New tires - white knuckles
02-22-2016, 01:35 PM
#11
Senior Member/Vietnam Vet
A Load Range E tire inflated to 50-55psi has more carrying capacity than the factory tires inflated to the pressure noted on the door sticker (which inflates them enough to be rated to carry more than the axle is rated to carry).
So, if you think he was underinflated, that means he would also have been over weight.
If the tires were pretty much brand new, I could see that as a contributing factor. First few hundred miles with new tires always feels a little different...
And yeah, the hitch needs to be adjusted. Ideally, dropping the head an inch should work but the head tilt may need to be adjusted as well...
So, if you think he was underinflated, that means he would also have been over weight.
If the tires were pretty much brand new, I could see that as a contributing factor. First few hundred miles with new tires always feels a little different...
And yeah, the hitch needs to be adjusted. Ideally, dropping the head an inch should work but the head tilt may need to be adjusted as well...
The following users liked this post:
strorg (02-27-2016)
02-22-2016, 02:13 PM
#12
Senior Member
A Load Range E tire inflated to 50-55psi has more carrying capacity than the factory tires inflated to the pressure noted on the door sticker (which inflates them enough to be rated to carry more than the axle is rated to carry).
So, if you think he was underinflated, that means he would also have been over weight.
So, if you think he was underinflated, that means he would also have been over weight.
The part in blue, incorrect. The inflation on the sticker is not for carrying maximum load with the given tires. See the tire inflation charts. This is especially important when you have changed from the stock tires in make, model or size.
Last edited by Dirttracker18; 02-22-2016 at 02:43 PM.
02-22-2016, 10:53 PM
#13
Senior Member
The part in bold, you are making an assumption that is not based on the given tires.
The part in blue, incorrect. The inflation on the sticker is not for carrying maximum load with the given tires. See the tire inflation charts. This is especially important when you have changed from the stock tires in make, model or size.
The part in blue, incorrect. The inflation on the sticker is not for carrying maximum load with the given tires. See the tire inflation charts. This is especially important when you have changed from the stock tires in make, model or size.
The load inflation table for a 285/65r18 shows that at 50psi it is rated to carry 2600# which exceeds any axle option available on an F150 since at least 2011. Oddly enough, a 275/65r18 (the likely factory tire size, in a P-rated tire) is rated to carry 2601/1.1(because...truck) or 2367#.
Page 25 for the 285, page 19 for the 275: https://toyotires2-1524598101.netdna...s_20151020.pdf
Here are the ratings for the 285/65r18
.............................35....40....45....50. ...55....60.....65...............70.....75.....80
LT285/65R18 Single 2035 2235 2425 2600 2790 2965 3195 (D) 121 3305 3470 3640 (E) 125
Then there is this for a little light reading (I think the P.E. after his name indicates that he is a Professional Engineer but maybe he is just really good at gym class...): http://www.dawsengineering.com/linke...ducedloads.pdf
Skipping to the conclusions brings you to this: The simple ratio method given by Equation 9 provides a slightly more conservative, but computationally simpler, method of developing a safe operating pressure for tires operating at less than maximum loads. Equation 9 being this:
(Pressure/MaxPressure)=(Load/MaxLoad).
Manufacturer's usually list MaxLoad and MaxPressure and at that point it is pretty simple to solve for Pressure.
Pressure= (Load/MaxLoad)*MaxPressure
And yes, the pressure indicated on the sticker IS the correct pressure for the factory installed tires to be able to carry AT LEAST what the axles are rated to carry. I've checked that against the load tables as well. You remember the Explorer fiasco? I know I do and I bet Ford does too. There is no way they are going to list a pressure that cannot carry every bit of load that the truck is rated to carry.
Now, my 275/55r20's are rated to carry quite a bit less than the 275/65r18's that came on my last truck but if I go to an LT in the same size, 50psi is again correct. If I go up to 285/55r20's in an LT, according to the Tables, 45psi is enough.
Last edited by 11screw50; 02-22-2016 at 11:10 PM.
02-23-2016, 09:41 AM
#14
Senior Member
That is really weird, I got pretty familiar with the charts with my last truck as I wanted to be sure everything was good before towing. Between referencing the tables and calculating it myself, I came to the conclusion that 50-55psi on a load range E tire was more than enough to exceed the axle rating of the truck. In fact, I looked at the charts for that exact size tire that the OP has installed for my last truck because that is what I was going to buy...then I traded the truck.
The load inflation table for a 285/65r18 shows that at 50psi it is rated to carry 2600#
Recheck that table because you have quoted the wrong pressure. More importantly this does not take into consideration the differences in weight capacity for tire other than stock, [I]which is noted at the beginning of the charts you quoted (Replacement tires must be of a size, load range, and load capacity (by inflation)that are capable of
supporting theload of the vehicle’s originally installed(O.E.)tires.)/I]. Again this chart makes assumptions which you must account for, you did not.
which exceeds any axle option available on an F150 since at least 2011. Oddly enough, a 275/65r18 (the likely factory tire size, in a P-rated tire) is rated to carry 2601/1.1(because...truck) or 2367#.
Page 25 for the 285, page 19 for the 275: https://toyotires2-1524598101.netdna...s_20151020.pdf
Here are the ratings for the 285/65r18
.............................35....40....45....50. ...55....60.....65...............70.....75.....80
LT285/65R18 Single 2035 2235 2425 2600 2790 2965 3195 (D) 121 3305 3470 3640 (E) 125
Then there is this for a little light reading (I think the P.E. after his name indicates that he is a Professional Engineer but maybe he is just really good at gym class...):
No need to be cocky unless it is your P.Eng. designation related to automotive tires we are talking about. Then you can expose your brilliance and I will bow to your superior knowledge.
http://www.dawsengineering.com/linke...ducedloads.pdf
Skipping to the conclusions brings you to this: The simple ratio method given by Equation 9 provides a slightly more conservative, but computationally simpler, method of developing a safe operating pressure for tires operating at less than maximum loads. Equation 9 being this:
(Pressure/MaxPressure)=(Load/MaxLoad).
Exactly, I have been doing this for years since I started setting up race cars over 20 years ago. For most this is not useful as most people do not know their weight on each tire or even axle nor the load they are carrying.
Manufacturer's usually list MaxLoad and MaxPressure and at that point it is pretty simple to solve for Pressure.
Always list max load and related max pressure
Pressure= (Load/MaxLoad)*MaxPressure
And yes, the pressure indicated on the sticker IS the correct pressure for the factory installed tires to be able to carry AT LEAST what the axles are rated to carry. I've checked that against the load tables as well. You remember the Explorer fiasco? I know I do and I bet Ford does too. There is no way they are going to list a pressure that cannot carry every bit of load that the truck is rated to carry.
Actually they strike a balance between many factors including proper tire wear (which would not happen if you ran you tires at the pressure for the maximum weight capacity of the truck with no load), fuel economy and ride quality. The ride quality at the inflation needed for the maximum load on the truck, when empty, would result in a harsh ride.
The Firestone fiasco was about the quality of the tires and their issue with failures. Well that and stupid people that cannot drive. Studies since have repeatedly shown that reasonable drivers did not have roll over issues after a blowout. Tire pressure was not the issue here, it was tire construction. The low tire pressure specified by Ford were based on Firestone recommendations for weight capacity. Apparently they were wrong.
Now, my 275/55r20's are rated to carry quite a bit less than the 275/65r18's that came on my last truck but if I go to an LT in the same size, 50psi is again correct. If I go up to 285/55r20's in an LT, according to the Tables, 45psi is enough.
The load inflation table for a 285/65r18 shows that at 50psi it is rated to carry 2600#
Recheck that table because you have quoted the wrong pressure. More importantly this does not take into consideration the differences in weight capacity for tire other than stock, [I]which is noted at the beginning of the charts you quoted (Replacement tires must be of a size, load range, and load capacity (by inflation)that are capable of
supporting theload of the vehicle’s originally installed(O.E.)tires.)/I]. Again this chart makes assumptions which you must account for, you did not.
which exceeds any axle option available on an F150 since at least 2011. Oddly enough, a 275/65r18 (the likely factory tire size, in a P-rated tire) is rated to carry 2601/1.1(because...truck) or 2367#.
Page 25 for the 285, page 19 for the 275: https://toyotires2-1524598101.netdna...s_20151020.pdf
Here are the ratings for the 285/65r18
.............................35....40....45....50. ...55....60.....65...............70.....75.....80
LT285/65R18 Single 2035 2235 2425 2600 2790 2965 3195 (D) 121 3305 3470 3640 (E) 125
Then there is this for a little light reading (I think the P.E. after his name indicates that he is a Professional Engineer but maybe he is just really good at gym class...):
No need to be cocky unless it is your P.Eng. designation related to automotive tires we are talking about. Then you can expose your brilliance and I will bow to your superior knowledge.
http://www.dawsengineering.com/linke...ducedloads.pdf
Skipping to the conclusions brings you to this: The simple ratio method given by Equation 9 provides a slightly more conservative, but computationally simpler, method of developing a safe operating pressure for tires operating at less than maximum loads. Equation 9 being this:
(Pressure/MaxPressure)=(Load/MaxLoad).
Exactly, I have been doing this for years since I started setting up race cars over 20 years ago. For most this is not useful as most people do not know their weight on each tire or even axle nor the load they are carrying.
Manufacturer's usually list MaxLoad and MaxPressure and at that point it is pretty simple to solve for Pressure.
Always list max load and related max pressure
Pressure= (Load/MaxLoad)*MaxPressure
And yes, the pressure indicated on the sticker IS the correct pressure for the factory installed tires to be able to carry AT LEAST what the axles are rated to carry. I've checked that against the load tables as well. You remember the Explorer fiasco? I know I do and I bet Ford does too. There is no way they are going to list a pressure that cannot carry every bit of load that the truck is rated to carry.
Actually they strike a balance between many factors including proper tire wear (which would not happen if you ran you tires at the pressure for the maximum weight capacity of the truck with no load), fuel economy and ride quality. The ride quality at the inflation needed for the maximum load on the truck, when empty, would result in a harsh ride.
The Firestone fiasco was about the quality of the tires and their issue with failures. Well that and stupid people that cannot drive. Studies since have repeatedly shown that reasonable drivers did not have roll over issues after a blowout. Tire pressure was not the issue here, it was tire construction. The low tire pressure specified by Ford were based on Firestone recommendations for weight capacity. Apparently they were wrong.
Now, my 275/55r20's are rated to carry quite a bit less than the 275/65r18's that came on my last truck but if I go to an LT in the same size, 50psi is again correct. If I go up to 285/55r20's in an LT, according to the Tables, 45psi is enough.
Use your own calculation method noted above and you will see that 50 PSI in that particular tire is low for the weight being carried.
02-23-2016, 10:55 AM
#15
Senior Member
Hopefully that clears it up for you a bit. I understand what you are trying to say but you are misunderstanding what you are reading and using.
Use your own calculation method noted above and you will see that 50 PSI in that particular tire is low for the weight being carried.
Use your own calculation method noted above and you will see that 50 PSI in that particular tire is low for the weight being carried.
As for the simple calculation, assuming the OP has the 4800# axle, that is only 2400# per tire. (2400/3640)*80=52.75psi.
Since the instructions include that the tires must be of a size, load range and inflation capable of carrying the load of the original (oe) tires, they only need to carry 2365# (unless he had something different for stock tires than 275/65r18's which is possible and also why I stated what I had assumed).
P275/65r18 is 2601# on a car and 2365# on a truck, the axle was rated 4100# so 2050# per tire. (That was my last truck). Those tires would have exceeded the axle capacity for everything except HD Payload.
P275/55r20 is 2403# on a car2184# on a truck. My axle is rated for 3800# or 1900# per tire.
I'd like to hear why you say the factory tires inflated to the pressure on the sticker are not rated for more than the axle. Maybe I am missing something? Why do you think he needs to run those tires at greater than 65psi (per your original comment that you would have run them closer to max pressure)?
So far you've told me I am not accounting for variables and am making assumptions but you have not clarified where the assumptions are wrong or what variables are not being accounted for. You're saying I'm wrong and being pretty vague as to why you think I am wrong. I've showed you exactly where I my information comes from and you tell me I'm reading the table wrong but not what the correct reading is.
So, now that we've completely hijacked this thread, help me out. What am I doing wrong? If I can be more safe with my setup, I surely want to be and I think it might help others as well.
02-23-2016, 01:56 PM
#16
Senior Member
You are correct on few things.
First I read the table wrong, your number for the 285 was correct. Totally my bad and I was wrong.
Second, I did the math on that particular tire and you are again correct as the max load for the axle (assuming the 2400# axle) would put that Cooper at about 52 PSI. Again I was incorrect and should not have called you out on it without checking for certain. My mental math failed me.
Finally, we are highjacking this thread and I will stop it now
Back to the issue at hand.
First I read the table wrong, your number for the 285 was correct. Totally my bad and I was wrong.
Second, I did the math on that particular tire and you are again correct as the max load for the axle (assuming the 2400# axle) would put that Cooper at about 52 PSI. Again I was incorrect and should not have called you out on it without checking for certain. My mental math failed me.
Finally, we are highjacking this thread and I will stop it now
Back to the issue at hand.
02-24-2016, 12:26 PM
#17
What about the fact that the tires are bigger and have a taller sidewall. I went from 275/55R20s to a 275/60R20, which was about 1" increase in diameter, and noticed the difference immediately when I left the shop, no weight in the bed or anything. The new tires are more squishy for sure. You're looking at a 2" increase in diameter on a smaller wheel so you have A LOT of sidewall height. Combined with the fact that you now have the trailer hitch raised up an inch higher from the pavement which allow the trailer weight to have more effect on the truck and you are looking at a less stable ride.
I would just fill them to 80 psi to get the sidewalls as stiff as possible.
I would just fill them to 80 psi to get the sidewalls as stiff as possible.
Last edited by mass-hole; 02-24-2016 at 12:35 PM.
The following users liked this post:
strorg (02-27-2016)
02-24-2016, 12:54 PM
#18
Regardless of what the inflation tables say, why would you want to inflate the tire to the minimum required inflation pressure for the RAWR? Even if the tires only have to deal with 4100 lbs, they still also have to deal with horizontal loads which is exactly what the OP experienced. knowing that the rear tires of the truck are having to not only deal with a load, but also deal with towing a 30' sail while passing semi-trucks, I would assume you would want that tire as stiff as safely possible and would want it right at 80 psi.
Last edited by mass-hole; 02-24-2016 at 01:08 PM.