Track forum general chit chat

[shaddy]

Originally Posted by F80Speed77

Good stuff! Track Night In America is the best deal around.

As far as tires, get Hankook RS4's for track day fun...
Also Bridgestone stopped production on the RE71R so they are going to start to get pretty limited in the more popular sizes.

Yeah the entry fee for this event was pretty low and it was a perfect track IMO to get started! No walls just open grass if any mistakes were made.

I don't think there are RS4s in 19s for the size I'm needing And thanks for the info on RE71Rs. There are not many 200tw 19 inch options (AD08 R?), may be an excuse for me to get a 18 inch setup

[Suds]

I have a set of 4 x 513M Rear 10” rims with new Bridgestone RE-71 tires in 275/35/18 tires, square set up that I was going to use for a wet track day. If there is any interest let me know.

Originally Posted by shaddy

Yeah the entry fee for this event was pretty low and it was a perfect track IMO to get started! No walls just open grass if any mistakes were made.

I don't think there are RS4s in 19s for the size I'm needing And thanks for the info on RE71Rs. There are not many 200tw 19 inch options (AD08 R?), may be an excuse for me to get a 18 inch setup

[F80Speed77]

Originally Posted by SYT_Shadow

What???? Can you please speak into my good ear?

Lol, only 500 or so 275/35/19 left in the US other sizes are dwindling as well. Molds are deleted, they are not bringing the RE71RS that is in Japan to the US.

The Falken RT660 is coming out with more 19" sizes over the winter along with the Advan A052.

Nexen is allegedly releasing a new tire in the spring of next year too.

[adc]

Originally Posted by F80Speed77

Yeah it was Dominion.

So oddly, he had a pretty similar thing happen to him as to what happened to me at Mid Ohio where the car starts to slide and you just can't get it to snap back no matter how much input you feed it. Luckily I had a ton more pavement to help get the car whoa'd down but I wonder if there is some sort of computer system that is taking over or the e-diff does something weird?

I’m not going to Dominion, and apologies to those here who do if what I’m about to say offends them. Several years back when it was about to open and the buzz was huge (I mean another track just an hour away from DC, really big deal!), I was at WGI and met an instructor who was a road safety engineer. He had given a free eval to Dominion owners as a thank you from a track enthusiast, in which he highlighted two dangerous areas on track. As memory serves, one was just before entering the underpass (too narrow essentially), another was a berm he said could propel the car airborne. Sure enough not even a year later I watched a video of a Mustang flying over that berm.

Now, safety may have been improved since, I have no way of knowing since I’ve never been. And the berm in question may be in a totally different area of the track than these esses. Lots of people go there from the DC area, since it’s so convenient. But personally, I’m not ever going there - there are so many places close to the concrete, I find it unnerving. Just my personal opinion and others may find it amazing. YMMV.


As to your situation, I’m guessing it’s just simply momentum. Max grip is constant, and once you are exceeding it if the rear swings around at 90mph as opposed to 30mph, momentum (and rotational force) is three times stronger, so the car will just keep on rotating. I think these high speed movements have to be caught on and neutralized much earlier - quick small corrections very early on.

[SYT_Shadow]

Originally Posted by F80Speed77

Lol, only 500 or so 275/35/19 left in the US other sizes are dwindling as well. Molds are deleted, they are not bringing the RE71RS that is in Japan to the US.

The Falken RT660 is coming out with more 19" sizes over the winter along with the Advan A052.

Nexen is allegedly releasing a new tire in the spring of next year too.

It's odd they wouldn't replace it. The death of a great tire, how sad

[jmg]

Originally Posted by F80Speed77

Lol, only 500 or so 275/35/19 left in the US other sizes are dwindling as well. Molds are deleted, they are not bringing the RE71RS that is in Japan to the US.

The Falken RT660 is coming out with more 19" sizes over the winter along with the Advan A052.

Nexen is allegedly releasing a new tire in the spring of next year too.

What on earth is going on?! Why?! Is it covid related?

[drroc]

Originally Posted by F80Speed77

Yeah it was Dominion.

So oddly, he had a pretty similar thing happen to him as to what happened to me at Mid Ohio where the car starts to slide and you just can't get it to snap back no matter how much input you feed it. Luckily I had a ton more pavement to help get the car whoa'd down but I wonder if there is some sort of computer system that is taking over or the e-diff does something weird?

If you play the video in slow motion, you will see that there is a moment when the driver hesitates to start going hand over hand to turn the steering wheel. That hesitation was enough to make the slide unrecoverable. I had a similar thing at Laguna. I started to slide, and I applied opposite lock. Once my hands crossed over so that I couldn't turn the steering wheel anymore, I had the oh shit moment and some brief hesitation before I started going hand over hand. By that point, it was too late.

However, catching high speed lift off/trail brake oversteer events is quite tricky.

[F80Speed77]

Originally Posted by SYT_Shadow

It's odd they wouldn't replace it. The death of a great tire, how sad

It is sad, from what I understand they are just letting RE71R stock die out over 2021 and should have a replacement at some point in 2022. The RE71RS was deemed not good enough for the US market and the contact I have at Bridgestone is pretty excited about what they have planned for their US replacement.

So if you have size you like maybe look into buying them early next year or put some in storage over the winter!

[SYT_Shadow]

Originally Posted by F80Speed77

It is sad, from what I understand they are just letting RE71R stock die out over 2021 and should have a replacement at some point in 2022. The RE71RS was deemed not good enough for the US market and the contact I have at Bridgestone is pretty excited about what they have planned for their US replacement.

So if you have size you like maybe look into buying them early next year or put some in storage over the winter!

Fortunately I have 4 sets at home, mounted and ready to go!

I look forward to its replacement. I wouldn't be surprised if it were as fast as the BFG R1

[F80Speed77]

Originally Posted by adc

As to your situation, I’m guessing it’s just simply momentum. Max grip is constant, and once you are exceeding it if the rear swings around at 90mph as opposed to 30mph, momentum (and rotational force) is three times stronger, so the car will just keep on rotating. I think these high speed movements have to be caught on and neutralized much earlier - quick small corrections very early on.

Yeah I was at around 90-100mph when I lost the car too and I think physics just took the wheel. It was 100% driver error in my situation and I was too slow to correct after being too confident in my drifting abilities lol.

[CanAutM3]

Originally Posted by adc

I’m not going to Dominion, and apologies to those here who do if what I’m about to say offends them. Several years back when it was about to open and the buzz was huge (I mean another track just an hour away from DC, really big deal!), I was at WGI and met an instructor who was a road safety engineer. He had given a free eval to Dominion owners as a thank you from a track enthusiast, in which he highlighted two dangerous areas on track. As memory serves, one was just before entering the underpass (too narrow essentially), another was a berm he said could propel the car airborne. Sure enough not even a year later I watched a video of a Mustang flying over that berm.

Now, safety may have been improved since, I have no way of knowing since I’ve never been. And the berm in question may be in a totally different area of the track than these esses. Lots of people go there from the DC area, since it’s so convenient. But personally, I’m not ever going there - there are so many places close to the concrete, I find it unnerving. Just my personal opinion and others may find it amazing. YMMV.


As to your situation, I’m guessing it’s just simply momentum. Max grip is constant, and once you are exceeding it if the rear swings around at 90mph as opposed to 30mph, momentum (and rotational force) is three times stronger, so the car will just keep on rotating. I think these high speed movements have to be caught on and neutralized much earlier - quick small corrections very early on.

I am not sure I fully follow you here when you say rotational force is 3 times stronger at 90mph vs 30mph. Since tire lateral grip is for the most part constant with speed, so is rotational force. IMO, the biggest issue with high speed oversteer is mostly due to the amount of distance travelled in a given time. At 3 times the speed, you need to react 3 times faster before going off. And if you hit, you hit 9 times as hard !

[adc]

Originally Posted by CanAutM3

I am not sure I fully follow you here when you say rotational force is 3 times stronger at 90mph vs 30mph. Since tire lateral grip is for the most part constant with speed, so is rotational force. IMO, the biggest issue with high speed oversteer is mostly due to the amount of distance travelled in a given time. At 3 times the speed, you need to react 3 times faster before going off. And if you hit, you hit 9 times as hard !

What I meant is the momentum of the rear of the car is directly proportional with the speed. If the rear starts to rotate at 90mph, it will have 3 times the momentum than at 30mph. Then again maybe I'm wrong, because the front of the car is also moving at 90mph, and maybe then what matters is the difference in momentum between the front and the rear. Anyway.

Your explanation - distance traveled - seems more intuitive.

[jmg]

Originally Posted by adc

What I meant is the momentum of the rear of the car is directly proportional with the speed. If the rear starts to rotate at 90mph, it will have 3 times the momentum than at 30mph. Then again maybe I'm wrong, because the front of the car is also moving at 90mph, and maybe then what matters is the difference in momentum between the front and the rear. Anyway.

Your explanation - distance traveled - seems more intuitive.

Momentum is a product of velocity and mass. Velocity is distance over time, so you are both right because they are all part of the same event: catastrophic loss of control.

[CanAutM3]

Originally Posted by jmg

Momentum is a product of velocity and mass. Velocity is distance over time, so you are both right because they are all part of the same event: catastrophic loss of control.

Not quite. When we are talking a bout a spin, it is about angular momentum. In the car's reference frame, the angular momentum from a spin is not affected by the car's longitudinal velocity.

[jmg]

Originally Posted by CanAutM3

Not quite. When we are talking a bout a spin, it is about angular momentum. In the car's reference frame, the angular momentum from a spin is not affected by the car's longitudinal velocity.

What you are saying is true, linear/lateral velocity is not part of angular momentum, angular velocity is. That is why a spinning top spins. With only gravity acting upon the object, it will not have movement in any other direction but down, hence it balances itself. So yes, the velocity of the car itself will not affect angular momentum. BUT, that is not the scenario adc described exactly. He is describing the force it takes to stop a spinning car. That scenario is an object with angular momentum AND velocity and thus linear momentum acting on another object–the road.

Angular momentum is a conserved quality just like linear momentum and when acting against another object, linear momentum and angular momentum are BOTH conserved. Linear momentum has an angular component when acting upon a rotating axis. The angular momentum of the car's point of contact (hopefully the wheels and not the car lol) will act against the angular component of the road relative to the car's rotating axis. Since the linear momentum of the road is p=mv where v is the velocity of the car (it's relative after all), then the car's speed (or the road's speed, relatively speaking) will indeed increase the net forces when the road and car act against each other.


Practical observation:

As track rats, we know tires can only do 100% of the work to one thing at a time... it cannot 100% brake AND 100% turn at the same time.

So if a car is SPINNING, there is both a load on the tires from the spin itself in the form of angular momentum, PLUS the linear momentum of the car's movement, in this case p=m*30mph.

Assuming the same angular momentum at 90mph, the tires also have to deal with p=m*90mph... an increase in load on the tires.

So like I said, adc and you were both kind right. Angular momentum itself does not increase as the speed of the car increases, BUT it takes MORE force to stop a spinning car if it's going faster because the tires have to deal with more load overall.

This is why it is catastrophic... more speed is more load to overcome, and less time to do it in because of the distance covered over time.

[CanAutM3]

Originally Posted by jmg

What you are saying is true, linear/lateral velocity is not part of angular momentum, angular velocity is. That is why a spinning top spins. With only gravity acting upon the object, it will not have movement in any other direction but down, hence it balances itself. So yes, the velocity of the car itself will not affect angular momentum. BUT, that is not the scenario adc described exactly. He is describing the force it takes to stop a spinning car. That scenario is an object with angular momentum AND velocity and thus linear momentum acting on another object–the road.

Angular momentum is a conserved quality just like linear momentum and when acting against another object, linear momentum and angular momentum are BOTH conserved. Linear momentum has an angular component when acting upon a rotating axis. The angular momentum of the car's point of contact (hopefully the wheels and not the car lol) will act against the angular component of the road relative to the car's rotating axis. Since the linear momentum of the road is p=mv where v is the velocity of the car (it's relative after all), then the car's speed (or the road's speed, relatively speaking) will indeed increase the net forces when the road and car act against each other.


Practical observation:

As track rats, we know tires can only do 100% of the work to one thing at a time... it cannot 100% brake AND 100% turn at the same time.

So if a car is SPINNING, there is both a load on the tires from the spin itself in the form of angular momentum, PLUS the linear momentum of the car's movement, in this case p=m*30mph.

Assuming the same angular momentum at 90mph, the tires also have to deal with p=m*90mph... an increase in load on the tires.

So like I said, adc and you were both kind right. Angular momentum itself does not increase as the speed of the car increases, BUT it takes MORE force to stop a spinning car if it's going faster because the tires have to deal with more load overall.

This is why it is catastrophic... more speed is more load to overcome, and less time to do it in because of the distance covered over time.

I love it when we start geeking out

Without going in depth into tire dynamics, the forces a tire is able to transmit are for the most part constant regardless of road speed. For example a given tire that is able to provide 1g of static friction is able to do so at 30mph and at 90mph, same concept applies to kinetic friction (tire 100% slipping). Taking threshold braking as an example, the tires are essentially able to provide the same braking force throughout the braking period yielding constant deceleration. The force the tire is able to transmit to change the car's momentum is not affected by the car's velocity.

At low speeds, if you are too slow to react, the car can get in pretty bad shape before you run out road, giving you more time to recover. Not the case at high speed.

So all that to say that no, no more force is needed to recover from a high speed spin. However, more speedy driver input is what is needed to avoid catastrophic consequences .

[jmg]

Originally Posted by CanAutM3

I love it when we start geeking out

Without going in depth into tire dynamics, the forces a tire is able to transmit are for the most part constant regardless of road speed. For example a given tire that is able to provide 1g of static friction is able to do so at 30mph and at 90mph, same concept applies to dynamic friction (tire 100% slipping). Taking threshhold braking as an example, the tires are essentially able to provide the same braking force throughout the braking yielding constant deceleration. The force the tire is able to transmit to change the car's momentum is not affected by the car's velocity.

At low speeds, if you are too slow to react, the car can get in pretty bad shape before you run out road, giving you more time to recover. Not the case at high speed.

So all that to say that no, no more force is needed to recover from a high speed spin. However, more speedy driver input is what is needed to avoid catastrophic consequences .

Yes, the tire can only do so much, if the coefficient of friction (μ) between the road and the tire is the same:

μ=F/N
F=ma
and
a=Δv/t

Therefor μ=(Δv/t)/N

Velocity contributes to the coefficient of friction between the tire and road. What you are describing is the tires limit of transmitting friction. When the velocity increases, μ increases. μ is the grip (friction) required to maintain traction. If it increases beyond the tire's limit, then we have loss of traction.


Practical observation:

A stickier tire has a higher coefficient of friction on the track. What does this allow us to do? It allows for more velocity in all directions (braking, accelerating, cornering) because it takes more force, F=m(Δv/t), and therefor more velocity to exceed its limit. This leads to faster lap times (god willing!).

I love geeking out about this because I get to use that college physics crap I thought I never would again lol! Plus it deepens our understanding of what's happening on the track!

[CanAutM3]

Originally Posted by jmg

Yes, the tire can only do so much, if the coefficient of friction (μ) between the road and the tire is the same:

μ=F/N
F=ma
and
a=Δv/t

Therefor μ=(Δv/t)/N

Velocity contributes to the coefficient of friction between the tire and road. What you are describing is the tires limit of transmitting friction. When the velocity increases, μ increases. μ is the grip (friction) required to maintain traction. If it increases beyond the tire's limit, then we have loss of traction.


Practical observation:

A stickier tire has a higher coefficient of friction on the track. What does this allow us to do? It allows for more velocity in all directions (braking, accelerating, cornering) because it takes more force, F=m(Δv/t), and therefor more velocity to exceed its limit. This leads to faster lap times (god willing!).

I love geeking out about this because I get to use that college physics crap I thought I never would again lol! Plus it deepens our understanding of what's happening on the track!

Woah , seems like you need to go back to physics class.

μ is not the "grip". μ is the coefficient of friction and is pretty much a constant for a given material interface. "Grip" is simply the force being transmitted by the tire. It is not μ that varies when traction loads vary, it is simply the transmitted force that varies. As long as μstatic*N is not exceeded, the tires will be able to transmit the full force between the chassis and the ground. When μstatic*N is exceeded, it is μkinetic that takes over and the tire starts to slide. But even when a tire slides, it still provides some level of grip. Velocity has notionally no incidence on the coefficient of friction.

Disclaimer: this is a fair bit oversimplified since tire dynamics are way more complex than this, but the general concept remains true.

Your equation derivation and conclusion is also flawed.

Originally Posted by jmg

Therefor μ=(Δv/t)/N

Velocity contributes to the coefficient of friction between the tire and road.

It is not velocity in itself that has an incidence on grip, but rather a change of velocity (Δv), i.e. acceleration. In velocity without acceleration there is no force, hence no required grip.

[jmg]

Originally Posted by CanAutM3

Woah , seems like you need to go back to physics class.

The coefficient of friction (μ) is pretty much a constant and your equation derivation is also flawed.

Darnit, first of all, OBVIOUSLY I'm going back 20 years pulling this out of my ass!

My wording is flawed, I can see that now. I didn't mean to say the tire's μ ITSELF changes.

I meant to say that the coefficient required to maintain grip changes as acceleration changes.

This goes back to how I used to solve equations. I usually calculated the required amount and compare to the actual amount. So my μ was the required amount, not the actual amount.

You stated it much better here:

Originally Posted by CanAutM3

It is not μ that varies when traction loads vary, it is simply the transmitted force that varies. As long as μstatic*N is not exceeded the tires will be able to transmit the full force from the chassis to the ground. When μstatic*N is exceeded, it is μdynamic*N that takes over and the tire starts to slide. But even when a tire slides, it still provides some level of grip. Velocity has notionally no incidence on the coefficient of friction.

Here was my mistake:
"Velocity contributes to the coefficient of friction between the tire and road. "

I should have said:
"Velocity contributes to the required coefficient of friction between the tire and road to maintain grip."

...because isn't the difference between μstatic and μdynamic determined by motion aka velocity? By definition of F=ma, it is the acceleration that changes (Δv). Mass is constant.

Which goes back to my original post... , momentum, velocity, and mass all contribute to the loss of control.

EDIT: looks like you edited your post in the time it took me to start my reply, eat a sandwich, then come back and finish it.. I think we are thinking along the same lines, you are better at explaining it.

[CanAutM3]

Originally Posted by jmg

Darnit, first of all, OBVIOUSLY I'm going back 20 years pulling this out of my ass!

LOL, I beat you though, it's been 27 years for me . Time sure flies .

Fun chatting technical and get those neurones firing a little

[DRLane]

Originally Posted by CanAutM3

LOL, I beat you though, it's been 27 years for me . Time sure flies .

Fun chatting technical and get those neurones firing a little

[jmg]

Originally Posted by CanAutM3

LOL, I beat you though, it's been 27 years for me . Time sure flies .

Fun chatting technical and get those neurones firing a little

Seriously never thought I would be trying to dig through those cerebral cobwebs on a bimmer forum!