head tube angle - how much difference is 5 degrees?

danlightbulb

I was looking at some cube bikes. The xc bikes eg the LTD or the Acid, have a head angle of 70 degrees. Other bikes I've looked at have a tube angle of around 68.5 ish degrees. The top of the range DH cubes have a head angle of 65 degrees. Only 5 degrees difference across the whole spectrum? Is it an advantage to have a slighter slacker head angle on xc trails?

Thanks

supersonic

For some. It adds stability (in combination with a longer wheelbase).

But DH bikes mostly point down - so when you look at how they 'level out', and the very narrow usage for them (ir they don't climb, or even do level ground), then always having a slack HA ia advantageous.

XC and trail bikes climb as well, and too slack slows the steering and makes it want to tuck under.

delcol

go to your lbs and sit on a xc bike with a 70 degree angle then sit on a dh bike with a 65 ha you will see the difference.
like supersonic said dh bikes are good for going down hill but dont climb very well... xc bikes climb well but dont decend steep stuff very well..
i dont like steep 70 degree head angle bikes i prefare slacker headangle somewere around 67 degrees decends well and still climbs...

.blitz

5 degrees is a huge difference.

A 70 degree head tube is typical XC territory it allows you to get over the front on the climbs and puts the rider in a very efficient pedalling position. I have a short-travel bike with a 70 degree head tube it absolutely flies uphill but by the same token it is super sketchy downhill it's difficult to get back far enough to keep my weight centered.

65 degrees puts the front wheel 'out there' like a chopper which feels completely wrong everywhere except downhill when it all suddenly makes sense by allowing the rider to keep their C-of-G over the bottom bracket when the bike is pointing 'down'

A lot of this depends on the seat tube angle as well modern trail bikes have slacker head angles combined with steep-ish seat tubes so that they can pedal and descend reasonably well.

YeehaaMcgee

.blitz wrote:

5 degrees is a huge difference.

A 70 degree head tube is typical XC territory it allows you to get over the front on the climbs and puts the rider in a very efficient pedalling position.

It doesn't move the rider at all. And it has no effect on pedalling position.

Plyphon

YeehaaMcgee wrote:

.blitz wrote:

5 degrees is a huge difference.

A 70 degree head tube is typical XC territory it allows you to get over the front on the climbs and puts the rider in a very efficient pedalling position.

It doesn't move the rider at all. And it has no effect on pedalling position.

heeeeeereeeee we go!

Jomox

YeehaaMcgee wrote:

.blitz wrote:

5 degrees is a huge difference.

A 70 degree head tube is typical XC territory it allows you to get over the front on the climbs and puts the rider in a very efficient pedalling position.

It doesn't move the rider at all. And it has no effect on pedalling position.

Again physics disagrees with you.

http://www.bikecyclingreviews.com/Frame_Geometry.html
http://en.wikipedia.org/wiki/Mountain_bike
http://mountain-bikes.findthebest.com/b ... -Explained

Those are just the basics, but as said no point debating if someone is denying physics law/geometry (This is something you learn when studying physics)

YeehaaMcgee

Jomox wrote:

YeehaaMcgee wrote:

.blitz wrote:

5 degrees is a huge difference.

A 70 degree head tube is typical XC territory it allows you to get over the front on the climbs and puts the rider in a very efficient pedalling position.

It doesn't move the rider at all. And it has no effect on pedalling position.

Again physics disagrees with you.

http://www.bikecyclingreviews.com/Frame_Geometry.html
http://en.wikipedia.org/wiki/Mountain_bike
http://mountain-bikes.findthebest.com/b ... -Explained

Those are just the basics, but as said no point debating if someone is denying physics law/geometry (This is something you learn when studying physics)

Nothing you've linked to seems to disagree with my statement - so here's the question, YOU TELL ME, where you think there's holes in my thinking.
It appears to me as though you're completely misunderstanding what's going on.

Chunkers1980

What does it disagree with?

With the same length fork the steeper the angle, the further you can get over the front yes, but it doesn't change rider position in any way.

cooldad

Deja farking vu.
That's all

mrmonkfinger

Jomox wrote:

Again physics disagrees with you.

http://www.bikecyclingreviews.com/Frame_Geometry.html
http://en.wikipedia.org/wiki/Mountain_bike
http://mountain-bikes.findthebest.com/b ... -Explained

Those are just the basics, but as said no point debating if someone is denying physics law/geometry (This is something you learn when studying physics)

There's no physics on those pages.

Ignoring any effects that friction has on the whole endeavour (from either air, ground, drivetrain, etc), the effort required to winch a bike up a hill (as compared to a flat bit of ground with the same surface distance) depends on precisely two things:

weight of bike + rider
height of climb

styxd

There's no physics on those pages.

Ignoring any effects that friction has on the whole endeavour (from either air, ground, drivetrain, etc), the effort required to winch a bike up a hill (as compared to a flat bit of ground with the same surface distance) depends on precisely two things:

weight of bike + rider
height of climb

You've also ignored the fact that humans arent 100% efficient machines.

YeehaaMcgee

styxd wrote:

There's no physics on those pages.

Ignoring any effects that friction has on the whole endeavour (from either air, ground, drivetrain, etc), the effort required to winch a bike up a hill (as compared to a flat bit of ground with the same surface distance) depends on precisely two things:

weight of bike + rider
height of climb

You've also ignored the fact that humans arent 100% efficient machines.

You've neglected to explain why that should affect anything. I say it won't, because the rider's relative position is identical.

bennett_346

I always thought that a slack head angle was just to give a longer wheelbase without lengthening the top tube or reach.

And cornering characteristics.

I can't see how head angle alone would affect climbing efficiency (though the terminology people are using is a bit wishy washy vague).

ilovedirt

With the same stem/bars, a steeper head angle will put the rider further over the front wheel, fact.

but yeah, 5 deg is a big difference. I don't like anything any steeper than 68, and to be fair, 65 isn't super slack. Some bikes (mondraker summum) can get to around 60/61 deg. Think my orange is around 63ish.

bennett_346

ilovedirt wrote:

With the same stem/bars, a steeper head angle will put the rider further over the front wheel, fact.

Right, but that will affect the energy required to move the bike through a distance how exactly?

ilovedirt

It doesn't really, but if the angle is slacker, it often means the bike is heavier/has more travel etc which can make the bike harder to pedal. The actual angle itself doesn't though, not in my experience anyway.

supersonic

This all depends how you look at it - change one parameter of a bike and you often change another, so it depends WHAT you change, and IF you compensate elsewhere.

If you change the head angle by using a longer fork, then lot of other things change too, ie seat angle, effective top tube length, BB height, front centre, wheelbase.

If you actually change the headtube of the frame (make it slacker), and fit the SAME length fork, you will STEEPEN the seat angle and lower the BB when the frame is built up. If you fit an angleset this is precisely what happens.

But if you keep all things equal ie the headtube is made longer to compensate for any angle changes (and bar and stem), then relatively speaking you can have the head angle as slack as you like but you'll still be in the same position on the bike.

So why do people say steeper head angles climb 'easier'? Well define easier. I find the front wheel is more planted which allows a more efficient riding position.

ilovedirt

supersonic wrote:

So why do people say steeper head angles climb 'easier'? Well define easier. I find the front wheel is more planted which allows a more efficient riding position.

Like I said, I've never had a problem climbing with a slack head angle. Got my new bike out for the first time. It's 65deg before sag and I had no issues on the climbs at all. It was easier than on the full sussers i've owned with steeper angles.

CraigHarris

It's scary that people don't understand the affect of the head tube angle on climbing etc!
The physics aren't overly relevant, if you've ridden enough different bikes you'll know exactly why steeper angles climb better and slacker angles descend better.

To get the best of both worlds, simply buy a Talas fork and change the travel to suit climbing or descending; or if you don't mind compromising traction on technical climbs DT Swiss's RTLC forks lock down to give a shorter steeper front end too.

When all other things are equal, it's way easier to climb with a steeper head angle and there are a few reasons which contribute to such (I'm working these out from how the bikes feel to ride):
- rider position, relative to wheel centres
- stability of steering
- direction of motion versus easiest path of suspension compression

Note you can't directly compare head angles for different wheel sizes, especially when length of travel is equal.

DH bikes have enough travel and slack enough angles to plough through the straightest lines even on gnarly descents; whereas for technical climbs you ideally need to be able to carefully steer the smoothest path avoiding anything your wheels might hook up on plus having the front wheel's centre closer to you makes it easier to lunge up onto steps / rocks if needed. Slack front ends run through the travel slightly easier and are far more forgiving on steep stuff, especially when transitions are harsh.

If you're only looking to change the wheelbase, it's best done by picking a frame with longer (or shorter) top tube rather than messing with head angle as the latter effects everything else too.

Anyone who thinks rider position doesn't change when geometry and/or lengths change is very mistaken.

YeehaaMcgee

But you're another one missing the point... it still doesn't take any more effort to take a bike of the same weight, with the same gearing, up the same hill, whether it has a 0 degree or 90 degree head angle. You're still moving the same amount of mass up the same slope in the same time.

CraigHarris

YeehaaMcgee wrote:

But you're another one missing the point... it still doesn't take any more effort to take a bike of the same weight, with the same gearing, up the same hill, whether it has a 0 degree or 90 degree head angle. You're still moving the same amount of mass up the same slope in the same time.

You seriously don't understand this.
Actually it does - is your brain still tied to the over-simplified views of physics and mechanical mathematics that are taught in schools?
The real world is very complicated; try different angles without changing anything else - there is a HUGE difference!

The Rookie

On straight 'laws of physics' YHMG is right, the amount of 'work' done (mass multiplied by altitude increase) is the same, however I agree with others that it's not quite that simple, a slacker bike is 'less easy' to pedal uphill and thus energy is wasted and it is that which makes a slacker bike 'more effort' to get uphill.

Having said that my 69deg XC frame I usually go up my local hills with the front wheel skipping off the ground as I keep my weight right back to optimise traction, often getting up the local (tending to be muddy) hills wile stronger/fitter guys I ride with don't as they loose traction and grind to a halt.

felix.london

Personally I wouldn't say the HA made the slightest bit of difference to climbing. It's where you centre of gravity is that makes the difference when climbing. You could have a super slack bike but if you've got a super steep seat tube you'd be able to climb without issue

YeehaaMcgee

Or, to extend that idea, a really long back end, like a drag motorcycle.

Dirtydog11

CraigHarris wrote:

It's scary that people don't understand the affect of the head tube angle on climbing etc!
The physics aren't overly relevant, if you've ridden enough different bikes you'll know exactly why steeper angles climb better and slacker angles descend better.

To get the best of both worlds, simply buy a Talas fork and change the travel to suit climbing or descending; or if you don't mind compromising traction on technical climbs DT Swiss's RTLC forks lock down to give a shorter steeper front end too.

When all other things are equal, it's way easier to climb with a steeper head angle and there are a few reasons which contribute to such (I'm working these out from how the bikes feel to ride):
- rider position, relative to wheel centres
- stability of steering
- direction of motion versus easiest path of suspension compression

Note you can't directly compare head angles for different wheel sizes, especially when length of travel is equal.

DH bikes have enough travel and slack enough angles to plough through the straightest lines even on gnarly descents; whereas for technical climbs you ideally need to be able to carefully steer the smoothest path avoiding anything your wheels might hook up on plus having the front wheel's centre closer to you makes it easier to lunge up onto steps / rocks if needed. Slack front ends run through the travel slightly easier and are far more forgiving on steep stuff, especially when transitions are harsh.

If you're only looking to change the wheelbase, it's best done by picking a frame with longer (or shorter) top tube rather than messing with head angle as the latter effects everything else too.

Anyone who thinks rider position doesn't change when geometry and/or lengths change is very mistaken.

Not as scary as the latest "must do" fashion of fitting the smallest stem and widest bars possible irrespective of the type of bike. The cycle press have a lot to answer for with regards to this.

IMO Weight distribution has a far bigger impact on climbing ability than head angle, I've got a Talas and previously owned a Marzzochi MX comp that had ETA.

For example, you could run a 100mm fork with a 71 - 72 degree head angle, however, if you where to run high rise bars with plenty of spacers under the stem it will still wander despite the steep head angle.

Biggest advantage of a slack head angle is the long front center, again this relates to fore and aft weight distribution.

Pretty much what Felix said!

EH_Rob

CraigHarris wrote:

It's scary that people don't understand the affect of the head tube angle on climbing etc!

I, for one, am not scared of this in the slightest.

mrmonkfinger

Dirtydog11 wrote:

Not as scary as the latest "must do" fashion of fitting the smallest stem and widest bars possible irrespective of the type of bike.

Why is that scary?

Dirtydog11

mrmonkfinger wrote:

Dirtydog11 wrote:

Not as scary as the latest "must do" fashion of fitting the smallest stem and widest bars possible irrespective of the type of bike.

Why is that scary?

It's not really, I made that up for effect!

However it does demonstrate that people will do whatever the press advise and have little understanding of the effects.

Have you ever seen a Boardman with a 50mm stem and a set 750mm bars fitted?

It must be obvious to all by now that when it comes to bike setup Chris Boardman hasn't got a clue, I mean what is he thinking fitting narrow bars and long stems, the man must be a complete idiot?

YeehaaMcgee

Do boardmans have narrow bars?

Dirtydog11

YeehaaMcgee wrote:

Do boardmans have narrow bars?

640- 670 depending on frame size and a 90mm stem, the man hasn't got a clue.