nadir_s

hey guys... this might sound dumb, but someone teach me how to pump the right amount of air into my tires! Basically I wanna know what's the correct PSI... is there a way to calculate this? I checked the 4th gen faqs and I think it only gave me stock tire information. I always thought I should pump the tire to the PSi number that's actually on the tire... which is 51 PSi in my case (and the stock ones are like in the low 30's!). I'm just curious why it's so high... I feel as if I over inflated it.

my tires: 235 50/ZR-W17-Pirelli P7000 SuperSport Tires

Kashoggio

iTrader: (11)

Nissan puts 32 psi in all tires , the 350 z takes 38. Your tires will have a max pressure number on the sidewalls. I would put in like34psi

redmaxpa007

iTrader: (21)

agreed 32-38 psi is fine..


the sidewall of you tire will have a max PSI pressure rating..

nadir_s

hmmmm.... so i filled it up to the MAX PSi (51psi). I guess tomorrow I will deflate it down to 38. So how do you guys determine this number? Is there a formula or something that ppl use? I want to make sure I am using the optimal pressure..

thanks, i think the 50psi right now in the tires is a bit too much.

nadir_s

ok, i just read all about tires on howstuffworks.com and I seem to learn a bit... but when it came to the pSI part the only thing that made sense to me about my question was:

optimus1

Yes on the sidewall it gives MAX pressure for a certain weight load ... ie: 2000# @ 51 psi (called a load rating, DOT). Look at the placard on your door sill GVWR ...

(add all tire ratings)/GVWR = MAX Pressure psi/ X psi

figure X, is algebra ...
basically tire rating should exceed GVWR and ride tire pressure should be a percentage of the Max ...that's how the Factory does it ... However, higher pressures give more road feed-back ...



Did that come out rite !! duh

Frank Fontaine

Not a dumb question at all. imho it's trial/error. When I went to 18's I had to get a flat fixed right away. The dude asked me what are you putting in these things? I said 36 front, 33 rear. He said "way too low," that I should be doing something like 48/44, because the sidewall says something like 51. I thought it was strange but I did it. That I said what a sec., what's the difference because the load capacities are similar. You'd never put a wider tire/lower profile if the load rating were less than stock.

So unless I'm wrong, PSI is the same aftermarket or stock size. Overinflation is not good either as the center of the tire will wear. I do 36/33 on 235/40WR-18's.

Sprint

iTrader: (10)

why are you running 235/50

Dave B

I've calculated the correct tire pressure for the 4th gen running 235/45R17s. It's a factor of the % of weight over the two axles vs the max psi of the tire and some other factors. Pretty much on the lighter weight 4th gen, you're looking at ~33-34 psi in the front and ~30psi in the rear when the tires are COLD. When the tires warm up during normal driving, they typically gain 1 psi or so.

Most Z-rated 235/45R17s are rated at a max of 51-psi HOT. Exceed this psi and you're looking at potential failure. Z-rated tires are built to handle extreme speeds (149+mph) and with those speeds comes extreme heat. As the tire goes faster and faster, the tire gets hotter and hotter. I don't know the true calculation, but a tire gains heat at nearly an exponetial rate as speeds exceed 110mph, so I've been told. If you start turning, the tires can get really hot. Throw in a heavier car and the tires will get hotter even quicker.

Tire rating have little to with ultimate traction, the rating system is more about the tires ability to withstand heat at high speeds. There are plenty of summer H-rated tires that will hook up and out corner an all-season Z-rated tire.


Dave

WaarrEagle

iTrader: (1)

I also have a question about inflating my tires. I am running 235/45/17 Yokohamas and had them at 32.5. Then I read on the FAQ here that 33 up front and 30 in back is the ideal setup so it did that. When I get on the ground and look at my tire the very outside of the tread does not touch the ground. Is this normal? I would think that the whole tread pattern should touch the ground?

nadir_s

whoa thanks for the info guys! I think I understand now. Well, when i filled up the tires to 50psi yesterday, it was after a long ride so the tires were hot. I'll head out soon to deflate them down to the average of what you guys suggested.

One more thing that's been buggin me... it's hard to describe this by words so I just photoshopped something to give you guys an idea of what I'm talkin about. I noticed this after it rained... like when the sidewalls look dry... I can see a continuation or marking of my rims' spokes on the sidewalls! I thought it was perhaps rain flying off the spokes anad the rain caused that pattern but I did not noticed it on the rear tires... only the front 2. I was kinda worried but never noticed it after it had stopped raining. I thought it could have been that the tires were underinflated or something... here's the PS:

Frank Fontaine

First of all, sweet rims!

If that photo is not retouched, the only thing I could imagine is that when you're parked and water runs off the edge of the rim, something in those rivets are throwing off a residue that winds up on your sidewall.