2018 FIM Moto GP World Championship

[Andres125sx]

So downforce doesn't help at braking? Funny to hear that at a F1 technical forum...

Funny or not, bikes are far from F1 cars, their rear wheel can literally jump while braking if they take a bump because maybe 90-95% of the weight is at the front wheel while braking, so DF at the front does not help, if it would be at the rear it would be a completely different matter, but that´s not the case

I´ve read that´s one of the problems of Pedrosa in MotoGP, he´s too light and can´t load the rear end at the brakings so he literally can´t brake as hard as heavier riders, his read wheel loose contact sooner

F1 cars don´t have any problem of a jumpy rear end, it becomes lighter too but not to the point the wheels can loose contact with tarmac as we see on MotoGP (in F1 brake balance is around 55-45% or 60-40% as much, front-rear, wich is an evidence the rear end is more planted), and the DF is more balanced so it also aids keeping the rear planted

Got references for those assertions, Andres?

Reference about MotoGP rear wheel jumping under braking?
Or about F1 brake bias?

I´m amazed you´re asking for references about these obvious assertions, but if you need it here they are:


Or even better, look at this video, how many turns of the rear wheel while in the air?

About brake bias, at this track Hamilton toggle during the lap from 58.5 to 60 (front percentage)

As stated, very little rear brake is used, ('cept to help with cornering, as previously - & correctly, noted),
& indeed, several expensive ( slipper clutch/electronic over-ride) 'fixes' - were needed to reduce unwanted
'engine braking' effects from the high inertia big 4T engines, too.. as it happens..

Obviously, just as in F1, added downforce via aero-means - allows for harder braking to be transmitted to the
front tyre contact patch.. but.. sans anti-lock systems - it is fully incumbent on each rider to carefully modulate
the pressure applied, as the aero-downforce drops - with the speed..

(I´ve skiped your usual offensive comments)

Sorry but you´re confusing different things. They barely use any rear brake because the rear wheel is almost on the air, if not completely as shown above, so any rear brake input will only lock the wheel, stall the bike, and cause a crash. That´s the reason they had to reduce unwanted engine braking effects, any engine retention can cause a lock and the engine stalling. Not good.

Ducati´s longer wheelbase OTOH reduce this problem (so Ducati riders might use the rear brake more than their rivals), but magnifies a different one, steering while entering the corner, as longer wheelbase is more stable, but less agile, so they need to use the rear brake to cause some oversteering, or reduce understeering.

But DF while braking, if located at the front end, is useless. No bike need anti-lock systems on dry conditions (on tarmac!), as the limiting factor is not the front wheel grip, but the rear wheel becoming too light, jumping, and moving sideways causing serious stability problems to the rider

This is far from the most scary braking I´ve seen, but it´s the best I found on a quick search, I hope you get the idea (sorry you need to click for watching on youtube)


So DF at the front end, for braking, is useless. They´d need DF at the rear end to keep the rear wheel planted so they can hit the front brake harder and improve braking, but nowadays, unlike F1, front wheel grip while braking is not the problem, it´s the rear wheel becoming too light

[etusch]

2,46 sec of this video was one of scary moment.
.

[etusch]

This video for bike aero. I couldn't watch. I will watch when I have time

[Nonserviam85]

Funny or not, bikes are far from F1 cars, their rear wheel can literally jump while braking if they take a bump because maybe 90-95% of the weight is at the front wheel while braking, so DF at the front does not help, if it would be at the rear it would be a completely different matter, but that´s not the case

I´ve read that´s one of the problems of Pedrosa in MotoGP, he´s too light and can´t load the rear end at the brakings so he literally can´t brake as hard as heavier riders, his read wheel loose contact sooner

F1 cars don´t have any problem of a jumpy rear end, it becomes lighter too but not to the point the wheels can loose contact with tarmac as we see on MotoGP (in F1 brake balance is around 55-45% or 60-40% as much, front-rear, wich is an evidence the rear end is more planted), and the DF is more balanced so it also aids keeping the rear planted

F1 have a weight shift under braking of around 10%. I’m guessing that a MotoGP bike is probably nearer 50%. I can find a wheelbase figure but not CG height, so I can’t do a calc.

Another difference is that the drag vector during braking on an F1 car is around CG height and so doesn’t make much contribution to balance change. When a MotoGP rider sits up for braking the drag vector will rise and so help reduce forward weight transfer. This may be another issue for a short rider, such as Pedrosa, since he doesn’t lift the drag as high, and he can’t shift his weight as far rearwards as taller riders because of arm length. Rossi has always been regarded as good under brakes, perhaps his stature helps.

I’ve never really thought about the physics of bikes, so I may be well off.

Interesting, I had never considered drag vector influence while braking, not sure if accurate, but to me it makes perfect sense

Sorry mate, from your comments it is obvious that you have never ridden a superbike motorcycle

[etusch]

[J.A.W.]

Funny or not, bikes are far from F1 cars, their rear wheel can literally jump while braking if they take a bump because maybe 90-95% of the weight is at the front wheel while braking, so DF at the front does not help, if it would be at the rear it would be a completely different matter, but that´s not the case

I´ve read that´s one of the problems of Pedrosa in MotoGP, he´s too light and can´t load the rear end at the brakings so he literally can´t brake as hard as heavier riders, his read wheel loose contact sooner

F1 cars don´t have any problem of a jumpy rear end, it becomes lighter too but not to the point the wheels can loose contact with tarmac as we see on MotoGP (in F1 brake balance is around 55-45% or 60-40% as much, front-rear, wich is an evidence the rear end is more planted), and the DF is more balanced so it also aids keeping the rear planted

Got references for those assertions, Andres?

Reference about MotoGP rear wheel jumping under braking?
Or about F1 brake bias?

I´m amazed you´re asking for references about these obvious assertions, but if you need it here they are:
https://s3-eu-west-1.amazonaws.com/cras ... k=yExCV0Bd

Or even better, look at this video, how many turns of the rear wheel while in the air?
https://www.youtube.com/watch?v=tpI2S3GQ-gA
About brake bias, at this track Hamilton toggle during the lap from 58.5 to 60 (front percentage)
https://vimeo.com/233704211

As stated, very little rear brake is used, ('cept to help with cornering, as previously - & correctly, noted),
& indeed, several expensive ( slipper clutch/electronic over-ride) 'fixes' - were needed to reduce unwanted
'engine braking' effects from the high inertia big 4T engines, too.. as it happens..

Obviously, just as in F1, added downforce via aero-means - allows for harder braking to be transmitted to the
front tyre contact patch.. but.. sans anti-lock systems - it is fully incumbent on each rider to carefully modulate
the pressure applied, as the aero-downforce drops - with the speed..

(I´ve skiped your usual offensive comments)

Sorry but you´re confusing different things. They barely use any rear brake because the rear wheel is almost on the air, if not completely as shown above, so any rear brake input will only lock the wheel, stall the bike, and cause a crash. That´s the reason they had to reduce unwanted engine braking effects, any engine retention can cause a lock and the engine stalling. Not good.

Ducati´s longer wheelbase OTOH reduce this problem (so Ducati riders might use the rear brake more than their rivals), but magnifies a different one, steering while entering the corner, as longer wheelbase is more stable, but less agile, so they need to use the rear brake to cause some oversteering, or reduce understeering.

But DF while braking, if located at the front end, is useless. No bike need anti-lock systems on dry conditions (on tarmac!), as the limiting factor is not the front wheel grip, but the rear wheel becoming too light, jumping, and moving sideways causing serious stability problems to the rider

This is far from the most scary braking I´ve seen, but it´s the best I found on a quick search, I hope you get the idea (sorry you need to click for watching on youtube)
https://www.youtube.com/watch?v=55wJ4dbIFfA

So DF at the front end, for braking, is useless. They´d need DF at the rear end to keep the rear wheel planted so they can hit the front brake harder and improve braking, but nowadays, unlike F1, front wheel grip while braking is not the problem, it´s the rear wheel becoming too light

Andres - your vengeful downvote propensity - yet again betrays a piquant touch of inadequacy - in understanding..

A momentary front brake lock up on an F1 car is 'no biggie' - but for a Moto GP machine, unless bolt upright, it is
a big deal.. & as shown by all the front-end low-side crashes on corner entry, its difficult to save..

Added tyre adhesion via aero downforce - does give the rider greater confidence to 'trail brake' into high-speed
curves, as J.L. stated, & as other members here, have duly pointed out.. &.."useless" - it.. is def' not..

Obviously you do not ride a hi-performance tarmac motorcycle &/or do not use the front brake effectively..
Or you'd have an idea of how wrong your ideas of braking dynamics & weight transfer, really are..

[Andres125sx]

F1 have a weight shift under braking of around 10%. I’m guessing that a MotoGP bike is probably nearer 50%. I can find a wheelbase figure but not CG height, so I can’t do a calc.

Another difference is that the drag vector during braking on an F1 car is around CG height and so doesn’t make much contribution to balance change. When a MotoGP rider sits up for braking the drag vector will rise and so help reduce forward weight transfer. This may be another issue for a short rider, such as Pedrosa, since he doesn’t lift the drag as high, and he can’t shift his weight as far rearwards as taller riders because of arm length. Rossi has always been regarded as good under brakes, perhaps his stature helps.

I’ve never really thought about the physics of bikes, so I may be well off.

Interesting, I had never considered drag vector influence while braking, not sure if accurate, but to me it makes perfect sense

Sorry mate, from your comments it is obvious that you have never ridden a superbike motorcycle

We´re talking about MotoGP, not superbike. Did you notice for how long they keep the front brake lever fully applied before releasing it a bit for corner entry?


Anycase, as I´ve stated previously, I was asking for sources to learn about the subject, my reply was to JAW who is very fast criticizing people for not being technical, while he barely add any technical bit. He´s very technical saying people how ignorants they are and how wise he is, that´s all, but meanwhile he even misses some basics about motorcycling

[Andres125sx]

Etusch, thanks for teh videos, will watch later

[henry]

https://www.youtube.com/watch?v=Y3nEbwOTN3g

Thanks for this video, some interesting facts.

He mentioned the CG as being around handlebar height, and the coefficient of friction about 1, a little higher for racing bikes.

With no aero forces, Assuming a 50:50 weight distribution, a wheelbase 1.5 m and CG height 0.75m a CoF of 1 would put all of the weight on the front wheel, and the back would lift under any disturbance.

With aero, but no wings, the drag vector is potentially below the CG when the rider is crouched and would tend to keep the front wheel down under acceleration particularly at high speed. Any downforce or drag from the wings would help that.

Under braking the rider raises the CG by sitting up, but also lifts the drag vector. I don’t know any values that would allow the calculation of the effect on weight distribution. The additional downforce at the front would increase the braking potential, but since the braking force is limited by rear wheel lift it probably can’t be exploited.

From the video the explanation that the downforce would help in cornering by reducing the lean angle would support the claim that it might be useful in trail braking, albeit at the cost of rear end corner grip. Whether that gives more or less confidence to the rider is down to others.

The practise of hanging out one leg during braking would appear to offer a similar benefit. The leg position will move the CG in to the corner, and together with the drag from the leg will tend to rotate the bike into the corner without the need to lean as much, improving the contact patch available for braking.

[Tommy Cookers]

[quote=henry]
With aero, but no wings, the drag vector is potentially below the CG when the rider is crouched and would tend to keep the front wheel down under acceleration particularly at high speed. Any downforce or drag from the wings would help that.[/quote]

IMO
the drag vector always contributes towards reducing front contact load and increasing rear contact load
because its effect is due to its height above the track not height above/below the CG
ie drag doesn't alleviate the effect on contact loads of acceleration - it adds to the effect

fwiw I imagine .....
front braking potential is not clipped by the rear contact load falling to zero - they're matched at the design stage
Mr Pedrosa's weight limits him via needing more bike lean (for equally competitive combined bike+rider CG angle)
his braking should be competitive and his straightline acceleration greater (or he can use less fuel for equal acceleration)
he should have a shorter wheelbase ie the rear wheel forward ie rider-normalised to same behaviour as Mr Marquez's bike
(EDIT - this braking bit is wrong as Andres later says)

yes this front 'boxkite' aero DF is quite clever - and presumably there's a DF part to internal airflow
though DF from a rear wing (tried by one rider) could easily act well ahead of the wing (this of undesirable in aviation)

[Nonserviam85]

I think Guys you are missing a couple of fundamental aspects of motorbike racing. The target is to have the best front traction in order to carry the highest entry speed. To achieve that you need to load the front in order to increase traction in the front tyre. This is always mandated by the rebound and stifness settings of the front fork. This dictates mostly the lift of the rear. If the rear lifta it is a combination of the rider overbraking and reaching the dive limits of the front. However you cannot go extreme to the front stiffness because then you will lose agility and ability to change direction. So everything is a compromise based on rider style and track layout. Believe me, this front winglets help a lot for loading the tyre during braking especially on corner entry, wheremost of the lap time is gained.

For your interest the rider rises to act as an aerobrake to help with shortening the brake distance. But this is very stength demanding and this is one of Pedrosa’s issues (second being the strength required to change direction fast, i.e). If you check closey the drive rises but also moves forward in order to load the front tyre. Again more loading, more patch contact better performance but always within limits.

[Tommy Cookers]

[quote=Nonserviam85]
....... If the rear lifta it is a combination of the rider overbraking and reaching the dive limits of the front....[/quote]

so you're saying the rider can't use the maximum braking that is available because that would lift the rear and cause trouble ?
ie the designer is choosing to settle for less deceleration than the tyre could give - what I called clipping

[henry]

With aero, but no wings, the drag vector is potentially below the CG when the rider is crouched and would tend to keep the front wheel down under acceleration particularly at high speed. Any downforce or drag from the wings would help that.

IMO
the drag vector always contributes towards reducing front contact load and increasing rear contact load
because its effect is due to its height above the track not height above/below the CG
ie drag doesn't alleviate the effect on contact loads of acceleration - it adds to the effect

....

I think I agree with what you say here, under acceleration, but I need to have a further think about braking and the other points you raise, which are interesting.

[Andres125sx]

Just to clarify, when I said DF does not help while braking, I´m thinking about braking phase, ie while the bike is straight and brakes are fully applied. Once they lean the bike to the point they need to release the brakes a bit, to me that´s a different phase, corner entry. In this phase is where I get lost and would like to learn about DF effects.


Anycase I must say since winglets are at the front of the bike, but a bit behind the front wheel center (footprint?) as explained at the end of second video posted by etusch, they may add some DF at the rear wheel too. I guess with current winglets DF transmitted to the rear wheel might be negligible, but since this is MotoGP and they´re constantly on the limit any bit might be noticeable for riders

[Andres125sx]

This video for bike aero. I couldn't watch. I will watch when I have time
https://www.youtube.com/watch?v=3Zu5_7lXFvQ&t=68s

Thanks for posting again.

OT, but I´m surprised about those drag figures at the beginning of the video. Does a half sphere really have less drag than a full sphere? I´m assuming the flat part of the half sphere is at the back. That does not increase turbulence and drag compared to a complete sphere?