Just wondering what everyone that has the 19's is running for tire pressure. It says 45F and 45R, are you going with this?
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The 45 psi is the starting point--then you adjust it for temperature and other conditions. Tire pressure recommendations are always based on 65F 18C ambient temperature. If it gets hotter than that you need to increase the pressure to compensate. There are other factors as well.
I was delivered with PSI of 44-45 on all four tires. That caused some real yaw. 42 is what P85 needed. Hard to believe, but 3 people all agree. If you apply so much torque to the rear tires, you need to be careful on this.
The 45 psi is vehicle placard pressure for the 19" tires. I should have made that clear. Adjusting for conditions could be lower or higher depending upon what the conditions are, although adjustments are usually higher).
Why the reason behind the between between the 19" and 21" inflation pressures? Is it because the 21's are 8.5 wide vs. 8" for the 19's? (I am running 19x8.5 aftermarket wheels, so I'm wondering if 42 or 45 is a more appropriate pressure.)
My opinion is that the pressures were chosen mainly because of the handling differences between the sport tuned P85 suspension and the normal S85 suspension based on test track evaluation. Also lower pressure for the 21" tires creates a slightly larger contact area which helps traction on dry pavement. Conversely the 19" tires likely have the higher pressure to reduce rolling resistance. Tesla stated that the 19" tires get about 5% more range--the higher pressure helps them keep that promise. (Presumably those who don't purchase a P85 are more interested in economy than performance.)
The difference air volume between the 8" and 8.5" rim width isn't enough to matter--I'd still run 45 on the 19" (it will help the tires survive pot holes). To determine the best handling pressure for dry pavement, use an infrared temperature meter or chalk to get the most even contact pressure. Your local SCCA should be able to help with this.
Not wanting to start any arguments here, but with my old EV, I'd run the tires at 50 lb, when the tire said 44. The tire dealer said there was no problem over inflating by 10% "or so", and I wanted range back then.
Really?? They're not setting the bead!