Hello.

It is my understanding that stack and reach are the most important measurements when considering bike fit. With this in mind, I have the following question regarding potential bikes, and which one might best relate to the fit of my current bike (Lynskey).

The chart below shows Stack and Reach measurements for my current bike, as well as those for three other bikes. Two of those bikes, SystemSix and Foil are listed in size 51/52 and 54. The third, Cervelo, is only listed in size 54.



So when I look at the chart, would I be correct in thinking that the bike who would best match in fit is the Cervelo S Series?
Also, is there one of those two measurements which correlates better in order to obtain a similar fit? It seems that the SystemSix and Foil become quite longer in reach as the stack approximates that of the Helix....so in those cases, which would be of higher importance in getting as close as possible.

Thank you for any feedback with this.

You are correct - that Cervelo with the same stem/ setback/ bars will fit identically within 2mm of your current. You'd be hard-pressed to tell the difference.

Now, they may handle differently because of tube angles, fork offset, etc, but your contact points will be located in the same spots.

The SystemSix and the Foil are both old-fashioned long and low, which works well for some people (like me) and less well for others (apparently you). The shorter and taller fit has gotten more popular of late. This is why it's important to not fall in love with a bike before checking the geometry.

Use bikegeo.net.

Stack and reach are good starting points, but if one has a very steep seattube and one has a very slack seattube, that can change your fit and position.

Reach can only be compared accurately at the same stack height. To correct the reach for a stack height difference, assume that spacers will be used on the frames with lower stack heights and subtract 3mm from the reach for each 10mm of stack height difference.

That is the whole point of stack and reach. It is not affected by frame angles.

But they affect how your body interacts with those numbers. Different seat tube angles will put your body in different places in relation to the crank, and you may not be able to make up for that with saddle setback.

For instance, the reach on my two bikes are exactly the same, and the seat tube angle differs by only 0.5°
Yet, I have to have the seat slammed all the way forwards on one, and all the way backwards on the other (both 25mm offset posts), in order to give me the same fit. Same can be true with HT angle, only less drastically due to the short distance.

The whole point of a bike fit and its dimensions are based around the BB centre. The same as stack and reach numbers.
How the frame geometry allows you to achieve that fit within normal parameters of stem lengths, spacers, and saddle position on the post is why stack and reach numbers are the best for comparison.
The only down side is how stack affects reach numbers which has been pointed out in a previous post and easily compensated for by a simple calculation.

This assumes you are willing and able to, if need be, exchange the seat, seatpost, stem, crank and/or bar. Else, there is no guarantee two bikes with identical og very similar stack and reach will fit the same. All of them affect the final fit.

This basic premise is often neglected, sadly.

Are you using different saddles on different bikes or you have fairly short saddle rails? Half a degree in seat tube angle equates to roughly 5 mm difference in setback, not that much.

Not disagreeing with you in any way, to be clear. I also pay a lot of attention to seat tube angle when checking a new bike because even half a degree can be a lot depending on which saddle I intend to use and what seat post options there are available for the frame. Still, going from slammed backwards all the way to slammed forwards seems unusual for such a small difference in angle, so I'm just wondering on the details of your two setups.

You are quite correct in that the Cervelo is the closest match to the Lynskey you already have. However, the other two bikes are definitely close enough that they might fit fine with some extra spacers and/or a different stem, depending on what your current setup is exactly. I possible, I think all the bikes proposed warrant test rides if possible, since in the end it's not just about how the bike fits on paper. Otherwise, the Cervelo is the safest choice, but some more details on your current setup would help us advise on how plausible the other two models would be for you.

The saddle is the same (Airone Evo) on both bikes. The adjustment range on it isn't the largest, so it's not as extreme as it wounds. But the difference between the two is larger than I was anticipating, as well. I was expecting it to be in the 5-10mm range, and it ended up being about 20mm

That doesn't sound right; your saddle would have to be over 2 metres high for 0.5 degrees to make that much of a difference. I would guess there are some other factors at play as well.