Framebuilders - Head Tube / Stem strength question
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03-30-11, 03:59 PM
Hello - I'm a new framebuilder and have a headtube question!
I have a 250lb client who rides a lot and uses a front rack to carry up to 50lbs. I'll be building a steel lugged frame and front rack. He wants 1" headtube to use with a quill stem. Because of the geometry of the frame, and client's desire to easily change riding position, this (NITTO) quill stem may extend upward quite a bit, say 90mm, but never past the limit. It'll probably be a 110mm reach stem. I am concerned about the flex in the stem (and possibly with the 1" HT).
Anyone have comments regarding if this may be too flexy? If so, any suggestions to remedy would be greatly appreciated!
I've probably ridden that combination, possibly not with the extension involved. I would probably try to get him to go for a threadless and in the larger diameter, but I suppose that is a conversation that has already been had. As far the the threadless is concerned, even such lugs icons as Richard Sachs use them.
They don't adjust as easily as the quill stem you are speaking of, but normally the stem gets left in one position after a while. If that is going to happen here, then it may as well be decided before the custom build is undertaken, and built out as needed.
Another option is to allow the head tube to project above the lug, and sleeve that extension, then you get a higher take off point for your quill, and it will be solid. You maintain the possibility of adjusting the stem and yet it is supported above the normal position. That would work so long as the adjustment isn't going to be the full 4 inches, which would seem to me to be a little odd.
If the customer needs that much rise it doesn't sound like he's going to be in a position to put a lot of weight on the bars, so you probably won't have any trouble using a 1" steerer. The trick will be to get the front end geo correct so the bike handles well with 50lbs of crap. As the bars go up the rider weight moves farther back and the handlebars move farther back from the center of the front hub.
Will the 50lbs load make up for the rearward rider position? Possibly. Do you go with rando trail (3-4.5cm) or something more neutral (5-6cm)? This is when being a newbie custom builder can be a challenge.
Or you can do what I do and just tell him to drop the weight and assume the position. :)
Actually I am slightly serious. Back when I used to make golfclubs, I was always loath to make some kind of kluge, particularly for the still physically able player who could just take that whack-a-mole swing to the range and get some help for it, rather than have me make him some drastic compensation in the clubs themselves. But if a person is physically disabled it is a different thing. Partly because if they are able, then they will likely be doing something different soon enough, and the whole set will be useless to them. Not to say there is anything wrong with your client...
03-30-11, 10:46 PM
Thanks Folks! I am glad to not hear a barrage of comments towards the like, "1-inch??!?!?! whaddaya crazy". And I do like the idea of increasing the lug/HT length above the TT. I think I know what direction to take.
1" is fine, there are those who say the 1.125 was not required, and even if it is, I think it mostly provides a larger bearing surface, and proportionality for larger frame tubes. Seatposts take a greater loading and are in a similar size range with far greater extension.
03-31-11, 06:13 PM
Droppin' Knowledge like the Professor!
I am the Cliff Claven of frames for sure!
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