Tires and tire pressures

HellaBroke

HellaBroke

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So long story short side walll blew out on my wifes kia... ordered 4 new michelin pilot sport a/s3 tires.
Factory tires 215/55-17 pressures front and rear per door pannel is 33psi
Front axle weight gvrw is 2425
Rear axle weight gvrw is 2116
Total 4299 gvrw
New tires are 245/50-17 where can I go to figure out required pressures for new tires? Dealer had no idea...
 
I would check with Michelin.

Sometimes the recommended PSI is even labeled on the tire.
 
There is no required pressure, and when you change the tire/wheel size there's not any set formulas that I've ever seen.

Every tire manufactured has a maximum rating stamped into the side wall. You should never exceed that number.

Tires can run their entire life at that pressure without problems. But, the car will ride very hard. You'll get maximum mileage out of those tires, but you'll pay for it on every pebble in the road.

The suggested maximum set by the car manufacturer is a compromise based on maximizing tire mileage with a comfortable ride.

I'd start with the 33psi setting. If you go below that setting, you'll find the tires wearing out on the edges faster than in the center.

If you want to experiment, bump it up a few PSI at a time, until the ride is too harsh for your taste. But, don't exceed that maximum on the tire itself.

Every pound of increased pressure will get you more mileage, better handling, less flex (and heat) on the sidewalls.

Set the pressure with a good quality gauge (no pencil type gauges) when the vehicle has been setting for at least 3 hours, and not in the sun.

Jim
 
the answer i was looking for was 26psi ( not that i will run 26psi...)
the factory kumhos needed 30psi minimum to support the weight of the car... the new michilins only need 26 psi to support the weight... handling will be garbage at 26 however the gain in load rating and minimum pressure being a full 4psi less should get me away from blowing a side wall from overloading again...

something to look at when everyone changes tires from factory sized... stamp in the door jam is a good rule of thumb however not always what is best for the new sized tire and possibly rim.

the Chalk trick is another really good way to figure out tire pressure...
cover a 2" wide band of chalk across the tread and run the car forward and backwards total of around 25' in as straight of a line as possible play with tire pressure up and down until an even wear of chalk is worn from the tires...
chalk trick isnt a scientific/mathmatical formula that i normally like to use however it has worked in the past when fine tuning and hasnt let me down.. mostly was looking for a new tip/trick
 
Glad no one was hurt due to the blowout.

Also: I'm glad you figured out your new tires' inflation-psi...and Thanks for the chalk-tip! :props:

It's also pretty nice to know that your new tires:
-Will take 9.62 less revolutions to travel one mile
-Will allow your vehicle to use 1.27% less fuel
-Will cause your vehicle's: "Speed" to be 1.27% more than the speedometer's
'read-out' showed when the original tires were in use.

busted.gif


Bob
 
HellaBroke said:
the answer i was looking for was 26psi ( not that i will run 26psi...)
the factory kumhos needed 30psi minimum to support the weight of the car... the new michilins only need 26 psi to support the weight... handling will be garbage at 26 however the gain in load rating and minimum pressure being a full 4psi less should get me away from blowing a side wall from overloading again...

something to look at when everyone changes tires from factory sized... stamp in the door jam is a good rule of thumb however not always what is best for the new sized tire and possibly rim.

the Chalk trick is another really good way to figure out tire pressure...
cover a 2" wide band of chalk across the tread and run the car forward and backwards total of around 25' in as straight of a line as possible play with tire pressure up and down until an even wear of chalk is worn from the tires...
chalk trick isnt a scientific/mathmatical formula that i normally like to use however it has worked in the past when fine tuning and hasnt let me down.. mostly was looking for a new tip/trick
Click to expand...

Not to flame you or anything, but did you inflate the tires yourself?
In order to measure the psi in a wheel, the vehicle has had to be siting overnight or for a good amount of time so the tires can cool down. The ideal temp has to be 75 degrees outside. I don't remember exact psi, but you are around there. If you are keeping stock, the psi on the door jambs should tell you.

I don't know why you thought the 26psi, they perform test on the tires before they let them go into the public. Rubber expands and retracts all the time, specially during climate changes. The only time you should add a little more psi is in the winter.
 
So you put more than an inch additional width and more than an inch worth of tire height on your wife's car, after over inflating the tires and causing a blow out? Did you do this research and decide a 245/50 was a good idea or did the dealer recommend this size to you? I'm not trying to be a jerk, but you will factually see zero increase in vehicle handling, not to mention the speedometer and odometer that were calibrated to a particular size tire height+/- a specific tolerance is now off. I'm all for aesthetics too, but huh. I'm just looking at your situation from the outside in...
 
Going from a Kumho tire to pretty much the best tires on the road now, Michelin. Is normally a big upgrade in itself ride quality and overall road noise reduction are the two most noticeable. But now I would be concerned about rubbing on the fenders after taking big bumps. Also if you car is all wheel drive do not drive very far with a spare tire on, different size tires can cause driveline problems. Best of luck to you
 
You will need to test and tune as you drive. Always start at the OEM inflation spec for the car. The max pressure rating on the tire is the most pressure you can put in to push the tire to its max load capacity. Keep in mind a larger tire has a larger air volume, so less pressure is needed to support the same amount of weight. I went from a 215/55r17 to a 245/45r18 on my G35 and dropped from 35psi stock to 32psi to stop the crack slap on our roads.
 
FUNX725 said:
-Will allow your vehicle to use 1.27% less fuel


Bob
Click to expand...

Not entirely true, the added width and diameter of the tire will add unsprung weight. Also increasing the tires rolling resistance using more power to get down the road.
 
Ok there is all kinds of stuff going on in here now...
anyone looking to change there tiresize should use this site:
Ejelta.com: Tire Size Calculator

and this site
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

factory tire specs. 215(215mm)/55(aspect ratio of width)/17 et43 total height of factory tire = 668mm factory circumference= 2098mm

new tire specs. 235mm(235mm)/50(aspect ratio of width)/17 et 43
height of new tire= 668mm new circumference =2098mm

the second number in a tire metric tire measurement isnt mm like it is the first.... its a % of the width..... side wall height did not change even though the number did.... while width increased the percent of height decreased there fore making the same circumference....

and in regards to the pressure
michilin finally wrote me back and informed me that 32psi factory is acceptable. they recommend 35psi. and 26psi is the minimum pressure required to support the vehicle...
 
how to read a tire side wall size:
Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91S

The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.

source:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46


tire pressure in regards to temprature
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=73

federal mandated that tire pressure max read on the side wall is taken at 70* F
 
jamesalanb said:
So you put more than an inch additional width and more than an inch worth of tire height on your wife's car, after over inflating the tires and causing a blow out? Did you do this research and decide a 245/50 was a good idea or did the dealer recommend this size to you? I'm not trying to be a jerk, but you will factually see zero increase in vehicle handling, not to mention the speedometer and odometer that were calibrated to a particular size tire height+/- a specific tolerance is now off. I'm all for aesthetics too, but huh. I'm just looking at your situation from the outside in...
Click to expand...

Im not going to read this and take offense. 26psi is the minimum pressure required to support the vehicle. I will be inflating to 35psi as per michilins directions directly.
As for the sizing. The tires are almost a full inch wider. However sidewall height, overall height, and circumference is identical to the factory 215/55-17. For example factory width is 215mm factory sidewall height is 55% of 215 @ 118.25mm
New tire is 245mm wide and 50% of width for height or 122.5 mm (3.25mm difference)

My other two posts should answer some of these misconceptions on tire aspect ratios..

Sent from my SGH-T889 using AG Online
 
That's all stuff I never knew about tires... Thanks for sharing it.

I too am glad no one was hurt as a result of the sidewall blowout.
 
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