Do you trust reach and stack ?

[bmeryman]

Another thing to add to this discussion (because it's an important discussion to have):

Stack and reach are becoming more and more commonly used in mountain bikes as well, but mountain bike geometry is changing very quickly. I've seen folks hop on a bike that's a size too small because they think reach is getting too long only to forget that seat tube angles are getting crazy steep (like 78 degrees up from 74 the previous year) and stems are shorter. Then they find themselves cramped while seated pedaling.

In short, the above advice is valid for both road and mountain! Look at the whole picture when comparing geometry.

[davidb]

Yes, seat angle will effect reach. Also look at bottom bracket drop and head tube angle. You are correct. At least stack and reach give one a starting point. Most mtn forks have same trail and offset? Right? Being more of a road fit person how big of an impact does chain stay length have on handling?

[bmeryman]

Originally Posted by davidb

Yes, seat angle will effect reach. Also look at bottom bracket drop and head tube angle. You are correct. At least stack and reach give one a starting point. Most mtn forks have same trail and offset? Right? Being more of a road fit person how big of an impact does chain stay length have on handling?

I think we're on the same page here, but the big factor to get over for a lot of people is that seat tube angle does not affect the "reach" on the geometry chart since it's a measurement from the bottom bracket to the headtube. Which is why effective top tube also has to be considered.

A lot of mtb forks have the same offset (although that's changing again) but trail will change as a function of head tube angle and other factors.

Chainstay length has a noticeable impact on handling, but it's partially up to the rider to determine which qualities they want in a frame. Ultra-short chainstays (even down around 420mm for 29er FS bikes) have been trendy and popular because they can feel more playful and nimble, but for certain riders the stability and tracking of a longer wheelbase and longer rear end is more confidence inspiring. It depends on the riding style you're going for!

And as always, tire pressure matters much more than people give it credit for, so that's an important variable to dial in.

I certainly have opinions about mountain bikes and which would be suited best to certain riders, but for the most part people tend to forget about the minutiae once they're out enjoying the trail.

[Clean39T]

In general, what I want to know is.....with my setback and desired drop, what is the saddle-tip to bar-center with a stem that works for the size of the frame (that's the "reach" that matters to me), and with those points triangulated off the BB, where am I between the wheels and from a COG standpoint.....which should tell me whether its going to handle okay and not feel too rearward or forward biased.

Stack and reach tables help a bit there, but definitely aren't foolproof.

BikeCAD is much more useful.