[bluekitty]

Hi,

It's really cool the g87 has tire and temperature sensors for all 4 corners. I did a track day and it got really hot out. I forget the exact temp/pressures, but the car started showing tire pressure way to high. So, I took some air out of each to get it to about 36lbs. that made a big difference in handling.

I am new to the car and sports cars in general, but with the stock tires, what is the ideal tire pressure? or, range of temperature/pressure? Personally, really am enjoying learning the car and tire/wheel set ups. the G87 is a really fun car to get exact with.

Matt

[DutchBoysRacing]

My qualifications: none...I just go to two track events a month (on average) and compete in time trial for specifically bmw's called Bimmer Challenge. I usually place 1st-3rd in my class. Check out my IG to see me do dumb car stuff (@dutchboysracing).

To save you a read: In the dry I aim for 30-34 hot dependent on the tire and track conditions with 200tw tires (RE71RS, CRS, SuperCar3R), for semi slicks (R7,A055) I aim for 28-30 hot. This means I sometimes go out at 25-26 PSI cold, I take two laps to warm up the tires to temp and avoid hopping curbs until they are hot.

Tire pressures should be determined by weight, ambient temperature, track conditions, and also a pyrometer...but I am a track junkie so I am only going to provide a "rule of thumb" for each of these.

My Lecture

Remember a tires contact patch is about the size of your hand. That means you're throwing a 3800lb+ piece of metal with 450whp through a corner with not that much rubber actually on the road...pretty nuts....but I digress

If you overinflate a tire it will wear in the center tread of the tire. This is because you are losing contact patch as the center patch of the tire physically expands past the shoulders of the tire. Less contact patch, less grip. Google over inflated tire wear.

Note: In wet conditions this can actually help as narrower tires can "cut" through standing water better than larger tires. This is also why you get better MPG with over inflated tires, less contact patch, less rolling resistance = better MPG.

If you under inflate a tire, you will wear the outside shoulders of a tire and also damage the side wall. The side wall provides stability for the tire...damaged tires = bad.

Note: Track tires have more sturdy sidewalls can usually handle lower pressure better than street tires. You should avoid hitting anything that could impact your tires side wall when its under inflated *cough* curbing *cough*.

You're striving for a perfect balance. Soft (low enough pressure) to be more malleable to the road, but inflated enough not to cause damage to the sidewall.

Weight: Heavier cars require more air pressure to avoid damaging the sidewall. Lighter cars require less air pressure. My buddies E36 M3 weighs 2500 LB with him in the car, he aims for 28 hot and some actual racing slicks call for the same pressure, that means he goes out at 20 cold.

Ambient Temperature: If its 90 out and you go out at 30 cold, and you actually drive the car hard, you'll run into issues with the pressure rising. If its 50 out and cold, I would go out at 30-32 as I probably won't keep the heat in the tire compound as well.

Tire Pyrometer: This measures the temperature at different parts of the tire (inside, middle, outside). If you middle is A LOT hotter than the outsides, then you can drop pressure. If the middle is A LOT cooler than your center, drive faster.

If you are using a street compound its safe to assume that your hot pressure should be a bit under your road pressure. If you drive at 36 PSI, you want 34 PSI HOT.

Now to address everyone that wants to quote the Hoosier or Toyo recommended pressure of like 40+ PSI. That's insane, no one is doing that that is very competitive. That's a CYA because they've had liability issues with tires going out at 100mph.

I've tested the Toyo RS1 and Toyo RR (old) at 38-42psi pressures and its driving on glass.

[bluekitty]

Thanks for the info. I did notice one track day at PIR and the oem tires were never the same again. lol. I really should go take a closer look at how the tires got worn. I am having a blast getting to know this car and what it's capable of.

Do you go with a lower psi when it's wet out?