High tyre pressures from dealer - check your pressures!

[rtv900]

Not for RWD, it's reversed from AWD. There are no AWD Stingers In Aus.

seriously?
what the
do you have the staggered set up?

 

[bfglitch]

My RWD staggered setup is 36 all around. Says so on the placard at least.

 

[LordKOTL]

seriously?
what the
do you have the staggered set up?

If I'm not mistaken, the pressure needed in a tire is a function of the volume of the tire (i.e. the rim diameter and the cross-sectional area of the tire), coupled with the size of the contact patch, and the weight the tire/axle has on it.

For the staggered setup the rear tires have a larger cross sectional area than the fronts for the same diameter, meaning that they would need less pressure to achieve the same inflation level as the fronts assuming the same amount of weight was on them.

But they don't see the same amount of weight. RWD is missing the transfer case, front differential, and front CV's. Thus, it would make sense that the RWD's would need more pressure in the rear or equal pressure all around because the front axle in RWD would see comparatively less weight than the front axle in the AWD models.

Thus why it's always a good idea to check the placard on your specific car. I believe AWD vs RWD has a role, as well as 3.3 vs 2.0 vs 2.5; All of those engines have different weight and so they would affect the weight on the fronts.

 

[Nedstand]

If I'm not mistaken, the pressure needed in a tire is a function of the volume of the tire (i.e. the rim diameter and the cross-sectional area of the tire), coupled with the size of the contact patch, and the weight the tire/axle has on it.

For the staggered setup the rear tires have a larger cross sectional area than the fronts for the same diameter, meaning that they would need less pressure to achieve the same inflation level as the fronts assuming the same amount of weight was on them.

But they don't see the same amount of weight. RWD is missing the transfer case, front differential, and front CV's. Thus, it would make sense that the RWD's would need more pressure in the rear or equal pressure all around because the front axle in RWD would see comparatively less weight than the front axle in the AWD models.

Thus why it's always a good idea to check the placard on your specific car. I believe AWD vs RWD has a role, as well as 3.3 vs 2.0 vs 2.5; All of those engines have different weight and so they would affect the weight on the fronts.

Thanks for this! I'm no car expert, but it makes common sense to me that staggered tires (my first car with this setup) would have different pressures.
What doesn't make sense to me is that AWD and RWD would be exactly flip flopped.
To add further confusion I found this thread where people posted photos of their door tags, and looks like the 19" rims got the 39 PSI in front, while the 18" rims get 39 PSI in the rear.

Thread 'Why is the Tire Pressure different between AWD Front and Rear Tires for the GT ?'

Oct 21, 2018

Don’t know if this has been covered but I’m curious why the GT requires 39PSI for the rear tires and 36 PSI for the front . Usually cars have the same PSI for both front and rear tires

• NYstingerGT2
• Replies: 19
• Forum: Kia Stinger Exterior Discussion

 

[Nedstand]

With regard to 50 PSI when the Stingers were delivered, could that have caused this sort of cracking?
Not sure exactly when the happened, but I noticed it at about 8K miles. Kia dealer told me to take to any Michelin authorized dealer.
The guy at the tire shop said he had never seen anything like it. It was all 4 tires. All 4 tires were replaced under warranty.

 

[D.J.]

With regard to 50 PSI when the Stingers were delivered, could that have caused this sort of cracking?
Not sure exactly when the happened, but I noticed it at about 8K miles. Kia dealer told me to take to any Michelin authorized dealer.
The guy at the tire shop said he had never seen anything like it. It was all 4 tires. All 4 tires were replaced under warranty.

No,
What did the tire shop tell you about the root cause? They must have had an opinion?

 

[Nedstand]

No,
What did the tire shop tell you about the root cause? They must have had an opinion?

This was about 3 years ago. I mostly remember 2 guys using a lot of 4 letter words to describe the situation. It's a shop here in LA, West Coast Tires, that we've used for 20 years to service multiple cars. Not just tires, but routine service. Most everything but recalls and other stuff that can only be performed by the dealer.

Other than cussing a lot, I don't recall any specific reason. No idea if Michelin sent someone to inspect the tires. They gave me fresh rubber and I left happy.

 

[BIG-D]

40 psi all round works for me tyres wear evenly !!

 

[Volfy]

Not sure where the confusion is coming from. The tire pressures listed on door jamb placards are mostly for load-handling purposes. Some placards even explain this explicitly. Any additional passenger/luggage load generally is generally biased towards the rear axle. So, for cars that come with the same 18" front and rear, the rear tire pressures are higher to handle that higher load.

I didn't find a chart for the Kia Stinger tire sizes, but any tire will have a similar characteristic curve as this example:


As for those with 3.3T AWD cars that specifies higher front tire pressure than rear, that makes sense too. Not only are there more weight over the front axle, due to the transfer case, front diff, drive shafts, etc., the front tires are also smaller and carry a lower load rating (93 vs. 95). That means tire pressure needs to increase to compensate for that additional load.

Again, front axle load handing isn't affected as much by " live loads" (passengers + luggage), so the "dead loads" (engine + drivetrain) accounts for greater portion of the load rating calculation.

BTW, those of us who change tire sizing on our cars need to be mindful of the fact that larger tires typically have higher load ratings, so not as much pressure (as on door jamb placard for OEM tire sizing) is needed for the same load rating. So... the pressures you set need to be adjusted to suit the larger tire sizes. Otherwise, if you follow the OEM guidelines, your larger tires could be over-inflated, which can lead to sub-optimum handling and traction.

 

[rtv900]

my z06 has a perfect 50/50 weight distribution and calls for 30psi cold all around despite 335's in the back and 285's front

 

[Volfy]

my z06 has a perfect 50/50 weight distribution and calls for 30psi cold all around despite 335's in the back and 285's front

That is interesting. I suspected that there are other factors in play for a car like that, so I did some quick googling and came up with some fascinating tidbits here:

https://www.caranddriver.com/news/a41465969/chevrolet-corvette-z06z07-track-pack-cornering-skidpad-testing/

Excerpt from that article:

"...we adjust tire pressure according to the manufacturer's recommendations that are printed on the placard located on the door jamb or B-pillar, or in the owner's manual. If there are multiple choices, we'll use the high-speed, low-load specification. Oddly, the Z07's placard required the Cup 2s to be set at 35 psi cold, some 5 psi higher than the base Z06's tire pressure. Since the tires on the two versions of the Z06 are the same size, we wondered if something was off.

That had us digging deep into the Z06 owner's manual where we discovered a well-hidden suggestion: owners should lower the Cup 2 R's tire pressure all the way down to 24 psi cold for maximum cornering on the track. Huh? It took discussions with both the Corvette engineers and engineers from tire-maker Michelin to fully explain the situation.

The reason the Cup 2 tires are supposed to be run on the street at 35 psi instead of the base tires' 30 psi has nothing to do with handling, ride, or fuel economy but rather wet-weather traction. The Cup 2s have so little tread depth—the outboard half of their tread is essentially slick, like a full-on racing tire—that they have trouble shedding water. Pumping the tire up that extra 5 psi crowns the tread enough to make a significant improvement in their grip when the road is wet according to the Vette engineers.

But it turns out that, counterintuitively, these newest Cup 2 Rs deliver maximum dry road grip at the lower 24-psi pressure."


FWIW, performance driving introduces a whole lot more variables than just load ratings. With our G70/Stinger, we don't run door-jamb placard tire pressures at the track either. Besides, different tires like different pressures, under different conditions. We bring a temp gun to gauge temp across the tire tread, but quite often the tires will tell you if they are happy with the set pressure or not.

 

[rtv900]

yeah I had those sport cup 2's when I first bought it since it's a Z07. Basically street legal slicks.
They were good for July and August street driving basically. Even under 80 degrees ambient they felt sketchy.
Under 70 forget about it.
I sold them after a few months

 

[Volfy]

The Kumho V730 track tires we have are pretty much slicks on the outside 1/2. The very shallow grooves were gone after a few events. One tech inspector at a local event wasn't familiar with them and questioned whether to allow us to run on them. I told him that's how they are, but he was still skeptical. I had to pull up pics of brand new ones on my phone and showed him, before he was convinced.

I wouldn't run barely street-legal slicks like those on public roads, other than maybe drive to a local event on a sunny day. They are brilliant at what they do best, but they suck bad at what they aren't designed to handle. That's why we have as many sets of wheels/tires as we do.

 

[rtv900]

I wouldn't run barely street-legal slicks like those on public roads, other than maybe drive to a local event on a sunny day. They are brilliant at what they do best, but they suck bad at what they aren't designed to handle. That's why we have as many sets of wheels/tires as we do.

yeah I agree, that's why I sold them. They were however great in July/August weather on dry roads, but other than those two months they were not fun. I now have a set of summers and a set of snow tires for my Z06 also and I drive it all through winter if the roads are clean

 

[Ah GetFd]

Wr

it's 38 front 36 rear
you have it reversed

Wrong.

It is 36 front and 38 rear here like all cars

On the tyre plate..........mate..........

 

[Ah GetFd]

Not for RWD, it's reversed from AWD. There are no AWD Stingers In Aus.

Correct

Front 36

Rear 38

On every car not just Kias.

Has been for decades

 

[Thomby]

We bring a temp gun to gauge temp across the tire tread, but quite often the tires will tell you if they are happy with the set pressure or not.

This is the truly correct answer, since so many factors go into what "ideal" pressure is. More work than most people are willing to do, but those temp guns are like $20. I wonder if there would be any apparent difference after, say, a 5/10 drive around town (vs. 9/10 at the track). Maybe I'll grab mine the next time I think about it.

Front 36
Rear 38
On every car not just Kias.
Has been for decades

I sincerely hope nobody is taking this advice seriously...

 

[Nedstand]

This is the truly correct answer, since so many factors go into what "ideal" pressure is. More work than most people are willing to do, but those temp guns are like $20. I wonder if there would be any apparent difference after, say, a 5/10 drive around town (vs. 9/10 at the track). Maybe I'll grab mine the next time I think about it.


I sincerely hope nobody is taking this advice seriously...

I have a couple of infra-red temp guns that I use to check my A/C and report back to my HVAC guy.
If I wanted to use this to check my tire, what would I be looking for? Same temp center of tire vs outer edge? And what adjustment would I make?

Thanks!

 

[Thomby]

I have a couple of infra-red temp guns that I use to check my A/C and report back to my HVAC guy.
If I wanted to use this to check my tire, what would I be looking for? Same temp center of tire vs outer edge? And what adjustment would I make?

@Volfy may have better Stinger-specific advice, but in general I'd expect to see higher temps at center for overinflated, higher at edges for underinflated, and higher from one side to the other for excessive camber.

I forgot to check mine when I got home and wasn't driving aggressively, but with an outside temp of 70 degrees and after sitting for ~45 minutes, my fronts showed around 84 degrees on 4 of the 5 tread bars, with the outermost one maybe 2 degrees lower. The rears more like 79-80 degrees, and less noticeable drop on the outside edge.

So maybe higher temp up front from smaller/higher pressure tires, and outside edge lower due to negative camber or just how they wrap around to the sidewalls which get free airflow?

 

[D.J.]

I have a couple of infra-red temp guns that I use to check my A/C and report back to my HVAC guy.
If I wanted to use this to check my tire, what would I be looking for? Same temp center of tire vs outer edge? And what adjustment would I make?

Thanks!

Are you talking about measuring the rubber temperature after a hot lap at a track? Or measuring the rubber temperature after driving down a straight road for some minutes?

Not sure what useful information you would get from either that you wouldn't also get from simply measuring the air temperature inside the tire with the existing sensors that already measure temperature