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  1. #1
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    Slack head tube angle and handling?

    I have a Soma B Side v3 with a headtube angle around 67-68 degrees. I have a Salsa Cromoto grande steel fork on it as well. I have been riding this bike for 2 years. I have always felt unsteady on tight single track and around obstacles such as bridge crossing or log rail type technical stuff. The steering has always felt just "unsteady" and it can be a little unnerving when approaching a ditch crossing or other obstacle that requires a steady straight wheel. I also notice that I tend to over shoot tight turns at speed frequently and end up brushing trees or in the grass before I get back on the track. I have always chalked this up to my inexperience and that may very well be what it is. But lately I noticed that when I ride on the city streets where I live, if I relax my hands on the bars and slightly "influence" them (if you know what I mean) the wheel wants to flop one way or the other pretty hard. It reminds me of sitting on a chopper with a raked fork and letting the bars go and the front wheel falls to the side. Obviously this is due to my extra relaxed HTA+ the fork rake. I think I am going to swap all my components over to a cheaper aluminum XC frame I got laying around with a 72 HTA and go try it. But I had to ask here.....Am I on the right track or should I just work on my skills more and quit blaming the frame? I am rockin 720 bars and an 80 mm stem in case anyone wonders.

  2. #2
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    Slack usually feels more stable/slower steering.

    Going steeper to like a 72 would be quick or "twitchy". The rigid fork may be to blame somewhat.
    Kind of hard to explain but have you ever heard or seen when someone is about to turn, lets say to the right, and they actually turn the bars left first?..followed by carving back to the right into the turn?
    That little trick kind of helps get the bike leaning the right way. I hope I made sense of that for you. It really does help.

  3. #3
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    longer, slacker bikes need to be leaned a bit more to carve a turn quickly. Doesn't take as much "steering input" as you might use on a bike with a steeper HTA, so there's some getting used to it involved. if it's really slow a tight, it can be tricky with a long and slack bike. but it makes up for that slightly slower handling by being much more stable when you open things up at speed.

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    Ok all that makes sense. I wonder if changing forks to something with less rake would help. I knew that steeper head to the angles were more twitchy but since a slacker angle tends to want to fall over more I thought that contributed to it being twitchier on more technical stuff as you fought to hold the wheel straight.

  5. #5
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    Fork geometry might be something relevant to consider changing, as it can absolutely affect the handling of the bike. You might want to consider the fork geometry that Soma recommends for that bike (axle-crown length and offset). If they recommend axle-crown length for suspension forks, it's important to note the "sagged" a-c if you are looking to install a rigid fork. If your rigid fork has the a-c that's the same of the unsagged a-c of a suspension fork, you'll effectively be slackening the bike even more than the manufacturer's specifications.

    Wheel flop issues are related to head tube angle, but also to fork offset (oftentimes referred to as rake on rigid forks). They definitely affect steering characteristics of a bike. This article is more focused on these topics from a road bike standpoint (so the absolute numbers might be off for mtb applications), but they're still generally meaningful in relation to mtb's as being descriptive of how these aspects of geometry affect handling.
    https://calfeedesign.com/tech-papers...bike-handling/

    Again, consider manufacturer recommendations when looking at your setup.

  6. #6
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    Check out this calculator to get trail and flop numbers, then play with changing HTA and Offset. You'll find that HTA changes have a HUGE impact on wheel flop -- that's what I believe the OP is describing -- and Offset of the fork (rake) not so much. Bikes with slack head tube angles with a trail equal to X have more wheel flop that bikes with steep head tube angles with trail equal to X. In real world conditions I find this to be more than theoretical -- bikes with steep HTA are more precise at slow speeds and all else being equal.

    If you have a road bike, ride up a steep hill standing up in a slightly too big of a gear -- feel and see how the front end moves side to side? Now try that with your current MTB which will have a lot shallower HTA (and different trail measurements to be sure), and I think you'll see how much more effort it takes to keep the front end tracking straight. That's wheel flop in action.

    The "twitchy" term comes from trail measurement issues, not HTA directly. Smaller trail numbers (steeper HTA, more rake, combination of both) require smaller steering inputs to get a response. Shallower HTA or less rake lead to a larger trail number which requires more steering input (so less "twitchy") to get a similar response. It's my opinion that people are discovering that the shallower HTA and more offset are putting the front wheel out in front in a way that allows the rider more time to deal with impacts and not overweight the front of the bike (less endo prone or inappropriate lightening of the rear wheel).

    If you (iowamtb) have the energy, I think you would enjoy the experiment of trying out a bike with different geometry. If you do it, report back on your impressions.
    "The plural of anecdote is not data." -- Attributed to various people in a variety of forms, but always worth remembering...

  7. #7
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    Quote Originally Posted by Ptor View Post
    Check out this calculator to get trail and flop numbers, then play with changing HTA and Offset. You'll find that HTA changes have a HUGE impact on wheel flop -- that's what I believe the OP is describing -- and Offset of the fork (rake) not so much. Bikes with slack head tube angles with a trail equal to X have more wheel flop that bikes with steep head tube angles with trail equal to X. In real world conditions I find this to be more than theoretical -- bikes with steep HTA are more precise at slow speeds and all else being equal.

    If you have a road bike, ride up a steep hill standing up in a slightly too big of a gear -- feel and see how the front end moves side to side? Now try that with your current MTB which will have a lot shallower HTA (and different trail measurements to be sure), and I think you'll see how much more effort it takes to keep the front end tracking straight. That's wheel flop in action.

    The "twitchy" term comes from trail measurement issues, not HTA directly. Smaller trail numbers (steeper HTA, more rake, combination of both) require smaller steering inputs to get a response. Shallower HTA or less rake lead to a larger trail number which requires more steering input (so less "twitchy") to get a similar response. It's my opinion that people are discovering that the shallower HTA and more offset are putting the front wheel out in front in a way that allows the rider more time to deal with impacts and not overweight the front of the bike (less endo prone or inappropriate lightening of the rear wheel).

    If you (iowamtb) have the energy, I think you would enjoy the experiment of trying out a bike with different geometry. If you do it, report back on your impressions.
    I have a Jamis Trail x 650 hanging on the wall that never gets ridden anymore. Cross country geometry so it would be a perfect example of what you was referring to. I need to go try it sometime and see how it feels. And you hit it right on the head what I am experiencing is wheel flop. And my original question was asking if we will flop inhibited precise steering at slow speeds.

  8. #8
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    Don't forget to cut your bars down to 600mm and swap that short 80mm stem for a 120mm at least when you go back to the 72* HA frame, then you can really party like it's 1992 all over again!





    IMO 67-68* isn't particularly "slack" by modern standards. Without knowing too much about you or your trails I'd suggest trying a 50-60mm stem and some wider (~760mm) bars. I've never found wheel flop to be a noticeable issue on the trail riding bikes with 65-67* HA, and I can't help but wonder if the long-ish stem isn't exaggerating it a little.

  9. #9
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    Quote Originally Posted by David R View Post
    Don't forget to cut your bars down to 600mm and swap that short 80mm stem for a 120mm at least when you go back to the 72* HA frame, then you can really party like it's 1992 all over again!





    IMO 67-68* isn't particularly "slack" by modern standards. Without knowing too much about you or your trails I'd suggest trying a 50-60mm stem and some wider (~760mm) bars. I've never found wheel flop to be a noticeable issue on the trail riding bikes with 65-67* HA, and I can't help but wonder if the long-ish stem isn't exaggerating it a little.
    Well I used to run a 60 and still have it. The reason I put the 80 on is because if I ride the bike in other ways beside single track I feel crowded with a 60 but I guess on single track I am standing and mashing more as I prefer that to sitting on my bum and spinning. As far as wider bars I am comfortable with 720. That's shoulder width for me and beyond that gets uncomfortable after enough miles.

  10. #10
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    Quote Originally Posted by David R View Post
    Don't forget to cut your bars down to 600mm and swap that short 80mm stem for a 120mm at least when you go back to the 72* HA frame, then you can really party like it's 1992 all over again!





    IMO 67-68* isn't particularly "slack" by modern standards. Without knowing too much about you or your trails I'd suggest trying a 50-60mm stem and some wider (~760mm) bars. I've never found wheel flop to be a noticeable issue on the trail riding bikes with 65-67* HA, and I can't help but wonder if the long-ish stem isn't exaggerating it a little.
    :church:

    65.5░ HTA here, 50mm stem + 785mm bars.

    HB's should be wider than shoulders :imho:

    Press up protocol

    I'd say go 750 w/ 50mm stem & you'll be rockin' it

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  11. #11
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    Quote Originally Posted by Harold View Post
    longer, slacker bikes need to be leaned a bit more to carve a turn quickly. Doesn't take as much "steering input" as you might use on a bike with a steeper HTA, so there's some getting used to it involved. if it's really slow a tight, it can be tricky with a long and slack bike. but it makes up for that slightly slower handling by being much more stable when you open things up at speed.
    This.

    I find with my Spitfire, you are less able to follow the center of a trail. At slow speeds and in tight switchbacks it can seem a little twitchy, but you just always have to be mindful of where the back wheel is. It does not like to be turned by the handlebars.

    All around I find it likes to enter corners high and quickly cut the apex of the corner (think driving an autocross track with a nice sports car).

    At medium to high speeds you really need to get your body involved, engage your lower body weight with your hips and heals. Again, it still likes to enter high in the corner high and turn quickly across the turn. At speeds a degree of trust between you and the bike will come into play, but once you figure it out, you'll never think about old-school xc geo again.

    It's best to pretend like your handlebars don't move, and your body is the fulcrum from which all turns come.

    Find a section of trail with stuff that's giving you trouble and session it, even better if you have a trail network with miles of tight switchbacks.
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  12. #12
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    What I am going to do for now is put a shorter stem on and go play with it. I originally had a 60 on this with 720-740 bars and thought it was ok but that was a year ago. I have only been single tracking 3-4 times since then. Once I swapped out a longer stem for a weekend trip and didn't like it. Another few times I had Jones H bars on with a different stem. I haven't ridden the 60 mm stem and wider bars in so long that I think I need to go back and give it a try. I appreciate all the advice and I am sure glad to know that my HTA is not crazy slack cause I really loved this frame and wasn't thrilled about shopping for another one. But I was willing to do what I had to if that would have helped. Again thanks fellas.

  13. #13
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    Quote Originally Posted by iowamtb View Post
    What I am going to do for now is put a shorter stem on and go play with it. I originally had a 60 on this with 720-740 bars and thought it was ok but that was a year ago. I have only been single tracking 3-4 times since then. Once I swapped out a longer stem for a weekend trip and didn't like it. Another few times I had Jones H bars on with a different stem. I haven't ridden the 60 mm stem and wider bars in so long that I think I need to go back and give it a try. I appreciate all the advice and I am sure glad to know that my HTA is not crazy slack cause I really loved this frame and wasn't thrilled about shopping for another one. But I was willing to do what I had to if that would have helped. Again thanks fellas.
    Body position, how wide the handlebars are in relation to your arm/shoulder width and chain stay will influence your nimbleness in corners and technical sections. I don't believe Head angles play a key role in this unless you're on a steep decline or steep incline.

    Stem length is going to influence your body's weight position when going up or down. Longer the stem the better it will be for the rider to place his/her self while climbing so that the wheel can stay grounded. However, there is a cost when using a longer stem since a longer stem puts the rider at a disadvantage when going downward.

    You should tinker with stem length depending on what type of trails you use. If you mostly ride going down I'd opt for a shorter stem. If you battle tough steep climbs most of the time I'd opt for a longer stem.

    However, the stem isn't going to help improve your steering. That boils down to how well you fit the bike overall.
    My bike is all tricked out. It has pedals, a handle bar, a seat and two wheels! H8tRs gunna H8t!

  14. #14
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    If you have an epiphany, please post here:

    http://forums.mtbr.com/frame-buildin...e-1041624.html

    Thanks!

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  15. #15
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    I think the HTA is not as slack as you think it is. the geo chart on Soma's website has figures that represent a longer fork than you have. i think...

  16. #16
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    Certainly if you have the other frame laying around, try a swap. You never know until you try. You gotta monkey around to find what works best.

    I certainly prefer a steeper HTA on a hardtail. The sections of trail that would benefit from BOTH no rear squish and a slack HTA are few and far between where I ride.

  17. #17
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    Quote Originally Posted by mack_turtle View Post
    I think the HTA is not as slack as you think it is. the geo chart on Soma's website has figures that represent a longer fork than you have. i think...
    I looked at a rigid Fork that Soma offers that I believe it's designed for this bike as well as the Soma juice And it has a similar axle to crown as my current Fork (465 compared to 468). CrMo MTB 29er/650b Fork | SOMA Fabrications

    So I don't think I'm too far off. In fact it's been a few years ago but I believe I consulted Soma about using this Fork because I already owned it when I purchase their frame and I think they said that was right in the ballpark of what they would recommend. But don't quote me on that like I said that was over 2 years ago

  18. #18
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    Also as far as climbing if you're running a shorter stem can't you to lean your body further forward to get the same effect as having the longer stem? I like the way this bike always rode in the past with a 60 millimeter stem but a lot of the trails I ride have a lot of steep climbs.

  19. #19
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    Quote Originally Posted by targnik View Post
    :church:

    65.5░ HTA here, 50mm stem + 785mm bars.

    HB's should be wider than shoulders :imho:

    Press up protocol

    I'd say go 750 w/ 50mm stem & you'll be rockin' it

    Sent from my kltedv using Tapatalk
    What Targnik said! Newer bikes built with slacker head tube angles are meant to be set up with short stems and long handlebars or else they will never feel right.

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    I think new bikes are great, but it's a bit rediculous with all the standards and angles. I think a good full suspension all around bike is 67░ HTA. Anything slacker isn't good for climbing and anything steeper feels sketchy going down hill. Bars are always a rider preference. I have 760mm with 60mm stem and that's the widest I would ever go. Many of us worry about numbers and newest trends way too much. Ride it, learn it and enjoy it.

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    ^that's a really random, irrelevant thought to share in order to bump a thread that's a year old.

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    ^ no it isn't.
    Do the math.

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    Quote Originally Posted by mack_turtle View Post
    ^that's a really random, irrelevant thought to share in order to bump a thread that's a year old.
    Just happened to run in to the post.

  24. #24
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    Quote Originally Posted by gtzaskarrider View Post
    Just happened to run in to the post.
    Maybe with better steering geometry you could have swerved right around it.
    No dig no whine

  25. #25
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    Quote Originally Posted by mack_turtle View Post
    ^that's a really random, irrelevant thought to share in order to bump a thread that's a year old.
    Nothing wrong with reminiscing an older thread.

  26. #26
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    Quote Originally Posted by gtzaskarrider View Post
    Anything slacker isn't good for climbing
    Can you explain how [all other things being equal] HTA effects climbing performance?

  27. #27
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    Quote Originally Posted by David R View Post
    Can you explain how [all other things being equal] HTA effects climbing performance?
    I didn't think he would.

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    I got some bad ideas in my head.

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    Quote Originally Posted by Travis Bickle View Post
    I didn't think he would.

    Sent from my SM-G935S using Tapatalk
    he's prolly tired from holding the bars from flopping over
    Just kidding I use to ride slack and loved it! Then 68* became not-slack and I still have that bike. ha
    It is surprising how slack some trailbikes are. Anyone here read the Tantrum thread? He's setting trailbikes up at 64* and loving it.
    oops I wasn't clipped in

  29. #29
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    I hate overly slack rigid bikes with floppy suspension-corrected forks. The entire bike is designed to fight you every inch of the way.

  30. #30
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    Quote Originally Posted by esXso View Post
    I hate overly slack rigid bikes with floppy suspension-corrected forks. The entire bike is designed to fight you every inch of the way.
    What do you consider too slack?
    I got some bad ideas in my head.

  31. #31
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    Quote Originally Posted by esXso View Post
    I hate overly slack rigid bikes with floppy suspension-corrected forks. The entire bike is designed to fight you every inch of the way.
    I guess that's one of the reasons why bikes have super steep seat angles now...to put more weight over the handlebar? What I've found with "slack" bikes is at low speeds...the front end will wander and oscillate back and forth.

  32. #32
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    Correct. Seat tubed are becoming steep now and really the bikes are more ugly that way. Very slack front will cause bars to be forced in to sides so steering needs to be corrected more often. I'm not saying it isn't good, but middle ground is always a better way for multiple applications. My bike climbs okay, but steep hills is definitely a challenge with 150mm front and 140mm rear travel.

  33. #33
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    Quote Originally Posted by gtzaskarrider View Post
    Correct. Seat tubed are becoming steep now and really the bikes are more ugly that way. Very slack front will cause bars to be forced in to sides so steering needs to be corrected more often. I'm not saying it isn't good, but middle ground is always a better way for multiple applications. My bike climbs okay, but steep hills is definitely a challenge with 150mm front and 140mm rear travel.
    A steep seat tube is ugly, that's funny.

    My new bike with a 64.75░ HTA, 160mm front, and 135mm rear travel is the best climbing bike I have been on in my 30+ years of mountain biking. I feel like I'm cheating, up and down.
    I got some bad ideas in my head.

  34. #34
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    I'm sure it is

  35. #35
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    MTBR members come from all over the world with a myriad of trail types and conditions. One person's fun little section is another's poop in the pants. We were discussing this on last nights ride when I voted for a certain fav trail of mine that one of the guy's says is too straight. He says straight (it ain't), I say fast. He also likes it so steep that I see my life flash in front of me. We both agree on ebikes and pizza though. I seem to have wandered a bit OT, as happens at my age.
    I got some bad ideas in my head.

  36. #36
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    Quote Originally Posted by David R View Post
    Can you explain how [all other things being equal] HTA effects climbing performance?
    All else equal, slacker HTA = slower steering (more trail and more wheelbase), which makes it harder to maintain your balance by countersteering, because it requires more steering input for the same amount of lean angle. At speed, where the gyroscopic forces keeping your bike upright are more apparent, slower steering is a non issue and often a benefit. On a technical climb where you're progressing a half pedal stroke at a time, it makes a difference.

    Slacker HTA also moves the balance point of the bike rearward, again, great for descending, not so much for climbing.

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