Slack Head Angle + Steep Seat Angle- Mtbr.com
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  1. #1
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    Slack Head Angle + Steep Seat Angle

    Looking for list of what 140-160mm bikes that have a slack head angle with a steep seat angle. I know the new Commencal Meta AM is designed this way. Looking for similar geo bikes. Thanks!

  2. #2
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    Lower slacker geo's

    The Rocky Mountain Slayer has their "StraightUp" geometry, which for a 160mm travel frame has a 66.5*HA and 75*SA.

    Similarly the Rocky Mountain Altitude also with "StraigtUp" geometry, which for a 140mm travel frame a has a 68.5*HA and 76*SA.

    There are a lot of other mfg's moving to slack out the front....sort of lower slacker movement. Turner 5Spot, Yeti 575, and Pivot 5.7 to name a few. Another potential standout here is the Specialized SJ FSR EVO....great looking geo on this ride.
    Last edited by ebeer; 12-07-2011 at 02:36 PM. Reason: a few more options

  3. #3
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    Specialized Enduro and Rocky Mountain Slayer come to mind first. I think several other frames can be tweaked to that geo with adjustable headsets.

  4. #4
    some know me as mongo
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    The tomac vanish and snypers are much steeper in the seattube than the headtube. its the only reason the shorter than normal toptube is acceptable. Im actually really looking at the Vanish as my next bike.

  5. #5
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    The 2012 trek bikes Fuel EX and Remedy have slacker head angles.

    I don't think the seat angle by itself is an important measurement. If you have given foward-aft position you like where you place your seat, you can accomplish that by choosing different seatposts and adjusting the rail mounting position of your saddle, regardless of seat tube angle.

  6. #6
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    The 2012 trek bikes Fuel EX and Remedy have slacker head angles.

    I don't think the seat angle by itself is an important measurement. If you have given foward-aft position you like where you place your seat, you can accomplish that by choosing different seatposts and adjusting the rail mounting position of your saddle, regardless of seat tube angle.

  7. #7
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    Nukeproof Mega 66° HA, 75°SA but, they are sold out. If you can find one it seems to be what your looking for.
    Last edited by Hutch3637; 12-07-2011 at 07:41 PM.
    Yip yip yip nope nope nope

  8. #8
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    2011 Marin Mt Vision 140 has a 67.5HA and 73.5STA (73.6 for the large)

    Put a 650B front wheel and a 150 fork (140 is stock) on the Rocky Mountain Altitude and you could drop the HA down to 67.5 and still maintain a 75 degree STA. Climbing fool and now less twitchey and more stable on decents. 30lbs or less.

    Installing a 650B front wheel is a nice way to drop a 1/2 degree on the HA on 26' bikes. Noticeable improvement as well. I have yet to read a negative review of this mod. Fox forks work with this wheel size although not officially approved by them.
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    Ragley Blue Pig! But it's a steel hardtail. may not be your cuppa tea.

  10. #10
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    [QUOTEI don't think the seat angle by itself is an important measurement. If you have given foward-aft position you like where you place your seat, you can accomplish that by choosing different seatposts and adjusting the rail mounting position of your saddle, regardless of seat tube angle.[/QUOTE]

    +1 on that. There is a certain fore-aft saddle position relative to the bottom bracket for each rider, where it should be set for optimal pedaling biomechanics. So with a steeper SA, you push the saddle back or get a setback post, and slacker SA get a straight post/push saddle forward. however, SA combined with top tube length tell you the bikes "reach", or horizontal distance between BB and top of headtube, which is the most important number for sizing and cockpit setup. 2 bikes with the same TT length, the one with a steeper seat angle will have a longer reach, especially noticeable when descending out of the saddle (unless you put a shorter stem).
    '18 banshee rune

  11. #11
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    Quote Originally Posted by the.vault View Post
    I don't think the seat angle by itself is an important measurement. If you have given foward-aft position you like where you place your seat, you can accomplish that by choosing different seatposts and adjusting the rail mounting position of your saddle, regardless of seat tube angle.
    Moving a seat for/aft is only good for about +1/-1 degree in seat angle. So a 72 degree seat angle will never get to 75 degrees through saddle manipulation. But with a setback post + back on the rails you might be able to go from 75 degree SA to 73/72.

    Yes, steep SA is important. It removes the need for a travel adjust fork for climbing.

    I ride a 2010 Enduro, 66.5 HA, 75 SA.

    P

  12. #12
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    -1 on that.

    It seems that some riders are always ramming their seats as far back as possible. Seat posts with setback can help with that, but some of us need a slack seat tube angle, a setback post, and still need to ram the saddle all the way back--and we look for saddles with long rails to provide even more reward positioning. If we started with a 75 degree seat tube, the reach would most likely be waaayyy tooooo long. In addition, it's a nice thing to be able to attach the dang saddle in the middle of the rails.

    The first thing I look at is the seat tube angle. 73 degrees or higher---forget it. 70 to 72 1/2 degrees, then it might work for me if the top tube is short enough. I ride a Blur LT2 with the seat rammed all the way back.

    SA combined with top tube length tell you the bikes "reach", or horizontal distance between BB and top of headtube, which is the most important number for sizing and cockpit setup.
    Agreed.
    Last edited by happyriding; 12-08-2011 at 07:01 PM.

  13. #13
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    Quote Originally Posted by happyriding View Post
    some of us need a slack seat tube angle, a setback post, and still need to ram the saddle all the way back--and we look for saddles with long rails to provide even more reward positioning.
    I agree that people have different bodies, longer legs or torsos or arms, but riding a moderate angle SA + set back post + long rails to the end, sounds like a stepping up in frame size might be the better answer (unless you like short bikes, which is cool. )

    You still did not address that the steeper seat angle means you can do steep climbs on a stupid slack frame with a 160mm fork. My previous 160mm frame with lower SA could not do that - it would sag into rear travel when it got steep, lightening the front and floppiness ensued.

    P

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    sounds like a stepping up in frame size
    Usually not possible.

  15. #15
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    You still did not address that the steeper seat angle means you can do steep climbs on a stupid slack frame with a 160mm fork.
    I can see the merits of that. Though I would think you'd feel like you were going to pitch over the bars if you ever sat in your seat on a downhill. To your point, I do use a Talas fork. Is the steep seat tube and slack head tube a DH specific setup?

  16. #16
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    Quote Originally Posted by Mr.P View Post
    Moving a seat for/aft is only good for about +1/-1 degree in seat angle. So a 72 degree seat angle will never get to 75 degrees through saddle manipulation. But with a setback post + back on the rails you might be able to go from 75 degree SA to 73/72.



    P
    If you do a little trigonometry you can see that every degree of change in seat angle results in a little less than .2 inches of change in effective top tube length.

    I have known some people who have done odd looking things to get a steeper effective seat angle. Mark Jordan, who's the tech writer for 'decline' used to run his maverick speed ball post backwards, in the triathlete position, to get his seat where he wanted. That was on gen 1, nomad which had a slack seat angle.

  17. #17
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    Quote Originally Posted by happyriding View Post
    sounds like a stepping up in frame size
    Usually not possible.
    ok, and I can't judge fit on the interweebs either.


    Quote Originally Posted by happyriding View Post
    Though I would think you'd feel like you were going to pitch over the bars if you ever sat in your seat on a downhill.
    On the downs, my saddle is down, and I am off it so the steep SA becomes a non-issue.

    Quote Originally Posted by happyriding View Post
    Is the steep seat tube and slack head tube a DH specific setup?
    It's an AM set up, the position is more forward like an XC bike when riding the flats. Out of the saddle for the downs or FR stuff & scoot forward a bit for the steep ups. I run a 50mm stem as well and it still goes up better than it should.

    P

  18. #18
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    Quote Originally Posted by the.vault View Post
    If you do a little trigonometry you can see that every degree of change in seat angle results in a little less than .2 inches of change in effective top tube length.
    My experience came from a slacker SA 06 Enduro (~72*) that I used a straight post & pushed the saddle forward as far as possible. My imperfect measurements in Photoshop showed me only a degree change (73*, but come to think of it, the bike was over forked by 20mm A-C). No way I could get close to the position I'm in now with the 2010, Enduro, and the TT length is similar on both.

    Seems odd just .2 inches would be 1 degree. That would mean 1 inch, would = 5 degrees. 1 inch would be like going from XC to DH in position. Offset seatposts are almost an inch. Would that be .2 at the TT? or .2 at seat height? it just seems odd.

    I will say that a steeper SA is a better starting point if one was looking at buying a frame.

    P

  19. #19
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    Although your post supports my argument, I must point out this is false. Given a common length from bottom bracket to saddle of, say, 29", each degree = about .5" (sin1 x 29 = .5"). However, that can still give up to 3-5 deg adjustment range, depending on saddle rail length and seatpost setback.

    Quote Originally Posted by the.vault View Post
    If you do a little trigonometry you can see that every degree of change in seat angle results in a little less than .2 inches of change in effective top tube length.

    I have known some people who have done odd looking things to get a steeper effective seat angle. Mark Jordan, who's the tech writer for 'decline' used to run his maverick speed ball post backwards, in the triathlete position, to get his seat where he wanted. That was on gen 1, nomad which had a slack seat angle.
    '18 banshee rune

  20. #20
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    Quote Originally Posted by skidad View Post
    2011 Marin Mt Vision 140 has a 67.5HA and 73.5STA (73.6 for the large)

    <snipped>
    I was about to mention the 2010 and 2011 Marin Attack Trail models which have a HA of 66° and a seat tube angle of 73.5°. The top level trim comes with a 160mm fork in both years, 2011 6.9 using a Fox 36. The rear shock is 150mm for both years in all trim levels.

    I have a 2010 6.8 that I built up -- and it works awesome. Started out with a Rock Shox Revelation Team dual air 150mm but changed out to a Fox 36 TALAS RC2 160mm. Climbs and descends all day. It is my go-to bike.

    The 2011 MV would be a great choice too. I have a 2009 model year but it has more classic XC-ish geometry and less travel at 120mm.

    2010 and 2011 Marin ATs can be had at deep discount pricing if you hunt around. I'd snap them up because I am not convinced the newer 2012+ suspension design is going to be as good as the Quad Link 2. Remains to be seen I suppose. Quad Link 2 rocks.

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    Quote Originally Posted by Mr.P View Post
    I agree that people have different bodies, longer legs or torsos or arms, but riding a moderate angle SA + set back post + long rails to the end, sounds like a stepping up in frame size might be the better answer (unless you like short bikes, which is cool. )

    You still did not address that the steeper seat angle means you can do steep climbs on a stupid slack frame with a 160mm fork. My previous 160mm frame with lower SA could not do that - it would sag into rear travel when it got steep, lightening the front and floppiness ensued.

    P
    Try a DW link bike. The suspension doesn't sag into the travel when climbing. My Pivot mach 5.7 has a 67.1 HTA and a 71.1 STA. Your unlikely to find a better climbing bike with that amount of travel (even with the slack STA).

  22. #22
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    Quote Originally Posted by dwyooaj View Post
    Although your post supports my argument, I must point out this is false. Given a common length from bottom bracket to saddle of, say, 29", each degree = about .5" (sin1 x 29 = .5"). However, that can still give up to 3-5 deg adjustment range, depending on saddle rail length and seatpost setback.
    As long as people are interested and I didn't catch my own mistake...you are correct the change effective top tube length works out closer to 0.5 inch per degree.

    To do the calculation correctly you really need look at the change in Sin for a degree shift. Basically Sin (angle 1) - Sin (angle 1 + 1 degree). That value will change as the angle 1 varies from 0 degree to 90 degrees. When I made my mistake I calculated (sin 72 - sin 73) * 30 inches. I should have been using the complimentary angles.

    For what's worth I like having bikes with steeper seat angles as well. I also have shorter upper leg length relative to my lower leg length.

  23. #23
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    Quote Originally Posted by Vega77 View Post
    Try a DW link bike. The suspension doesn't sag into the travel when climbing. My Pivot mach 5.7 has a 67.1 HTA and a 71.1 STA. Your unlikely to find a better climbing bike with that amount of travel (even with the slack STA).
    While the DW link is a great suspension design, no suspension can get past the rearward shift of weight to the back of the bike on steep climbs (more weight on the rear suspension = more sag) and a slacker STA will add to the rearward bias.

    I had a DW Link bike in 04. Climbed like a goat.

    P

  24. #24
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    Quote Originally Posted by Mr.P View Post
    ...(more weight on the rear suspension = more sag) and a slacker STA will add to the rearward bias....
    Very true, when there's less than 100% anti-squat at static sag. And then squatting suspension compression is compounded increasingly deeper as the climb become steeper.

    Remember the physics, anti-squat adds to spring force to support the suspension while pedaling. It is impossible for the center of mass, when anywhere between the wheelbase, to squat below static sag, on average, when there is 100% or more anti-squat force.

    Considering the interest of the original post.... Steeper seat tube angles and climbing.... For the same suspension travel, bikes with lower anti-squat suspension rate need steeper seat angles than higher anti-squat designs for similar rider position and power over the pedals and front wheel weight while climbing. A high anti-squat design can climb just as easily with over 3 degrees slacker seat angle than a low anti-squat design with the same travel, etc. Chain stay length, shock and it's leverage rate, and platform damping are other big climbing balance factors too.

    JMO, of course!

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    anyone know the angles on the new Scott Genius? Can't seem to find the specs.

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    Quote Originally Posted by motard5 View Post
    anyone know the angles on the new Scott Genius? Can't seem to find the specs.


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    skidad, thanks much. I just put down a deposit for the Genius 700 woot.

  28. #28
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    My Rocky Mountain Altitude coupled with a dropper post is a real killer in descents (note that my rear wheel doesn't like me much!). Then pop back the seat to it's highest point, and you also have a killer climber.

    Love the geometry. Love the ride.
    Main bike : Altitude RSL 70 '11
    DH bike : Aurum 2 '12

  29. #29
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    Quote Originally Posted by motard5 View Post
    skidad, thanks much. I just put down a deposit for the Genius 700 woot.


    Make sure to post pics and a ride review in the 650B forum!

    My Rocky Mountain Altitude coupled with a dropper post is a real killer in descents (note that my rear wheel doesn't like me much!). Then pop back the seat to it's highest point, and you also have a killer climber.

    Love the geometry. Love the ride.
    I'd like to see Rocky build a 650B Altitude. That would be sweet.
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