Hi! First post, first bike build, seeking advice on tubing selection- Mtbr.com
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  1. #1
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    Hi! First post, first bike build, seeking advice on tubing selection

    Hi everyone


    I'm under way on my first frame build so thought I'd post here with some info and ask your advice on tube size selection.

    The bike I'm building is to replace my existing hack bike (Kinesis Crosslight, c.2000) for use on a mix of local errands and long(ish), leisurely days on country lanes, bridleways and gravel paths with my wife. The geometry is adapted from my road bike (Specialized Allez, 2011). I'm aiming for a ride which is comfortable, fairly upright and predictable - slightly shorter and more upright than the Allez, but without the toe-overlap problems or twitchiness of the Kinesis. Think along the lines of a gravel/monstercross bike but for chilling, not shredding.

    Outline spec is wide, flared drop bars, cable discs, Headshock-style single-shock hybrid forks (~50mm travel) or similar dimension rigid Chinese carbon jobbies, hub gears (probably Nexus 8spd), Maxxis Ravager or Conti Double-Fighter (29x2") tyres.

    Here's the design I've come up with:




    As this is my first build, I'm not (yet) any good at welding and my tooling and processes are rudimentary (at best), I'm working to the adage: "if a job's worth doing, it's worth doing badly"

    Some of the tubing (ST, BBKT, possibly SS and dropouts) is being sourced from a scrap steel hybrid bike I picked up a while back with cheap ERW steel to fill the gaps - it's going to be a tank! The ST measures 25.4mm internal (narrow but I'm not planning on using a dropper so I'm cool with it). The HT is for a standard 1 1/8" external headset. I don't have any real understanding at the moment of tube size selection so I'd really appreciate any advice on that or recommendations for reading material on the subject.
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  2. #2
    pvd
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    The front center is very short, the chainstays are very long, and the wheels look very small. Also, if the effective seat tube angle is really 71 degrees, it's going to be a bit hoopty. Maybe bump that up a bit to make riding easier.

  3. #3
    pvd
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    Quote Originally Posted by stuartm2 View Post
    Some of the tubing (ST, BBKT, possibly SS and dropouts) is being sourced from a scrap steel hybrid bike I picked up a while back with cheap ERW steel to fill the gaps - it's going to be a tank!
    Terrible idea. It's a waste of time and effort and will only make everything harder for you. Just buy some cheap bike tubes and parts from Nova and your life will be easier and your results will be better.

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    Hi, thanks for the reply.

    Quote Originally Posted by pvd View Post
    The front center is very short, the chainstays are very long
    What sort of numbers would you expect to see here? Bear in mind, I'm not looking for anything like your Bird of Prey for this build. It's essentially a slightly shorter-reach version of my Allez road bike but more relaxed ("comfortable, fairly upright and predictable"). I will go out and check my measurements though, in case I've transposed a measurement badly into the design.

    Quote Originally Posted by pvd View Post
    the wheels look very small
    722mm diameter seems about right for a pair of 700x40c Ravagers, don't you think?

    Quote Originally Posted by pvd View Post
    if the effective seat tube angle is really 71 degrees, it's going to be a bit hoopty. Maybe bump that up a bit to make riding easier.
    Hoopty?

  5. #5
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    I'm in the UK. Cheap tubes from Nova will cost me an arm and a leg in shipping costs alone

    As I said in my original post: "if a job's worth doing, it's worth doing badly"

    Cheap bike tubes for me in the UK would be around 50-80 from what I've seen and some places have minimum order values too. I don't know if I'll even produce a usable bike at the end of this - it really is a learning experience - so super-cheap is how I want to do it, and I accept that means serious compromise. I've already welded (or "cooked" might be a more accurate word) the salvaged BBKT and seat tube, which came from an old junky Raleigh hybrid - the seat tube of this commercially-produced POS was (wait for it) ERW tubing

    Anyway, think "disposable". If it ends up being built into an actual bike, I'll ride it for a while, maybe tweak the geo if I'm not happy with it, then do it again, but better.

  6. #6
    pvd
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    Quote Originally Posted by stuartm2 View Post
    Hi, thanks for the reply.



    What sort of numbers would you expect to see here? Bear in mind, I'm not looking for anything like your Bird of Prey for this build. It's essentially a slightly shorter-reach version of my Allez road bike but more relaxed ("comfortable, fairly upright and predictable"). I will go out and check my measurements though, in case I've transposed a measurement badly into the design.



    722mm diameter seems about right for a pair of 700x40c Ravagers, don't you think?



    Hoopty?
    1. With a 50mm stem, you could increase the front center at least 25mm. Every little bit helps. This is keeping your saddle and bars in the same position and your head angle the same. I'm going to leave head angle out of this because it's fine for your use.

    2. Fair point. It looked like you were doing circus wheels.

    3. Yeah. That can't be right. I'd check that out.

    About the use of new parts vs scrap, if things are that much more expensive over there than here it may make sense. Generally, when I'm building a bike, I look at my time being the most expensive part of the equation and I want the results to be a worthy investment of that. Spending 30 hours producing something that needs to be thrown away is not what I'm interested in doing. Better to spend the money and build something worth having. Your mileage may vary.

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    1. I'll take a look at increasing front-centre by 25mm and using a shorter stem. What I've done so far is tweak my Allez's geometry (it's already fairly comfy - more audax than racer) towards the kind of ride characteristics I want in a fairly conservative manner, so 20mm off the reach, 20mm on the stack, 3 slacker head angle and a 20mm shorter stem to stop it feeling like a complete barge. Is the reasoning behind your suggestion that the extra 25mm wheelbase will increase stability?

    3. I was concerned that I'd measured reach (BB->HT) then transposed it into the bar-reach (BB->bar) setting by mistake but no, it's where I want it. The Allez is 390mm reach/460mm bar-reach and I want it just a smidge shorter. Obviously not where your head's at but it's what I want for this bike. When I build my hardtail shredder, I'll definitely be raiding your brain for the geo.

    On the materials, I'm a total newb at frame building and metalworking. I have a 1-day TIG intro course and a few hours of practice under my belt. I have soooo much to learn and so many more holes to blow in tubes before I can build a good bike, so I have plenty of time and not so much money I want to put into this hobby at this time. As I improve, that balance will shift.

    Bike #1 is intended to be a sh!t bike. If it actually turns into something rideable, even if it's a freaking tank, then I'll be totally stoked!

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    For number 2 - which you'll make very quickly after the pos no.1 :-)

    Use Ceeway or Reynolds direct in the UK. No minimum order at Ceeway but you pay a flat 8.50 ish shipping so repeated very small orders quickly get spendy in that respect. Minimum order at Reynolds was 150.

    This useful page lists the cheap Columbus tubes - they do 1.5m x 0.8 wall in many diameters and it is around 13 + VAT a length so not crazy expensive and much better than ERW for strength / weight. Some bike tubes are seamed tubes which have then gone through drawing processes anyway (so not that dissimilar to ERW in manufacture but in a better grade of steel that allows the thinner wall without buckling / denting).
    https://www.framebuilding.com/Spare%20Tubes.htm

    If you want to go the next step up then a Zona top or down tube is about 22 + VAT. Equivalent in Reynolds 853 would be about 35.

    A nice quality threaded Silva bb sleeve is 7.50 + VAT. Peter at Ceeway is quite helpful and might have some cheaper options for practice.

    I've salvaged dropouts and bb shells for brazing. For TIG it won't be very clever trying to weld on top of previous ground down welds (but not impossible).

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    Even if you are thinking "disposable" I'd only ever use the salvaged crap as welding practice. It will really hinder the process trying to re-use garbage and expecting anything other than bad results. Speak to Peter at https://www.framebuilding.com/ he's super helpful and has lots more in stock than listed on his "antique" website.

    Edit,,,,,,,

    Beaten to it!!!!!

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    Hi Cord - I though you downhillers were supposed to be quick :-P

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    Thanks for the UK-centric info, I contacted Reynolds earlier in the year and will use them when I get better at welding and am ready to invest in the minimum order amount. I've seen Ceeway's catalogue online which is quite limited in tube stock but haven't contacted them directly yet and didn't realise they have other stuff. I will definitely hit them up for some cheap tubing for practice and for bike #2 - as you say, it will happen quickly

    My salvaged BB shell seemed to weld without too much trouble, although without any experience of welding a new one, I have nothing to compare it with. I blew a hole in the seat tube on one side (imperfect mitre and poor direction of the arc, I think) then completely cooked it patching that up. The distortion was pretty bad as a result: one side pulled in about 0.75mm at the top, the other 0.5mm. Weirdly, the threads distorted less than the outer dimension so the UN50 sealed BBKT still went in and was well-enough aligned that it would be perfectly servicable. All I need to do is square off the ends of the shell. As I said, "learning experience" and sh!t bike

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    Yeah, think "welding practice" which produces something bike-shaped at the end - bad results are what I'm expecting with bike #1 I am absolutely aware of the trade-offs I'm making

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    You just need to dig deeper and maybe ask to find out what Ceeway really stock......

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    I fired off a quick email to him. Your quoted price of 13+vat for a basic tube does put a whole frame in the ballpark of 50, which is about where I was expecting. I will definitely splash out that kind of money for a length of straight gauge I can chop up and practice with - lots of practice joints in a 1.5m tube! I'm getting really excited about bike #2 already

  15. #15
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    I think in reality you'll end up nearer 100. I noticed the last order (2019) was 9.50 shipping which is a chunk compared to the material cost. You'd probably get both a top and down tube out of a length of 31.7 dia.

    The standard 1.6mm head tube for 1 1/8" fork is a bit chunky and you probably don't need 600mm of it.... They do a nice 44mm head tube with thicker ends for about 15 which might be a better option for a similar cost / single frame if you want more fork options (HT44 on the "what's new" page).

    Chainstays are probably the bit you need to think most about - straight tubes will need bending and crimping to get through the tyre-chainring gap. Ready shaped 29er stays will add cost but probably the best option at this stage. Anything super short will need more work in that area (multiple options such as crimping, plates, fancy yokes, tiny tube diameters etc).

    I've done stuff with small diameter tubes but wouldn't recommend as the design / alignment / jigging is quite a headache - but it can be done ghetto style with wood, door hinges and nails......
    Attached Thumbnails Attached Thumbnails Hi! First post, first bike build, seeking advice on tubing selection-dsc_0602-1-.jpg  

    Hi! First post, first bike build, seeking advice on tubing selection-p1040100.jpg  


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    Quote Originally Posted by stuartm2 View Post


    I like it!


    The only time i'd recycle random tubes is because i can reuse an entire rear triangle. Never done that, though. The tubes are such a small part of the cost of building even an amateurish frame that if it makes sense... maybe building the frame doesn't. Also, cleaning/preparing used tubes is a hassle and recycling introduces more places to make mistakes. I built my first two frames for <200$ each, and while they worked... that cost constraint drove a lot of poor decisions and cost me a LOT of time.


    WRT tube selection- how much do you weigh, and do you think you'll carry a fairly heavy rear rack? Assuming you're a normal weight for your apparent ~5'10 height, i'd probably go with 28.6/31.8 front triangle, in 9/6/9. This might be a good candidate for a big DT and small TT. There's some sense in intentionally making a odd tubing choice on your first couple frames, so you can learn what weird feels like.


    As a fellow bad metalworker- spending a whole day sticking tubes together can easily be more valuable than spending the day building your frame. Took me a couple frames to figure that out.
    "Things that are complex are not useful, Things that are useful are simple."
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    Quote Originally Posted by mickuk View Post
    Hi Cord - I though you downhillers were supposed to be quick :-P
    Lost my touch!!!!!!!

    Love that trellis chainstay.

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    Quote Originally Posted by mickuk View Post
    You'd probably get both a top and down tube out of a length of 31.7 dia.
    Is it typical to use the same diameter for top and down tubes? I think I recall seeing it on old-school steel road frames which had quite narrow tubes anyway but haven't seen it on recent bikes, especially with larger diameter tubes. This is an area I'm really keen to learn more about. I'd assumed the down tube would be a larger diameter for extra lateral stiffness while the top tube would be narrower for more compliance, but that's potentially a flawed understanding on my part.

    Quote Originally Posted by mickuk View Post
    They do a nice 44mm head tube with thicker ends for about 15 which might be a better option for a similar cost / single frame if you want more fork options (HT44 on the "what's new" page).
    That sounds like the kind of thing I'll want. I imagine it'll be a whole lot easier than mitring for an externally tapered headtube.

    Quote Originally Posted by mickuk View Post
    Chainstays are probably the bit you need to think most about - straight tubes will need bending and crimping to get through the tyre-chainring gap. Ready shaped 29er stays will add cost but probably the best option at this stage. Anything super short will need more work in that area (multiple options such as crimping, plates, fancy yokes, tiny tube diameters etc).
    Yeah, I haven't really thought about this part of the build yet. I was considering getting a basic tube bender and having a crack at it.

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    Quote Originally Posted by scottzg View Post
    WRT tube selection- how much do you weigh, and do you think you'll carry a fairly heavy rear rack? Assuming you're a normal weight for your apparent ~5'10 height, i'd probably go with 28.6/31.8 front triangle, in 9/6/9. This might be a good candidate for a big DT and small TT. There's some sense in intentionally making a odd tubing choice on your first couple frames, so you can learn what weird feels like.
    I'm 6', about 11st and I'm not planning on carrying any luggage on this frame so it sounds like those diameters would be what to go for. Thanks!

    It hadn't really occurred to me to build an intentionally bad bike (geometry, tube sizes) to get a feel for what's *not* right. I will definitely consider it but not for this build.

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    Quote Originally Posted by pvd View Post
    1. With a 50mm stem, you could increase the front center at least 25mm. Every little bit helps.
    So I modified the design as you suggested (attached). My initial thought is that I'd be concerned about the short stem making the steering faster than I'd like. That's an entirely gut response on my part and I'm totally open to being wrong about it. I guess the fact that I spend most of my time on the hoods when riding drops gives it a longer effective stem length to counter that but I don't know that for certain. I have more confidence that the original 75mm stem would give the kind of steering characteristics I want. What's your experience with this?

    Hi! First post, first bike build, seeking advice on tubing selection-hackone_pvd.png

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    Quote Originally Posted by stuartm2 View Post
    It hadn't really occurred to me to build an intentionally bad bike (geometry, tube sizes) to get a feel for what's *not* right. I will definitely consider it but not for this build.
    IMO...
    It's not about building a 'bad bike,' but about learning where there's room for optimization. If you're not a good metalworker with a jig... your first bikes aren't gonna be amazing. My call for oversize/undersize tubing is similar (but less) to PVD's push for the longest front-center. There's potential to make something significantly better than what's commercially available, so it's smart to explore the concepts. You can't completely explore either idea with 1 frame anyway.

    Even if you ignore the suggestions, considering how those design changes might impact your result is invaluable. Again, IMO.

    More imo... professional custom framebuilders capitalize on innovations that the homebrew framebuilding community explore. The best hobbyists inform the pros.
    "Things that are complex are not useful, Things that are useful are simple."
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  22. #22
    pvd
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    Quote Originally Posted by stuartm2 View Post
    I'd be concerned about the short stem making the steering faster than I'd like.
    The stem length is changed to move the front wheel. It has nothing to do with steering the bike.

    1. Your saddle and seatpost look off. I know you steepened the tube but its intersecting at the top terribly. We don't use offset posts in modern bike design. Better to spec a zero offset and a real saddle.

    2. The chainstay is still absurdly long.

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    I only mentioned using the same tube for tt / dt as you were initially working to a budget and it was a cheap compromise.

    Quite fun how it has quickly gone in the right direction from scrap parts and ERW > plain gauge cromo > 44 head tubes, specific diameters and butting :-))

    I am absolutely no expert, and even when I've deliberately chosen different tube sizes it is quite hard to tell the difference. Go jump on an old 1980s 531c lugged road frame with tiny tubes - the overwhelming thing you feel compared to a modern bike is the flex in the 1" solid aluminium quill stem (it is actually quite unpleasant / alarming). The frame itself is fine.

    Scottzg's tube suggestions sound sensible - they're still a size up on the old school road sizes or the typical Dawes Galaxy gravel bike of old.

    Looking back on my choices for generally lightweight people I've used:-
    That latest orange MTB^ is 35mm dt, 35mm tt, ovalised for some extra lateral stiffness. Can I actually feel it with a 120mm fork and 2.4 tyre? - maybe just a little.

    Other 29ers 35mm dt, 32mm tt.

    WIfe's CX 35mm dt 32mm tt but that has to survive stuff like the 3 peaks race so essentially MTB terrain. Added a bit of flex with curvy 12.7mm seatstays.

    Kids 26er MTBs 32mm dt and 25.4mm tt. The lightest regular chainstays I could find and 12.7mm seatstays.

    Tube bending opens up waaaay more options for creativity. But there is no way around the need for tooling. I've had acceptable results for personal use with a cheap bender - but even that needs significant modification to support the tube better and reduce indenting. To produce anything better quality needs a draw bender and mandrels. I've not found any commercial bending places in UK that had the correct sized tooling for bike tubes. The local motorbike places were full of bravado until they saw the wall thicknesses and then chickened out :-)

    If you aren't going radically short on the chainstays then it is overall MUCH cheaper just to buy some ready shaped and removes issues with joining bigger diameter tubes to regular dropouts - I always design my own dropouts and get them zapped out at the profiling place I use for day job stuff. But steel plate, a drill and a hacksaw works just as well......

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    Quote Originally Posted by scottzg View Post
    My call for oversize/undersize tubing
    The numbers you suggested didn't seem outside what I'd expected. I was much more suspicious of mickuk's suggestion to use the same diameter on both DT and TT but he's explained that so now it makes more sense to me.

    Quote Originally Posted by scottzg View Post
    Even if you ignore the suggestions
    I'm unlikely to ignore but I always try to understand where someone's coming from and allow them to influence my opinions accordingly because all opinions have some kind of personal bias, even my own Certainly there's been some useful info in this thread which I've found really useful and I've adjusted my designs and mental map of the build process based on the things they made me question/think about. So let's not say "ignored" but, rather, "influenced/shaped" as I've never been someone who just does what he's told (I'm too headstrong!) but I'm not too arrogant (I hope) to completely ignore others' experience

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    Quote Originally Posted by pvd View Post
    The stem length is changed to move the front wheel. It has nothing to do with steering the bike.
    Are you suggesting, all other pertinent factors being equal, that chopping 25mm off the stem length won't have any effect on steering characteristics?

    Quote Originally Posted by pvd View Post
    1. We don't use offset posts in modern bike design.
    Is that the Royal "we"? If this frame makes it out the other side of the construction process intact and I decide to proceed with a full build, it'll get some junky alloy seat post from Amazon. That seat post will, in all likelihood, have some kind of offset.

    Quote Originally Posted by pvd View Post
    2. The chainstay is still absurdly long.
    "I'm Toydarian; hyperbole mind tricks don't work on me, only money"

    450mm chainstays are well within normal parameters (albeit on the higher end). For example, in my current stable I have:

    Giant Fathom e1+: 470mm
    Kinesis Crosslight: 420mm
    Voodoo Hoodoo: 420mm
    Isla Beinn 29er: 430mm
    Specialized Allez: 395mm
    Specialized Crosstrail: 440mm

    The 450mm chainstays are staying.

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    Quote Originally Posted by mickuk View Post
    Quite fun how it has quickly gone in the right direction from scrap parts and ERW > plain gauge cromo > 44 head tubes, specific diameters and butting :-))
    Yes, but bike #1 is still being built out of scrap parts and ERW Your info has been invaluable for bike #2, however. I will report back on the success (or not) of bike #1 in due course.

    I'm old enough to remember the flexiness of the bottom brackets in 80s era road bikes I remember my first late 80s/early 90s MTBs. The Peugeot with its normal diameter steel tubes ... the oversized steel tubes on the Ridgeback which replaced it ... and the slightly embarrassed look on the poor shop owner's face when I took that Peugeot back with a snapped down tube. I think I can feel differences in frame flex, even on modern bikes, but there are so many factors (tyres, wheels, suspension, etc) that it's difficult to really tell without going properly sciency about it.

    I'm going to play with tube bending for bike #1 - I really do want to go through the process. It might be a dead-end but a tube bender (even a cheap one which needs modifying) feels like an essential piece of the toolkit. As with most other things I do, I'll start cheap and upgrade if my usage/demands justify the expenditure.

  27. #27
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    Quote Originally Posted by stuartm2 View Post
    Are you suggesting, all other pertinent factors being equal, that chopping 25mm off the stem length won't have any effect on steering characteristics?
    Correct.

    https://www.peterverdone.com/stupid-about-stems/

    Quote Originally Posted by stuartm2 View Post
    If this frame makes it out the other side of the construction process intact and I decide to proceed with a full build, it'll get some junky alloy seat post from Amazon. That seat post will, in all likelihood, have some kind of offset.
    I don't understand this. Why would you intentionally purchase an offset post for a frame that you are prototyping in a class that generally uses a dropper post? This is strange thinking.


    Quote Originally Posted by stuartm2 View Post
    Giant Fathom e1+: 470mm
    Kinesis Crosslight: 420mm
    Voodoo Hoodoo: 420mm
    Isla Beinn 29er: 430mm
    Specialized Allez: 395mm
    Specialized Crosstrail: 440mm

    The 450mm chainstays are staying.
    I thought that you were building a custom bike frame? Why are you referencing garbage commodity frames that were designed to be mass produced junk for "everyone". This is a bike for you, not the accountants at Specialized or the 12 year old charged with selling it. If your argument was based on design, I could understand. An argument based on bad comparisons is not valid.

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    Cool, I just re-read this article a few hours ago. It explains the mathematical reason why there isn't 100% difference in rider input between the different stem lengths which makes perfect sense but doesn't explore any noticeable changes in ride characteristics, if they exist. The only experience I have with this is changing stem length on an existing bike where I've felt the change in responsiveness a 25mm increase in stem length (and, approximately, reach) can cause. I've never been able to test with the reach being kept the same and the wheelbase and stem length changing, hence my question. Considering your wealth of experience, I'll take you at your word.

    Quote Originally Posted by pvd View Post
    I don't understand this. Why would you intentionally purchase an offset post for a frame that you are prototyping in a class that generally uses a dropper post? This is strange thinking.
    I'm not aware that the "Sunday afternoon moocher" class generally uses dropper posts. There's nothing in my requirements for this bike that even comes close to needing one, which is why it doesn't have one.

    Quote Originally Posted by pvd View Post
    Why are you referencing garbage commodity frames that were designed to be mass produced junk for "everyone".
    Because they're the reference points I have. If I wasn't referencing *them*, I'd be plucking numbers out of my arse. As I said in my original post, this geometry is essentially taken from a drop-bar bike I know (Specialized Allez 2011) but which needs some adjustments for the kind of riding I intend to do on this new bike. In this case, raising the stack, reducing the reach, slackening the head angle, lengthening the back end. Of the bikes I have available to me for reference, the ones with longer chainstays give the kind of ride I want, the ones with shorter chainstays don't. So I'm going with the longer chainstays.

    I know this bike isn't going to be responsive or "flickable"; I know I won't be getting the front wheel up in the air. This is intentional, I don't want it to be responsive or "flickable". I don't want the front wheel up in the air. It's not going to be going fast, or downhill, or through rock, or even through gloopy mud. I'm not going to be racing commuters or shaming pro Enduro racers, I'm going to be pootling about on Cornish lanes with Mrs. M. on her e-bike and that's why I've "designed" it this way. You might consider the finished bike "junk" - that's fine, it's not for you - it's for me If I consider the finished bike "junk", I'll change the design and do it again. Hell, even if I love it I'm going to do it again because it's going to be a sh!t bike

    FWIW, I don't listen to salespeople - I tell them to hand over the bike so I can give it a ride. I've done my time in bike sales - I know how clueless most of them are.

    Anyway, thanks. I'm going to work to the updated designs using the 50mm stem as you suggested. Really appreciate you sharing your knowledge in this.

  29. #29
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    Quote Originally Posted by stuartm2 View Post
    It explains the mathematical reason why there isn't 100% difference in rider input between the different stem lengths which makes perfect sense but doesn't explore any noticeable changes in ride characteristics, if they exist. The only experience I have with this is changing stem length on an existing bike where I've felt the change in responsiveness a 25mm increase in stem length (and, approximately, reach) can cause. I've never been able to test with the reach being kept the same and the wheelbase and stem length changing, hence my question.
    That is why people that don't design bicycles are so confused about bicycle geometry and setup. We can change any variable we please while most folks are just stuck with the bike in front of them.


    Quote Originally Posted by stuartm2 View Post
    I'm not aware that the "Sunday afternoon moocher" class generally uses dropper posts. There's nothing in my requirements for this bike that even comes close to needing one, which is why it doesn't have one.
    If you've read my most recent post on evil all-road bikes, you'd see that much of the point of the post was that a good design can be used and re-applied over a long period of time and is prepared for changes that might be made. You may not be thinking about dropper posts now, but you will be in 2 years if you stick with all this. Having a bike worthy of re-configuration then is the goal of a design today. In essence, we design for tomorrow, not yesterday. And by the way, of course you should have a dropper on a bike like this. It's so much more fun and useful.


    Quote Originally Posted by stuartm2 View Post
    Because they're the reference points I have. If I wasn't referencing *them*, I'd be plucking numbers out of my arse. As I said in my original post, this geometry is essentially taken from a drop-bar bike I know (Specialized Allez 2011) but which needs some adjustments for the kind of riding I intend to do on this new bike..
    That's what this forum is for. We've all built lots of different bikes. We may not all agree on what shape it should take, I'm sure that we all agree that copying some garbage production bike you have in front of you is a terrible plan. Geometric parameters are adjusted for reasons. The parts have to all fit together for a specific goal. You need to learn about this BEFORE you start spending money and cutting metal. Prototypes are expensive, don't waste one on building obvious crap. Really, learning the design is the least expensive part of this whole process.

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    Quote Originally Posted by pvd View Post
    You may not be thinking about dropper posts now, but you will be in 2 years if you stick with all this. Having a bike worthy of re-configuration then is the goal of a design today. In essence, we design for tomorrow, not yesterday. And by the way, of course you should have a dropper on a bike like this. It's so much more fun and useful.
    I think you misunderstand the nature and purpose of this bike. I have bikes with dropper posts and bikes without. This is a "without" bike. I know the difference. I might as well ask you whether you plan to fit 180mm Lyriks to your Airspeeder or dutch-style town bars and a shopping basket to your Warbird.

    Quote Originally Posted by pvd View Post
    That's what this forum is for. We've all built lots of different bikes. We may not all agree on what shape it should take, I'm sure that we all agree that copying some garbage production bike you have in front of you is a terrible plan.
    You may view all production bikes as "garbage". That's your opinion and you're welcome to hold it. I don't share your opinion and I'd be quite surprised if it was an opinion universally held by forum members too, so I will cordially disagree with you and continue with my existing plan to base my first design on familiar geometry.

    Quote Originally Posted by pvd View Post
    You need to learn about this BEFORE you start spending money and cutting metal. Prototypes are expensive, don't waste one on building obvious crap. Really, learning the design is the least expensive part of this whole process.
    You seem to be assuming that design is the greatest impediment to me producing a bike. I can assure you that's not the case. Right now, I think getting a handle on the metalworking skills is far more useful to me than designing the perfect bike. The approach I'm taking here is an approach I've taken many times in life and it's always worked for me before. I might be wrong this time but it's my time and money to waste discovering that.

  31. #31
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    I like the general design for what the use it. I'd probably steepen the head angle a touch, that's more flop than I'd like to see for flared bars, especially given the likely weight distribution.

  32. #32
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    Quote Originally Posted by dr.welby View Post
    I'd probably steepen the head angle a touch, that's more flop than I'd like to see for flared bars, especially given the likely weight distribution.
    Flop can also be addressed with fork offset.

    I went from (Sopwith Camel) 50mm offset and 64deg head angle to (Spitfire) 42mm offset and 65deg head angle. Trail is 1.7% longer but wheel flop is reduced 2.1%. It doesn't seem like much but the front end feel is dramatically improved, like, amazing now. I'm really stoked on it now.

    Assuming a 774mm wheel diameter, mechanical trail grew from 119.6mm to 121.6mm but flop height reduced from 52.5 to 51.4mm.

    MT = (WR*cos(HA)-O)
    FH = (WR*cos(HA)-O)*cos(HA)

    MT = Mechanical Trail
    FH = 'Flop' Height
    WR = Wheel Radius
    HA = Head Angle
    O = Offset

    It was an interesting gamble but it really paid off in sorting out one of the gremlins I've been dealing with.
    Last edited by pvd; 03-09-2020 at 07:53 AM.

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    Quote Originally Posted by mickuk View Post
    I think in reality you'll end up nearer 100. I noticed the last order (2019) was 9.50 shipping which is a chunk compared to the material cost. You'd probably get both a top and down tube out of a length of 31.7 dia.

    The standard 1.6mm head tube for 1 1/8" fork is a bit chunky and you probably don't need 600mm of it.... They do a nice 44mm head tube with thicker ends for about 15 which might be a better option for a similar cost / single frame if you want more fork options (HT44 on the "what's new" page).

    Chainstays are probably the bit you need to think most about - straight tubes will need bending and crimping to get through the tyre-chainring gap. Ready shaped 29er stays will add cost but probably the best option at this stage. Anything super short will need more work in that area (multiple options such as crimping, plates, fancy yokes, tiny tube diameters etc).

    I've done stuff with small diameter tubes but wouldn't recommend as the design / alignment / jigging is quite a headache - but it can be done ghetto style with wood, door hinges and nails......
    Those chain stays are very interesting, I quite like the look of them, is there any photos of the full bike by chance?
    Ding! Ding! Coming through!
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    Quote Originally Posted by dr.welby View Post
    I like the general design for what the use it. I'd probably steepen the head angle a touch, that's more flop than I'd like to see for flared bars, especially given the likely weight distribution.
    Thanks! The head angle is probably the least conservative aspect of the geometry (from my perspective - not necessarily shared by everyone here ) but I'm going to go with it and see how it handles. It's not a bike for out-of-the-saddle honking so hopefully won't be such a big issue. I'll be quite prepared to admit you're right in the post-build assessment, of course.

  35. #35
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    Quote Originally Posted by dr.welby View Post
    I like the general design for what the use it. I'd probably steepen the head angle a touch, that's more flop than I'd like to see for flared bars, especially given the likely weight distribution.
    You forced me to write a post on flop. Not a rabbit hole I was looking to go down right now but it seems like something that can help some folk.

    Flop | Peter Verdone Designs


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    The flop force is also going to be proportional to the load on the front wheel, so the longer front-center of the Spitfire should reduce the flop force you feel at the handlebars.

  37. #37
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    Quote Originally Posted by dr.welby View Post
    The flop force is also going to be proportional to the load on the front wheel, so the longer front-center of the Spitfire should reduce the flop force you feel at the handlebars.
    That is true and is a part of the difference. I will add that in the post.

    "Another factor that had been changed between the two bikes is the weight distribution over the wheels when going from the Camel to the Spitfire. The Camel had a BB distribution of 403/795 (33.6%/66.4%) while the Spitfire had 404/841 (32.4%/67.6%). That's a 1.8% change reducing the weight over the front assuming identical body position. As explained further below, where the weight is on the bike has a real difference on front end geometry choices."

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    Thanks for posting that article - very informative! I ran the numbers on my bikes:

    Allez - MT: 60.1 / FH: 18.6
    Crosstrail - MT: 85.4 / FH: 30.6
    Kinesis - MT: 84.5 / FH: 30.3
    Voodoo - MT: 91.9 / FH: 35.2
    Fathom - MT: 87.9 / FH: 32.9
    Frame #1 (68 HA) - MT: 90.2 / FH: 33.8
    Frame #1 (69 HA) - MT: 84.4 / FH: 30.2

    That puts frame #1 slightly above my Fathom in terms of flop height although that's not surprising as they both have 68 head angle and almost identical fork offset. If I increase the head angle to 69, flop height will be almost the same as the Kinesis (same HA, shorter fork offset and smaller wheel diameter on the Kinesis).

    Any idea how similar flop height on a 27.5+ hardtail (fairly traditional geo, long back end, 110mm stem, wide bars) would compare, in real terms, to frame #1 with 68 HA, 50mm stem and a set of wide flared drops?

  39. #39
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    Every decision comes at a cost and benefit. Losing front center is a very high price to pay for other factors. Still, the devil is in the details and it is a big collection of decisions that make a bike great.

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    So, I finally finished this first build. It's been a long slog getting the tooling sorted along the way but the frame is done and roughly assembled with a load of (mostly) junk parts. The good news is that the wheels go round, it survived the first few short test rides, and it hasn't tried to kill me yet.


    There were plenty of screw-ups along the way. I got my measurements wrong on my jig early in the build so cut the top tube wrong and needed to order a replacement. There are a few holes which many would put down to bad welding but I'm sticking with my "weight saving" story . I ended up welding the chainstays in place without checking back with my designs so had them further out than intended, which necessitated some unplanned dimpling. And I screwed-up the initial mitring of the seat stays so I chose to re-mitre them and join them lower down the seat tube rather than replacing them. I have no idea how well aligned the frame is but, with the wheels in, the tyres seem to be parallel to the tubes and central in the stays, and the head and seat tubes look parallel by eye, so I'm guessing it isn't dreadfully bad.


    As for the ride characteristics, it's surprisingly close to what I wanted. The mild steel certainly makes for a heavy and dull-feeling frame but that was expected and will be resolved with the proper build. There's barely any noticeable flop in the steering, even when out of the saddle and honking on the bars, and it's nicely stable at anything over walking speed. The reach is what I wanted but I think I over-did the stack so will reduce that a bit in the next version. It also feels like the bottom bracket could come down a bit in the next build to get me feeling more like I'm riding 'in' rather than 'on' the bike. Overall, it feels like a comfortable and stable all-day ride although I doubt I'll be riding this iteration 'all-day' to test that feeling.


    Here's a photo of my ugly little duckling.

    Attached Thumbnails Attached Thumbnails Hi! First post, first bike build, seeking advice on tubing selection-img_0441.jpg  


  41. #41
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    Nice work. You have the essence of what you are working towards. The learning comes from making mistakes and doing a low cost 'bitsa' option allows for feeling an accomplishment. This is where you can go forward and make #2 in a more complete form. This is a very satisfying hobby.

    Eric
    If I don't make an attempt, how will I know if it will work?

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