13 replies to this topic

[SuperT]

I'm having problem with generating enough heat into my tyres both front and rear.

What can I do to help this. Can chassis stiffness affect this?
I have the possibility to adjust damping and springs and also suspension geometry like rollcenters camber gain etc. If you have some ideas please share them.

[GregorV]

The heat generated during cornering is roughly a product of the lateral force and the slip angle. By getting the dynamic camber of the tyres right the lateral force can be maximized but you are likely close to that already. To generate more heat the car therefore needs to drift through corners more.

By e.g. dropping the tyre pressures the tyres will generate the peak force at a larger angle, but of course going too far will reduce the cornering capability. Also, going for a bit more oversteer (harder at the back/softer at the front) will help the car to attain larger yaw angles when cornering. As with anything else, lack of chassis stiffness can of course have an effect (it tends to put less load on the most loaded corner of the car, thereby reducing the heating there) but as you mention that the problem is not localized I would imagine that this is not the main issue.

The thing with heating the tyres is that it can be a vicious circle. There is not enough force to generate heat and warm the tyres, and because the tyres are cold they can not generate sufficient force. One thing to try and break this circle would be to put more negative camber onto the tyres. This will tend to heat up the insides of the tyres first instead of the whole surface uniformly, thereby raising temperature on just a part of the tread. As that part attains more grip this would then tend to deform the tyre more when cornering, thus bringing the rest of the tread into contact with the road, heating that as well.

[Greg Locock]

More toe?

[Limits]

Interesting topic for me since I just read about Red Bulls problem generating heat into their tyres, similar as Toyota last year. As GregorV mention - when there is little grip there is also less heat generated, so how do they know that the problem is heating the tyres?
Greg Locock asks "more toe?" and that was what I asked myself. What else can be done apart from camber, toe and tyre pressure? All those seem to be part of the daily setup routine (at least on a F1), so... well, it must be something else also?

[Oho]

What is the contribution of internal deformations of rotating tire in its heating process?

[Greg Locock]

Didn't we have a not very conclusive thread on that just recently?

Here s my appallingly bad guess at an answer.

Say the average horizonatl load on the tire is 4000N. Say the average slip is 10%. Say the average speed is 150 kph.

The power generated at the patch is then 150/3.6*.1*4000=20 kW

Um. Bloody hell.

The other useless piece of information is that the internal damping of a tire is about 7%

So if you can work out an average tire deflection speed you might able to figure out an internally absorbed power.

A third completely useless factoid is that a car shock absorber might be around 1 kW on a rough road, I doubt an F1 tire hits that.

But I'm gonna stick to bloody hell. 20 kW.

[McGuire]

First, I will assume this is normal road racing on a closed course and not autocross or something weird like that where you don't get normal tire temps. I am also assuming normal race weather. Generally speaking, if you are on the same tire with more or less the same car as everyone else in the class, if you can't even get the tires up to operating temp the driver is too slow. Tell him to get after it and see if there is a softer compound available.

Assuming you have one compound available, I would lower the tire pressures all around until the temps are in a sensible and consistent range, and then start reacting with the other adjustments --wheel rates, roll distribution, static camber and rate, toe, etc etc -- depending on what you see on each corner of the car, meanwhile sneaking the tire pressures back up as you get the car closer to right. Adjusting tire pressures is far easier than changing everything else, and easier to change back too. You can make progess from session to session instead of day to day or one weekend to the next.

If you are developing a car and a driver at the same time and lowering the tire pressures is not enough, softening the wheel rates and shock forces and raising the ride height will also help a lot. When the tire temps are up to normal, then you start stiffening and lowering again. What you are doing is giving the driver a comfort zone where he can feel the tires working, and then gradually taking it away from him as he gets feel and confidence.

IMO you want to use camber and toe last to heat the tires as 1) it will affect the tire temps unevenly, and b) it will make the car more difficult under braking and turn-in etc. It will also be more difficult to find your way back to the normal setup from those changes.

[shaun979]

Originally posted by McGuire

If you are developing a car and a driver at the same time and lowering the tire pressures is not enough, softening the wheel rates and shock forces and raising the ride height will also help a lot. When the tire temps are up to normal, then you start stiffening and lowering again. What you are doing is giving the driver a comfort zone where he can feel the tires working, and then gradually taking it away from him as he gets feel and confidence.

Isn't that reversed? Doesn't driver confidence come with a car that has quick response, rather than a slower responding but ultimately higher grip car that requires a more skillful driver to handle (picking the right line in advance and committing to it with easy and instant adjustments along the way more difficult to carry out)?

[Fat Boy]

I'd go with Mac on this one. Most proper racecars react too fast for an inexperienced driver to deal with. Slowing the car response is generally not a bad thing. Here's the other side. I'm of the general opinion that a softly sprung racecar is good for every driver. Older drivers have generally driven stiff cars more often and think that's how it's has to be to be fast. Especially the guys that cut their teeth in the late 80's/early 90's.

If I've got a good racecar and a novice is going to drive, I generally just give it little bit of aero push and raise the ride height a bit so they don't tear it up when they go off track. I've seen people that stick tons of push in the car for a novice. I find that this makes more problems than it solves because then you have an inexperienced driver dealing with what amounts to a bad racecar. I never understood how that was supposed to work.

Tire temp is generally developed by tire deformation. Most of the time, this means putting a lot of load on the tire. With someone that will never put a lot of load on the tire, lower pressures mean the tire will deform adequately with a moderate amount of load. Stick a real race driver on too low of pressures, though, and he'll be liable to destroy the tire by overloading the tires. Tire pressure is a huge factor in how much load a tire can carry.

[shaun979]

ok I guess I was just thinking about a different area of the stiffness curve

[McGuire]

It's like a rain setup when you think about it. In the wet the comfort zone between grip and slide is too narrow... just as it is with a brand new race car with a baseline setup, or with an inexperienced driver. So lowering the wheel and roll rates and raising the ride height will give the driver a wider zone to feel the loads distributing and the tires working before the car slides, allowing him to get the temps up into range.

A real pro driver will seldom have trouble getting the tires up to temp, as he will just throw the car around to do it. He doesn't need much of a comfort zone. But really you don't want to start out at minimum ride height and max rates; you want to start conservative and work toward them. That is lots easier than starting on the far side and trying to find your way back.

[Greg Locock]

I was a bit baffled, or a bat biffled, when I read McG's comment that toe was hard to dial out.

Until I cross referenced a previous discussion where Fatboy was using toe as fake Ackerman. (Which I really like as an approach).

So, on that subject, on real Ackerman you have to move the lateral position of the outer tie rod bj by a lot (say 10 mm) to make much difference. Is that what you do, or can you move the rack fore/aft easily?

[McGuire]

Originally posted by Fat Boy


Tire temp is generally developed by tire deformation. Most of the time, this means putting a lot of load on the tire. With someone that will never put a lot of load on the tire, lower pressures mean the tire will deform adequately with a moderate amount of load. Stick a real race driver on too low of pressures, though, and he'll be liable to destroy the tire by overloading the tires. Tire pressure is a huge factor in how much load a tire can carry.

That is exactly right... you never want to go much under recommended pressures to get the temps up as that will feed false info to the driver wrt to the tire load curve. And the real race driver will just cook them and tear them off the wheels.

[McGuire]

Originally posted by Fat Boy


I've seen people that stick tons of push in the car for a novice. I find that this makes more problems than it solves because then you have an inexperienced driver dealing with what amounts to a bad racecar. I never understood how that was supposed to work.

Me neither. It comes from the ovals and over there it makes some sense. I think it is the fallback position from the crew chief playbook: we don't what to do, so let's do that and go run some laps.

If you just soften the entire car up it will develop plenty enough apparent push as it will turn more slowly, but it makes no sense to deliberately unstick one end. As you say, you are just training a guy how to drive a bad car.