Race tire mu, non aero car

[Eager Learner]

If a car with zero lift is able to corner at 2.5G on a flat circuit, does that mean its tyres have a mu of at least 2.5?
Go karts are often measured at around 2.5G sustained but then I thought I read somewhere else that F1 tyres have mu only around 2.0?
How can go kart tyres have higher mu than F1?

What is the highest confirmed mu of modern F1 tyres?

[Tommy Cookers]

the thread 'Acceleration and braking figures at different speeds' (currently on P.2) in General Chat is useful
(I am an old fool who can't even give you a link to it)

my understanding is that these g values are mostly raw data, just peak amplitudes of accelerometer signals uncorrected for body attitude (roll, yaw etc), and not even broken down into centripetal and tangential components

[Eager Learner]

thank you but the numbers I have seen have been broken up into centripetal and tangential components and the pure centripetal force is already 2.5G and sustained over a few seconds too. There is almost zero roll.

[Tommy Cookers]

Define: Tyre Grip in this section this page is full of opinions and interesting (also look at 'similar thread' list at foot of that thread, or search - sorry if this sounds a bit irritating)

there are arguments about the tyres biting into the track ('geared grip', it has been called)
ie actual grip being more than expected Mu

surely a kart is more or less overturning at 2.5 g ?
can your values be confirmed by calculation from corner radii and speeds ?
(some would say !)

motorcycle lean angles suggest less than 2g (some lean is used to yaw the wheels etc against gyroscopic reaction)

[olefud]

If a car with zero lift is able to corner at 2.5G on a flat circuit, does that mean its tyres have a mu of at least 2.5?
Go karts are often measured at around 2.5G sustained but then I thought I read somewhere else that F1 tyres have mu only around 2.0?
How can go kart tyres have higher mu than F1?

What is the highest confirmed mu of modern F1 tyres?

Isn’t mu the slip ratio of a tire, i.e. a locked tie has a mu of unity and very little traction? While cornering traction is optimized at some mu that varies from tire to tire, the magnitude of the traction isn’t a function of mu. Or perhaps I’m thinking of another mu.

That said, karts have tenacious traction. But I’d be surprised if they out G a F-1.

[gato azul]

Isn’t mu the slip ratio of a tire, i.e. a locked tie has a mu of unity and very little traction? While cornering traction is optimized at some mu that varies from tire to tire, the magnitude of the traction isn’t a function of mu. Or perhaps I’m thinking of another mu.

The coefficient of friction (COF), often symbolized by the Greek letter µ, is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together.

CoF = Fs/Fn

Fs = Side Force ( in the context of the tire/OT)
Fn = Normal Force/load on the tire ( weight + downforce + inertia effects/load transfer etc.) a.k.a. vertical load/force

as for the OT, not sure about the actual figures, it's possible, but someone with real data will need to confirm this.
One thing which will make it "easier" for the kart to extract a higher value of CoF compared to a F1 or other race car is the
low(er) weight of the kart compare to the car. As CoF tends to reduce with and increase in vertical force/load ( see "load sensitivity of tires" etc.)

[Jersey Tom]

How can go kart tyres have higher mu than F1?

F1 tires aren't the highest grip tires out there. However, I'd be surprised if karts sustained 2.5G lat.

[olefud]

Isn’t mu the slip ratio of a tire, i.e. a locked tie has a mu of unity and very little traction? While cornering traction is optimized at some mu that varies from tire to tire, the magnitude of the traction isn’t a function of mu. Or perhaps I’m thinking of another mu.

The coefficient of friction (COF), often symbolized by the Greek letter µ, is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together.

CoF = Fs/Fn

Fs = Side Force ( in the context of the tire/OT)
Fn = Normal Force/load on the tire ( weight + downforce + inertia effects/load transfer etc.) a.k.a. vertical load/force

“mu” is used as a term of art with regard to anti-locking brakes. I think you’re correct in the lower case Greek letter for CoF was intended –though CoF and g forces are not really synonymous.

[jtc127]

How can go kart tyres have higher mu than F1?

F1 tires aren't the highest grip tires out there. However, I'd be surprised if karts sustained 2.5G lat.

TAG and shifter kart chassis peak around 3G. I just sold my formula car and I'm buying a TAG. I need to hit the gym, I'm not in good enough shape to handle those forces for 30 minutes at a time.

As said above, tires are load sensitive. The friction coefficient decreases as vertical load increases. This means the F1 tire's coefficient of friction is lower during high speed corners than it is in lower speed corners due to the downforce.

[gato azul]

“mu” is used as a term of art with regard to anti-locking brakes. I think you’re correct in the lower case Greek letter for CoF was intended –though CoF and g forces are not really synonymous.

not sure what you mean with "term of art", it is the greek letter which is normally associated with a coeficient of friction.
This can be friction between the tire and the road/track or between the brake pad and the brake disc.

From your first post and your ABS reference, I guess (but maybe I'm wrong), that you had something like this in mind.



but that's not really what the OT poster asked. The COF (mu) does not only depend on vertical load, it will change due to a variety of factors, but this is beside the point, as far as the OT is concerned.

In the most simple way to look at it, you have a mass (of the kart) and a lateral acceleration, which in this case is said to be 2.5G (24.525 m/s^2 --> based on an average acceleration due to gravity of 9.81 m/s^2), therefore you will need a centripetal force (N) reacted/generated by the tires of m (kg) x 24.525 m/s^2 [F=m x a].
As we assume a none downforce/lift vehicle and a flat track (as defined by the OP) the vertical force (N) on the vehicle/tires is only the weight of the kart m(kg) x 9.81 m/s^2.

As m is equal in both cases, the CoF of the tires in lateral direction will need to be 2.5, as the centripetal force needed to achieve the lateral acceleration of the mass is 2.5 times the vertical force acting on the tire(s).
Sure, that is a very simplified "lumped model" but will hold true nonetheless.
How the tire achieve this CoF and which other factors affect it, is a different matter.

The CoF (mu) is a measure for the "efficiency" of the tire to translate a vertical force into a lateral force if you like (or longitudinal if we talk about braking/driving).

Even if the efficiency of the tire reduces with an increase in vertical load, adding downforce (a "mass less" force) will still help to achieve higher lateral accelerations (larger centripetal forces) for a given vehicle (mass), as seen in the F1 example.

though CoF and g forces are not really synonymous

I agree, but I never said they were, but as the OP specified a none downforce vehicle on a flat track, CoF (mu) is the parameter which will affect/govern the max. lateral acceleration of a given mass.

[olefud]

“mu” is used as a term of art with regard to anti-locking brakes. I think you’re correct in the lower case Greek letter for CoF was intended –though CoF and g forces are not really synonymous.

not sure what you mean with "term of art", it is the greek letter which is normally associated with a coeficient of friction.
This can be friction between the tire and the road/track or between the brake pad and the brake disc.

We’re doing a “mu’s on first” here. Mu, as opposed to σ, is a term of art. No disagreement with the substance of what you’re saying.

www.motortrend.com/.../1207_launch_control_vs_traction_control/

[Jersey Tom]

How can go kart tyres have higher mu than F1?

F1 tires aren't the highest grip tires out there. However, I'd be surprised if karts sustained 2.5G lat.

TAG and shifter kart chassis peak around 3G.

Ah yes, but peak values are a lie. Roll and yaw dynamics with non-fixed reference frames add all sorts of fun. In any event, 2 is a pretty sport number. 2.5 is huge.

Suffice to say one thing we can agree on is that F1 tires aren't the stickiest rubber out there.

[ubrben]

Mu is a perfectly acceptable term for friction from a tyre in any context.

I suspect a non-downforce assisted 3G cornering is a quirk of the data. Corrected for roll? Low past filtered to remove inertial effects?

Ben

[olefud]

If a kart made such numbers, it could be a result of light weight and optimizing all parameters which, as JT points out, is not done in F-1. The light weight would allow ultra gumball tires that in conjunction with a smooth track with a high density of cogging openings could produce 3-D “keying” grip, i.e. into rather than on the track.

[ubrben]

If a kart made such numbers, it could be a result of light weight and optimizing all parameters which, as JT points out, is not done in F-1. The light weight would allow ultra gumball tires that in conjunction with a smooth track with a high density of cogging openings could produce 3-D “keying” grip, i.e. into rather than on the track.

I'd be surprised. 2G maybe, 2.5G unlikely, 3G not a chance.

Ben