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Framebuilding Lecture in SF w/PVD

5K views 64 replies 20 participants last post by  jtmartino 
Menso said:
Every bike pictured on your site has an absolutely hilariously high rise stem. This is what we do in bike shops when people buy the wrong frame size and then come to us for help. Why do you design your bikes that way? Not only does it look whacko, but bikes set up like that handle terribly. There's a reason why every major manufacturer sets of geometry so stem are run low or negative rise. Seriously, what is your rational?
Straightest line between two points to eliminate weight and flex, instead of zigzaging upwards along a bunch of extra streerer then over with a flat stem then back up with a riser bar. Notice that he pairs the angled stem with a flat bar and no steerer spacers. If it's designed properly it handles exactly the same as a "normal" looking alternative because the grips are in the same exact place relative to the frame
 
grrrah said:
That may be his theory, but I'm gonna respectfully disagree and when going custom, prefer a longer head tube with a shorter/horizontal stem (for stiffness and aesthetics). I think we all agree about spacers.
Yep, just 'splaining. My preferences are different too
 
beaverbiker said:
a short top tube with a long stem keeps your hands far from the steering axis and over the contact patch more. a longer top tube with a short stem keeps your hands closer to the steering axis and behind the contact patch.
I see what you're saying, but I'm talking about keeping all of the geo numbers the same and only varying headtube length and stem sizing. If PVD's preference is for a longer stem/short ETT then that is a separate discussion. Besides stems at such a high angle look much longer than they effectively are in terms of reach, as the distance from the bar clamp to the steerer is the same as a shorter stem mounted higher on the steerer
 
iheartbicycles said:
What is it that you're arguing?

That PVD intentionally uses short steer tubes and high rise stems to save weight?

Is this conjecture on your part - or is this really PVD opinion?

I would never order a bike this way - it creates too small of a triangle, requiring very long seat posts. Not to mention it limits fitment. There aren't too many high rise stems on the market.

And total weight saved is not going to be much.
I certainly don't speak for PVD, but from an engineering perspective those are the obvious reasons to me. Who knows, maybe he's just pedantic about the wasted material regardless of the real-world difference.

The topic is custom bikes and I'm definitely not trying to stretch these points out to say that the same designs make sense for most bikes and especially not for production bikes. You're right that practical usefulness is not always the same as the perfectly engineered solution, but when you're doing custom and know exactly what the fit is, why not do it technically correct? PVD apparently builds his own custom stems at times to match the frame design as well, so that part isn't a problem. Also, some people prefer long seatposts for the extra flex
 
iheartbicycles said:
what may be "obvious" to you, isn't.
that's why I qualified it with "to me" and that's why I was trying to explain

iheartbicycles said:
Adjustibility?

I just had a custom frame made in December an opted for an angleset instead of a fixed head tube angle.

Many people questioned this decisino - but all things being equal - having options is always preferable.

This is the same reason I never cut my steer tube all the way down.
Adjustability is exactly why I said that "practical usefulness is not always the same as the perfectly engineered solution". It's his choice to build something with less adjustability, whether his reasons are aesthetics or engineering or even just a whim. Given that he is a custom builder himself and could build a new stem and such I don't think he is really without adjustability anyway, it would just be less practical. I wasn't trying to start an argument over what is right or better, just trying to provide insight into why someone would do what he did
 
iheartbicycles said:
but there's a guy on the turner forum making them custom for 1 1/8" headtubes (see slack 5 spot thread).
Heck yeah, I just ordered one this past weekend for the purpose of experimenting. I'd rather pay for an expensive headset now and know from personal experience what I would like in a future production or custom frame than to just guess on a much more expensive purchase. So my Inbred 29er will be 1.5deg slacker next month :cool: He's been great to deal with so far, but unfortunately his volumes haven't been working out so he had to raise the price after my order
 
Menso said:
Thanks! One of the things I've learned as I have gotten older is to think about things when people tell me I'm wrong, figure it out, and admit it if they are right.

From watching the news, it unfortunately seems to to work the other way around (age wise) these days. Political "debate" is nothing more than each side blowing their hot air on each other, so I'm glad we can have reasonable discourse on forums like this. Who woulda thunk... people being reasonable on the internet?
Wise words there. I enjoy a good debate about engineering, science, etc but I can't stand to go near politics. The problem is that, just like religious debates, no one has any way of guaranteeing or measuring the outcome of any choice; plus it's hard for people to leave emotion behind when they take most issues personally, and when you drag emotion in through the door your throw reason out the window
 
iheartbicycles said:
I think the better question is why does PVD think everyone but him and Ericsen are missing the mark?
to pedantic (it's really the spirit of this thread anyway :D ), he didn't say everyone, he said all of the one's he's actually talked to so far (not that that changes the spirit of his comment ;) )
 
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