a newbie question about stack and reach

[picstloup]

I just want to know if I understand this correctly, so any help appreciated.

I've never looked at these measurements. Am looking to 'maybe' buy a new frame.

My current frame : Stack - 53.5 and Reach : 39

A frame I'm looking at buying : Stack - 56.8 and Reach : 39.5

Does this mean that the new frame front end would be higher, so maybe less back bend and less pain for me but also a bit longer, so maybe the longer reach would stretch me out more?

Is this how it works? I am looking for more comfort. I don't mind my position being a bit more 'in the wind' cause the position is slightly more upright.

Here are my current frame's more old school details. Not sure it matters.

my current frame,
55.5 top tube
73 degree head and seat angles
12.8 head tube length, with old style headset and tall nitto stem at 10cm...The bars are almost level with my saddle right now...


the new frame would be,
56 top tube
73.5 head and seat tube angles
160 head tube length with new style threadless headset, spacers, stem etc. I was thinking I could go to a shorter stem, 90 if need be, but not sure.

thanks for any help on this to help me clarify what i'm doing. My current frame was bought in 1989 or so, when I was 34. I'm now 65. Looking for comfort if I buy new. But i do like going fast sometimes for the thrill

ok, thank you thank you thank you...

[kohagen]

As you can see, the difference in stack between the two frames (56.8-53.5=3.3) is almost exactly the difference in the length of the head tubes (16.0-12.8=3.2). And the difference in reach of half a cm is the same as the difference in the top tube measurements.

But when you rotate your shoulders up, with the greater stack, you’re also rotating your shoulders back. The difference in the effect of the longer reach is going to be greater than the half cm longer reach.

You could offset the longer reach frame with bars that have a shorter reach, or with a slightly shorter stem. It might be better to get a frame with the greater stack you’re looking for, and a somewhat shorter reach than you now have. But you might not be able to find one with the exact measurements you’d like, along with all the other characteristics you’re looking for. So the new frame you’re looking at can work for you, as long as you can get your contact points in the right spot.

[picstloup]

Originally Posted by kohagen

As you can see, the difference in stack between the two frames (56.8-53.5=3.3) is almost exactly the difference in the length of the head tubes (16.0-12.8=3.2). And the difference in reach of half a cm is the same as the difference in the top tube measurements.

But when you rotate your shoulders up, with the greater stack, you’re also rotating your shoulders back. The difference in the effect of the longer reach is going to be greater than the half cm longer reach.

You could offset the longer reach frame with bars that have a shorter reach, or with a slightly shorter stem. It might be better to get a frame with the greater stack you’re looking for, and a somewhat shorter reach than you now have. But you might not be able to find one with the exact measurements you’d like, along with all the other characteristics you’re looking for. So the new frame you’re looking at can work for you, as long as you can get your contact points in the right spot.

Thanks for this kohagen. Read your response a few times so I think I've got it. Then went searching around some bike sites, measurements, to see pretty much what you described. Stack might be good/better, but then Reach doesn't really work, and vice versa.

Started looking at handlebar reach, seat post set back or zero offset, to help with reach and I think here I can make some important decisions.

My current bars seem to measure 120mm reach. I can find bars with as little as 73mm. And instead of buying a seat post with built in offset i can buy one with zero.

I remember years ago trying a short stem on a road bike while playing with position. I think it was 90, but it made the handling feel 'off' for me. A 100 stem felt better. So I think I will try to stay with that as the short side on stem length and hope to position the rest so I'm comfortable.

I think for sure I'll be playing with the help of a proper fit this time at a Specialized dealer. Now. Gotta talk to them. See how I feel about the person doing the fit. Also, with the covid 19 store closings here in France i think i might be waiting a while to do this.

thanks again
M

[Smitty2k1]

if you haven't seen it before, this site does overlay of bike geometry that I found very useful: https://bikeinsights.com/

[ANAO]

Stack and reach are important, but your fit needs to be centered around your saddle setback.

If you can't keep that in line with your current ride, it's all for naught.

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[macaroon]

Originally Posted by ANAO

Stack and reach are important, but your fit needs to be centered around your saddle setback.

If you can't keep that in line with your current ride, it's all for naught.

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Not really. Different bikes can necessitate different saddle setbacks.

[ANAO]

Originally Posted by macaroon

Not really. Different bikes can necessitate different saddle setbacks.

Assuming we're discussing replicating a position (i.e. road to road, not road to TT), can you elaborate?

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[macaroon]

Originally Posted by ANAO

Assuming we're discussing replicating a position (i.e. road to road, not road to TT), can you elaborate?

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It depends on the bike and what you're using it for doesn't it? Look at these new breed of aero bikes, manufacturers are now building them with lower front ends and steeper seat tube angles for an aero position. You'd certainly set your sportive bike up differently to how you'd set up one of those (or at least I would anyway).

[ANAO]

Originally Posted by macaroon

It depends on the bike and what you're using it for doesn't it? Look at these new breed of aero bikes, manufacturers are now building them with lower front ends and steeper seat tube angles for an aero position. You'd certainly set your sportive bike up differently to how you'd set up one of those (or at least I would anyway).

Your saddle setback? If you're trying to replicate your position?

Why?

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[robt57]

Originally Posted by macaroon

You'd certainly set your sportive bike up differently to how you'd set up one of those (or at least I would anyway).

In my minds eye, you're just in your same best road aero position rotated forward x degrees to be even more aero. So saddle set back measured on a level horizontal plane is not going to work out.

Put a smaller front wheel on your road bike and measure the saddle setback to approximate maybe? In other words rotate the rider position forward and measure the setback change for a range??

Of wait until a math wizard here posts the math or link to the math. I was sleeping during math in school...

[ANAO]

Originally Posted by robt57

In my minds eye, you're just in your same best road aero position rotated forward x degrees to be even more aero. So saddle set back measured on a level horizontal plane is not going to work out.



Put a smaller front wheel on your road bike and measure the saddle setback to approximate maybe? In other words rotate the rider position forward and measure the setback change for a range??



Of wait until a math wizard here posts the math or link to the math. I was sleeping during math in school...

First, you're going backwards. OP is looking to be more in the wind, not more aero.

But my premise is that saddle setback is a more important fit metric than stack and reach. That is the number the OP should be looking to replicate first, and only afterwards moving on to analyzing how the stack and reach differ, if at all, once adjusting for setback deviation.

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[RWL2222]

Originally Posted by Smitty2k1

if you haven't seen it before, this site does overlay of bike geometry that I found very useful: https://bikeinsights.com/

This fit site looks useful. Has anyone you know of tried it?

[Cornfed]

As I'm sure you know, the only way to know is to ride it, but I'm assuming: you're not as tall as you were at 34, you're not as flexible, and you're more about comfort than speed. If those are correct, rather than recommend specific numbers, I would go for a specific style of bike - a gravel bike seems appropriate; taller head tube, supple tires, built for comfort, still good on the road - and then just go with a brand that offers size ranges, like S, M, L. Those ranges will work for 90% of the riding population and you'll avoid the rabbit hole of fitments. Main thing is get out there and ride. Be safe and have fun!

[Smiley]

Originally Posted by ANAO

Assuming we're discussing replicating a position (i.e. road to road, not road to TT), can you elaborate?

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You have the correct answer if you are replicating a road position, if a TT position all bets are off. So same saddle same set back and you are giving the best advice.