Influence of RCH on tire temperature

[Ralph_]

Hey Guys!

Just a thing I was thinking about. I always though that increasing my roll center height increases my tire temperatures. Why? Because I increase the geometrical weight transfer which occurs faster. So i have less movement because of the body's inertia.

Let me explain this thought by taking corner entry as example.

If I have a high roll center, I will have a high(er) geometrical WTF.
Which means, the movement of the body is less (inertia movement?! (if I can call it like that)).

The lower the RCH, the longer the car takes to reach constant/max wheel loads at the outside tires?!
This is because the inertia results in a slower roll movement and so the weight transfer "takes longer" to happen.

But some people (including my boss) say, that lowering the RCH brings more tire temperature.
Because the tires is "more loaded" because of "increased roll moment".
This, in my view, is only true, when I lower just one RC (front or rear), because I can't influence the size of the total load transfer by the RC.

What's your thoughts or better, what's your experience about that?!

Ralph
Ex-Member of joanneum racing graz, jrX

[Ralph_]

Hey Guys!

Just a thing I was thinking about. I always though that increasing my roll center height increases my tire temperatures. Why? Because I increase the geometrical weight transfer which occurs faster. So i have less movement because of the body's inertia.

Let me explain this thought by taking corner entry as example.

If I have a high roll center, I will have a high(er) geometrical WTF.
Which means, the movement of the body is less (inertia movement?! (if I can call it like that)).

The lower the RCH, the longer the car takes to reach constant/max wheel loads at the outside tires?!
This is because the inertia results in a slower roll movement and so the weight transfer "takes longer" to happen.

But some people (including my boss) say, that lowering the RCH brings more tire temperature.
Because the tires is "more loaded" because of "increased roll moment".
This, in my view, is only true, when I lower just one RC (front or rear), because I can't influence the size of the total load transfer by the RC.

What's your thoughts or better, what's your experience about that?!

Ralph
Ex-Member of joanneum racing graz, jrX

[Pete G]

To the best of my knowledge, increasing your roll center height (further above the ground) will tend to increase the scrub of your tyres during suspension travel, resulting in more tyre temperatures

[Ralph_]

when i compare my track-change over. suspension travel chart for 2 different Roll centers, it show no big difference.

I think that the scrub depends more on the the instant axis and the movement of the whole upright. I can design the same roll center height (for example in OptimumK) with 2 absolutely different instant axis position. Afterwards the scrub change will be very different.

And when i think of a change of +/- 5mm, i bet you will not really see it or feel it because the tire does move much more due to side wall deflection and so on!

I can not prove what I'm saying, that's the problem http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Chris Texas]

When the sprung mass rolls, you disipate energy into both the springs and dampers. If you do not roll, you still have to disipate the energy somehow. So, the energy is disipated into your tires, raising there temperature. I've always wondered how the change in RC height would effect the temperature. I know Western Australia usest to change their roll center height between Detroit and Australia. Back when they came to the US. Anyone have experience testing this or theoretically calculating it?

[exFSAE]

I'd guess the effect is pretty damn small. You'll probably have more variation getting consistent measurements of the temperature itself than whatever this amounts to.

[Ralph_]

That's how I see it!

The harder the suspension gets, the more compliance you'll have at the tire contact patch, so more heat in the tires!?

No-one with experience on that here?

[Zac]

Why does the energy have to go into the tires if your vehicle doesn't roll? This point seems rather hand-wavy to me.

Rubber is a hysteretic material (some compounds more than others). You get more heat into the tire by increasing the deformation of the tire. You increase the deformation of the tire by either increasing the loading (normal force or lateral force) or reducing the pressure (try running on a flat sometime). If changing your RCH gets you higher loading it will increase tire temps by default.

[ben]

This is a really hard subject to be definitive on. It's just as possible to generate tyre temp by running soft - if you have a soft suspension that reduces load variation on the tyre causing it to grip better it will generate more temperature.

I tend to agree with exFSAE that within the range of RC heights we're probably talking about the effect of changing the RC will be negligible within the natural variation in temp you'll see from various other factors.

I would hazard a guess that what settings you run in your dampers will have a much larger effect.

Ben

[Z]

Another "How long is a piece of string?" subject. Too many unspecified variables. Here are two more;

If you lower your RCs at both ends, without any other changes, then with typical (???) suspension you get more roll angle > more positive camber on the outer tyres > tyres run on their shoulders > more deformation > more heat.

If you raise your RCs both ends, then more jacking > (slightly) higher CG > more LLT to outer tyres > etc. (incl. slightly more positive camber from higher CG) > more heat.

Therefore, -1 = +1, QED! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z

[Chris Texas]

The answer I gave was actually the answer Claude told me a few years back. But as always in suspension, theres a thousand ways to do the same thing.

[Ralph_]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
Another "How long is a piece of string?" subject. Too many unspecified variables. Here are two more;

If you lower your RCs at both ends, without any other changes, then with typical (???) suspension you get more roll angle &gt; more positive camber on the outer tyres &gt; tyres run on their shoulders &gt; more deformation &gt; more heat.

If you raise your RCs both ends, then more jacking &gt; (slightly) higher CG &gt; more LLT to outer tyres &gt; etc. (incl. slightly more positive camber from higher CG) &gt; more heat.

Therefore, -1 = +1, QED! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z </div></BLOCKQUOTE>

You're right, but you have to start somewhere.
If you make every topic confusing by including everything you can imagine, you'll never get a result.

As i can see here, all have the same opinion about that. You can't really influence (directly) tire temperature with the RCH hight.

Would it make sense to make a setup, test the car on a track, and log the tire temperature. Afterwards, build in a different RCH and make the same roll distribution with the ARB (maybe be springs-&gt;influence of damper different) so that you don't have a different roll angle?

I think that this would give a result?!

Cheers

[Chris Texas]

As far as starting somewhere, as long as you keep your roll centers from moving 5 in during roll. You should be able to tune most of the other effects out. Assuming you don't put it above gravity.

I think your missing the point. We're not saying you can't change the temperature with roll center location. We're saying like everything in suspension there's multiple ways to do it, and that it might be very small or negligible.

As for designing different suspension with different RCH, I would say like everything else in FSAE. Do it only if you have the time, money, and resources. Actually, I'd love to see those results if you ever do run it.

[Ralph_]

I didn't say that it's not possible. I said it's not 'really' possible. Maybe that's to german-englisch?!

I'm no student anymore so I can't try it on the FSAE car. But I will talk to the actual Team and maybe they can do some research.

Maybe we will see some difference on the car I'm in at the moment. In January/February we will try lower RC heights and than I'm maybe able to show some results. But the tire temperature of a GT3 car changes way faster and more than on an FSAE car. We'll see!

Cheers

[Chris Texas]

Yah, if you guys get to it post some general trends. I tried to convince the grand-am team I worked for to do it. We even had enough adjustment to change the roll centers without too much effort, but active tire temps are against the rules in GT.

[js10coastr]

Raising the RC height also usually raises the instant center height too, which would introduce more scrub into the tires too. I'm pretty sure raising the RC would heat up the tires (partly because you do have this helping you), however I'm also pretty sure that the driver has a larger influence over the outcome than normal RC height changes.

I want to say I've read or seen this test somewhere, but I can't for the life of me remember where or what the results were.

[Warpspeed]

Individual tire temperatures are going to be dependent on a great many factors.
I doubt if a RCH change will have very much measurable effect on tire temperatures, provided relative roll stiffness is also changed at the same time to re balance the car.

I believe there are far more important issues to be considered with selecting and tuning roll centre heights than tire temperatures.
Transient response, (slalom) and how it actually feels to drive would be how I fine tuned the roll axis inclination, after everything else in the suspension geometry was just about finalized.