Question about tires...
#11
09-22-2005, 10:35 AM
Re: Question about tires...
Thanks to everyone!
I suppose, I will leave it the way the are now. I'm the beginner-driver, so safety is number one for me. I'll try more psi on spring, and low it on winter.
I suppose, I will leave it the way the are now. I'm the beginner-driver, so safety is number one for me. I'll try more psi on spring, and low it on winter.
#12
09-22-2005, 05:55 PM
Re: Question about tires...
Originally Posted by FoX
I wonder what is the best pressure in tires? I have a sign that 51 psi is maximum on my tires, and on the car itself I see 30 psi suggestion. What is the best pressure? The difference between 30 and 51 is pretty big. Now we have 40-41 psi in our tires. Any advice?
HTH
Terry
#13
09-23-2005, 12:46 AM
Re: Question about tires...
Hi FoX:
___A fellow automobile enthusiast posted this over at Edmunds a few years ago. The details are from GY themselves.
___Our own Krousdb posted these results a few months ago …
Prius II
62/62 PSI. 98.8 mpg at 77F.
44/42 PSI. 97.4 mpg at 82F.
35/33 PSI. 96.0 mpg at 86F.
___I know of Insighter’s that have gone far beyond 100,000 miles on their OEM Bridgestone RE92’s when pressed up to 50 + #’s. I also know of Insighter’s that have had to replace their RE92’s at < 30,000 miles when set at 38 #’s or below … The exact use/abuse may have something to do with it but pressed up tires have always worn less in my personal experience.
___Good Luck
___Wayne R. Gerdes
___Waynegerdes@earthlink.net
___A fellow automobile enthusiast posted this over at Edmunds a few years ago. The details are from GY themselves.
Here are published numbers for Goodyear Tires with a Max Sidewall Inflation Pressure of 35 PSI for vehicles that 'recommend' a pressure below the maximum.
#############################
Dry Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________75.5____76.2____75.8
1/2 Depth Tread with ABS__________69.9____68.1____66.3
Full Depth Tread without ABS______98.3____95.9____91.6
1997 Ford Ranger
Full Depth Tread with ABS_________80.8____78.2____77.6
1/2 Depth Tread with ABS__________79.0____74.8____71.4
Full Depth Tread without ABS______97.8____96.5____94.1
#############################
0.02 Inch Wet Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________79.8____78.5____77.1
1/2 Depth Tread with ABS__________84.7____73.7____81.4
Full Depth Tread without ABS_____111.1___110.2___108.6
1997 Ford Ranger
Full Depth Tread with ABS_________83.8____81.5____79.8
1/2 Depth Tread with ABS__________91.5____89.4____84.6
Full Depth Tread without ABS_____131.9___126.0___118.4
#############################
0.05 Inch Wet Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________80.0____81.1____82.7
1/2 Depth Tread with ABS_________103.7____99.7____92.2
Full Depth Tread without ABS_____118.0___112.2___111.7
1997 Ford Ranger
Full Depth Tread with ABS_________89.7____86.0____81.5
1/2 Depth Tread with ABS_________125.7___118.5___104.5
Full Depth Tread without ABS_____142.9___134.8___125.7
#############################
Specialty snow tires on specific snow conditions are, obviously, a special case, but it has nothing to do with the general behavior of the average passenger tire in most conditions. It also doesn't cover slush where again, the ability to bring maximum point pressure to bear is more important than a big footprint.
Manufacturers set the vehicle 'recommended' pressure for many reasons besides safety and performance. Remember the Bridgestone fiasco with Ford. Ford recommended a low pressure on the Exploder, because it decreased the chance of rollover (at least partially because you couldn't corner as fast with the sidewalls rolling over ). But, that caused the tires to blow out. Bridgestone took the heat, but it was Ford's fault. The tires were rated for higher inflation, and should have been run there.
Most instances now where the vehicle manufacturers recommend lower tire pressures are for comfort.
But, in the vast majority of real world situations you will get better performance and longer tire life by going closer to the sidewall rating. The possible exceptions being mud and some rare snow situations where you are looking more for a snowshoe than a tire. But, Slush, Ice, and Plowed snow all benefit greatly from higher pressure.
What's really bad is when people buy into this 'big footprint' myth and let air out of their tires in the winter
I'm not saying to always inflate tires to the sidewall max, but 99.9% of the time you'll do far better to inflate a bit over what's printed on the vehicle. I know many tire professionals who use the '5 Pounds Over' rule on their own cars. IE, if the vehicle manufacturer wants 28 pounds in the tires, they do 33. If the manufacturer wants 32, they do 37.
This has another benefit. It makes sure you don't run under-inflated, because it's ALWAYS far safer to be a few pounds over than a few pounds under.
#############################
Dry Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________75.5____76.2____75.8
1/2 Depth Tread with ABS__________69.9____68.1____66.3
Full Depth Tread without ABS______98.3____95.9____91.6
1997 Ford Ranger
Full Depth Tread with ABS_________80.8____78.2____77.6
1/2 Depth Tread with ABS__________79.0____74.8____71.4
Full Depth Tread without ABS______97.8____96.5____94.1
#############################
0.02 Inch Wet Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________79.8____78.5____77.1
1/2 Depth Tread with ABS__________84.7____73.7____81.4
Full Depth Tread without ABS_____111.1___110.2___108.6
1997 Ford Ranger
Full Depth Tread with ABS_________83.8____81.5____79.8
1/2 Depth Tread with ABS__________91.5____89.4____84.6
Full Depth Tread without ABS_____131.9___126.0___118.4
#############################
0.05 Inch Wet Macadam Surface
(Stopping Distance in Feet)
2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________80.0____81.1____82.7
1/2 Depth Tread with ABS_________103.7____99.7____92.2
Full Depth Tread without ABS_____118.0___112.2___111.7
1997 Ford Ranger
Full Depth Tread with ABS_________89.7____86.0____81.5
1/2 Depth Tread with ABS_________125.7___118.5___104.5
Full Depth Tread without ABS_____142.9___134.8___125.7
#############################
Specialty snow tires on specific snow conditions are, obviously, a special case, but it has nothing to do with the general behavior of the average passenger tire in most conditions. It also doesn't cover slush where again, the ability to bring maximum point pressure to bear is more important than a big footprint.
Manufacturers set the vehicle 'recommended' pressure for many reasons besides safety and performance. Remember the Bridgestone fiasco with Ford. Ford recommended a low pressure on the Exploder, because it decreased the chance of rollover (at least partially because you couldn't corner as fast with the sidewalls rolling over
). But, that caused the tires to blow out. Bridgestone took the heat, but it was Ford's fault. The tires were rated for higher inflation, and should have been run there. Most instances now where the vehicle manufacturers recommend lower tire pressures are for comfort.
But, in the vast majority of real world situations you will get better performance and longer tire life by going closer to the sidewall rating. The possible exceptions being mud and some rare snow situations where you are looking more for a snowshoe than a tire. But, Slush, Ice, and Plowed snow all benefit greatly from higher pressure.
What's really bad is when people buy into this 'big footprint' myth and let air out of their tires in the winter
I'm not saying to always inflate tires to the sidewall max, but 99.9% of the time you'll do far better to inflate a bit over what's printed on the vehicle. I know many tire professionals who use the '5 Pounds Over' rule on their own cars. IE, if the vehicle manufacturer wants 28 pounds in the tires, they do 33. If the manufacturer wants 32, they do 37.
This has another benefit. It makes sure you don't run under-inflated, because it's ALWAYS far safer to be a few pounds over than a few pounds under.
Prius II
62/62 PSI. 98.8 mpg at 77F.
44/42 PSI. 97.4 mpg at 82F.
35/33 PSI. 96.0 mpg at 86F.
___I know of Insighter’s that have gone far beyond 100,000 miles on their OEM Bridgestone RE92’s when pressed up to 50 + #’s. I also know of Insighter’s that have had to replace their RE92’s at < 30,000 miles when set at 38 #’s or below … The exact use/abuse may have something to do with it but pressed up tires have always worn less in my personal experience.
___Good Luck
___Wayne R. Gerdes
___Waynegerdes@earthlink.net
#14
09-23-2005, 08:38 AM
Re: Question about tires...
That was really helpful Wayne! Thanks.
It makes sense when you think about it that tires would wear less at higher PSI because they are flexing less, especially around corners. Flexing is not free either, it represents the tire continually impacting with the road, which creates wear as well as reducing mpg.
Basic laws of physics dictate that friction increases linearly with pressure. Therefore, a simple calculation will show that reduced patch size is exactly compensated for by increased friction per square inch. Real world things are rarely that simple however, and data above 35 PSI would give us the real scoop. But at least we can defeat the naive assumption that friction (thus tire braking and cornering) is exclusively related to patch size, and point out that physics sides with those who claim no significant loss of traction at 45-50 PSI.
It makes sense when you think about it that tires would wear less at higher PSI because they are flexing less, especially around corners. Flexing is not free either, it represents the tire continually impacting with the road, which creates wear as well as reducing mpg.
Basic laws of physics dictate that friction increases linearly with pressure. Therefore, a simple calculation will show that reduced patch size is exactly compensated for by increased friction per square inch. Real world things are rarely that simple however, and data above 35 PSI would give us the real scoop. But at least we can defeat the naive assumption that friction (thus tire braking and cornering) is exclusively related to patch size, and point out that physics sides with those who claim no significant loss of traction at 45-50 PSI.
#15
09-26-2005, 03:14 PM
Re: Question about tires...
Ok... so some retraction is in order, I stated earlier that I noticed no difference between 34 and 41 psi.... well I ran another test and found that in fact my FE went up by 3 mpg.
So I went from 34 to 44psi on each corner. And my FE without doing anything different has gone up to 55mpg. I can take corners even harder and not lose as much (if any) momentum too (I only do this on corners that I'm very familar with). So when I ran this test early on I might not have got the psi right. The tires could have been warm to begin with, this time around I made sure I entered in 10psi into a cold tire (from 34psi). I didn't go to max because my wife drives the HCH more than I do and she already complained about how slippery the car is in the wet. I'll bring it down if she feels unsafe.
I still don't get how anybody can get 32 mpg in this car, this weekend I put in over 550 miles on a tank and was hauling up to 5 people in the car with the A/C on and driving like I stole the car and still managed to get 49mpg on the meter. The actual I didn't calculate (didn't remember the actual milage and I put like 11.something gallons of gas). But it had to have been close.
Anyway, I find the avg mpg reading to be close if not exact to the actual calculated average.
So I went from 34 to 44psi on each corner. And my FE without doing anything different has gone up to 55mpg. I can take corners even harder and not lose as much (if any) momentum too (I only do this on corners that I'm very familar with). So when I ran this test early on I might not have got the psi right. The tires could have been warm to begin with, this time around I made sure I entered in 10psi into a cold tire (from 34psi). I didn't go to max because my wife drives the HCH more than I do and she already complained about how slippery the car is in the wet. I'll bring it down if she feels unsafe.
I still don't get how anybody can get 32 mpg in this car, this weekend I put in over 550 miles on a tank and was hauling up to 5 people in the car with the A/C on and driving like I stole the car and still managed to get 49mpg on the meter. The actual I didn't calculate (didn't remember the actual milage and I put like 11.something gallons of gas). But it had to have been close.
Anyway, I find the avg mpg reading to be close if not exact to the actual calculated average.
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