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If you were buying a bike without trying it first, what would you consider to be the most important measurements to check against your current bike? I'm thinking TT length and reach but I could be totally wrong. Don't want to make a very expensive mistake as there's no chance at all of even sitting on most bikes these days.
Depends on your current bike really. If you were comparing a bike from 15 years ago to new, you may as well go off wether it’s a small medium or large.
To illustrate my point, my large 2014 V1 5010 (that I still ride and really like) is 435mm reach. I wouldn’t dream of getting a bike so short now, I’m looking at bikes in the 475-500mm range. Im 6ft 1.
What do you have and what are you considering buying?
Reach, head angle and room for a 150mm dropper as a minimum.
If you mean to get the right size… reach. Don’t just assume you need the same as your current bike though. Measure yours (or look it up) and then talk to someone at the company you’re getting the new bike from. Like for like isn’t always the right answer, depending on what your old and potential new bikes are.
Reach and seat tube length / insertion depth.
The most important measurement?
Me.
For my height, I'm leggy - consequently I've a lot of seat post showing on pretty much any bike (my Scandal has a 200mm dropper, with 80mm of post showing between the collar & clamp), my FS is the same. This also means my saddle is way above the bars even with 50mm of spacers and 40mm risers. Also because of my legs, I've the saddle well forward, so could really benefit from even steeper seat tubes.
Therefore a high-front end is a benefit to me, and I've no problem with seat tube length but too much reach isn't good as I've shortish arms (for my height).
But for some folk who are 'average' sized, S/M/L/XL is an easy option with an understanding that they'll need to just play around with the components.
Also, don't forget that where you ride (the majority) has an impact. Lot's of super-steep stuff for me, so a relaxed head angle is a benefit (mine's 63 degrees), whereas if I rode flatter stuff, not so important.
Somebody somewhere will have the bike you're interested in stock and/or riding one already, you'll just have to accept the cost of going to see it and/or asking around.
If you mean to get the right size… reach. Don’t just assume you need the same as your current bike though. Measure yours (or look it up) and then talk to someone at the company you’re getting the new bike from. Like for like isn’t always the right answer, depending on what your old and potential new bikes are.
Kelvin,
being an employee of bike nobility, explain Reach to me. It appears to be an arbitrary measurement fromstaight line up from the BB to the front of the bike. Fair enough. Most of us do not spend most of out time standing on the pedals - obviously you and the Cotic boys probably never sit down but the average man of the Clapham Omnibus does - hence the distance from the seat tube to the head tube is very important - as "true reach" not Gnarresist's Reach.
Prove me wrong!
Reach and seat tube length / insertion depth.
This, then I look at head angle, chainstay length and seat tube angle to complete the picture. And maybe stack just to make sure it's not wacky.
But reach is always the first one I look for. That's the primary qualifier.
It depends if you want to change or stay about the same doesn't it?
I'd agree with Kelvin though, ring them up and have a chat with the distributor about it. Tell them what you want, let them help you
Reach and seat tube angle for me. I'm tall and need a stupidly long seatpost so anything with a slack seatpost angle puts my backside towards the rear axle when seated.
explain Reach to me. [snip] Most of us do not spend most of our time standing on the pedals
True, but any bike is capable of the sitty-downy bits. The prevailing idea is that trail bike* geometry should be optimised for descending. Reach describes, better than any other single metric, how a bike will feel when you're riding aggressively - so that's why people like it. If a bike can additionally manage the techy climb bits, that's a bonus but it's seemingly not a requirement, and mostly just needs the seated rider weight to be sufficiently far forwards (seat angle).
If you're buying a bike for mega-long rides, bikepacking, XC racing etc then you might need something else.
*Or downcountry, or enduro, whatever you want to call it.
What is the most important geometry measurement?
I'd probably say for most people who don't already know what they want, S/M/L/XL. Beyond that, reach. Then head angle. Beyond THAT, I don't really believe people can add all those measurements up and work out how a bike will ride - you'd just have to try it. Or read reviews, I suppose.
It’s a combination and no one measurement will tell you how a bike rides. That said I look at reach first and foremost as if it’s too long or too short I’m not going to be comfortable at speed out of the pedals. I know at 5’9 with longer legs and shorter arms that somewhere between 450-470mm is the range I’d be after. Having had a bike at 481mm reach I know that was really too long and I was always nervous on flat and fast corners - just couldn’t get enough weight on the front wheel easily (especially not when tired towards the end of a ride).
Head angle is important as is seat angle, seat tube length and chainstay length. I know I like short chainstays for more nimble cornering particularly on steep hairpins, and I like to run a long dropper.
What do you ride now - and what sort of terrain do you ride on?
Preach the reach.
A lot of other geo measurements can be changed (head angle, effective seat angle, even bb height on full sussers).
Reach you are stuck with.
Reach is not arbitrary btw. It's a horizontal straight line from centre of BB to centre-top of head tube.
All of them
Its reach for me too, and realistically I am looking at top tube length (horizontal) to give me an idea that i'm in the right ball park. Then I look at seat tube length to give me an idea of how much seat post I'll have out. Finally I look at head tube height to give me an idea of how high the front end 'might' be. Obviously there are a ton of variables though and i'm typically looking at one class of bike ie 100mm xc, rather than going from one to another, if you follow
I went for years on bikes that were too short and were never truly comfortable, I then went up a size and instantly felt in the sweet spot, all day comfort and a position sitting that didn't move about back and forth.
explain Reach to me. It appears to be an arbitrary measurement
It is useful for comparing different bikes because it is not arbitrary, where as “top tube length” is. It doesn’t mean that I think that reach is the only thing to consider, but the thread title asked for opinions on the “most important” measurement to consider… and that’s where I’d start when comparing bike size.
People used to use seat tube length as the main “sizing” measurement, but those days are behind us.
π
Just came across this old BikeRadar article explaining why, when comparing bikes, reach is far more useful than “top tube length”… a good place to start…
https://www.bikeradar.com/features/your-top-tube-length-is-irrelevant/
Most of us do not spend most of out time standing on the pedals
Almost certainly nobody does if the measure is purely time. Easyish climbing, connecting road/fireroads, just easing off to recover for a minute.
But for the bits that are challenging and or fun* stood up, even if its just a fraction of an inch with your taint still gently grazing the saddle, then reach is the key element of the frame sizing.
*what is considered fun will vary person to person. Uphill or down, high speed or low, we all ride bikes for slightly different reasons.
Reach, seat tube length (as I have short legs for someone 5'10"), stack.
ETT, Reach. Both really as it's got to fit when you are sat down on a long slog and also feel good out of the saddle.
It does, but “ETT” sadly rarely informs you if that will be the case. Comparing metal double triangle hardtails with straight non-offset seat tubes being the exception… and even then you often have to measure them yourself rather than trust manufactures have measured in the same way.
Thinking of ways to explain this reminded me of these…
Overlay your nice neat hardtail, with a straight seat tube running from the centre of the BB up the centre of the seat tube and seatpost, and you can see why ETT won’t let you compare your seated position on the two bikes. That’s an extreme example, but it might be easier to understand.
Luckily we can move our saddles fore and aft a fair bit (being able to have more adjustment here would be real innovation, rather than 3mm wider hub axles) so can adapt our seated position on the bike to a degree. We cannot change a frame’s reach as easily.
Reach and 180 post minimum
Prove me wrong!
We sort of had this topic yesterday.
ETT is made up of the reach and the consequence of the seat angle to the bit of the ett from the BB backwards. The latter part is relatively simple trig and unless the designer has gone crazy with the (virtual) seat angle is not changing too much. The reach element though can be varied massively by relatively simple tweaks at the design phase. If I was only going to be given one number about a bike imo reach would inform me more than ett.
For me it would be, in order:-
Reach
HA
SA
Chainstays
Standover and seat tube length have never been a problem for me on any bike as I'm not of freaky proportions.
BB height
That Klein is an extreme example. I am short and with less extreme comparisons then it is more useful for me than someone tall with the sort of comparison you have suggested.
But, yeah, really it's better to get one in the flesh. When reach started to increase I went to demo a couple of sizes to find out. 475mm is what I ended up with which surprised me as I would have thought shorter would be right.
convert
We sort of had this topic yesterday.
ETT is made up of the reach and the consequence of the seat angle to the bit of the ett from the BB backwards. The latter part is relatively simple trig and unless the designer has gone crazy with the (virtual) seat angle is not changing too much
Yeah, you do need to take it into account though... bikes like the Privateer 161, which has long reach, but people have found the seated position cramped because the seat angle is so steep and so ETT is relatively short.
Reach is the first thing I'd look at too, but yeah, when other measurements are unusual/crazy then it's not enough.
I start with a long reach, then I'd generally rule a bike out if the seat tube is longer than the reach. ETT needs to be somewhat normal, seat angle steep, head angle slack. BB drop - I didn't think I'd be that sensitive to it, but the first time I put 29er wheels on a 27.5+ hardtail I was really surprised how odd and high it felt, so it's another thing I look at now.
Good Q.... first thought was there's no one dimension that you can rely on but Reach being fixed and about front triangle length is the obvious one plus it's changed a lot in recent years or between bike types.
MBR used to list down tube lengths on test bikes which didn't make much sense to me until I tried to measure the reach of a bike with a tape measure and thought about HT sag or how a FS frame pitches. BB to top or bottom of head tube for bikes with similar fork specs is similar to reach as a guide and easy to check.
In terms of stuff you can't check between bikes as easily but is most important, Front- to Rear-Centre ratio with an idea of what your position on the bike will be gives you overall weight distribution. The best bikes to ride are the ones where your weight distribution puts you in the optimum base position or stance for the way you want to ride as well as the bikes natural handling bias. Your weight distribution between the wheels combined with steering geometry is most of what makes 2 bikes feel different to ride (before getting into stuff like flex and bike weight) and the BB location is fixed, your position is dictated by 2 or 3 points with the BB being one of them.
Reach is a key dimension but really it's still all about where your weight ends up vs the 2 contact patches and whether that weight distribution suits how/what/where you ride.
RAD - centre of bottom bracket to 1 cm below a line drawn between your grips where your hands naturally sit. Apparently Sam Hill also swears by it.
RAD – centre of bottom bracket to 1 cm below a line drawn between your grips where your hands naturally sit. Apparently Sam Hill also swears by it.
Interesting. After faffing with EBB and sliding dropout SS bikes and not being very consistent (good) at bunnyhops these days I wondered if bar to rear axle was a key dimension in how a bike handled on the fun/downhill stuff. Where my BB was on the EBB bike seemed less important than the change in bar and BB to rear axle on the slider-equipped bike, and if my BB position in the EBB bike wasn't so important then CS length alone wasn't so important. It seemed to explain why I wasn't enjoying long FC bikes at the time (also explained by where I ride not being what a long reach bike is for anyway) - my lever from bar to BB was longer but my starting point weight position was further fwd. I'd take Sam Hills word for it though. He's on a FS and I was riding rigid bikes but I'm not sure if that'd make much difference in which measurement may be worth more. Probably more about the cosmic-sized gap in riding ability..
I would put Effective Top Tube over reach.
Reach doesnt account for seat tube angle, so a slacker seat tube pulls you further from the bars, or a steeper one pushes you on to them.
It does seem that when it comes to bike fit its a real dogs dinner of measurements, most of which are flippin useless. It matters not what the "Frame size" is, as long as you can get a seatpost long enough to be safe. Easy to measure, i suppose.
Surely there must be a 3 part metric base on the triangle between youre feet (or BB at least), Butt and hands.
Thanks for all the replies.
Currently ride a 170mm travel enduro bike and looking at getting a (sorry) 160/170mm Ebike. Use the current bike all over from local flowy trails to BPW and will use the eeb for the same stuff….just more of it in an evening.
Olly
I would put Effective Top Tube over reach.
Reach doesnt account for seat tube angle, so a slacker seat tube pulls you further from the bars, or a steeper one pushes you on to them..
That's the idea though - reach is all about standing position which is key for mountain bikes (or at least the trail/enduro/downhill), other measurements like ETT are more related to seated
Surely there must be a 3 part metric base on the triangle between youre feet (or BB at least), Butt and hands.
This is generally what I'm getting at about having the rider positioned over the wheelbase. There's a triangle of contact points and the aim is for them to position you with your c of g in the right place relative to the wheels, at least the start or neutral point being in the right place and you can move it about from there.
The BB is fixed, bars can move about a bit and you do your most dynamic riding off the saddle so their importance in terms of position vs the axles is in that order, hence reach -or BB to Bar- being important but to many riders ETT or saddle position isn't. Even for us highposters our seated position can move +/-30mm at least between inline and layback posts and saddle rails, saddle shapes etc.
Just remembered that Peter Verdone wrote some interesting stuff about BB to Bar and the importance over just reach dims. Still, one is fixed and that's the one to look at first.
As per @n0b0dy0ftheg0at
Reach, seat tube length (as I have short legs for someone 5’10”), stack.
I'm also 5ft10/178cm but with short legs. My height puts me usually on the 'large' taking the basic manufacturers guidelines yet it depends very much on there seat tube length - my large Hightower is about right in Length terms at 470mm reach (and using 165mm cranks and a 35mm stem too), but I can only squeeze a 125mm drop post in - as standard I think a large ships with a 170mm post!
My searches for a new frame generally have me looking at head-angle, reach, and seat tube length.
The benefit of the ever longer, lower, slack trend is now I find myself being more likely to choose a medium as some of them are 'long enough' now, and my preference is maybe to go a fraction shorter on my next bike. Bracketing, if you will...!
I'd say that "down tube length" which is the hypotenuse of reach and stack is the best single thing for sizing when riding anything interesting, and ETT is the best for boring riding. But as you can get all the numbers, I'd look at all of them - they all make a difference.
Also, you can't always trust ETT or seat angle because few bikes have seat tubes that are straight and intersect with the BB. And reach without stack can be misleading, especially between bikes with different wheel sizes and/or fork travels.
Also, you can’t always trust ETT or seat angle because few bikes have seat tubes that are straight and intersect with the BB.
This is very true. My (geeky) bugbear about virtual seat angles are that they presume a given seat height. The longer your legs, the higher your saddle and the for all those bikes with effectively a doglegged seat tube the slacker the SA. The real SA of that Klien above would go from relatively steep to stupidly slack depending on saddle height.
“This is very true. My (geeky) bugbear about virtual seat angles are that they presume a given seat height.”
I’d written off the Pipedream Moxie as having way too steep a seat angle for a hardtail for me - then I saw a side on photo of it vs some other hardtails and realised it wasn’t so crazy steep at saddle height, especially with a 160mm fork.
How many times have people said 'girth'?
Reach is not arbitrary btw. It’s a horizontal straight line from centre of BB to centre-top of head tube.
yeah - I explained that probably wrongly. If you have a bike with a 70 degree seat angle then it will be a very long bike ( so ETT becomes important)
If you have a very step Seat angle - such as the Privateer , then the reach might be long but the "cockpit" will be cramped - and pedalling up anything will be horrid. Obviously may that is not what a Privateer is meant for - but sooner or later you will have to pedal on the flat or an uphill bit.
So I will accepted on a balls out Gnarr machine , reach is really important ...
Ten years ago it was all handlebar width. Then reach. But now it seems like offset is flavour of the month.
These days I don't think you can use a single measurement. When I look at 'my' size in many bikes, the reach is 18", which sounds fekkin mad considering a few years ago it was less than 16". Then I look at seattube angle, adjust the stack for fork length and sag, adjust the ETT for the adjusted stack, and realise I'm pretty much right back where I started from.
Unless it's On One, cos they do theirs weird.