Tire pressure on new rims

[ILikeMy240sx]

I have a 96 240sx with 225/45/17 tires...

I know that the manufacturer recommends 29 lbs for 205/55/16 tires but what about for aftermarket tires with a size like mine?

Do I still use 29 lbs or more?

Tire shop recommeded 36 lbs...

any thoughts?

[Nismo_Freak]

32 psi - 34 psi cold

[808DRFTR]

Check on the tires too, they'll say a maximum press. some low pro tires have them at 44 or 51 psi. cold

[ILikeMy240sx]

my tire said 50psi max but... I dont think i should be putting that much air into it...

I think 32-34 sounds good.. Is that what most people run on their s14?

[Nismo_Freak]

my tire said 50psi max but... I dont think i should be putting that much air into it...

I think 32-34 sounds good.. Is that what most people run on their s14?

Tire pressures are determined from load ratings of the tire as well as taking temperatures from the tire after driving it (hotter on edges = pressure too low, hotter in center = pressure too high), but you have to be able to differentiate how your driving and alignment are affecting the tires temperature as well.

Honestly OEM tire pressure is a trade-off between ride quality and performance, and is configured to the cars load requirements. Since the tires you have are only slightly higher in load index you could theoretically lower the pressure slightly and see roughly the same performance from the tire. I would just suggest going with a slightly higher tire pressure to help the tire maintain it's full load capacity and you will see a more linear attitude from the tire.

[mys13rocks]

well that also depends what your doing with your car .daily drive, drifting, auto x, touge? tire pressure can change on all those events. any body have any experience on some of these fields?

[Q45tech]

The linear part of the load vs slip angle curve is good to about 70-75% of the stated load index at 35-37 psi on street tires. Oem tires are usually selected so at static [just sitting] they are on the ragged edge of beginning to be non linear in the front [to promote understeer] as any turning overloads [begins non linear rollover of graph slip angles].

http://www.insideracingtechnol...2.htm

"At light loads tires behave as we were taught in high school physics. A coefficient of friction (unique for each pair of materials in contact) times the force pressing the materials together gives the amount of friction force produced. The equation is Cf x F = Ff.

But at some point the relationship between a new increment of force down on the tire and the next increment of grip produced changes. The next 10 pounds of load on the tire produces less grip than the last 10 pounds did, maybe only 8 pounds. This is the load sensitivity of tires." ..........what is shown in the slip curve graphs.

1160 static front/ 1521 [95V] load index ~~=0.7626

Why increasing the load index above oem is so beneficial especially on front tires. Rear tires having the same load index have some extra reserve:

989/1521= ~~0.65 so they can allow 170 extra pounds of handling force before getting non linear........so you use up some of this with a rear sway bar----- say half to shift away from understeer [20-22mm rear bar ~~= 40-80 pounds per inch on many Nissans].

Obviously this is very simplified version of what happens.

Tires are lab tested and speced at 35 psi [tire industry standard] so any lower pressure will have detrimential effects as far as slip angles are concerned. Any higher pressure will improve the slip angles up to a point, but the contact patch AREA decreases as inflation increases.......so a constant trade off.

The 29 psi cold assumes the tires will get to 33-35 psi under severe operating conditions.......the harder you push the tires the warmer they get and self inflate to 33-35psi [hopefully].

The higher the inflation pressure the higher the start to hydroplane speed because of the molecular forces [pounds per smaller square inch] ripping at the road.

[mys13rocks]

what your saying is 35 psi is standard on every tire and any higher is depended on the driver and feel of the road ...cool. nice write up there

[Nismo_Freak]

well that also depends what your doing with your car .daily drive, drifting, auto x, touge? tire pressure can change on all those events. any body have any experience on some of these fields?

Well my pressures are as following:

Daily Driving - 30 psi :: 32 psi Auto-X - 30 psi :: 32 psiDrifting - Haven't "drifted" my car (yet... Ryan is evil) Touge - 30 psi :: 32 psi

Talk about a pain in the *** to constantly modulate your tire pressures. I setup the tire pressures the same way so that the cars attitude doesn't change. If I need to change something I'll change a pre-load, dampening rate, or alignment setting.

[Q45tech]

No 35 psi is the standard lab test pressure where engineers can exchange graphs and talk apples to apples..............just as zero and -0.5 camber are the typical test angles.

Each tire is different and camber and caster and toe angles change the RUNNING load stiffness.

35 psi is just a good safe spot to start your testing.

[szh]

On my M45, I have 36psi cold pressure all around. For me, this is a good balance between too much and too little, with reasonable wear on the tire.

Allows a bit of room above the car mftr recommendation (32psi, as I recall) for a margin of error (I never want it too low) and the inevitable 1 or 2 psi drop between checks. I verify, and inflate as needed, the pressure cold (in the garage in the morning) before the car has been driven, once every week or two.

Z

[Bosrudorfer]

I just got 17's too and just put them to 33psi on all 4 several hours ago. I think I will make the rear 35 with front 36.

Or should I just go with 35 all around?

[KATwo40]

Interesting...

What would you say should be the recommended tire pressure for an S13 running 215/35/18 Traction AA, Temp A, Max 50psi?

[Eddie]

Like nismofreak said, you could theoretcially set your tire presure lower and with the same performance as the factory pressure. If you are interested in what that theoretical lower pressure is you can look at a load index chart. I have looked on the net, but can only find charts for the load carrying capacity of the max pressure for load indexes. I work at a discount tire and I know they have one that shows the carrying capacity of load indexes at different pressures up to the standard lab test pressure of 35 on their computer(other reputable tire dealers should have access to one). Just stop by one and tell them what the factory tire load index and tire pressure is and they should be able to tell you what pressure to set it. Make sure you mention the load index chart because they are bound to just tell you 35psi.

For example:I run 225/50/16 with a 93 load index and I believe the factory tires on s14s (SE) had an index of 89 so instead of 29psi I could run 27psi and still mantain the same load carrying capacity(according to the chart).

I wish I could provide one of those charts. The moderators really know their stuff and they make some really good points that show how complicated all that load index/tire pressure crap can get.