Having a blonde moment…

How come on a motorbike to turn a corner more easily the rider counter steers and leans his weight to the inside of the tyres and drops his head down to the inside bar ie he’s leaning over more than the bike to try and keep the tyres upright more and put less angle on them.

On a mountain bike – we also counter steer but emphasis is put on weighting the outside of the bike through your foot and normally the position of the rider is a more upright position than the angle of the bike?

Weight of vehicle and grip contact patch, your CofG dominates the MTB, it merely influences the heavier Motorbike.

Or summink.

Centrifugal force innit, much much higher on motorbike as speeds way higher, so have to get more weight right over to inside of corner.

If motorbike tried going round corner at 30mph in same position he would topple over to inside, as would you on mountain bike.

Conversely if you tried going round corner at 140mph on mountain bike in normal position you would find yourself flung off on outside of bend.

Dunno but it squares off rear £200 tyres on my old big thumper supermoto sure quick!

But by hell it’s fun

Ah yes that little gem! I totally forgot about weight.. I find it hard going onto the road bike (motorbike) after being on the mountain bike so long as I almost always find myself sat up in certain random corners in a mountain bike position and having to have a word with myself to get back down into them!

I’ll just do a CofG chant next time I’m out 😀

It’s also to do with slip and grip and surface traction, not method of propulsion… I can’t use words this morning so here are some pictures

Motocross is generally ridden the same as MTB

Road bikes can let you hang off the inside

ie because the surface of a road is usually consistent and doesn’t break away like a varied off road surface?

ie because the surface of a road is usually consistent and doesn’t break away like a varied off road surface?

Because the coefficient of friction between tarmac and a road tyre (even though its skinny in comparison to a mtb tyre) is higher than between an mtb tyre and a loose off road surface.

Never really thought about it but on an mtb I do lean the bike over more than my body and countersteer and on the road I’m hunched with my body low, following the angle of the bike. In both cases I’m pressing hard on the outside pedal. But I don’t consider myself a cornering god by any stretch of the imagination.

I think there are lots of things going on. But I’d say

Mass of bike relative to rider. Hanging off the side of a 200kg motor bike moves the C of G a bit towards the inside but a huge amount on a 20 kg MTB

The force that makes a bike steer is call camber thrust steering. If you role a bike wheel on its own at an angle it goes round in a cirle. When a wheel is leant over it will start to turn as the radius of the wheel on one side of the contact patch is less than the other. By moving along a curved path whole contact patch can avoid slipping

This means the angle of the lean for the wheels is determined by the radius of the turn. But the faster you are going around the same radius turn the more you need C oF G inside the contact patch. That would explain why MTBs on a loose surface need the most pronounced lean the bike and sit above it technique.

Mass of bike relative to rider. Hanging off the side of a 200kg motor bike moves the C of G a bit towards the inside but a huge amount on a 20 kg MTB

This, you steer a motorbike by leaning the bike. You steer the bicycle by leaning your body.

On an MTB, you want the bike leant over more to get it onto the knobblies on the edge of the tyre for more grip.

Racing motorbikes hang off the inside so that the bike is more upright to avoid grounding out.

awesome thanks guys a nice bit of information for the knowledge bank

What pdw said.

And furthermore in relation to what ampthill said, on those wide tyres road/racing motorbikes use, the contact patch at full lean will be way off-centre, possibly weight-shifting helps deal with that in some mysterious way. That camber steer effect sounds as if it is proportional to the width of the contact patch, actually no as the extra width will counteract it. But the torque generated by the effect will be proportional to the tyre contact patch width (and the stickiness of the tyres) so the effect will still be ie damn all on a road bike, a bit on an mtb (but a lot on a fatbike) and loads on a motorbike.

Any fatty riders out there want to comment?

I think the motorbike comparison is a very important one as when I started riding mtb’s I thought that was the technique (ie lean inside/under the bike) as thats what I saw most often and was inside my head. TBH it was only after a trip to Jedi I understood that was 100% wrong !

Currently practising getting one’s knee down on the fat bike

Lots of grazes so far I might try the other knee

pdw has it right. It’s tyre design, not anything else.

On a knobbly tyre you get the most cornering grip from the inside edge of the outside knobbles. The same reason downhillers sometimes cut the transition knobs off between the centre tread and outside tread, to allow more dirt to get rammed in there and grip more. Push these knobbles into the ground more and you get more grip.

Road bikes and road motorbikes don’t have to lean the bike for edge grip … so don’t.

It isn’t just tyre design, it’s also gyroscopic effect and CoG of bike+rider (you have to haul a motorbike over when going fast), and positioning rider CoG so you can remain balanced when the bike slides a lot (hang off the inside and as soon as the tyres lose grip you fall over).

In terms of physics, it’s this.

On an MTB, you want the bike leant over more to get it onto the knobblies on the edge of the tyre for more grip.

Racing motorbikes hang off the inside so that the bike is more upright to avoid grounding out.

But it’s also to do with the consistency of the grip. A road bike doesn’t just slide, you have to break the traction between the tyre and road and that takes some doing, and it happens consistently, so you ride to maximize speed by leaning as far as possible, then hanging off a bit further.

On a MTB or MX style bike, there’s less consistent grip, so by standing ‘over’ the bike when it slips, it comes up towards you, you can push is down again and find a balance. on the motorbike you don’t have that ability when hung off the inside (google: high side crash, which is what happens when traction is broken for a split second on a motorbike, the bike moves away from the rider, regains traction when the rider instinctively shuts the throttle, then fires him/her over the top like a catapult).

Engine, init.

Bloody heavy thing, very low down. Low centre of gravity. Needs to be kept as near directly above the contact patch of the tyres as possible. Hence rider leans, bike doesn’t (as much).

Rider on MTB. Bloody heavy thing, very high up. High centre of gravity. Needs to be kept as near directly above the contact patch of the tyres as possible. Hence bike leans, rider doesn’t (as much).

This arrangement also has the advantage of being able to react to sideways sliding.

This the conclusion I reached from armchair thinking on this once (after watching THAT Fabien Barel video that made me realise I’d been doing pretty much everything wrong on an MTB for ever).

you have to haul a motorbike over when going fast

erm – there’s absolutely no need to be “hauling” anything – how exactly are you steering?????

Rachel

Hmm

all those that think you steer anything two wheeled by shifting your weight need to find a big motorbike and a long car park then try and get it to turn without touching the bars. Its quite entertaining (more to watch).

anything two wheeled is always going to require a steering input to turn not a weight shift. The fact is that key contact points for a rider tend to be the bars so if you use them as leverage to shoft your weight its possible to think that the weight shift is responsible for the turn when in fact its tha hauling on the bars to shift the weight that causes a counter steer input.

the orignal piunt about lean in vs lean on is largely about tyre contact patch and the effect that it has on grip Supermotos are an odd exception and largely tend to have a stylised off road riding bias where as on tarmace they can go either way (in or on). Its also the fact that supermoto riders tend to think of themsleves as gods capable of “backing it in” anywhere (normally those racing supermoto at a high level are pretty close to deity status).

You can either turn by initiating countersteer through a weight shift or by turning the bars. Much of the turning force then comes from tyre camber thrust. So you can absolutely steer a two wheeled vehicle without turning the bars directly – how do you think anyone manages to ride no-handed otherwise?

Practicing a quick lap I got my knee down on the push bike, followed by my leg, arse, hip, ear, hip (other side), etc………I wouldn’t recommend it..

On a MTB or MX style bike, there’s less consistent grip, so by standing ‘over’ the bike when it slips, it comes up towards you, you can push is down again and find a balance.

Not following this. Agree that the grip off road is less consistent, but whatever the surface, the bike is going to fall over more once it starts to slip. Sitting up might help you get a foot down when it does, as per the MX rider in the photo above.

Bloody heavy thing, very low down. Low centre of gravity. Needs to be kept as near directly above the contact patch of the tyres as possible.

Why do you think that’s important?

Once in a turn, the sum of forces acting on the CofG (gravity plus apparent centrifugal) will pass through the contact patch. If it doesn’t the lean angle will change. By moving your weight around you can make the bike lean a bit more or a bit less, but the overall lean of rider + bike remains the same.

Once in a turn, the sum of forces acting on the CofG (gravity plus apparent centrifugal) will pass through the contact patch. If it doesn’t the lean angle will change. By moving your weight around you can make the bike lean a bit more or a bit less, but the overall lean of rider + bike remains the same.

Literally no idea what you are going on about. A diagram might help though.. 🙂

Why do you think that’s important?

Well… for a bit of fun. I drew a really bad diagram below that conveys my thoughts on this. I’m not in any way qualified in this area (did A-level physics once), but the logic (as a motorbiker and MTBer) sorta seems to make sense to me. Have fun with it.. 😆

something not mentioned before: suspension angle/ cornering surface. the road motorcyclist is cornering against a horizontal surface. if he’s at 60 degrees to the road and hits a bump, a lot of the force from the bump is going to push his tyre straight up in the air, rather than in the direction of the suspension travel. If he minimises the angle of bike lean for a given speed, (by hanging his body off the inside) he maximises the ability of the suspension to react to bumps.

Extreme cornering angles on dirt bikes usually come with camber or ruts, so bumps are encountered more in line with suspension travel, so keeping the bike upright isn’t as important as ability to control a slide.

It’s all a compromise though, some road racers have a more upright stance, body across the tank, for the slide-catching reason (possibly going back to Schwantz and Doohan here), some change from bike to bike depending on feel, and what works and what doesn’t: IIRC, the first proper hanging off the bike was done by Kenny Roberts senior, when he found out mid weekend that it was the only way he could get the new bike round corners. then there’s supermoto, where they’re on tarmac, but controlling slides is the most important thing to maximise, so they’re more upright, feet out.

Ground clearance isn’t a major reason with modern race bikes, there’s loads of clearance, and racers hang off in loads of corners that don’t get close to worrying the bodywork/footpegs/exhaust/

no_eyed_deer:

Once in a turn, the sum of forces acting on the CofG (gravity plus apparent centrifugal) will pass through the contact patch. If it doesn’t the lean angle will change. By moving your body weight around in relation to the bike you can make the bike lean a bit more or a bit less, but the overall lean of rider + bike remains the same.

any easier?

Literally no idea what you are going on about. A diagram might help though..

The image on this page makes it quite clear.

There’s a gravitational force pulling the bike+rider over labelled “mg” and a centrifugal force pulling the bike+rider to the outside of the bend (mv^2/R). You can treat those two forces as acting on the combined centre of gravity of the bike+rider, which because the rider is hanging off the left is somewhere to the left of the centreline of the bike (I think the dot in the photo probably exaggerates how much effect an 80kg rider has on the overall CofG).

If you add the two forces together (i.e. stick one force arrow on the end of the other) you’ll end up with a line that goes from the CofG straight towards the contact patch i.e. the direct opposite of the big diagonal arrow. If the two arrows aren’t exactly opposite, the bike will fall one way or the other.

The photo also gives a good idea of why the rider is hanging off. If he sat straight on the bike, the bike would have to be leaned over more to make it around the same corner at the same speed, and the bike would hit the ground.

EDIT: this image is probably clearer:

…awesum! 😀

…and do we have the mountainbiking / motocrossing version of this diagram..? 🙂

This is like airplane on a treadmill.

This diagram is broadly correct. Although of course cornering is “fictitious” from our point of view, it is actually friction acting on the tyre at road level. But it does get confusing if we do it like that

So in an ideal corner we have 2 things to get right. This diagram and we have camber thrust steering. The inside of the contact patch is closer to the wheel axis than the outside. This makes the bike want to move round a corner of a certain radius. A push bike going round the same radius corner more slowly wants the lean angle of the tyre to about the same but with centre of gravity much closer to the tyre patch. This will keep the resultant pointing through the tyre patch