Thanks for all the advise!!
Correct tire pressure???
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This is a real bone of contention for me. The door sticker for my Tahoe states the orginal tire as P245/75-16. Not long ago I replaced my tires. I asked the guy at Discount Tires what pressure he put in my new tires, a new set of LT265/75-16 Load Range D BFG AT's. His reply "whatever the door sticker says." (35 PSI)
Duhhh, The original tires are P245's and the replaced tires are LT265's.
Of course this was the same guy that torqued the wheel lug nuts to 165 ft/lbs.
Duhhh, The original tires are P245's and the replaced tires are LT265's.
Of course this was the same guy that torqued the wheel lug nuts to 165 ft/lbs.
Doug,
Just so you know:
Your LT265/75R16's need to be inflated to 40 psi to get the same load capacity at the P245/75R16's at 35 psi.
Just so you know:
Your LT265/75R16's need to be inflated to 40 psi to get the same load capacity at the P245/75R16's at 35 psi.
thats only assuming you have a 50 50 weight distrobution and you never turn, accelerate, or brake. then yes, 4000lb vehicle can be supported on 20psi.
FWIW-
When I swapped my factory wheel and tires, I called Bridgestone to ask what pressure to inflate them to.
WAs transferred to a tire engineer, who asked what my factory GAWR was.
With this info, he recommended 28 psi front, 32 psi rear, to maintain my load ratings.
While I do run a few PSI higher, he did recommend something lower than 32 psi for a radial in this instance.
When I swapped my factory wheel and tires, I called Bridgestone to ask what pressure to inflate them to.
WAs transferred to a tire engineer, who asked what my factory GAWR was.
With this info, he recommended 28 psi front, 32 psi rear, to maintain my load ratings.
While I do run a few PSI higher, he did recommend something lower than 32 psi for a radial in this instance.
28/32 at maximum load?
CapriRacer
Member # 1059
posted December 20, 2005 06:25
"Doug,
Just so you know:
Your LT265/75R16's need to be inflated to 40 psi to get the same load capacity at the P245/75R16's at 35 psi. "
I think you have that backwards bubba. You're comparing a "P" to an "LT" tire. The LT can hold more weight with less air than a P-metric can.
Consider this : You have a 4000 lb vehicle. If your tire can support 2000 lbs ea.@40 psi, then you can safely support the 4Klb vehicle with 20psi in each tire and have no problems.
My Jeep has 35/12.5R15's. I run 6 PSI on the trail and 20 PSI on the street, safely.
Member # 1059
posted December 20, 2005 06:25
"Doug,
Just so you know:
Your LT265/75R16's need to be inflated to 40 psi to get the same load capacity at the P245/75R16's at 35 psi. "
I think you have that backwards bubba. You're comparing a "P" to an "LT" tire. The LT can hold more weight with less air than a P-metric can.
Consider this : You have a 4000 lb vehicle. If your tire can support 2000 lbs ea.@40 psi, then you can safely support the 4Klb vehicle with 20psi in each tire and have no problems.
My Jeep has 35/12.5R15's. I run 6 PSI on the trail and 20 PSI on the street, safely.
"I think you have that backwards bubba. You're comparing a "P" to an "LT" tire. The LT can hold more weight with less air than a P-metric can."
That is a common misconception. LT metric tires work on the "low deflection = long life" approach to tire design, while P metric tires use the "high deflection = soft ride" school of thought.
So let's compare load curves:
P245/75R16: 1884# at 29 psi, 1975 @ 32 psi, 2065 @ 35 psi (max for Standard Load) Please note the loads have been derated 10% because of the LT application.
LT245/75R16: 1700# @ 35 psi, 1865# @ 40 psi, 2030# @ 45 psi, 2205# @ 50 psi (max for Load Range C). The curve for a Load Range D continues with higher loads and pressures.
Hope this helps.
That is a common misconception. LT metric tires work on the "low deflection = long life" approach to tire design, while P metric tires use the "high deflection = soft ride" school of thought.
So let's compare load curves:
P245/75R16: 1884# at 29 psi, 1975 @ 32 psi, 2065 @ 35 psi (max for Standard Load) Please note the loads have been derated 10% because of the LT application.
LT245/75R16: 1700# @ 35 psi, 1865# @ 40 psi, 2030# @ 45 psi, 2205# @ 50 psi (max for Load Range C). The curve for a Load Range D continues with higher loads and pressures.
Hope this helps.
CapriRacer - help me out please, my truck, a 4,750# Isuzu Rodeo, probably weighing close to 5k# now with additions -
Came stock with P225/75 16's rated for 29 Front/32 Rear psi. Always ran them at 30 front/34 rear.
New tires are LT265/75 R16's which I'm currently running at 38 Front/40 Rear - not sure how accurate this is, but the ride is great as is the handling.
Am I running these with too low a PSI?
Came stock with P225/75 16's rated for 29 Front/32 Rear psi. Always ran them at 30 front/34 rear.
New tires are LT265/75 R16's which I'm currently running at 38 Front/40 Rear - not sure how accurate this is, but the ride is great as is the handling.
Am I running these with too low a PSI?
Ramblin':
Tire Guides doesn't show an Isuzu Rodeo with P225/75R16's and 29/32 as the placard info. It does show 29/29 - but let's assume you are correct with 29/32.
A P225/75R16 at 29 psi in an LT application (SUV's count as LT's) has a load capcity of 1624# and for 32 psi - 1704 #.
To get the same load capacity in an LT265/75R16 you would need 28 and 30 psi. And since it is best to keep the pressure differential - I think 28/31 seems right.
So, no, 38/40 seems, if anything, high.
Tire Guides doesn't show an Isuzu Rodeo with P225/75R16's and 29/32 as the placard info. It does show 29/29 - but let's assume you are correct with 29/32.
A P225/75R16 at 29 psi in an LT application (SUV's count as LT's) has a load capcity of 1624# and for 32 psi - 1704 #.
To get the same load capacity in an LT265/75R16 you would need 28 and 30 psi. And since it is best to keep the pressure differential - I think 28/31 seems right.
So, no, 38/40 seems, if anything, high.
MasterAcid,
Yep, that's what I was told for the new tires. Vehicle is an Expedition 2WD with trailer-towing package.
Original equipment was Goodyear Wrangler RTS, 255/??R16
New tires are Bridgestone Dueler HP, 285/60R18.
28/32 in the new tires would maintain the factory GAWR front and rear is what I was told. The engineer (or whatever he was) said they maintain data for a tire's load rating at each psi up to the tire's max. So it was easy for him to just look it up on the data table.
That being said, I actually run 30/34.
I will tell you that ALL the tire pressure guides I've found before do in fact state 29/29 as that is the pressure listed for OEM P245/70 16's, which was an upgraded option on Rodeo's.
I didn't get that upgrade, but no where have I ever found a listing for the P225/75 16's that came OEM on my Rodeo and are listed on the door placard; even my owner's manual states that it should have come with P225/75 15's and not 16's.
But, I have also seen other weird things that came as an option that I shouldn't technically have for the model I chose.
You know I failed to mention that these LT265's are Load Range D tires, if that makes a difference??
I'd heard somewhere, Big O Tire, I think, that said that I shouldn't run an LT tire below 35psi - is this accurate?
I didn't get that upgrade, but no where have I ever found a listing for the P225/75 16's that came OEM on my Rodeo and are listed on the door placard; even my owner's manual states that it should have come with P225/75 15's and not 16's.
But, I have also seen other weird things that came as an option that I shouldn't technically have for the model I chose.
You know I failed to mention that these LT265's are Load Range D tires, if that makes a difference??
I'd heard somewhere, Big O Tire, I think, that said that I shouldn't run an LT tire below 35psi - is this accurate?
Ramblin':
"...but no where have I ever found a listing for the P225/75 16's that came OEM on my Rodeo and are listed on the door placard..."
Just another example why the placard is important.
"...even my owner's manual states that it should have come with P225/75 15's and not 16's."
If Isuzu can't get it straight, how should we expect folks further down the foodchain to get it right?
"You know I failed to mention that these LT265's are Load Range D tires, if that makes a difference??"
Only if the pressure required exceeds 50 psi.
".... said that I shouldn't run an LT tire below 35psi - is this accurate? "
I tend to use the limits of the load tables as limits for usage. For LT metric tires the lowest pressure listed is 35 psi, so I tend to agree. (For P metric tires, the lower limit is 20 psi, but I think that's too low, so 26 psi is my normal recommendation.)
Why? First, the bead unseating force is greatly controlled by the inflation pressure. Recent vehicle stability tests performed by NHTSA have had beads unseat during the manuevers, so NHTSA has amended the test setup to include tubes.
Second, the amount of stiffness of the tire sidewall is also greatly controlled by inflation pressure. soft sidewalls ride better, but also adversely affect vehicle stability.
Hope this helps.
"...but no where have I ever found a listing for the P225/75 16's that came OEM on my Rodeo and are listed on the door placard..."
Just another example why the placard is important.
"...even my owner's manual states that it should have come with P225/75 15's and not 16's."
If Isuzu can't get it straight, how should we expect folks further down the foodchain to get it right?
"You know I failed to mention that these LT265's are Load Range D tires, if that makes a difference??"
Only if the pressure required exceeds 50 psi.
".... said that I shouldn't run an LT tire below 35psi - is this accurate? "
I tend to use the limits of the load tables as limits for usage. For LT metric tires the lowest pressure listed is 35 psi, so I tend to agree. (For P metric tires, the lower limit is 20 psi, but I think that's too low, so 26 psi is my normal recommendation.)
Why? First, the bead unseating force is greatly controlled by the inflation pressure. Recent vehicle stability tests performed by NHTSA have had beads unseat during the manuevers, so NHTSA has amended the test setup to include tubes.
Second, the amount of stiffness of the tire sidewall is also greatly controlled by inflation pressure. soft sidewalls ride better, but also adversely affect vehicle stability.
Hope this helps.
CapriRacer
Member # 1059
Icon 1 posted December 21, 2005 06:41 PM Profile for CapriRacer Send New Private Message Edit/Delete Post "I think you have that backwards bubba. You're comparing a "P" to an "LT" tire. The LT can hold more weight with less air than a P-metric can."
"That is a common misconception. LT metric tires work on the "low deflection = long life" approach to tire design, while P metric tires use the "high deflection = soft ride" school of thought.
So let's compare load curves:
P245/75R16: 1884# at 29 psi, 1975 @ 32 psi, 2065 @ 35 psi (max for Standard Load) Please note the loads have been derated 10% because of the LT application.
LT245/75R16: 1700# @ 35 psi, 1865# @ 40 psi, 2030# @ 45 psi, 2205# @ 50 psi (max for Load Range C). The curve for a Load Range D continues with higher loads and pressures.
Hope this helps."
It's not a misconception. I have two Cooper Discoverer's out back, one's an LT 235/75R15 rated for 1945lbs @35 PSI, the other is a P235/75R15 rated for 1745 @35 PSI. There you go.
Member # 1059
Icon 1 posted December 21, 2005 06:41 PM Profile for CapriRacer Send New Private Message Edit/Delete Post "I think you have that backwards bubba. You're comparing a "P" to an "LT" tire. The LT can hold more weight with less air than a P-metric can."
"That is a common misconception. LT metric tires work on the "low deflection = long life" approach to tire design, while P metric tires use the "high deflection = soft ride" school of thought.
So let's compare load curves:
P245/75R16: 1884# at 29 psi, 1975 @ 32 psi, 2065 @ 35 psi (max for Standard Load) Please note the loads have been derated 10% because of the LT application.
LT245/75R16: 1700# @ 35 psi, 1865# @ 40 psi, 2030# @ 45 psi, 2205# @ 50 psi (max for Load Range C). The curve for a Load Range D continues with higher loads and pressures.
Hope this helps."
It's not a misconception. I have two Cooper Discoverer's out back, one's an LT 235/75R15 rated for 1945lbs @35 PSI, the other is a P235/75R15 rated for 1745 @35 PSI. There you go.
"It's not a misconception. I have two Cooper Discoverer's out back, one's an LT 235/75R15 rated for 1945lbs @35 PSI, the other is a P235/75R15 rated for 1745 @35 PSI. There you go. "
mmmm...
It seems Cooper is not following the Tire and Rim Association Standards for either P metric or LT metric tires. I don't understand why they wouldn't, and I don't understand why they chose the load/inflation combination they printed on the sidewall. Neither load makes sense, nor does it make sense for the LT's pressure. Are you sure that is what it says?
I have come across a few instances where some manufacturer doesn't follow one of the standards, but that doesn't change the fact that these are exceptions, not the rule.
mmmm...
It seems Cooper is not following the Tire and Rim Association Standards for either P metric or LT metric tires. I don't understand why they wouldn't, and I don't understand why they chose the load/inflation combination they printed on the sidewall. Neither load makes sense, nor does it make sense for the LT's pressure. Are you sure that is what it says?
I have come across a few instances where some manufacturer doesn't follow one of the standards, but that doesn't change the fact that these are exceptions, not the rule.
I respect the spec given by the car manufacturer.
Also, in playing around, I use 75% of tire sidewall maximum cold pressure as a minimum .
Latest set of tires are 41 psi at sidewall (passenger vehicle, driver and load to 200# current road trip); 33# is the door placard, and 30.75# is the minimum per above.
Tire size was changed about 6/10's inch taller, and a good bit wider (225/70-16 to 255/65-16)
33# is being used, as the same tires on an identical vehicle ran over 50,000 miles with about one-half of treadwear gone.
Also, in playing around, I use 75% of tire sidewall maximum cold pressure as a minimum .
Latest set of tires are 41 psi at sidewall (passenger vehicle, driver and load to 200# current road trip); 33# is the door placard, and 30.75# is the minimum per above.
Tire size was changed about 6/10's inch taller, and a good bit wider (225/70-16 to 255/65-16)
33# is being used, as the same tires on an identical vehicle ran over 50,000 miles with about one-half of treadwear gone.
Tan Sedan,
Be careful using what is on the sidewall as a reference, because there are different philosphies with regard to what should be there. The regulation that covers this is a little unclear.
To illustrate: A Load Range E is an 80 psi max tire, but there are some applications where 45 psi is what the placard says. Using 60 psi (75%) seems out of line.
Another example: A P metric standard load tire could come with 35, 44 or 51 psi written on the sidewall. Some applications use 26 psi on the placard, so 38 psi (75% of 51) also seems out of line.
So use caution when using something other than the placard inflation.
Hope this helps.
Be careful using what is on the sidewall as a reference, because there are different philosphies with regard to what should be there. The regulation that covers this is a little unclear.
To illustrate: A Load Range E is an 80 psi max tire, but there are some applications where 45 psi is what the placard says. Using 60 psi (75%) seems out of line.
Another example: A P metric standard load tire could come with 35, 44 or 51 psi written on the sidewall. Some applications use 26 psi on the placard, so 38 psi (75% of 51) also seems out of line.
So use caution when using something other than the placard inflation.
Hope this helps.
Here is what I heard from a Michelin Technical Representative and read in Cycle Magazine on procedures for establishing correct tire pressure.
1. Measure COLD tire pressure
2. Drive vehicle at highway speed for 25 minutes with representative load (passengers or cargo) upon vehicle.
3. Measure tire pressure immediately after item #2. Tire pressure increase should be between 3 PSI and 5 PSI. Note that a 3 PSI increase indicates the initial cold pressure was at the HIGHER end of the acceptable range resulting in less flexing and subsequent lower heat build up.
1. Measure COLD tire pressure
2. Drive vehicle at highway speed for 25 minutes with representative load (passengers or cargo) upon vehicle.
3. Measure tire pressure immediately after item #2. Tire pressure increase should be between 3 PSI and 5 PSI. Note that a 3 PSI increase indicates the initial cold pressure was at the HIGHER end of the acceptable range resulting in less flexing and subsequent lower heat build up.
I use the recommended tire pressure (listed on the door) as the minimum that I put into my tires. Going higher will give a stiffer ride, but will improve gas mileage. The higher you go, the stiffer it will be.
It's personal preference on how stiff you want to tolerate. You should not exceed the maximum listed on the tire.
As it's been stated... tire pressure should be measured "cold". That doesn't mean when it's cold outside, but rather before you've driven it (or at most a few miles) or after it has sat for a few hours.
It's personal preference on how stiff you want to tolerate. You should not exceed the maximum listed on the tire.
As it's been stated... tire pressure should be measured "cold". That doesn't mean when it's cold outside, but rather before you've driven it (or at most a few miles) or after it has sat for a few hours.
CapriRacer: Regarding the back of the gas flap indicating different pressure recommendations for light versus heavy loads you wrote: I've only seen this on German cars - the VW group and BMW. I don't think that would qualify as "many", as everyone else lists one pressure.
My wife's 2003 Volvo XC90 does this as well. So you can add Volvo to those you mentioned. I don't know if this is the trend in European cars in general, or not. Anybody with a recent model Mercedes Benz out there want to chime in on this?
Brock in Bristol
My wife's 2003 Volvo XC90 does this as well. So you can add Volvo to those you mentioned. I don't know if this is the trend in European cars in general, or not. Anybody with a recent model Mercedes Benz out there want to chime in on this?
Brock in Bristol
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