## Front and Rear roll stiffnesses

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Yep, throttle can really affect the balance of a car. That's one thing I've found out when testing my own car with suspension modifications and adjusting the weight distribution.

'10-'11 Head of Powertrain - Glasgow University Formula Student
Scotracer

Joined: 22 Apr 2008
Location: Edinburgh, Scotland, UK

So lateral load transfer is undesirable because the grip that is lost on the outside tyres is not made up for on the inside tyres. But for and aft load transfer addd's grip to the loaded side because it effects both inside and outside tyres?

Doesnt load transfer decrease the efficiency of the loaded tyre, thus decreasing 'grip'? How does this apply to the braking and throttle applications?

Thank you again, Birel
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Birel99 wrote:Doesnt load transfer decrease the efficiency of the loaded tyre, thus decreasing 'grip'? How does this apply to the braking and throttle applications?

Thank you again, Birel

Coefficient of friction goes down.. but grip still goes up.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

Grip a tyre has is the Coefficient of grip multiplied by the load on the tyre (Cgr*m*g). As you increase load on a tyre however the Cgr goes down, even though the load is going up - you still increase the grip but it is not a purely linear function. As Tom said.

'10-'11 Head of Powertrain - Glasgow University Formula Student
Scotracer

Joined: 22 Apr 2008
Location: Edinburgh, Scotland, UK

Jersey Tom wrote:Also, you may have the case where a car is fairly undersprung and likes to "wallow around" and snap to oversteer while changing directions quickly. In that case stiffening the rear would "free" the car up through the center of the corners, yet make the car more "settled" in dynamic maneuvers.

Jersey Tom,

Can you please explain why this is?

Regards,
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Birel99 wrote:
Jersey Tom wrote:Also, you may have the case where a car is fairly undersprung and likes to "wallow around" and snap to oversteer while changing directions quickly. In that case stiffening the rear would "free" the car up through the center of the corners, yet make the car more "settled" in dynamic maneuvers.

Jersey Tom,

Can you please explain why this is?

Regards,

What are you unclear on? Stiffening the rear WILL shift the steady state balance to less US / more OS. However, it also means you increase the roll stiffness so the car doesn't move around as much. Less roll-steer and roll-camber, chassis takes a "set" quicker. More predictable.

A lazy chassis can be misinterpreted, and the cause of snap balance transitions.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

Jersey Tom,

I am slightly confused on why a softly sprung front and rear would lead to transition oversteer/ instability? Besides the fact that it would move around alot.

Thank you for your help Jersey Tom, I truely appreciate your assistance!
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Any system has a phase-lagged output to a given input. Any time you steer in, there's a phase delay for the chassis to catch up.

With a high phase lag on an undersprung car... if you were just turning one direction and entering corners slowly the balance might feel awesome. But then if you have to go through a chicane with quick left/right inputs, the chassis will still be in the "turn left" mode while you're trying to get it to turn right.. and then still turning right while youre trying to go straight. You get crossed up and the car spins out.

Stiffening the suspension quickens how fast the chassis takes a set with a change in inertial force, but there's a point of diminishing returns.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

I have heard that if you bring a tyre up to temperature too fast, you will change the 'oil' density/location and loose grip. Is this true?

Also, Why is it when you get more and more heat cycles in a tyre, it takes longer to get it up to temperature?

Regards,
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Where did you hear #1? Not much you have much option either way. Bolt on a set, go race... if you do a "parade lap" on L1 it will hurt you a lot more than any tire degradation would!

#2 - Not sure about heat cycles.. but as you wear the tread away it will generate less and less heat.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

Jersey Tom wrote:but as you wear the tread away it will generate less and less heat.

Is that because they generate less friction (lose grip) with the road surface?

What happens as a tyre goes through more and more heat cycles and begins to lose grip?

Regards,
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Tires primarily generate heat by the strain (deformation) of rubber. That simple. Whereas metals are essentially purely elastic in most of their use range and have only an elastic (storage) modulus, rubber is not. Hysteresis means for each strain cycle some energy is lost to heat.

More deflection -> more energy released per revolution -> higher temp.

Higher speed -> more energy released in a given period of time (higher power output) -> higher temp.

More rubber -> More energy released per strain cycle -> more heat.

As you wear that tread down you have less rubber, so it runs cooler.

When you "heat cycle" rubber, or just let it sit, it continues to cure. As it cures, it gets harder. Typically for a given tire, as it hardens it loses grip.

Where'd you hear that bit about the oil and crap with coming up to temp too quickly?
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

I heard the oil mumbo jumbo from a "Tuner" in the kart industry... There is a lot of mumbo jumbo in the kart industry.

So, I assume that the lower the tyre pressure, the faster the tyre will come up to operating temperature?

Do tyre pressure sort of 'self regulate'? Lets say that you have too low of TP's heading onto the track, they generate too much heat and the pressure rises, do they then start to cool back down with the rise in tyre pressure?

Is the surface temperature uniform across the tyre? Or do the shoulders get noticably hotter?

Regards,
Birel99

Joined: 14 Nov 2006
Location: Northern USA

Birel99 wrote:So, I assume that the lower the tyre pressure, the faster the tyre will come up to operating temperature?

Hmmm. Should be careful with how you word that. Low tire pressure does generally generate a lot of heat, excessive enough (ex. flat tire) and you'll fail the tire. Low air will probably generate a lot of heat though. Doesn't necessarily mean it will go to "operating temperature."

Do tyre pressure sort of 'self regulate'? Lets say that you have too low of TP's heading onto the track, they generate too much heat and the pressure rises, do they then start to cool back down with the rise in tyre pressure?

Not sure "self regulate" is the word. They start at temperature "X" and rise, level off to temperature "Y."

Is the surface temperature uniform across the tyre? Or do the shoulders get noticably hotter?

If you take pyrometer temperatures I think you'll be hard-pressed to find uniform temperature spread. Generally though the rule of thumb has been that lower pressures lead to elevated shoulder temperatures.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

Birel99 wrote:I heard the oil mumbo jumbo from a "Tuner" in the kart industry... There is a lot of mumbo jumbo in the kart industry.

So, I assume that the lower the tyre pressure, the faster the tyre will come up to operating temperature?

Do tyre pressure sort of 'self regulate'? Lets say that you have too low of TP's heading onto the track, they generate too much heat and the pressure rises, do they then start to cool back down with the rise in tyre pressure?

Is the surface temperature uniform across the tyre? Or do the shoulders get noticably hotter?

Regards,

No, the lower the pressure the faster it does not get up to temp. Many factors contribute to tire temp. Say you scrub the tires in the front more they are going to have a higher psi then what you started with. But the psi went up because the amount of friction you put into them went up, not because you started with a lower temp. There is more to this but i feel like i may confuse you if i try to explain it more.

They will not cool down unless the amount of friction they are trying to produce is lessened.

I am not too sure on this one but tire temp across the tire should not be the same. I remember reading about this, must've been carroll smith, but it is usually hottest on the out side of the tire and then decreasing the further in you go.
fastback33

Joined: 29 Aug 2007

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