Help me understand bike fit numbers on a Kirk

[bob59]

Looking at picking up the Kirk in the classified. Seller is driving down from Montreal and just happens to be staying just a few minutes from Sailorboy who graciously said he would facilitate (go Navy). The stars are aligning. I ride a 54.5 TT, 16cm HT and 51cm ST - CC. Looking at the geo chart posted besides the ST being 47.5cm CT it looks workable.

1. What is throwing me is the 660.6mm measurement center of seat post to center of handle bars at a 72.5 cm seat height.

2. My bikes are all 73.0 cm seat height, but the measurement center of seat post to center of handle bar are all 640.00mm with a 100mm -6 stem. 2cm difference

3. I assume this is due to my bikes having a 73.5' - 74.0' ST angle vice the Kirk which has a 72.5' angle???

4. Seems like this bike is more of a 56.5 TT. What am I missing??


Thanks in advance.

[Louis]

There are several online bike geometry comparison/plotting tools I'd use one of those to check the details.

[donevwil]

A "Reach" measurement would help by taking STA out of the equation. Here, you'll have to gauge saddle setback. The 72.5° here vs your 73.5° - 74° is the big deal. You're likely setup on this frame, all else being equal, will necessitate the saddle being significantly further forward than shown.

Things get strange when you say you ride a 545mm eff TT, 73.5-74° STA and 100 stem for C-C of 640, while this Kirk yields a 660.6 with the same TT and stem yet a 1-1.5° slacker STA.

FYI, at 73cm saddle height, setback increases 1.8cm when going from 74° to 72.5° STA, so, one could say, 660.6mm - 18mm = 642.6mm (based on a lot of assumptions). Much closer to your desired fit, but you'd need to resolve the forward saddle - seatpost aesthetic paradox.

[bob59]

Yep, that is what I was afraid of. Hate he slammed forward saddle look.

[tv_vt]

That's not maybe as bad as you think. First, would a 0 setback post work for you? Different handlebars have different reach numbers, so that's another way to make adjustments. You could also try a 90mm stem on this frame and see how that feels. Finally, you might be surprised at what you can adapt to - I have half a dozen bikes (plus) and the saddle to handlebar measurement varies by 1.5cm between them, yet they all feel nice to me.
Good luck with your decision.

[Clean39T]

Originally Posted by Louis

There are several online bike geometry comparison/plotting tools I'd use one of those to check the details.

This is the easiest/best one for the job: https://www.bikegeocalc.com/.

[bob59]

Changing the ST angle from 72-74 increases about 2cm which confirms my measurements on my bikes.

[robt57]

I always roughly figure [within range of adjustment] each degree STA is slack the ETT is 1 CM shorter. Because my saddle setback is always the same behind BB regardless of STA. A 72 STA is sure going to have a zero setback seatpost for me.

[Kyle h]

Originally Posted by tv_vt

That's not maybe as bad as you think. First, would a 0 setback post work for you? Different handlebars have different reach numbers, so that's another way to make adjustments. You could also try a 90mm stem on this frame and see how that feels. Finally, you might be surprised at what you can adapt to - I have half a dozen bikes (plus) and the saddle to handlebar measurement varies by 1.5cm between them, yet they all feel nice to me.
Good luck with your decision.

This does not change the important numbers, which is saddle setback. If that geo is specd with a 0 offset post, the seller will have to slam their saddle fwd to maintain their saddle setback. If they can get that then all the other numbers should be fine, assuming bar and stem length is equal between bikes.

[tv_vt]

Originally Posted by Kyle h

This does not change the important numbers, which is saddle setback. If that geo is specd with a 0 offset post, the seller will have to slam their saddle fwd to maintain their saddle setback. If they can get that then all the other numbers should be fine, assuming bar and stem length is equal between bikes.

You may have misunderstood my post. I asked if a 0 setback post would work for OP. The Kirk was not specced with that post - unless I totally missed something (edit: I did). Kirk usually builds for use of normal setback seatpost, from what I've seen.

EDIT: Oops, my bad here. I just checked the build in the Classifieds and indeed, the seller is using a Thomson 0 setback post. Missed that. OK, I'll check out of this conversation.

[LouDeeter]

Center of saddle may not equate to center of seat post. Looking at some of my bikes, center of saddle is a good 2cm behind the center of the seat post. Could be how my saddle is set up and set back of the seat post, but.....

[Andy sti]

Just FYI, the seller got the bike used so it was likely not drawn with a straight post.

Why don’t you just ask the seller for the measurement with the straight post that’s on currently. Or have them put the saddle into the position that gives the measurement you want and then they can take a picture of it so you can see what it looks like.