This spring I took a frame building class with Dave Bohm and had a really wonderful time. I was gone during the summer trying to escape the AZ heat, so just getting back home and starting to get rolling on a few frames. I figure I’ll build a few front triangles at the same time for a couple different projects. The first two will be track bikes for the track that’s being built in Tucson, and those seem easy enough and I figure they’ll get my skills up before diving into some more challenging builds.
The real project will be a gravel bike for a friend that’s about 6’ 6” and makes a whole load of power. With the help of BikeCAD Pro, I think I have decent geometry figured out, but wanted to make sure that I’m not totally messing it up. The saddle height of 875mm is a number I’m a little skeptical of, but it comes right from my buddy, so we’re going with it. Everything else is just a tad bit larger than his current 58cm Diverge, that’s a tad too small for the big boy. I’ve attached a screenshot of the primary dimensions, and I’m sure there’s one million different opinions about what the right and wrong geo, but I’m all ears!
And question two about the same frame is regarding the tubing choices I’m planning on making. It’s a bit all over the board, mostly because of the large tubes needed. I certainly went with oversized tubes, as he wants a stiff bike (and I think they look better). Mostly concerned with the front triangles at the moment, as I’ll really nail down the CS and SS options later. Also, planning on going with the Reynolds Flat mount Dropout Set from Firsthand, unless the consensus is that they’re difficult to work with as a new frame builder. Again, I’m sure everyone’s got a different opinion here, but really just want to make sure I’m not going too big on the tubes and that there aren’t tubing options on this list that I should steer clear of or add.
Looks good! The only problem I foresee (which is not insurmountable) is that it’s annoying attaching such a fat TT and DT to a regular sized ST. You’re going to have 1/4 inch gaps either side of the ST where you’re trying to attach the DT. Best thing probably to ovalize the end of it in a vice. But you could consider a more oversized ST (DT will probably still need some ovalizing but it will be more subtle).
Buying pre-cast flat-mount dropouts is a great idea I think, especially on a first frame as it’s easier than the other options. If it’s a TIG frame you could try to find some “breezer” style ones (Ceeway in UK have them).
I admit I had to google how much 6’6” was in non-freedom units
I second the optinion that joining a 34.9 TT to a 29.8 ST might be a bit of a challenge. On the BB end I think there will not be a problem since you’re using a 2” T47 shell.
I would maybe try to use a 31.8 ST and TT and then use a sleeve for the 27.7mm seat post, or even switch to a larger post diameter and get an according seat tube.
Maybe consider using a headtube from paragon which is a bit beefier than the flimsy 1mm wall spirit tubing. Lightweight tubing should probably not be a priority for someone 2m tall and putting out a lot of power
Ya he’s defiantly big! Good call on the head tube. I considered these, but went with spirit to save some weight. I think you’re right though. The 60 grams or so saved is probably not worth it.
Good call on the ST and TT connection. I’ll probably end up just going oversized with the ST and a little smaller TT. Probably a slightly smaller DT too, just so its all somewhat matching.
Ok, changed the seat tube to a 31.7 that comes with a sleeve for a 27.2 seat post and knocked the top tube down to 31.7 as well, but kept the larger 42 mm down tube. I guess its about time to order some tubes and get the files out!
Just be aware that if you’re using that seattube then you’re going to end up with a seattube OD that’s going to be tricky getting a clamp for. If you’re brazing/welding a binder on, then no problem obviously but if not, you’re going to be hunting around for an odd size clamp or having something custom made. That’s the main reason I avoid externally butted seattubes and prefer a sleeve/collar to provide the wall thickness needed to work with standard* seatposts and standard size clamps.
(I know ‘standard’ is a vague word in this context but for a steel frame, I’d be looking for something to fit a 34.9, 31.8 or 28.6 clamp. I know there are some vendors that supply less common sizes but it’s just something to be aware of.)
Another way to fit a TT that’s larger than the ST is to keep the TT round at the ST and miter the seat stays to mostly overlap the ST and also fit against/flow into the TT ears. With nice fit up and brazing the stays can look seamless with the TT. This would also set the SS slightly wider apart at the top to better fit the huge (in my world any tire wider than 42ish on a drop bar bike is huge) tire.
Can you source an externally butted ST that’s also long enough? If not consider a sleeve over the top end of the ST. Big guys can sometimes need a lot of post securement…
How are you joining? Andy.
I should have read the entire thread before posting this. Lots of good ideas sent in.
The “regular” externally butted STs like the one he started with (29.8mm at the top) are very easy to find clamps for. But yes larger sizes may be harder. I used a Columbus ZONI113550001 on one build, 33.5mm at the top, and ended up having to shim the closest clamp I could find with bits of coke can. That was before I had my minilathe– I always make my own binders now.
seems like you’ve received great advice above. I would add, I think you’re definitely not going too big on the tubes. though knowing the guys weight might allow some better feedback on this..
When I build bikes for much bigger and/or more powerful people I often choose down-tubes up to 44.45X0.8 or even 50.8X0.75 and they say exceptionally nice things about them (to me at least) . mtb top tubes up for normal large sized people can go right up to 38X0.9.
34.9 tt is big but manageable and I wouldnt say crazy. i’m 6’2 and 200lbs (I googled the freedom units!!) and have a 34.9 butted downtube as a top tube in my latest track bike and really like it.
with the really tall fellas, double check you have enough fork steerer.. and for the really tall guys, the steerer comes pre-cut! bonus!
Thanks for all of the advise! Rider is about 230 pounds, for those asking and the bike will be brazed. I’m practicing my TIG on the side, but still brazing at the moment as my TIG skills are well below where they should be to build a bike.
Maybe adding to what @crowe-molybdenum said, especially the TT you have in your list is maybe a bit optimistic with a 7-5-7 wall… Maybe the velospec AC31090609-650 might be a more sensible choice, or even a bigger diameter as was suggested earlier.
According to my calculations, a 31.7mm tube which is 0.5mm in the middle is stiffer than 25.4 at 1mm wall or 28.6 at 0.6. It also weighs more than 25.4 tubing at 0.6.
Add diameter for stiffness, wall thickness (or heat treating) for strength. But I think most of us don’t need excessive strength. You only need that on an MTB if you’re also a highly skilled rider (or an OEM who needs to pass ISO testing).
I wasn’t referring to strength or stiffness of the tube itself, but about the strength of the joint. Both WT and diameter make the joint more resilient and less sensitive to imperfections, since there is just more of it. It’s like redundancy in a way.
The more similar the wall thicknesses of the tubes are, the easier it is to get them holding together nicely, with whatever joining method you’re using. And that Paragon HT is a bit on the chunky side…
Also on a first frame thicker walls are a bit easier to deal with (especially with TIG). I used 9-7-9 on my frame #1. In theory the joint should always be stronger than the tube (you make up for the filler material having a lower strength by having a slightly bigger fillet). But theory isn’t always what happens especially on a first frame!
A gravel bike can mean a lot of different things… some might just want a road bike with more clearance, others might want something closer to a drop bar MTB.
I’m 6’6” and here are the tubes I’m using. Probably could’ve used a 38mm DT, but oh well, I’m not looking for something super stiff. A 35mm 9/6/9 DT has worked for me in the past.
Here are the tubes I’m using:
TT: 31.8mm 9/6/9
DT: 34.9mm 9/6/9
ST: 35mm 1.65/.9
HT: 44 x 200mm
BB: T47, 73mm
CS: 19mm 0.9 straight gauge
SS: 16mm tapered
For reference, my distance from the center of the BB to top of the saddle is 857mm with 175mm cranks.
Great point. I think this is designed to be more racey, thinking Speicalized Crux equivalent. And great to know about saddle height, actually helps a lot. I’m 5’ 9” myself so my dead average brain is having a hard time with all of these big boy numbers!
Funny enough, I was rewatching your MTB series as I opened up CFF to check for any new replies. Watched all your videos at least three or four times, and this series more than that. Really makes it all seem a little more manageable with your videos, so thanks for the content! Excited to see how that gravel bike ends up
As a low budget, garage hack builder, its great to have your info to reference. I think most of us fall in that category and while I love watching people with more equipment and skill, its most helpful to see people getting it done with a set of tools that I can replicate more easily.
