Hello Single trackers,

I have a frame sizing question.

When considering my next hard tail frame, should i read the Effective top tube figure as my seated reach and the actual reach figure as my out of the saddle and dropped saddle reach figure. Then choose a frame that juggles both figures accordingly?

If I’m thinking correctly, then I assume I’m looking for the optimum seated reach (ETT) for long days in the saddle and hill climbing comfort, followed by as much ‘Reach’ as possible without compromising the ETT for the rough and descending action.

Can anyone clarify if my assumption is correct?

Pretty much, remember that the designer will have designed it around a stem length so your ‘seated reach’ will be in part determined by that.

Best to have a ride on the bikes you fancy, and see how the numbers stack up in real life. My old Pitch for example had remarkably similar reach/HA/stem numbers to new bikes today, but felt incredibly short when sat down pedaling. Whereas some bikes have some sort of voodoo space shifting magic going on that makes them fit.

ETT for how close to the bars you are when seated

reach for when you are sitting up.

ETT is affected by seat tube angle, reach is not

I might be mistaken but are reach figures not independent to stem lengths?

I might be mistaken but are reach figures not independent to stem lengths?

Yup, reach is the horizontal distance from the BB to where the steerer exits the headtube.

The way I see it is 2 different measurements, with the ETT length not really that interesting.

Reach (BB – headset) + stem will give you how stretched out you are, and how long a stem you want to run.
Seat position should be based on what fits you, and how far back it is set from the BB. This is independent of seat tube angles etc, and should be based on your fit to the bike.
This will give you seat to handle bar, with no bearing on ETT since your seat could be further back with a setback post, or right forward.

ETT is affected by seat tube angle, reach is not

Well, no, the three are inter-related. If you keep ETT constant and vary seat angle you change the reach. Keep the reach constant and vary the seat angle and? you change the ETT.

Stack has an effect as well: adding spacers under the stem effectively reduces reach and (to a lesser extent) ETT. So if you end up looking at a frame with the right reach but the front end is too low for you then it ends up being equivalent to a frame with the right stack but too small a reach.

Also, adjusting saddle fore/aft position is like adjusting seat angle and ETT, but has no effect on reach. With a road bike that’s determined solely by physiological parameters, but on an MTB weight distribution comes into play.

But yes, reach for standing and ETT for sitting is roughly on the money.

demo the bike first 😉 all bikes are different

Well, no, the three are inter-related. If you keep ETT constant and vary seat angle you change the reach. Keep the reach constant and vary the seat angle and? you change the ETT.

seat angle has nothing to do with reach

What Bez said is tecnhically right but an odd way of looking at it (if you keep the ETT the same but change the seat angle, you move the BB and therefore change the reach).

well not technically right at all, you are moving the BB and changing a load of other characteristics of the geo.

Doesn’t make what he said wrong. Just, a bit of an unintuitive way of thinking about it

ETT while once important, now needs relegated to the bin. It made sense when almost every bike had a seat tube and used the same angle, now though set tubes are offset, or are bent in the middle, or both.

So ETT, which is measured at headset level, no longer tells you where your saddle will be as your saddle will be many inches higher and so will differ position significantly depending on the design on your seat tube. It also doesnt cater for how the bike is designed, with steep angles on enduro bikes meaning they often arnt designed to have the saddle set in the same place as an XC bike so using ETT (which is now a false number) to set something you cant anyway makes no sense.

My brief moment of potential clarity has passed. Think I might still be vaguely correct and will try and see if it’s possible to track down a complete bike to try for size.

Well, no, the three are inter-related. If you keep ETT constant and vary seat angle you change the reach. Keep the reach constant and vary the seat angle and? you change the ETT.

The first sentence is technically correct, but the inter-relationships aren’t all the same:

ETT depends on SA and reach. If you change either then the ETT will change.

reach changes only if you fix the SA and tweak the ETT, or you fix the ETT and tweak the SA.

SA changes only if you fix the reach and tweak the ETT, or you fix the reach and tweak the ETT.

But yes, reach is a much better way to understand geo these days.

You need to look at both really as you sit down on the bike to climb

The first sentence is technically correct,

This being a technical discussion, I will read that as “correct”.