Racing Motor Cycle Adhesion

[Peter Cook 6Participant @petercook6]

Thanks again for the educational discussion. I think I will follow Arthur C Clark’s position “Any sufficiently advanced technology is indistinguishable from magic” and stick with magic controlled by DC31K’s nuts.

[DiogenesParticipant @diogenes]

Tony Foale has interesting comments relating to a possible reason for the stupendous power outputs of modern race-bikes, towards the bottom of this article..

Tyres and how they work

[old mart]

On old mart Said:

… What exactly gives the extreme cornering grip is hard to answer as it is not an exact science, one tyre manufacturer referred to “geared grip”between the road surface and the tyre.

…

To be pedantic, in this case science gives the right answer in that it establishes without doubt the maximum lean angle possible before a known tyre on a known road surface will slip.

The inexact bit isn’t the science, it’s the technology needed to achieve maximum performance: not easy!   And even when the technology is top-notch approaching the theoretical limit in practice is dangerous because there are so many variables – like the weather!

Duncan’s formula is valuable because it sets the engineering target and enables customers to spot the worst Snake Oil and wishful thinking.   And the science allows mechanised ABS and traction control to outperform human drivers.   Not to mention efficiency and emissions control.

Dave

 

 

[duncan webster 1Participant @duncanwebster1]

If the aerodynamics of the gap between the fairing and the road apply a vertical down force between the centre of contact with the road and the centre of gravity I fancy you can do rather better than my previous post would suggest. I must admit I’d missed that possibility

All this talk of countetsteering leaves me wondering how I ever used to ride motorbikes. I just did it. If you go hands off and hit the left hand bar forward with your hand, the bike tries to turn right, and so it leans over to the left (lack of a centripetal force to stop it). The steering geometry then sorts everything out and you curve off the the left, the opposite direction to where you hit the bars. For a bet I once entered a roundabout, went all the way round and left back up the same road without touching the bars. As I say, no idea how, just did it. Must have been shifting weight around I suppose. Then returned the twist grip to snapping shut, didn’t like the friction thing which you could adjust to keep it open.

[duncan webster 1]

On duncan webster 1 Said:

If the aerodynamics of the gap between the fairing and the road apply a vertical down force between the centre of contact with the road and the centre of gravity I fancy you can do rather better than my previous post would suggest. I must admit I’d missed that possibility

Probably they do better largely because the actual coefficient of friction for MotoGP tyres is closer to 2.0 than the 1.2 you extrapolated across from F1 car tyres. Today’s street motorcycle tyres have a coefficient of friction of circa 1.2 and are nowhere close to as sticky as track tyres, let alone the creme de la creme MotoGP tyres. As I don’t know the formula you used, not sure how much lean angle difference there would be between a coefficient of 1.2 and 2.0 but I feel sure it would largely explain the actual lean angles regularly recorded by data loggers in MotoGP of up to 68 degrees or so.

F1 car tyres have to handle a lot more weight and a lot more horsepower than bike tyres without shredding and melting away before race end, so probably use a harder compound than the bikes. Race tyre compounds are a constant battle between soft for grip vs hard for longevity. Softer stickier rubber is great for cornering but no good if the rider/driver has to pull in for a tyre change before the race ends and his competitors don’t because they have a harder longer-lasting compound.

But as you say,there could be other factors. The new fairing design is interesting, using ground effect between the side fairings and the ground when heeled over, based on the belly pan designs of F1 cars. The air passes through a sort of venturi-shaped space, increasing its velocity and reducing its pressure, thus “sucking” the bike down towards the track surface and putting more downward force on the tyres and thus increasing friction between tyre and track.

As for counter-steering, LOL. Has been endlessly debated on countless motorcycle forums and YouTube videos already, without an agreed conclusion.  Along with synthetic vs mineral engine oil, it is the equivalent of the ME forums’ Chinese vs Myford lathe debate.

Here is the expert advice from a guy who knows, with some interesting demonstrations on a bike with the handlebars mounted so they don’t turn the forks.

The Tony Foale article Diogenes posted a link to above gives an idea of the complexity of motorcycle chassis design and physics, just a small part of his whole book on the subject. Reading a few sample book pages on the linked site will get most of us scratching our heads!

 

[duncan webster 1]

On duncan webster 1 Said:

Then returned the twist grip to snapping shut, didn’t like the friction thing which you could adjust to keep it open.

Stiff twist grip was useful to me in my early days as a student in the mid ’70s. Riding a Vespa 90 at its maximum speed of 42mph on the M5 from Birmingham down to mid Devon was quite a miserable experience in the colder parts of the year. I could. however, open the throttle, hunch up and wrap my arms around me and wait for the miles to go by. My record is just over 90 miles no-handed from the M5 junction to Gordano services. That’s where I had to buy another gallon of petrol to last for the other half of the journey. 😀

[Taf_PembsParticipant @taf_pembs]

Ah the tones of Mr Julian Ryder.. very very knowledgeable man on pretty much anything motorcycling. When he was commentating for Eurosport with Toby Moody on MotoGP, World Superbike etc that was the best.. I think they got more excitable that the team!! Far better than most of the current ones.

 

I remember having a ‘discussion’ in my old bike shop with a chap about counter steering –  ‘I don’t do that’ he insisted. I tried to explain that we as humans riding anything, motorbike / pushbike etc, had to counter steer or we wouldn’t turn. We do it without realising, light counter steer to get the thing into the corner then normal steer to prevent it falling on it’s side and varying degrees of both to manage the turn (along with weight movement etc etc and lots of physics!).

He still flatly insisted that he most certainly didn’t ride like that and did not counter steer.

I fairly quickly gave up and agreed that he didn’t and only rode on motorways without leaving or joining.. he didn’t understand that 🙄😁

 

However, DC31K has most certainly summarised how in reality it works!

 

[Taf_Pembs]

On Taf_Pembs Said:

..
However, DC31K has most certainly summarised how in reality it works!

 

As the Americans succinctly put it: “cojones”.

[duncan webster 1Participant @duncanwebster1]

I’m surprised no-one noticed my deliberate mistake early in this thread. Must not have had my thinking head on. The formula should have been

arc tan (coeff friction)

so 1.6 gives 58 degrees, 2 gives 63 degrees. 1.6 is the figure I found for F1 tyres. This does not allow for aerodynamics or the rider leaning off the bike, and as I said before is not the centreline of the bike but a line twixt contact patch and centre of gravity.

[HopperParticipant @hopper]

The rider leaning off the bike decreases the angle the bike has to lean over to get around the corner at the same speed. So if the bike’s data logger is showing the bike itself is leaning at 68 degrees, and the rider is “hanging off like a gibbon” then the angle of lean to the C of G will be even more than 68 degrees. Pretty crazy stuff.

Tyres may in fact be sliding at that point, but under control of the extremely skilled rider. (Skills mere mortals can merely dream of!). So co-efficient of friction has been exceeded.  Track camber would come into it too. Banked corner vs flat corner vs off-camber corner makes a difference. I would bet that Marquez’s 68 degree leans were happening on slightly banked corners and almost certainly not on off-camber corners.

[Author]

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