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Here's one for C-40.....(6 posts)

Here's one for C-40.....mainframe
Nov 21, 2002 7:43 AM
Hopefully to clarify once and for all the notion of seattube angle, I pose the following question: Are the degrees of STA (73, 74 or whatever) assuming the tube is "rising from horizontal" or is it assuming to be "falling from vertical"? This will also clarify the terms steeper vs. slack. I know I'm confused trying to conceptualize which way the tube is moving given "degrees of angle" change. From there, I can easily follow the movement of the seat and the implications to effective TT length and ultimately reach. Thanks in advance.
"rising from the horizontal"TJeanloz
Nov 21, 2002 8:08 AM
A 10 degree seattube would be practically horizontal, an 80+ degree seattube would be nearly vertical. 74 is more upright than 73.
slack vs. steep...C-40
Nov 21, 2002 9:42 AM
The seat tube angle uses the ground or horizontal as the reference or zero line. The greater the number the steeper the angle. 90 degrees would be as steep as you can get.

The terms slack or laid back are used for angles of 72 or less and 74 or greater are generally considered steep. 73 is about the middle of the range.

It is also assumed that the centerline of the seat tube intersects the center of the bottom bracket and act as the pivot point. Most frames are made this way, but there are exceptions..
slack vs. steep...mainframe
Nov 21, 2002 10:35 AM
A somewhat related question: How much increase in drop is added by a 120 mm stem designed with 10 degree negative rise as opposed to a stem with neutral rise (horizontal)?
slack vs. steep...B2
Nov 21, 2002 12:53 PM
I believe the difference to go from a 120mm x 80 degree stem to a 120mm x 73 degree stem would be a little more than a 1/2" increase in drop. The reach would increase by a little less than a 1/16". Hopefully I did the math right :-)

Bryan
Let's get this straightKerry
Nov 21, 2002 5:48 PM
When most people talk about a -10 degree stem, they are referring to one that rises from the horizontal at an angle of 7 degrees (or so). You seem to be describing a stem that has the bars lower than where the stem joins the steerer tube. The only time I've seen such a stem is on a time trial bike. There is not a solid convention on this, but a "-17 degree" stem is considered to be one that gives zero rise of the bars, though some would call this a zero degree stem. Stem brands that call out a negative number for a stem with no rise then would refer to a zero degree stem as one where the stem is perpendicular to the steerer and rises from the horizontal at an angle of 17 degrees. Since there is not a convention, it gets confusing. What are you saying?