stack and reach,,,, frame sizing

Home Forum Bike Forum stack and reach,,,, frame sizing

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  • stack and reach,,,, frame sizing
  • ade ward
    Member

    i see that this is catching on with companies even ragley publishes these numbers,,

    a good explaination here

    stack and reach

    i like it ,,

    ooOOoo
    Member

    Nice one, I will ummm… read it all at some point πŸ™‚

    Maybe after they standardize this, they can move on to metricising the whole **** ing industry too! I never understand this:

    Forks – " or mm, dependent on mood
    Headtubes – "
    Seatposts – mm
    Handlebars – mm
    Cranks – mm
    Frame size – "
    Wheeels – "
    Rotors – mm
    Hub width – mm

    It's those darn yanks ain't it

    ade ward
    Member

    it'a pain when trying to compare frames that half in imperial and half metric,,

    but at least with stack and reach you are comparing apples with apples and not some fictional top tube floating in space

    GW
    Member

    No thanks! – it's still a stupid stiffback roadie measurement!

    downtube measurement would be far more useful for a bike you stand up to control properly (obviously, along with the other important measurements ie. BB height, head angle and chain stay length).

    ade ward
    Member

    I think you could almost have the same downtube measurment on an old style long xc bike as a dh bike same length different angle but very different bike,

    Premier Icon guitarhero
    Subscriber

    Given these two measurements you could work out downtube length.

    ade ward
    Member

    just done some quick numbers on a DH bike and a 29er I am working on

    downtube length dh 721.4 29er 711.35

    dh stack 594 reach 404
    29er stack 566 reach 412

    GW
    Member

    guitarhero – no you couldn't
    you'd need stack, reach and also head angle and headtube length to work out the downtube length.

    Ade – you've missed my point, I said along with – Chainstay length, BB height and headangle, Downtube length would tell me a lot more about how a bike would ride/feel.

    jonb
    Member

    What you really need is a very simple tool that let's you put in as many measurements as you have and then overlays different frames. Haven't found anything. I found Bikecad to be too complicated.

    It worked for me when choosing a new frame but it's laborious if you have to compare everything in excel rather than simple drawings.

    Not sure about stack and reach, there's more to it than that surely?

    ade ward
    Member

    I dont see it as a replacment to quoting the headangle, chainstay length but i think it gives a better idea to sizing and comparing bikes than the virtual top tube measurments or small medium and large

    I also made a spread sheet to compare bikes , but as they are measured in a number of non std ways it's difficult to compare without drawing them and overlaying as jonb suggests,, i think that would be a great product

    james-o
    Member

    reach and stack works well on rigid / road bikes – look at the cervelo site for more, they have promoted it for many years now – but if front centres are limited by toe overlap regs (CEN) then the seat angle / top tube variations that cervelo say are wrong actually come into their own. it depends on what kind of bike you're working on – a cervelo 51cm has a really short FC, one that wouldn't work on say, a cross style bike.
    on an MTB, reach and stack varies massively with fork travel so you'll need to know the R+S at a set frok length, or how it varies with fork length, to make a comparison between different bikes.

    ade ward
    Member

    ragley quote them with fork travel fully topped out

    Ragley says

    It’s the new way, apparently. Makes sense!

    See more here – http://www.sicklines.com/2008/12/18/reach-and-stack-a-good-idea/

    Centre of the BB to the top of the head tube – horizontal and vertical = reach and stack.

    You need a plumb bob.

    Here’s what numbers come out, unsagged on a Ragley mmmbop, Ti or Blue Pig.

    UPDATED ::(I got a new version of the very ace BIKECAD which gave more accurate dimensions).

    16in – 23in top tube, 73deg seat angle.
    reach = 390mm, stack = 576mm (140mm fork)
    reach = 378mm, stack = 584mm (160mm fork)

    18in – 23.5in top tube, 73.5deg seat angle.
    reach = 408mm, stack = 576mm (140mm fork)
    reach = 396mm, stack = 584mm (160mm fork)

    20in – 24in top tube, 74deg seat angle
    reach = 424mm, stack = 581mm (140mm fork)
    reach = 413mm, stack = 589mm (160mm fork).

    glenp
    Member

    The basic premise, which is that seat tube length is totally irrelevant (because, guess what, the saddle goes up and down) is what we should have had 20 years ago. Eff top tube length tells you so much more.

    Clearly you can fill the picture out with more info on front centre, head tube and all the rest of it – but you get a bloody long way down the list of useful measurements before you need to know the one measurement that manufacturers currently lead with.

    brant
    Member

    I guess it depends how you're measuring downtube. I'm loathe to agree with anything mbr come up with (joke), but I can see some degree of sense if you're measuring centre of BB to base of head tube. Is that where their "downtube length" is measured?

    Premier Icon DoctorRad
    Subscriber

    The position of the seat is highly relevant if you sit down lots. Thus, this only really works for particular kinds of bikes.

    Personally, as someone who does sit down lots, I want to see a virtual / horizontal top tube measurement. I spent years in the early 90s riding a bike which was about an inch too long for me and them wondering why I had a bad back after every ride…

    brant
    Member

    If you sit down lots, you're doing it wrong.

    Premier Icon DoctorRad
    Subscriber

    Depends entirely on the length and terrain of your ride. I'm always going to spend a lot more time – not, necessarily, having a lot more fun – on the flat or climbing, neither of which I ride much of out of the saddle.

    Even if I do go by reach / stack to determine the 'funtime' dimensions of the cockpit, I'm still going to want a virtual top tube length to make sure I'm going to be comfortable for the majority of the ride… not to mention afterwards.

    Premier Icon scaredypants
    Subscriber

    why would you measure it with a topped-out fork ? – especially if it's intended to illustrate how the bike works when you stand up

    b r
    Member

    But luckily bikes aren't uniformly sized, otherwise they'd probably never fit the oddballs amongst us…

    I find that I need a large-ish frame, a lot of seatpost, a good stack of washers under the stem and a high-riser bar. Why, 'cos I've a 34"/86cm inside leg, long arms, wide shoulders but a shortish body.

    Every bike I'd bought, tried, demo'ed etc ended up with my arse in the air – so I took the view that I needed to accept my long legs, and then build the bike around them.

    Consequently I've settled on a 20" 456 (thanks Brant), a long seatpost, an uncut steerer on my 120mm forks (or 36's), a pair of high-rise Sunline V2's and long crank arms. This feels good, and well controlled plus climbs well – others though reckon it feels like they are sailing…

    STATO
    Member

    Right, i dont live halfway up a mountain, therefore 90% of my riding time is spent on the flat (unless im riding my DH bike, but they shouldnt be included in this discussion as they are an anomoly for sizing, like trials bikes).

    As im mostly riding on the flat i want my saddle in a comfortable position, and funnily enough this is where it has always been, with ny knee rougly over the pedal axle, not miles forward like all these new 'nu-school' geometry bikes. In this situation 99% of bikes i look at can be compared equally, as they all tend to run similar seat tube angles. Its only these wierd geo's that we now apparently 'need' to climbs hills and huck back down that are causing the problem.

    The obvius solution is for the designers of these bikes <cough> certain designers listening? </cough> to post 'equivalent' geometry of their bikes based on a typically seat tube angle.

    Take a nu-bike with a 74degree seat angle which has say a 600mm top-tube, for me this frame would require a large layback post to get the saddle far enough back to be comfortable. If you now draw a line from the bb to the centre of the saddle it would prob be around 71/72 degrees, this might make the effective top tube from this line to the headtube more like 625mm. Meaning its actually bigger than it seemed at first.

    Coming up with all these fancy ways of measuring are all well and good but if your a company producing an odd bike then why try and confuse people? why not do the comparision (that they will inevitably try and make) for them! It might give you an opertunity to explain why your bike is better than a generic one, and just maybe youll sell more bikes?

    Premier Icon scaredypants
    Subscriber

    stato, I really don't get this "over the axle" bit

    your feet, arse and hands make a triangle when looked at laterally – in terms of pedalling position it wouldn't matter whether you were upside down – the only alteration is what proportion of your weight your arse & hands bear (assuming you're upright πŸ˜‰ )

    GW
    Member

    Brant, sorry, never read magazines, but by "downtube length" I meant centre of BB shell to centre of lower head tube.

    STATO
    Member

    the only alteration is what proportion of your weight your arse & hands bear

    Thats exactly it, if i ride a nu-school bike with the saddle forward much more of my weight has to be supported by my arms = not comfortable. I have/had a on-one 456, ive tried it with normal seatpost and a layback (with the saddle slammed back), much more comfortable for me with the saddle further back tho i still couldnt get it where i do on my XC bike. The best solution i could find was to ride around on with the fork wound out to 140mm to slacken it all off a bit.

    brant
    Member

    GW – yeah – I think that works well. And doesn't need a plumbbob.

    Calling it "Downtube length" causes confusion though, like top tube/effective top tube, etc. BB to crown race? πŸ˜‰

    Your comment about stack/reach being a stiffback measurement is funny though – I think it'd matter far less there, where you are going to spending more time seated.

    I tend to only sit down when I'm going up hills. And I want the saddle forward to keep the weight over the pedals to control the front end properly.

    A steep seat angle and shorter top tube also means when you slide the saddle down, it's more out of the way too.

    If people just look at the top tube dimension on a steep seat angled bike, they might thing it's short, but actually the "reach" dimension could be longer than a slacker seat angled frame with a longer top tube.

    brant
    Member

    Slack seat angles work fine with long chainstays (or big wheels), but with short ones, it gets wheelietastic.

    Unless you're not actually riding up hills, or if you're prepared to dick around with fork height on every incline.

    Premier Icon scaredypants
    Subscriber

    if only manufacturers could give us, say, effective top-tube plus seat angle and head tube length we'd be able to know what was going on once we knew the a-c of our fork

    …. oh

    πŸ™„

    GW
    Member

    STATO – ~I'd say DH & trials bikes sizing is even more important that whatever bike it is you sit down most of the time on as generally they are ridden properly πŸ˜‰

    STATO
    Member

    Slack seat angles work fine with long chainstays (or big wheels), but with short ones, it gets wheelietastic.

    It depend on where you put the saddle tho dosnt it, and why do you need a steep seat angle if your not riding stupid steep (and long) hills?

    Unless you're not actually riding up hills, or if you're prepared to dick around with fork height on every incline.

    But im not riding up silly steep hills all the time, im mostly riding on the flat. When i do go somewhere steep i can still get up, just sit on the front of the saddle or stand up, as you say "If you sit down lots, you're doing it wrong"

    STATO
    Member

    STATO – ~I'd say DH & trials bikes sizing is even more important that whatever bike it is you sit down most of the time on as generally they are ridden properly

    yes but for the sake of this topic we are talking about your general normal shaped bike, not the funny protrusions, extensions bends and generally moving things about that happens with DH bikes, they very rarely these day have a seat tube anyway. Infact most use a virtual seat-tube angle, much like im suggesting some other companies adopt.

    brant
    Member

    STATO – yeah, you're quite right. I can see for this very static, flat, not-standing up riding, reach and stack is nonsense. As would be "nu school" bikes and other things like it.

    I can't imagine riding anywhere like that – show us a pic of your bike?

    ooOOoo
    Member

    I'm with you Stato – always have to slam the seat back to get a decent pedalling position. Maybe I just have long body/short legs. A steep seat angle means as you raise the saddle your arse doesn't go as far back, so I find I can't pedal efficiently.

    Ride flat terrain a lot more than climbing and if it's too steep, well I just push anyway.

    Some graphical way of comparing all this would be better though.

    ade ward
    Member

    i still think even if you stand up reach and stack tells you what you need to know,,

    you stand on the pedals and you stick you arms out in front to hold onto the bars,, reach and stack tells you how far forward and how high you are grasping

    i think i showed in an earlier post that two bikes can have a simular down tube length but a hugely different ride postion

    Premier Icon BillOddie
    Subscriber

    Lots of talk about long legs/short bodies on here.

    It's worth remembering that the relative lengths of the shin and thigh can vary markedly for the same length of leg.

    This obviously affects seated pedalling and optimal saddle positioning.

    Premier Icon scaredypants
    Subscriber

    stack & reach work for standing up, seat tube angle & ett work for sitting down

    if manufacturer gives you the conventional geometry you can work out the stack, reach, front thingy etc easy. Can you predict what a triangle looks like if given the length of one side (downtube) ?

    STATO
    Member

    I can't imagine riding anywhere like that – show us a pic of your bike?

    Easy tiger! Thats the problem living near the coast, it tends to be flat, we cant all live in a shed in the hills. To get to anything fun for me means at least a 20mile round trip on disused railways or similar (i dont have a car), not really much point standing up when riding that. This is my current bike, 72 degree seat angle (according to the brochure at the time anyway), picture from a trip with some mates in the lakes, just to prove it goes up hills just fine ;0)

    b r
    Member

    Looks like on the run up to High Street?

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