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  1. #1
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    27.5+ tire height

    How close in size (overall height) is a 27.5 plus tire, say a 2.8" on a 35mm rim, to a 29er: arguments sake lets say a 2.35" on a Stans Flow ex? I know there are many variables to consider, just looking for an approximation if they are close? Thanks!

  2. #2
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    Too much variation in tires to say for sure, but the plus tire will be smaller by 5-15mm of radius most likely. That's a big range so you should measure what you have and what you want to use before swapping around.

    -Walt

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    Quote Originally Posted by Walt View Post
    Too much variation in tires to say for sure, but the plus tire will be smaller by 5-15mm of radius most likely. That's a big range so you should measure what you have and what you want to use before swapping around.

    -Walt
    Hey Walt,

    cool... I thought as much just thought I would ask around. Thanks!

  4. #4
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    Quote Originally Posted by tatuowen View Post
    How close in size (overall height) is a 27.5 plus tire, say a 2.8" on a 35mm rim, to a 29er: arguments sake lets say a 2.35" on a Stans Flow ex? I know there are many variables to consider, just looking for an approximation if they are close? Thanks!
    Yeah, I'm interested in the height difference too as too much BB drop would not work for me. I see WAlt said the radius would be anywhere from 5mm to 15mm smaller on the 27.5 plus but I read on another forum that it could be up to an inch difference between the 27.5+ and a 29. Anyone got pics and or measurements of a 2.35 tire on 29" flows or similar rims next to a 2.8" NN or similar tire on a asym 35 or similar rim?

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    For what it's worth, I took a quick measurement of my 27.5+ vs 29er.

    The pics shows the height difference between the...

    Specialized Purgatory 27.5x3.0 on a Roval SL38 (38mm ID) = (28 3/4 inches tall)

    Specialized Purgatory 29x2.3 on a Kappius KR-29-XCW (40mm ID) = (29 3/8 inches tall)

    Here's the thread

    John
    Attached Thumbnails Attached Thumbnails 27.5+ tire height-20160228_114015_resized.jpg  

    27.5+ tire height-20160228_113919_resized.jpg  


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    Thanks John.

  7. #7
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    Quote Originally Posted by darkhorse13 View Post
    For what it's worth, I took a quick measurement of my 27.5+ vs 29er.

    The pics shows the height difference between the...

    Specialized Purgatory 27.5x3.0 on a Roval SL38 (38mm ID) = (28 3/4 inches tall)

    Specialized Purgatory 29x2.3 on a Kappius KR-29-XCW (40mm ID) = (29 3/8 inches tall)

    John
    nice work.

  8. #8
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    I was considering converting my TB to 27.5+ but the lower BB convinced me not to. Very rocky where I ride and I'm already getting pedal strikes. I did put Ibis 941 rims and 2.35 Ikons. Almost like riding a + bike. 15-17 psi gives great traction.


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  9. #9
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    Some 29er tires vary a lot in diameter. My kendas 2.2 are a good bit taller than my bontrager xr2 2.2,2.35 or xr3 2.3.

    I'm gathering that's why Walt gives a good size range of change. For me it's be closer to the 5mm drop (which I'm looking forward to) when I convert.

    Also, a tire has a pretty fixed diameter. They'll stretch a little from new but rims don't have much effect in overall diameter of a tire.
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  10. #10
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    Quote Originally Posted by darkhorse13 View Post
    For what it's worth, I took a quick measurement of my 27.5+ vs 29er.

    The pics shows the height difference between the...

    Specialized Purgatory 27.5x3.0 on a Roval SL38 (38mm ID) = (28 3/4 inches tall)

    Specialized Purgatory 29x2.3 on a Kappius KR-29-XCW (40mm ID) = (29 3/8 inches tall)

    Here's the thread

    John
    If this is an extreme case then that's only a 5/16" drop in bottom bracket height. Personally I'll take the better traction over a taller bottom bracket for that little amount.

  11. #11
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    Quote Originally Posted by prj71 View Post
    If this is an extreme case then that's only a 5/16" drop in bottom bracket height. Personally I'll take the better traction over a taller bottom bracket for that little amount.
    That is not an extreme case at all. He is using a 27.5x3.0 tire, which will be taller than a 2.8. That tire will not fit into most 29er frames, so most are forced to use a 2.8 tire for conversions. That's more like a best case.

  12. #12
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    His math is extremely flawed though. 1/4+3/8 does not equal 5/16, it's 5/8 or approx 17mm. That's actually A LOT.

    But those 29" tires are a bit on the tall side though. My bontragers aren't that tall so my loss will hopefully be less.

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  13. #13
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    Quote Originally Posted by tigris99 View Post
    His math is extremely flawed though. 1/4+3/8 does not equal 5/16, it's 5/8 or approx 17mm. That's actually A LOT.

    But those 29" tires are a bit on the tall side though. My bontragers aren't that tall so my loss will hopefully be less.
    5/8th it is and yes thats a heap off BB reduction.

  14. #14
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    Quote Originally Posted by tigris99 View Post
    His math is extremely flawed though. 1/4+3/8 does not equal 5/16, it's 5/8 or approx 17mm. That's actually A LOT.

    But those 29" tires are a bit on the tall side though. My bontragers aren't that tall so my loss will hopefully be less.

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    No his math is correct, yours is flawed. The diameter difference is 5/8", which makes the ride height difference half of that, 5/16", or about 8.0mm.

    And 5/8" is 15.875mm, not 17mm.

  15. #15
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    Bikeny is correct on all counts, but the main point here is *measure your tires* (both the ones you have and the ones you want to use) and consider the BB height before pulling the trigger on a conversion.

    -Walt

  16. #16
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    Quote Originally Posted by bikeny View Post
    No his math is correct, yours is flawed. The diameter difference is 5/8", which makes the ride height difference half of that, 5/16", or about 8.0mm.
    not really flawed in the context of the conversation as we are all on the same page just different parts of the page. In not seeing the total ramifications of ride height diff it's easy to miss.

  17. #17
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    Oh yes your correct, I was thinking diameter and not filling in that he cut the result in half to equal bb drop, I very much stand corrected on that one. So both our numbers are right, I just forgot the other half of the equation (gotta stop trying to think when I first wake up lol)

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  18. #18
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    Quote Originally Posted by tigris99 View Post
    I just forgot the other half of the equation (gotta stop trying to think when I first wake up lol)
    as did i.

  19. #19
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    Ibis says the increased 'sag' in 27+ tires from the lower pressure means that they're even lower. Basically the same height as a regular 27.5.

    Is that being taken into account here too?

  20. #20
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    I was in my LBS to see the new Fuze compared to whatever Spec. HT 29er they had. The diff. in axle height is ~3/8" without sag or tire compression. 3/8 lower bottom bracket on a converted 29er would make me think about getting a B+ specific frame.

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    Seems BB heights are all over the board with the different tire sizes and frame designs. It doesn't appear that a switch from 29 to 27.5+ equals a huge drop in BB height. Here are some figures I dug up from the manufacturers:

    Specialized Stumpjumper 29 = 336mm
    Specialized Stumpjumper 650b = 335mm
    Specialized Stumpjumper 6fattie = 331mm

    Cannondale Habit 27.5 = 334mm
    Cannondale Bad Habit 27.5+ = 334mm
    Cannondale Scalpel 29 = 332mm
    Cannondale Jeckyll 27.5 = 364mm
    Cannondale Trigger 27.5 = 351mm

    Santa Cruz Hightower 29 = 337mm
    Santa Cruz Hightower 27.5+ = 335mm

    Trek Fuel EX 29 = 334mm
    Trek Fuel EX 27.5 = 333mm

  22. #22
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    Quote Originally Posted by schnee View Post
    Ibis says the increased 'sag' in 27+ tires from the lower pressure means that they're even lower. Basically the same height as a regular 27.5.

    Is that being taken into account here too?
    Depends if your putting a 150 lb person or 225 lb person on 15 psi.

  23. #23
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    Quote Originally Posted by schnee View Post
    Ibis says the increased 'sag' in 27+ tires from the lower pressure means that they're even lower.
    not much in it to squak about.

  24. #24
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    Quote Originally Posted by prj71 View Post
    Seems BB heights are all over the board with the different tire sizes and frame designs. It doesn't appear that a switch from 29 to 27.5+ equals a huge drop in BB height. Here are some figures I dug up from the manufacturers:

    Specialized Stumpjumper 29 = 336mm
    Specialized Stumpjumper 650b = 335mm
    Specialized Stumpjumper 6fattie = 331mm

    Cannondale Habit 27.5 = 334mm
    Cannondale Bad Habit 27.5+ = 334mm
    Cannondale Scalpel 29 = 332mm
    Cannondale Jeckyll 27.5 = 364mm
    Cannondale Trigger 27.5 = 351mm

    Santa Cruz Hightower 29 = 337mm
    Santa Cruz Hightower 27.5+ = 335mm

    Trek Fuel EX 29 = 334mm
    Trek Fuel EX 27.5 = 333mm
    I think you misunderstood the OP. We are talking about converting an existing 29er, not BB height in general, which does vary a ton based on intended usage, crank length, suspension design/sag, etc. 10mm is a huge change in BB height that can potentially cause you big problems when riding.

    -Walt

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    Understood. Was just putting out some numbers for reference.

    Although in the case of the hightower that uses the same exact frame for 29 and 27.5+, the switch from 29 to 27.5+ only results in a 2mm drop in BB height. Obviously that's affected by the choice of tires used.

  26. #26
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    Quote Originally Posted by prj71 View Post
    Understood. Was just putting out some numbers for reference.

    Although in the case of the hightower that uses the same exact frame for 29 and 27.5+, the switch from 29 to 27.5+ only results in a 2mm drop in BB height. Obviously that's affected by the choice of tires used.
    Same frame... sorta.

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  27. #27
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    One may assume that in order to get the equal height with 29er tyres on 27.5 + one needs almost real 27.5x3.5". Such a frame would be fully swappable between a 29er and 27.5+ I guess.
    Is Santa Cruz Hightower is the closest?

  28. #28
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    Quote Originally Posted by Davidcopperfield View Post
    One may assume that in order to get the equal height with 29er tyres on 27.5 + one needs almost real 27.5x3.5". Such a frame would be fully swappable between a 29er and 27.5+ I guess.
    ...
    I think you just described a fatbike.

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  29. #29
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    ^^x2

    Once you start hitting 3.5" tires were into fat bike territory.

    But again things very so much just on the tires your comparing.

    Example: most of what I read was a 29" 2.3-2.3 tire and a 26x 4.7 tire are the same diameter give or take a couple mm.

    But that's off. My bontrager 29" tires, 2.2 or 2.3 are about the same as my 3.8/4.0 Surly Nate's. My 4.7 tire on the front is quiet a bit taller.

    So my difference converting to b+ will be different than the next person.

    Seems to me that b+ is making 27.5 tires wider, but not that much taller than a normal tire.

    Right now im trying to decide on wheels to build up for b+. But I welcome a tad lower bb height.

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  30. #30
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    Quote Originally Posted by tigris99 View Post
    ^^x2

    Once you start hitting 3.5" tires were into fat bike territory.

    But again things very so much just on the tires your comparing.

    Example: most of what I read was a 29" 2.3-2.3 tire and a 26x 4.7 tire are the same diameter give or take a couple mm.

    But that's off. My bontrager 29" tires, 2.2 or 2.3 are about the same as my 3.8/4.0 Surly Nate's. My 4.7 tire on the front is quiet a bit taller.

    So my difference converting to b+ will be different than the next person.

    Seems to me that b+ is making 27.5 tires wider, but not that much taller than a normal tire.

    Right now im trying to decide on wheels to build up for b+. But I welcome a tad lower bb height.

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    I'm not sure where you saw that 29x2.3 and 26x4.7 are the same height. Everything I've seen suggests 26x4.8 and 29x3 are about the same height. I've also read that 26x4.0, 27.5x3, and 29x2.2ish are about the same height. Those seem to be pretty accurate, except that the 27.5 needs to be bigger, like 3.25 to 3.5 to match up. This will of course vary depending on the exact tire and the rims as well.

    Also, any time a tire gets wider it will also get taller, no way around that.

  31. #31
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    Quote Originally Posted by tigris99 View Post
    ^^x2

    Once you start hitting 3.5" tires were into fat bike territory.
    indeed.

    Example: most of what I read was a 29" 2.3-2.3 tire and a 26x 4.7 tire are the same diameter give or take a couple mm.

    But that's off. My bontrager 29" tires, 2.2 or 2.3 are about the same as my 3.8/4.0 Surly Nate's.
    my findings as well

    So my difference converting to b+ will be different than the next person.

    Seems to me that b+ is making 27.5 tires wider, but not that much taller than a normal tire.
    yup, hence the + size rim movement to accommodate.

    Right now im trying to decide on wheels to build up for b+. But I welcome a tad lower bb height.
    mine will be i35 spank oozy 395+ trail for B+ wheelset. Curious to see how the ikon & rekon 2.8 measure.
    Last edited by nvphatty; 09-09-2016 at 06:34 AM.

  32. #32
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    Handy chart from Jamis, although missing 27.5 fat:27.5+ tire height-tire-sizes.jpg

  33. #33
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    Quote Originally Posted by bikeny View Post
    Handy chart from Jamis, although missing 27.5 fat:Click image for larger version. 

Name:	tire sizes.jpg 
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    See how, graphically, they continue to insist that 29 = 27.5+, when in the "Outer diameter" note, there is a discrepancy of ~3/4" - which falls right into my prior posting that the 27.5+ axle is ~3/8" lower than the 29er. This is the reality of it. They are not the same size. They are not really interchangeable.

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  34. #34
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    Quote Originally Posted by bikeny View Post
    I'm not sure where you saw that 29x2.3 and 26x4.7 are the same height. Everything I've seen suggests 26x4.8 and 29x3 are about the same height. I've also read that 26x4.0, 27.5x3, and 29x2.2ish are about the same height. Those seem to be pretty accurate, except that the 27.5 needs to be bigger, like 3.25 to 3.5 to match up. This will of course vary depending on the exact tire and the rims as well.

    Also, any time a tire gets wider it will also get taller, no way around that.
    Actually a tire can get wider and not get taller. Tire diameter is not a function of anything except manufacturing specifications. A tire can be made to have the exact same inflated diameter whether it's 1" wide or 5" wide.

    It's just what happens when they design tires. Bigger all around when they go wider in many cases.

    Been reading a thread that mentioned 26" vs 27.5 fat tires. The 27.5 versions have less sidewall in an attempt to maintain overall diameter. And it's catching on it seems, according to those that have both are saying the "lower volume" 27.5 fat tires have several points of superiority due to the smaller diameter/sidewalls.

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  35. #35
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    Quote Originally Posted by Fleas View Post
    See how, graphically, they continue to insist that 29 = 27.5+, when in the "Outer diameter" note, there is a discrepancy of ~3/4" - which falls right into my prior posting that the 27.5+ axle is ~3/8" lower than the 29er.
    -F
    Unless one uses 3,25-3,5"x27.5" and up from 3" is for me a plus size and those may be as tall as a typical 2,3x29" tyre. Any frame designed up to 27.5x 2,7"-2,9" makes little sense in terms of full 29er compatibility.

  36. #36
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    anyone know if I went to a maxxis rekon (27.5 x 2.8) from the maxxis chronicle (27.5 x 3) how much my bottom bracket would drop? on 40 mm internal rims if that matters. my pony rustler is pretty low as it is, but the more aggressive treat on the rekon looks nice (and I assume the new plus high roller and minions would be same size as the rekon as well?)

  37. #37
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    Maxxis Rekon 2.8 on a 34mm ID Derby rim has a overall diameter of 28 3/16" at 17psi. Tire has been installed on the front and ridden for a few weeks.

    It has been an excellent match with a 2.4 Ardent (edit: 27.5x2.4) on the back of my Knolly Warden for summer riding. (just under 28" diameter)
    Last edited by bubba13; 09-09-2016 at 10:10 AM.
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  38. #38
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    Interesting. Your plus tire is bigger than your 29 er tire? I thought plus tires were always a little smaller (that's why they are making flip chips etc to compensate).

  39. #39
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    Here's the particulars on the plus wheelset I had built.

    Spank Oozy 395+ trail rims (i35mm)

    Schwalbe NN 2.8s 67tpi KNOB-KNOB =68mm/ 2.7

    CASING = 67mm/2.64

    Dia = 28 3/8th

  40. #40
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    And new plus-lite tires, like the Nobby Nic 29 x 2.6" should allow you to get even closer to a plus bike experience.

  41. #41
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    Quote Originally Posted by Newbie10 View Post
    Interesting. Your plus tire is bigger than your 29 er tire? I thought plus tires were always a little smaller (that's why they are making flip chips etc to compensate).
    The Warden is 27.5 bike, so I assume Bubba13 has a 27.5x2.4 Ardent in the rear and a 27.5x2.8 Rekon on the front

  42. #42
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    Quote Originally Posted by Tjaard View Post
    The Warden is 27.5 bike, so I assume Bubba13 has a 27.5x2.4 Ardent in the rear and a 27.5x2.8 Rekon on the front
    Yes, I should have added that the Ardent is 27.5x2.4. Sorry for the confusion
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  43. #43
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    Ok. So a 29er is still more diameter than the rekon. Makes sense. Anyone know the difference in diameter/bottom bracket height between a chronicle and rekon?

  44. #44
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    Anyone know the difference in diameter between the stock Maxxis 2.8 Rekon+ tires and Magic Mary/Hans Dampf 2.35 on the same rim - like a Stans Flow MK3? I can't imagine they are much different... but if someone knows, please post it up.
    "It looks flexy"

  45. #45
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    depends on the tire. the innova gneiss 27.5x3 is exactly 29" tall on an i50 rim at 16psi. a terrene chunk 27.5x3 is 28.75" tall on an i45 rim at 16psi.

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