Question about open up geo

[tuscanyswe]

Open list 2 differnet toptube lengths on there website

1 is lokger than the other the other is called norm* and says its for comparison purpose but im not sure i understand it anyways they also list st angle so im bit confused. Im thinkinh it has something to do with the seattube beeing offset?

[prototoast]

Per their website:

Normalized dimensions to compare to frames with standard (non-zero-offset) seattubes.

I believe their stated explanation is that they intend their frames to be ridden with a zero-offset seatpost, and they compensate with a slightly slacker seat tube angle. This mechanically makes the top tube longer, though the contact points are in the same place as they would be with a person on a bike with a steeper seattube, shorter top tube, and setback seatpost.

With that said, for the math to work as they say, they are effectively comparing it to a bike with a seat tube angle steeper than what's generally found in the market. I would recommend just ignoring the "Norm*" top tube value.

[tuscanyswe]

Its very confusing tbh. Why say the frame has a sta of x and a toptube of x but then have a 2nd toptube comparison that would be accurate if the frame had a different sta? Just making it very complicated imo

They are not helping those who know little about geo while also making it hard for those that thought they knew their stuff

Cheers

[sparky33]

Originally Posted by tuscanyswe

Its very confusing tbh. Why say the frame has a sta of x and a toptube of x but then have a 2nd toptube comparison that would be accurate if the frame had a different sta? Just making it very complicated imo

They are not helping those who know little about geo while also making it hard for those that thought they knew their stuff
Cheers

It is confusing, but the explanation about seat tube angle above is on point.

I sized my UP by comparing its stack and reach figures with a bike that fit me well. The large UP is a 56 or so.

Bike Insights offers a useful geo comparison tool with a huge library of bikes
https://bikeinsights.com/

[tuscanyswe]

Originally Posted by sparky33

It is confusing, but the explanation about seat tube angle above is on point.

I sized my UP by comparing its stack and reach figures with a bike that fit me well. The large UP is a 56 or so.

Bike Insights offers a useful geo comparison tool with a huge library of bikes
https://bikeinsights.com/

Which makes no sense as they also list the xl for ppl at 188-201 cm so everone shorter should ride a 56 then i guess. Tihi
Also the sta is 73.5 degrees on this one, how is that slack? So its even more confusing. Its not like im going to compare this to most other bikes with what 74.5 stas? In that case i guess the toptube would be about 1cm shorter in comparison but if anything many other bikes will have slacker sta and then the comparison would be even more off than the other toptube measurement.

[alessandro]

Not sure which size? Want to get your hands on the new U.P. Lavender limited edition? Or just want an explanation? Email them: https://opencycle.com/contact

That's what I did a few years back, because I was concerned about stack height on the U.P. Gerard Vroomen responded. I told him I had a 2001 Cervelo Prodigy, which he appreciated--his was stolen outside of his office building. He asked me a bunch of questions, and to measure the total height of my road bike's head tube + spacers under the stem. He recommended an XL, and the fit is great. Don't know if he's still responding to customer queries, but make yours appropriately techy--I bet he bites.

[jimoots]

I think you ignore the top tube measurement entirely.

Look at the stack and reach, making sure that you can achieve your desired saddle position with respect to the bottom bracket.

Generally saddle position with respect to BB should not change between bikes, which is the key reason that stack and reach work so well.

I suspect Open list the normalised TT because so many people still eyeball a top tube length for their fit.

[Dave]

Yes, the modern way to size a bike needs stack, reach and seat tube angle to determine the saddle setback needed. My Cervelo Rouvida has a 74 degree STA on the smallest size. But 0.5 degree less than the most common 74.5 isn't enough to justify the zero setback post that came with it. Every degree is only 10-15 mm. I changed mine to a 25mm setback.

No need to consider TT length anymore.