Guys....I'm trying to wrap my brain around this and make the right decision on sizing. Any help would be greatly appreciated.

Current ride
Colnago C50
Reach 395
Stack 546
Headtube 158


Desired bike
Which size is correct for me ?
Parlee Z5 Medium
Reach 383
Stack 545
Headtube 140

Parlee Z5 Medium Large
Reach 388
Stack 564
Headtube 158

Based on the reach and stack, it seems as though I should be riding the medium Parlee.....however, I'm confused by the sharp contrast of headtubes on the C50 at 158 and medium Parlee at 140. Can this difference be explained entirely due to the C50 having a much slacker headtube ?

Can someone explain this to me ....am I thinking correctly ?

Thanks

Do you have access to a Parlee to measure it personally or do you have to figure it out from the numbers?
Help from whoever you are getting it from? Expensive bike I would expect good service for this sort of thing.

Stack is measured from the BB to the top of the head tube vertically. If the head tube is placed lower relative to the BB, it can be long and still not stack up high.

BTW, be careful. Integrated head tubes make up shorter than conventional head tubes do. It is very complex. Fortunately spacers and stem length and angle make up for small differences.

Frames also have more or less bottom bracket drop. You need to take that into account when comparing headtube lenghts. More BB drop gives a shorter headtube for the same stack. Imo headtube lenght is not very relevant. Stack, reach and horisontal top tube lenght is where its at.

frames come with all manner of headtube lengths. it's a fundamental part of the size. however, when the size is something as vague as 'medium' or 'medium/large' all bets are off when speaking of products from different manufacturers.

Your height, inseam and arm lengths don't figure into the equation? You didn't mention them... Are we supposed to be mind readers???

These new bike frames - fugetaboutit.

When I bought my Mk V, I straddled the bike and made sure I could clear the top tube standing flat. Actually since it was special ordered I used a couple other bikes of the same geometry for sizing. When it arrived, I adjusted the height of the saddle and bars to my arm lengths, and that was that. Strange how it still fits after 39 years.

If you are going to buy by the numbers, you need all the numbers. And no geometry chart provides that nor have you given all the numbers for your current ride (think headtube angle, headset cup and spacer stack, plus handlebar and stem choice). If I were spending 'Parlee money' on a frame I would be asking them to recommend a frame size, and likely doing my own comparison with my current frame once I had all the relevent numbers to plug in.

Thanks for the input guys....
I'm 5' 11"
Weight 158
Very flexible

Guess I kind of got hung up on the stack and reach numbers attempting to think they were the most important. But i see the points about bottom bracket heights and everything else pointed out.

Unfortunately, I'm buying used so just trying to get as close as possible to my current geometry....I would actually like a bit longer stem (currently 90mm)....the consequences of attempting this is resulting in a headtube that puts my handelbar drop to a point of discomfort. I'm currently on an effective toptube of 556 but as noted, would love to go down to a 545 effective toptube for longer stem length....this results in a bike with a) shorter headtube with too many spacers under it or b) a headtube that simply looks odd (lonnng) in proportion to the rest of the bike.

Anyhow....I understand now that the stack certainly is not as useful as I had thought it to be when making these bike comparisons.

Keep in mind that the stack (top of the HT relative to the BB) is essentially the same between the two bikes so the extra length of the HT is extending downwards - not necessarily a big deal. Also keep in mind that the difference still less than 3/4".

Sounds like the bars on the Parlee Medium would be lower. If they're too low for you, and the steerer's been cut, then the only option would be to have your stem point upward.

Try it first. Measure your current bike to compare with the ones you'll go see:

- Saddle height - measured along the seat tube;
- Saddle - bb - horizontal distance;
- Saddle - bar drop;
- Saddle distance to bars and hoods (different bars have different reach).

Also, different saddles have different lengths, so you should measure from where you sit on the saddle rather than from the tip.

You need to figure out whether the frame is the right size for your measurements and whether the components can accommodate that (saddle rail lengths, seatpost offset, stem length and angle, handlebar reach and drop).

Whenever you get your bike, whichever it is, install the saddle first, set it correctly relative to the bb (height and horizontal distance), then adjust your reach to the hoods with stems/handlebars.

My question is, are the seat- and headtube angles the same? Sometimes different sizes of the same frame have different geoetry. In order to get similar ride characteristics and still get toe clearance, wheel clearance, and such, larger frames will be more upright ... wjoch could account for the larger head tube.

I am getting tired of saying this ... but I got a dollar-store drawing kit and sketched out the actual geometry of the frame w\I was looking at, so I could draw in different spacer stacks, stems, and seat posts.

If you jack up the seat on a smaller frame with a slacker angle, it moves way back, so seat to bar might be longer than on a frame with steeper head- and seat tubes. Add that taller head tube and you might be looking at a slammed short flat stem instead of spacers and a long up-angled stem to get the same bat position relative to the seat ... and the bike my handle differently and balance differently.