Stack and Reach Question

[fourflys]

So I've been looking at the OBED gravel bikes and my question is the following:
would a tad taller stack and longer reach roughly feel similar to a tad shorter stack and shorter reach? I do know STA plays a role as well, so I'll include that also in addition to BB drop (just in case).

Numbers are as follows:
GVR: Stack- 570mm, reach 380mm, STA 74*, BB Drop 71mm
Boundary- Stack 568mm, reach 376mm, STA 73*, BB drop 67mm

Just curious how different the geometry gurus think these two bikes will fit or feel different?

For reference: https://obedbikes.com/

[fredd]

Assuming you have the saddle in the same place in relation to the BB on both bikes, I doubt you'd be able to tell the difference stack wise, but you may feel a bit of a difference on the reach.

[Mark McM]

These two bikes are fairly close in "cockpit" dimensions, that they likely feel very similar. A 2mm difference in handlebar height is barely noticeable, and the differences in reach are less than typical increment in stem length, so the total "cockpit" lengths are within the limits of being able to adjust anyway.

Ultimately, there may be some other factors that make the bikes feel and ride differently (such as different forks, different trail dimensions, and differences in overall frame stiffness), but the differences in the frame fit dimensions will probably not be a significant part of differences in feel.

[cuda]

here is a frame comparison online application that will allow you to overlay bike with different geometries for comparison.
https://bikeinsights.com/

Between the 2 frames mentioned I don't think the average person is going to notice something less that 5mm and that too might be imperceptible. Plus the differences are so minuscule that spacers, bar reach and stem length will get you to your optimal fit.
imo base your decision on the seat tube angle and bb drop or better still if possible test ride.

[prototoast]

1) get the GVR
2) generally for the same size rider, between two bikes, if stack goes up, you'd want reach to go down, and vice versa. A rider sitting upright would want a high stack and sort reach. As the rider bends forward more, the stack would go down, but the reach would increase
3) you can adjust for any differences in fit between those two bikes with stem choice--many people prefer longer reach/shorter stem for gravel because it increases the wheelbase and reduces toe overlap
4) get the GVR

[fourflys]

Originally Posted by prototoast

1) get the GVR
2) generally for the same size rider, between two bikes, if stack goes up, you'd want reach to go down, and vice versa. A rider sitting upright would want a high stack and sort reach. As the rider bends forward more, the stack would go down, but the reach would increase
3) you can adjust for any differences in fit between those two bikes with stem choice--many people prefer longer reach/shorter stem for gravel because it increases the wheelbase and reduces toe overlap
4) get the GVR

so... get the GVR?

[dddd]

The good thing about using modern "stack and reach" dimensions is that you can all but ignore the seat tube angle, since you aren't now looking at the measured virtual top tube length (and the saddle will end up being adjusted to the same position relative to the bottom bracket).

The seat tube angle (if even provided) will still be useful for deciding what offset that your seatpost needs to have.

The downside of using stack and reach is that unless you are comparing frames having similar stack, the reach measurement isn't really wanting to be the same between the two frames because the headtube angle isn't 90-degrees.
So assuming that you would adjust both frames with the same handlebar height, the frame with the shorter stack but the same reach will actually position the handlebar more rearward relative to the bottom bracket.

So to compare the reach of frames having a different stack height, multiply the stack difference by 0.3 and then subtract that amount from the frame having the shorter stack height (or add that to the frame having the taller stack height).

[AJosiahK]

thus far this thread has been incredibly useful. Ive learned a significant amount surrounding fit and geo but sort of lacking the context around stack etc. Its just something I never grasped wholly until now.

Posting to just thank you all for the input, and for that website. Love me some visual comparisons

cheers!

[Dave]

Seat tube angle does not affect your choice of stack and reach. I pick stack first and know exactly what combination of headset top cover and spacers I need to get a desired total stack, then look at reach. Most stems only come in 10mm increments, so reach to the bars can't be altered in fine increments, unless saddle position relative to the BB is altered.

Reach can only be compared at one stack height. To compare different stacks, assume spacers are used on a smaller frame and subtract 3mm from the reach for each 10mm of stack height difference.

Don't forget the effect of stem angle on bar height. A -6 stem will raise the bars by 15-20mm, compared to a -17.