Framebuilders - Steel "Integrated Seat-Mast"...Good Idea?
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07-16-08, 02:53 AM
I've been perusing the Giant bicycle catalog and their high-end road-bikes have "integrated seat-masts", which basically means the seat-tube doesn't stop at the top-tube and keeps going up, serving as the seatpost. According to them it's "stiffer", but it's only an option on CARBON frames, which is why I am asking the following...
If one were to go with a custom steel frame, would this option increase stiffness and/or help with racing performance, or is going with a standard alu/carbon seatpost system a better way to go? Obviously you would still need a seatpost binder at the top with a severely cut-down alu/carbon seatpost to get the saddle attached to the frame (unless you welded the seatpost binding system to the seat-tube?). Seems like it would be more weight than a traditional seatpost setup?
I ask because I am considering going with a custom steel frame from a local framebuilder and I might as well go balls to the walls with the design and an integrated seatpost would look awesome! :p
I also desire a triple-triangle setup, and with an integrated seatmast, well...it'd definately be unique. ;)
07-17-08, 02:56 PM
Integrated seat mast is mostly a marketing feature or maybe, an aero enhancement if the tube is appropriately shaped. I doubt there would be any meaningful stiffness increase, although there is sure to be someone claiming so.
Bicycles tend to be emotional purchases and if something as simple as an integrated seat mast motivates you and makes you want to ride more or harder, I can’t see anything wrong with that. I’ve seen some photos of Vanilla frames with an extended seat post so you might want to look for photos for inspiration.
doesn't that mean you can't adjust the seat height?
07-17-08, 05:44 PM
30 years a go I saw a Bruce Gordon bike (BG's personal ride, IIRC) that goes ya one better:
dunno if this is the same bike, but it is the seme concept. In case it isn't clear, there is no seatpost. The saddle clamp is part of the (extended) seat tube. Y'just have to be SURE you've got the right saddle height...
07-17-08, 10:00 PM
I would wonder whether or not it would be strong enough, depending on how extended it was. Usually when you put a seatpost in, you want to be submerged past where the top tube attaches or past the seat stays if they are lowered. Not having a seatpost at all may have a negative effect if it is not reinforced somehow but I am not experienced enough to know for sure. Maybe use a seat tube with a thicker wall or weld/braze a sleeve inside to reinforce.
doesn't that mean you can't adjust the seat height?
Well, you can always adjust it down...
I also seem to recall a steel frame with the extended seat tube in the road forum a while back, but can't seem to find it right now.
The idea was brought up that concerning raising your seat and not have the seat tube look awkward. That was if the tube had been cut too far, you could, in theory, (I know I messed up some major part of grammar there) cut the entire mast off to more standard proportions and install a traditional clamp and post.
The adjust thing is an issue because the continued tube is probably heavier being steel and larger in diameter. Strength shouldn't be an issue for that reason, but if you had to have a small adjustible post near the top it is going to add a number of parts and undermine the weight budget. The strength of the tube increases by the square of it's diameter, all else equal (which it won't be, but very nearly is), and stiffness increase by the cube of the diameter. So if you have a 28 mm steel tube vs a 27mm alloy tube, it will work fine.
One bike that has some features like this is the Bike Friday. It is part of the folding issue, but there is a long upper mast section.
Indeed, they are structurally stiffer.
However, with a round pedalling stroke, the seat between your legs is right at the end of the "lever" that it is (that keeps your bottom bracket from swaying from side to side), hence you wouldn't be gaining any actual pedalling efficiency from it. (plus the dowtube contributes immensely to keep the BB in place)
I do see a reason for carbon frame manufacturers using this setup: although I've never seen a survey or test data on this, I do suspect that carbon tubing is rather sensitive to compression! It may be good for general rigidity-to-weight ratio, but the mere nature of it's construction makes it poor at resisting strong forces squeezing it, such as a seat clamp! So it definitely has it's place in the carbon world.
However, the drawback is that the bike becomes hard to sell, because it's really made to measure for you. Also, you better make sure you get it right the first time, because contrary to a seatpost, there isn't much adjustment possible there. Once it's cut, that's it!
As the other guy said, marketing-wise it is a good way to give a blow to the pre-owned bicycle sales and increase new bike sales...
One thing though, this definitely does NOT have it's place on a custom steel frame! Do yourself a favor, kill that thought.
If you're looking for more rigidity, you'll gain infinitely more of that with a ROUND downtube and seat-tube (stay AWAY from "aero tubing, stay away from clover or triangular cross-sections, because that IS 100% marketing and 0% sanity), and possibly extra wall thickness too. If you go carbon, a frame such as a Merkx with extra material around the bottom bracket is the way to go.
If you would like a nice vintage ultra-stiff bike, I have a Cannondale for sale. I have too many bikes, just bought a recumbent, and my knees and back don't forgive me anymore for serious riding or racing. The Cannondale is equipped with the lightest components available in the 90's (no not Campy S-R, lighter than that!) but not as light as the new stuff available to the pros today.
Vanilla has one. Another disadvantage would be packing the bike since you can't lower the seat.
I can't believe cantilevers are making a comeback! They are nothing but useless dead weight!
Too bad he registered his domain name before running it through a spellchecker.
I assumed it was a real german word on conflation.
I didn't know cantis ever left, and they seem downright popular with the cross crowd, not that I know much about that kind of thing.
07-31-08, 01:08 PM
Go for it. While your at it, just get rid of the seatpost completely. Weld the part that clamps the seat directly onto the mast. I mean, its custom. Go nuts.
I've wanted to adjust my seat height when I change my shoes, or the thickness of my pants. I don't see why a custom should have less flexibility than a stock bike unless one is building some kind of hyper specific bike. However one could end up with a seat post of extremely short length, and with different cool routings for cables etc... as per some of the pics. Also as a hobbyist, I like to keep in mind different methods of eliminating expensive tools like reamers. Though in this case there are several other more practical workarounds, like buying machinists cheap models, or using sleeved tubes.
08-04-08, 03:41 AM
It's the ultimate statement in custom which I think is both insane and insanely awesome, especially in conjunction with a non-adjustable stem.
There's absolutely no advantage to either and there is some real practical PITA elements to it like getting your bike into small cars, boxes, opening it up to irreplaceable seatpost damage etc.
Not to mention the horror I feel trying to freight the things.
08-12-08, 09:42 AM
I built a steel frame with an extended seatube. I built the frame from 4130 and that was the length of the tube I had. So instead of wasting it, I left it just the way it was. I found I could mount an extra bottle cage on it and make actual use of it.
It's steel so I can alway cut it off later.
08-23-08, 03:13 PM
Unless the st/tt/ss intersection is beefed up either internally, or externally, that seat mast will break(unless it's really thick which defeats the purpose). Having a post that extends below that junction adds a ton of strength.
I think the brake cable through the st is goofy.
08-25-08, 03:28 AM
I'm guessing Sacha wouldn't blow his reputation on a design that wouldn't work. It's a pretty safe bet the Speedvagen seatmasts aren't going anywhere.
What jiggery-pokery he does to ensure that it won't is anyones' guess, but it's hardly an insurmountable task.
08-25-08, 08:39 AM
I'm sure Vanilla has it figured out, but for all the garagers out there, beware.
As for the st cable routing, who was it at the last NAHBS show that also did that? I think they got best new builder'. Whoever it was they also slotted the seat post to slide down and around the cable. Twist your post in the frame and let the fun begin.
08-25-08, 11:26 PM
A couple months ago I built this out of straight guage 4130. http://i130.photobucket.com/albums/p260/BillyGoat71/1-2.jpg
The seat post is about 3 inches long. It was a busted one I found at the bike shop. Heavy Yes I think that frame weights around 4.2 Lbs. 26.8 post or .035/.9mm wall thickness. I'm not sure why anybody would want one. It just happened that was the last of that tubing so it was either leave it or cut it off. So I left it and added a 3rd bottle mount. I routinly take in on 50 miles rides.
4130 in great stuff. So I have 2Lbs. of static weight. I have an extra 10 around my waist right now.
"Having a post that extends below that junction adds a ton of strength."
So does having an uninterupted tube. You want to see an actually stressed tube look at the mast on BFs.
08-26-08, 08:27 PM
But clover leaf sections look amazing! I'd call it 100% style rather than marketing :)
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