# Tire Pressure Test

Discussion in 'General Discussion' started by vegaguy5555, Dec 20, 2017.

1. ### vegaguy5555Registered

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I did an experiment in AC, PC2 and rF2 of lowering the pressure to 20psi on one side while increasing it to 40psi on the other. The wheel will pull to the lower pressure side in real life but all three sims drive straight.

Why is this basic physics missing?

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Several things

1. From what I could see when i analysed Radical SR3 LHD which has a 56-44 lateral weight ratio you are looking for quite a big radius which needs to be measured with telemetry. You should create the track layout from the lap where you did the tests in order to properly visualize it. I also suggest to use AZ keyboard profile to guarantee a straight wheel position.

2. By lowering pressures that way you are not substantially changing the load distribution. Try lowering only front tire or diagonal tires next time in order to boost the effects.

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3. ### LgelRegistered

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When you lower the pressure of a tire you change the shape and area of the contact patch (increase), and the amount of deformation of the tire under loads.

What should show in your test is the different rolling resistance of left and right tire which increases with lower pressure of the tire, and ride height of left and right side.

So maybe, the missing factors are the correct increase of rolling resistance and lower ride height when lowering pressure of a tire.

Cheers.

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4. ### ComanteRegistered

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How long a straight should be to detect this deviation? On the road we often see people driving with a deflated tire, and they don't even notice it. In a car with servo I don't think you could feel the pull, while in a car without servo, you would feel an increased resistance turning the wheel at low speed.

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5. ### Seven SmilesRegistered

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I drive a Caterham so no PAS, very direct steering (1.7 turns lock to lock) and rose-jointed front suspension. I assumed I'd notice even small changes in tyre pressure so I was shocked to find under 10 PSI in one front tyre once with no effects felt when driving on the road. OK, so Caterhams only run about 18 PSI anyway but that's the same percentage difference vegaguy5555 tried.

Last edited: Dec 20, 2017
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6. ### CortiRegistered

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I think you should feel something like that.

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Use telemetry instead. Inverse corner radius (curvature) is logged. Use keyboard controllers to make sure steering is straight. You can use EuskoTestTrack straight it is completely straight and flat.

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8. ### Seven SmilesRegistered

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Yeah but there are differences - I assume all four tyres are flat in the video and it's not driving in a straight line (and the pressure difference is slightly greater).

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9. ### vegaguy5555Registered

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I'm not a coder so I have no idea the problems they face. My guess is there is not enough bits to add more detail needing to correct steering all the time the way I need to do in a real vehicle on a real road. Although, having said that I lost control of the 917k on the descending straight through a village on the Targa Florio. The car got off balanced. Once the tyre flex started to rebound I couldn't keep up. Very realistic rF2!!

Where you can really see missing physics detail is drag racing in AC. Having drag raced a V8 Vega in real life at the Calgary Race Way in the the early 90's, I can assure everyone that it is much harder in real life. The road gets dramatically narrow at speeds over a hundred mile an hour. You get the feeling of threading a needle while having thoughts of loose wheel nuts!

In most sims it's a good time to take a sip of beer.

Edit No disrespect to AC intended. I only referenced it because of drag racing offered in AC.

Last edited: Dec 20, 2017
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Without any doubt tire pressure is influencing in terms of car trajectory.
FL with min pressure made the car pull to the right.
RR with min pressure made the car unstable on throttling
The combination of both was a mix of both things.
I uploaded to video of the tests so that you have an idea what those values are.

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11. ### PLAYLIFEMember

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I expected 1 and 2 above to have the opposite effect.

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And you are right I would expect as well.
The reason for this is that there is a bug in rF2 which I reported long time ago and I guess nobody among the devs took the time to read. Contrarily to what expected reducing tire pressure increases the load in the tire.

https://www.dropbox.com/s/1hxr3k7i2afyfsn/Pressure Effects on rF2 Tire Model.pdf?dl=0

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