I ran 32 psi for the past two years....and it road good (comfortable). And that is exactly why it is there...for comfort. I did A LOT of research on this last week and there is NO exact science on it. The conclusions "I" came up with based on my "Google'ing" was: -OEM tire pressure is mainly for driver comfort. For "spirited" driving bumping up the pressures in 2 psi increments to find out where you like it is a good guide. Most guys I've talked to with SRT8's run around 36-38 psi in the OEM tires. -If you have aftermarket tires it is "recommended" to take the OEM (say 32 psi) and the max tire pressure on the tires sidewall (say 48 psi) and meet somewhere in the middle (39 psi)....and again bump it down or up a couple psi and find what YOU like. -Also, a little higher psi creates "less" rolling resistance and gives you a little better fuel economy. -A lot of folks typically run higher pressure in the front and lower in the rear. For daily driving this method has become common practice based on the fact that "most" cars have more weight in the front. Since our cars have a 50/50 weight distribution it is recommended to have the pressures equal front and back. -Run your pressures a little higher when its cold out....and a little lower when its hot out. Again, no real science here....but some general guidelines that I've discovered. Please add additional comments or myths that I may have missed. Hope this helps! - Rick
Sounds totally reasonable to me... I'm gonna adjust my new Vredesteins accordingly. *there's your reply! BTW: Dave (Quick) has been viewing this thread for over 30 minutes... this should be a good response!
Best way to home in on the correct tire pressure for the majority of your driving is to invest $5 in a tread depth gauge. This is a little thing about 2" long with a plunger on one end and a scale on the other like what comes out of the old style pressure gauges. Available at most of your popular auto parts stores. Measure tread depth at least every 3K miles. You want to take 3 readings on each tire. Outside, center and inside. On the sides don't measure on the very edge but the first groove in where the tire sits on the road. Don't inadvertently measure on a wear bar (2/32" bumps spaced around the tire in each groove). Write down your readings and keep a record for each tire (if you rotate tires it's best to just give them a number since RR, LR, etc. doesn't work when you rotate). You're looking for even wear across the tread. This gives you the longest tread life and the largest tread patch on the road. More wear in the center means your pressure is too high. More wear on the edges means your pressure is too low. Uneven wear on the inside compared to the outside indicates alignment problems. 4 psi will make a measurable difference in tread wear. Surely there are occassions where you might want to run your tires at a higher or lower pressure than normal due to some of the dynamics involved. Pumping them up will give better mpg and cooler running temps on the highway. Running them low can give you getter traction at the drag strip. Outside of the extremes, even wear across the tread will give you the best economy and performance. Tire rubber is not competely impermeable to air. They will lose pressure over time (month(s)). We got a TPM system so that's not a problem. Tire pressure measurements are ALWAYS cold (ambient air temp). It takes your tires about 4 hours to completely cool down after driving (and only about 1 mile to start to heat up where it makes a pressure difference). From cold to hot you can expect to see about a 4 psi rise due to temperature. Yes, the MAX pressure rating on your tire is a cold pressure and takes into account for the tire getting hot under operation. Nitrogen is a crock. Yes it's true that nitrogen has larger molecules and therefore it will pass through tire rubber much more slowly. This is good for the idiots who don't check their tire pressure for years if ever. Most all excessive tire wear (and failures) can be attributed to improperly inflated tires. Most drivers are idiots and/or can't be bothered with checking their tire pressure (ever). Because there are so many idiots they have actually made it a requirement that newer cars have some sort of TPM system. Nitrogen doesn't expand quite as much as air with temperature but it still obeys all the gas pressure laws of physics. Unless you're an idiot or just want to tell people you're running nitrogen in your tires it's not worth paying for it. Did you know that air is mostly nitrogen? 78%
I too agree w/everything stated. I prefer higher psi than the dealer/manual calls for. In the Jeep I try to keep all four above 36psi. I almost never see extensive center tread wear on any 4wd/awd vehicle I've owned. I have had outside chopping on most of these vehicles.
:cry2: my little seal trainer is growing up! You make me proud to be part of the "EQ", HONKEY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!:hug:
YOU are the reason I did the research Ryan....Thanks! When I road in Ryan's car the ride felt a little harsh....so I checked his pressures. They were at 49-50 psi!!! I mentioned even though they're hot that's probably a little high. LOL
On our stock 17X6 rims i ran 50-55 because anything under that the edge of the tire would roll over in a hard turn and it didnt matter what tire was on there. with the current rims i have i run them at 42 a
Another bit. Most tires for public consumption start out with 10/32" - 12/32" of tread. Our RSA's start with 10/32". Yokohama Geolanders for the Expedition started out with 12/32". Rule of thumb (and most state inspections) determine minimum safe tread depth to be 2/32". For your convenience tires are made with little bars in the tread spaced around the tire that just happen to be 2/32" high. When these are level with the tread surface it's time to replace (the top of Lincoln's head on a penny is roughly 2/32" away from the edge). You should notice that your tires get a bit noiser when they get down to the wear bars. A whole lot of design goes into how your tread reacts under loads. If they just put an inch of tread on the tire it'd be like driving on a sponge with the tread blocks squishing all over the place. Seems that around 10/32" to 12/32" works about right. Tread blocks are there to channel water/snow/mud but they need to be rigid to maintain traction under lateral, acceleration, and braking. It's a tradeoff. Less tread depth is generally better for dry traction. Some specialized performance tires start out with a lot less tread. Like 6/32" or 8/32". Sometimes racers will take new tires and shave them down. Naturally they don't last as long. So you'd think you would have better and better dry traction as your tread wears out? Not generally the case. Problem is that tread compounds are effected by being exposed to the elements, heat and cold. They generally get stiffer as they start to break down and lose the stickiness they had when new. The tread design also doesn't work as well under dynamic loads as it hardens over time. A couple of manufacturers have tires with variable tread compound as you get deeper into the tread. The compound underneath is more "sticky" and softer so that as it ages, and gets exposed as the tire wears, it's much closer to what the outside was when new. Nice idea, don't know how well it works in practice. Everybody needs one of these.
Oh, yea. One more thing:sleep: Tires have a shelf life. As above, they age once manufactured and exposed to the air. Old tires won't wear or perform quite as well as newer tires. Worst thing is UV but since they generally live in warehouses that's not so much a problem. All tires (maybe it's only DOT approved tires) have a manufacture date stamped on them. Usually encoded but you can look it up. When you buy new tires check to see that they're less than a year or so old. I think less than 6 months is ideal. If you buy from tire chains it shouldn't be a problem. Naturally it's more of a problem with low volume/odd size tires... like ours.
The only benefit from pure nitrogen is that it is dry, which can help with corrosion of the wheel and TPMS. I don't know if I'd call it a total crock...maybe just a partial crock. But, you are 100% right, it definately doesn't do what most think... I've actually done the "tread depth" technique when setting tire pressure on a set of slicks...the only difference was I ran the tires where I thought it should be. Then, after they were worn out, I cut the tire in 3 or 4 places across the flat part of the tire...it works great. Keith
Umm, this is not quite right. If it gets cold you will need to add air to maintain the same pressure you had when it was hot (and visa/versa). But you still want to maintain the same pressure. So if you've decided 35 psi is the right pressure for you and your tires, then air the tires to 35 psi. If it's hotter outside it just takes less air to do that. If you keep an eye on your pressure you will be adjusting for seasonal changes. Don't worry about spring and fall where you might have a big temperature swing from daytime to night time. Note that direct sunlight on your tires will make a significant pressure change due to heating them up (black tires absorb a lot of heat from sunlight). Maybe 2 psi or more. Ambient air temp would be in the shade.
Here's where I read this....more geared for track or hard driving (which is what I do ALL the time!) "Adjusting For Ambient Temperature We mentioned earlier that 10 degrees F changes the tire pressure about 1 psig. If a tire starts with a certain cold pressure in the morning, the warming of the day is effectively adding pressure to the tire over the course of that day. The temperature the tire runs at will be affected by the combination of the ambient air temperature, the track surface temperature, and the amount of friction introduced (how hard you drive). If for your first session of the day, it's overcast, the air temp is 65 and the track temp is 70, then in the afternoon the sky is clear, the air temp is 85, and the track temp is 105, there is considerably more heat to influence the temperature of the tire surface. If you drive just as hard, the tire will be hotter, and the pressure will be higher. This change from morning to afternoon is going to be much more pronounced in some climates than others. The southwestern U.S. can see days with a 45 degree morning and a 90 degree afternoon. This will increase the starting tire pressure by 4 psig by the end of the day. This will make a world of difference in the handling of the car during each session. To maintain the same racing pressure settings in the afternoon as achieved in the morning, you'll have to compensate for the increased pressure due to ambient temperature. While there is probably a formula to understand the effect of the relationship of the ambient temperature and the track temperature, it will be complicated by the aerodynamics around the tires, and the heat generated by the brakes. You can generally use the ambient air temperature and the 10 degrees per 1 psig relationship as a guide for adjusting tire pressures throughout the day. Take ambient air temperature readings at the start of each session, and use this to determine how to adjust the tire pressures. As the day warms, you'll have to drop tire pressures accordingly before each session. One more item related to ambient temperature--you’ll find that if the car is parked with one side of the car facing the sun, those two tires might be 10 to 20°F warmer than the shaded side (and therefore 1 to 2 psig higher in pressure). You should cover those tires up with some simple plywood panels, or at least know not to set them to the same pressure as the cooler side of the car." From below link: http://www.turnfast.com/tech_handling/handling_pressure
thats the issue with air, it expands, thats why they all go nitrogen now with the high perf sports cars.
Well, sure. You're going to want to adjust if you're on the track. It's going to be a bit of a guessing game because you're probably going to be adjusting your pressure hot -- probably won't have 4 hours to let your tires cool all the way down between sessions. So you'd want to take the pressure immediately before adjusting it and go up or down from there. It's also likely to be more of a feel thing after the first session anyway. Depending on how the car handles you're going to decide you need a bit more or less air in the tires for the next session. Not so much based on the fact that the ambient air temp went up or down. Nitrogen expands too.
yup, but the coefficient is much less. its .8 compared to air which is around 1.1 or 1.2. it also doesnt oxidize and damage the inside of your tire and of course you know that air is almost 78% nitrogen to begin with.
All I can say is Quick is a smart smart man. Oh...and nothing erks me more then people swearing by nitrogen. I work with Nitrogen daily in my line of work......It succumbs to pressure changes just like regular air.....to a lesser degree....but it does change.
Would they age if sealed in a nitrogen enviroment? Nope...Nitrogen is an "inert" gas. Just maybe it is a better enviroment for the inside of the tire. I know air is about 78% Nitrogen but it is the other 22% I wonder about, plus the humidity of the "air" (Unless you know your gas station air compressor has a dryer on it....of which I doubt).. I am not here to debate using Nitrogen, but I have seen us do mods to our cars for lees of an effect. Due to the bashing coming....I know I am going to regret even "partially" supporting Nitrogen in tires. Maybe we should discuss "Cold Air Induction" instead.......lol
