Experts, help me with tire pressure

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Burammm
From my years of playing GT I've picked up quite a bit of tuning knowhow and I can do a decent setup for different types of cars and drivetrains. But setting tire-pressure was never an option in GT. Can any of you shed some light on what the best use of tire pressure is in Shift 2?

I usually set front and rear to 40'ish for any car, but that's because I don't really know how to get the most out of it.

Any insights?
 
Ideally you'd want the pressure to be around 32 psi, but since for some reason Unleashed doesn't use psi like the first one did, it's become a process of elimination. To keep it simple, work on one end at a time; if the car is understeering lower the front pressure, if it's oversteering then lower the rear pressure. Do a couple of practice runs while tuning the pressure and pay attention to the grip graphic in the telemetry. If off the line the car essentially runs circles around itself your tire pressure is way too low. If when cornering you encounter snap oversteer, the rear tire pressure is either too high or low (extremes on either end of the spectrum will kill lateral grip, acceleration, and even increase your braking distances every step of the way).

You want to look at the graphic and monitor what the extremes are, if the graphic jumps from green to red, green to red, green to red, then you have a problem. You want a calm and steady transition. You want just enough of the contact patch touching the tarmac for optimal or near optimal performance. Ideally, the tires should only be on the thresholds of grip when you're exceeding the load on the tire and you'll know when you've done that because the rear end will break loose. If I haven't helped one bit and just confused you more, come back to me after I've gotten some sleep. :lol:
 
Awesome! Thanks. So I guess I will start with low pressure and do some trial and error going up until I've overdone it :)
 
Tire pressure is, IMO the foundation for all other suspension tuning. If your pressures aren't right, the rest of the car will never be perfect. The tire of course, is the only part of the car that touches the road.

The plot for tire pressure over mechanical grip is vaguely shaped like a bell curve. Meaning it gradually goes up, then comes back down. Actually it looks more like a lopsided muffin, but moving on...

That means at too low pressures, the tire will deform under load and you won't achieve maximum grip. You may have good initial grip because at first, contact patch is larger, but as you transfer weight onto the tire, the sidewall collapses and the shape quickly changes to a far less useful one. The result is sloppy handling and non progressive/unpredictable breakaway.

Ever see someone at the track draw lines with chalk or shoe polish on their tires? They are making sure their sidewalls aren't rolling over. If the markings start to disappear as the day goes on, they know they need to increase the pressure.

But at too high pressures, the tire will bow out and reduce the size of your contact patch. This is somewhat oversimplifying, but imagine the tire standing on its tip-toes. Not enough surface area to interface with the road. The result is sharp handling, but reduced grip.

So adjusting tire pressure is like finding the best bed for Goldilocks. Not too high, not too low.

Two important things too keep in mind as you search for the golden combination.

#1- In real life, tire temps directly affect pressure. As air heats up, it will expand. So as your tires get hotter, the air pressure will increase. S2U models tire temperature, but I don't know if the simulation actually adjusts pressure accordingly. It wouldn't surprise me if it did, though.

#2- The correct tire pressure is partly determined by how much weight the tire has on it. Put very generally and simply, the heavier a car is, the more tire pressure is generally needed to maintain the correct contact patch --all else being equal (such as tire size).

My 3,950 lb. Audi S4 runs a street tire pressure of 38 PSI and an eye watering 44 PSI at the track (in fact, I have to buy special 'XL' or 'extra load' tires for it). Whereas my 3,250 lb. BMW Z4 M only needed 32 PSI for street driving and 36 for autocross.

This is further complicated by several factors, not the least of which is different tires like different pressures and different suspensions like different tires and so on. But I would guess S2U uses a monolithic tire model for each tire catagory, so you won't have to worry if Kumhos like 40 PSI while a Toyo likes 42 PSI like in real life. In S2U, a street tire is a street tire. And a slick is a slick. As far as I know. I could be dead wrong.

Furthermore, in S2U, we have cars with aero downforce, which effectively makes the car heavier at high speeds... Which you can change based on how much wing you add....

Everyone got MEGO (My Eyes Glaze Over) yet? :)

In closing, I'll say my personal preference is not to tune tire pressure to adjust car balance (ie, oversteer or understeer) In my opinion, you are just making one end of the car worse than the other when you do that. Adjust tire pressure for max grip and use sway bars or spring rates to trim your car's balance if you really need to.

Hope that helps.


M
 
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I've learned that tire pressure should be whatever makes the temperature of the middle part of the tire the average of the outer and inner part.

This means that if you're running with camber and your tire temps read like:
outer: 95c, inner 99c, you should set the tire pressure to whatever psi or value makes the middle part 97c, since (95+99)/2=97.
 
I just wish they'd show tire PSI instead of a made up value. That and they need to show tire PSI in the telemetry so you can see what pressure you have when the tires are fully heated.
 
haehre
I've learned that tire pressure should be whatever makes the temperature of the middle part of the tire the average of the outer and inner part.

This means that if you're running with camber and your tire temps read like:
outer: 95c, inner 99c, you should set the tire pressure to whatever psi or value makes the middle part 97c, since (95+99)/2=97.
Click to expand...

That would make sense, since the hardest working portion of the tire will have the highest surface temperatures. The goal would be to try to spread the load as evenly over the tire as possible.

I don't know if this is realistically possible on street car suspension geometry and street tires. Most max performance street tires have their widest, largest tread blocks near the tire shoulder --they are designed with the knowledge that the outside portion of the tire will bear the highest cornering loads. Take a look at a Michelin Pilot Sport 3 for example. That tire even has a different compound at the edge.

However, on a real race car running tailor designed racing slicks, this would probably be SOP. That'd be why the tire guys with their pyrometers come out during certain pit stops.


As for what units S2U is actually using, it could a metric unit of some sort. Kilo per square centimeter or something like that. Or maybe they just made something up that the game engine can crunch easily.


M
 
///M-Spec
As for what units S2U is actually using, it could a metric unit of some sort. Kilo per square centimeter or something like that. Or maybe they just made something up that the game engine can crunch easily.


M
Click to expand...

Haha I hate to nitpick, as Ive found this thread very informative and helpful, but I just had to point out that the metric unit of pressure is Pascals (Newtons per square meter). Kilo's are a unit of mass, not force!(unlike pounds). People from countries that use the Imperial system often seem to get that confused. Anyways, nerdiness out of the way, good thread for visualizing the effects of changing tire pressure- thanks :cheers:
 
powersaurus
Haha I hate to nitpick, as Ive found this thread very informative and helpful, but I just had to point out that the metric unit of pressure is Pascals (Newtons per square meter). Kilo's are a unit of mass, not force!(unlike pounds). People from countries that use the Imperial system often seem to get that confused. Anyways, nerdiness out of the way, good thread for visualizing the effects of changing tire pressure- thanks :cheers:
Click to expand...

That being said, there is also Bar, which is Kg/cm^2. Roughly 14psi.

Also, I dont know if this is the case in S2U, but race cars actually have their tires fill with nitrogen, because this gas doesnt expand as much as air when heated, reducing the ballooning effect on the tire. This means that the tire pressure wont change during a race, only the surface of the tire will heat up.
 
///M-Spec
Tire pressure is, IMO the foundation for all other suspension tuning. If your pressures aren't right, the rest of the car will never be perfect. The tire of course, is the only part of the car that touches the road.

The plot for tire pressure over mechanical grip is vaguely shaped like a bell curve. Meaning it gradually goes up, then comes back down. Actually it looks more like a lopsided muffin, but moving on...

That means at too low pressures, the tire will deform under load and you won't achieve maximum grip. You may have good initial grip because at first, contact patch is larger, but as you transfer weight onto the tire, the sidewall collapses and the shape quickly changes to a far less useful one. The result is sloppy handling and non progressive/unpredictable breakaway.

Ever see someone at the track draw lines with chalk or shoe polish on their tires? They are making sure their sidewalls aren't rolling over. If the markings start to disappear as the day goes on, they know they need to increase the pressure.

But at too high pressures, the tire will bow out and reduce the size of your contact patch. This is somewhat oversimplifying, but imagine the tire standing on its tip-toes. Not enough surface area to interface with the road. The result is sharp handling, but reduced grip.

So adjusting tire pressure is like finding the best bed for Goldilocks. Not too high, not too low.

Two important things too keep in mind as you search for the golden combination.

#1- In real life, tire temps directly affect pressure. As air heats up, it will expand. So as your tires get hotter, the air pressure will increase. S2U models tire temperature, but I don't know if the simulation actually adjusts pressure accordingly. It wouldn't surprise me if it did, though.

#2- The correct tire pressure is partly determined by how much weight the tire has on it. Put very generally and simply, the heavier a car is, the more tire pressure is generally needed to maintain the correct contact patch --all else being equal (such as tire size).

My 3,950 lb. Audi S4 runs a street tire pressure of 38 PSI and an eye watering 44 PSI at the track (in fact, I have to buy special 'XL' or 'extra load' tires for it). Whereas my 3,250 lb. BMW Z4 M only needed 32 PSI for street driving and 36 for autocross.

This is further complicated by several factors, not the least of which is different tires like different pressures and different suspensions like different tires and so on. But I would guess S2U uses a monolithic tire model for each tire catagory, so you won't have to worry if Kumhos like 40 PSI while a Toyo likes 42 PSI like in real life. In S2U, a street tire is a street tire. And a slick is a slick. As far as I know. I could be dead wrong.

Furthermore, in S2U, we have cars with aero downforce, which effectively makes the car heavier at high speeds... Which you can change based on how much wing you add....

Everyone got MEGO (My Eyes Glaze Over) yet? :)

In closing, I'll say my personal preference is not to tune tire pressure to adjust car balance (ie, oversteer or understeer) In my opinion, you are just making one end of the car worse than the other when you do that. Adjust tire pressure for max grip and use sway bars or spring rates to trim your car's balance if you really need to.

Hope that helps.


M
Click to expand...

I like this explanation. Pretty clear how it all works now :)
 

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