2005 6MT Sedan Tire Pressures & Wear

[MK G35 Sedan]

Hello all! First post here. I own 2 G35's - a 2005 6MT and a 2003 A/T - both are sedans. The '03 is my wife's daily driver and the '05 is mine. We love our cars!!!!!

Anyway - down to business - I've done a lot of reading about tire pressures on this forum already, but it mostly all deals with coupes. I've been experimenting with tire pressures and am curious what everyone else is using.

My tire story (pertains to the '05 6MT):
On my stock set of tires, I was using the Inifiniti recommended 33 psi fr & rear. At 9100 miles, the inside and outside shoulders of the front and rear tires were worn down to 'about' 1/8". These were Goodyear Eagle NCT-5's. 235/45 18. The center of the tires had 'about' 1/4" left. I use the word 'about' because I'm averaging the tread depth I measured in several spots across the tire with a gauge that reads in thousandths of an inch (think it's called a micrometer).

Unfortunately I got a nail in the tire that could not be repaired shortly after the 9100 mile mark.

I upgraded all four tires to the Michelin Pilot Sport A/S and did a "plus 0" size change to 245/45 18. The new tires are great (plus much better in the rain) and have about 2000 miles on them. I started these tires out at 36.5 psi front 35 psi rear. This was creating too much wear on the shoulders up front and too much wear on the middle of the rears. Now I've settled into 37 front and 34 rear and it seems to be working well.

I've been compensating for tire temperature when inflating the tires too. I have a digital tire pressure gauge from Accutire that reads in 0.1 psi increments, which has proven very handy. I figured out experimentally that for every 10 degrees F change in tire temp, my tires change 0.7 psi. I set the pressure based on the historical average temperature for the month, and calculate the difference of my tire temperatures (garage warmer than outside) to the avg temp and inflate accordingly.

So if the average temp for the month is 74 deg, and the front tire is 84 deg when I check it prior to inflation (cold temp - first thing in the morning) then I would inflate the tire to 37.7psi.

I don't do autocross, just a daily driver. Mostly Highway, some City.

Any advice/comments out there on tire pressures for the 2005 6MT (18" wheels) would be appreciated. I'm trying to maximize the life of my tires, and thought my info thus far may help someone else too.

Thanks in advance!

[MikeG356MT]

Hey MK, it seems you have quite a handle on this already. If you follow the mfrs inflation recommendations and do even compensate for temperature and check your tires closely (you already do all of this, hell, I don't even compensate for temperature and I live in the desert!), you sound like all will be fine. Good job!

[MK G35 Sedan]

MikeG356MT - Thanks for the reply!


Usually, I've always been one to follow the (car) manufacturer's recommended pressure, but on this car, it seemed that excessive shoulder wear of both the inside and outside of all 4 tires occurred if I used 33 psi. It seemed my tires would be worn out by 15,000 on both shoulders on the W-Rated OEM Goodyears if I stayed at 33.


That's why I experimented with higher pressures than Infiniti's recommendation. After my 7500 mile service at the dealership, I noticed that they had inflated the tires to 37 front, 35 rear, which at first seemed quite excessive. I inquired as to why they inflated them so high, and they indicated that it would increase the life of the tires. This got me started on this whole tire pressure experiment.


I've even noticed that on the 2003.5 A/T with OEM 17" wheels, the shoulders wear a bit more than the centers, but it seems to be less pronounced, with the harder V rated tires and all. On that car, we've always used 30 psi (Infiniti spec). But now I'm trying 31 all the way around.


So I guess I'm wondering... Is anyone else having to inflate to pressures higher than Infiniti spec to keep the shoulders from wearing?

[jmcclain]

Yeah, you've done more research and have a way better idea on this then I do that's for sure. I just keep about 34 PSI in all of them and it seemed to work fine. I got 23,000 miles out of the stock set. Also upped the size with my replacements, but went to 245/40/18. I did not know 245/45/18 would fit or I would have done that for sure. Would have filled the wheel well much better. Do you have any pictures of this set up?

[MK G35 Sedan]

jmcclain...
Yeah, I started the research due to the $$$ of tires. I really don't want to put V-rated tires on my car, I'd rather pay extra and maximize some Y or W tires and know the car will stick in the occasional aggressive turning/merge ramps. But I need rain traction too - thunderstorms in the southeast can dump a lot of water down fast.

About pictures.... I'll post a new thread about that once I take some pictures. I like the look much better. I wouldn't have known about the size working without Tire Rack's website.

When you had to replace your tires at 23k, what part of the tread was worn out?

[jmcclain]

Originally Posted by MK G35 Sedan

jmcclain...
Yeah, I started the research due to the $$$ of tires. I really don't want to put V-rated tires on my car, I'd rather pay extra and maximize some Y or W tires and know the car will stick in the occasional aggressive turning/merge ramps. But I need rain traction too - thunderstorms in the southeast can dump a lot of water down fast.

About pictures.... I'll post a new thread about that once I take some pictures. I like the look much better. I wouldn't have known about the size working without Tire Rack's website.

When you had to replace your tires at 23k, what part of the tread was worn out?

They were worn pretty falt across the tire. I do mostly highway driving, I don't know if that matters in wear patterns or not. I felt lucky to get that many miles out of them. I upsized due to lack of options in the stock size. Wanted to keep the performance rating as close as possible just because I guess. I started a thread with all the numbers on them. I'm getting a lot more vibration now then I was with stock tires. Have you noticed this? Only happens at about 70 mph toabout 85 mph. Pretty good other then that. Took it back to discount and they reblanced them, better now but still not as smooth as stock. I don't think an alignment would help this at all since the car's not pulling. Nay thoughts?

[jmcclain]

I am loyal about rotating them every 5000 miles at the most. Could help as well.

[MK G35 Sedan]

I drive mostly highway too, with some "city". I do get to 70+ on my daily commute, and haven't noticed any increase in overall vibration. If anything the new tires are smoother on smooth roads. Likely due to the even wear at this point. Running the higher pressures certainly transmits more of the road ruts, bumps, etc, though, but that was about the same between the Michelin's and the Goodyears. These tires (Mich. Pilot Sport A/S) clearly enhanced the feel for the road, especially in the turns. For a while in all this testing I tried 37 front and 35 rear. 35 was too high for the rear. I was glad to see that I needed to reduce the rear pressure, because when I went to 37/34, the ride was more comfortable. The bump-up from 36 to 37 on the front was not as noticable of a change in ride quality, however. We'll see how it goes, I may need to try 37.5 or 38, but I need more miles to find out for sure.

Overall the car is still really smooth, especially on smooth pavement and I love the handling.

On an aside (balancing) ... when Discount balanced the new tires they removed the old tape weights first, and the balance job has seemed to be really good on the first try.

[MK G35 Sedan]

Oh, I wonder about the 40 series vs the 45 series... maybe that would be the vibration difference. ie stiffer sidewall/lower profile. Just a thought.

[EWOK]

I have an 05 6MT and I am very careful to rotate my tires every 5k miles as well. I know they are high performance tires and they are not supposed to last 40K miles but I wonder for all those people who complain about tire wear, do they rotate their tires and check the pressure as often as you do MK?

Just thinking out loud.

I've got about 12k' on my car and the tread is still good. I have noticed a little wear on the shoulders but I thought it had a bit to do with my aggressive driving style. I keep my tire pressure at 34 psi and check it about once a week or whenever the weather changes drastically. I might have to increase it based on your findings.

I was in TX when I bought the car about a year ago and it was warm weather, about 100F and a cold front came through with normal thunderstorms. The next morning I went to breakfast and the low tire pressure warning chime and caution light came on. The tire pressure was about 24 psi when I checked and filled up the tires but it was hard to tell by looking at the tires that they were that low.