Look 585

[chismog]

Originally Posted by slowpoke

Can someone check my math here?

According to Geometry Geeks, the Look 585 in a medium supposedly has a reach of 386mm: https://geometrygeeks.bike/bike/look-585-2008/

Checking the geo chart, and calculating it, I get a different reach.

585 geocharts:
https://ep1.pinkbike.org/p4pb14497764/p4pb14497764.jpg

This should just be virtual top-tube - setback from BB (B - E), right?

Calculating my own E here:

sin (90º*- STA) * A1 - we want A1 because it meets with B in the diagram
= sin (90º - 73.73º) * 530
= 0.27982901 * 530
= 148.3mm - this matches up with the E in the chart

The virtual top-tube B is 545mm.

545 - 148.3 = 396mm for reach.

This seem right? Thanks!

I didn't check your math, but I did check your variables. In the chart, there are three lengths shown for seat tube. There's a mistake in the chart!

A1 cannot be longer than A as shown in the drawing. But it is in the chart. Comparing this against my own 585, I see that in reality:

A1= Actual, center to top
A2= Actual, center to center
A= Virtual (traditional size), center to center.

So my my large is 53.5 to top, and it fits about like a 55-56.

[slowpoke]

Originally Posted by chismog

I didn't check your math, but I did check your variables. In the chart, there are three lengths shown for seat tube. There's a mistake in the chart!

A1 cannot be longer than A as shown in the drawing. But it is in the chart. Comparing this against my own 585, I see that in reality:

A1= Actual, center to top
A2= Actual, center to center
A= Virtual (traditional size), center to center.

So my my large is 53.5 to top, and it fits about like a 55-56.

Thanks Chris! Oh gosh, why didn't I even think of that! Blindly looking at the numbers without seeing if they even make sense....

Also, I realized that stack and reach are calculated at the top of the headtube, but B is based on the top tube/headtube junction. so we need to factor in K + K0 to get that.

The stack in my diagram is wrong because I'm relying on the incorrect seattube, but the reach should be.

I'll update things again in the morning with your new findings. Thanks!

[thwart]

Originally Posted by chismog

So my my large is 53.5 to top, and it fits about like a 55-56.

I’d agree. My large fits like a 56.

With a 20 mm setback post, the saddle in a slightly back position on the post and a 100 mm stem, my saddle tip to bar measurement is approximately 54 cm, FWIW.

Here’s a pic shortly after I built it up and before final bar tape application. Saddle height is 75.5 cm.