as the same, no matter how wide (tall) they are. At the extremes, (700x23 and 29x 2.125) that difference likely equals a shift in cogs, or even more!

Probably my favorite gear calculator presently, especially since Sheldons calculator dropped the 700x28 tire option for some reason, (my favorite road tire size) is Mike Shermans. Lots of fine tuning, info, and cool graphs are available here:

Mike Sherman's Bicycle Gear Calculator
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Old 05-04-20, 11:37 AM
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Originally Posted by Sergio_CH View Post
I am new to all this, just got my first bike with Di2 Ultegra, but I already know, that next bike will have wireless shifting, which is currently SRAM.

I was looking around and I wonder the following:

I have Ultegra with 50/34 and 11/32

SRAM Force eTap has 48/35 and 10/33.

I have questions:
1. 50-11 is faster at same cadence than 48-10?
2. 34-32 makes climbing easier than 35-33?

Cheers!
S.
Question 1 answer. The 48/10 is slightly faster at the same cadence.

Question 2 answer. Close enough to exactly the same to make no difference.

The gear calculator I linked to I find to be the most useful one Iíve ever used. The fact that you can compare drivetrains is perhaps itís most useful feature. Additionally it offers a range of tags to put over the gears. You can use ratio, speed, gear inches, meters development and others.
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Old 05-04-20, 05:53 PM
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Originally Posted by Sergio_CH View Post
. Coupled with SRAMís 48 tooth large chainring, that gives you a top gear ratio just smaller than a 53◊11, but with a smaller, lighter front plate.
What you're reading is just marketing lingo, like saying 650B is stronger than 700C but forgetting to mention that it's weaker than 559. I would take it as axiomatic that if you're comparing two gears that have similar ratios, the one using the bigger chainring ("front plate") will be more efficient and faster. A 10T cassette gear will be terribly inefficient no matter what chainring it's paired to.
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Old 05-05-20, 03:14 AM
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Originally Posted by BlazingPedals View Post
What you're reading is just marketing lingo, like saying 650B is stronger than 700C but forgetting to mention that it's weaker than 559. I would take it as axiomatic that if you're comparing two gears that have similar ratios, the one using the bigger chainring ("front plate") will be more efficient and faster. A 10T cassette gear will be terribly inefficient no matter what chainring it's paired to.
Why is 10T cassette inefficient?
I understand that the chain probably takes more beating when curling over a smaller cassette (similar to motorbike with a smaller drive sprocket).
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Old 05-05-20, 03:15 AM
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Thank you everyone for the replies!
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