Hi, there were tons of discussion about how air pressure in tyres affects grip and heat. But what about acceleration and top speed? What about fuel consumption?
IRL i have noticed that my car accelerate better when changed the pressure from 2,0 bar to 2,5 bar. But in LFS the difference between 1,25 and 3,75 is very tiny (watched G forces). It's mad!

Then you can see hotlappers speeding without air in their tires lol.
In fact, even I'm fan of realism, I had to drop the pressure down a little to be competitive in online racing

My times where better, yes, but what is fun in using setup that cheats the physics laws?

Well, decreasing tyre pressure increases grip, thus increasing acceleration (when traction is an issue), and improves cornering speeds, making you faster on the straights too. However decreasing tyre pressure also increases rolling resistance, which decreases acceleration and top speed. Those affects are usually quite slight though. The increased rolling resistance generate more heat, which can bring the tyre closer to optimum temperature, which again increases traction.

Cornering speed is far more important than losing 2mph at the end of the straight, since the average speed for the track would have gone up.

I don't think there's really anything cheating the laws of physics.

Yes, I understand that (I suppose) after reading this forum o lot.

One day I was speeding through corners (not even close how I do it in LFS), and after a corner my steering wheel was hardly shaking. There was something wrong with the wheels so I checked the car. There was 1,5 bar in whole 4 wheels (maybe because of winter temperatures). Usually I use 2,2 bar.

Cornering on the limit with low tyre pressure is just scary and dangerous! Also the car feels wobbly on the road.

And I don't think it will be 2mph drop on the end of the straight. It could be 2-20km/h on the whole straight, not the end. IMHO of course.

Maybe someone knows what pressures are used in real racing, in cars similar with those we have in lfs. WTCC or something?

Did a little test, because I was/am bored.

RB4, 10% fuel, minimum and maximum tyre pressures, RACE_S set.

Kyoto Oval
Maximum Tyre Pressures

0.9% Fuel per lap, managed 11.5 laps on 10%
Best Lap : 50.34
Tyre temp, FR 68,67,70 RR 57,56,56

Mimimum Tyre Pressures
0.9% Fuel per lap, managed 11.25 laps on 10%
Best Lap : 52.13
Tyre temp, FR 93,89,103 RR 84,80,89

Drag Strip

Maximum Tyre Pressures
Best Lap : 13.46

Mimimum Tyre Pressures
Best Lap : 13.55

Only thing I found unusual was the fuel consumption, tyre pressure doesnt seem to have any effect of fuel consumption, which is wierd.

Dan,

I run 26psi on my Mazda, and ~14psi on the Reynard (Avon slickies). Most racing tyres seem to be run at between 15 and 25psi cold.

Quote from danowat :

Only thing I found unusual was the fuel consumption, tyre pressure doesnt seem to have any effect of fuel consumption, which is wierd.

Dan,

Maybe it's because in racing you are keeping the pedal down most of the time? In normal driving you just need to press the pedal little deeper to get to the desired speed if you have less pressure on the tires because the increased rolling resistance...

Regardless of throttle position (its flatout all the way round the oval anyway), tyre pressure causes, especially 15PSI against 48PSI, large amounts of rolling resistance, it should at least have SOME effect.

I know in my car if my PSI is off by more than a few PSI it can knock 5mpg off.

Quote from danowat :

Regardless of throttle position (its flatout all the way round the oval anyway), tyre pressure causes, especially 15PSI against 48PSI, large amounts of rolling resistance, it should at least have SOME effect.

I know in my car if my PSI is off by more than a few PSI it can knock 5mpg off.

Only way it could affect while racing is that your lap times would drop meaning that spend more time per lap = more time with the accelerator flatout = more time to consume fuel. More rolling resistance doesn't itself increase the fuel consumption.

You don't drive 6000rpm at full throttle 95% of the time with your car irl. Or maybe...

Dan - it might knock 5mpg off, but over a 400mile tank of fuel. You ain't gonna notice much over 10 laps.

Besides, in your test you didn't manage the same amount of laps - 0.25 difference - so maybe it does. Maybe it does MASSIVELY.

I say: Test Inconclusive (with regards Fuel Consumption).

Quote from Hyperactive :

You don't drive 6000rpm at full throttle 95% of the time with your car irl. Or maybe...

No, I leave that for when I am riding the bike

Quote from Hyperactive :

More rolling resistance doesn't itself increase the fuel consumption.

Why not?

Quote from tristancliffe :

Dan - it might knock 5mpg off, but over a 400mile tank of fuel. You ain't gonna notice much over 10 laps.

Besides, in your test you didn't manage the same amount of laps - 0.25 difference - so maybe it does. Maybe it does MASSIVELY.

I say: Test Inconclusive (with regards Fuel Consumption).

The lap difference is down to (I think) the increased lap time, I just found it wierd that fuel consumption was 0.9% per lap for both 48PSI and 15PSI

If someone can prove to me that

A) Tyre pressure doesnt influence fuel consumption

And/Or

B) LFS fuel consumption is effected by tyre pressure

I will be a happy bunny

Quote from danowat :

Only thing I found unusual was the fuel consumption, tyre pressure doesnt seem to have any effect of fuel consumption, which is wierd.

thats simply not true.

Quote from KiDCoDEa :

thats simply not true.

Ok, so prove me wrong, rather than just posting a useless statement

Quote from tristancliffe :

Dan - it might knock 5mpg off, but over a 400mile tank of fuel. You ain't gonna notice much over 10 laps.

Also, 50mpg is 50mpg regardless of how many miles you are doing on a tank

Quote from danowat :

Ok, so prove me wrong, rather than just posting a useless statement

how about you go prove yaself right since obviously u care.

i dont need to prove you anything, i just helped dev it and test it for years/months. useless it was obviously, since u cant see it.

Quote from tristancliffe :

I run 26psi on my Mazda, and ~14psi on the Reynard (Avon slickies). Most racing tyres seem to be run at between 15 and 25psi cold.

So Tristan, does it follow that you use 15-25psi in your FOX sets in LFS? Would you go as low as 14 as in the Reynard?

Quote from danowat :

Ok, so prove me wrong, rather than just posting a useless statement

Dan, I think he's referring to the fact that you got about 2.5% worse fuel economy in the test that you did. Don't know if that's enough, but it looks like a difference.

Quote from KiDCoDEa :

how about you go prove yaself right since obviously u care.

i dont need to prove you anything, i just helped dev it and test it for years/months. useless it was obviously, since u cant see it.

1) I don't know you

2) I don't know your involvement with LFS

3) If you are privvy to information that would give me the answer, why not, instead of trying to be a wise-ass, just say so instead of trying to massage your already huge ego some more

50mpg is 50mpg no matter the distance travelled, but in real life you'd measure the change over a lot of miles. You'd never do 15 miles and measure your mpg, because it wouldn't be accurate.

Generally Kid is right about this sort of stuff, having been involved with LFS from the early days.

I think I should clarify - the Reynard tyre pressures I quoted above are for Crossply tyres. The radials we could use are rated at a higher pressure (22 iirc), but we're sticking with crossplies for forgivingness reasons

Maybe the AI can help. Some XFG's with a benign setup (that they can lap consistently with), but different pressures and 100% fuel. Maybe have two or three using each set, and see how varied the 'run out of fuel' points are. I'd hope to see two 'groups', which would confirm pressure vaies consumption. If they are all close together then it proves it doesn't. If they are randomly scattered it means the test is faulty.

So who wants to make the AI do 50 or 60 laps of Blackwood?

Just stick the AI on the oval - they're much less likely to screw up then

Quote from AndroidXP :

Just stick the AI on the oval - they're much less likely to screw up then

We can't do that, as per the other thread, rolling resistance doesn't (apparently) effect fuel consumption when using WOT

Errrrr.... but.... it does.

At a given gas consumption (f.e. full throttle constant rpm) the increased rolling resistance lowers speed.
At a given speed (driving on the highway at given mph) the increased rolling resistance increases the fuel consumption necessary to maintain that speed.

Does that make sense to you?

Vain

Now I am REALLY confused (yeah, yeah, it doesnt take much)

Quote from Vain :

At a given gas consumption (f.e. full throttle constant rpm) the increased rolling resistance lowers speed.
At a given speed (driving on the highway at given mph) the increased rolling resistance increases the fuel consumption necessary to maintain that speed.

Does that make sense to you?

Vain

Only speed limit you are obeying while racing is the pit speed limit. Only time when you don't use full throttle is through turns. With more grip (less pressures within reason) you can brake later and start accelerating earlier.

Try with equations:
P1 = power needed to drive 200mph with p-1 pressures
P2 = power needed to drive 202mph with p+1 pressures

now P1 = P2
prove me wrong

I think that tyre pressure doesn´t affect fuel consumption directly, but indirectl. At least in real life:

If i´m driving my car ( crappy car with low horse power :-P ) i notice quite a lot difference in fuel consumption if i have low pressure. I think its because there is more rolling resistance that my car has to handle, so more power for keeping the same speed, so its like going uphill.

Quote from Vain :

At a given gas consumption (f.e. full throttle constant rpm) the increased rolling resistance lowers speed.
At a given speed (driving on the highway at given mph) the increased rolling resistance increases the fuel consumption necessary to maintain that speed.

And the point of this thread was: what/how much/in which way, must be changed to make LFS closer to reality, in the tyre pressure case.

Once again, anybody knows the tyre pressures used in motorsports?
It should be a good base for discussion.