# Framebuilders - Geometry conundrum

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

View Full Version : Geometry conundrum

Hida Yanra
09-26-11, 10:34 PM
Hey all, I've never posted on this subforum before, but I'm pretty active over in the racing section.
I'm working towards getting a custom bike in the next year or two, and as I've talked with my frame-builder-to-be, we've talked about a few geometry things that have me thinking.

I'm trying to understand the similarities/handling between different bikes I've ridden, or currently own, and thus I’ve been modeling some bikes in BikeCad (online) for comparison.

Having now hit my head against a wall, firmly & repeatedly, I’m open to explanations from anyone here who can help me out.

The current bike I’m modeling is a Cervelo S1 (my current bike)
The geometry per Cervelo is a given, but it won’t pencil out for me in BikeCad.
If the ST, TT, HT, Front-Center, STA, & HTA are all adjusted to their given values, the Stack & Reach are both off (8mm long & 3mm short, respectively)

One thing that still confuses me, the way the BB looks offset on the bike... but from what I read, Cervelo claims that it isn’t offset at all, and it’s placement is a way to keep the STA consistent through the whole series run?

All measurements are in the notes (icon at the top of the screen that looks like a notepad)

unterhausen
09-26-11, 10:39 PM
don't think we can see it. 3mm is pretty close to measurement error. The 8mm could easily be them measuring differently, or a variation in headset dimensions

Hida Yanra
09-27-11, 07:31 AM
it does take a while of sitting on the bikecad screen for the applet to load for me... but there may be something in the permissions set incorectly.

Thanks - I'm new enough at this to not know when close is "close enough" - that is helpful

09-30-11, 06:25 PM
If you're not going to build the frame, a BikeCad model is mainly to visualize differences between different bike designs or to explore design options that you could make to you your builder. But on a computer screen, it's hard to see the effect of small differences in frame geo.

unterhausen
09-30-11, 07:38 PM
it does take a while of sitting on the bikecad screen for the applet to load for me... but there may be something in the permissions set incorectly.

It gives me an error about saving my design. You might want to ask Brent on his forums. I don't know if you can save the design and post it somewhere, I can look at it in bikeCad

Hida Yanra
10-03-11, 05:36 PM
It gives me an error about saving my design. You might want to ask Brent on his forums. I don't know if you can save the design and post it somewhere, I can look at it in bikeCad

I'll give this a try this evening. Thanks again to all for the input.

Hida Yanra
10-03-11, 06:58 PM
221289
and 221290

the geometry should be showing the critical dimensions, and the frame values chart is also here, ... does that help?