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  1. #1
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    Running 7.875X2.25 on HD to lower bb?

    I currently have an HD 160 & am running 2.5 tires. this brings the bb height higher than I would like as in my silicon valley riding where I can get away with low bb heights.

    I had read about some venturing in the 650b space run a 875X2.25 with HD140 limbo chips to lower the bb @ 1/4" and get 150'ish mm of travel. Not a bad compromise in my opinion but wanted to see if anyone else has tried this.

    opinions appreciated,
    Dre

  2. #2
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    i'm on a medium hd, i've got 140mm limbo chips and am running a 200mm long bos vipr with a 57mm stroke, if my calculations are correct i'm getting 158mm of travel and a nice low bb, i'm running a 160mm bos deville fork and couldn't be happier with the angles I've got, the bike handles everything superbly, I've come from a cannondale Jekyll which I ran with 150mm 160mm and 180mm forks and the mojo hd is a better ride than the Jekyll, im riding up stuff I couldn't on the Jekyll, both were good on the downs but the ibis is way ahead on the climbs,

  3. #3
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    hell yeah that is what I wanted to hear

  4. #4
    #AINTNOBODYGOTTIMEFERDAT
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    Interesting. Posting for more thoughts on this.

    Wonder how much the angles change and how much the bb drops.
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  5. #5
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    From what I have read the bb drops 1/4", not sure about the angles

  6. #6
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    I don't think its gonna be worth the effort.

  7. #7
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    well I never rode my bike with the standard 200mm shock with 51mm stroke because I got the bos fork and shock at the same time as the frame and built it up into a bike with the bos stuff, my bottom bracket height is whatever an ibis mojo hd 140 is but I have almost 160mm travel, I've got hans dampf tyres on enve am rims and with all the air out of the shock there is about 15mm clearance between tyre and seat tube (its a 2013 frame) if I get chance tomorrow i'll try and measure the bb height, and head tube angle with 160mm devilles, all I can say is it rides better than anything else I've had, (cube sting, giant trance, santa cruz blur, cannondale Jekyll) its realy stable at speed, eats lumps bumps and drops, climbs stuff i'd think twice about on my last bike and is easy to ride for 4 or 5 hours without any problems,
    I love my bike

  8. #8
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    Although 2.25 is 12.5% more shock stroke than a 2.0, the HD swingarm leverage is rising in deep travel, the axle path rotates at some average angle forward and vertical while arcing near bottom. If all vertical travel, then 140 x 1.125 increased shock stroke=157.5mm travel. Next, very roughly figuring near 50% vertical axle travel, or a 45' axle path average rotation angle, with the added .25 inch stroke, 140 x 1.0625=148.75. The axle path average angle is probably far under 45' near bottom, so I figure over 150m travel, roughly 152mm with 2.25 shock stroke.

    To me 1/4 inch BB height is a big difference and worth changing up or down, depending on conditions. The loss of about 8mm bottom travel is less important, I don't do very big jump landings.

    I have measured the BB height using the same fork and wheels to be 1/4 inch lower with the HD140 chips and 7.875 i2i shock, vs. the HD160 chips and 8.5 i2i shock. Visually, at top travel the difference can be seen, the HD160 rear shock puts the swingarm shock mount about 1/8 inch closer to the seat post vs. the HD140.

  9. #9
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    Derby I think you just broke the internet, thanks for the details!

  10. #10
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    152mm travel with 1/4" bb drop. Got the HTA change on that? With the right build (maybe an angleset) could that be a TRc contender with a 160 34 fork? You'd probably get within a half in drop but with more slack. I don't mind slack when climbing if the geo is biased to going down.

    I lost around a 1/4" on the bb when running a 1.5 angleset on a 180 fork.

    Unless Hans chimes in and says this is a big no no, I may try this setup but with a works headset instead of the angleset.
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  11. #11
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    You may want to reach out to Bajaguy for his feedback. He's been running a 7.875x2.25 Vector Air and a -1.5 Works Headset (Angleset prior to that) for months on his HD with a 36 Float 160 and liked it. Dropped it down and slacked it out as surmised. Seeing him do it was what first turned me onto the idea. I'm thinking of giving it a go with a Vector Air, a -1 or -1.5 Works Headset and the new Pike, to replace my Lyrik, if the fork lives up to the hype. On paper the shorter shock, -1 Works and Pike 160 has essentially the same HA I have today (its a 0.25 of a degree slacker) with the Lyrik 170 but its a lot lower.

    Quote Originally Posted by JoeBMX View Post
    152mm travel with 1/4" bb drop. Got the HTA change on that? With the right build (maybe an angleset) could that be a TRc contender with a 160 34 fork? You'd probably get within a half in drop but with more slack. I don't mind slack when climbing if the geo is biased to going down.

    I lost around a 1/4" on the bb when running a 1.5 angleset on a 180 fork.

    Unless Hans chimes in and says this is a big no no, I may try this setup but with a works headset instead of the angleset.
    Last edited by seleniak; 05-08-2013 at 07:30 AM.
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  12. #12
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    thanks for the heads up , that is the same setup I have.

  13. #13
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    I run this setup with a -1.5 works headset and it's great. I don't even notice not having 160mm of travel in the rear. BB dropped 1/4 inch and the bike still feels balanced with this setup. I was thinking of switching to a Fox 34 float 160 since it has a lower a2c then a fox 36 160 but I like the rc2 damper too much and have my fork dialed.

  14. #14
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    exactly what I wanted to hear, now I have to find a 7.875 X 2.25 shock

  15. #15
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    Wonder what this does to the DW Link kinematics? Can't imagine it being good

  16. #16
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    Quote Originally Posted by Yody View Post
    Wonder what this does to the DW Link kinematics? Can't imagine it being good
    HD shock question

    Only issue is making sure you don't run too huge of a tire so it doesn't contact the seat tube on bottom out. I ran a 2.5 Minion DHF and had plenty of room. Just make sure to cycle the shock before hand.

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