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Old 12-12-13, 12:15 AM
  #24  
thook
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Bikes: '83 univega gran turismo x2, '85 schwinn super le tour,'89 miyata triple cross, '91 GT tequesta, '90 yokota grizzly peak, '94 GT backwoods, '95'ish scott tampico, '98 bonty privateer, '93 mongoose crossway 625, '98 parkpre ariel, 2k'ish giant fcr3

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Originally Posted by MassiveD
"Also, it would reduce the effective reach for my height and body geometry relative to my usual saddle position. Eg., I could have a TT of 54 or 55cm's that would perhaps give the same effective reach of a smaller frame with a steeper ST and a TT of perhaps 53cm's."

I can't quite make sense of this. If you tip the ST back, all else equal you increase reach. If you steepen the relative angle of the HT, you increase reach. If you are after a comfort posture (sorta a misnomer), where you are more upright, then you will probably be raising the bars, since putting the ST back will create a deeper torso angle, otherwise. Raising the bars, increases relative reach. ?

When I put the ST back to 72, it doesn't change reach because I am adjusting the post and the seat.

When you swing a 24 inch seat post back from 73 to 72 degrees, it moves back and down .4" on the horizontal, and .13" on the vertical (24" from center of BB). It isn't a ginormous change.
You probably can't quite make sense of it because I'm not always good at illustrating verbally. I am still trying to put all this together in my head. Also, I'm certainly not a frame builder, but I'm not sure agree entirely with what you've said. I don't think comfort exclusively means raising the handlebars. I already have them at saddle height as it is. I really believe my problem has been weight distribution. When I move back on the saddle end, the weight comes off of my hands a great deal. Of course, it will.

If the saddle position relative to the BB doesn't change, yet you tip the ST back while the HT angle remains a constant, the top tube is going to move backwards latitudinal thereby drawing the handlebars backwards towards the rider. I don't mean to imply while also steepening the HT angle. If I were to have a custom frame, I'm just saying I'd like to have/keep a steep'ish HT angle. Most frames that might otherwise fit me tend to have somewhere around 72* or 71*. My current frame has one of 73*, best I can tell. I used an angle finder and compared it another frame with a known geo.

Grant Peterson explained in the article I mentioned that when you change the angle even by one degree, at a certain height....I don't remember that height, either.....but, it was right about where I do have my saddle height currently...... reach has effectively changed by one cm. Is he correct? I assumed he would be since he designs frames. I guess that's what I've been going by. And, it's probably why most of his frames have a slack seat tube. Even with small ones.

Sam, the owner/designer of Singular Cycles, also explained this to me once in a conversation I had with him when I queried him on the med. size Peregrine. He said by my account of measurements, it should fit me quite well because of the difference in ST angle compared to my current frame. Particularly since it also has a 54cm TT. Problem is with 29er tires it has a SOH of 32.75 inches. Right up there in the neighborhood of too close for me, though! With riding shoes on, my PBH is only a tad over 33".

Lastly, I read somewhere (not by Mr. Peterson or Sam) that a change in HT angle wouldn't change reach much. Atleast, not compared to a change in seat tube angle. Something about the angles' point of origin starting from different horizontal planes? Man, that was a while back. I'm probably totally wrong about that.

Edit: Well, when I look up there at that frame chart, I guess I was right. They do have different points of origin.
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