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  1. #1
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    Custom hardtail geometry check!

    I'm putting together some numbers for a custom steel hardtail using true temper platinum ox and wanted to run the numbers by you guys. I think these are pretty standard, but not sure if I should consider increasing or decreasing angles by 0.5 degrees. I'll be using it as a trail bike with the ability to handle drops, jumps, etc. Pretty much like a Chameleon, Sinister, etc in a steel singlespeed format. Hopefully comes in ~6lbs. I ride in the SF bay area in Northern CA. Rides vary from XC rides with a lot of climbing, to drops, rock gardens, stunts, log drops, technical descents, depending on where we ride. And occasionally i'll hit some doubles.

    #s based on a 150mm 535cm a-c fork (EDITED from 160mm)

    Effective top tube length: 23.25" (EDITED from 23)
    Seat tube length: 17"
    Bottom bracket height: 12.5"
    Chainstay length: TBD, This should be optimized based on 32x18 singlespeed gearing, where the axle position is slightly forward of the halfway mark in the flanged Paragon drop outs to maximize the dropout & plate overlap.
    Probably comes in around 16.75 or so? According to the calculator here.. if someone familiar with these calculations can double check, would be great.

    Seat tube angle: 72
    Head tube angle: 68 (EDITED from 68.5)
    Head tube length: any opinions here? Will be using press fit headsets like chris king


    Thanks!
    Last edited by unfluid one; 02-26-2009 at 07:39 PM.

  2. #2
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    SS'ing with a big fork sucks, imo (so do long forks on hardtails), but if i was gonna do it, i'd prolly steepen the STA, lengthen the TT and run the shortest stays i possibly could. Give me a little more breathing room and keep the rear wheel weighted as i stand up every climb.

    STA isn't a super important measurement since you can really adjust it with an offset post and sliding the seat. I like short head tubes and high rise bars for the nad clearance and possibility to really lower the bars if you shrink or something.

    If it were me, and i was dead-set on a 160mm fork (rather than, say, a 36 spacered down to 120-130...) I'd slacken the HT to something like 67. I've got a 130 on my hardtail with a 69* hta and previously had a frame with 67.5 but otherwise the same geo, and the slacker frame was definitely more stable when i went deep into the fork's travel. I didn't really care about the steering either way, just got accustomed to it.

    I'm just a idiot in front of a keyboard, what does your builder think?
    Hell is eternally climbing manzanita trail on your singlespeed.

  3. #3
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    Thanks for your opinion!
    So I have a 29lb Sinister Ridge which I run SS and have a pike up front. I usually wind it down on the climbs and i have no problems keeping up with the others.. i do all my climbs on platform pedals as well. The #s below are pretty much the same as the ones on the Ridge except a tweak here and there (TT & ST are shorter by .5) and I'm asking for very small TT/ST taco (size will be similar to the one on my Ventana Terremoto) to increase standover.

    I did run a 36Van on the Ridge for a while and I like the pike a whole lot more, so I figure i'd keep the #s generally the same and maybe slacken the HTA by .5 degrees and shorten the rear

    What is considered a short headtube for a steel frame? 4"?

    My builder thinks the #s are just fine at a first glance but so far we've only been really focused on which dropout implementation to go with and frame material

    Ideally I'd like 16.5 CS, but using the SS gearing calculator, i'd have to go shorter to 26.45 and increase my gearing to a 34x18 which I've been considering, or go long with 16.75 and keep my 32x18. The Ridge is 16.7 and have no complains (love it on the downhills.. a bit long at the dirt jumps) but I'm always up to tweak things.
    Last edited by unfluid one; 02-26-2009 at 03:04 AM.

  4. #4
    local trails rider
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    I went for 34/19 gearing, which works out close enough to 32/18:
    http://gallery.mtbr.com/showphoto.ph.../ppuser/266295

    I like Brant's (On-One) thinking that people have two main reasons to put tall forks on trail hardtails:
    - to get the bar higher (silly way to accomplish that)
    - to get a slacker head angle (unnecessary if the frame is designed to be slack)

    ... the downside of big forks on HT's being that you have huge brake dive that varies your angles by several degrees ...
    At least in my case, tall forks tend to reduce standover clearance to nothing, too.

    Quote Originally Posted by scottzg
    STA isn't a super important measurement since you can really adjust it with an offset post and sliding the seat.
    Except that STA and seat position on the post also play together with TT length.

  5. #5
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    You sure you want to use True Temper OX platinum on a long travel HT? There might be something more suitable out there - I'd ask whoever you are having build said frame about that aspect of things.

  6. #6
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    Quote Originally Posted by MMcG
    You sure you want to use True Temper OX platinum on a long travel HT? There might be something more suitable out there - I'd ask whoever you are having build said frame about that aspect of things.
    If there are other better opinions, I am all ears. But my builder-of-interest recommended the Platinum.. i think he uses it on all his DJer type of bikes. I wasn't exactly sure on what tubing i specifically wanted so i left that up to him.

  7. #7
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    go to bikeforest.com and play around in their free bikeCAD software to see what happens with changes in HT length, ST Angle, bb height etc. It is fun as hell - but be warned, it can get addictive. These are two that I worked up based around a Manitou Nixon Comp at 445mm of travel and with an AC height of 510mm and an offset of 41.25mm.




  8. #8
    FM
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    Quote Originally Posted by unfluid one
    #s based on a 160mm 545cm a-c fork.
    Thanks!
    Quote Originally Posted by scottzg
    SS'ing with a big fork sucks, imo (so do long forks on hardtails)
    Here is my take on it: Adjustable travel forks are the way to go! So design your geometry around the amount of travel you will use most often- then just make sure the frame is built to take the extra leverage of a longer fork, even if you only use that longest travel setting occasionally.
    Another way to look at it, is to choose your fork first, then design the frame with the geometry you want based around the middle of the travel adjustment range.

    Unfluid One and I have been rappin' and I've shared the CAD drawing I've created for my upcoming custom frame. If you look at the specs, I designed the frame at 68.5 with a 517mm a2c fork, but specified I may use up to a 545 a2c fork on it. The idea being it will spend %80 of the time with a Fox Talas 36 at 130mm travel setting, but I want to be able to slacken it out just a bit further for the steepest trails.

  9. #9
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    FM - what's the ETA on delivery of your frame from Curtlo?

  10. #10
    FM
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    Quote Originally Posted by MMcG
    FM - what's the ETA on delivery of your frame from Curtlo?
    I think sometime this century

    I'm expecting a sketch any day.
    I expected 4-6 months going into it, so I am still waiting patiently (coming up on 5 months). Really, how it comes out is more important to me than how long it takes. However... the longer it takes the higher my expectations become

    Long as I have it when the snow melts off my favorite trails here, I will be OK with it.

  11. #11
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    The reasoning behind my #s are kind of round about but I took my current hardtail's geometry based on the 160mm fork it was designed around. Sure I ride a pike at 110 most of the time and drop it or raise it accordingly. The uturn gets used every single ride. As a result my actual riding # are lower and steeper than on paper but I don't know the exact numbers and probably will mess up trying to calculate it myself. But I like the setup so far. Just not sure on chainstay length!!

  12. #12
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    btw FM has been very helpful with all his charts and diagrams.

    who knows.. i may get my bike before he does! and i haven't even placed my official order yet..

  13. #13
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    BTW - I asked FTW about the Ridge's geometry numbers that you see on the Sinister Site - and those are based around a 150mm travel fork (as opposed to your 160mm fork).

    Just in case that helps you out a bit.

  14. #14
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    Quote Originally Posted by MMcG
    BTW - I asked FTW about the Ridge's geometry numbers that you see on the Sinister Site - and those are based around a 150mm travel fork (as opposed to your 160mm fork).

    Just in case that helps you out a bit.

    Oh nice thanks for that info! i sent him and skye an email about that as well this morning but you got it to me faster. 150mm.. what is the a-c on that you think? 535mm probably then?
    I have the 2006.5 model, but i don't think they changed the geo too much.

  15. #15
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    The numbers look really close to the Inbred 456 i will be finished building tomorrow!
    Should be nice. Based on a 6" fork the geo is
    HTA 68.5
    STA 72
    Chainstay 16.75
    TT 23.9"
    Center to Top 20"
    BB height 12.5 -ish

    http://www.on-one-shop.co.uk/acatalo...ue_456_30.html

    Sounds like you are on the right track! Can't wait to see it.

  16. #16
    aka baycat
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    what builder are you considering? Inquiring minds want to know since the bike setup is ideally what I am going for on a Chromag waiting to get my grubby hands on and we ride in the bay area.

  17. #17
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    Quote Originally Posted by baycat
    what builder are you considering? Inquiring minds want to know since the bike setup is ideally what I am going for on a Chromag waiting to get my grubby hands on and we ride in the bay area.
    Talking primarily to evil4bc at nemesis projects. he's been very responsive and helpful considering that I have been sending emails to him at all sorts of hours over the past 2-3 days. He is local so that's a big +.
    I also tried to get a hold of Dobermann over email and mtbr since late last week but they haven't responded. I essentially wanted a big brother to the Molosse to take advantage of the nifty sliding dropouts.
    I did consider Chromag and contacted mike truelove + ian about a custom stylus built by mike using custom sliding/horizontal dropouts, but the cost will be the same as their samurai which is more than i want to spend. great guys there as well though.

  18. #18
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    Nice! I'm hashing out #s for the positioning of the paragon dropouts.. in 32x18 will run in the 16.75" mode. To accommodate 34x18, I can go either 16.45 or 16.95, but not both while maintaining 16.75" and keeping the slider in the front 1/2 of the dropouts (more overlap = stiffer interface).

    So..16.45 or 16.95. Thoughts?

  19. #19
    Te mortuo heres tibi sim?
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    If anything, I'd got with the same head angle but based around a shorter fork like the Pike. IMO, 160mm on a 68.5* HTA is a bit odd. I'd either base that around a shorter fork height like the Pike, or slacken the HTA more to accomodate the travel.

    Considering the back end won't have any sag/compression, that 160mm up front will steepen things up quick coming from 68.5*. Granted, that's under quick hard compression, it's not as if you'll ride it that way, but still... With newer forks these days, at least it's pretty easy to dial in some damping to ease up on brake dive and bobbing when pedaling yet still letting the fork remain plush and active when needed.

    Got one hardtail with a Pike and a 68.5* or so HTA, and another with a Lyric at 67.5* or so and I kinda' wish I'd had the second built to have the 67* around the same size fork as the other -518mm. I've found the sweet spot on the Lyric hardtail to be running it at 150mm vs. the 160mm full travel. Shorter overall, and burly enough for what I do for sure. Or if you just want the increased stiffness and burl, desing it with your angles around the shorter fork, but run the taller fork at 140mm.

    I'd also go for a shorter/braced seat tube, but that is personal preference/ a personal size thing. I've got short legs, and just prefer the aesthetics of the steeply sloped TT that give a bikes appearance. Depends on how much you like to have your seat dropped when the time comes as well. Less an issue if using a dropper type post, but still a consideration.

    Unless your builder goes nuts, you ought to be even able to get a frame nearer the 5# mark vs. 6# IMO. Beefiness I guess depends on how big and burly you plan on jumping and dropping. My Peyto frame is gussetted pretty damn well, and beefy and it comes in just a hair over 5#. My burly ti frame is near exactly a pound less.

    It's tough tot hink of all the little details, but fun at the same time!
    Florence Nightingale's Stormtrooper

  20. #20
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    Thanks SL.
    I changed the specs so that the geometry is based on a 150mm (as the Ridge i find out is), and slacked out the HT to 68* and lengthened the TT to 23.25. What is the rule.. you lose a degree for every 20mm? 10mm? I figured with 140mm, I'll still come in around 68.5ish.

    I thought about going slacker, but I like the quick handling of my Ridge, even when set at 120mm. I have a 67.5 dualie in the garage for the hairy stuff, and wanted a stiff quick bike. That and I've never tried a slack hardtail.. so a bit apprehensive going that route on a custom frame without trying it first.

    Good call on the brace cuz I also asked for a tiny little brace.. something along the size of the ones on Ventanas. I don't really have a issue with standover, but i thought a tiny brace would give it some extra flair.

    Thanks for the suggestions so far!

  21. #21
    Te mortuo heres tibi sim?
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    I've always read about a degree change for every 25mm or so seems to bear out in my experience. If you have known numbers to work with, you could bust out some trig to figure things out for sure.

    Cool. I'll just throw other ideas out there, not really knowing what you're after, but what the hell:

    ISCG mounts?

    Disc side stay braces?

    Running a dropper post, and if so, want cable guides for that?


    Quote Originally Posted by unfluid one
    Thanks SL.
    I changed the specs so that the geometry is based on a 150mm (as the Ridge i find out is), and slacked out the HT to 68* and lengthened the TT to 23.25. What is the rule.. you lose a degree for every 20mm? 10mm? I figured with 140mm, I'll still come in around 68.5ish.

    I thought about going slacker, but I like the quick handling of my Ridge, even when set at 120mm. I have a 67.5 dualie in the garage for the hairy stuff, and wanted a stiff quick bike. That and I've never tried a slack hardtail.. so a bit apprehensive going that route on a custom frame without trying it first.

    Good call on the brace cuz I also asked for a tiny little brace.. something along the size of the ones on Ventanas. I don't really have a issue with standover, but i thought a tiny brace would give it some extra flair.

    Thanks for the suggestions so far!
    Florence Nightingale's Stormtrooper

  22. #22
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    All comments are welcome since I should consider everything.

    Yes to ISCG mounts!! I nearly forgot about this detail. 05 or old?

    Haven't thought about the disc stay braces.. i figured that is up to the builder if it's needed depending on the tubing. This is just to keep the stays from collapsing under braking right and is primarily for thinner tubing? Brad doesn't have any on his DJ bikes so i'm guessing he hasn't run into problems. I will ask him though.

    I used to run a speedball on my old Intense and really liked it. For the sake of simplicity, I prefer just to use a normal post nowadays. I opt for the lever actuated droppers to eliminate cable clutter.

    Are you running the seattube collar slot in the front or back?

    My next concern is color:
    http://nem-pro.blogspot.com/2007/12/...oothpaste.html
    http://www.clubstuttgart.net/gallery...ashiongrey.jpg
    I was also thinking of a washed out peach color. Like how the mint is a washed out green.


    Quote Originally Posted by scrublover
    I've always read about a degree change for every 25mm or so seems to bear out in my experience. If you have known numbers to work with, you could bust out some trig to figure things out for sure.

    Cool. I'll just throw other ideas out there, not really knowing what you're after, but what the hell:

    ISCG mounts?

    Disc side stay braces?

    Running a dropper post, and if so, want cable guides for that?

  23. #23
    mtbr member
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    Quote Originally Posted by scrublover
    I've always read about a degree change for every 25mm or so seems to bear out in my experience. If you have known numbers to work with, you could bust out some trig to figure things out for sure.

    Cool. I'll just throw other ideas out there, not really knowing what you're after, but what the hell:

    ISCG mounts?

    Disc side stay braces?

    Running a dropper post, and if so, want cable guides for that?
    This is like deja vu for me!

    Scrubs and I had this same exchange a week or so ago.

  24. #24
    Te mortuo heres tibi sim?
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    Haven't actually used ISCG mounts - can't say as to if one is better than the other. Figured for guide or Hammerschmidt use - it's supposed to work with both versions though. I'd guess to go for whichever one is in most popular use/has most product/support out there if doing a mount. Non-driveside slider Rohloff compatable for future use?

    A brace probably isn't needed, but that'd be up to you and Brad as to how beefy/burly you two think things need to be. I had one put on my frame more for the hell of it/longevity/my own worries.

    I like the seat slot in front. IMO, it ends up looking cleaner, and marginally less crap gets thrown down the seat tube that way. Dopn't know if there is a functional difference. My non-engineer mind thinks forward facing would be slightly beefier, not having the slot hanging out back with a backwards leaning postpushing against the slot tabs. Granted with a collar on, it's surely a non-issue.

    That mint color is nice looking.


    Quote Originally Posted by unfluid one
    All comments are welcome since I should consider everything.

    Yes to ISCG mounts!! I nearly forgot about this detail. 05 or old?

    Haven't thought about the disc stay braces.. i figured that is up to the builder if it's needed depending on the tubing. This is just to keep the stays from collapsing under braking right and is primarily for thinner tubing? Brad doesn't have any on his DJ bikes so i'm guessing he hasn't run into problems. I will ask him though.

    I used to run a speedball on my old Intense and really liked it. For the sake of simplicity, I prefer just to use a normal post nowadays. I opt for the lever actuated droppers to eliminate cable clutter.


    Are you running the seattube collar slot in the front or back?

    My next concern is color:
    http://nem-pro.blogspot.com/2007/12/...oothpaste.html
    http://www.clubstuttgart.net/gallery...ashiongrey.jpg
    I was also thinking of a washed out peach color. Like how the mint is a washed out green.
    Florence Nightingale's Stormtrooper

  25. #25
    Te mortuo heres tibi sim?
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    Quote Originally Posted by MMcG
    This is like deja vu for me!

    Scrubs and I had this same exchange a week or so ago.


    Progress on yours?
    Florence Nightingale's Stormtrooper

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