I am looking at a new road bike. I have the stack and reach for each bike but have a question on how they will fit relative to stack and reach.

My current bike has a stack/reach of 580 / 403. The bike I am looking at has a stack/reach of 605/396. On my current bike, I am stretched a bit.

My question - since the stack is shorter on my current bike (580), does this mean my effective reach is further because the seat post will need to be extended more than on the bike I am looking at (605)? On that extra extension, the seat post is traveling away from my handlebars at an angle of 90* minus the seat post angle.

Bottom line, I believe I will be less stretched on this new bike because of the low relative stack vs. reach. Is this true?

Your situation is that you feel too stretched out on your current bike and you are questioning whether a frame with a shorter reach but a higher stack will be a better choice for you. Any answer that you get will simply be a guess. The reason is that nobody knows what is your ideal measurement. If one knows the ideal coordinates (x,y) of your handlebar height, it is possible to work backwards and determine the frame/stem coordinates that will get you there.

The higher stack frame does have a shorter reach than your current frame; however, the reach measurement is not directly comparable as the measurement occurs at a different stack height. If the lower stack frame were stretched upwards to the height of the higher frame, the current frame’s reach would shorten. I don’t recall exactly but it maybe something like for every 10mm of height, the reach shortens by 1.5mm.

While you are focussing on reach, don’t overlook stack. Getting the reach (x) to be correct but having the stack (y) wrong does not remediate your situation.

Bottom line, I believe I will be less stretched on this new bike because of the low relative stack vs. reach. Is this true?

No. Once you normalise for stack the reach is the same - as evidenced by the same stem being required to match bar reach

http://i60.tinypic.com/333bn9h.png

What the seatpost does is irrelevant as you should be working with a fixed saddle height and setback.

You could consider the size 56 to get the same stack as your current bike with a reduction in reach. Or if you have a long stem just go a bit shorter. Or fit shorter reach bars.

It sounds like you could benefit from seeing a good fitter.

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Thanks for the replies. I should have asked the question this way:

My road bike is a 58 Cervelo s1. I am thinking of upgrading to an R3 because a) I believe the ride will be better and b) I believe the geometry is a bit more relaxed.

I will have the same seat and the same stem. Is (b) true? Is the new R3 a bit more relaxed than my S1 from 2009 and by how much? The stack/reach numbers are reflected above.

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Kindly forgive me if this seems obtuse. That’s not my intent. But I used to be in IT, and we can’t communicate… :-))

Are you too stretched when on the tops, hoods, or in the drops? All 3? 2 of the 3?…

By swapping stems and bars, you can make a lot of changes before actually buying a new bike that you’ll dial in perfectly. With stem angles of 5, 6, 7, 8, 10, and 17 readily available, bars with a reach from 73 to 90 and drops from 123 to 150, it’s likely that you can find something that will put you in a more comfortable position before you buy the new bike. For the cost of a bar and stem, you’ll have a pretty good idea of what your new position should be and will likely be more confident in your new bike purchase.

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I am not stretched out that much. Bad original question. Trying to understand difference between R3 and S1 geos…

My road bike is a 58 Cervelo s1. I am thinking of upgrading to an R3 because a) I believe the ride will be better and b) I believe the geometry is a bit more relaxed.

I will have the same seat and the same stem. Is (b) true? Is the new R3 a bit more relaxed than my S1 from 2009 and by how much? The stack/reach numbers are reflected above.

a) will most likely be true

b) no. The new R3 has a steeper HTA (thus less trail) and is a lot stiffer than your S1 so will likely feel more responsive. The wheelbase is 2mm longer on the R3 but that is thanks to the 6mm longer chainstays - the front end is shorter.

What you should notice is a smoother ride, a lot more lateral stiffness, a bit more bump smoothing and probably more precise steering. But it is not more relaxed, you would have to look at another brand for that.

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Very helpful post. - thanks.

I understand what you mean by relaxed.

Go back to my original question - with the same stem and seat and the seat set at for the same rider inseam, is the distance to the bars shorter?

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If you look at the chart I posted earlier you’ll see that the saddle to bar reach is the same with the same stem length and bar drop equal.

The S1 is the same geo as the S2 and the R3 is same geo as S5.

So you will not be less stretched unless you change the stem or bar reach.

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Hi Mike,

You’ve gotten good advice so far.

To answer your question, the steering axis on the new R3 is on the same line as your S1. That means, the changes in stack and reach coordinates, simply correspond to a point a little higher on the same steering axis. Essentially, for conceptual fitting purposes, it’s as if the R3 head tube is ~25mm longer on top compared to your S1. (Not literally true - the R3 fork is 6mm longer, so the R3 head tube is 6mm shorter on the bottom, which cancels perfectly.)

So, if you change from your S1 to the R3, you’ll want a shorter stem if you want to feel less stretched out.

Cheers,

Ok, I understand. I already have a 90 stem on my 58 s1. I was thinking of just transferring the entire cockpit to the r3. Based on what you presented, the bikes will fit the same.

Thank you ST.