97 replies to this topic

[Peter Dron]

Is it better in GPL to set up the chassis to give even temperatures across the tyres or to have the inner temperatures a few degrees higher than the outside, with the centre at roughly the halfway point?

I have always gone for the former, but I spent quite a time recently experimenting with the staggered idea, aiming to get a difference of roughly 10deg F from inner to outer. It did not seem to give any advantage...

[Lee200]

As a good rule of thumb, having the temps even across the tire should be your goal.  And Tommie certainly knows as he is an expert driver.

However, the program actually displays the three core temps inside the tire which are averaged to compute the tire pressure and then grip..  The tread temps are not displayed (unless you are using Pribluda).  The highest of the three tread temps is also used to compute grip.

So even tire temps within the setup menu doesn't necessarily mean you are getting the most grip.  Only experiment will tell.

Edited by Lee200, Jan 09 2014 - 06:06 PM.

[dbell84]

Lee200, on Jan 09 2014 - 06:06 PM, said:

As a good rule of thumb, having the temps even across the tire should be your goal.  And Tommie certainly knows as he is an expert driver.

However, the program actually displays the three core temps inside the tire which are averaged to compute the tire pressure and then grip..  The tread temps are not displayed (unless you are using Pribluda).  The highest of the three tread temps is also used to compute grip.

So even tire temps within the setup menu doesn't necessarily mean you are getting the most grip.  Only experiment will tell.

Lee, isn't overall tire temp range more important than even tire temps across the tire?  For example, If optimum temp range for tire grip is between 190-220, just to throw out some numbers, isn't it more important to be in that range than it is to be 161 degrees of temperature across the tires?

Dave

Edited by dbell84, Jan 09 2014 - 10:47 PM.

[JonnyA]

I thought that the idea was to get the pressures (when up to temperature) correct (~24 to 26 psi depending on the mod you are using) so that the size of the contact patch is optimised. Then, get the surface temperatures across the tyre even so that the contact patch is being used to the maximum. I don't remember seeing any optimum temperatures mentioned in the set-up guides I have read?

[JonnyA]

OK so is there an optimum tyre surface temperature? And which is more important, getting the temperature or the contact patch size correct?

[Lee200]

I've attached a spreadsheet which shows the percentage of grip versus temperature and pressure for the original '67 F1 front tire.  The temps are in Kelvin and the pressure is in psi.  For this tire, the optimums are 400 degrees Kelvin and 24 psi.

I'll try to answer each of these questions:

1.  There is only one optimum temperature and grip is highest when the tire temperature is exactly at optimum.  Above and below optimum, the grip decreases.  There is no defined range over which grip is maximum.  But as you can see from the spreadsheet, if the tire temp is kept within 25 degrees Kelvin or so of optimum, you are getting close to maximum grip.  The tire temp used to compute grip is the maximum of the three tread temps.

2.  There is only one optimum pressure and grip is highest when the tire pressure is exactly at optimum.  Above and below optimum, the grip decreases.  There is no defined range over which grip is maximum.  From the spreadsheet, if the tire pressure is within a couple of psi of optimum, you are getting close to maximum grip.  There is no excuse for not achieving optimum pressure though as you can adjust it in the setup menu.  Pressure is based on the setup menu pressure and is adjusted by the average of the three core temps.

Conduction heating and cooling is simulated between the three core temps and the three tread temps...they affect each other.  So for most drivers, equaling the core temps is a good goal as that also tends to equal the tread temps.

The setup menu displays the three core temps.  Pribluda can display the three core and the three tread temps.

If you are a very slow driver such as I who cannot get enough heat into the tires, you possibly can get better grip by having one tread temp higher than the other two.  This is because grip is based on the highest of the three tread temps.  Only experimentation will tell.

Attached Files

•  Grip V Pressure and Temperature.jpg   118.66K   455 downloads

Edited by Lee200, Jan 10 2014 - 12:53 PM.

[Iestyn16]

Very interesting.. so the peak grip is coming at the right temperature, and psi can vary around that 24 psi range. What temperature units are used in Pribluda? Fahrenheit?

[Robert Fleurke]

Lee200, on Jan 10 2014 - 10:12 AM, said:

I've attached a spreadsheet which shows the percentage of grip versus temperature and pressure for the original '67 F1 front tire.  The temps are in Kelvin and the pressure is in psi.  For this tire, the optimums are 400 degrees Kelvin and 24 psi.

I'll try to answer each of these questions:

1.  There is only one optimum temperature and grip is highest when the tire temperature is exactly at optimum.  Above and below optimum, the grip decreases.  There is no defined range over which grip is maximum.  But as you can see from the spreadsheet, if the tire temp is kept within 25 degrees Kelvin or so of optimum, you are getting close to maximum grip.  The tire temp in use is the maximum of the three tread temps.

2.  There is only one optimum pressure and grip is highest when the tire pressure is exactly at optimum.  Above and below optimum, the grip decreases.  There is no defined range over which grip is maximum.  From the spreadsheet, if the tire pressure is within a couple of psi of optimum, you are getting close to maximum grip.  There is no excuse for not achieving optimum pressure though as you can adjust it in the setup menu.  Pressure is based on the setup menu pressure and is adjusted by the average of the three core temps.

Conduction heating and cooling is simulated between the three core temps and the three tread temps...they affect each other.  So for most drivers, equaling the core temps is a good goal as that also tends to equal the tread temps.

The setup menu displays the three core temps.  Pribluda can display the three core and the three tread temps.

If you are a very slow driver such as I who cannot get enough heat into the tires, you possibly can get better grip by having one tread temp higher than the other two.  This is because grip is based on the highest of the three tread temps.  Only experimentation will tell.

Interesting, first you talk of real life or GPL, or both? Secondly, it's a shame the tires are modelled with grip based on highest of 3 temps...that's why ppl use such high tirepressures in mods I guess (like default), when the tiretemps are all over the place, but it seems to be faster...I seem to run lower pressures than most...

Personally I have always setup pressure and camber on roadcourses evening out tiretemps. But this new knowledge will make me to use a new approach...

PS: Lee, why should I run 75/75/4 rather than 50/50/1, when the locking percentage is the same...what's the (dis)advantage in running more clutches keeping the same locking percentage?

Edited by Robert Fleurke, Jan 10 2014 - 12:59 PM.

[Lee200]

Robert, my post was only about how GPL models grip versus temp and pressure.

Uh, the differential physics are a totally different ball of wax.  There are several threads that cover this in pretty good detail.  But to answer your question, if two different diff settings result in the same locking percentage, there is absolutely no difference in how the car reacts.  So there is no advantage of one setting over the other.

[Lee200]

Iestyn16, on Jan 10 2014 - 12:14 PM, said:

Very interesting.. so the peak grip is coming at the right temperature, and psi can vary around that 24 psi range. What temperature units are used in Pribluda? Fahrenheit?

I use F, but I believe Pribluda can display C if desired.

[Michkov]

Pribluda displays the units set in the game options. Obviously you should use metric anyway.

[Peter Dron]

Michkov, on Jan 10 2014 - 03:47 PM, said:

Pribluda displays the units set in the game options. Obviously you should use metric anyway.

Why is that obvious?

Apart from that, what an interesting discussion - I have had a hunch confirmed and learned several new things.

[Robert Fleurke]

Lee200, on Jan 10 2014 - 03:22 PM, said:

Robert, my post was only about how GPL models grip versus temp and pressure.

Uh, the differential physics are a totally different ball of wax.  There are several threads that cover this in pretty good detail.  But to answer your question, if two different diff settings result in the same locking percentage, there is absolutely no difference in how the car reacts.  So there is no advantage of one setting over the other.

Thanks, the spreadsheet does only apply to GPL67, and not to other mods I now understand. Also thanks for answering my off-topic question, thought more friction might cause slight power-loss with more clutches (not sure if it is modelled in GPL's physics), but should expand on that in a different thread.

Always good to learn new things and discovering new info about Grand Prix Legends!

Edited by Robert Fleurke, Jan 10 2014 - 05:29 PM.

[Saiph]

I've been driving Papyrus sims for many years, Indycar, Nascar and GPL. Originally, I tried to adjust my setups so that the temps were even across the width of all tyres. My thinking was that this would maximise the size of the contact patch at the "correct" temperature, and give me maximum grip. However, after reading Steve Smith's and Doug Arnao's comments in "Four-Wheel Drift" (p45-46), I decided to experiment, and I found that I actually got better turn-in performance with GPL if I adjusted my front tyre camber so that the inner edge was 2-3 degrees higher than the outer edge. They refer to this effect as "camber thrust", and although I am not an expert, and can't verify the physics of what they said, my experience is generally that it works. I now try to achieve this with all my setups, with all mods.

[JMF]

Saiph, on Jan 10 2014 - 05:32 PM, said:

I adjusted my front tyre camber so that the inner edge was 2-3 degrees higher than the outer edge.

Thanks for the tip. I'll give that a try in the future. I don't relly worry about getting my tire temps exactly even but I'll lean towards making the inside hotter now.

[Robert Fleurke]

BTW, on ovals, in Papy IndyCar & Nascar sims, we used 10 degree degradation, like 220-210-200 (F), using a lot of negative camber on the right, and positive camber on the left. Not sure if it applies to GPL ovalracing, as Lee stated that only the highest of 3 temps determines the grip for the tire. It still puts me off it's like that...need to experiment with that...

Edited by Robert Fleurke, Jan 10 2014 - 07:18 PM.

[Lee200]

Robert, in general the spreadsheet also applies to the other mods.  There are some slight differences in the curve, but basically, all the mods use the same curve although optimum temp and pressure do vary from mod to mod.

[John Woods]

Came up with following using on-line converter:
  K   =   F
275    35
300    80
325    125
350    170
360    188
375    215
380    225
400    260

Am I reading Lee's spreadsheet correctly? As I understand it, 1.0 = 100% grip, so .917 = 91.7%.
If so, it seems there's at least 90% max grip over a wide range? From what it looks like to me, most of the time my tires are up around 95% of max. For an average driver not working on a WR attempt, how critical is it to seek absolute optimum tire temps, on average, given the big range of variation on a typical lap? (As evident using TireTemp utility).

Edited by John Woods, Jan 10 2014 - 06:28 PM.