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How useful is "reach" as a specification?

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lefthanded

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Discussion starter · #1 · (Edited)
Reach seems to be an important number that people use to pick the size of a bike, like someone said in a different thread recently
"reach is really the only measurement that you need to look at when buying a new bike."

But how useful is the "reach" really? It depends on where in the steering axis you measure it (the horizontal distance from the bottom bracket).
It seems this measurement can be largely misleading.

Below two bikes with the exact same geometry and handlebar position. All that is different is the length of the head tube and the length of spacers. The bikes will ride exactly the same, yet their reach is different by 19 mm. Note that the "old-fashioned" ("effective") top tube length is the same in both bikes.

So what does "reach" really tell us, and how useful is it for bike sizing, comparison and guestimations of ride characteristics?

Image

Image

(Image source: Bikegeocalc.com)
 
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#3 ·
The two bikes shown may have the same cockpit position as configured, but don't have the same range of adjustment. Bike 1 is at the bottom of it's range while bike 2 is near the top. This is much like what one does to fit a bike that's a bit too large or too small. Reach and stack are still useful specs as they give some idea of where that range will lie.
 
#4 ·
You bring up a good point. Reach is useful, if you take it with a grain of salt. Two bikes with identical reach can feel way different. Reach and stack together paint a way better picture. Even then, someone's ideal reach and stack on an XC bike with 68deg HTA will be different than their ideal reach and stack on an enduro with 63deg HTA. But it gets you ball park for size. Someone who knows they like a modern trail bike with 480mm reach can probably take any other modern trail bike with 470-490mm reach and get it dialed to how they like it, and bikes out of that range may feel too far out of whack. One thing that your example misses is that head tubes and A2C lengths don't vary that much in MTB world, like they do in road and gravel. Most trail bikes of the same size are going to have head tube lengths with +/-10mm or so of each other, so the reach itself actually is a useful measurement.

When I can't test ride a new bike, I'll use this calculator https://madscientistmtb.com/bike-geometry-compare/ to see where the steering axis and handlebar grips will actually end up.
 
Discussion starter · #7 ·
ehfour said:
I prefer looking at Top Tube length, as reach can be adjusted by stem length and seat placement
Click to expand...
"Reach" as a geometry spec can't be adjusted, it's built into the frame, welded, glued, whatever.
 
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#8 ·
Reach is a great indicator for the bike fit when standing. Top tube is better seating down.

Reach would be even better if it was given with a "standardized" reach (instead of measuring at the top of the heat tube, it would be measured at a set stack height).
 
Discussion starter · #9 ·
faul said:
Reach is a great indicator for the bike fit when standing.
Click to expand...
Reach is not at all an indicator (of how long the bike is) as shown in the graphics.


faul said:
Reach would be even better if it was given with a "standardized" reach (instead of measuring at the top of the heat tube, it would be measured at a set stack height).
Click to expand...
That would certainly take away a lot of room for misinterpretation.
Maybe it should be the bottom of the head tube, or just where the steering axis hits the height of the bottom braket.
But on the other hand, top tube length and seat tube angle describe the length of a bike pretty well.

Actually seat tube angle, head tube angle, and the "front-center" from the BB to the steering axis would describe the main frame of any bike much better (apart from its height, which doesn't play a role for its riding, add BB drop).
 
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#10 ·
lefthanded said:
Reach is not at all an indicator (of how long the bike is) as shown in the graphics
Click to expand...
There are so many variables on mountain bike type that I think that reach is reasonable proxy for size.

For example a friend of mine and I have bikes with almost identical reach. However I have 150mm and he has 115mm so I would think my wheelbase is much longer simply because that travel has to fit in somewhere.

Using seat angles in any way becomes problematic as well as they aren't always measured equally so which point do measure the angle?

Personally I feel like stem length should almost standardised, it's really only a hangover from road sizing.
 
#11 ·
Reach matters more to me when I'm setting up 2 similar bikes (XC, in my case). 2 bikes with the same TT length, but different ST angles won't fit the same. When setting up a bike, my fore/aft position over the BB will be consistent, regardless of ST angle, adjusted by the seat position. 2 bikes with the same reach will be very easy to match fit.
 
#13 ·
plummet said:
Reach = Standing cockpit, ie descending cockpit.
Effective TT = seated cockpit. ie seated pedaling cockpit.

More reach = less playful, more stability, less reach = more playfull, less stable.
Click to expand...
That's the general rule, but to play devil's advocate and to OP's point, which bike is more stable or playful, the bike in OP with 390mm reach or the bike with 409mm reach?

Here's an overlay of the two geometries. Handlebar position identical, steering axis identical, the bike will handle exactly the same, despite a 19mm difference in reach. All-in-all, reach gets you ballpark for standing fit, but there is more to it. You can't buy a bike solely on reach, gotta either trust the manufactures size chart then tune in yourself, test ride before purchase, or take in all the geo to make an informed decision.

Image
 
#14 ·
acedeuce802 said:
That's the general rule, but to play devil's advocate and to OP's point, which bike is more stable or playful, the bike in OP with 390mm reach or the bike with 409mm reach?

Here's an overlay of the two geometries. Handlebar position identical, steering axis identical, the bike will handle exactly the same, despite a 19mm difference in reach. All-in-all, reach gets you ballpark for standing fit, but there is more to it. You can't buy a bike solely on reach, gotta either trust the manufactures size chart then tune in yourself, test ride before purchase, or take in all the geo to make an informed decision.

View attachment 2105411
Click to expand...
I just realised op must be on my ignore list as the first post is actually post number two.

Note that I never said only to use reach as a metric. As I cant see op post your drawing makes little sense to me. But i do agree that shorter headtubes will have longer reach figures than longer head tubes. Thats why you figure out what is the range you like to work with.

One thing i do not do, have not done for many many years is trust the manufactures size charts. They have no clue about my preferences and riding style and simply have size range based on generic averages. I look at the geo charts and select the bike with the geo i want. That could be anything from size small to large depending on how out of wack that manucturer was with their recommendation.

For me, important number are reach, Effective TT, HTA, Chainstay length seat tube length, dropper insertion, bb drop, head tube length.
 
#16 ·
lefthanded said:
Reach seems to be an important number that people use to pick the size of a bike, like someone said in a different thread recently
"reach is really the only measurement that you need to look at when buying a new bike."

But how useful is the "reach" really? It depends on where in the steering axis you measure it (the horizontal distance from the bottom bracket).
It seems this measurement can be largely misleading.

Below two bikes with the exact same geometry and handlebar position. All that is different is the length of the head tube and the length of spacers. The bikes will ride exactly the same, yet their reach is different by 19 mm. Note that the "old-fashioned" ("effective") top tube length is the same in both bikes.

So what does "reach" really tell us, and how useful is it for bike sizing, comparison and guestimations of ride characteristics?

View attachment 2105366
View attachment 2105367
(Image source: Bikegeocalc.com)
Click to expand...
Reach doesn't "depend on where in the steering axis you measure it." It's always the horizontal (to the ground) distance between the center of the BB to the center of the top of the head tube. It's a measurement taken on the frame only. It doesn't depend on the "length of spacers" at all.
 
#18 ·
Yes, you need to look at what stack height the reach is measured at. If you know how many spacers you will be running, there are calculators which will calculate your "effective" reach (treating the top spacer as the top of the head tube.

Using this method, I have consistently been able to predict pretty accurately how my last few frames would fit. Very accurately with road/gravel bikes, pretty close with MTBs (differences in suspension can throw things off a little).
 
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#19 ·
faul said:
Reach is a great indicator for the bike fit when standing. Top tube is better seating down.

Reach would be even better if it was given with a "standardized" reach (instead of measuring at the top of the heat tube, it would be measured at a set stack height).
Click to expand...
Reach is a standardized measurement, and it is measured at the same intersection as stack height is already.

Reach is measured across the horizontal plane from BB center line to the top of the headtube centerline. Stack is the BB centerline to the headtube centerline in a vertical plane.


You're thinking of the handlebar height, often called stack but it is not. It's a fit measurement, not a Geo measurement. You can change that number by rotating a handlebar a fraction of a degree, stem, rise, sweep, etc etc all play into. It would be insane to try to standardize that.
 
#20 ·
lefthanded said:
Reach is not at all an indicator (of how long the bike is) as shown in the graphics.



That would certainly take away a lot of room for misinterpretation.
Maybe it should be the bottom of the head tube, or just where the steering axis hits the height of the bottom braket.
But on the other hand, top tube length and seat tube angle describe the length of a bike pretty well.

Actually seat tube angle, head tube angle, and the "front-center" from the BB to the steering axis would describe the main frame of any bike much better (apart from its height, which doesn't play a role for its riding, add BB drop).
Click to expand...
You are misinterpreting the diagrams you are referring to. And also the diagrams are confusing. "Reach" is purely a frame measurement. The stem and handlebars are NOT part of the reach measurement. Reach is measured from the center of the top of the headtube (not the intersection with the toptube or anyplace on the stem).
 
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