Getting my head round reach & stack after years of effective top tube.

I understand where the measurements are taken from.

Surely reach & toptube length have similar traits?

With reach, it doesn’t account for seat tube angle?

How do i best update my aging grey matter to the newer concepts???

Reach is going to be much more relevant to DHers for example than road riders due to time spent out of the saddle. It’s just a different way of measuring that’ll suit some riding (or styles) more than others.

It also gives a better indication of weight distribution (more reach = more front wheel load)

this explains it better than your picture from 1987

http://www.transitionbikes.com/PDF/GETDIALED_FrameGeo_Part1_ETTvsReach.pdf

Reach is going to be much more relevant to DHers for example than road riders due to time spent out of the saddle.

I’m a definate XC kinda rider, but do now own a droppa!

clicks tranny link

As the link says, you really need to consider both unless you’re going to spend almost all your time either in the saddle or off it.

It also gives a better indication of weight distribution (more reach = more front wheel load)

Other way around.

The other thing about reach is it doesn’t vary much with stack height, whilst ETT varies a lot – so a 29er with a tall stack height and slack seat angle will have a much longer ETT than a smaller wheeled bike with a steep seat angle which has the same reach.

More reach means you move the rider forward so you get more front end load.

Unless you then shorten the rear of course.

EDIT – actually I’m not 100% on this – trying to think of a theoretical bike and extending the reach, whether the rider moves forward or just straightens their arms more – suppose it depends on the starting position to some extent. Also, for out of the saddle, I’d expect the result to be more likely to move the rider’s weight forward than when sat in the saddle which I reckon means a more likely straightening of the arms, lowering of the back to compensate. Given that reach is all about out of the saddle, that kind of goes with my original point.

I find the best way to measure a bike is to look at the wheel base and the chainstay length.

If you subtract the chainstay from wheelbase it gives you a good front length – compare it to a bike you previously owned and liked and you are onto a winner IMO.

More reach means you move the rider forward so you get more front end load.

Unless you then shorten the rear of course.

EDIT – actually I’m not 100% on this – trying to think of a theoretical bike and extending the reach, whether the rider moves forward or just straightens their arms more – suppose it depends on the starting position to some extent. Also, for out of the saddle, I’d expect the result to be more likely to move the rider’s weight forward than when sat in the saddle which I reckon means a more likely straightening of the arms, lowering of the back to compensate. Given that reach is all about out of the saddle, that kind of goes with my original point.

You’ve definitely got this the wrong way around. Default weighting of a bike when standing up is basically 100% through the BB. Thus the weight distribution between the wheels is the inverse of front-centre/wheelbase for the front, and chainstay/wheelbase for the rear.

Front centre measurement = reach + fork offset + ((fork a-c length + headtube length)x sine head angle)

I’m struggling with this, from the point of view that up till now my previous bikes have been large but with 70/80mm stems and set back seatposts..
New frame manufacturer suggests a 50mm stem and obviously droppers don’t come with setback options.. so do I go up a size?
..But then I’ve ridden/tested other ‘large’ frames with simliar reach/ETT & short stems and they have felt fine.

Very confused

(my current bike is a medium.. don’t ask)

Default weighting of a bike when standing up is basically 100% through the BB

“Through the BB” doesn’t mean anything unless the rider’s CoG is directly over the BB which I don’t reckon it is – otherwise you’d never have any weight on your hands which you definitely do…

So given that riders do have weight on their hands (when standing), the CoG must be forward of the BB. And the more you extend the reach, the more weight they’ll have on their hands, so the CoG is moving forward.

“Through the BB” doesn’t mean anything unless the rider’s CoG is directly over the BB which I don’t reckon it is – otherwise you’d never have any weight on your hands which you definitely do…

So given that riders do have weight on their hands (when standing), the CoG must be forward of the BB.

If your body is in the correct position you should have almost no weight on the bars except when you choose to load them.

But your body position will be determined by reach to some degree at least – take it to the extreme and make the reach longer by a foot for example and you’ll have more weight on your hands/less on the pedals.

FWIW, I’m not sure that there is a fixed ‘correct position’ is there? Some riding styles or setups may work better with more weight forward than others for example

And if your correct position is right, then you’d agree that by extending reach beyond that correct position will add weight to your hands so it will move the weight distribution forward.

And if your correct position is right, then you’d agree that by extending reach beyond that correct position will add weight to your hands so it will move the weight distribution forward.

Generally increased reach results in a lower stance on the bike, so torso becomes flatter as hips shift further back to balance shoulders coming down and forwards. Lower is better, hence the shift towards bikes with longer reach.

If your bike is so long that you’re tipping forwards to reach the bars and thus leaning on them at all times then I don’t see the bike riding very well! Watch any DH race footage and you’ll see what I mean.

I agree with that theory but I wonder if in the real world that’s actually how it works. Especially with middle aged chuffers with guts, dressed up as storm troopers who aren’t world class DHers 🙂

hence the shift towards bikes with longer reach.

Oh so we have come full circle have we ? 😆

Whats wrong with sitting on a bike and riding it, thats how I find out if a bike is right for me.

I’m struggling with this, from the point of view that up till now my previous bikes have been large but with 70/80mm stems and set back seatposts..
New frame manufacturer suggests a 50mm stem and obviously droppers don’t come with setback options.. so do I go up a size?

Simple answer
Large is a word not a measurement, 2 manufacturers can’t agree what large is so don’t expect it to be constant.
You can do the maths or sit on the bike, it’s the only 2 ways to size it.

Whats wrong with sitting on a bike and riding it

I’ve never been able to get a bike in my size to test ride. I always go by the numbers. I’m definitely not the only one and in these days of online sales, it makes sense to understand what the number mean (or may mean 🙂 )

Default weighting of a bike when standing up is basically 100% through the BB

seriously? I don’t think you should go around telling people that.

OP – I have two bikes, one has too short a reach for my height and the other is OK. When I ride out of the saddle on the one that is too short, in a good riding posture with elbows bent etc, my weight is too far back on the bike because of the short reach, to bring it forward to get good weight on the front wheel and less over the back wheel, I have to really make an effort. On the bike with longer reach, I have a good posture and a good amount of weight on the front wheel without having to try. It seems like there is a trend for longer reach these days, like those new Transitions.

Mike, I canne sit on a pre-order… & need to pre-order the correct size..
Maths suggest I need an XL, previous bikes & one’s I’ve demo’d lately are all Large and have tended to have the same/similar ETT/reach

seriously? I don’t think you should go around telling people that.

It’s not just me, it’s every skills coach out there! Google it. Heavy feet, light hands, etc etc.

There’s often a big difference between the right way to think about things (eg coaching) and the actual reality… Feeling that your weight is all over the BB isn’t the same as that actually being the case. If we’re going to base bike design on the way we think things should be, we’d have some funny feeling bikes I reckon.

BRANT, BRANT, BRANT!

This strikes me as the kind of thing he’d understand from both the theoretical and actual POV because I reckon they’re quite different for most mere-mortals.

FunkyDunc – Member
hence the shift towards bikes with longer reach.
Oh so we have come full circle have we ?

Whats wrong with sitting on a bike and riding it, thats how I find out if a bike is right for me.

Me to 😆
I placed my old Kona beside my new bike(RM) to check whether I needed med or large, large it was. Being 6ft both were “my size” but the med felt small as did the Whyte bike I tried.

z1ppy – Member
Mike, I canne sit on a pre-order… & need to pre-order the correct size..
Maths suggest I need an XL, previous bikes & one’s I’ve demo’d lately are all Large and have tended to have the same/similar ETT/reach

Wish I had the kind of money this may be costing but even then I’d struggle to take the risk, there are enough good bikes out there without doing so.

Good luck….

There’s often a big difference between the right way to think about things (eg coaching) and the actual reality… Feeling that your weight is all over the BB isn’t the same as that actually being the case. If we’re going to base bike design on the way we think things should be, we’d have some funny feeling bikes I reckon.

When I’m balanced in the attack position I can completely unweight the bars without my body moving. There are plenty of times when you load the inside hand heavily in a turn but that’s transient. Watch a slo-mo of a good rider hitting a turn and you’ll see the turn being initiated by a combination of lateral hip shift (weighting the outside foot), weighting the inside hand and counter-steering. As the bike reaches the apex the weight focuses through the feet to get that pump to the exit.

how long are you zippy? I’m just under 6’5″ and have always had large frames as I have short legs and just don’t like big bikes, however I recently got an XL frame and it has opened my eyes. I’m hopefully getting an XL transition smuggler, which has really long reach.

It’s not just me, it’s every skills coach out there! Google it. Heavy feet, light hands, etc etc.

I don’t think a good coach is going to tell you to put 0% weight through the bars when riding out the saddle.

6’2″ and alway ridden large & been happy as hell, never even sat on an XL. Current bike 600 ETT (which turns out to be different from the geo chart), a 20mm set back seat & a 70mm stem all add up to suggesting a large 620mmETT and 50mm stem ‘shouldn’t’ be right.
Several demo’s of bikes with 620ish ETT and 50mm stem feel fine, so tried a 50mm on my current bike and it’s horrible, I’m pushing myself off the back of the seat.

Trekster.. a small guilt free cash injection, but yes it is a huge fricken risk. I’ve tried the bargain option, and didn’t like it.. tried a more expensive option and still didn’t like it, this is only a little more expensive again to that just no option to even sit on one.

I don’t think a good coach is going to tell you to put 0% weight through the bars when riding out the saddle.

“I don’t think” doesn’t count. Do some research and you’ll find you’re wrong.

Nemesis and CGG re reach and weighting – I’d say you’re both right, sort of : )

Default weighting of a bike when standing up is basically 100% through the BB

This isn’t quite correct as a rule, but

When I’m balanced in the attack position I can completely unweight the bars without my body moving.

– for you at that point it’ll be true if your weight is almost entirely on your feet.
Reach and Stack vs ETT + SA, knowing both will give you more of an idea of how a bike may be than either in isolation, but applying numbers from an old bike or preconceptions to a new one won’t get you that far. A fit that works on one bike isn’t optimum for another with different geometry, the 2 have to work together.

Reach and Stack vs ETT + SA, knowing both will give you more of an idea of how a bike may be than either in isolation, but applying numbers from an old bike or preconceptions to a new one won’t get you that far. A fit that works on one bike isn’t optimum for another with different geometry, the 2 have to work together.

That’s what I wanted to say. Except I couldn’t put it quite so eloquently.

There’s often a big difference between the right way to think about things (eg coaching) and the actual reality… Feeling that your weight is all over the BB isn’t the same as that actually being the case. If we’re going to base bike design on the way we think things should be, we’d have some funny feeling bikes I reckon.

That’s basically an argument to pursue the lowest common denominator~

It’s almost as if you’re asking designers to engineer in traits that encourage bad habits.

😀

If you’re doing things right, the vast majority of your weight should be through the BB… that said, if you can hit a gnarly trail with this kind of position, I salute you (though you’d have to post a video to prove it):

Even when you have mad long Top Tubes, most weight will be going through the BB, unless you are intentionally goon riding:

A shorter top tube/shorter reach will however focus more weight on the front wheel:

This isn’t entirely relevant, but I’m including it for the hell of it:

You’ve definitely got this the wrong way around

Hmm, if your reach is under a foot you’ll be stood almost upright on the pedals, if your reach is >4foot you’ll be reet stretched with a lot of weight on your hands and even less able to unweight the front if you need to while going down hills.

How minor variations on a sensible sized reach work I’m not so sure but the general more reach = more weight on front wheel sounds fairly accurate to me.

And that’s why I’m interested as to whether someone like Brant actually has better info or insight into what actually happens rather than some idea of what it should feel like.

I have to say that looking at some google images of riders side on (mainly DH or at least out of the saddle (OOS) since we’re talking about reach) suggests to me that CoG is forward of the BB and there is weight on the hands but that’s far from scientific.

You have to remember that the weight is transferred to the front wheel via the axle~ with a longer reach, the majority of your weight is further behind the front axle.

Your core muscles are supporting your upper body, not your arms (unless you’re doing it wrong)

With your arms stretched out in front of you, try crouching until your hands touch the floor… you can pull some pretty funky shapes without any weight on your hands

with a longer reach, the majority of your weight is further behind the front axle.

Only if your body or at least, the majority of your mass remains static in relation to the rest of the bike as you extend the reach. I’m questioning if that’s what happens in the real world.

Even when you have mad long Top Tubes, most weight will be going through the BB

If that were the case no-one would ever complain of sore wrists or shoulders. It’s only all going through the pedals when, while stood up, you can take your hands off the bar an inch or so and remain in that position without anything more than side-balance support from the saddle. Not many mtbs have that sort of position, mainly DH bikes.

Jive dunno how true your argument is but you’re examples aren’t working (for me anyway) on your picture post there’s only 1 pedal cycle there and he’s riding it like a gimp.
To use your latest idea, crouch down with your hand on the floor just infront of your feet, you can rest them there without any effort, now move your hands 1-2 meters away from your feet, how much weight are you placing on your hands now? The longer the distance the more weight on your hands.

Bikes are more complex but reach on it’s own seems to move your weight forward not back.

OK, referring back to this:

Even though the 2nd guys hands are in front of the front axle, the bike will be more stable because more of his weight is lower down, behind the front axle.

That will be much of the reason the bars are placed where they are, to get more weight back onto the front wheel for traction

This is a similar concept to the switch to 27.5: in addition to improved rolling, one of the major advantages is the BB is lower in relation to the wheel axles, giving more inherent stability.

Sore wrists and the like are usually down to poor positioning of controls (or poor technique)

There will be some weight going through your arms, but is should be minimal by comparison.

Sore wrists and the like are usually down to poor positioning of controls (or poor technique)

Sometimes yes, or because some bikes simply have positioning that means more weight is more on the hands.