[mtnbikinggolfer]

Thought I addressed it, must've forgot. No reason really, just sort of based it off what I had ridden since I don't really know anything else. I'll be more than happy to hear if you have any advice about that.

 

[mtnbikinggolfer]

I wasn't aiming for smaller tubes, I just forgot about Henry James. Would a 44.5mm 1/.7/1 ST be better for the downtube then, or is that pushing it too large? I'm not too concerned about weight. As far as seat tube angle, that was more so an arbitrary number and I welcome suggestions. I may considering shortening the front end too.
Thanks,
Aaron

 

[Eric Malcolm]

SuperTherm, where's Walt, this is his area.

 

[mtnbikinggolfer]

He gave me suggestions for the Supertherm, and said 38 for the downtube. I didn't notice there was a 44 Supertherm downtube. I don't really care about the extra weight, but was unsure if there would be a reason not to use that.

 

[dr.welby]

Since crank arms don't scale proportionately to the range of frame sizes, you often see bigger guys on slacker seat angles to account for it. But without knowing your proportions and seeing what you ride now we can't say whether it will or won't work for you. You won't run into any mechanical problems with it, like you would if you were trying to do a really slack seat angle with really short stays.

Same goes for the front end - hard to say without more information. It's long, but you're tall, and the long back end would probably balance it out.

 

[mtnbikinggolfer]

Alright thanks. Do you think a 72 degree angle would be better to try?

 

[Eric Malcolm]

OK.

I think maybe a halt might be wise here. The reason is that there is a need to digest the info a bit, but also suggest more info might be needed to not confuse the original request. Progress has been made, but a proper fitting with an experienced builder might be a good direction to go, then, a purpose built frame can be successful. The right elements exist here, but a personal fit would really be needed to go forward on.

Eric

 

[TrailMaker]

Hey;

I am exactly your size, although you being so young, I imagine we have it distributed a bit differently! My inseam is 36, with a 37" sleeve, so I am quite evenly proportioned frame-wise. When I built my first fatbike frame, I used an amalgam of bikes I knew fit me (my Niner RIP9), and the Salsa Mukluk fatbike. Those bikes are surprisingly similar, believe it or not. I used the basic Salsa geo. I made the front center longer by 30mm or so, but otherwise copied what the pros had done. I am generally happy with the results. The base numbers are 70* HT, 73* ST, 744mm Front Center, 450mm CS, 484mm ST, 330mm BB height.

I developed a friendship with a fellow that has worked in the bike industry for many years as a fabricator/welder/machinist, and also builds bikes "on the side." He suggested tubing sizes for me based on my size, his experience, and my desire to keep things a bit simple to start. I used all straight gauge .035 CroMo. 1.375 TT, 1.5 DT, 1.25 ST, .75 stays. The results have been quite good, if I do say. I am interested in building one with shorter stays, and I might like to try shortening the FC back to where you are speaking of, but other than that I am happy with what I have, for my style of riding, which is techy, rocky, rooty, creek beds, and tight tree filled classic Northeast trails. Oh... and as little climbing as possible. I'm better pointed DOWN hill!

 

[briderdt]

OK.

I think maybe a halt might be wise here. The reason is that there is a need to digest the info a bit, but also suggest more info might be needed to not confuse the original request. Progress has been made, but a proper fitting with an experienced builder might be a good direction to go, then, a purpose built frame can be successful. The right elements exist here, but a personal fit would really be needed to go forward on.

Eric

+1 on this. If you're considering a 2 degree slackening of the STA and asking if that would be better, then you need to understand more about your particular fit before you start making a frame to fit it.

 

[Walt]

Don't sweat the seat tube angle. Make sure your front center is where you want it. Then even if you miss the target by a few degrees on STA, you can just move your saddle around and/or get a setback post to get you where you need to be.

People obsess over STA for no good reason. It's 15mm per degree if you're tall, folks. Less if you're short. You can move a couple degrees in either direction just by moving your saddle and/or swapping posts.

-Walt

 

[briderdt]

15mm per degree, and he's talking about 2 degrees already. How many 30mm set-back seatposts are on the market? I think Velo Orange's 32mm is about the only one (and it's a roadie, so would likely be short). I submit it's pretty important, if this frame is meant to be a keeper. If it's just a throw-away educational experience, by all means go for it.

 

[Walt]

Did you miss the part about moving the saddle on the rails?

Most have ~40mm of total adjustment (so plus/minus 20mm) or more. You can make up most of the difference between 74 and 72 degrees without even swapping posts. Once you throw even a 15mm setback post into the equation it's pretty much academic.
From the center of the rails, assuming a 74 STA, you can go forward about 1.5 degrees and back about 2.5 degrees using commonly available stuff.

Is it a good idea to know what your saddle setback needs to be and design for it? Of course! Is it the end of the world if you miss by a degree or two? No.

-Walt

 

[Francis Buxton]

I would just buy the 1.6mm wall headtube stock from either HJ or Nova.

Also, keep in mind that 42 and 44mm downtubes mean that you have to do a little bit of ovalization at the HT and BB to get them to fit up right, as they have a larger diameter than the HT and BB shell. It's not hard to do (just carefully squish it in a vise). The hardest part is making sure you have the orientation correct.

 

[dr.welby]

Is it a good idea to know what your saddle setback needs to be and design for it? Of course! Is it the end of the world if you miss by a degree or two? No.

Sure, but if you don't know what you want, why not at least put it somewhere in the middle to give you the most range in both directions to experiment with? If most of his range is going to come from shoving things backwards, at his weight (and with a 27.2 seatpost) that's not where you'd really want to end up. There's certainly nothing gained by the steeper seat tube unless he has odd proportions.

 

[TrailMaker]

Hey;

I think there is merit in ALL the ST talk here. From my less than experienced perspective, I think that while it is not critical to hit the target dead on (and I certainly have not), it is at the least an exceptionally good thing to HAVE one, and further, to have one based on some solid reasoning. I know little of fitment, but from what I can reason, it seems like to me that a steeper ST angle would benefit a shorter leg, putting the body over the BB more. Is this correct? If so, that would not seem to be indicated here, as the boy is a biggun like me. Adding to that, and from my own experience, a 20-30mm shorter FC than I have on my builds would at the least set him quite upright, and might even overly cramp the cockpit.

As mentioned, I might like to try an FC shorter by 20mm or so. Alternately, I might simply try a shorter stem. Besides reasons of Clydesdale fitment, I don't guess I would want to decrease my ability to loft the front by setting myself farther forward with a 74* ST angle.

 

[Walt]

It is really all preference. You can find >80 STA on some TT and tri bikes, especially from back in the days before the UCI killed the funnybikes (smaller front wheel than rear) but obviously those don't need to get wheels off the ground (or worry about going over a drop). Recumbents run less than zero effective STA, and there are head-first 'bents that are something like 180! So you can ride a bike with almost anything, but as I think everyone agrees, it's good to have a target for some kind of reason.

I guess my point was that there are a lot of things that I'd obsess about before STA: trail, FC, BB height, CS length being the big ones. I'm not arguing that it's entirely pointless. But 95% of production bikes have a 72-73 STA for a reason - it works for almost everyone for most riding. Unless you have unusual tastes or physical attributes it's pretty safe to be anywhere near that range.

I think it's also worth remembering that most of places where how the bike handles/weight is distributed matters are also places where you aren't actually sitting on the saddle.

-Walt

 

[TrailMaker]

Well...

Nice of you to get to your point, Walt!

No, seriously... I'm about the least technically knowledgeable "builder" you'll ever meet, and so I find when there is a discussion like this - like a funnel where wide ranging ideas merge at the center before hitting the container - I get a fuller, rounder understanding of the variables at play. It's all good!

 

[mtnbikinggolfer]

Gravedig

While a new thread may be more appropriate after all this time, it is still my first build so I will carry on here. Everyone's input so far has been appreciated and not forgotten. Like many of similar origin, this frame project had gone to the wayside. It's held firm to its place on the back-burner and I'm pleased to be making progress once again.

Since last time, I have acquired a blanchard ground table that I am working through machining fixture parts for. I will be TIG welding my frames but did just put together an oxy-propane brazing setup as I found an oxygen concentrator at an estate sale.






I got a batch of 4130 cut on the tube laser at my work for practice joints. A little bit a filing after and they fit tightly. Glad I cut a batch of these, as my welding needs much more practice.









Still a long ways to go, but in terms of this project's timeline I hope I am far past the halfway point.