Can someone tell me what PSI i should be running in my tires?
04-06-2009, 05:01 PM
#21
New Member
trying to name a specific tire would be a little tedious but to simple put it any tire with a load index of 87 or less would be unacceptable for the z. Any tire on the z should be able to carry at least 1200-1300lbs @ a psi level below max psi. to calculate the load more approximately you need the original oem tire specs.
if you have oem rims and buy exactly the same spec tires as oem, go with the stock recommended. if you changed out to different tires with a different load index spec and max psi spec than oem, then the psi you run will vary. you can call the tire manufacturer up and they'll figure it out for you. it will be different.
the document posted by bdblackz is helpful if one wishes to figure it out for themselves. looks like you just need to do some simple proportionality problems to get the correct psi.
lets put it another way. lets say someone here has new after market tires with a load index of 99 vs i believe stock was 96(rear). if you recommend that person to use the oem psi @ 35 and the max psi level for the new tire is 51. oem max psi was 40(IIRC).
the new tire is now carrying ~1196lbs @ 35psi
while the original oem tire was carrying ~1369 @ 35psi
to carry 1196 lbs with oem tire it needed ~30psi...
what i'm trying to say is to recommend what it says on the door jam to someone who is using a different tire spec is not correct @ that psi level their tire is actually under/over inflated. think about how many tire reviews have been done with under inflated tires now!
if you have oem rims and buy exactly the same spec tires as oem, go with the stock recommended. if you changed out to different tires with a different load index spec and max psi spec than oem, then the psi you run will vary. you can call the tire manufacturer up and they'll figure it out for you. it will be different.
the document posted by bdblackz is helpful if one wishes to figure it out for themselves. looks like you just need to do some simple proportionality problems to get the correct psi.
lets put it another way. lets say someone here has new after market tires with a load index of 99 vs i believe stock was 96(rear). if you recommend that person to use the oem psi @ 35 and the max psi level for the new tire is 51. oem max psi was 40(IIRC).
the new tire is now carrying ~1196lbs @ 35psi
while the original oem tire was carrying ~1369 @ 35psi
to carry 1196 lbs with oem tire it needed ~30psi...
what i'm trying to say is to recommend what it says on the door jam to someone who is using a different tire spec is not correct @ that psi level their tire is actually under/over inflated. think about how many tire reviews have been done with under inflated tires now!
--Spike
04-06-2009, 11:16 PM
#22
225/45/18 91W 51max
245/45/18 96W 51max
any load rating less than 83 would be no good for the z.
04-07-2009, 01:17 PM
#23
Registered User
iTrader: (4)
Join Date: Jan 2006
Location: CA
Posts: 191
Likes: 0
Received 0 Likes
on
0 Posts
The answer is 34-36 psi on all tires.
And, that answer applies to any suitable and correctly sized tire for the Z, whether you place the tire on a 17”, 18”, or 19” wheel.
Leave it to an engineer to add a lot of confusion to something that is this simple.
…Just kidding of course since your input is appreciated.--Spike
That is still incorrect.Here's an example for those who don't understand or want to learn something. If you have any questions ask. And this is why Spike's "answer" is wrong.
Stock front tires on my car: 245/40R18 RE050A. Load rating = 93
My front winter tires: 225/45R18 Blizzak LM25. Load rating = 95 XL
The XL is important because it represents a whole different set of loads. It is a "reinforced" tire.
Step 1
Look up load tables I have mentioned (I looked up the ETRTO tables at work today to give this example) and see what the max load is for a 93 load rating at stock pressure (Stock pressure ~35psi). The table says 630kg.
Step 2
Go to the XL load tables (because the new tire is XL rated) and look up the pressure that corresponds to 95 (for the Blizzak) and 630kg (the load from before). The pressure for the Blizzak is 38psi.
Summary
The Blizzak needs to be inflated to 38psi in order to carry the same load the stock RE050As can carry at 35psi.
Now I did this again for the RE-11 tires I just bought, which are 245/40R18 and 97 XL load rating. The pressure for the RE-11 is 35psi.
So, as I said before, the correct pressure does not just depend on vehicle weight - it also depends on tire size, load rating, construction (XL). Sometimes it could be the same as stock, and sometimes it can be different. You should not just assume OE tire pressures, and you cannot guess this by looking at tire wear.
Can't make it any clearer than that guys!
04-07-2009, 03:28 PM
#24
New Member
I understand, but I don’t think your example (you mention snow tires as a deviation) provides a good argument here. That’s simply because some manufacturer’s recommend a slightly higher psi (2 psi isn’t that much) realizing that there will be fluctuations in very cold environments. A couple extra lbs. will help preventing running on under-inflated tires (which is usually a bad thing). Most drivers don’t want to check tire pressures when it’s minus 20F (who want to do this when it’s so cold).
In fact my tire shop recommended 37-39 psi for my snow tires, and that is how they filled them. But, after several weeks of driving I felt they lacked correct grip on the ice that is common during winter months where I live.
So I dropped to 35 psi. At that psi the car became much more stable on icy roadways. I’ve run these snow tires for two seasons, and have not experienced any loss of mileage (albeit, winter mileage is difficult to evaluate) or adverse wear. Since I’m running lower than the tire’s recommended psi for my car, I check pressure levels at least twice weekly (and for sure when the ambient temperature drops significantly).
Some members here also report that there are summer-performance tires that have a recommended psi as high as 39 for the Z, but I don’t have personal experience with the tires they mention.
My comments are based in personal experience, so they are only one person’s opinion and certainly cannot be considered the “final word.” Additional discussion is welcome and helpful.
--Spike
In fact my tire shop recommended 37-39 psi for my snow tires, and that is how they filled them. But, after several weeks of driving I felt they lacked correct grip on the ice that is common during winter months where I live.
So I dropped to 35 psi. At that psi the car became much more stable on icy roadways. I’ve run these snow tires for two seasons, and have not experienced any loss of mileage (albeit, winter mileage is difficult to evaluate) or adverse wear. Since I’m running lower than the tire’s recommended psi for my car, I check pressure levels at least twice weekly (and for sure when the ambient temperature drops significantly).
Some members here also report that there are summer-performance tires that have a recommended psi as high as 39 for the Z, but I don’t have personal experience with the tires they mention.
My comments are based in personal experience, so they are only one person’s opinion and certainly cannot be considered the “final word.” Additional discussion is welcome and helpful.
--Spike
04-07-2009, 04:43 PM
#26
Registered User
iTrader: (4)
Join Date: Jan 2006
Location: CA
Posts: 191
Likes: 0
Received 0 Likes
on
0 Posts
I understand, but I don’t think your example (you mention snow tires as a deviation) provides a good argument here. That’s simply because some manufacturer’s recommend a slightly higher psi (2 psi isn’t that much) realizing that there will be fluctuations in very cold environments. A couple extra lbs. will help preventing running on under-inflated tires (which is usually a bad thing). Most drivers don’t want to check tire pressures when it’s minus 20F (who want to do this when it’s so cold).
In fact my tire shop recommended 37-39 psi for my snow tires, and that is how they filled them. But, after several weeks of driving I felt they lacked correct grip on the ice that is common during winter months where I live.
So I dropped to 35 psi. At that psi the car became much more stable on icy roadways. I’ve run these snow tires for two seasons, and have not experienced any loss of mileage (albeit, winter mileage is difficult to evaluate) or adverse wear. Since I’m running lower than the tire’s recommended psi for my car, I check pressure levels at least twice weekly (and for sure when the ambient temperature drops significantly).
Some members here also report that there are summer-performance tires that have a recommended psi as high as 39 for the Z, but I don’t have personal experience with the tires they mention.
My comments are based in personal experience, so they are only one person’s opinion and certainly cannot be considered the “final word.” Additional discussion is welcome and helpful.
--Spike
In fact my tire shop recommended 37-39 psi for my snow tires, and that is how they filled them. But, after several weeks of driving I felt they lacked correct grip on the ice that is common during winter months where I live.
So I dropped to 35 psi. At that psi the car became much more stable on icy roadways. I’ve run these snow tires for two seasons, and have not experienced any loss of mileage (albeit, winter mileage is difficult to evaluate) or adverse wear. Since I’m running lower than the tire’s recommended psi for my car, I check pressure levels at least twice weekly (and for sure when the ambient temperature drops significantly).
Some members here also report that there are summer-performance tires that have a recommended psi as high as 39 for the Z, but I don’t have personal experience with the tires they mention.
My comments are based in personal experience, so they are only one person’s opinion and certainly cannot be considered the “final word.” Additional discussion is welcome and helpful.
--Spike
It appears that the OP does not care anymore anyway - maybe he is driving around on Z04's advice? 
I just picked Blizzaks because I had them in the garage to look at - a quick search of TireRack for the 225/45R18 size revealed several summer tires (Mich PS2 for example) with the same load rating as the Blizzak (95), which also means they would be run at 38 psi on the Z front (and 39 rear). Therefore my point does apply to summer tires also.
I understand your point about lowering your pressures but after my experience in the tire testing department 2psi really does make a difference. I can't force you to keep your pressures exactly at the recommended pressure - it is up to you whether you follow the recommendation or not, but with so much misinformation spread on these forums I had to explain the correct method, and I can tell you that we do give that recommendation for a reason. After that, it's up to you!
04-07-2009, 05:55 PM
#27
New Member
^^ Thanks for the reply and staying with this thread since your input is very informative.
Now… I’m going to reveal my “dirty little secret.”
Recently I’m running my Goodyear Eagle F1 GS-D3 tires at 37/38psi instead of 35/36 psi. I do this slightly higher psi (and I probably should not) to get a little more rigidity out of the soft side-walled Eagle’s (it feels better to me when driving the Z on with this tire, but possibly causes excessive center wear).
But, please don’t tell anyone that I’m doing this.
When I replace these tires, I will probably go with Michelin PS2’s, and start out with a 36 psi (and go from there, but I doubt that I will do 38/39 which seems high for the Z).
--Spike
Now… I’m going to reveal my “dirty little secret.”
Recently I’m running my Goodyear Eagle F1 GS-D3 tires at 37/38psi instead of 35/36 psi. I do this slightly higher psi (and I probably should not) to get a little more rigidity out of the soft side-walled Eagle’s (it feels better to me when driving the Z on with this tire, but possibly causes excessive center wear).
But, please don’t tell anyone that I’m doing this.
When I replace these tires, I will probably go with Michelin PS2’s, and start out with a 36 psi (and go from there, but I doubt that I will do 38/39 which seems high for the Z).
--Spike
04-07-2009, 06:34 PM
#28
Registered User
iTrader: (4)
Join Date: Jan 2006
Location: CA
Posts: 191
Likes: 0
Received 0 Likes
on
0 Posts
I guess I'll come clean with my "dirty little secret" too then. I used to run the PS2s on my Z (before working at Bridgestone) and had to run them over 40 when autocrossing because of the soft sidewalls - the RE050As and RE-11s I have been fine running 35-36psi.
04-07-2009, 08:39 PM
#29
New Member
^^ Wow… 
>40 psi on the Michelin PS2’s. Well… OK then.
We may have completely destroyed our credibility (I’m kidding of course).
You wouldn’t believe how low I run psi (way off the chart) on my off–road vehicle when antelope hunting in Wyoming. I need to do this so the tire folds over rocks and doesn’t dig into the sand.
You must be flexible when deciding upon the correct psi (excuse the weak pun).
--Spike
>40 psi on the Michelin PS2’s. Well… OK then.We may have completely destroyed our credibility
(I’m kidding of course).You wouldn’t believe how low I run psi (way off the chart) on my off–road vehicle when antelope hunting in Wyoming. I need to do this so the tire folds over rocks and doesn’t dig into the sand.
You must be flexible when deciding upon the correct psi (excuse the weak pun).
--Spike
04-10-2009, 05:27 PM
#31
New Member
^^ There really isn’t a formula. Some of the members posting on this thread have added unnecessary complication to what is really a very simple standard.
For just about any application (17”, 18” and 19” wheels with all sorts of different tires), you follow Nissan’s recommendation, which is 34-36 psi for the Z.
You would never go under the recommended 34-36 psi standard; and if you go past this, it will only be a difference of 2 to 3 psi. (if even that much).
So… Never go below 34/35 psi or above 38/39 psi… and maintain around 35/36 psi… and you will be fine.
Geez… I cannot believe that we added so much confusion here.
--Spike
For just about any application (17”, 18” and 19” wheels with all sorts of different tires), you follow Nissan’s recommendation, which is 34-36 psi for the Z.
You would never go under the recommended 34-36 psi standard; and if you go past this, it will only be a difference of 2 to 3 psi. (if even that much).
So… Never go below 34/35 psi or above 38/39 psi… and maintain around 35/36 psi… and you will be fine.
Geez… I cannot believe that we added so much confusion here.
--Spike
Thread
Thread Starter
Forum
Replies
Last Post
