Just installed new tires (98 i30), and my mechanic put 40psi on all 4, cause it says on the tire "44 psi max". But, my manual shows 30 psi. So, the question is, 30 psi for stock tires only or should I make new Khumos 30 psi as well?

 

They're still the stock size wheel? Then do as the manual suggests. I thought it was 32F/33R though? That's what 4th gens are...I would find it odd that the I30 would be different.

 

Higher PSI = more rim protection and better ride
Lower PSI = better handling but worse tire wear

 

Front 33
Rear 32

A tire shop recently suggested I use 40PSI and would benefit from improved handling, treadwear and fuel economy on my OEM Goodyear Eagle RSAs which have maximum 44 psi. I haven't tried it yet.

 

Higher PSI results in a smaller contact patch at the fringes of the tire so handling would actually deteriorate.

 

HERE'S THE DEAL:

Soft tires = 1) more comfy ride 2) slightly better straight-line traction.

Hard tires = 1) harsher ride, 2) better cornering b/c of stiffer sidewall, 3) slightly lower traction on the straight-aways due to smaller contact patch, 4) better gas mileage b/c less rolling resistance on harder tires

 

ONE MORE THING: I personally think that 40psi is a little too high. 36-38 is more reasonable. Your tires might not wear evenly b/c the shape will be deformed. You might lose tread life on your tires.

I'd recommend sticking to stock for a "normal ride" (~33 PSI) OR going up to 36-38 PSI for a little bit better cornering and gas mileage.

I run my 17-inchers at around 36 PSI. But it's up to your preference.

 

Thanks to all of you.
I'm going to make 35 Front/36 Rear

 

You should probably try it like that the other way around = 36 front, 35 rear. That's what I'm going to do on my next road trip, instead of 33/32.

 

I have a 98 I30, and the recommended tire pressure is 29 front AND rear. Check under the arm rest cover.

I am running 33 front and rear. The only time you should add more than that is if you are carrying extra weight like passengers.

Running 36psi for the life of the tire will wear out the center faster than the edges. I used to run 36 in my Max that had over 302k. I bought 9 sets of tires over that period, and if you do the math, you can see that I did not get much wear out of my tires -- Bridgestones and Kumos.

Just my $0.02

 

That's over 33,500 miles per set of tires! That's not bad at all for performance oriented tires, especially if you don't drive like a granny..