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  1. #1
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    Feedback on Gravel Bike Geo and build specs

    Hey All,
    I've lurked this thread for a few years now and am thinking of making an attempt at a gravel bike frame. With this in mind, I am looking for some feedback on the geo and tube set etc.
    The geometry is loosely based on a Salsa Fargo and would be built around a 2.2-2.35" tire. However I altered the geo to make it a bit sportier (longer reach, shorter cs, lower stack) and better fit my preferences. Also, I plan on making detailed CAD drawings to work out all the minutia of it. The numbers below should give a pretty good idea of what I'm going for though. To give the numbers some context I am 5'10'' and fit pretty well on a 56cm or a large across most manufacturers.

    Head Angle: 69*
    Seat Angle: 73*
    Reach: 410
    Chainstay: 440
    BB drop: 70
    HT length: 140
    Fork Length: 483
    Seatube: 520
    Stack: 650ish

    For the build itself everything is from nova. I plan on using their 142x12 sliders with an integrated hanger/brakemount to make things easier on myself.
    https://www.cycle-frames.com/bicycle-frame-tubing/NEW-DROPOUT-REAR-MTB-SLIDER-ADJUSTABLE.html

    Also, I intend on using their 73mm bb shell and run of the mill looking headtube. It comes in a 200mm length but I should be able to cut it roughly to size and face to down to dimension on the lathe.

    Other specs are as follows:
    Down tube: Nova 9/6/9 31.7 diameter
    TT: 9/6/9 31.7
    ST: 9/6 31.7
    CS: 12* single bend 30/16 oval 425 length 1.0/.7
    SS: https://www.cycle-frames.com/bicycle-frame-tubing/NOVA-MTB-29R-S-BEND-24mm-OVAL-x-450mm-NOV_COCS_SBND_29R.html
    I guess my main concern is if this tubeset is suitable for a dropbar mtb/gravel bike application. Based on my research its seems like it would be reasonable but this is not my area of expertise. I weigh about 135 geared up, and the bike might see an extra 35lbs of gear for bikepacking.


    I have access to both brazing and tig setups and would practice a good while on each to see which I prefer. I have some experience welding and am pretty comfortable with mig and stick, but need a lot more practice on tig and oxy. Also, I have access to both a vertical mill and lathe for other odds and ends. Tubes would be hand mitered though. I plan on constructing the jig on thin plywood or mdf and laser cutting tube holders and either machining or resin casting other fixtures. Similar to whats going on in this thread:https://forums.mtbr.com/frame-building/homemade-full-suspension-29er-1076824.html


    Sorry for the long winded post, but thanks for reading and for your feedback!
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  2. #2
    pvd
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    Here are two recent gravel bikes that I've done, one uses traditional drop bars. The other uses flat or bi-plane drops. I'm 5'10" and aout 205 lbs (so fat). Notice the geometry.

    Airspeeder! | Peter Verdone Designs
    2018 PVD Bird of Prey | Peter Verdone Designs

    If you weigh just 135 lbs, you'll be happier with a 25.4mm top tube and 12.7mm seatstays. You will want a 35mm seat tube to make use of a 31.6mm dropper, even if you don't plan on using one now, you will. Thus, geometry around a zero offset post.

    It's a waste of time to aim for 2.25" tires with drop bars. You probably wont make use of it except in special cases. 622-46 is excellent for almost any drop bar dirt bike. I tested (Hybrids are back! | Peter Verdone Designs)

    Also, 1x12 (10-50) is ok for smaller flatter rides or urban use but for real gravel you'll need a front derailleur. Make sure you have the space for this option.

    Post a print. That's where we can see what you intend.

    Bits of advice for the aspiring framebuilder | Peter Verdone Designs

    Also, Surly bikes are pretty terrible. You'd do well to break free of them as reference.

  3. #3
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    Quote Originally Posted by pvd View Post
    Here are two recent gravel bikes that I've done, one uses traditional drop bars. The other uses flat or bi-plane drops. I'm 5'10" and aout 205 lbs (so fat). Notice the geometry.

    Airspeeder! | Peter Verdone Designs
    2018 PVD Bird of Prey | Peter Verdone Designs

    If you weigh just 135 lbs, you'll be happier with a 25.4mm top tube and 12.7mm seatstays. You will want a 35mm seat tube to make use of a 31.6mm dropper, even if you don't plan on using one now, you will. Thus, geometry around a zero offset post.

    It's a waste of time to aim for 2.25" tires with drop bars. You probably wont make use of it except in special cases. 622-46 is excellent for almost any drop bar dirt bike. I tested (Hybrids are back! | Peter Verdone Designs)

    Also, 1x12 (10-50) is ok for smaller flatter rides or urban use but for real gravel you'll need a front derailleur. Make sure you have the space for this option.

    Post a print. That's where we can see what you intend.

    Bits of advice for the aspiring framebuilder | Peter Verdone Designs

    Also, Surly bikes are pretty terrible. You'd do well to break free of them as reference.
    The smaller diameter tubing seems like a good call, I'm assuming it reduces bike weight without any negative effects given my weight? I disagree on the 2.25 tires being a waste of time on drop-bars though. I've ridden the teravail sparwood 29 x 2.2 extensively on gravel roads in my area and have drawn a couple of conclusions. Firstly, its more comfortable than a 700x40 and not appreciably slower either. Plus, I often find myself on minimum maintenance forest roads or atv trails where the added volume is nice. I'm not overly concerned about space for a front derailleur either, I live in northern MN where its pretty flat so a 36t or 38t ring with a 10-42 gets me where I need to go.

    Your gravel bike builds look pretty interesting, I looked over the geo charts for them and have a couple questions.
    Your seattube angles are relatively slack given your headtube angles, when paired with a long reach, wouldn't that give you a really long ETT and make the bike feel really long when seated? I see the benefits of long reach etc. I just want a relatively upright position on the bike for long days and bikepacking, in comparison to my crosscheck (as "terrible" as it is) which is set up in a pretty racy position and does road/good gravel road/gravel race duty.

    Also, I am curious as to what specific elements makes the salsas and surlys "terrible"? As you can see from my signature, I have three of them and while I don't pretend like their super bikes or better than anything else, i've largely been happy with them. Perhaps I just don't know any better-haha.

    On another note, I examined the geometry of pretty much every production gravel bike and noticed that there is not a ton of variation: 72* degree seat angles, 70* degree headangle, 390mm reach, and a 620mm stack height etc. Except, the surlys seem to have a stupid short headtube/ low stack and the salsa cutthroat and fargo have a much taller front end and a little more progressive geo. I kind of want something along the lines of a more mtb inspired gravel bike. Should I push my design more into left field (like your bird of prey) or is the industry fixated around a relative stagnant ideal of a gravel bike because the design works?
    Also, I'll get going on some drawing once I know what I'm drawing-possibly Monday or Tuesday I should have some ready
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  4. #4
    pvd
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    The seat tubes on my bikes are offset, so the angle isn't a comparitor. Effective angle is 74 degrees or so. See that in the prints.

    We don't refer to top tube length when discussing geometry. I don't know what you are referring to.

    Almost every production 'gravel bike' is not properly designed. The industry is selling product, not performance.

    Surly bikes are designed to be terrible. They are joke bikes. They are also super heavy. Just, don't.

    Stop thinking about bike weight as a top metric. Be sensible but don't think it's going to be a huge factor.

    The McNamara Fallacy and bikes | Peter Verdone Designs

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    pvd
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    Please post a print. Drawings are important.

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    Quote Originally Posted by pvd View Post
    The seat tubes on my bikes are offset, so the angle isn't a comparitor. Effective angle is 74 degrees or so. See that in the prints.

    We don't refer to top tube length when discussing geometry. I don't know what you are referring to.

    Almost every production 'gravel bike' is not properly designed. The industry is selling product, not performance.

    Surly bikes are designed to be terrible. They are joke bikes. They are also super heavy. Just, don't.

    Stop thinking about bike weight as a top metric. Be sensible but don't think it's going to be a huge factor.

    The McNamara Fallacy and bikes | Peter Verdone Designs
    Ok, that makes more sense if your effective seatube angle is 74*. I realize that effective toptube is not really a good fit metric as it is determined by reach and seatangle.. However, it does tell you the distance from the seatube to the headtube which should give a better idea of how the bike will feel when seated, at least that's my understanding. I will cease desist from posting until I have some drawings.
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    Consider a shorter seat-tube, even if you're not planning on using a dropper-post...since you plan to bike-pack, stand-over space starts to disappear when you add gas-tank and storage packs to the seat-post/top-tube area. On that same note, the "sportier" feel of a lower stack/shorter top-tube is a bit at odds with bike-packing. I prioritize the height/reach of the drops for all-day comfort; but, you know your terrain and what you want better than I do. I definitely agree with keeping clearance for 2.2-2.3" tires; always leave the possibility open for an epic ride to turn into downright stupidity!!!

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    What length stem and which drop bars do you plan to run? You want to design holistically so everything is in harmony. If you start cherry-picking numbers out of context you could end up with elements of the bike fighting themselves.

    Related is are you running flat pedals? Do you also ride any progressive mtbs?

    Also do you plan to maybe run a suspension fork? If the answer is no then you could run a shorter fork and get some more frame bag space.

    Also how much pedal clearance do you really need for your terrain? For bigger-tired drop bar bikes I've gone as low as the 93mm in bottom bracket drop, and that can help you out with standover if you're running gas tanks as mentioned above.

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    Quote Originally Posted by dr.welby View Post
    What length stem and which drop bars do you plan to run? You want to design holistically so everything is in harmony. If you start cherry-picking numbers out of context you could end up with elements of the bike fighting themselves.

    Related is are you running flat pedals? Do you also ride any progressive mtbs?

    Also do you plan to maybe run a suspension fork? If the answer is no then you could run a shorter fork and get some more frame bag space.

    Also how much pedal clearance do you really need for your terrain? For bigger-tired drop bar bikes I've gone as low as the 93mm in bottom bracket drop, and that can help you out with standover if you're running gas tanks as mentioned above.
    I plan on running a 60mm stem and Salsa Cowchipper bars, giving me a pretty short cockpit and allowing the longer reach. My current mtb isn't really all that progressive (surly karate monkey w/ 130mm fork) but I've spent significant time on a trek fuel ex and have a pretty clear idea of what modern geo is and its effects on handling, i'm just not used to picking out every single number and really considering all the minor details. I don't intend on running suspension so a shorter fork would definitely be an option to consider. As far as pedals go, I like flats and will likely run crankbros stamps on the bike.
    I don't need a ton of bb height as most of the terrain this bike will see at least resembles a gravel road, in other words, it will see gravel/atv trail etc. but for real mtb'ing I would just use a different bike. Also, I'm working on some drawings, so that should give me a better idea of the bike will work as a whole too. Ill post those up for further scrutinization once I get them finished up.
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  11. #11
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    Some thoughts

    -tubes look much too big. They're appropriate for me, and i'm like 90lbs heavier and taller. I'd be looking at roadie diameter tubes at your weight.

    -how are you going to carry your load? Front/rear racks twist the frame more than a frame bag set up.

    -CX forks are ~395mm and it makes a lot of sense to design around that. More space in the front triangle, less lever.

    -do you have a specific fork in mind? IMO even on a rigid bike the fork is pretty influential and should be designed/selected as part of the frame design process.

    -cowchippers are narrow. High trail (looks like you're going for high trail...?) and narrow bars isn't my jam, even with the short stem you propose. It's my impression you either haven't thought through the steering behavior and/or are coming at it from a MTB'ers wide flatbar perspective.

    -bb height looks good to me!

    -i really like paragon head tubes. They don't cost much more than the nova tube stock, and they're lighter, look great, and are nice to work with.

    -you can run in to crank arm clearance issues with single bend CSs and sliding dropouts. Be sure to check.

    -those dropouts should be tigged. I believe tabbed ones are easier...? Paragon makes a tabbed version of those. (idk how to tig, just repeating what i've been told)

    -i guess you'll be using a seat tube topper or a sleeve with that single butt seat tube. Don't forget!

    -i'm interested to see your drawing. Hopefully you're doing it in cad. BikeCAD and rattleCAD have free alternatives. If you're hand drawing- it works better to locate by distances rather than angles. Eg- saddle setback and front-center.

    -i like this affordable jig more than the wood one.





    I've done a whopping 2 gravel/touring bikes, so not an expert at all.
    "Things that are complex are not useful, Things that are useful are simple."
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    Quote Originally Posted by BufaloBill View Post
    I kind of want something along the lines of a more mtb inspired gravel bike. Should I push my design more into left field (like your bird of prey) or is the industry fixated around a relative stagnant ideal of a gravel bike because the design works?
    If I were in your situation, I would try to push the design a little bit, that is the main advantage and fun of designing and building a frame from scratch.

    I think some of the back and forth of this thread is people’s different interpretations of what a gravel bike is.

    What you seem to be describing is a drop bar mountain bike. Something with upright geometry, wide handlebars, and mountain bike tire clearance. Example: Salsa Cutthroat.

    Another interpretation is the mainstream "high performance" gravel bikes of the roadie world. They have similar handling to road bikes, long stems, aggressive body positioning, clearance for 45mm tires. Example Cannnondale Topstone

    I would describe PVD's interpretation as merging forward geometry concepts of the mountain bike world (short stem, long reach, long front center, dropper post) with the concepts of the road bike world (road gear ratios, narrow tires, aggressive fit). The new BMC URS seems to be trending towards that direction.

    I don't think there is a wrong interpretation. Everyone rides differently, in different places, and has different expectations.

    The limiting factor of your design seems to be the fork availability. It looks like all forks with clearance for 29x2.2 tires are suspension corrected, with long axle to crowns. I think this looks goofy and as other posters have commented, takes away from frame bag space. It appears that the current crop of carbon gravel forks can clear at most 700x50mm.

    I think it would be cool to design a bike around the columbus CX fork (http://www.henryjames.com/futura-cro...-fork-rtp.html) to handle two sizes: 27.5x2.1 (Ø690mm) and 700x40mm (Ø702mm). The rake flip chip allows you to adjust the trail of the two wheel sizes to be similar.

    I recently bought bikeCAD pro (highly recommended), and threw your numbers in for practice and this is what I got:

    Feedback on Gravel Bike Geo and build specs-large-gravel.jpg

    After going down that path, I looked up the geo of your 2014 Karate monkey (https://surlybikes.com/uploads/downl...14_catalog.pdf), and the dimensions are quite similar to the above bike. I think a good starting point would be to order parts to convert your karate money into a dropbar mountain bike. If you push your saddle as far forward as possible and use a 50mm stem, it will get the seated reach within 5mm. Ride, it, tweak it, experiment, see what you like and dislike, then you can be more informed to design a better gravel bike. You would need to order parts for a gravel bike anyways!

    Feedback on Gravel Bike Geo and build specs-karate-monkey-large.jpg

    See, Surly are good for something after all (kidding).

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    Quote Originally Posted by natzoo View Post

    The limiting factor of your design seems to be the fork availability. It looks like all forks with clearance for 29x2.2 tires are suspension corrected, with long axle to crowns.
    This seemed silly to me, so i wasted some time trying to find good monstercross forks. Here's the list of what i found that might be appropriate... but it's not that useful. You're right- forks that are super suitable for this project don't exist.

    https://blackmtncycles.com/shop/fram...er-cross-fork/

    IRD MCX Max CX Carbon Fork (For 15mm Thru-Axle Hub) — Interloc Racing Design / IRD

    https://www.enve.com/en/products/cross-fork-disc/

    https://www.curvecycling.com.au/coll...2mm-flat-mount

    https://www.somafab.com/archives/pro...el-carbon-fork

    https://www.somafab.com/archives/pro...axle-crmo-fork

    https://ninerbikes.com/products/nine...t-rdo-mtb-fork


    I have a custom fork i built around this crown. It was designed around the 395mm CX spec, and i'm pretty sure it can fit a 29x2.4. The fork came out really stiff and stupidly heavy at 1200g with through axle and disk tabs, but that's my fault because i'm a huge destructive force and idgaf about weight. (imo weight reduction is a consequence of refinement) I'm certain it could be built lighter even for an oaf like me. I can check maximum tire clearance and share lessons learned if anyone asks... but i haven't built many forks.

    Personally, i feel like the value of drop bars has severely diminished by the time you want a >50mm wide tire. But i understand how more clearance is only good.


    Are there good production monstercross fork options that i missed?
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    Quote Originally Posted by scottzg View Post
    Some thoughts

    -tubes look much too big. They're appropriate for me, and i'm like 90lbs heavier and taller. I'd be looking at roadie diameter tubes at your weight.

    -how are you going to carry your load? Front/rear racks twist the frame more than a frame bag set up.

    -CX forks are ~395mm and it makes a lot of sense to design around that. More space in the front triangle, less lever.

    -do you have a specific fork in mind? IMO even on a rigid bike the fork is pretty influential and should be designed/selected as part of the frame design process.

    -cowchippers are narrow. High trail (looks like you're going for high trail...?) and narrow bars isn't my jam, even with the short stem you propose. It's my impression you either haven't thought through the steering behavior and/or are coming at it from a MTB'ers wide flatbar perspective.

    -bb height looks good to me!

    -i really like paragon head tubes. They don't cost much more than the nova tube stock, and they're lighter, look great, and are nice to work with.

    -you can run in to crank arm clearance issues with single bend CSs and sliding dropouts. Be sure to check.

    -those dropouts should be tigged. I believe tabbed ones are easier...? Paragon makes a tabbed version of those. (idk how to tig, just repeating what i've been told)

    -i guess you'll be using a seat tube topper or a sleeve with that single butt seat tube. Don't forget!

    -i'm interested to see your drawing. Hopefully you're doing it in cad. BikeCAD and rattleCAD have free alternatives. If you're hand drawing- it works better to locate by distances rather than angles. Eg- saddle setback and front-center.

    -i like this affordable jig more than the wood one.





    I've done a whopping 2 gravel/touring bikes, so not an expert at all.
    Quote Originally Posted by pvd View Post
    Please post a print. Drawings are important.
    Quote Originally Posted by natzoo View Post
    If I were in your situation, I would try to push the design a little bit, that is the main advantage and fun of designing and building a frame from scratch.

    I think some of the back and forth of this thread is people’s different interpretations of what a gravel bike is.

    What you seem to be describing is a drop bar mountain bike. Something with upright geometry, wide handlebars, and mountain bike tire clearance. Example: Salsa Cutthroat.

    Another interpretation is the mainstream "high performance" gravel bikes of the roadie world. They have similar handling to road bikes, long stems, aggressive body positioning, clearance for 45mm tires. Example Cannnondale Topstone

    I would describe PVD's interpretation as merging forward geometry concepts of the mountain bike world (short stem, long reach, long front center, dropper post) with the concepts of the road bike world (road gear ratios, narrow tires, aggressive fit). The new BMC URS seems to be trending towards that direction.

    I don't think there is a wrong interpretation. Everyone rides differently, in different places, and has different expectations.

    The limiting factor of your design seems to be the fork availability. It looks like all forks with clearance for 29x2.2 tires are suspension corrected, with long axle to crowns. I think this looks goofy and as other posters have commented, takes away from frame bag space. It appears that the current crop of carbon gravel forks can clear at most 700x50mm.

    I think it would be cool to design a bike around the columbus CX fork (http://www.henryjames.com/futura-cro...-fork-rtp.html) to handle two sizes: 27.5x2.1 (Ø690mm) and 700x40mm (Ø702mm). The rake flip chip allows you to adjust the trail of the two wheel sizes to be similar.

    I recently bought bikeCAD pro (highly recommended), and threw your numbers in for practice and this is what I got:

    Click image for larger version. 

Name:	large gravel.jpg 
Views:	107 
Size:	126.9 KB 
ID:	1292641

    After going down that path, I looked up the geo of your 2014 Karate monkey (https://surlybikes.com/uploads/downl...14_catalog.pdf), and the dimensions are quite similar to the above bike. I think a good starting point would be to order parts to convert your karate money into a dropbar mountain bike. If you push your saddle as far forward as possible and use a 50mm stem, it will get the seated reach within 5mm. Ride, it, tweak it, experiment, see what you like and dislike, then you can be more informed to design a better gravel bike. You would need to order parts for a gravel bike anyways!

    Click image for larger version. 

Name:	Karate Monkey Large.jpg 
Views:	53 
Size:	106.0 KB 
ID:	1292637

    See, Surly are good for something after all (kidding).



    Thanks for the info everybody. I finally got a chance to make a couple drawings. The first one is my original design, designed around a 483mm fork. I chose this fork length because there are a several affordable forks with this length. It looks like there a shortage of shorter a2c forks that will clear a wide 29er tire too. The second one is exploring the concept of a 650b gravel bike, as natzoo suggested.. ( I cant remember if the drawing reflects the ability to go with shorter chainstays though). Also, I did a couple sketches of what the back end of the bike would look like to kind of see what is realistic regarding tire and chainring clearance. It looks like I have to choose between one or the other, the sketches I did prioritize tire clearance.

    A couple of other notes: I am rethinking my tubeset as there seems to be a consensus that it will result in a ridiculously overbuilt bike. I am reconsidering my dropouts too for that matter, suggestions are more than welcome Also, as far as the geo goes, I need to put some thought into the front end and steering behavior. Scott, as you pointed out, I did overlook steering behavior and need to put some more thought into that. The design is fairly high trail (slackish headangle plus 47mm offset fork), and I am coming at it from a mtb wide bar/short stem perspective. Perhaps something along the lines of a 46cm woodchipper would be a better fit?
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    Quote Originally Posted by BufaloBill View Post
    Thanks for the info everybody. I finally got a chance to make a couple drawings. The first one is my original design, designed around a 483mm fork. I chose this fork length because there are a several affordable forks with this length. It looks like there a shortage of shorter a2c forks that will clear a wide 29er tire too. The second one is exploring the concept of a 650b gravel bike, as natzoo suggested.. ( I cant remember if the drawing reflects the ability to go with shorter chainstays though). Also, I did a couple sketches of what the back end of the bike would look like to kind of see what is realistic regarding tire and chainring clearance. It looks like I have to choose between one or the other, the sketches I did prioritize tire clearance.

    A couple of other notes: I am rethinking my tubeset as there seems to be a consensus that it will result in a ridiculously overbuilt bike. I am reconsidering my dropouts too for that matter, suggestions are more than welcome Also, as far as the geo goes, I need to put some thought into the front end and steering behavior. Scott, as you pointed out, I did overlook steering behavior and need to put some more thought into that. The design is fairly high trail (slackish headangle plus 47mm offset fork), and I am coming at it from a mtb wide bar/short stem perspective. Perhaps something along the lines of a 46cm woodchipper would be a better fit?
    Decide what fork you want to use before you proceed with the design.



    Consumers look at reach and head angle because they're marketing descriptors and popular fit parameters. When you're building the frame yourself you can design the cockpit fit independently of the steering behavior and weight distribution. So like, front-center tells you about stability, and trail tells you about steering behavior... but mtb'ers use head angle and reach because they summarize both characteristics (and fork offset hasn't traditionally been something they could control). So imo part of the learning/fun of designing frames is figuring out how all this stuff really works together. You might end up designing a ~production bike (that's all i've done the last couple years), but how you get there is different. That's 100% tmi for your first frame build...

    For me, i know my cockpit (which took a couple iterations with road bikes because historically they're shitty when you're tall), so now i just put the wheels where i want them, and then adjust the chainstays/head angle/stem/bars/fork offset to provide the handling and steering i want. Now i don't care what any of those numbers are in isolation, but a 10mm change is easily perceptible.




    I'm seeing ~90mm of trail with your design? That's a lot of trail for a drop bar bike. My inclination is to go even wider than 46cm bars, but i've never owned a drop bar bike with such high trail, so i'm totally speculating. Once you get in to the range of 'appropriate' it doesn't seem to matter as much. I've never ridden a bike like what you're building and it's interesting!

    There's something wonky in your chainstay drawings. Like, your chainstays are way too fat, maybe. I dunno what it is, but i know i've been able to cram more tire than what you're showing in to a 73mm bb an 1x setup. It might just be that i don't mind dimpling stays just enough that a dropped chain can pass through. Chainstay selection/execution/yolks are their own topic.

    I asked before about how you're planning on carrying a load. If you have a rear and fork mounted panniers those can twist up a frame pretty good and the big front triangle tubes you specified make some sense. "it rides better with a load."


    Here's my own gravel bike. I designed it with the idea that it wouldn't be fun to descend on trails, handle a load acceptibly, and love crappy/dirt roads and social road rides. In practice, it's a stupidly good road descender. I'm babbling in your thread because i think your project is really interesting and has tons of room for nonstandard optimization. Don't hesitate to PM me for babbling or more specific comments, i just feel weird dictating my hobbyist opinions on forum where real experts participate.
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    pvd
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    Your "prints" are incomplete. They don't show the required fit or handling dimensions necessary for evaluation. Add the saddle and handlebars and go through the documentation again.

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    Feedback on Gravel Bike Geo and build specs-slolo.jpg

    My latest gravel bike, those are 700 x 48 tires.

    70 ha, 74 sa, 38 fo, 91 trail, 91 bb drop, 452 stays (42-18 magic gear), 614 stack, 436 reach, full housing to both ders, ported for internal dropper.

    It uses a generic eBay 26" carbon fork, 420 a-c I think? It's a standard 9mm QR to work with my existing wheels. It does look like you can get a T-A model now but it has a much taller crown so you probably would have to go to the 27.5" model which is around 450mm if I remember correctly.

    Adding 1" of headtube to your frame bag space is going to add at most 1 liter of capacity. So you can think about balancing the capacity of a big feed bag versus mud clearance.

    I first built up the bike with some random parts and had 40cm handlebars and the bike felt too floppy. With 44cm handlebars it feels pretty normal, the flop is only noticeable when doing wheelstands. Though for a given trail figure using less offset (this fork has only 38mm) results in less wheel flop. The flop force is also proportional to the weight on the front wheel so adjusting the weight distribution backwards (longer front center, shorter chainstays) can help.

    I went with longer stays to offset some of the long front center, but I haven't measured the weight distribution yet.

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    Quote Originally Posted by scottzg View Post
    Decide what fork you want to use before you proceed with the design.



    Consumers look at reach and head angle because they're marketing descriptors and popular fit parameters. When you're building the frame yourself you can design the cockpit fit independently of the steering behavior and weight distribution. So like, front-center tells you about stability, and trail tells you about steering behavior... but mtb'ers use head angle and reach because they summarize both characteristics (and fork offset hasn't traditionally been something they could control). So imo part of the learning/fun of designing frames is figuring out how all this stuff really works together. You might end up designing a ~production bike (that's all i've done the last couple years), but how you get there is different. That's 100% tmi for your first frame build...

    For me, i know my cockpit (which took a couple iterations with road bikes because historically they're shitty when you're tall), so now i just put the wheels where i want them, and then adjust the chainstays/head angle/stem/bars/fork offset to provide the handling and steering i want. Now i don't care what any of those numbers are in isolation, but a 10mm change is easily perceptible.




    I'm seeing ~90mm of trail with your design? That's a lot of trail for a drop bar bike. My inclination is to go even wider than 46cm bars, but i've never owned a drop bar bike with such high trail, so i'm totally speculating. Once you get in to the range of 'appropriate' it doesn't seem to matter as much. I've never ridden a bike like what you're building and it's interesting!

    There's something wonky in your chainstay drawings. Like, your chainstays are way too fat, maybe. I dunno what it is, but i know i've been able to cram more tire than what you're showing in to a 73mm bb an 1x setup. It might just be that i don't mind dimpling stays just enough that a dropped chain can pass through. Chainstay selection/execution/yolks are their own topic.

    I asked before about how you're planning on carrying a load. If you have a rear and fork mounted panniers those can twist up a frame pretty good and the big front triangle tubes you specified make some sense. "it rides better with a load."


    Here's my own gravel bike. I designed it with the idea that it wouldn't be fun to descend on trails, handle a load acceptibly, and love crappy/dirt roads and social road rides. In practice, it's a stupidly good road descender. I'm babbling in your thread because i think your project is really interesting and has tons of room for nonstandard optimization. Don't hesitate to PM me for babbling or more specific comments, i just feel weird dictating my hobbyist opinions on forum where real experts participate.
    I appreciate all your babblings as they are largely helpful, I sent you a PM with some more comments and questions. It appears that I need to put some more thought into trail too.

    Quote Originally Posted by pvd View Post
    Your "prints" are incomplete. They don't show the required fit or handling dimensions necessary for evaluation. Add the saddle and handlebars and go through the documentation again.
    Right, more drawings. I'll get some more worked up and go out and do some measuring on my current bikes as well. Plus, try to figure out what really fits me and what doesn't.

    Quote Originally Posted by dr.welby View Post
    Click image for larger version. 

Name:	slolo.jpg 
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ID:	1293015

    My latest gravel bike, those are 700 x 48 tires.

    70 ha, 74 sa, 38 fo, 91 trail, 91 bb drop, 452 stays (42-18 magic gear), 614 stack, 436 reach, full housing to both ders, ported for internal dropper.

    It uses a generic eBay 26" carbon fork, 420 a-c I think? It's a standard 9mm QR to work with my existing wheels. It does look like you can get a T-A model now but it has a much taller crown so you probably would have to go to the 27.5" model which is around 450mm if I remember correctly.

    Adding 1" of headtube to your frame bag space is going to add at most 1 liter of capacity. So you can think about balancing the capacity of a big feed bag versus mud clearance.

    I first built up the bike with some random parts and had 40cm handlebars and the bike felt too floppy. With 44cm handlebars it feels pretty normal, the flop is only noticeable when doing wheelstands. Though for a given trail figure using less offset (this fork has only 38mm) results in less wheel flop. The flop force is also proportional to the weight on the front wheel so adjusting the weight distribution backwards (longer front center, shorter chainstays) can help.

    I went with longer stays to offset some of the long front center, but I haven't measured the weight distribution yet.
    Thanks for the Info, the bike looks super nice. How do feel about the handling with the long stays? Also, what is your height to give the numbers a bit of context? Thanks for the fork suggestions too.
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    Quote Originally Posted by BufaloBill View Post
    How do feel about the handling with the long stays? Also, what is your height to give the numbers a bit of context?
    The stays don't feel long, overall the bike feels well balanced and smooth. But I don't ride anything on it where shorter stays have any advantage. There's more payoff for a smooth and stable ride. Also with all that drop they're not quite as long as they seem...

    I'm 6' tall, but between long arms and yoga my handlebar reach/drop might not be applicable to most people.

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    Quote Originally Posted by dr.welby View Post
    The stays don't feel long, overall the bike feels well balanced and smooth. But I don't ride anything on it where shorter stays have any advantage. There's more payoff for a smooth and stable ride. Also with all that drop they're not quite as long as they seem...

    I'm 6' tall, but between long arms and yoga my handlebar reach/drop might not be applicable to most people.
    I just noticed how much bb drop you had, 91mm seems like a lot. I assume the big tires raise the height of it up enough that your not smacking your pedals in every other corner?
    A 436 reach does sound awfully long for a drop bar bike, but you are a couple inches taller, plus it looks like you have a much racier position than I would want. On another note, what tires are you running on that bike? I can never seem to find 43mm+ gravel tires.
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    Quote Originally Posted by BufaloBill View Post
    I just noticed how much bb drop you had, 91mm seems like a lot. I assume the big tires raise the height of it up enough that your not smacking your pedals in every other corner?
    A 436 reach does sound awfully long for a drop bar bike, but you are a couple inches taller, plus it looks like you have a much racier position than I would want. On another note, what tires are you running on that bike? I can never seem to find 43mm+ gravel tires.
    The bike was built for shorter distance midwest gravel racing, experimenting with idea of making something long, low, and stabile that would support a really aggressive position. There's no rocks and not many corners where I used to live so I gave the bike a road bike bottom bracket height with those big tires (also an experiment). If I ran anything smaller the bottom bracket would be reaallly low, but I haven't touched my road bike in 15 years so that answers that question.

    If you went with 70mm then you'd have something like a road bike when you mount road tires, and then when you put on 29er tires you'd boost the bottom bracket up for more clearance off-road. Or you could do the 700c/27.5x2 mix and keep the bottom bracket closer to the same height. Maybe since it's a touring bike you want to maximize frame bag room with a big frame and you don't want to lose standover when you're in big tire mode.

    Now that I live it the Sierra I'd probably want it 10-15mm higher, and I'd like bigger tires too since the roads are much rougher here. Right now it still has the tires in the photo, which are Schwalbe G-One Speeds in 700x50. On road rims they measure more like 48mm.

    Like I said, my position is stretched out and I have really long arms. This frame is basically a 90's 29er with the bottom bracket 2 inches lower.

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    Quote Originally Posted by pvd View Post
    Your "prints" are incomplete. They don't show the required fit or handling dimensions necessary for evaluation. Add the saddle and handlebars and go through the documentation again.
    This totally fits my own perspective on frame design, looking at bufalobill's prints. Pete, what are the fit dimensions, and what are the handling dimensions? How do the fit dimensions influence the handling dimensions? What compromises do you make between both when you design a bike?
    Last edited by scottzg; 11-18-2019 at 11:20 AM.
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    Quote Originally Posted by scottzg View Post
    What are the fit dimensions, and what are the handling dimensions? How do the fit dimensions influence the handling dimensions? What compromises do you make between both when you design a bike?
    Generally, the fit dimensions are the location of the pedals, saddle, and handlebar. The handling dimensions are (very roughly) the location of the tires, the height of the bottom bracket, and the location of the rider/COG between the wheels. Head angle and trail do come into play but are a much smaller component than most think. A print should show these elements or it's really not a sorted concept.

    What compromises do I make between both when you design a bike? All of them.

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    Quote Originally Posted by dr.welby View Post
    Click image for larger version. 

Name:	slolo.jpg 
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ID:	1293015

    My latest gravel bike, those are 700 x 48 tires.

    70 ha, 74 sa, 38 fo, 91 trail, 91 bb drop, 452 stays (42-18 magic gear), 614 stack, 436 reach, full housing to both ders, ported for internal dropper.

    It uses a generic eBay 26" carbon fork, 420 a-c I think? It's a standard 9mm QR to work with my existing wheels. It does look like you can get a T-A model now but it has a much taller crown so you probably would have to go to the 27.5" model which is around 450mm if I remember correctly.

    Adding 1" of headtube to your frame bag space is going to add at most 1 liter of capacity. So you can think about balancing the capacity of a big feed bag versus mud clearance.

    I first built up the bike with some random parts and had 40cm handlebars and the bike felt too floppy. With 44cm handlebars it feels pretty normal, the flop is only noticeable when doing wheelstands. Though for a given trail figure using less offset (this fork has only 38mm) results in less wheel flop. The flop force is also proportional to the weight on the front wheel so adjusting the weight distribution backwards (longer front center, shorter chainstays) can help.

    I went with longer stays to offset some of the long front center, but I haven't measured the weight distribution yet.
    Nice looking ride Dr Welby.
    Some very practical advice too!

    I have come in late into this discussion and most of what I could offer has been said.
    But I will confirm the wheel flop/geo statement made by Dr Welby. This is also my experience on my own bike designs. I will add that if you stay using ‘narrow’ width bars and ride at low speed that you may prefer a trail figure slightly less at around 80-85mm. You have to build a bike and then fine tune it.
    Forks, by the way, are not hard to make. They seem to be avoided as a build item, which is unfortunate. It is easy to just purchase this item, but this does not necessarily mean that they are ‘right’ for the application. Offset, width and AC become flexible items if you build this way.

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

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    Quote Originally Posted by Eric Malcolm View Post
    Forks, by the way, are not hard to make. They seem to be avoided as a build item, which is unfortunate. It is easy to just purchase this item, but this does not necessarily mean that they are ‘right’ for the application. Offset, width and AC become flexible items if you build this way.
    I have the parts to build a steel fork for this bike, but the carbon model was too cheap and convenient not to try since it was the length and internal width I wanted. With 38 offset it also gave me an interesting starting point. My main worry is that it would have turned out too floppy, so I had plenty of room to increase the rake on the next fork to more "normal" territory to reduce the trail.

  26. #26
    pvd
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    Steel forks are serviceable when combined with 3.00" tires but once you get below 2.5" tires, they really are terrible compared to carbon options. I'd stay away from them if there is any care for ride quality.

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    Quote Originally Posted by pvd View Post
    Steel forks are serviceable when combined with 3.00" tires but once you get below 2.5" tires, they really are terrible compared to carbon options. I'd stay away from them if there is any care for ride quality.
    Not enough information? I've used steel forks that were excessively noodley, and steel forks that were infinitely stiff. Neither had a significant impact on ride quality, imo, once you factor in the billion other ways to influence ride quality.

    I'm like 220lbs so maybe it's different when your lighter...?
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    Quote Originally Posted by Eric Malcolm View Post
    Forks, by the way, are not hard to make. They seem to be avoided as a build item, which is unfortunate. It is easy to just purchase this item, but this does not necessarily mean that they are ‘right’ for the application. Offset, width and AC become flexible items if you build this way.
    I've only built a couple forks, but it makes sense to me why they're avoided. None of the forks i've built have hit the generic carbon fork benchmark for anything. They've been heavy and excessively stiff. I've ridden steel forks that overshot in the other direction- too flexy and vague, so i know a sweet spot exists, at least at my size. I think learning how to design a great fork is almost as tricky as learning to design a great frame. I'm somewhat confident the next steel fork i build for myself is going to be reasonably lightweight while outperforming the chi-chi carbon options, but so far it only exists in my mind.

    I've got a lot of respect for someone like dave kirk, who can confidently claim his steel fork (as part of a frameset) is superior to any mass market carbon alternative. While building for someone who isn't himself. I know it's possible.
    "Things that are complex are not useful, Things that are useful are simple."
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