My very old road bike has an effective top tube of 54cm and has always felt a little big for me at 5ft4.
Looking for my first gravel bike and trying to work out the best size. I know I need to sit on a few but its not always possible. Just looking for a starting point at the moment. Manufacturs size guides seem to vary a lot from 50cm to 55cm effective top tube. Stack ranges a lot too.
How does stack affect the feel and length of a gravel bike? Other than just the obvious height of the bars.
My pinnacle arkose 2 is probably 1 size too big for me, but it works.
If I remember correctly the head tube is 170mm tall. And I can lift my seat post around 130mm out of the frame.
When riding it it feels fine. The taller head tube makes it comfortable compared to the 100mm on the mountain bike.
I think sizing down would have still given me the tall head tube and I would of benefited from a lower top tube.
I am happy with it as the price was right, it pretty much fits and I ride it more than the mtb at the moment.
In summary my next gravel bike will aim to have a similar head tube height but at least 150mm of seat post extension.
Reach can be easily adjusted by altering the stem length a little. Which I haven't done on mine. Only thing I did change was the tyres for some 40c narrower ones rather than the 45c that came with it.
Definitely sit on a couple, it's really important to have a drop-bar bike that you can comfortably ride in the drops without being too stretched or being too bent over. Definitely get the bike shop to set this up for you at the point of sale. If you're between sizes you might need a stem/bars/seatpost change to get the best fit, again, better the bike shop do this.
Also note IME gravel bike geometry is just like road and mtb geometry, a longer bike is more stable and better for longer days in the saddle, where's a shorter bike is more twitchy and more fun in the turns. On my Trek Crockett, you can slide the rear wheel forward and backwards so you can subtly alter the bike's handling.
An added complication is stem length and head angle. Bikes with head angles around 71 degrees seem to be roughly on a road stem. Those on a 69 degree head angle are designed round a shorter stem
Only ever really ridden my gravel bike so can’t answer your question. But I’m not that flexible so I’ve spent ours looking for bike that might replace it with plenty of stack
Sonder do test rides and hire bikes at Glorious Gravel events
I'd suggest finding a bike on at your local shop that fits comfortably and then comparing the geometry of that to the bikes you are interested in.
You can use geometrygeeks to compare bikes of different sizes - as you've already noticed top tube size is no longer an accurate gauge of actual size - stack and reach are more useful
Generally speaking gravel bikes will have a taller stack than a road bike, which gives a more upright position and is more comfortable off road. They'll also be a bit longer to help with stability. Headtube angles will be bit slacker and wheelbase a bit longer for stability. There's loads of variation there so you'll need to decide whether you want something that more off-road orientated (slacker headtube) or more road/touring
heres an example of how bikes of the variation - the bokeh is definitely "racey" , revolt is middle of the road, digger is more off road biased and the tripster is an old school touring/adventure type bike