estebe

Hello,

I would need some help with a custom project of mine; i want to build a monster cross bike based on a Surly Karate Monkey frame. In the attached pic I have included a comparison chart (from bikegeo.net) with a bike I own and fits (incidentally another SUrly) yet I`m lost with what do I have to watch out for, since there are 3 different stack/reach values? Would be great if someone could look at the chart (first row data is the one that fits/ second row of data are for the project frame) and tell me if it`s doable or what do I have to change? The only other change I plan on is to run a 2 cm wider drop handlebar on the project.. Thank you

AnthonyG

The 3 sets of figures are a little bit of a red herring because you have used different stem lengths in the calculations although I will run through them.
Nominally any Stack and Reach figures that you will be quoted are frame stack and reach. This is the point where the top headset race is fitted or in this diagram, where the top tube meets the head tube.
The second figures are at the top of the spacers (vertical) and the third figures are at the top of the stem (horizontal).

The drawings though are good and if you look at the drawings you will see what's going on.
Your current frame is a smaller frame, the project frame is larger.
Answer: If you use a shorter stem and angle it down rather than up, you will be able to place the handlebars in the same place on the bigger frame.

HOWEVER, using a short stem on a large frame just to make it fit is a sign of a bad fitting frame. You can do it but why?
I wouldn't recommend it.

Meflselo

this is very useful, thank you!

estebe

Thank you for your reply.
Let me explain the situation. The first bike is designed for drop bars, the second is a rigid 29er mtb that i want to turn into a monstercross with drop bars. Hence the size/geometry differences. They both fit me but I wanted to see if I can make the larger frame fit with drop bars hence the shorter stem...

AnthonyG

Do you want to place the handlebars in the same position on both bikes or are you going to have them in different positions?

Shorts stems make the steering twitchy so they aren't recommended although they can work.

On the diagram there are 3 points (with a knee in the middle) representing the stem. First point is where the top tube meets the head-tube (this is the normal reference point for Reach and Stack). The second point is above it at the knee, the third point is at the end of the stem. The software is allowing you to provide custom values (spacer height and stem length) so that you can visually see what it takes to get the handlebars in the same place. You have deliberately (or accidentally) placed them in different positions. Nominally if you used a 10mm longer stem and angled it down rather than up the handlebars would pretty much be in the same place.

Useful program although it doesn't seem to be taking into account measurements such as how thick are the stems (in reality you have to measure from the centrelines of stems so there is no such thing as a zero height stem) and what the height of the upper headset race is above the top tube and how this differs between the frames.

Other than that your not being 100% clear in what your asking.