RattleCAD Users Please! How Do I Change Stack and Reach Parameters??

[fca...@gmail.com]

Hi there.  I am trying to design my own 26" touring/city bike in RattleCAD and I can't seem to adjust my top tube height.  How do I manipulate parameters like Stack Height or Reach?  I've played with the base concept parameters but I can't figure out what parameters I should change to get closer to my desired Stack and Reach values.  I am using RattleCAD 3.4.02.62.  Thanks in advance!!

Fernando

[satanas]

I don't use stack/reach, so don't attempt to input them directly; I know pretty well where the contact points need to be so move other parameters around until everything looks right.

Having said that, for stack, you can adjust head tube length and/or top tube slope depending on what you're trying to achieve; these will change stack.

Re reach, I tend to figure out what the front centre needs to be, then work back from there to get a suitable top tube length/stem length/head angle/offset/trail, and saddle position/seat angle at the other end.

In rattlecad it's not always obvious which parameters are the driving ones and which are driven, and like most software rattlecad isn't well documented(!). Time and experimentation are your friends.

IMHO, it's best to start off from a "known good" fit, then use the contact points from that to fix the BB, saddle and bar centre in place; everything else can be adjusted to suit.

Stack and reach are useful for comparing frames but (IMHO) shouldn't be set in stone and used as primary inputs. YMMV.

Later,
Stephen

[satanas]

PS: Perhaps the easiest way to change reach or top tube length is to adjust the stem length, as if you've put in your fit dimensions rattlecad will hold the sum of top tube + stem length constant.

[Johan Larsson]

To change stack and reach you adjust the parameters that decide stack and reach - head tube length, top tube length, top tube offset on head tube, headset height, stem length and angle, and to some extent fork geometry. With RattleCAD you start with the contact points, not the other way around. http://rattlecad.sourceforge.net/howto.html

Johan /Sweden

[Johan Larsson]

On Tuesday, May 9, 2017 at 9:01:50 PM UTC+2, Johan Larsson wrote:

To change stack and reach you adjust the parameters that decide stack and reach - head tube length, top tube length, top tube offset on head tube, headset height, stem length and angle, and to some extent fork geometry. With RattleCAD you start with the contact points, not the other way around. http://rattlecad.sourceforge.net/howto.html

Of course, you _could_ also click the big arrow in the upper left corner, and select "Stack and Reach" mode... just noticed that... :)

[fca...@gmail.com]

Ah ha! That is it, thanks!
I am using stack and reach because most of the manufacturers post these numbers online. I was looking at different frame geometries like the Surly Long haul trucker and trying to incorporate their sizing to suit me. I really like RattleCAD, great program and it is free!! Thanks everyone!

[David Bohm]

It Is open source but Manfred who has worked hard to make it does take donations. So if you found it valuable you might think of coughing up some coin.

Dave Bohm

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[fca...@gmail.com]

Thanks for the reminder, I will certainly make a donation.