What tire pressure?
Thread Starter
|
Junior User
Joined: Jul 2002
Posts: 81
Likes: 0
What tire pressure?
Hey guys, I know this is kind of a basic question...I've searched the forum and can't find an answer. What tire pressure should I be running my tires with? It's an f-350 4x4 with LT305/70/R16s on it. when I bout it they were at about 45 psi (50 is the max). Empty, it rides like #$@% over my washboard roads. I expect it to be rough, a one ton running empty, but would lower pressure help? How low? Would my (non-existent) gas milage suffer? (It has a 460, so surely it can't make much difference, it already gobbles all the gas in sight). What about the effect on tire wear?
By the way, what do those numbers really mean...305/70/16? Is a 305 wider, or taller than a 255? and the 70 is what?
:-X11
By the way, what do those numbers really mean...305/70/16? Is a 305 wider, or taller than a 255? and the 70 is what?
:-X11
Posting Guru
Joined: Dec 2000
Posts: 1,594
Likes: 0
From: Campbell River, BC Canada
What tire pressure?
[updated:LAST EDITED ON 02-Aug-02 AT 01:15 AM (EST)]Heres a run down of your tires in comparison to what would most likely be your stock tire depending on the year of your F-350.
305/70/16's 235/85/16's
Width 12.01" (305mm) 9.25" (235mm)
Sidewall Height 8.41" (213.5mm) 7.86" (199.75mm)
Overall Height 32.81" (833.40mm) 31.73" (805.9mm)
Circumference 103.08" (2618.20mm) 99.68" (2531.81mm)
The first number (305) is the width of the tire in mm, and the second number (70) is the percentage (70%) of the first number which relates to height. 12.01" multiplied by 70% equals 8.41" or in metric 305mm multiplied by 70% equals 213.5mm. I hope this helps you out a little bit. Good Luck
I edited this because the columns don't line up so I hope that doesn't make it confusing. the first set of numbers is for the 305's and the second set is for the 235's
305/70/16's 235/85/16's
Width 12.01" (305mm) 9.25" (235mm)
Sidewall Height 8.41" (213.5mm) 7.86" (199.75mm)
Overall Height 32.81" (833.40mm) 31.73" (805.9mm)
Circumference 103.08" (2618.20mm) 99.68" (2531.81mm)
The first number (305) is the width of the tire in mm, and the second number (70) is the percentage (70%) of the first number which relates to height. 12.01" multiplied by 70% equals 8.41" or in metric 305mm multiplied by 70% equals 213.5mm. I hope this helps you out a little bit. Good Luck
I edited this because the columns don't line up so I hope that doesn't make it confusing. the first set of numbers is for the 305's and the second set is for the 235's
Moderator
Joined: Jan 2001
Posts: 57,027
Likes: 2,763
From: Virginia
What tire pressure?
Tire pressure will make a big difference in fuel mileage. I always run at the sidewall max pressure EXCEPT when I am running an oversize tire for the rim. Sounds like your tire is bigger than stock. If the rim pulls the sidewall inward because the rim is a little narrow, this will make the tire wear more in the center of the tread. Pumping the tires up will only aggravate the situation. With a non-stock tire on a stock rim, you will have to experiment to see what gives the best wear.
Being a heavy duty truck, you might as well forget about any ride quality. Large carrying capacity and cushy ride are not normally associated together.
Being a heavy duty truck, you might as well forget about any ride quality. Large carrying capacity and cushy ride are not normally associated together.
New User
Joined: Jun 2002
Posts: 19
Likes: 0
From: Canada
What tire pressure?
Here is an idea, Don't hunt me down if it doesn't work, but it may help you find a good empty (unloaded) tire pressure. Always use the recommended pressure on the tire sidewall for heavy loads (That's what I do). Anyway, if you think the tires have to much or too little air just head out on a quiet street some Sunday morning. With the tires cold make a mark across the tread with a tire marker, or maybe with whatever will make a line you can see. Then drive the truck for a short distance, stop & check the mark. If the mark is worn off in the middle of the tread & not the side your tire is overinflated. If it wears off at the side and not so much in the middle, the tire is underinflated. You should try to even wear across the tread. You may improve your ride by airing down, as long as you don't go so far down as to cause premature wear on the outer edges of the tread. Good luck.
Randy
PS By side I mean the outer edges of the tread, not the sidewall.
Randy
PS By side I mean the outer edges of the tread, not the sidewall.
New User
Joined: Feb 2002
Posts: 10
Likes: 0
From: bluffton usa
What tire pressure?
Good explanation of aspect ratio.
You should always run your tires according to the VEHICLE manufacurers recommendation. Usually on a truck the pressure requirements will be different for the front and rear axles. This is because of the weight difference caused by the motor. If you are going to be towing or carrying a heavy load, then go with the max rating on the tire. Do not exceed the pressure rating of the tire. This can cause a lot of different problems. If you find that you need more air to do what you need to do, then you really need more tire. Not always bigger, but a heavier load rating. A tire is just a container for air. The air is what carries the load. A tire with a higher load rating is simply capable of carrying more air safely.
You should always run your tires according to the VEHICLE manufacurers recommendation. Usually on a truck the pressure requirements will be different for the front and rear axles. This is because of the weight difference caused by the motor. If you are going to be towing or carrying a heavy load, then go with the max rating on the tire. Do not exceed the pressure rating of the tire. This can cause a lot of different problems. If you find that you need more air to do what you need to do, then you really need more tire. Not always bigger, but a heavier load rating. A tire is just a container for air. The air is what carries the load. A tire with a higher load rating is simply capable of carrying more air safely.
Moderator
Joined: Jan 2001
Posts: 57,027
Likes: 2,763
From: Virginia
What tire pressure?
I disagree. An 8 ply tire will carry more load than the same size tire that is 4 ply. A LT235/75/r/15 will carry more load than a P/235/75/r/15
Trending Topics
Senior User
Joined: Aug 2002
Posts: 274
Likes: 0
From: DeQuincy, LoUiSiAna
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
New User
Joined: Feb 2002
Posts: 10
Likes: 0
From: bluffton usa
What tire pressure?
You are correct. When I said more tire, I also said not always bigger or smaller. More tire means higher load rating, the same as ply rating. These days there is almost no difference between a load rand C and D. A D does not have more belts in the belt package, it has more body plies per inch. The ply rating system goes back to the days of bias tires and has not changed. I will be glad to let you in on the whole story, if you really want, but it will probably put you to sleep.
Moderator
Joined: Jan 2001
Posts: 57,027
Likes: 2,763
From: Virginia
What tire pressure?
Yea, I thought about how the LT's have a higher pressure rating than the P's(only 35psi) after I posted. And I also read through your post too quickly. And I will also agree that it's more complicated than just the air theory(heat build-up comes to mind). One thing I think can be said is, a tire is always a compromise. You can't build one that's good for all types of use.
Thread
Thread Starter
Forum
Replies
Last Post
Chris Haynes
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
2
Oct 16, 2015 02:25 PM
rowdyredneck
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
1
Jun 26, 2013 06:22 PM