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A million and one variables - front center, HTA, fork offset

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A million and one variables - front center, HTA, fork offset

Old 12-08-23, 01:05 PM
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A million and one variables - front center, HTA, fork offset

Hi all - I spent last summer dialing in the fit on my touring bike, which I have had since it was unboxed at the shop I worked for in high school. After all the fiddling, I think that fit is pretty good (if only I could stop thinking about it, I'd probably be happy!), but the esthetics of the situation is less pleasing. As seen here, my 1986 23" Schwinn Voyageur:

Note the extend stem with a 40mm reach. Blech. The Voyageur is 23" ST (c-t) and 22" TT (c-c), which is basically as small TT/ST ratio as one can find in a production bike. So I take this as the perfect excuse to finally build that frame I've always wanted.

Moving onto design, I've been playing with CAD, BikeCad and this guy:https://www.bikegeocalc.com/ to come up with a frame which with the same fit, but will allow a 6deg, 80mm-ish reach stem. This was chosen because it (a) looks pretty good to me, and (b) gives me 40mm more room for adjustment, and (c) even more options with varying stem angle, and (d) pushing beyond 40mm will make the concerns below more concerning.

Drawing up the designs with the 80mm stem, the geometry which results has me wondering about the relationship of front-center, HTA, fork offset, wheelbase and everything else. More specifically, wondering how much I should be wondering about this stuff. I would appreciate any thoughts on my musings below.

For reference the Voyageur is:
HTA/STA: 72/74
WB: 1051
FC: 613
CS: 451
Rake/Trail/Flop: 50.8/62/18

Primary objective: I need to shorten my reach about 30mm, and I want a flat top-tube. So to get there we need to shorten the TT and/or lower HTA which will impact FC and WB.

Some options (using 50.8 rake, because this is what I have, and this seems to be middle of the road in touring bikes):

HTA 72 = 583FC and 1021WB, 60Trail, 18Flop (I'm converting to 700c from 27)
HTA 71 = 593FC and 1031WB, 67Trail, 21Flop
HTA 70 = 601FC and 1041WB, 73Trail, 24Flop

I am aware of toe overlap, and I already have it with my fenders at the current 613FC, but it doesn't bother me, so not a deal breaker, but I'm wondering if any of the above tradeoffs should be considered critical? Specifically, all the above HTAs are within the realm of the popular touring bikes smaller frames (LHT, 520), but the WB will be 20-30mm shorter. Is there anything in the ratio of CS:FC which would cause trouble?

How about converting between any of the above choices with a fork change? I can adjust trail/flop by offset for a given HTA...are the fork parameters going to be more important. Bike with a HTA 72 + 60Trail going to feel like a HTA 70 + 65Trail, all other things equal?

Is there anything else I'm missing? Is it reasonable to cut 30mm reach out of a nice touring bike and expect the result to also be nice?

Thanks for any thoughts. I know there are lots of experimenters out there who have probably done similar things, so I'd appreciate any input.

Don

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Old 12-08-23, 02:42 PM
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It's one thing to live with a few MMs to a CM of toe overlap, especially if one doesn't ride in traffic much. But increase the overlap to 4ish CM... Try adding a pencil or wire extending 3+ CM out forward of your current shoe's front and ride the bike to see if that much overlap is workable for you. I know I would never design a bike for another with so much overlap.

Your challenge is much like the wish for minimal reach to the bars that smaller women have suffered with. One industry solution was to run a smaller ft wheel to reduce overlap, whether you have the same size rear wheel or not. This is why I chose 559 x 38 tires/rims for my touring bike. If I were to run 38ish MM tires on a 622 wheel and include the fenders I would have close to 2+ CM of overlap. The other beauty of smaller tire diameters is that the steering geometry can retain snappier handling specs, no need to chopper out (or actually "back" as the front center would remain nearly the same) the steering angle to lose TT length.

I could rant on the current industry solutions for wanting short reaches but I won't Andy
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Old 12-08-23, 04:51 PM
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If you look at the front wheel clearance of your bike, it wouldn't make sense to reduce it. Absent Andy's suggestion of smaller wheels, there is no way to reduce that front center without making the bike a mess.

Mountain bikers are going to zero length stems. I would get one of those and be happy with it.

I am seriously thinking about building a frame with a 90 degree head tube, a negative rake, and a negative stem length. Because people keep saying those things will make a bike unrideable. Possibly I'll learn something.
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Old 12-08-23, 05:39 PM
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Originally Posted by Andrew R Stewart
It's one thing to live with a few MMs to a CM of toe overlap, especially if one doesn't ride in traffic much. But increase the overlap to 4ish CM... Try adding a pencil or wire extending 3+ CM out forward of your current shoe's front and ride the bike to see if that much overlap is workable for you. I know I would never design a bike for another with so much overlap.

Your challenge is much like the wish for minimal reach to the bars that smaller women have suffered with. One industry solution was to run a smaller ft wheel to reduce overlap, whether you have the same size rear wheel or not. This is why I chose 559 x 38 tires/rims for my touring bike. If I were to run 38ish MM tires on a 622 wheel and include the fenders I would have close to 2+ CM of overlap. The other beauty of smaller tire diameters is that the steering geometry can retain snappier handling specs, no need to chopper out (or actually "back" as the front center would remain nearly the same) the steering angle to lose TT length.
The 559s are definitely a possibility. I just wanted to start with 700c, primarily for the better options in tires and rims. But I was also thinking about fiddling with the BB drop such that I could run either. Thinking 700c most of the year and big 559s during the winter/spring when things are messy here (seems doable without a super high BB).

I will see about rigging up something to test the toe-overlap concern. I was going to wire some hard foam blocks to the bottom of my pedals and go for a ride, in the hopes that I could see about pedal strike, to determine my lowest BB height (basically see how much is scraped off when I get back). So maybe something similar with toe clearance.

Over my fitting experiment, I shortened my cranks by 10mm without any obvious difference, so I agree with the 1cm assessment.

Note that I don't ride in traffic, and instinctively adjust when making low speed turns, etc.

Originally Posted by unterhausen
If you look at the front wheel clearance of your bike, it wouldn't make sense to reduce it. Absent Andy's suggestion of smaller wheels, there is no way to reduce that front center without making the bike a mess.
Are you thinking of toe-overlap, or the HTA, or something else? Relooking at the LHT/520 specs, they do FC values which are going to be around 600 or less (estimated from WB-CS). The 56cm LHT is there, but the HTA is 72.

Not ruling out smaller wheels, just seeing what the options are.

Thanks for the reponses.
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Old 12-08-23, 08:14 PM
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BB height (or for a frame builder "drop") has very little effect on front center. It does interact a lot with stand over and stack. Andy
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Old 12-08-23, 10:06 PM
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Originally Posted by Andrew R Stewart
BB height (or for a frame builder "drop") has very little effect on front center. It does interact a lot with stand over and stack. Andy
Understood, the height concern/interest was in the context of supporting multiple wheel sizes. Sorry for the confusion.
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Old 12-08-23, 10:40 PM
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Is it possible to "lock in" the top tube/head tube junction and kick the down tube/head tube junction forward a degree or 2 and make up the difference with more fork rake? You'd have more flop. But so long as the trail was a bit lower, say, lower than average (58?) you'd still have a light feeling bike that would want to hold corners with stability.

I should think that flop really isn't that much of a component unless you are going to extremes like building a chopper or putting a very heavy load on the handle bars.

Crunch the numbers for a 70 degree head tube and kick the rake out until the trail gets to the high 50's-low 60's (58, 59, 60, 61, 62?) and see where that gets you. Then shorten the front center, bringing everything closer to you until the hoods are in the right place. What's the toe overlap then? IIRC the RB1 had a 73/70-ish geo and people, so far as I can tell, people really liked how they rode.

I'm just spit ballin' I've misplaced the bikecad program I used to play with. The worst that can happen is a few wasted electrons at this stage of the game to rule in/out some ideas. In looking at your current set up, everything about it says you are trying to replicate the fit of a utility Dutch bike. The high close bars and the angle of the brake levers say a lot. It's going to be hard to get different results than you already have with a horizontal top tube unless you have a 38 inch inseam. You might consider a non-diamond frame design or touring/North Road handlebars and just outright own the upright fit.


You can also cut 30mm of reach by handlebar selection. 65-75mm reach on modern bars is a lot more common these days than the 100-120mm reach found on vintage bikes. Then even a bit more can be found to work with between various shifters. TRP brake hoods are loooong. Gevenalle and SRAM are really short. Shimano is somewhere in between.

Edit: While we're here. Short chain stays suck. Err on the long side. The rear contact patch sort of acts like tail feathers on a dart or an arrow. The bike will track nicely. It's subtle. But it's there. IME long(er) chain stay bikes tend to have really nice manners for no real tangible performance trade-off. Especially if you have a very upright fit, the longer rear center will help with weight distribution; taking a bunch of weight off the rear wheel to share more evenly between the two. How long are the stays on the bike you currently ride? It might be a good idea to think about shooting for a similar or maybe even a bit longer. 18+ inches? 20? More?

559x57 is similar in diameter to 700x23 both approx 2120-25 circumference (~340mm-ish radius) For brevity it's not worth hashing out 700x25, 28, versus 559x60, 65 whatever. You get the idea... Point being: Longer chain stays in general will help with tire clearances. Boost spacing of 73 or 83mm bottom brackets and 148mm axle widths and 55-58mm chain lines will also help with wide 60+ 26 inch tire widths. All that boost broohaha may well be beyond the scope of this project. But if you intended to have the 26, 700 "freedom option" in the future it could make sense to consider it from the beginning. 60+ tire widths are hard to stuff in a frame otherwise.

You really should have a strong idea of what components you are going to use before you commit to a frame design.

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Old 12-09-23, 08:27 AM
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Originally Posted by dschad
Are you thinking of toe-overlap, or the HTA, or something else? Relooking at the LHT/520 specs, they do FC values which are going to be around 600 or less (estimated from WB-CS). The 56cm LHT is there, but the HTA is 72.
I was just looking at how close your fender is to your downtube.
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Old 12-09-23, 08:50 AM
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Wow, thanks for this. A lot of interesting stuff to get through....some comments below.
Originally Posted by base2
Is it possible to "lock in" the top tube/head tube junction and kick the down tube/head tube junction forward a degree or 2 and make up the difference with more fork rake? You'd have more flop. But so long as the trail was a bit lower, say, lower than average (58?) you'd still have a light feeling bike that would want to hold corners with stability.

I should think that flop really isn't that much of a component unless you are going to extremes like building a chopper or putting a very heavy load on the handle bars.
This is one of the key questions I'm trying to understand - is there/what is the "key" number. May ways to get to the same trail/flop via HTA and rake. So is that the key numbers (trail/flop?). Looking at some key players in the touring bikes, the HTA/Offset/Trail/Flops are in a fairly tight range (trail flop calculated from https://yojimg.net/bike/web_tools/trailcalc.php):




That last option is your suggested hta/trail which gives a FC of 611, which is 2mm less than the current design. So the question is really - is that 70/58 a good number for a touring bike? Interestingly, the LHT 46cm with 26s is 70HTA, but they use the same fork offset for all, so the trail/flop is out of the norm.

Originally Posted by base2
Crunch the numbers for a 70 degree head tube and kick the rake out until the trail gets to the high 50's-low 60's (58, 59, 60, 61, 62?) and see where that gets you. Then shorten the front center, bringing everything closer to you until the hoods are in the right place. What's the toe overlap then? IIRC the RB1 had a 73/70-ish geo and people, so far as I can tell, people really liked how they rode.
I looked up the RB1, which seems to be a bit more aggressive. HTA 73.5/74 @56cm (see: https://farm4.static.flickr.com/3186...d42cb8ed_o.jpg)


Originally Posted by base2
I'm just spit ballin' I've misplaced the bikecad program I used to play with. The worst that can happen is a few wasted electrons at this stage of the game to rule in/out some ideas. In looking at your current set up, everything about it says you are trying to replicate the fit of a utility Dutch bike. The high close bars and the angle of the brake levers say a lot. It's going to be hard to get different results than you already have with a horizontal top tube unless you have a 38 inch inseam. You might consider a non-diamond frame design or touring/North Road handlebars and just outright own the upright fit.
I've been playing with this (https://www.bikegeocalc.com) which is really fast for this type of fooling around:


The dotted is my existing setup (with short stem), the colored is the design I'm fiddling with. I am trying to match the BB position and handle bar position (note picture actually has 26 wheels, which end up very close toe overlap to the current bike).

Originally Posted by base2
You can also cut 30mm of reach by handlebar selection. 65-75mm reach on modern bars is a lot more common these days than the 100-120mm reach found on vintage bikes. Then even a bit more can be found to work with between various shifters. TRP brake hoods are loooong. Gevenalle and SRAM are really short. Shimano is somewhere in between.
This is partly why I want to have a significant amount of stem to work with - so I can get flexibility in my component selection. My bars are 75mm reach with 102mm drop. In theory I could even reverse my 40mm stem and still have my hoods in front, but then things are getting really funny looking.

Originally Posted by base2
Edit: While we're here. Short chain stays suck. Err on the long side. The rear contact patch sort of acts like tail feathers on a dart or an arrow. The bike will track nicely. It's subtle. But it's there. IME long(er) chain stay bikes tend to have really nice manners for no real tangible performance trade-off. Especially if you have a very upright fit, the longer rear center will help with weight distribution; taking a bunch of weight off the rear wheel to share more evenly between the two. How long are the stays on the bike you currently ride? It might be a good idea to think about shooting for a similar or maybe even a bit longer. 18+ inches? 20? More?
The Voyageur has 17.75s, so pretty long. Those are what are in my design, although I have heard people complain that long makes things sluggish, but your point about weight distribution is a good thing to consider. The overall weight distribution was also a concern with the FC seeming to get so short.

Originally Posted by base2
559x57 is similar in diameter to 700x23 both approx 2120-25 circumference (~340mm-ish radius) For brevity it's not worth hashing out 700x25, 28, versus 559x60, 65 whatever. You get the idea... Point being: Longer chain stays in general will help with tire clearances. Boost spacing of 73 or 83mm bottom brackets and 148mm axle widths and 55-58mm chain lines will also help with wide 60+ 26 inch tire widths. All that boost broohaha may well be beyond the scope of this project. But if you intended to have the 26, 700 "freedom option" in the future it could make sense to consider it from the beginning. 60+ tire widths are hard to stuff in a frame otherwise.

You really should have a strong idea of what components you are going to use before you commit to a frame design.
"Boost"? What next, a sloping top tube?! 1x drivetrain?

60's may be too much, and I haven't really gotten to the thickness dimension yet, but I thinking that 700x40s and 559x54 would be good upper ends. I think beyond that the frame starts to get beyond my (hoped) esthetic parameters. But I don't know.

Thanks again for the great food for thought.
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Old 12-09-23, 09:33 AM
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Originally Posted by unterhausen
I was just looking at how close your fender is to your downtube.

Ah ha...that is an interesting point...

It would be somewhat compensated by lower HTA, I'll play around with that as a 370mm wheel. Going down the "mess path" - maybe a super-tall fork...

Thanks.
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Old 12-09-23, 10:52 AM
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Originally Posted by dschad
Wow, thanks for this. A lot of interesting stuff to get through....some comments below.


This is one of the key questions I'm trying to understand - is there/what is the "key" number. May ways to get to the same trail/flop via HTA and rake. So is that the key numbers (trail/flop?). Looking at some key players in the touring bikes, the HTA/Offset/Trail/Flops are in a fairly tight range (trail flop calculated from https://yojimg.net/bike/web_tools/trailcalc.php):

Rake and trail have the biggest effect on how a bike feels. It's actually trail. Rake is how to get the trail number you want. How much trail is appropriate for a given use is why there are so many different manufacturers out there duking it out with each other with all manner of design. Different uses will tend to cluster together.

There really isn't key number. Flop is a product of head tube angle and wheel diameter. Mostly it's useful for estimating a bikes desire to keep going the way that it's going in a turn. It's the rise/fall of the front end of the bike when you turn the bars. Really high flop bikes like modern 62 degree downhill bikes foe example have really wide handlebars to give the rider enough leverage to counter the force of gravity (lift the front of the bike/counter the flop) when attempting to turn the bars. It's not good or bad. It just is.

I really wouldn't pay "flop" too much mind. If you were to draw a parabola graphing a really floppy bike for stability, the shape would be very pointy. Perfect for riding in a straight line, but it would want to quickly stuff itself in to a corner. A road racing bike would be almost hemispherical. Consistant, predictable. A shopping cart, naturally, would be a flat line since there isn't any head tube angle at all.

That last option is your suggested hta/trail which gives a FC of 611, which is 2mm less than the current design. So the question is really - is that 70/58 a good number for a touring bike? Interestingly, the LHT 46cm with 26s is 70HTA, but they use the same fork offset for all, so the trail/flop is out of the norm.
I would say "Yes" Someone else may say "No" The 58 trail number may feel a bit light when riding unloaded or only rear loaded. But with front low-riders largely undoing the lightness, it'd ride more neutral. The 70hta would offer straight line stability. The flop would lend itself to wider handlebars or even flat bars for an upright posture.

I looked up the RB1, which seems to be a bit more aggressive. HTA 73.5/74 @56cm (see: https://farm4.static.flickr.com/3186...d42cb8ed_o.jpg)
Ok. I was wrong about that. I was going from memory.

I've been playing with this (https://www.bikegeocalc.com) which is really fast for this type of fooling around:


The dotted is my existing setup (with short stem), the colored is the design I'm fiddling with. I am trying to match the BB position and handle bar position (note picture actually has 26 wheels, which end up very close toe overlap to the current bike).

This is partly why I want to have a significant amount of stem to work with - so I can get flexibility in my component selection. My bars are 75mm reach with 102mm drop. In theory I could even reverse my 40mm stem and still have my hoods in front, but then things are getting really funny looking.
I think it's a useful tool but BikeCad starts with your own personal body dimensions then maps the bike to fit. I would defer to Andrew R Stewart from up thread. He's the actual hobbiest builder here.

The Voyageur has 17.75s, so pretty long. Those are what are in my design, although I have heard people complain that long makes things sluggish, but your point about weight distribution is a good thing to consider. The overall weight distribution was also a concern with the FC seeming to get so short.
So much of the short chain stay trend (?) is the faster feeling bike tends to get the sale. So manufacturers stuff the rear wheel forward to make the bike feel responsive. The weight of the rider being directly over the wheel also helps in steep climbs with low traction. It save the rider from body position skills. The trade off is the bikes propensity to tip over backwards with rear loading or really steep climbs weak riders would rather walk instead. A racing bikes also need to stuff themselves into smaller spaces behind the other riders for aero, draft, cornering position, etc...A touring bike has none of those concerns. Cadillacs and Rolls Royce's are not sports cars. The extra weight of a 6 inch longer frame is completely irrelevant. But the mild manners is something that has to be experienced to be appreciated. At almost 18 inches, your current bike is already at where modern gravel bikes are returning to.


"Boost"? What next, a sloping top tube?! 1x drivetrain?

60's may be too much, and I haven't really gotten to the thickness dimension yet, but I thinking that 700x40s and 559x54 would be good upper ends. I think beyond that the frame starts to get beyond my (hoped) esthetic parameters. But I don't know.

Thanks again for the great food for thought.
This is why it's fun to play with ideas on paper first
Good luck! 😉

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Old 12-10-23, 05:28 AM
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Originally Posted by unterhausen
If you look at the front wheel clearance of your bike, it wouldn't make sense to reduce it. Absent Andy's suggestion of smaller wheels, there is no way to reduce that front center without making the bike a mess.

Mountain bikers are going to zero length stems. I would get one of those and be happy with it.

I am seriously thinking about building a frame with a 90 degree head tube, a negative rake, and a negative stem length. Because people keep saying those things will make a bike unrideable. Possibly I'll learn something.
I think that might be unrideable to someone used to a regular bike. But with a lot of practice it could be ridden. Would certainly be an interesting experiment though
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Old 12-10-23, 05:46 AM
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I think the best way to reduce reach is to use a slack head angle with lots of rake (to get the trail back to a sensible figure), and a short stem. If you want a high stack I would go with a sloping TT, but not so sloping that you don't have enough standover. If necessary extend the HT a bit above the HT/TT junction. This is better than having loads of steerer or stem stickout IMO.

Agree that long CS are just plain better. Much easier to fit everything in without dimples or scallops in the CS, and you won't get dreaded foot-slap on your panniers.

As for handling my experience has been that your brain just gets used to whatever you're riding and it feels absolutely right after a little while. Low BB makes it nice and easy to put your foot down and will help you achieve the high stack you want. So you could consider a drop of 80mm. I wonder though if a higher BB helps keep one's feet a bit drier when riding through puddles? My touring frame ended up with it slightly higher than intended (because reasons) but I actually really like it.

Do you need a drop handlebar? Could consider an old-school flat handlebar that actually curves backwards towards the rider.

This is my most "trad yet rad" opafiets style build:

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Old 12-10-23, 07:21 AM
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Originally Posted by guy153
I think the best way to reduce reach is to use a slack head angle with lots of rake (to get the trail back to a sensible figure), and a short stem. If you want a high stack I would go with a sloping TT, but not so sloping that you don't have enough standover. If necessary extend the HT a bit above the HT/TT junction. This is better than having loads of steerer or stem stickout IMO.
I agree - this seems to be where it is going to end up. With 26" wheels and 70.5 you actually don't need a whole lot of rake to get things to fit. Really, the biggest battle I am fighting is not just committing to 26s, that seems to make things a lot easier.

I am also considering dialing back on the stem length a bit. I do want flexibility in there, but perhaps 15MM will open things back up a bit in terms of the FC.

The one thing I don't want is sloping TT...can't do it. I would be devastated if someone looked at my bike someday and said: "nice gravel bike!". Using the extended HT does look a lot better and less kludgy (I agree with your thoughts on steerer and/or stem). My iteration from last night is looks like that:



(never mind the extra steerer). This design has the same toe clearance to fender that I currently ride, with a shorter FC.

Originally Posted by guy153
As for handling my experience has been that your brain just gets used to whatever you're riding and it feels absolutely right after a little while. Low BB makes it nice and easy to put your foot down and will help you achieve the high stack you want. So you could consider a drop of 80mm. I wonder though if a higher BB helps keep one's feet a bit drier when riding through puddles? My touring frame ended up with it slightly higher than intended (because reasons) but I actually really like it.
I completely agree with the brain-adaption. Ultimately I think that it'll end up great, but of course always have me wondering... I'm in the the pre-build over-thinking phase. Since there is a range of options that no one can agree upon, I'm probably safe as long as I'm within that range.

Regarding BB - I'm probably going to go with a pretty big drop. My Voyageur is 85mm already (27"), and I use 165 cranks recently, after going from 175 for a long time. Never a strike, so that's 10 there. I did an experiment yesterday where I rode one of my favorite routes with 1" foam blocks on the bottom of my pedals and by the end, no contact. I suspect I could go 2", although that might start to get limiting in the future. It was an unnatural effort to get them to scrape when I tried to at the end.. But I don't want to overdo it. That drop starts to give me a bit more HT also to minimize extra stem extension.

Originally Posted by guy153
Do you need a drop handlebar? Could consider an old-school flat handlebar that actually curves backwards towards the rider.

This is my most "trad yet rad" opafiets style build:

Show us your builds
I'm not sure I do need the drops, but I find the hoods and flats to be very comfortable and the options to move my hands around is nice. I like the wrist angle, but honestly haven't tried like a NorthRoads. Into the wind maybe I'll ride the drops, but not too much. I do have some Albastash bars which I liked for shorter rides, but longer didn't offer me good options to move around. For zipping around town they are probably great, but require even less reach.

That is cool build there. I looked at that and the "previous build" also very nice...seems like we have similar reach requirements.

Thanks for the response, good stuff to keep thinking about.

Don

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Old 12-10-23, 07:29 AM
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Originally Posted by guy153
I think that might be unrideable to someone used to a regular bike. But with a lot of practice it could be ridden. Would certainly be an interesting experiment though
In an early Rivendell Reader, Grant Petersen said that, as an experiment, he'd once switched from his usual sport touring geometry bike to one with a cyclocross frame geometry that included a very high bottom bracket. He said he found the bike to feel unstable to the point of wanting to give up on it immediately.

But he persisted with it and, after a half hour or so of riding, found he'd adjusted to it, to the point where he didn't notice the handling any more.

Then, when he went back to his sport touring bike, the bike felt weirdly slow and unresponsive, but only for the first half hour or so. Then it was back to feeling normal.
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Old 12-10-23, 07:42 AM
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Originally Posted by dschad
The one thing I don't want is sloping TT...can't do it. I would be devastated if someone looked at my bike someday and said: "nice gravel bike!". Using the extended HT does look a lot better and less kludgy (I agree with your thoughts on steerer and/or stem).
Level top tube as the standard is a modern idea! Up to the early teens of the 20th century, "safety" bikes were routinely built with top tubes that sloped upward from the seat tube to the head tube.



Standardization of the level top tube was probably introduced when bike manufacturers figured out that it was faster and cheaper to build frames using lug-based construction, which eliminated the need for careful mitering of tubes by highly paid skilled workers. Any semi-skilled worker could push thick tubes into lugs and apply a torch.


Edit: To clarify, using a level top tube design for lugged construction meant that manufacturers were able to keep their stock of head and seat tube lugs to a minimum. Fewer tube-to-tube angles, fewer lugs.

In fact, many bikes were designed with standardized parallel head and seat tube angles and standardized top and down tube lengths over the range of frame sizes, the only variables being the seat and head tube lengths, thus reducing stock requirements to the bare minimum.

This approach was used by many Japanese bike companies even in the 1960's and 1970's, when they were making their first forays into building and exporting derailleur-equipped bikes.

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Old 12-10-23, 09:28 AM
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Originally Posted by guy153
I think that might be unrideable to someone used to a regular bike. But with a lot of practice it could be ridden. Would certainly be an interesting experiment though
Sorry to derail op's thread. But the idea is that everything important would be the same as one of my normal bikes. Trail and reach being the main things. I think it will not be any different.
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Old 12-10-23, 09:48 AM
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Originally Posted by Trakhak
Level top tube as the standard is a modern idea! Up to the early teens of the 20th century, "safety" bikes were routinely built with top tubes that sloped upward from the seat tube to the head tube.



...

Edit: To clarify, using a level top tube design for lugged construction meant that manufacturers were able to keep their stock of head and seat tube lugs to a minimum. Fewer tube-to-tube angles, fewer lugs.

In fact, many bikes were designed with standardized parallel head and seat tube angles and standardized top and down tube lengths over the range of frame sizes, the only variables being the seat and head tube lengths, thus reducing stock requirements to the bare minimum.
History repeats itself. I haven't looked too hard, but it seems like most have gone to sloping and welding, so perhaps to your point about lugs. It certainly make sense for custom configurations in that it gives you more freedom. Looking the Disc Trucker - they seem to be riding the middle road - mildly sloping TT + tall head tube, evolving away from the level LHT.

Here is my early 20th century revision:



Not terrible, but I do prefer the flatty.

I must admit that it isn't immediately obvious to me that flat mass-production would result having to have fewer lugs in stock, but I can see about cuts. Maybe I need my thinking cap.

Don
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Old 12-10-23, 10:14 AM
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Originally Posted by dschad
I must admit that it isn't immediately obvious to me that flat mass-production would result having to have fewer lugs in stock, but I can see about cuts. Maybe I need my thinking cap.

Don
Building lugged frames over a range of head tube and seat tube angles (for angle differences greater than about 2 degrees or so, which stamped lugs would be able to accommodate, as I understand it) would require a corresponding range of lug angles.

Keep the top tube horizontal, and you've eliminated two variables: the angles at the junctions with the seat tube and head tube.

Keep the seat tube and head tube angles constant (and parallel), and you've eliminated two more. And so on.

In the U.S., at least, the balloon-tired bikes with curved frame tubes that were ubiquitous in the 1930's and after were even simpler to build. The only variable was the wheel size: 20", 24", or 26". Three (wheel) sizes to fit everyone.
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Old 12-10-23, 10:24 AM
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When it comes to level TTs I quite like them all things being equal, but I dislike excessive stickout of stems (or seatposts) even more. So my least favourite is the modern "road" frame with a really short ST, loads of seatpost extension, and a low stack. If you're going to have a low stack just give it a horizontal TT. I know the long seatpost is supposed to give you "suspension" or something but to me it just looks goofy. If I am making a high stack frame I would rather slope the TT to avoid lots of spacers and things up at the front.
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Old 12-10-23, 11:54 AM
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Originally Posted by guy153
When it comes to level TTs I quite like them all things being equal, but I dislike excessive stickout of stems (or seatposts) even more. So my least favourite is the modern "road" frame with a really short ST, loads of seatpost extension, and a low stack. If you're going to have a low stack just give it a horizontal TT. I know the long seatpost is supposed to give you "suspension" or something but to me it just looks goofy. If I am making a high stack frame I would rather slope the TT to avoid lots of spacers and things up at the front.
Yes, "vertical compliance" of frames is far less important than you'd think from reading Bike Forums. Adequate comfort comes from choosing a saddle and a pair of tires that provide flexibility and having a bike with a reasonably longish wheelbase.
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Old 12-10-23, 12:31 PM
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My learning experience was when I was asked to make some bikes for a local track program. They wanted really small bikes (46-47cm) but the kids didn't like the current bikes with 26" 'Kids' wheels, so the velodrome insisted on 700c. The compromises were significant and I have heard from adults that they ride funny. Any time a 6 footer rides a size 47cm track bike, they are likely going to say it rides funny but, the point remains there were too many compromises and I learned my lesson. Go with 650b wheels. There are many great options for wheels and tires for 650b so no reason to not use that and gain a couple cm of clearance.
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Old 12-11-23, 04:08 PM
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Originally Posted by duanedr
My learning experience was when I was asked to make some bikes for a local track program. They wanted really small bikes (46-47cm) but the kids didn't like the current bikes with 26" 'Kids' wheels, so the velodrome insisted on 700c. The compromises were significant and I have heard from adults that they ride funny. Any time a 6 footer rides a size 47cm track bike, they are likely going to say it rides funny but, the point remains there were too many compromises and I learned my lesson. Go with 650b wheels. There are many great options for wheels and tires for 650b so no reason to not use that and gain a couple cm of clearance.
So you *had* to bring up 650b...I did consider this, and I like the idea in principle, but I was generally discounting it because my research (internetting) I am not finding many options for rim brake rims. Disc seems to be plentiful thanks to MTBs, but the rim brake, touring selection seems to be limited to $30 Wiennmans, which people aren't too impressed with as far as I can tell, or $100 VO ones. And one aero rim which isn't my style for sure. Makes me worry that they won't be any in another few years.

That said, in terms of the measurements, these definitely work. The 650bx40 and 26x2 have the same OD, so I could go skinny without changing the sizing much. The skinnies on a 26x1.5s start to look a bit dinky.

Am I overly concerned about the demise of the rim-brake 650b?
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Old 12-11-23, 06:42 PM
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There are enough 650b rim brake rims available that it's not going to be a problem for my lifetime. It's not even single source, Velocity and others make them. A lathe to cut the brake tracks is a fairly simple machine in contrast to actually doing the extrusion/bending. All rim brake rims are going to be high-end at some point, the low-end is going to be disc. As long as Jan Heine is alive, you'll have no problems getting a 650b rim.
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Old 12-11-23, 07:48 PM
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I explored my toe-overlap issue the other day by adding some foam to the back of my fender. I decided after that ride that it would be better to have no more overlap then my current bike, which has a touch. (I also decided that next time, I'd add foam to the front of my shoe, and put a bit of marking compound on there, just for fun).

After careful measuring of the existing setup I've got this table for your viewing pleasure:



Which gives me the minimum FC for each size wheel (basically wheel R + 17mm space) + my toe radius. I donno what standard space between tire/fender is, but 17 was my current setup which seems okay.

I can pretty easily get to a 600FC with a 71hta/65 trail which seems within the common range of the popular touring bikes.




So it seems like the 26s and/or 650bs (I'm so easily swayed!) might be a nice solution.
Above is a 26rear, 650b front at 670 for comparison.
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