New to mountain bikes and wondering if this can be done (700c on a 27.5)- Mtbr.com
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  1. #1
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    New to mountain bikes and wondering if this can be done (700c on a 27.5)

    i'm looking at a 2016 Scott Scale 700 and using a set of Velocity aileron wheels (700c).
    i found a Scale 700 SL build with rear tire Continental Mountain King, 27.5" x 2.4"

    so i did a bit of math

    27.5 wheel BSD = 584
    584 x 0.5 = 292 (radius)
    2.4" tires = 61mm
    292 + 61 = 353mm which is the theoretical full radius of 27.5 wheel, plus 2.4" tire

    so if i want to use a 700c wheel:
    622 x 0.5 = 311
    353 - 311 = 42

    so a 700c wheel, with a 42mm tire should theoretically be the same radius as the above 27.5 with 2.4

    does this look sound so far?

    my current bicycle (focus mares cx) has a 42.5 chainstay
    65mm bb-drop
    73.5 deg. seat tube angle and the Scale has a 42.7mm chainstay.

    scale:
    42.7 chainstay
    44mm BB-drop
    73-deg STa

    so the Scale should have a bit more clearance behind the seat tube.
    so i could probably go a bit bigger than 42mm with the tire

    i've also noticed, at least with road, cyclocross and gravel tires, that the height of a tire is about 4-5mm shorter, than the width of the tire.... which is more representative of the number on the sidewall.
    which would maybe give even a bit more clearance for an even larger 700c tire

    for a visual reference:

    scale with 2.4"



    Clement X'plor mso 40 x 700

    Attached Thumbnails Attached Thumbnails New to mountain bikes and wondering if this can be done (700c on a 27.5)-screen-shot-2020-03-03-8.47.44-am.jpg  

    New to mountain bikes and wondering if this can be done (700c on a 27.5)-img_1060.jpg  


  2. #2
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    my next question:

    i have contacted Scott, and they say that the maximum chainring size is 44-tooth
    as we all know, bicycle- and component manufacturers tend to lean towards the side of caution with a lot of their numbers, especially when tolerance-, and capacity-caps are involved.
    rear derailleur cage-length, and chain capacity jumps immediately to mind.

    i'm wondering if Scott claims that this frame's maximum chainring size is 44t, what is the real-world chainring size?

    i would probably like to go with a 34-46, or 48 crankset

  3. #3
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    Are you trying to build what is essentially a super gravel bike? All of the modifications you're considering move the bike away from its capability as a mountain bike. Or do you plan to keep the original wheelset for mountain biking and run the other wheelset for other types of rides?

    You also might want to check whether the wheels you have are compatible with the bike's hub spacing/attachment method.

  4. #4
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    mostercross type thing
    i already have a Ritchey Swiss Cross. and the Mares is just kind of redundant.

    so i'd like to go a little more upright, more relaxed angles, and a bit larger on the tires
    the Scott seems to tick all of the relevant bullet points

    the last 2 summers i've been going up to vermont for the gravel events, and the pave/class-4 "roads" were a bit more than a pure cyclocross bike could handle... at least *ME* on a cyclocross bike could handle.

    rear hub spacing is 142

  5. #5
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    Well, it sure looks like you're doing your homework.
    Would the Gravel Bike forum be a good source of info?

  6. #6
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    Quote Originally Posted by MSU Alum View Post
    Well, it sure looks like you're doing your homework.
    Would the Gravel Bike forum be a good source of info?
    could be?
    but i'm looking at a 27.5" mountain bike frame. so i figured this would be the place to check in

    and i love Love LOVE cobbling together bits that aren't supposed to work, and making them work.
    like the aforementioned Focus Mares.
    Campy 11-speed shifters v.1
    campy 10-speed FD, 10-speed med-cage RD
    sram 11-36 11-speed cassette

    shifts flawlessly!

    now, how to get that Ultra Torque crankset into a BB92 bottom bracket shell??

    oh, does anybody know about that supposed 44-tooth maximum chainring that scott states?
    is that a theoretical limit, or a real-world limit?

  7. #7
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    looking at the BB-drop in the geometry chart for this frame.
    is 44mm around standard for mountain bikes?
    that is an obscenely shallow drop, in the road/cyclocross realm.
    how are the ride characteristics altered, with this kind of geometry?

    also, i found that mountain bike cranks aren't offered in the 172.5mm length.
    at 5'8" and a 33" inseam, i am inclined to go 2.5mm shorter to 170mm
    would there be any benefit to going 175?
    with a 44mm BB-drop, i can't see pedal strikes being much of an issue with any length of crank arm

  8. #8
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    Cranks most likely aren't going to work. MTB's typically have a 73mm wide bottom bracket shell, road uses a 68mm shell.
    EXODUX Jeff

  9. #9
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    Quote Originally Posted by Hurricane Jeff View Post
    Cranks most likely aren't going to work. MTB's typically have a 73mm wide bottom bracket shell, road uses a 68mm shell.
    i get the feeling you are correct.
    the measured length of the Campy ultra torque splindle seems to be 96.5mm

    don't know if this would be long enough or not?

  10. #10
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    You may be able to use the cranks, but only 1x with the chain ring on the outside of the spider. The other problem is Campy spiders are incompatible with other 110mm or 4 bolt chain rings.
    EXODUX Jeff

  11. #11
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    any opinions on 170 vs 175 crank arm length?

  12. #12
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    [QUOTE=Life_Dweller;14592427]i'm looking at a 2016 Scott Scale 700 and using a set of Velocity aileron wheels (700c).
    i found a Scale 700 SL build with rear tire Continental Mountain King, 27.5" x 2.4"

    so i did a bit of math

    27.5 wheel BSD = 584
    584 x 0.5 = 292 (radius)
    2.4" tires = 61mm
    292 + 61 = 353mm which is the theoretical full radius of 27.5 wheel, plus 2.4" tire

    so if i want to use a 700c wheel:
    622 x 0.5 = 311
    353 - 311 = 42

    so a 700c wheel, with a 42mm tire should theoretically be the same radius as the above 27.5 with 2.4

    does this look sound so far?

    my current bicycle (focus mares cx) has a 42.5 chainstay
    65mm bb-drop
    73.5 deg. seat tube angle and the Scale has a 42.7mm chainstay.

    scale:
    42.7 chainstay
    44mm BB-drop
    73-deg STa

    so the Scale should have a bit more clearance behind the seat tube.
    so i could probably go a bit bigger than 42mm with the tire

    i've also noticed, at least with road, cyclocross and gravel tires, that the height of a tire is about 4-5mm shorter, than the width of the tire.... which is more representative of the number on the sidewall.
    which would maybe give even a bit more clearance for an even larger 700c tire



    Wait a minute, you are adding the radius of the wheel with the width of the tire? Two different dimensions.

    42mm (1.5 inches) wide is going to be terrible for offroading, as at least one other reply mentioned.

    I've also thought about if a skinny 29" tire could fit into the front or back of different bike frames I have (or if a 27.5 can fit into a 26" frame). But the bottom line is that beginners need at least a 2.4 up front, if not more. You simply don't have the skills and experience to handle choppy/irregular conditions downhill on a skinny tire. Pros can handle it, lesser mortals need a wider tire. Many pros run 2.5's front and rear, that's a whole inch wider than your 1.5 inch 29" tire project.

    As far as hybrid/gravel tires having a more narrow casing between the 'tread' and rim, yes, that's true for older 26 x 2.0 tires as well, it's an entire 1/2 inch less radius of casing than normal. A 26 x 1.95 is only 25.5 inches in diameter, but a 26 x 2.4 is around 26.3 - 26.5 inches in diameter, essentially one inch higher, which makes a big difference rolling over stuff.

    Ride your 2.4's offroad; if you want to do easy offroad stuff/pavement, make sure to measure your fork arch clearance and back triangle before buying a new 29" wheelset and tires. In theory you'd need 0.75 inches of clearance (at least) from the fork arch or back triangle to the current 27.5 x 2.4 tires, minus the shorter casing of 0.15 inches according to your calculations, 0.15 x 2 (diameter) = 0.3, then 0.75 - 0.3 is around 0.45 inches clearance from the fork arch and back triangle. Make it at least 0.5 inches to play it safe.

  13. #13
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    Wait a minute, you are adding the radius of the wheel with the width of the tire? Two different dimensions.

    - well, there is no sidewall number for tire height, only width. but at least in the road/cyclocross/gravel world they are relatively similar. height often being smaller than the the width, or the sidewall number.

    42mm (1.5 inches) wide is going to be terrible for offroading, as at least one other reply mentioned.

    - well, i was running clement X'plor mso 40mm. and it wasn't really the tire size that was much of a limiting factor. just felt like i would have been even more effective if i was able to go a bit bigger.

    as far as intended use, needs, and riding conditions/terrain go, well that's all very individual and personal.
    i most likely would never-, could never-, or even want to do what i imagine many people seek out for a typical mountain bike ride. especially a pro mountain biker!

    still wondering about that 44mm BB drop, and how that affects handling?

  14. #14
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    I don't really understand why you are trying to do what you are trying to do, but I can tell you from actual measurements that my 27.5x2.35" MTB tire is actually about 28.0" tall, my 27x2.25" MTB tire is about 27.75" tall, my 27x2.6"MTB tire is about 28.3" tall, and my wife's 700cx32 road tire is exactly 27.5" tall.

    I suspect that the 700cx42 will fit fine.

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