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  1. #1
    Old Fart Greybeard712's Avatar
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    Roubaix hard to pedal

    I have a 2011 Roubaix SL3 Expert (double—approx 19lbs) that seems harder to pedal than my 2005 Aluminum Allez sport (triple—approx 22lbs).
    The Allez in big chain ring (52T) / 5th gear (15T) is easier and faster than the Roubaix 50T / 5th (17T) to get up to 15-18mph.
    I bought the Roubaix used with only 50 miles on it (according to the seller) and I have no reason to doubt there were no more than 100 miles on it. The bike is brand new. I've put 480 miles on it in 6 weeks.

    However, my question is: would the bearing grease in the crank stiffen up all that much from sitting in a garage for 2 years?
    Do I need to pull the crank and re-grease it? Nasty job.

    I did a quick test by lifting the rear wheel and reverse spinning the pedals. The Allez spun around 2 turns, the Roubaix only one. Dunno if this is an accurate test in that the Roubaix is a whole lot newer.


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  2. #2
    Mechanic/Tourist
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    Its not bearing grease. It's to be expected that a higher gear (52/15) will accelerate slower than a lower one (50/17). You have more leverage in a lower gear. The latter is 15% lower gear.bo

    That being said, it's unlikely that the bearing grease has stiffened significantly but only you can determine that after taking it apart. Also your "test" involved several variables, including chain and cassette as well as bottom bracket, so you can't conclude anything from it anyway.

    Finally, a 3 lb difference in weight cannot be expected in itself to have more than a 1% impact, even on acceleration.
    Last edited by cny-bikeman; 08-18-14 at 05:00 PM.
    There's no such thing as a routine repair.

    Don't tell me what "should" be - either it is, it isn't, or do something about it.

    If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

    Please take the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!

  3. #3
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    Quote Originally Posted by Greybeard712 View Post
    I have a 2011 Roubaix SL3 Expert (double—approx 19lbs) that seems harder to pedal than my 2005 Aluminum Allez sport (triple—approx 22lbs).
    The Allez in big chain ring (52T) / 5th gear (15T) is easier and faster than the Roubaix 50T / 5th (17T) to get up to 15-18mph.
    Those are considerably different gear ratios (52/15 is 94 gear-inches while 50/17 is 79 gear-inches), so it's not surprising that they feel different. How about when you go on the same ride while choosing whatever gear combinations feel best to you on each bike? The 3 fewer pounds of the Roubaix should provide a slight advantage - but only if you are climbing some hills on the route.

    Very little energy is lost in the bottom bracket bearing - as long as both seem to turn smoothly I doubt that this is the source of your issue.

  4. #4
    Mechanic/Tourist
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    Actually weight has an effect both when lifting (climbing) and when accelerating, but again the effect of 3 lbs is minor. Remember that inertia is one of many factors, including friction, rolling resistance and wind resistance.
    There's no such thing as a routine repair.

    Don't tell me what "should" be - either it is, it isn't, or do something about it.

    If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

    Please take the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!

  5. #5
    Andrew R Stewart Andrew R Stewart's Avatar
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    I now see there is a double posting of this thread. Andy.

  6. #6
    Old Fart Greybeard712's Avatar
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    Quote Originally Posted by prathmann View Post
    Those are considerably different gear ratios (52/15 is 94 gear-inches while 50/17 is 79 gear-inches)...
    See, I learn something new everyday. Than you for that - now - what's the formula for arriving at 94/79 gear inches? (inquiring cyclists want to know).
    Way back-in-the-day (high school-60's) I excelled in Languages & Girls, sucked in math.


    Quote Originally Posted by cny-bikeman View Post
    Its not bearing grease. It's to be expected that a higher gear (52/15) will accelerate slower than a lower one (50/17). You have more leverage in a lower gear. The latter is 15% lower gear.
    That being said, it's unlikely that the bearing grease has stiffened significantly...your "test" involved several variables, including chain and cassette as well as bottom bracket, so you can't conclude anything from it anyway.
    Finally, a 3 lb difference in weight cannot be expected in itself to have more than a 1% impact, even on acceleration.
    Penny Farthing.jpg That's good to know, I thought as much but needed confirmation. Thanx.

    Jan -216…..Apr -207…...Jul - 645…..Just Ride Baby!
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  7. #7
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    The gear inches formula is very basic, and based on comparing a geared bike to a Penny Farthing with the pedals attacged directly to the drive wheel.

    So, it's the diameter of the wheel multiplied by the ratio of the driving sprocket (chainring) over the driven (rear) sprocket.

    So, using 27" for the wheel to keep life simple,a 94" gear would need to have a chainring/sprocket ratio of 94:27 or roughly 10.5:3. using real sprockets that would be (roughly 53:15)

    There are plenty of gear ratio caluclators on line for the mathematically declined. This one lays out the entire range if you input the chainrings and cassette.

    I still prefer gear charts which let you see everything at a glance all in one place, without trial and error. (enter 27" wheel, and 53-39 typical chainrings to get a sense of how various cassettes would play out) Then find your target gear inches, and see which combinations will produce it.

    BTW- comparing apples to apples (similar gearing) IME the biggest difference between two bikes comes from the tires and tire pressure. Underinflated tires would make a Ferrari perform like a Yugo (maybe not that extreme).
    Last edited by FBinNY; 08-18-14 at 08:18 PM.
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  8. #8
    tcarl
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    [QUOTE=cny-bikeman;17049047]Its not bearing grease. It's to be expected that a higher gear (52/15) will accelerate slower than a lower one (50/17). You have more leverage in a lower gear. The latter is 15% lower gear.bo


    Re-read what the original poster said: The Allez, 52/15 gear is easier and faster than the Roubaix 50/17 to get up to 15-18 mph.

  9. #9
    Senior Member Delmarva's Avatar
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    Quote Originally Posted by Greybeard712 View Post
    See, I learn something new everyday. Than you for that - now - what's the formula for arriving at 94/79 gear inches? (inquiring cyclists want to know).
    Way back-in-the-day (high school-60's) I excelled in Languages & Girls, sucked in math.




    Penny Farthing.jpg That's good to know, I thought as much but needed confirmation. Thanx.

    Jan -216…..Apr -207…...Jul - 645…..Just Ride Baby!
    Feb - 87…...May - 440…..Aug - 297
    Mar -145…..Jun - 484…..2014: 2521 Miles


    Another possibly easier way to compare gearing is to just convert it to a gear ratio much like you find with automobiles. That ratio shows how many times the cassette cog rotates for every complete rotation of the chain wheel. Thus 52/15 gives a ratio of 3.46 while 50/17 gives a ratio of 2.94. The gearing is significantly different with the 52/15 combination requiring more effort but moving the bike a greater distance for every turn of the chain wheel. OTOH the 50/17 combination will accelerate faster because of lower gearing.

    The Sheldon Brown gear calculator will give you a table in ratios or gear inches for all possible combinations.

    Sheldon Brown's Bicycle Gear Calculator
    Last edited by Delmarva; 08-19-14 at 08:35 AM.

  10. #10
    Senior Member Black wallnut's Avatar
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    Check the Roubiax for brake rub, wheel wobble, low air pressure, tight bearings. The Allez is stiffer so it may feel more responsive. Could also be how you fit on each bike.


    Mark

  11. #11
    Old Fart Greybeard712's Avatar
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    Quote Originally Posted by FBinNY View Post
    BTW- comparing apples to apples (similar gearing) IME the biggest difference between two bikes comes from the tires and tire pressure. Underinflated tires would make a Ferrari perform like a Yugo (maybe not that extreme).
    Yeah, I considered that too. They both have custom wheels. The Allez has 28/24 Mavic w/23C Panaracer racing tires @ 130psi. The Roubaix has Fulcrum 24/20 wheels w/*23/25C Pro II @ 120psi.
    I love the Roubaix and ride it most of the time. Starting out in 3rd gear (50/21) works just fine, even up a medium incline. I rarely use the 34 chain ring except for steep hills.
    And thanx guys for the formula and the links. They're helpful. Even with all that one rides by feel.


    * Specialized put a 23C tread on a 25C casing and called them 23/25s. I have those on the Roubaix and the Sirrus Hybrid.

  12. #12
    Old Fart Greybeard712's Avatar
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    Quote Originally Posted by Black wallnut View Post
    Check the Roubiax for brake rub, wheel wobble, low air pressure, tight bearings. The Allez is stiffer so it may feel more responsive. Could also be how you fit on each bike.
    Yeah Black Walnut, I checked all of those things first off. The bearings might be tighter since it is new (barely used 2011), the Allez is a 2005 with unknown miles before I bought it. I've put 840 miles on it since late Jan. (530 miles on the Roubaix since Jun 30).
    You think the aluminum frame (Allez) is stiffer than the carbon fiber (Roubaix)? I'm no expert but the carbon fiber frame is pretty stiff. Either bike rides well.



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    coprolite fietsbob's Avatar
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    Have to go fast over those Ancient cobbled farm roads ..

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