How much lean angle have I got?

**Ocean1** · 14th March 2008, 15:00

Originally Posted by Mikkel

The way to look at it is this: The tyre grip (compound, design) does not dictate how fast you corner - it dictates how fast you CAN corner - i.e. how much lateral force you can apply to the road for a certain normal force.

Yup.

Originally Posted by Mikkel

As you lean over further your normal force decreases since the weight is not sitting "on top" the contact patch. There fore, the more upright you can keep your bike for a given cornering speed the less risk you have of loosing grip.

Can’t see that, the combined “normal” (1G vertical) and centrifugal forces maintain balance exactly over the tyres contact patch, or you fall over, no matter what the angle. The normal gravitational component isn’t a variable, (“normally”) and we’ve already established that there’s no advantage in changing the angle of the tyres wrt the road surface unless it’s to avoid over-leaning. I can easily see that being useful on a track, I just don’t see how it produces any advantage up to that “max tyre angle” point.

Originally Posted by xerxesdaphat

I would guess that's not quite right. Your suspension would surely be working better with a shallow lean angle -- when you're leaned over, bumps are trying to shift the suspension up and down at a different angle to what it works at. So if you're more upright, your suspension can keep the wheels in better contact with the road, right?

Arguably one of the things that can detract from suspension performance is lateral load, which can increase friction and slow response speeds. Hanging off the bike produces exactly such loads. Bear in mind the suspension “see’s” movement perpendicular to the bike’s vert centreline, it don’t care what lean angle you’re on.

Originally Posted by AllanB

The thing here is that when riding you have your weight etc on the bike - looks cool in the garage but differs on the road. I presume the tyre guys lean angles are actual riding ones, otherwise they are pointless.

Suspension compressed or not doesn’t affect the angle, 55deg is 55deg whatever weight is on the bike. It will affect ground clearance…

**enigma51** · 14th March 2008, 15:03

Originally Posted by FROSTY

One thing not mentioned (I think) is that every tyre brand and within reason model has its own way of "announcing" its about to start to slide.
For example Michellen tends to go vague fairly early and slide progressively whereas Metzlers grip longer but let go with more of a bang.
--The tyre "experts" dont knot knickers

these are examples only

Bridgestones are good that way they always slide and I like very much

**Mikkel** · 14th March 2008, 15:23

Originally Posted by Ocean1

Can’t see that, the combined “normal” (1G vertical) and centrifugal forces maintain balance exactly over the tyres contact patch, or you fall over, no matter what the angle. The normal gravitational component isn’t a variable, (“normally”) and we’ve already established that there’s no advantage in changing the angle of the tyres wrt the road surface unless it’s to avoid over-leaning. I can easily see that being useful on a track, I just don’t see how it produces any advantage up to that “max tyre angle” point.

I can see your argument. I am sorry but I can not provide you with an answer. There must be a reason for why you would want not to lean your bike over more in low-grip situations though.

Originally Posted by Ocean1

Suspension compressed or not doesn’t affect the angle, 55deg is 55deg whatever weight is on the bike. It will affect ground clearance…

I'd dare say that it is more complicated than that. What could be treated as a 2D system (bike upright traveling straight ahead) becomes a 3D system when you introduce lean. Hitting bumps would be more likely to cause you to loose grip when you are on a lean I'd bet.

**Badjelly** · 14th March 2008, 15:23

Originally Posted by Badjelly

That sounds dodgy to me, Mikkel. What do you mean by normal force? Normal to road? For a horizontal road, that's just the weight of the bike + rider.

Originally Posted by Mikkel

For a vertical bike on a horizontal road... yes. Trouble is what happens at the contact patch when you are on a lean?
Not all of your weight is pushing directly down on the tyre - some is being balanced by gyroscopic forces as well.

Once you're settled into the corner (and assuming there are no undulations in the road and ignoring tidal forces etc etc etc) then the COG of the bike + rider will not be accelerating up or down, therefore the weight of the bike + rider will be balanced exactly by the vertical component of the force exerted by the road at the tyre contact patch (or fairing contact patch, if you're Skidmark). Well, actually, a bike has two wheels, so I should have said the sum of the vertical components of the forces exerted by the road at the tyre contact patches.

By "gyroscopic forces" I assume you mean the forces required to change the axis of rotation of the wheels, or in other words, to change the orientation of the wheels' angular momentum vectors. These aren't accelerating the COG of the bike + rider, so they don't affect the total force at the contact patch (or the sum, see above). However they might affect the front-rear balance.

Racers clearly do lean off a bike to decrease the lean angle of the bike itself. There are various reasons this might be useful.

Use tyre nearer to centre
Avoid scraping stuff
More stable to bumps
Don't have to move the bike so far laterally on corner entry and exit
Allows contact of knee with surface, giving feedback

**Badjelly** · 14th March 2008, 15:30

Originally Posted by Ocean1

we’ve already established that there’s no advantage in changing the angle of the tyres wrt the road surface unless it’s to avoid over-leaning.

I'm not sure about that. It's not like a tyre is a wooden block with some rubber of the bottom, where the maximum lateral force it can sustain depends only on the coefficient of friction of the rubber. Tyres flex. This lets them do all sorts of interesting things like (I think) creeping across the road before they let go entirely. Perhaps tyres just work better at smaller lean angles.

**Ocean1** · 14th March 2008, 15:42

Originally Posted by Mikkel

I can see your argument. I am sorry but I can not provide you with an answer. There must be a reason for why you would want not to lean your bike over more in low-grip situations though.

In so far as I can be said to have a position on the matter it would be that there's a particular angle where a given tyre will provide maximum grip, and that that's the angle one should try to maintain regardless of that required to navigate a corner. That may well mean hanging of the inside when you're pushing the limit. It also means hanging off the outside on slow turns, although there's no point in doing so.

I am aware that body english seems somewhat to be influenced by things other than simple physics, fashion for example. Not that long ago it was rare to see racers moving so far inboard as most currently seem to, and even now some hardly move at all, with no apparent loss of cornering speed. Moving body weight around on a dirt bike has more effect but for reasons which mostly don’t apply to road bikes… then again, look at motards, and ask yourself why they do it all backwards.

Originally Posted by Mikkel

I'd dare say that it is more complicated than that. What could be treated as a 2D system (bike upright traveling straight ahead) becomes a 3D system when you introduce lean. Hitting bumps would be more likely to cause you to loose grip when you are on a lean I'd bet.

Yup, significant front wheel vert displacement through a hollow mid-corner messes up the geometry big time.

**Ocean1** · 14th March 2008, 15:48

Originally Posted by Badjelly

Racers clearly do lean off a bike to decrease the lean angle of the bike itself. There are various reasons this might be useful.

Use tyre nearer to centre
Avoid scraping stuff
More stable to bumps
Don't have to move the bike so far laterally on corner entry and exit
Allows contact of knee with surface, giving feedback

All entirely believable.

Originally Posted by Badjelly

I'm not sure about that. It's not like a tyre is a wooden block with some rubber of the bottom, where the maximum lateral force it can sustain depends only on the coefficient of friction of the rubber. Tyres flex. This lets them do all sorts of interesting things like (I think) creeping across the road before they let go entirely. Perhaps tyres just work better at smaller lean angles.

Be nice to have an expert confirm or deny eh?

Either way we're talking minscule differences, the wide range of tyre profiles and the variation in different rider's body english suggest any advantage is small enough to be inconsequential at the speeds I ride at.

**Mikkel** · 14th March 2008, 15:51

Originally Posted by Ocean1

In so far as I can be said to have a position on the matter it would be that there's a particular angle where a given tyre will provide maximum grip, and that that's the angle one should try to maintain regardless of that required to navigate a corner. That may well mean hanging of the inside when you're pushing the limit. It also means hanging off the outside on slow turns, although there's no point in doing so.

Unless there is a variation of the tyres compound across the width of the tyre you should be able to gain the most amount of lateral force from that tyre, before it looses grip, in the totally upright, vertical position.

Originally Posted by Ocean1

I am aware that body english seems somewhat to be influenced by things other than simple physics, fashion for example. Not that long ago it was rare to see racers moving so far inboard as most currently seem to, and even now some hardly move at all, with no apparent loss of cornering speed. Moving body weight around on a dirt bike has more effect but for reasons which mostly don’t apply to road bikes… then again, look at motards, and ask yourself why they do it all backwards.

The clearance of modern sportsbikes for lean angles are much greater than they used to be. It's fairly easy to scraped the peg on my '89 zxr250 - I would imagine it would be much more difficult on a modern fireblade or something like that.

Motards are very different. Their center of mass is much higher compared to sportsbikes - this gives more displacement between COM and contact patch for the same lean angle without hanging off.
Furthermore these bikes are much lighter with smaller wheels and they have a huge lean clearance...

**Ocean1** · 14th March 2008, 16:05

Originally Posted by Mikkel

Unless there is a variation of the tyres compound across the width of the tyre you should be able to gain the most amount of lateral force from that tyre, before it looses grip, in the totally upright, vertical position.

Why would you assume that?

Firstly, a lot of modern tyres do indeed have stickier compounds on the sides.
And secondly the sectional profile of most tyres is not a perfect arc, in fact some have a pronounced triangular section. So there is likely to be both a significantly larger contact patch and a higher COF at the designed optimum angle.

Originally Posted by Mikkel

Motards are very different. Their center of mass is much higher compared to sportsbikes - this gives more displacement between COM and contact patch for the same lean angle without hanging off.
Furthermore these bikes are much lighter with smaller wheels and they have a huge lean clearance...

And yet they typically lean OUT. Benefit of the doubt: it’s ingrained dirt riding behaviour, still, even when not sliding it seems not to detrimentally affect their corner speeds…