Tire pressure questions

[Nick Hill]

Does anyone have any insights as to why the concept of "ideal" pressures doesn't seem to exist (or, at least isn't talked about/documented)?

Old rFactor people will remember the old .tbc files, which listed an ideal pressure (and, I believe, temperature) range for a given set of tires. That tire data is now encrypted into the AMS .exe...which there is nothing wrong with, but wouldn't real-life racers/teams have access to this information from the tire manufacturer?

I don't think it's some crazy conspiracy; I just think it's a bit odd. The data is there all to see in rFactor. Hell, in Assetto Corsa, the tire app will even color-code it for you so you don't even have to read the numbers! But in AMS, the information seems to be nowhere to be found.

When I Google the topic, I can find several instances of people asking this same question across the interwebs, but the threads either go altogether unanswered or devolve into "tires r complicated" type discussions without really answering the question.

Perhaps as long as your temps/pressure are in a generally acceptable range, there isn't that much of a performance gain/loss, so people aren't really wasting much time thinking/talking about the topic...?

 

[muzarati]

Good question? I recently experienced better driveability by reducing tire pressures, hadn't really given them much notice till now?

 

[HansieCronje]

It exists, timetrial defaults to it.

Start a timetrial at Kansai with your chosen car - I use Kansai as the start finish line is a long way from the last corner so the loads won't be affected. As soon as you gain control escape back to the pit menu; the temp and pressure displayed is the ideal. I then note these in my default setup so I don't forget.

 

[Nick Hill]

It exists, timetrial defaults to it.

Start a timetrial at Kansai with your chosen car - I use Kansai as the start finish line is a long way from the last corner so the loads won't be affected. As soon as you gain control escape back to the pit menu; the temp and pressure displayed is the ideal. I then note these in my default setup so I don't forget.

Too funny, this was the exact same trick I have been using...and here I was thinking I was so clever - "I bet no one else has thought of THIS idea!"

The main reason I started doubting this approach is because, in testing it out with the Formula Trainer, I was getting "ideal" tire pressures that seemed unreasonably low. On the F-Trainer, using the "Time Trial/load your car/quickly hit escape" trick, I was seeing tire pressures of I believe 16.7/16.5 (can't remember which was front which was rear). Even if I crank the cold pressures all the way to the minimum (which I think is 11.6), after a few laps I will be in excess of 16.7/16.5 (and I found my laptimes to be slower...probably due to driving around on mushy donuts!)

But perhaps I need to take another "reading" using the Time Trial trick @ Kansai. And/or perhaps using a different car altogether (maybe this is only an oddity with the F-Trainer).

 

[Nick Hill]

OK, very odd - I tried the Time Trial/escape trick again with the F-Trainer across multiple tracks and I'm now consistently getting a reading of 20.3 psi on all 4 corners. I have no idea where I got the 16.7/16.5 from...perhaps I hit escape too quickly or maybe just a glitch. Who knows, but at any rate, 20.3 seems *much* more reasonable.

I'm going to try some more testing tonight to see if I can't dial in a setup that gives me roughly these temps and see what lap results that nets me.

 

[HansieCronje]

20.3 does look more on the ball, but it certainly is possible for front and rear tyres to have different ideal pressures; nowhere near the game at the moment but I *think* the Mini does. Other likely candiates would be the other openwheeler as that have different sizes on the front/rear.

There is one other method to get the ideals - setup an external app on a phone/tablet to get live readings. I use Dashpanel and setup a custom screen to give me tire and brake info. http://www.pyrofrogstudios.com/dashpanel.html

 

[Nick Hill]

Cool, thanks for the info, Hansie!

As far as my testing goes - jackpot! I worked out a setup that got me within a tenth or two (psi) of the "ideals" on the F-Trainer (novice). The result? I shattered my previous best by .9 on a track that I already knew extremely well.

So much for there "not being much of a performance gain/loss" for having ideal pressures, huh?

 

[Chris]

Cool, thanks for the info, Hansie!

As far as my testing goes - jackpot! I worked out a setup that got me within a tenth or two (psi) of the "ideals" on the F-Trainer (novice). The result? I shattered my previous best by .9 on a track that I already knew extremely well.

So much for there "not being much of a performance gain/loss" for having ideal pressures, huh?

Tyres are everything.

 

[Ben Cobbé]

It exists, timetrial defaults to it.

Start a timetrial at Kansai with your chosen car - I use Kansai as the start finish line is a long way from the last corner so the loads won't be affected. As soon as you gain control escape back to the pit menu; the temp and pressure displayed is the ideal. I then note these in my default setup so I don't forget.

Thank you for sharing this info.
Could you further explain why you use Kansai? I don't understand why the long straight/load matters.
I'm a total newbe so in layman terms would be greatly apreciated.

 

[HansieCronje]

When cornering weight transfers to the outside tyres, which generally results in higher temps and higher pressures on that side.

At the start of a time trial the AI controls the vehicle for a few seconds before giving over to player control. At Kansai the entirety of this AI period is on the straight whereas at Adelaide for example the final bend is included in the AI control sequence. The theory being that if AMS loads the ideal pressure/temp at the start of the AI sequence then by using Kansai it eliminates a potential variable. However it may be that the ideal temp/pressure loads upon handing control to the human meaning the track doesn't matter; I honestly have tested it. This works for me, so I figure why waste time doing further testing when I can be driving.

 

[Nick Hill]

I have had great success with the old "load the car in time trial; go to the track; hit Esc as soon as AI hands over control; check temps in garage" trick across multiple cars, but I've run into some questions regarding the F-Vintage pressures.

Taking the F-Trainer Novice as an example, using the time trial trick above, I come up with ideal pressures of 20.3 psi in all four tires. I've got a pretty good Brands Hatch Indy setup dialed in. I hit the track in this setup, turn a good number of consistent quick laps, then return to garage and check the pressures - I'm satisfied to see that all four tires are right in the 20.3 psi ballpark (+/- a tenth of a psi here and there). Also, wouldn't you know it but all four tires also have really nice heat distribution (hottest on the inner, coolest on the outer, middle right smack in the middle - and not too much temperature differential between hottest and coolest).

My confusion comes in now on the F-Vintage. Using the time trial trick on the two different '67 models, I get the following "ideal" readings:

'67 V8 - 29.5 Front, 30.3 Rear
'67 V12 - 28.6 Front, 29.5 Rear

It seems very plausible that the 2 different models would have different ideal pressures. The difference between front and rear pressures isn't really surprising to me either, as I don't think this is particularly unusual. So, I set to work creating setups for both cars at Johannesburg and, without too much trouble, I come up with a setup for each car that gets me in the ballpark of these pressures.

But now a bit of confusion sets in - going back to the F-Trainer Novice example, hot lapping with default pressures vs hot lapping with track-specific ideal pressures was like flipping a switch. I was instantly laying down significantly faster laptimes and noticing all sorts of desirable behaviors (e.g. going flat out where I previously needed to lift, etc). I have had very like experiences across numerous other cars (like the Boxer and F-Retro).

But with the F-Vintage '67 models, it feels like I'm all over the place - in some ways, they seem to actually feel/perform *worse* with the ideal pressures than the defaults. My suspicion is further enhanced by checking the pressures in the garage after a good number of consistent laps - the tire pressures are right in the ballparks of the ideals, but the temps seem to be all over the place. There doesn't really seem to be a consistent pattern across all four tires, but in a lot of cases I'm seeing the middle temps being the hottest (which would seem to indicate over-inflation...at least in a modern tire, it would).

Two theories:

(1) The "ideals" for these F-Vintage '67's as obtained via the time trial trick are off and I need to be a big boy and figure out some tire pressures via some old-fashioned trial and error experimentation.

(2) 60's ply bias tires are different beasts and shouldn't be expected to exhibit the predictable temp profiles I've come to rely on for modern tires. The observed inconsistencies in laptimes are a function of these being some of the trickiest (if not *the* trickiest) cars in the sim and me being a terrible driver.

 

[Qazdar Karim]

I think that "ideal pressure" in AC is the pressure at which slip curves are as defined in the .ini files, it doesn't necessarely mean it's better to be at that "ideal pressure".

 

[BillGuy]

Hmmm… very interesting.

I’ve looked at data I recorded from the F309, F-Reiza, and F-Ultimate in MoTec. On all three of those cars, the pressure in the default setup pretty much always gives me tire temps that vary over the course of a lap by no more than 2-3 degrees between the center and outside readings. The inside temp reading can vary from the center by 4-10 degrees but that changes directly based on how much camber I have set. Overall, I’ve always assumed this to mean that the default pressures are pretty close to ideal right from the get go. Thoughts?

I should clarify that the example numbers I stated are for the fronts and always after at least three or four laps have been run.

 

[BhZ]

Hmmm… very interesting.

I’ve looked at data I recorded from the F309, F-Reiza, and F-Ultimate in MoTec. On all three of those cars, the pressure in the default setup pretty much always gives me tire temps that vary over the course of a lap by no more than 2-3 degrees between the center and outside readings. The inside temp reading can vary from the center by 4-10 degrees but that changes directly based on how much camber I have set. Overall, I’ve always assumed this to mean that the default pressures are pretty close to ideal right from the get go. Thoughts?

I should clarify that the example numbers I stated are for the fronts and always after at least three or four laps have been run.

Testing the F3, i think the rear tyre pressure is not enough, in fact the mid temperature is almost equal to the inner one.

 

[roby13]

Maybe @Renato Simioni could chime in

 

[Nick Hill]

I might post my question over in the official Reiza threads, too...

One thing I have done since my original post was to dig up some old tips about GPL setups. Granted AMS != GPL, but I was curious to see how GPL hard cores approach tire pressures/temps when doing setups. One piece of advice I found interesting is that you should go for a flat temp profile across the tire (i.e. Inner, Middle, Outer temps all as close to the same as you can get). That is, unless you are at a track that could benefit from a straight line speed boost, in which case you might want to pump the tires up a bit more and thus generate Middle temps that are slightly higher than the Inner and Outers...which is exactly what I'm seeing in AMS if I go with the theoretical "ideal" pressures for the F-Vintages per the Time Trial trick.

I'm guessing it's probably about like everything else in racing (as in life itself) - it's a trade off. On cold tires, the F-Vintages feel very sloshy, but grippy to me. Once I get them up to temperature, they feel very jittery and less grippy...but I'm assuming I'm probably getting a few extra MPH on the straights.

It's just different because, again, with the other cars I've experimented with in AMS, when I hit a setup with tire pressures close to "ideal" they drive and perform better, period. With the F-Vintage, it may be much more subjective than that.