Tire Pressure Discussion

[Erik W. Treves]

You'll be surprised how much ride you'll get back with tire pressure. What most people don't understand about these extremely light component cars is that you can run much lower pressures. You'll want to run between 18-22PSI vs the 30PSI on the 3000lb car. 10PSI for every 1000lbs is a good rule of thumb and with the Hot Rod, I learned my lesson when I went through my first set of NT-01s on the center running 27PSI on the front and on the second set I ran 22PSI warm it they wore perfect. I also went down to 18-19 at the track (per Nitto's recommendation) and they were awesome. So check those pressures before the first run guys!

yep I am running the 10 psi per 1000 lbs on both the cobra and the 818.. the cobra has 600lbs and 300 lbs springs front and back and the ride isn't bad at all.

[Frank818]

So that's 10PSI warm per 1000lbs?
And cold, 2-3psi less?

Same pressures front and rear? I'd except a small difference, though.

[Erik W. Treves]

It all depends on if you are using straight air or nitrogen.....lol

so here we go again...

*** Disclaimer ***

this is a Rule of Thumb....it will get you in the ball park. Make your adjustments from there...lot's of things will effect how much air you put in the tire..best recommendation after that is take your car to an autox event and see what the car likes....

*** Disclaimer ***

this is also only, my method....

[metros]

Thanks for the tip. I wouldn't have thought of dropping the pressure because of the lighter overall weight.

[Erik W. Treves]

Yes... DO NOT run the recommended tire pressures on the side of the tires. I did that on the cobra the first time turned the wheels in the parking lot stepped on the gas the car turned for a second ( about 5 mph) and then just went straight!!! wicked understeer!

[metalmaker12]

I am running around 18-21psi all around, but will dial it in once I get her on the road and see where it holds lines best. Looking good Erik

[metalmaker12]

I am working on my harness now, maybe this week or next I will be installing and trying to fire up.
You have done great on time man!!

[Frank818]

Ok to make things clearer about tire pressures, since we were talking about air, I was talking about air we all breath (assume you are human, though can a human build a car that fast, let's put that question off topic :)). If one pumps some helium in his tires, well I guess he should go on a balloon party forum. loll But so that we have all the info, I'll specify both air and nitrogen.

Now what could be the recommended tire pressures, for the 818S and R if possible, based on FFR's recommended tire sizes for front and rear?

If using air we breath.
If using nitrogen.

Measured at cold or hot temps?

Tnx for the info. :)

[bstuke]

Just glad you didn't bring up Nitrox. It makes me want to quit working on the R and go diving...

[Wayne Presley]

Now what could be the recommended tire pressures based on FFR's recommended tire sizes for front and rear?

If using air we breath.
If using nitrogen.

Measured at cold or hot temps?


I measured tire temps and set pressures at the FFR 818 test days and based on that I set the fronts at 21 psi and rears at 22 on the street car running Toyo RA1's cold and they grew to 26-27psi on the track hot. The 21F-22R is what was run and will vary from there depending on tire, usage and alignment.

[Xusia]

I'm personally not sold on Nitrogen. If you've got free access to it, that's great. I'm just not going to pay for it when I have a compressor at my house and get regular air for essentially free.

Edmunds refutes the traditional arguments:
Less pressure loss?
In 2006, Consumer Reports conducted a year-long study to determine how much air loss was experienced in tires filled with nitrogen versus those filled with air. The results showed that nitrogen did reduce pressure loss over time, but it was only a 1.3 psi difference from air-filled tires. Among 31 pairs of tires, the average loss of air-filled tires was 3.5 psi from the initial 30 psi setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial setting. Nitrogen won the test, but not by a significant margin.

More consistent pressure?
When air is pressurized, the humidity in it condenses to a liquid and collects in the air storage tank you use at the local gas station. When you add compressed air to the tire, the water comes along for the ride. As the tire heats up during driving, that water changes to a gas, which then expands, increasing tire pressure. Because nitrogen is dry, there is no water in the tire to contribute to pressure fluctuations.

But this fluctuation in temperature isn't as significant as you might think. A 2008 ExxonMobil study plotted the changes in temperature over the course of various inflation pressures. The lines on the graph were virtually on top of each other. In other words, the change in temperature when using nitrogen was negligible.

Nitrogen proponents will also point out that water in a tire can lead to wheel rot. A tire engineer who anonymously maintains Barry's Tire Tech, a blog on a number of tire issues, says this isn't really a problem with modern cars.

Wheel rot?
"Alloy wheels don't really have a problem with water inside the tire," the engineer writes in a post on nitrogen inflation. "They are coated to keep aluminum from forming aluminum oxide, which forms a crust, which isn't very attractive. But even then, this crust protects the aluminum from further corrosion from the water."

[Frank818]

Good, tnx for the info guys. :)

[ClemsonS197]

I'm personally not sold on Nitrogen.

Don't forget that "air" is already 78% Nitrogen. You also have 1 tire volume of "air" in the tire, so at 30 psig, you basically still have 7% non-Nitrogen in your Nitrogen filled tires. You're paying a fair amount of money to go from 78% Nitrogen to 93% Nitrogen.

[SkiRideDrive]

Normally when converting to Nitrogen you will purge the tire. Some will go as far as running two valve stems to simplify the process.

[David Hodgkins]

bump. Moved from build thread to here...