Tire pressure.

All my tires are P195/65R15s. 3 of them print a max pressure of 44 psi. The lone standout is one in the driver's side rear that reads:max press 35 psi. Is that a bad combination? Is it simply a different type of tire and as long as the dimensions are consistent, I shouldn't worry about it?

Don't worry about it. Inflate them all to the recommended inflation (not the max) and drive it.

You always inflate the tire to the vehicle manufacturers recommendation which will be less that the max on the tire, usually.

If there is any question whether or not this is the correct way to inflate the tires look on any tire manufacturers web site and they will say the same thing.

Overinflating can cause excessive stress on the tire, Less traction, and more braking distance. Not to mention a ruff ride and the premature wearing of tire tread, typically the center tread.

All my tires are P195/65R15s. 3 of them print a max pressure of 44 psi. The lone standout is one in the driver's side rear that reads:max press 35 psi. Is that a bad combination? Is it simply a different type of tire and as long as the dimensions are consistent, I shouldn't worry about it?


Is it the same brand and model of tyre?
If so I wouldn't worry about it, just make sure it is inflated to manufactors specs (usually around 30-36psi for a tyre that size).

If it is a different brand and model of tyre, then beaware that it will have different levels of grip and response to the tyre on the other side at the back.
This is an illegal combination here in NZ, and if you try some hard breaking and swerving manuvers (like trying to avoide a hazard, e.g. a child or another car) you will find out why very quickly, as it becomes very easy to lose control of the car.

I wish it was illegal in MN! There are many cars on the road with 4 different tires on them! I would bet that half of those have steel cords showing in at least one of the tires, half of those have worn out front end parts, and half of those have brake issues.

So where do I find mftr's recommended inflation pressure? Do I do a ballpark figure as in: 44psi translates into 40? The rear driver side is a Uniroyal Tiger Paw. The rear passenger side is a Douglas Xtra Trac A/W. No two tires match on my car.

So where do I find mftr's recommended inflation pressure? Do I do a ballpark figure as in: 44psi translates into 40? The rear driver side is a Uniroyal Tiger Paw. The rear passenger side is a Douglas Xtra Trac A/W. No two tires match on my car.

The location varies somewhat by manufacturer. Some will put the recommended cold inflation numbers for front and rear on the VIN tag in the driver's door jamb, some will have a separate sticker on in the rear passengers door jamb (4-door) and I've seen other's that will have a sticker inside the fuel fill door. Most will likely also have the information in the owner's manual as well, or at least the manual will guide you to where to find the information.

-Rod

That's all well and fine, but I've got 3 tires that read max inflation 44psi, and 1 that reads 35psi.

That's all well and fine, but I've got 3 tires that read max inflation 44psi, and 1 that reads 35psi.

It doesn't matter what the tires say. Inflate them to what the vehicle says. The only time it would matter is if the vehicle manufacturer recommended an inflation that exceeded the tire manufacturers maximum inflation. this would be a pretty good sign you have the wrong tires installed on the vehicle.

Right, the sidewall inflation is a "Maximum" inflation number, what the tire can handle, but not what the car's manufacturer recommends. You should never inflate based on what's on the sidewall, it should always be what the "door sticker" suggests based on your load. That's true for all modern cars, and a common misunderstanding.

-Rod

as i am alignment man you need to go with what it sais on your door or manual don't go with what it sais on tire. you'll get better gas mls. if you do this.

Correct. It doesn't matter if you put 4 E-range truck tires on that car. Even if the sidewall says 80 psi max, it only takes about 30-35 psi to suspend the weight of your car. The pressure listed on the sticker (or owner's manual) of your car is the right inflation pressure. Those tires are designed to be installed on a few thousand different cars of different weights, but your car is what determines proper pressure, not the tire.

Never knew.

The rear driver side is a Uniroyal Tiger Paw. The rear passenger side is a Douglas Xtra Trac A/W. No two tires match on my car.



Do yourself, and other road users a favour, and get 4 tyres the same.
Even if you have to get 4 second hand ones, the car will be a thousand times safer.

Do yourself, and other road users a favour, and get 4 tyres the same.
Even if you have to get 4 second hand ones, the car will be a thousand times safer.

I'm not sure if its a tire difference, or if its just social perception. Using different tires here is not taboo at all. Its not ideal, but the amount of difference that having different tires could cause is so tiny. 99% of the drivers out there wouldn't know what to do except panic if they were in any hazardous situation, and the 2% increase in predictability you gain from having 4 tires the same is really not a big deal here. No state in the US requires 4 matching tires. In fact many cars specifically are shipped from the manufacturer with different tires.

If you think about it, a Corvette comes with 245mm tires on 17" wheels up front and 315mm tires on 18" rims in the back. That's a lot more difference than just a different brand of the same size.

Not disagreeing with you Moppie... just curious as to the different perceptions on different continents.

Mixing tyres is legal over here in the UK, which is just as well because I currently have at least three different types fitted. I happened to check the maximum permitted pressures a few months ago just out of curiosity, and they were something like 45, 45, 40, 38. The owner's handbook specifies 32 psi front, 29 psi rear, so that's what I run them at. It would never occur to me to purchase a matching set; I just replace them one at a time when they wear out, and I buy whatever happens to be cheapest on the day from amongst the well-known brands. I used to choose tyres more carefully when I was a motorcyclist, but on my cars I've always chosen according to price. I probably shouldn't do that, but old habits die hard so I doubt I'll change now.

Lets say you have 2 blizzaks, one off brand mud and snow and one performance tire? Now drive down the freeway in 2 inches of snow. Its going to make a huge difference where those tires are and what the car does.

How about 3 tripletreads and one tiger paw in a heavy downpour?

Everyday driving I have no issue with missmatched tires. But having four the same could make a huge difference in everyday situations.

but, consider the huge variations in the thousands of other factors that affect vehicle dynamics. Take for instance a 65 chevy pickup with 4-wheel manual drum brakes and a Ferarri with 14" ABS discs at all fours. The difference in their ability to safely handle emergency situations is night and day, but the tiny difference in handling between having four matched tires vs having one or two different ones is so unmeasurable that why even bother worrying about it. Its equally legal to drive the pickup and the Ferarri, why shouldn't it be perfectly normal and accepted?

The same argument could be made of my wife's Mercedes. I chose to put good Michelin tires on it, but I could have easily put no-name cheapies on it. The difference in handling and grip would be huge. Mildly unbalancing it by putting one different tire on it wouldn't be as bad as skimping on the cheap tires at all fours.

Its just relative. Sure, keeping all four tires identical would maximize its predictability and balance, but compared to the insanely wide array of vehicle types and abilities on the road, a one-tire difference isn't that much of a big deal.

I recently had a mechanic fill my tires up to 44psi after an oil change, he said because we had them low (35 psi per manufacturers instructions on an Echo)
Why wouldn't he have known that?:dunno:

You'd be surprised at what passes for a "mechanic" these days.

I'm not sure if its a tire difference, or if its just social perception. Using different tires here is not taboo at all. Its not ideal, but the amount of difference that having different tires could cause is so tiny. 99% of the drivers out there wouldn't know what to do except panic if they were in any hazardous situation, and the 2% increase in predictability you gain from having 4 tires the same is really not a big deal here. No state in the US requires 4 matching tires. In fact many cars specifically are shipped from the manufacturer with different tires.

If you think about it, a Corvette comes with 245mm tires on 17" wheels up front and 315mm tires on 18" rims in the back. That's a lot more difference than just a different brand of the same size.

Not disagreeing with you Moppie... just curious as to the different perceptions on different continents.



Given your knowledge and experiance in engineering I am somewhat surprised, but:


The Corvette is engineered to work with different sized tyres front and rear.
You know better than I do how suspension can be set up to alter traction at different ends of a car.
The Corvetter is simply set up to handle and be drivable, and safe, with more grip at the back than at the front.

Now, my Honda Prelude on the other hand has been set up to handle and be drivable, and safe, with equal amounts of tyre grip at the front, as at the back.
Since I am a cheap bastard, and rather arrogantly consider myself a better than average driver, I have been driving it with different tyres at the front, than at the back.
Consequently it has more grip at the front, than at the back, and consequently it does not stop or corner as well as it was designed to.
Stopping in an emergancy is especially compromised as the back end tends to want to come around and pass the front end. It has caught my by surprise once and left me facing the wrong direction in traffic. But, currently it is legal, and I am arrogant enough to think I can controll it.

However, driving the same model Prelude, fitted with 4 different tyres, front, rear, left and right, 2 young sisters went to slow down for a corner on a country road here a couple of years ago.
They had not expect the corner to be as tight as it was, and braked harder than normal.
The mis-matched tyres on all 4 wheels meant there was unequal amounts of traction accross both front and back axles, and the car, while braking in a straight line, spun out into a tree and killed both of them.
Not long after the coroner reported the cause was the mis-matched tyres, tests were done on how it effects performance, and a law was passed requiring the same make and brand of tyre on each side of each axle.



Your right that for 99% of the driving that 99% of the people on the road do, then the grip levels are never stressed enough for it to be a problem.
BUT, what about that 1% of the time when someone has to stop, or swerve to avoid something, and THIS will happen to everyone at least once in thier life.

That 1% of the time is all it takes for the different grip levels to turn the car in an unexpected direction and change what should have been an emergancy stop into a fatal accident.


Your ferriri vs pick up anology does not work either.
Drivers learn the performance parameters of thier cars, how they feel, how they handle etc, with in the limits of thier own driving.
The Pick up driver knows he can not corner as fast as the Ferriri driver, and so drives accordingly.
However, he also expects his pick up to behave in a predictable manner. When he stops he expects it to stop in a straight line, or maybe with a bit of a pull to the left because of that worn bushing or bad shock.
With tyres of equal grip on the same axle, then that predictably holds for an emergancy stop as much as it does for everyday driving.
With tyres of unequal grip on the same axle then things can suddenly change. Under everyday driving the tyres are never stressed, so the ute behaves predictably.
But, during an emergancy stop the grip levels will be reached and exceeded.
If one tyre has less grip than the other then the handling will become unpredictable, and it is much easier to lose control.


I feel the sameway about driving with worn and broken suspension parts.
It is important to remember that 2 tons of metal traveling at 60mph can do an aweful lot of damage if it hits something.
Hopefully not another road user.

I recently had a mechanic fill my tires up to 44psi after an oil change, he said because we had them low (35 psi per manufacturers instructions on an Echo)
Why wouldn't he have known that?:dunno:


I would suggest humbling your "mechanic" and go to some of the tire manufacturers websites, find the proper tire inflation procedures, print them out, and show them to him/her. If they have overinflated yours they have over inflated many others!!! Is it as bad as the people that pull up to the air hose and fill them up until there round and never use a guauge? No, but none the less it is still improper!!

I don't disagree with the technical part of your argument Moppie, just disagree with the importance that is placed on matching tires.

I think that drivers will very quickly re-learn their car's abilities. It took me three days to get comfy driving my new truck. I put new tires on my car and it took me 10 minutes to re-learn how it handled them.

I guess what I'm saying is; let's say you have a 2007 Camry and you blow one of the four Michelins on it. Now consider these two options: 1- You replace it with a $30 cheapy no-name tire, or 2- you replace the whole car with a 65 chevy pickup. Relearning a new tire is a lot easier than relearning a whole different vehicle, and the Camry will still out-brake, out-handle, and out-accelerate, that truck even with its cheap single tire; yet buying the pickup is perfectly accepted, while the off-brand tire isn't.

Maybe its because I'm an old-car guy. I had four different tires on a 66 Bonneville once, and trust me, it wasn't the limiting factor of any of its handling dynamics :) Squishy springs, weak shocks, worn bushings, 4-wheel drum brakes... it was a nightmare. I think tires were optional. It probably would have handled just as well on the rims :)

I would suggest humbling your "mechanic" and go to some of the tire manufacturers websites, find the proper tire inflation procedures, print them out, and show them to him/her. If they have overinflated yours they have over inflated many others!!! Is it as bad as the people that pull up to the air hose and fill them up until there round and never use a guauge? No, but none the less it is still improper!!

That is a valid point, though that was a while back and my employer wants us to use this mechanic, that would seem a bit awkward now.

I don't disagree with the technical part of your argument Moppie, just disagree with the importance that is placed on matching tires.



At the end of the day, the last thing keeping your car on the road is its tyres. Four hand sized patches of rubber are all that prevent you from an accident.
It is not something people should be compromising on. :cool:

That is a valid point, though that was a while back and my employer wants us to use this mechanic, that would seem a bit awkward now.

From a technicians point of view if I am constantly trying to better myself. If you handed me materials from a tire company that said inflate to the vehicles specs not the tire specs I would look into it for myself and correct my error. The Mech/Tech you are referring to will run into all sorts of problems with vehicles equipped with TPMS sensors if he is not inflating tires properly. Not only will these tell you when a tire is low but many will tell you when a tire is overinflated as well. I would bet that instead of realizing that he/she is wrong they will start preaching that these systems are junk and worthless because he/she has had so many problems with them. Not only that but he/she will likely not be able to give the customer a square answer or be able to resolve the problem. Thus leaving the customer frustrated and possible spending a lot of money and wasting time at a dealer who lets them know that there tires are overinflated and after being ajusted accordingly everything will be fine. Then the customer is edjucated on proper tire inflation (which by the way is in your owners manual) and the customer asks why wouldn't my mechanic know that?

Its a vicious cycle isn't it? :grinyes:

From a technicians point of view if I am constantly trying to better myself. If you handed me materials from a tire company that said inflate to the vehicles specs not the tire specs I would look into it for myself and correct my error. The Mech/Tech you are referring to will run into all sorts of problems with vehicles equipped with TPMS sensors if he is not inflating tires properly. Not only will these tell you when a tire is low but many will tell you when a tire is overinflated as well. I would bet that instead of realizing that he/she is wrong they will start preaching that these systems are junk and worthless because he/she has had so many problems with them. Not only that but he/she will likely not be able to give the customer a square answer or be able to resolve the problem. Thus leaving the customer frustrated and possible spending a lot of money and wasting time at a dealer who lets them know that there tires are overinflated and after being ajusted accordingly everything will be fine. Then the customer is edjucated on proper tire inflation (which by the way is in your owners manual) and the customer asks why wouldn't my mechanic know that?

Its a vicious cycle isn't it? :grinyes:

Yes, and our mechanic is a very friendly guy,maybe out of courtesy to him I will look up that info and the next time I go in for an oil change or tire rotation I will give it to him.

thanks!:)