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  1. #1
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    MTB geometry and shorter stems

    This isn't about building new frames, more making the most of what i've got. This forum seemed like good place to start though.

    Has anybody done experimenting with longer toptubes combined with shorter stems? I mean actually short stems, stuff approaching zero reach?

    I think Mondraker coined it Forward Geometry.

  2. #2
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    Aside from riding a frame size up for the longer reach, the only experimenting I've done with "short" stems is with dirt drop-bars, using the now defunct On/Off Stoic stem (which was spec'd on Mondraker's FG bikes...).


    MTB geometry and shorter stems-kimg0439.jpg

  3. #3
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    All I can say is wow, thatís a funky ass ride!

    I do a bit of mechanicing for a World Cup DH rider, weíve been playing with different size frames and different length stems. All chasing the ďidealĒ bike set-up. Iím kind of out of my depth now, and wanted someone to magically give me some answers having already gone down this road.

    I know this forum isnít very DH orientated, was just hoping someone may have explored this avenue on the All-mountain/Enduro/Trail whatever you want to call it descending side of riding.

  4. #4
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    Check out PVDs posts or his website. He made some custom bar/stem combos for his bikes-- and his bikes are very long in the front end.

    https://www.peterverdone.com/i-dont-...apons-systems/

  5. #5
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    Quote Originally Posted by Cord View Post
    All I can say is wow, thatís a funky ass ride!
    Handles remarkably well loaded or unloaded, suspended or rigid. It's been my N=1 bike for a bit (24+ hr to bikepacking race bike, long-distance commuting, etc).

    But, I have no insight for where you're at on the DH geometry, and how longer reach/FC and shorter stems would impact that set-up.

  6. #6
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    Quote Originally Posted by jsudar View Post
    Check out PVDs posts or his website. He made some custom bar/stem combos for his bikes-- and his bikes are very long in the front end.

    https://www.peterverdone.com/i-dont-...apons-systems/
    Thanks, Iíll have a nosey. Seems like the kind of info Iím after.

  7. #7
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    Quote Originally Posted by VegasSingleSpeed View Post
    But, I have no insight for where you're at on the DH geometry, and how longer reach/FC and shorter stems would impact that set-up.
    Cheers anyway.

  8. #8
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    Ah, i donít know if the info Iím chasing will be something youíve focused on, because I am purely interested in handling traits when stood up. Presumably you will be trying to make a far more rounded bike.

    Anyway, can I pick your brains? Iíve already arrived at longer reach/front centre. I think my issue is riders centre of gravity not moving as I expect, and not weighting the front wheel. Iíve lots more questions than Iíve vaguely got answers for. I suppose itís going to be quite long winded!!

  10. #10
    pvd
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    I post a lot of information on modern bike design. Just look at my posts for a while. Definitely, ignore everything the magazines and marketing folks say.

    This may help.
    Forward Geometry | Peter Verdone Designs

    For most riders, you're looking for as extreme an XC riding position as possible. Under the rider, we shape the bike for other factors.

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    Leelikesbikes has some on handling bike fit when stood up. His approach seems to be a little different than most though. I. E. He thinks most riders are on too long a frame for "stood up" riding.

    I haven't paid for his stuff or read that much of it. But I think he has a couple articles on Pinkbike if you want dig into some of it.

  12. #12
    pvd
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    Learning to draw a bike properly is the first step in all this. Few people do.

  13. #13
    pvd
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    Ignore LeeLikesBikes. He's lost.

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    PVD, thanks Iíve already read that stuff on your website, plus lots of other people thoughts including Chris Porter. Lots I agree with, some I donít, some is just plain contradictory. I figured youíre a good persons brains to pick further as you seem to have actually experimented with this for a while. Thatís not a position Iím capable of being in, so why not ask!

  15. #15
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    I still do the occasional bit of spannering for DH racers, all year my rider has been swapping from medium to large frame, not quite happy with either. Iíll try to not get too bogged down in minor details for now.

    On the smaller frame he prefers the front end feel, and is more confident to load up the front end and ride that end of the bike harder.

    On the the longer frame he prefers the stability at speed, but finds that in flat turns the front pushes, so he lacks confidence to attack in this situation, also feels its less planted on off camber stuff (which is essentially the same problem as flat corners i think) It seems like there isnít enough weight on the front wheel.

    Chain stay has 15mm of adjustment, but long is the only setting thats ever used, the short he feels is too twitchy, and he canít get used to it. Iíve made a +/-0.5ļ angle adjust headset. Steep is (a measured) 64.2ļ Slack is 63.2ļ standard 63.7ļ

    On the shorter frame we mainly use the slacker head angle. (And on the very odd occasion the mid head angle)

    On tracks that have some high speed sections weíve used the longer frame, and the same 35mm stem. Which is good for the fast, but he feels the front wheel is to far infront of him and lacks grip in fast corners and off camber. So weíve, experimented using the mid and steep head angle. This is an improvement. However, bike is now less stable on the real steep bits.

    Iíve made a super short stem that is either 0 or +10mm offset, same height as what was previous. Now with this set at 10mm he feels like thereís more grip on the front wheel and is confident to lean on it in flat corners. (Weíve not used the 0mm reach yet, hands being far behind the centre of steering may start adding other aspects and Iíve already got enough variables) This is with the mid head angle setting.

    This seems a bit counter intuitive to me. Iíd have thought longer reach equals riderís body leaning forward more, hence more weight on the front, and thats where the grip has come from? I need to get my head round this, otherwise I canít really help advise any further on set-up without understanding the mechanics.

    So is there actually more weight on the front and this is helping grip? Or is something else going on due to the shorter stem and hands now being approx in line with steering axis?

  16. #16
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    Not overly pretty, but plenty good enough for experiments. On the side view you can see a counter bored hole within the bar clamp, this allows it to be rotated 180ļ and be either 0mm or 10mm reach

    MTB geometry and shorter stems-img_1108.jpgMTB geometry and shorter stems-img_1109.jpg

  17. #17
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    Quote Originally Posted by Cord View Post
    This seems a bit counter intuitive to me. Iíd have thought longer reach equals riderís body leaning forward more, hence more weight on the front, and thats where the grip has come from? I need to get my head round this, otherwise I canít really help advise any further on set-up without understanding the mechanics.
    Any video of him riding flat turns with the 35mm stem to compare to the 10mm stem? Perhaps the longer stem makes him feel like he's too far forward and he's compensating for that "feel" by pushing his COG back and unloading the front; whereas with the 10mm stem, he feels more neutral and is positioning his COG where it needs to be for those turns?

  18. #18
    pvd
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    You really need to make some drawings. It will help you anaylize different setups better.
    One big thing that will change how you look at bike geometry is to ignore the crap between the grips, the pedals, and the tires. I use a reference at the end of the grip to do this.

    What CAD system are you using? Get something set up there that you can use to truly compare setups.

    This post addresses some of the important cockpit details: Bars, stems, and spacers | Peter Verdone Designs

  19. #19
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    I've used bikecad, But i'm slow at it and find it a bit clunky. I'm old fashioned and have already done plenty of actual drawings before going down this road. Focused on wheel centres, bottom bracket, handlebars and steering axis.

    When we swapped frames and i made a new stem i did as much as i could to put the handle bar grip (or the bar end reference point you speak of) back in the same position as it was on the smaller frame, ie height from floor, distance horizontally from BB.

    On the larger frame going from the 35mm stem to my 10mm stem has moved the grips vertically down 11mm and more importantly from being 16mm in front of the steering axis, to 8mm behind it.

    It's the fact that handlebars are now behind the steering axis i'm focusing on. I've no idea, what, if any, effect it is having on front end handling.

    Is the front end of the bike now gripping because previously the reach was just too long and the rider was leaning away from the front wheel to keep his position more relative to the BB. Or has moving steering input from in front, to behind the steering axis had some effect?

    I know a whole lot of this is based on feel so its all subjective, i may not arrive at a defined answer, but i still like to think about it!!

  20. #20
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    Quote Originally Posted by VegasSingleSpeed View Post
    Any video of him riding flat turns with the 35mm stem to compare to the 10mm stem? Perhaps the longer stem makes him feel like he's too far forward and he's compensating for that "feel" by pushing his COG back and unloading the front; whereas with the 10mm stem, he feels more neutral and is positioning his COG where it needs to be for those turns?
    I have some pictures and videos, but its soooooo hard to try and make comparisons. I know what you mean about him simply moving his body further back, it's quite possible.

  21. #21
    pvd
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    Without quality drawing, you're just throwing darts and hoping. It may seem like a bother but you will get nowhere without meaningful parameters to compare.

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    Quote Originally Posted by pvd View Post
    Without quality drawing, you're just throwing darts and hoping. It may seem like a bother but you will get nowhere without meaningful parameters to compare.
    What makes you say my drawings arenít good enough?

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    And the quality of my drawings do not change the parameters. My measurements are still the same, whether you deem me to be ďgoodĒ at drawing or not.

  24. #24
    pvd
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    Show your drawings.
    90% of framebuilders have no idea how to draw a bike so I'm doubtful yours are very good.
    Listen, I've told you how to get to the bottom of all this. You don't want that to be the case. You're making a choice.
    Learn the tools of the trade.

  25. #25
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    My drawing of a bike may or may not be up to your standard, however that has absolutely nothing at all to do with the subject at hand. As you even said yourself,

    Quote Originally Posted by pvd View Post
    ignore the crap between the grips, the pedals, and the tires. I use a reference at the end of the grip to do this.
    My drawings could be a scribble on the back of a cigarette packet, or an exercise in GD&T AISME 14.5 that would make Iain Macleod proud of what he taught me. That will never change the fact that the only points i'm intersted in are 3 axles, a steering axis and bar position. From here i'm just then doing some trigonometry to establish the difference in bar position, between 2 different stem lengths. The only thing you and i differ on is that you work to end of bar, my calcs were to a midpoint along the grips.

    Quote Originally Posted by pvd View Post
    I've told you how to get to the bottom of all this.
    Really? I genuinely must have missed it, all you've done is tell me you've been down this road yourself, and point me to your website which again tells me you've done it, and that your bikes are now better handling. Oh, and that i need better drawings.

    A drawing is just a visible way of showing data, I now have that data, i know what has moved, how far it has moved, in what direction and where it sits in location to other items. These are the parameters which count.

    What i don't have is firsthand experience of this style of geometry. It appears you do, yet you don't wish to share that info. Thats fine. Lets end the conversation here.

    By the way Teach, is it ok if i hand in my Tech Drawing and Maths homework tomorrow for you to check? Hope i get an A*

  26. #26
    pvd
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    I know about 10,000 bike geometry experts on PinkBike. Not one of them has drawn a bike. I've drawn about 10,000 bikes. Everyone says I don't know what I'm talking about.

    Make a proper print. That's your problem.

  27. #27
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    Have you busted out the scales to see what the front / rear tire weight balances do between the two bikes?

    My though on the solution to the problem will be a longer rear center to bring the weight distribution back into balance.

  28. #28
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    Quote Originally Posted by Cord View Post

    On the smaller frame he prefers the front end feel, and is more confident to load up the front end and ride that end of the bike harder.

    On the the longer frame he prefers the stability at speed, but finds that in flat turns the front pushes, so he lacks confidence to attack in this situation, also feels its less planted on off camber stuff (which is essentially the same problem as flat corners i think) It seems like there isnít enough weight on the front wheel.
    As someone who has been in a similar quandary I am following this, interested in results you might find.

    Additionally I am curious, do you adjust suspension pressure and tire pressure when changing stems/frames?
    Lucky neighbor of Maryland's Patapsco Valley State Park, 39.23,-76.76 Flickr

  29. #29
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    Quote Originally Posted by shirk View Post
    Have you busted out the scales to see what the front / rear tire weight balances do between the two bikes?

    My though on the solution to the problem will be a longer rear center to bring the weight distribution back into balance.
    Not tried the scales on this one, but have experimented with it in the past. We found it challenging to get repeatable results just on the same bike. My thoughts were itís too hard to get the rider to accurately re-create his actual attack position when ďgiving it the berriesĒ if I couldnít get good results on 1 bike, seemed kind of pointless to try it on 2. Maybe a pair of those quark shockwiz things and compare pressures, but Iíve never used one to see what actual data it gives you?

    I canít alter chainstays, itís already in the long setting.

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    Quote Originally Posted by shoo View Post
    As someone who has been in a similar quandary I am following this, interested in results you might find.

    Additionally I am curious, do you adjust suspension pressure and tire pressure when changing stems/frames?
    Tyre pressure we have a 2 psi window we rarely go outside, we know what gives grip, and we know what gives flats. With the longer frame and longer stem we did try changing pressure in the forks, but didnít really make any gains from it. On the smaller frame we do change pressure in the forks quite regularly, especially when swapping head angles. Generally a bit higher for the steep courses, but thatís a fairly standard thing.

  31. #31
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    I have also been reading over PVD's blogs with great interest. I don't think I'll become a frame builder by any means, but I do find the writings to help reinforce things I am learning in the Engineering degree I am taking.

    I particularly found this article, https://www.peterverdone.com/why-we-dont-draw-on-paper/ the most interesting as I had also assumed that drawings used to be done by hand. I didn't realize how much early builders used available technology to help with the process. I was under the assumption that most things were drawn on paper, including my own drawings with a product that I was hoping to bring to market. But after taking some classes (and I still have a long way to go), my original drawing was pure shit and needed a lot of working. It wouldn't have been fair to the people I approached to have them figure out all those intricate little details that I either never thought of or didn't account for.
    Silly bike things happening.

  32. #32
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    Quote Originally Posted by shirk View Post
    My though on the solution to the problem will be a longer rear center to bring the weight distribution back into balance.
    yep. you stretch the reach to the point where the front starts pushing (without requiring exaggerated front weight transfers), then you need to pull the rear out to balance. a fixed chainstay will limit the extent that you can grow the FC (at least in relation to having optimal corner carving capabilities). IMHO, of course.

  33. #33
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    Iíve worked as mainly a machinist and more recently an inspector In the Aerospace industry for 26 years. They certainly haven't designed anything on paper in that time. We program our machines directly from the CAD model, or from an engineering drawing taken from a certain part of the model. We inspect components and assemblies directly against the model via CMM or similar. Smaller details we inspect agains engineering drawings made by draughtsman that are made from information taken from the model.

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