Tire Pressure and Grip

OB · Post by OB » Sun Mar 15, 2009 1:11 pm

I've been toying with pressures to find maximum grip lately, and I figured I'd share the results of my experiments. Sorry about the novel! For a long time I was under the impression that lower pressure=more grip, due to increased contact patch. Therefore I had my pressures at around 32F/38R in attempt to create slight oversteer under throttle. However, I've since read in several credible articles that many FWD cars benefit from a higher front setting. While this contradicts the 'lower is better' theory, it also makes sense in its own way.

Basically, lower pressure causes more sidewall deflection, especially under high cornering load. This can lead to a lack of grip due to inconsistent tire shape and contact patch. Also, tire pressure can greatly affect spring rate. It is essentially a way of fine tuning the balance from front to rear. The problem is, too high a pressure is dangerous and could adversely effect handling due to too little contact patch. So a balance between spring rate and contact patch must be found for maximum handling performance.

I changed my pressures around, per the info I found via research. I'm now running 42F/35R, and with much success. Handling is very crisp now, and wheel return is excellent. Peak grip seems to be slightly better, but the improvement in steering feel is what I like most about the settings. The added spring rate actually solved another problem I was having: bottoming out. With a 2" drop, very little suspension travel is left over for compression. I used to hit front bumpstops all day long, while now the problem only occurs under severe conditions (i.e. potholes).

The old settings were good for on-throttle oversteer during hard cornering, which also meant tail happy brake oversteer. Almost as if they come in a package deal. The slight oversteer during accel was ok, but a bit scary and somehow it seemed useless for speed. While it was predictable and fairly easy to correct, any shift in weight to the front wheels (i.e braking) would cause a fairly sudden loss of traction. The new settings created optimum balance; no more oversteer. Instead, just sheer grip. I haven't pushed it to the limit yet, but I can now take corners at the same speed as before without losing traction in the rear. Brake oversteer has improved, but is hard to get rid of due to weight distribution and bushing deflection in the rear. Nothing those Prothane bushings sitting in the garage wont fix!

All comments are welcome. What pressure settings are you guys running for max grip? I plan to experiment a bit more soon, but I think I'm going to wait until I have the rear bushings taken care of. Thanks for looking

SOKADAO954 · Post by **SOKADAO954** » Sun Mar 15, 2009 2:54 pm

great write up. usefull info thank u ob.

INVUJerry · Post by **INVUJerry** » Sun Mar 15, 2009 3:29 pm

Great info. I had known that higher pressures lead to more grip from reading all tons of autocross stuff on .org, but it's still really good to see this written here. I would think more air in the front would be necessary, since that's where most of our weight ends up in the cars, and to have an even tire patch, more air in the front, and less in the back would seem better. I had a buddy with a 04 Nissan Sentra Spec-V, and he was running 51 pounds of air in his tires when he would autocross it. I'm currently running 40/40 in my 98 and 05 neon, but I'm mainly doing that for gas mileage reasons. I noticed that while driving my 98, it seems to spin less going into 2nd with 40 psi vs 28 psi, which is the exact opposite of what I've been told for years by drag racers.

Donkeypuncher · Post by **Donkeypuncher** » Sun Mar 15, 2009 5:21 pm

Same thing here, I always tried to keep the front tires just below 40, but it was more for gas mileage than traction. I guess I've unknowingly been doing the right thing for the past 10 years. I never really liked the sloshy feeling that the low pressure gives while cornering, just feels odd to me.

I'm guessing most people assumed the rules for RWD applied to FWD as well, I know I did.

Cabbs · Post by **Cabbs** » Sun Mar 15, 2009 5:50 pm

Good read. I'm gonna start experimenting with mine and seeing how it goes.

JeffM · Post by **JeffM** » Sun Mar 15, 2009 7:10 pm

Very nice write up OB. I haven't really experimented with tire pressure (normal 32psi) but I do love to take corners...maybe I'll check it out.

OB · Post by OB » Mon Mar 16, 2009 9:32 am

Thanks guys. I forgot to mention that during my first round of adjustments I recorded tire temperatures across the face of each tire. I ran a select course several times and recorded the temps with the new settings. I found the variation to be within limits, however, somehow the left tires ended up warmer than the right. This is most likely due to my uneven alignment settings, and possibly even due to the nature of the course I ran during testing. I'll edit this with the temps as soon as I get time.

jT · Post by jT » Mon Mar 16, 2009 11:26 am

Off topic but tire pressure + warranty = what?

All warranties will say proper tire pressure blah blah blah.

Obviously with air you can adjust them as needed, but I just had my tires filled with Nitrogen so I've got to go to them for fills.. and they probably wouldn't want to have anything other than proper inflation.

Now relating to your topic -- would this "enhanced" tire pressure be different for different size tires? You've got 42F/35R on what-- 16"? Would it be different for 14" or 15" or 17"? Different for stock suspension with no drop?

Possibly-- a lot of factors would change an individual's results.

Post by **racer12306** » Mon Mar 16, 2009 12:32 pm

It mainly depends on the tire.

On a stock size tire, the door rating is 32psi. And typical replacements are 44psi, so between 32 and 44psi is a "proper cold inflation"

Tam · Post by **Tam** » Mon Mar 16, 2009 1:08 pm

This is a good write up, I will experiment using your advice on mines because I am also currently trying to find the right set-up for myself.

OB · Post by OB » Mon Mar 16, 2009 7:37 pm

jT wrote:Off topic but tire pressure + warranty = what?

All warranties will say proper tire pressure blah blah blah.

Obviously with air you can adjust them as needed, but I just had my tires filled with Nitrogen so I've got to go to them for fills.. and they probably wouldn't want to have anything other than proper inflation.

Now relating to your topic -- would this "enhanced" tire pressure be different for different size tires? You've got 42F/35R on what-- 16"? Would it be different for 14" or 15" or 17"? Different for stock suspension with no drop?

Possibly-- a lot of factors would change an individual's results.

Nitrogen is good for people who are too lazy to check their tire pressure. If it was free and available everywhere I'd use it, but it's just not worth the extra effort IMO. As far as wheel size affecting tire pressure, I'd say the difference is probably minimal. Has a ton more to do with the tire type and ratings. Every tire is different. The key to pressure tuning is the ratio, not necessarily the exact pressure itself. The relationship between the front and rear pressures (relative to the max pressure) is the key to max grip.

NickKo · Post by **NickKo** » Tue Mar 17, 2009 1:34 pm

racer12306 wrote:It mainly depends on the tire.

True.... different tires get different results.

Like my older 512 Falken Zieks, for example.
They have rather squishy sidewalls, which helps the ride quality somewhat, at the cost of some handling ( and TIRE LIFE, because it will chew up the corners of the tread really fast.)

But as a trade-off, the Zieks can be run at some really high "max" PSI, like 52 (per the lettering on the sidewall.)

Mind you, this is "Maximum" pressure...... It's not saying you should run that pressure all the time.

- Nick

hybrid-Srt2001 · Post by **hybrid-Srt2001** » Wed Mar 18, 2009 3:22 am

Good info derek! I curreently run like 38f 33r tire pressure, and my car handles great, just steer in the direction you want to go and hammer the throttle. Only once did i spin out, and that was with my rear shocks on stiff, hotchkiss bars, and bald tires on a down hill sweeper. I find that i can run a bit lower pressures with the 45 series tire since the sidewall is stiffer. if you want to check your tires contact pattern, spray some paint on them and play with the tire pressure a bit.

NEON PARABOLA · Post by **NEON PARABOLA** » Tue Nov 06, 2012 10:55 am

can we get this stickied? great info!

OB · Post by OB » Wed Nov 07, 2012 8:21 pm

NEON PARABOLA wrote:can we get this stickied? great info!

I think there was enough positive feedback on here to warrant that. Done and done.