You can use a layback post or a straight post (or reverse a layback post?) You can move the saddle back and forth on the rails. And on much of the interesting stuff you’re not sitting down anyway! Yes, no, maybe?

YES

Cos if it’s wrong, your feet will be too far forward, or too far back in relation to your position on the bike. Much less consequential is saddle position, cos as you say you can use a variety of layback seatposts, and or run the saddle back or forward on the rails.

One of my old frames I had to sell, cos although the Top Tube was spot on for me, the head angle ideal, the seat tube was too slack and my feet further forward on the bike than ideal, so it was hard to get the power down, and it would just wheelie going uphills!

So couldn’t you have just moved the seat 20mm forward and bought a 20mm longer stem ?

I think mboy is maybe talking about his old Maverick?

I find it just right and the uppy downy post helps.

mboy – Member
YES

Cos if it’s wrong, your feet will be too far forward, or too far back in relation to your position on the bike

What problem does this cause?

So couldn’t you have just moved the seat 20mm forward and bought a 20mm longer stem ?

Then it would steer crap.

All angles matter.

all depends on what you are calling seat angle,,

1 the actual angle of the seat tube

2 virtual angle line drawn between bb and point where seatpost intersects a horizontal line drawn from center of the headtube

i think number two is the better description today

So couldn’t you have just moved the seat 20mm forward

What if it’s already at the end of its rails?

1 the actual angle of the seat tube

That’s the one manufacturers get excited about.

But I’d suggest the one that really matters is the angle between the centre point of your saddle and the BB relative to the vertical.

Top tube and stem length is surely a completely different kettle of fish?

What if it’s already at the end of its rails?

Yes, there is that possibility, in which case I suppose a new frame would be the answer, although it’s pretty rare to see a seat at the limit of its travel.

Then it would steer crap.

I’ve tried all sorts of combinations of handlebars and stems to try and sort out a wrist problem.
Some were more comfortable than others, but I found that in every case, if I turned the ‘bars, the bike went round the corner.

I find that ‘calderdale new skool’ or whatever Brant calls it doesn’t work with u-turn/eta style forks as if its all set up correctly with the forks sagged properly, by the time you’ve knocked another 5″ off the fork height locking them down for a climb the seat angle is enough to make a TT rider wince, if you try it it feels like you’ve got no energy left in your legs and going nowhere.

I keep meaning to try a size smaller out with a lay-back post and see what change that makes to things. After all you can always shift your weight forward on the saddle for a climb, but moving weight backwards is harder. And road bikes (surely a model for climbing efficiency) are designed around a 71/72deg seat angle to get your legs at the optimum angles.

So couldn’t you have just moved the seat 20mm forward and bought a 20mm longer stem ?

It would have handled like a bag of shit!

Then it would steer crap.

All angles matter.

Precisely… It’s also why I’ve found VERY few frames in my time I’ve really got on well with, but the ones I have done I generally still own!

What problem does this cause?

Weight behind your feet will make you wheelie! I thought I stated that above…

I think mboy is maybe talking about his old Maverick?

I wasn’t actually, although that was borderline too slack… I was on about a GT hardtail frame I had, that handled wonderfully in all respects except the seat angle was too slack! Going uphill I just couldn’t keep the bike from wheelieing, but going downhill it was ace. I found the main problem with my old Mav was the overly tall BB, which suits some people not others. My newer Mav’s BB is about an inch lower which I much prefer.

I’ve tried all sorts of combinations of handlebars and stems to try and sort out a wrist problem.
Some were more comfortable than others, but I found that in every case, if I turned the ‘bars, the bike went round the corner.

Errrr… Anyone got a medal spare to give the man? 😕

I’ve ridden hundreds of bikes over the years, and funnily enough if you turn the bars the bike does tend to turn yes. Does that mean we can all ride a CX bike down a World Cup DH track with complete confidence? Does it mean an 8″ travel DH bike is a perfect partner for the twisty singletrack down your local woods?

Bikes have different geometry and setups for a reason. One person’s cup of tea is not necessarily anothers. I personally like the way that on the whole, MTB seat tube angles have got slightly steeper in recent years. I think there are one or two that have perhaps taken it too far, but seeing as I do 99% of my descending stood up (when the seat position doesn’t matter) and 99% of my climbing seated (I’m a spinner rather than a pedal masher) bikes like my On One and my Genesis (both circa 73 degree seat angle) suit me for my style of riding. I think my old GT had a 70 degree seat angle with a 100mm fork fitted, and I had 120mm forks on it, so no wonder it didn’t feel right to me!

I find that ‘calderdale new skool’ or whatever Brant calls it doesn’t work with u-turn/eta style forks as if its all set up correctly with the forks sagged properly, by the time you’ve knocked another 5″ off the fork height locking them down for a climb the seat angle is enough to make a TT rider wince, if you try it it feels like you’ve got no energy left in your legs and going nowhere.

Then dont lock the forks down.

I don’t lock my forks down. No need.

Road bikes have 72 to 74 deg seat angles.

. And road bikes (surely a model for climbing efficiency) are designed around a 71/72deg seat

Touring bikes were always 72 deg parallel and sportier frames steeper.This also depends on size as some smaller frames have steeper angles

Yes, there is that possibility, in which case I suppose a new frame would be the answer, although it’s pretty rare to see a seat at the limit of its travel.

I’ve always had my mtb seat right at the end of the rails, on a 72 degree seat angle. It still feels like I’m hanging too far over the back wheel when compared to my road bike which is definitely easier to put the power down on. Longer stem doesn’t really help much either.

It depends on what part of the bike you consider to be “fixed”.

If you fix the position of the BB relative to the dropouts, headtube etc, then seat tube angle makes not a jot of difference – the change in the position of the top of the seat tube can be compensated for by moving the saddle/using a layback post.

However, if you fix the position of the top of the seat tube, and vary the seat tube angle, it will be the BB that moves, which certainly will affect the handling of the bike.

Unless you have an uppy-downy seat post that is.

Seat angle, very important as you can see..

I think the Ragley geometry is a clever one for making a hardcore HT that will descend and climb with a long fork. When I do get a long-fork HT I intend to ride it most of the time with it wound down (but not locked) because most of my riding is slower, techy and not that steep or gnarly – the fork will be wound out for visiting steeper gnarlier places, so the geometry choice will be geography dependant, not for climbing or descending.

Back to the seat tube, I currently have a layback post which will be replaced with a straight one when the dropper seatpost arrives. The saddle will then be shifted back a bit on the rails but not far. This is essentially steepening the seat tube angle isn’t it? I’m not worried about the distance between saddle and handlebars marginally shortening because I have arms with joints and stuff.

mboy – Member

What problem does this cause?
Weight behind your feet will make you wheelie! I thought I stated that above…

Depends…other factors in play too

Comparison with road bikes in respect of climbing is a bit of a joke – could the 2 be more different?

Seat angle only makes a difference if you size a bike by TT length.

I think stack and reach make far more sense.
http://www.singletrackworld.com/forum/topic/stack-and-reach-frame-sizing

Seat angle only makes a difference if you size a bike by TT length.

Reach and stack, combined with top tube length give you a clear idea of where the bits are when you’re stood up and sat down.

Ragley’s seat angle is forward of most people’s by a half degree or more, and is steeper on larger bikes to keep the rider forward of the rear wheel contact point- stopping “looping out” on climbs.

It’s an idea I’ve been using for a while now – http://www.bikemagic.com/bike-reviews/the-planet-x-compo-reviewed/2383.html

stopping “looping out” on climbs

……..and it works!

The Compo took a bit of getting used too, primarily I feel because of the fairly radical (at the time) geometry and also the high b/b which gave the feeling of sitting above the bike rather than on it. I regretted selling mine but in retrospect it was the wrong size, large, and I’m now on a 16″ Mmmbop which keeps everything in the right position, even with a lot of seatpost showing and 130mm Z1’s running about 30mm of sag. Having the option of sitting and spinning while staying in the same position ie. not having to drop elbows etc. when it gets steep, makes things a lot more comfortable with increased control, which you wouldn’t have with a slacker seat angle.

Yeah. Bb was kind of up there on the Compo. I remember the ground looking a long way down.

Weight behind your feet will make you wheelie!

not sure about that or recumbent riders would be flipping over left right and centre, or maybe that is why you don’t see many? Weight behind/close to your rearmost point of contact will make you wheelie, feet further forward will make you more likely to push your weight back when pressing on, and feel bloody strange when climbing though. So still not good.

Weight behind/close to your rearmost point of contact will make you wheelie

Indeed….it’s all a compromise anyway and if the only concern was climbing ability, there are other ways to prevent the front end coming up

have a think next time you are climbing ,,

what is the limiting factor in climbing the hill you are on

wheelspin or front coming up

for wheelspin you need more weight on the rear (or better tyre)

for the front coming up you need more weight on the front

when climbing seated near the limit it’s all a balencing act you are moving back and forth trying to stop the wheel spining or front lifting
i dont just sit in one position on the seat,

this is only theoretical as I am normaly walking at this time

I think Brant touched on an important aspect to this discussion with:

Reach and stack, combined with top tube length give you a clear idea of where the bits are when you’re stood up and sat down.

From my own personal experience, I prefer bikes with relatively steep seat tube angles because I do think they enable me to put power down more comfortably but, perhaps more importantly, I like predictability in a bikes handling. I like a bike’s suspension to feel like it works the same when seated and stood up, and I like the front and rear to work together and be stable around their sag points.

I think that bikes with slack seat angles cause all kinds of handling problems; if you set the sag when sat down the bike will feel fine when sat down, but as soon as you stand up there’s a big weight transferance forward, unweighting the rear and loading the front. This is a nightmare when riding technical steep terrain as it feels like you’re being pushed over the bars.

Bikes with steeper seat angles (orange for example) keep your weight fairly central in the bike whether seated or stood up (ok, the CofG will be higher but still faurl central front to rear), and to me feel more predictable and less hard work. That is, you don’t have to move your body around quite so much on technical terrain.

Bikes with steeper seat angles (orange for example) keep your weight fairly central in the bike whether seated or stood up

that’s rubbish!

IMO downtube measurement, combined with headangle and bottom bracket height is a better way of measuring an MTB than either toptube length, seat angle or stack and reach. (chainstays obviously need to be accounted for too but have nothing to do with fit but lots to do with handling)
As mentioned with the large range of saddle rail/seatpost adjustment available seat tube angle is not massively important if you’re only going to ride with the saddle set at one height, start adjusting it for other types of riding or fit a dropper post and it becomes more important.

Bikes with steeper seat angles (orange for example) keep your weight fairly central in the bike whether seated or stood up

that’s rubbish!

Why is that rubbish? just because you think a different set of measures are more important to you, it doesn’t make something rubbish, or incorrect or whatever.

As an example, if the BB is exactly midway along the bike, the seat is fairly close to directly above and you’re sat on your seat then all your weight is also pretty much directly above the bottom bracket. So, when you stand up all you’re doing is lifting the centre of gravity, not shifting it front or rear.

However, when your seat is placed far back from the BB and then you stand up so your weight is shifted forwards and upwards, meaning it has a more pronounced effect on the handling.

IMO downtube measurement, combined with headangle and bottom bracket height is a better way of measuring an MTB than either toptube length, seat angle or stack and reach. (chainstays obviously need to be accounted for too but have nothing to do with fit but lots to do with handling)

“Better way” – for what? handling, comfort & fit, lifting it over a stile, or all of the above? the question was “does seat angle really matter?” not “what is the best way to measure a MTB”.

OK so it’s been touched on but not very well… Can anyone explain why they think the saddle cares how it got to its position? ie, from a slack seattube and no layback, or a steep seat tube and layback, if the saddle is in the same position compared to the BB and other main componentry then what difference does it make?

Obviously seatpost slackness has an effect when you raise and lower the seat as it also moves it fore and aft but then you typically aren’t sat on it when it’s lowered. Also obviously very slack seatposted frames will sit their rider a long way back if they have a very long seatpost, possibly too much to compensate for with saddle positioon. But other than these, does it matter?

OK so it’s been touched on but not very well… Can anyone explain why they think the saddle cares how it got to its position?

of course the saddle doesn’t care it is an inanimate object!

The geometry of bikes is what it is because builders have fiddled for over 100 years and what we have is the result. You get the odd ball Steve Bauer bike but most have seat angles around 73 degrees because for most people most of the time on most bikes it works. Chainstay length and by implication wheelbase is then what will get the back wheel as close as sensible, ie how much clearance do you need.

Top tube is dependent on how tall the rider is and the balance between stem and top tube. Head angle depends on how fast you want the bike to handle. there are reasons why the numbers are the way they are.

But again, it doesn’t matter how long the top tube is as long as the reach is correct- you could have a really short top tube and a vertical seat tube, and an enormous amount of layback and have every component still in the exact same position in relation to each other. (but a short top tube and long seatstays)

Chainstay length is only related to seat tube angle inasmuch as you need the clearance, a very slack seat tube would need very long chainstays to clear the tyre… but since modern bikes are often tending towards steeper seat tubes not slacker, that’s a nonissue, you’re creating clearance not losing it.

“The geometry of bikes is what it is because builders have fiddled for over 100 years and what we have is the result.”

The geometry of bikes has constantly changed over recent years never mind over 100 years, we’re not suddenly at the end of 100 years of development here with a finished product.

Northwind, bikes have not evolved much in the last few years, seat tube angles are still around 73 degrees as they have for the last few decades. head angles on MTBs have slackened a bit to allow for longer travel forks, that is it.

The geometry of bikes is actually fairly static. 20 years ago 71/73 now your looking closer to 69/73 big change that!

Of course the top tube length matters, Seat tube angle is what it is because it fits the average persons legs. to accomodate the upper body the top tube and stem length is then chosen. If you put the saddle vertically above the bottom bracket, you loose mechanical leverage from the thighs. then to accomodate the upper body you need a long top tube. which means the bike has to be longer, which makes the wheelbase longer, which produces a barge.

” GT hardtail frame I had, that handled wonderfully in all respects except the seat angle was too slack! “

An Avalanche? My GF has this bike and also struggles to control the front wheel on seated climbing. It came with a layback seatpost and I think she would benefit from a straight seatpost.

I suspect the problem with a slacker seat angle is that on pedally terrain it’s more awkward to smoothly move between the seated/hovering and ready/attack positions. On descending, when the bike is angled down, the required movement is less and so it’s probably beneficial.

Heck I nowt about frame geometry really. It’s just my observation.

mrmo, you don’t seem to be understanding the basic point tbh.

“If you put the saddle vertically above the bottom bracket, you loose mechanical leverage from the thighs. then to accomodate the upper body you need a long top tube. which means the bike has to be longer, which makes the wheelbase longer, which produces a barge. “

In a world with no adjustment at the end of the seatpost you would be completely correct. Now obviously the vertical seatpost/huge layback example is just a nice simple thought experiment not a real world example, but it holds- saddle position obviously isn’t a product solely of seattube angle.

mrmo – Member

“Northwind, bikes have not evolved much in the last few years, seat tube angles are still around 73 degrees as they have for the last few decades. head angles on MTBs have slackened a bit to allow for longer travel forks, that is it.

The geometry of bikes is actually fairly static”

The advent of adjustable forks and frames designed for multiple fork lengths means that the geometry of some models isn’t static never mind the whole industry. What’s the seat tube angle of a Cotic BFe? And modern bikes cover a huge range of purposes and angles, 71/73 might be common but it’s hardly a default.

If you’re going to look exclusively at XC bikes then you’re closer to the mark but even then, you say geometry is fairly static, how many bikes still come with 120mm stems?

Why is that rubbish? just because you think a different set of measures are more important to you, it doesn’t make something rubbish, or incorrect or whatever

put simply, seat angle makes **** all difference to whether your “weight is kept fairly central” when you’re standing.

the other stuff I was on about was in reply to Brant but clearly over your head.
Reach and stack is helpful along with traditional geometry measurements but in reality was never needed if the importance of Downtube measurement, or BB – centre of lower headtube had been included in traditional geometry charts as it should have been all along.

Northwind, saddles are all supplied with a similar rail length, seatposts also have a small range of adjustment.

Everything is designed to work together which means a seat angle of 73degrees a seatpost with c20mm layback and 50mm long saddle rails. numbers do vary but not by much. You get the odd inline post, which suits some people, for others it won’t work, the seat angle might be kicked back to 72degrees or steepened to 74degrees.

As for 120mm stems. Stems have got shorter bars have got wider, and top tubes have grown a little, they work together and if you look the numbers your talking about are an inch here or an inch there, just tweaking to allow for longer forks.

And to say that inch here or there is radical!!, these are tweaks, nothing radical has happened for years. Look at the Steve Bauer bike picture above, that is a radical change and he himself went back to a normal bike afterwards.

As for the BFe, according to Cotic 69/72, so really radically different there isn’t it!!! the Soul is 70/73. and just to throw in the mix the Roadrat is 72/73. To throw something else in the Trek Session is 64/72 or an Orange 224 at a radical 64/72, A cinelli Supercorsa is 74/74ish.

My personal history has seen the bike go from 71/73 with a 22.5 top tube and 135mm stem, to 70/73 25″ and a 100mm stem. So the stem has shrunk a little whilst the top tube has grown by the same amount. What has changed? Fork travel has grown from zero to 100mm.

And why have head angles slackened? so when the fork is compressed the bike is still rideable.

I reiterate, the whole setup evolves a little as trends demand, but there is nothing radical here. And on the point of seat angles they don’t really change because riders are the same, the demands are the same. the components are the same.

Northwind, saddles are all supplied with a similar rail length, seatposts also have a small range of adjustment.

Everything is designed to work together which means a seat angle of 73degrees a seatpost with c20mm layback and 50mm long saddle rails. numbers do vary but not by much. You get the odd inline post, which suits some people, for others it won’t work, the seat angle might be kicked back to 72degrees or steepened to 74degrees.

– 1 degree steeper/shallower seatangle = 14mm difference in fore/aft saddle position at 800mm length.
ie. right around the bb-saddle rail height at full extension for your average 6′ tall male.

in other words, you are talking utter pish!

put simply, seat angle makes **** all difference to whether your “weight is kept fairly central” when you’re standing.

the other stuff I was on about was in reply to Brant but clearly over your head.
Reach and stack is helpful along with traditional geometry measurements but in reality was never needed if the importance of Downtube measurement, or BB – centre of lower headtube had been included in traditional geometry charts as it should have been all along.

Of course it has something to do with it – at the other end of the seat post is the bottom bracket and pedals – where all the weight is focussed when you’re stood up on the bike (as opposed to on the saddle when you’re sat). To take it to the extreme, you could say a recumbant cycle is merely a very very slack seat tubed bike; try standing up and you’ll find you weight has to go forward.

Having said that it could all be a load of rubbish – after all I’m not a bike designer of great repute like yourself, and only have 40 years of experience to comment upon. I know what I like, I know how I like my bike to behave, and I know from experience how the different angles interact and make the bike behave.

40 years of having your head stuck in the sand by the sound of things 😛
Seat angle does not even dictate where the BB is?