what tire pressure on upgrade to 17" from 16"

[vibebob]

I changed my rims and tires. the new tires are Goodyear Eagle LS. Should I still use the tire pressure that is on the door for my LS's ? The sidewall says 44 max psi.I did a search on tire pressure and found one where most say run what is on the door, but this was for the stock tires. for now I'm just going to run 32 and see what happens. I want y'alls input on thisthanks,bob

[Sublimewind]

I would play around with it.... The numbers in the door are NOT set in stone... I would work your way around the 34psi mark.. keep an eye on the tread, if you're to high, the center wil wear quicker, if to low the outter edges... Much changes in handling and comfort when messing with the PSI also

[Mavrik]

When I switched from 16" to 17" tires, I kept the pressure at about 35 regardless of size. seemed to work rather well for me. The ride was to rough when I set it to 40psi to experiment.

[engineertwin2]

Per this thread: http://forums.genvibe.com/zerothread?id=25958Quote, originally posted by engineertwin2 »I'm surprised at how common of a mistake it is for people to believe that if the tire size changes, so too does the pressure.Perhaps I'm off the mark for what makes people think this, but the volume of air contained within the tire and the wheel is not spec'd by the manufacturer and I believe that is what people some people interpret it to be. Rather they say the pressure should be at a specific level. This allows the volume of air to increase or decrease dependent upon ambient temperature, barometric pressure, wheel size, tire size, etc.Basically, when a manufacturer specs a pressure, they are stating that this is the pressure used when optimizing the ride and handling characteristics - to optimize your driving experience, keep the tire pressure at this point.This also gets confused with the maximum allowable cold pressure stamped on the tire. A majority of tires on the road today have a max all. cold pressure of 35 psi. People see this on the tire and say "ok, I need to fill it to 35 psi."I'm sorry if this turned into a rant, but it seems it needs to be written again - "Recommended tire pressure is independent of tire size. It is recommended that you always use the lower value of either the vehicle manufacturers recommended tire pressure or the tire manufacturers maximum allowable cold pressure. Using the lower value of these will ensure that your vehicle operates as safely as possible."Remember that the greatest danger to low tire pressure is overheating the tires, causing premature degradation or "catastrophic" failure (i.e. a blow out). The greatest danger to high tire pressure is loss of vehicle dynamics (rougher ride, longer braking distance, reduced ability to turn at speed).Because your tires are the only part of the vehicle that maintains contact with the road (and thus one of the most critical safety points on the vehicle), I will never discourage people to ask questions about their tires and I promote extreme caution. Unfortunately, there are way too many of us on the road with improperly maintained tires...I'll say it again - the pressure is not dependent upon rim diameter or tire size. Pontiac/Toyota don't change their recommendations based on whether you get stockers or the upgrades.The pressure recommended by the manufacturer of the car is based on a balance of vehicle handling characteristics (braking, turning) and fuel economy. If you want to inflate them more, feel free but understand that the recommendation doesn't change with tire size, but with vehicle load.My recommendation, always stick with the lower of what is printed on the sidewall of the tire or the recommended tire pressure (32 recommended vs 35 sidewall stamp for stock continentals - go with the 32).

[Sublimewind]

Quote, originally posted by engineertwin2 »Per this thread: http://forums.genvibe.com/zerothread?id=25958I'll say it again - the pressure is not dependent upon rim diameter or tire size. Pontiac/Toyota don't change their recommendations based on whether you get stockers or the upgrades.The pressure recommended by the manufacturer of the car is based on a balance of vehicle handling characteristics (braking, turning) and fuel economy. If you want to inflate them more, feel free but understand that the recommendation doesn't change with tire size, but with vehicle load.My recommendation, always stick with the lower of what is printed on the sidewall of the tire or the recommended tire pressure (32 recommended vs 35 sidewall stamp for stock continentals - go with the 32).IF you are on factory tires, as that is what the factory specs refer to, once you change to a different tire, doesn't that go in the trash like the crappy factory tires? I would certinly think so, i'm not an engineer though, which is why i ask... A general guidline is just that a guide and does not cover anything but "factory' specs... yes?

[engineertwin2]

Quote, originally posted by Sublimewind »IF you are on factory tires, as that is what the factory specs refer to, once you change to a different tire, doesn't that go in the trash like the crappy factory tires? I would certinly think so, i'm not an engineer though, which is why i ask... A general guidline is just that a guide and does not cover anything but "factory' specs... yes?Not exactly.Let's think about that 32 psi for a second. What is that really? Well, when the car is on the ground, we want the tire pushing on the ground at 32 lb per square inch. "But the pressure is in the air in the tires?" True, but that pressure is a measure of the force being enacted at every contact point - it's pushing at 32 lbs per square inch on the rim, but it all cancels out as it pushes in a complete circle, opposing itself. So the remaining forces are at the point of contact - 32 pounds per square inch down and the earth pushes back at 32 pounds per square inch. This means that if the Vibe is 2750 lbs, then each tire carries 687.5 lbs. And it also means that each tire has a contact patch of about 21.5 square inches (687.5/32). So, the engineers calculated vehicle dynamics based on a contact patch of about 21.5 sq in per tire, or about 86 total sq inches.Ok, how does changing the tire size affect this? Technically, it doesn't. "But I know that a wider tire makes handling improve - how does that work?" Well, technically a wider tire does improve handling, but your contact patch remains the same. And that handling is a tradeoff - if you improve your handling through turns by adding wider tires, you reduce your handling through braking and vice versa.Our goal is to keep the contact area the same as originally designed. As the tire changes, sure there are slight variations that may warrant adjusting the pressure, here and there but it won't be significant.The other thing you see is a higher inflation pressure if you are at max cargo. Well, say you load the car up and now it weighs 3400 lbs. That's 850 lbs per tire, requiring a pressure of 39.5 psi to keep the contact patch. "But Pontiac recommends 35 psi for a full load - why the discrepancy?"Well, for starters, they know not everyone will purchase high end tires that are good to 45 psi for a max rating. They also know that the American Tire Institute requires a 35 psi maximum inflation pressure at a minimum (I know, slightly confusing) to meet NHTSA DOT standards. So if Joe Schmoe buys el cheapo tires and he loads up the car, the maximum assumed pressure is 35 psi."But I did the math and 35 psi in this example gives a contact patch of 24.3 sq inches? Explain that, smarty pants." Well, so they didn't plan on you always having an extra 600 lbs in the car (w/o driver). But let's think about this. Heavier car means more torque applied by the rotors on the brakes translates into longer stopping distance. How can they improve the stopping distance at heavier loads? By giving you more tire to stop with (and increasing the contact patch), that's how. So the max load inflation provided is a compromise between tire capability and stopping control.

[vibebob]

thanks for the info engineertwin, my head hurts from all the thinking, but thanks for clearing it up. I didn't know there was so much to it.My tires do show 45 max psi. I kinda compromised, I'm running 34 psi bob