How important is a new fork when switching 29->27.5+ ?- Mtbr.com
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  1. #1
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    How important is a new fork when switching 29->27.5+ ?

    I have a 2017 Santa Cruz tallboy 29er. It has a 120mm travel fork. The frame is designed to allow for 27.5+ wheels as well, but when they sell the bike in that configuration, it comes with a 130mm fork. Can I get away with my 120mm fork with 27.5+, or do I really need that 130 fork?

  2. #2
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    You can get away with it. But youíll steepen the head angle a little and lower the BB. 27.5+ isnít as tall as the 29. Thatís where the increased travel fork comes in to get the geometry as close to original as possible.
    I no longer like to party. But I like the idea of it.

  3. #3
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    I don't think the head angle will change since both wheels will be the same size. The bottom bracket will be lower however, and it may or may not be too low. You can try it and see how it works, depending on which fork you have swapping in a longer air shaft shouldn't be a problem for a good shop.

  4. #4
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    Absolutely not true, your are changing both wheels to smaller, it has ZERO effect on any angles, the only thing that will change is BB height if he runs anything under a 3.25" B+ tyre (they're about as tall as a 29x2.25" tyre) and you can't fit one of them in a TB.

    Quote Originally Posted by almazing View Post
    You can get away with it. But youíll steepen the head angle a little and lower the BB. 27.5+ isnít as tall as the 29. Thatís where the increased travel fork comes in to get the geometry as close to original as possible.
    100% correct, only difference will be BB height. I would suggest if you're thinking of getting one of these bikes and using both wheel sizes, that you go with the B+ configuration and longer fork and just deal with the taller BB when using the 29" wheels. Since the OP already has the 29er version of the bike, as said, an air spring swap to make it 130mm travel would work and is probably the best option.
    Quote Originally Posted by jgdblue View Post
    I don't think the head angle will change since both wheels will be the same size. The bottom bracket will be lower however, and it may or may not be too low. You can try it and see how it works, depending on which fork you have swapping in a longer air shaft shouldn't be a problem for a good shop.
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  5. #5
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    Yeah, you'll probably want to adjust the air spring. I've found that on most of the bikes that can swap between 27.5+ and 29, you absolutely do not want to lower the BB unless you ride smooth trails.

    I run a 150 fork on my Hightower in both configurations since it's easier than swapping back to 140.

  6. #6
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    If your fork is Boost 110x15 you'll have the width for the wider tires.

  7. #7
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    Stick a 10mm spacer under the bars and see if you like it.

  8. #8
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    Thanks for the advice. I didnít even know that I might be able adjust my fork (Fox 34) to give it a longer travel.

  9. #9
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    Quote Originally Posted by LyNx View Post
    Absolutely not true, your are changing both wheels to smaller, it has ZERO effect on any angles, the only thing that will change is BB height if he runs anything under a 3.25" B+ tyre (they're about as tall as a 29x2.25" tyre) and you can't fit one of them in a TB.


    100% correct, only difference will be BB height. I would suggest if you're thinking of getting one of these bikes and using both wheel sizes, that you go with the B+ configuration and longer fork and just deal with the taller BB when using the 29" wheels. Since the OP already has the 29er version of the bike, as said, an air spring swap to make it 130mm travel would work and is probably the best option.
    I also have a brand new Tallboy 3 29er. I don't have any experience on a FS trail bike, so I opted for a set of 27.5+ wheels with 2.8" tires. Took my first ride on the 29x2.3 tires and it was great. Next time I'll swap wheels and see what the ride is like on those. It's supposed to be like a different bike. So I need to make an air spring swap and this gives me 10mm more travel?

  10. #10
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    If one runs it with 120 mm fork, 27.5+ wheels, and you flip the chip on shock to H, yes the result will be a slightly steepened head tube angle compared to 29er with chip on L.

  11. #11
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    Sorry to revive such an old thread, but I just went the other direction with my TB 3. I bought it as a 27.5+ And today at 29er wheels put on. I flipped the chip on the shock. Will I be fine with the 130mm fork that came stock? What differences will I feel?

  12. #12
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    Did you flip chip to low or high setting?
    Wait whuuut, who did he tell you that!?!?....

  13. #13
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    Quote Originally Posted by JMac47 View Post
    Did you flip chip to low or high setting?
    I flipped it to low.

  14. #14
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    Quote Originally Posted by levelseventysix View Post
    I flipped it to low.
    You'd probably be fine running it either setting. Depending on your terrain you might like it in the higher setting to get more clearances from obstacles and pedal strikes given the known low bb of Santa Cruz bikes.😎 If you want/need the clearance in high setting but feel like you're sitting too high you can adjust your stem stack height or go to a flat bar if you have a riser to settle that down abit.
    Wait whuuut, who did he tell you that!?!?....

  15. #15
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    Quote Originally Posted by JMac47 View Post
    You'd probably be fine running it either setting. Depending on your terrain you might like it in the higher setting to get more clearances from obstacles and pedal strikes given the known low bb of Santa Cruz bikes.😎 If you want/need the clearance in high setting but feel like you're sitting too high you can adjust your stem stack height or go to a flat bar if you have a riser to settle that down abit.
    So I'll be fine with the 130mm fork + 29er wheels? Sounds like the flip chip is where I will feel the most difference. Is that what you're saying? Thanks!

  16. #16
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    IDK what fork comes on your bike, but 34 Fox forks come with different axle to crown dimensions depending on tire size and travel. For a given travel, A to C increases going from 27.5 to 27.5+ to 29. Check here: https://www.ridefox.com/fox17/help.php?m=bike&id=804
    Do the math.

  17. #17
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    Quote Originally Posted by Lone Rager View Post
    IDK what fork comes on your bike, but 34 Fox forks come with different axle to crown dimensions depending on tire size and travel. For a given travel, A to C increases going from 27.5 to 27.5+ to 29. Check here: https://www.ridefox.com/fox17/help.php?m=bike&id=804
    I wish all of that made sense to me, but I'm not technical enough to understand it.

    My bike came with a fox 34 130mm fork. It is a 27.5+. I just switched out the 27.5+ wheels with a new set of 29er wheels. On Santa Cruz's website they say that when going from one wheel size to the next that the fork must be swapped out. In my case, 130mm to 120mm. So I'm wondering just how necessary that is and what can I expect to feel if I don't make that swap. I'm asking in terms of feel. Hope that makes sense.

  18. #18
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    It is not necessary at all, the BB will just be a bit higher and the bike will handle a bit different. You will get less pedal strikes with the slightly higher BB and then can maybe pedal through sections where before you might have hit them if you continued pedaling. Depending on personal preference, since your COG has been raised, cornering may not be as good, but as said, personal preference. With the higher BB and hence COG, you should be able to throw the bike around a bit easier.

    Don't own a SC, but I've done the wheel swap thing on my Banshee Prime and Phantom and I've never done anything other than swap wheels, handling changes have been minimal, IMHO. I say give it a try and see if you like it, you might, you might not, but it will not be so drastic that it will cause you to quit your ride. If you want a bit more DH prowess, flip the chips into the low setting and enjoy a more DH, plow feeling.

    Quote Originally Posted by levelseventysix View Post
    I wish all of that made sense to me, but I'm not technical enough to understand it.

    My bike came with a fox 34 130mm fork. It is a 27.5+. I just switched out the 27.5+ wheels with a new set of 29er wheels. On Santa Cruz's website they say that when going from one wheel size to the next that the fork must be swapped out. In my case, 130mm to 120mm. So I'm wondering just how necessary that is and what can I expect to feel if I don't make that swap. I'm asking in terms of feel. Hope that makes sense.
    One day your life will flash before your eyes, will it be worth watching??

  19. #19
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    Quote Originally Posted by LyNx View Post
    It is not necessary at all, the BB will just be a bit higher and the bike will handle a bit different. You will get less pedal strikes with the slightly higher BB and then can maybe pedal through sections where before you might have hit them if you continued pedaling. Depending on personal preference, since your COG has been raised, cornering may not be as good, but as said, personal preference. With the higher BB and hence COG, you should be able to throw the bike around a bit easier.

    Don't own a SC, but I've done the wheel swap thing on my Banshee Prime and Phantom and I've never done anything other than swap wheels, handling changes have been minimal, IMHO. I say give it a try and see if you like it, you might, you might not, but it will not be so drastic that it will cause you to quit your ride. If you want a bit more DH prowess, flip the chips into the low setting and enjoy a more DH, plow feeling.
    Thanks for the help!

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