Posted 2013-09-22 11:37 AM (#154897) Subject: Tire pressure
Extreme Veteran
Posts: 322 Location: Fort Madison, Iowa
HI all,I recently purchased new tires for my trailer before going on vacation next week. Getting everything ready and checked the tire pressure on my truck and trailer this morning which is at the pressure my mechanic put in them.I checked the past posts on tire pressure and I'm thinking I should put more pressure in them but I thought I'd double check with you all.On my truck door it recommends 55 front/70 back. My truck tires are LT 265/85R16. On the tire it says 80 PSI. He has them at 55 front/62 on back tire.My trailer tire is LT 265/75R16, E rating, 80 psi. He has them at 60.In the past I've ran 55/65 on the truck and 60or65 on trailer. I have had some blow outs but thought it was because of tires needing replaced but after reading the past forums, it could have been from not having enough pressure in tires. Should I leave the truck at 55/65? and put more pressure in the trailer up to 80?Also Jim Bob mentioned about your speed rating on a tire and how would you find that out? I usually travel on the interstate 65-70.Thanks for putting up with more tires pressure questions!
Posted 2013-09-22 3:12 PM (#154898 - in reply to #154897) Subject: RE: Tire pressure
Veteran
Posts: 178 Location: Richmond, Ky
all you ever wanted to know about tires I run mine at 90% of the tire rating....
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Automobile tires are described by an alphanumeric tire code (in American English and Canadian English) or tyre code (in British English, Australian English and others), which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa.
The code has grown in complexity over the years, as is evident from the mix of metric and imperial units, and ad-hoc extensions to lettering and numbering schemes. New automotive tires frequently have ratings for traction, treadwear, and temperature resistance (collectively known as The Uniform Tire Quality Grade (UTQG) ratings).
Most tires sizes are given using the ISO Metric sizing system. However, some pickup trucks and SUVs use the Light Truck Numeric or Light Truck High Flotation system.
Contents
1 National technical standards regulations
2 Explanation of tire codes
2.1 Flotation Sizes
2.2 Load range
2.3 Load index
2.4 Speed rating
3 Wheel/Rim widths
3.1 Additional marks
4 Tire geometry
4.1 Examples
5 See also
6 References
7 External links
National technical standards regulations
The European Tyre and Rim Technical Organisation (ETRTO) and the Tire and Rim Association (TRA) are two organizations that influence national tire standards. The objective of the ETRTO include aligning national tire and rim standards in Europe.[1] The Tire and Rim Association, formerly known as The Tire and Rim Association of America, Inc., is an American trade organization which standardizes technical standards.[2] In the United States, the Office of Vehicle Safety Compliance, a component of the Department of Transportation, is one of the agencies tasked to enforce the Federal Motor Vehicle Safety Standard (FMVSS).[3] Canada has published tire regulations, such as the Motor Vehicle Tire Safety Regulations SOR 95-148.[4]
Explanation of tire codes
Tire identification diagram
The ISO Metric tire code consists of a string of letters and numbers, as follows:
An optional letter (or letters) indicating the intended use or vehicle class for the tire:-
P: Passenger Car
LT: Light Truck
ST: Special Trailer
T: Temporary (restricted usage for "Space-Saver" spare wheels)
Use of the letter P indicates that the tire is engineered to TRA standards and absence of a letter indicates that the tire is engineered to ETRTO standards. In practice, the standards of the two organizations have evolved together and are fairly interchangeable, but not fully since the Load Index will be different for the same size tire.[5]
3 digit number: The "nominal section width" of the tire in millimeters; the widest point from both outer edges (side wall to side wall). The tire surface which touch the road usually has smaller width.
/: Slash character for character separation.
2 or 3 digit number: The "aspect ratio" of the sidewall height as a percentage of the total width of the tire. If the information is omitted, it is assumed to be 82% (if written, it should be like xxx/82). If the number is larger than 200, then this is the diameter of the entire tire in millimeters.
An optional letter indicating construction of the fabric carcass of the tire:
B: bias belt (where the sidewalls are the same material as the tread, leading to a rigid ride)
D: diagonal
R: radial
if omitted, then it is a cross ply tire
2 digit number: Diameter in inches of the wheel that the tires are designed to fit. There is the rare exception metric diameter tires, such as the use of the 390 size, which in this case would indicate a wheel of 390 mm in diameter. Few tires are made to this size presently.[6]
2 or 3 digit number: Load index; see table below Some light truck tires are approved for "dual use", that is they can be run in pairs next to each other. If so, separate load indexes will be specified for single and dual usage. In the example shown in the light truck tire illustration, the tire has a load index of 114 if used as a single tire, and a load rating of 111 if used in a dual pair. Tires without this designation for dual usage are unsafe to use as such.
1 or 2 digit/letter combo: Speed rating; see table below
Additional marks: See subheading below.
Flotation Sizes
Tire identification diagram, light truck specific features
Some light truck tires follow the Light Truck Numeric or Light Truck High Flotation systems, indicated by the letters LT at the end instead of the beginning of the sequence, as follows:
The tire diameter is given for High Flotation tires and omitted from Numeric tires.
2 digit number: The diameter of the tire in inches.
x: Separator character.
3 or 4 digit number: The section width (cross section) of the tire in inches. If the tire diameter is not given, section widths ending in zero (e.g., 7.00 or 10.50) indicate the aspect ratio is 92%, while section widths not ending in zero (e.g., 7.05 or 10.55) indicate the aspect ratio is 82%.
Construction of the fabric of the tire:
B: bias belt
D: diagonal
R: radial
2 digit number: Diameter in inches of the wheel rim that this tire is designed to fit.
LT: Designates that this is a Light Truck tire.
Load index and speed rating are sometimes not mandatory for flotation sizes, but must be for any tire approved for street and highway use.
2 or 3 digit number: Load index; see table below.
1 or 2 digit/letter combination: Speed rating; see table below.
Additional marks: See subheading below.
As an example, if a tire size has two sets of numbers (6-12, 5.00-15, 11.2-24) the first number (5.00-15) is the approximate width in inches; the second number (5.00-15) is the rim diameter in inches.
If a tire size has three sets of numbers (15x6.00-6, 26x12.00-12, 31x15.50-15) the first number (26x12.00-12) is the approximate height in inches, the second number (26x12.00-12) is the approximate width in inches, and the third number (26x12.00-12) is the rim diameter in inches.[7]
Load range
The Load Range Letter on light truck tires indicates their ply rating.[8]
Load Range Ply Rating
A 2
B 4
C 6
D 8
E 10
F 12
G 14
H 16
J 18
L 20
M 22
N 24
Load index
The load index on a passenger car tire is a numerical code stipulating the maximum load (mass, or weight) each tire can carry. For Load Range "B" tires, ETRTO (ISO-Metric) standards specify the load index rating at an inflation pressure of 36 psi (250 kPa) (table Below) while P-Metric standards measure the load capacity at an inflation pressure of 35 psi (240 kPa). The two standards vary slightly with the capacity required for different inflation pressures.[9]
While all ETRTO tires of the same load index will have the same maximum load, P-Metric tires with the same load index may have different load capacities depending on the tire size. The TRA Inflation Tables must always be consulted when comparing the load capacity of P-Metric tires—the Load Index alone is not sufficient. An example: a P205/50R15 Standard Load tire has a load index of 84 and a load rating of 505 kg (1,113 lb) at 35 psi (240 kPa). A P215/50R13 with the same load index of 84 only has a load rating of 495 kg (1,091 lb), also at 35 psi (240 kPa).[10]
ETRTO produces a Standards Manual (current edition 2010) which contains a number of specifications and tables. The load index table (2010 page G7) lists the Load index from 0–45 kg (0–99 lb) to 279–136,000 kg (615–300,000 lb) (although it appears to relate to an inflation pressure of 42 psi (290 kPa) it doesn't specify, but see Load Inflation Table).[11] The Load Inflation Table references the load index to inflation pressures between 22 psi (150 kPa) and 42 psi (290 kPa) at 1 psi (6.9 kPa) intervals which is too large to be included here.[10]
Standard Load Table (extract from ETRTO Standards Manual – 2010 page G7 - ref 42 psi (290 kPa))[11] Code Weight Code Weight Code Weight Code Weight
60 250 kg (550 lb) 80 450 kg (990 lb) 100 800 kg (1,800 lb) 120 1,400 kg (3,100 lb)
61 257 kg (567 lb) 81 462 kg (1,019 lb) 101 825 kg (1,819 lb) 121 1,450 kg (3,200 lb)
62 265 kg (584 lb) 82 475 kg (1,047 lb) 102 850 kg (1,870 lb) 122 1,500 kg (3,300 lb)
63 272 kg (600 lb) 83 487 kg (1,074 lb) 103 875 kg (1,929 lb) 123 1,550 kg (3,420 lb)
64 280 kg (620 lb) 84 500 kg (1,100 lb) 104 900 kg (2,000 lb) 124 1,600 kg (3,500 lb)
65 290 kg (640 lb) 85 515 kg (1,135 lb) 105 925 kg (2,039 lb) 125 1,650 kg (3,640 lb)
66 300 kg (660 lb) 86 530 kg (1,170 lb) 106 950 kg (2,090 lb)
67 307 kg (677 lb) 87 545 kg (1,202 lb) 107 975 kg (2,150 lb)
68 315 kg (694 lb) 88 560 kg (1,230 lb) 108 1,000 kg (2,200 lb)
69 325 kg (717 lb) 89 580 kg (1,280 lb) 109 1,030 kg (2,270 lb)
70 335 kg (739 lb) 90 600 kg (1,300 lb) 110 1,060 kg (2,340 lb)
71 345 kg (761 lb) 91 615 kg (1,356 lb) 111 1,090 kg (2,400 lb)
72 355 kg (783 lb) 92 630 kg (1,390 lb) 112 1,120 kg (2,470 lb)
73 365 kg (805 lb) 93 650 kg (1,430 lb) 113 1,150 kg (2,540 lb)
74 375 kg (827 lb) 94 670 kg (1,480 lb) 114 1,180 kg (2,600 lb)
75 387 kg (853 lb) 95 690 kg (1,520 lb) 115 1,215 kg (2,679 lb)
76 400 kg (880 lb) 96 710 kg (1,570 lb) 116 1,250 kg (2,760 lb)
77 412 kg (908 lb) 97 730 kg (1,610 lb) 117 1,285 kg (2,833 lb)
78 425 kg (937 lb) 98 750 kg (1,650 lb) 118 1,320 kg (2,910 lb)
79 437 kg (963 lb) 99 775 kg (1,709 lb) 119 1,360 kg (3,000 lb)
Some of the older letter-code load-range ratings for Light Truck Tires can be found in a chart[12] published by the Goodyear Tire Company. For example --
Tire Size Weight(lbs)@lb/in2 Weight(lbs)@lb/in2
LR Code D E
LT215/85R16 2335 @65 2680 @80
LT225/75R16 2335 @65 2680 @80
LT235/85R16 2623 @65 3042 @80
LT245/75R16 2623 @65 3042 @80
Speed rating
The speed symbol is made up of a single letter or an A with one number. It indicates the maximum speed at which the tire can carry a load corresponding to its Load Index.[11]
Speed rating[11] Code mph km/h Code mph km/h
A1 3 5 L 75 120
A2 6 10 M 81 130
A3 9 15 N 87 140
A4 12 20 P 94 150
A5 16 25 Q 100 160
A6 19 30 R 106 170
A7 22 35 S 112 180
A8 25 40 T 118 190
B 31 50 U 124 200
C 37 60 H 130 210
D 40 65 V 149 240
E 43 70 Z over 149 over 240
F 50 80 W 168 270
G 56 90 (W) over 168 over 270
J 62 100 Y 186 300
K 68 110 (Y) over 186 over 300
Prior to 1991, tire speed ratings were shown inside the tire size, before the "R" construction type. The available codes were SR (112 mph, 180 km/h), HR (130 mph, 210 km/h), VR (in excess of 130 mph, 210 km/h).
Tires with a speed rating higher than 186 mph (300 km/h) are indicated by a Y in parentheses.[citation needed] The load rating is often included within the parentheses, e.g. (86Y).
In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code (except for "Temporary Use" spare tires). In some parts of the European Union, tires that are not fit for a car's or motorcycle's particular maximum speed are illegal to mount. The sole exception are M+S tires, where a warning sticker stating the allowed maximum speed must be placed within clear sight of the driver inside the vehicle. Some manufacturers will install a speed governor if a vehicle is ordered with tires rated below the vehicle's maximum speed.
Wheel/Rim widths
To determine the allowable range of rim widths for a specific tire size, the TRA Yearbook or the manufacturer's guide should always be consulted for that specific tire—there is no rule of thumb.[13] Running a tire on a rim size or type not approved by its manufacturer can result in tire failure and a loss of vehicle control.
Additional marks
Metric to Imperial tire conversion chart
R15
215/75/15 27.7"x 8.5"
225/70/15 27.4"x 8.9"
225/75/15 28.3"x 8.9"
235/75/15 29.0"x 9.3"
245/75/15 29.5"x 9.6"
255/75/15 30.0"x 10.0"
265/75/15 30.6"x 10.4"
R16
205/85/16 29.7"x 8.1"
215/75/16 28.7"x 8.5"
225/70/16 28.4"x 8.9"
225/75/16 29.2"x 8.9"
235/70/16 29.0"x 9.3"
235/85/16 31.7"x 9.3"
245/70/16 29.5"x 9.6"
245/75/16 30.5"x 9.6"
There are numerous other markings on a typical tire, these may include:
M+S, or M&S: Mud and Snow; A tire that meets the Rubber Manufacturers Association (RMA) and Rubber Association of Canada (RAC) all-season tire definition.[14] These are all-weather tires, with self-cleaning tread and above-average traction in muddy or very light snowy conditions, and for low ambient temperatures. Spike tires have an additional letter, "E" (M+SE).
M+T, or M&T: Mud and Terrain; Designed to perform in mud or on other terrain that requires additional traction such as on rocks, in deeper snow, and in loose gravel.
Mountain Snowflake Pictograph: Winter passenger and light truck tires that meet the severe snow service requirements of Rubber Manufacturers Association (RMA) and Rubber Association of Canada (RAC).[14]
BSW: Black SideWall
WSW: White SideWall
OWL: Outline White Lettering
ORWL: Outlined Raised White Lettering
RWL: Raised White Lettering
VSB: Vertical Serrated Band
BSL: Black Serrated Letters
E4: Tire approved according ECE-regulations, the number indicating the country of approval.
030908: Approval number of the tire
DOT code: All tires for use in the USA have the DOT code, as required by the Department of Transportation (DOT). It specifies the company, factory, mold, batch, and date of production (two digits for week of the year plus two digits for year; or two digits for week of the year plus one digit for year for tires made prior to 2000). Although not law, some tire manufacturers do not
Tire manufactured in 10th week of 2001
suggest using a "new" tire that has been sitting on the shelf for more than six years (Ford Motor Company) or 10 years (Cooper Tire citing a tire association recommendation).[15] JATMA, the Japanese Automotive Tyre Manufacturers Association recommends that all tires be inspected at five years, and all tires that were manufactured more than ten years previous be replaced.[16]
TL: Tubeless
TT: Tube-type, tire must be used with an inner-tube
Made in ...: Country of production
C: Commercial; tires for light trucks (Example: 185 R14 C)
B: Bias belted; tires for motorcycles (Example: 150/70 B 17 69 H)—diagonal construction with belt added under the tread
SFI, or Inner: Side Facing Inwards; inside of asymmetric tires
SFO, or Outer: Side Facing Outwards; outside of asymmetric tires
TWI: Tread Wear Indicator; a device, such as a triangle or a small Michelin Man icon, located where the tread meets the sidewall. It indicates the location of the raised wear bars in between the tire tread channels.
LL: Light Load; tires for light usage and loads
SL: Standard Load; tire for normal usage and loads
XL: eXtra Load; a tire that allows a higher inflation pressure than a Standard Load tire, which increases the tire's maximum load
RF: Reinforced—for Euro-metric tires, the term 'reinforced' means the same thing as 'Extra Load'[14]
Arrows: Some tread designs are "directional", and designed to perform better when driven in a specific direction (clockwise or counter-clockwise). Such tires will have an arrow showing which way the tire should rotate when the vehicle is moving forwards. It is important not to put a "clockwise" tire on the left hand side of the car or a "counter-clockwise" tire on the right side.
MO: Original tires for Mercedes-Benz
MOE: Mercedes-Benz Original Extended[14]
N-x: Original tires for Porsche where "x" is a "0" for the first approved in that size, "1" the second, ...[14]
Star: Original tires for BMW
RSC in a Circle: BMW Runflat System Component[14]
TPC: General Motors OE Fitments[14]
AMx: Aston Martin OE Fitments[14]
"100T": Commonly appears after tire size. Meaning: Standard Load Inflation Table (100) & Speed Rating (T)
To facilitate proper balancing, most tire manufacturers also mark red circles (uniformity) and/or yellow dots (weight) on the sidewalls of their tires to enable the best possible match-mounting of the tire/wheel assembly.[17]
Tire geometry
When referring to the purely geometrical data, a shortened form of the full notation is used. To take a common example, 195/55R16 would mean that the nominal width of the tire is approximately 195 mm at the widest point, the height of the side-wall of the tire is 55% of the width (107 mm in this example) and that the tire fits 16-inch-diameter (410 mm) wheels. The code gives a direct calculation of the theoretical diameter of the tire. For a size shown as "T/A_W" use (2×T×A/100) + (W×25.4) for a result in millimeters or (T*A/1270)+ W for a result in inches. Take the common example used above; (2×195×55/100)+(16×25.4) = 621 mm or (195×55/1270)+16 = 24.44 inches.
Less commonly used in the USA and Europe (but often in Japan for example) is a notation that indicates the full tire diameter instead of the side-wall height. To take the same example, a 16-inch wheel would have a diameter of 406 mm. Adding twice the tire height (2×107 mm) makes a total 620 mm tire diameter. Hence, a 195/55R16 tire might alternatively be labelled 195/620R16.
Whilst this is theoretically ambiguous, in practice these two notations may easily be distinguished because the height of the side-wall of an automotive tire is typically much less than the width. Hence when the height is expressed as a percentage of the width, it is almost always less than 100% (and certainly less than 200%). Conversely, vehicle tire diameters are always larger than 200 mm. Therefore, if the second number is more than 200, then it is almost certain the Japanese notation is being used—if it is less than 200 then the U.S./European notation is being used.
The diameters referred to above are the theoretical diameter of the tire. The actual diameter of a specific tire size can only be found in the TRA Yearbook or the manufacturer's data books.[18] Note that the tire's cross-section and diameter are always specified when measured on a wheel of a specified width; different widths will yield different tire dimensions.
Examples
The tires on a BMW Mini Cooper might be labeled: P195/55R16 85H
P — these tires are for a passenger vehicle. However 'P' denotes P metric size load and speed rating changes for P tire & non-P tires.
195 — the nominal width of the tire is approximately 195 mm at the widest point
55 — indicates that the height of the sidewall of the tire is 55% of the width (107 mm)
R — this is a radial tire
16 — this tire fits 16 in (410 mm) wheels
85 — the load index, a maximum of 515 kg (1,135 lb) per tire in this case
H — the speed index, this means the maximum permitted speed, here 210 km/h (130 mph).
The tires on a Hummer H1 might be labeled: 37X12.5R17LT
37 - the tire is 37 in (940 mm) in diameter
12.5 - the tire has a cross section of 12.5 in (320 mm)
R - this is a radial tire
17 - this tire fits 17 in (430 mm) wheels
LT - this is a light truck tire.
Posted 2013-09-22 7:28 PM (#154904 - in reply to #154897) Subject: RE: Tire pressure
Veteran
Posts: 136 Location: Watertown, TN
Boy, now I'm confused. I think.I've been told any number of times, the number one reason for tire failure is under inflation.I have an F-350, load range E tires. When running empty I run them at 50 lbs. When I drop the trailer on it though the rears get 80 and the fronts get 70. The trailer stays at max all the time because it is usually loaded if it is hooked up. I've had great success with this plan and my truck tires usually run 70k before I need to replace them. I've started replacing the trailer tires every 5 or 6 years no matter how they look. I had a fender destroyed by a tire that looked fine, no cracks and plenty of tread. That repair cost more than four new tires would have. So never again.
Posted 2013-09-22 9:10 PM (#154906 - in reply to #154897) Subject: RE: Tire pressure
Expert
Posts: 3853 Location: Vermont
Originally written by horsin around on 2013-09-22 11:37 AM
HI all,I recently purchased new tires for my trailer before going on vacation next week. Getting everything ready and checked the tire pressure on my truck and trailer this morning which is at the pressure my mechanic put in them.I checked the past posts on tire pressure and I'm thinking I should put more pressure in them but I thought I'd double check with you all.On my truck door it recommends 55 front/70 back. My truck tires are LT 265/85R16. On the tire it says 80 PSI. He has them at 55 front/62 on back tire.My trailer tire is LT 265/75R16, E rating, 80 psi. He has them at 60.In the past I've ran 55/65 on the truck and 60or65 on trailer. I have had some blow outs but thought it was because of tires needing replaced but after reading the past forums, it could have been from not having enough pressure in tires. Should I leave the truck at 55/65? and put more pressure in the trailer up to 80?Also Jim Bob mentioned about your speed rating on a tire and how would you find that out? I usually travel on the interstate 65-70.Thanks for putting up with more tires pressure questions!
Fill your tires to the max COLD...it might be a little rough when running empty, but then you don't have to "remember" to get them back to max when you need to tow...:)
Posted 2013-09-23 8:53 AM (#154912 - in reply to #154897) Subject: RE: Tire pressure
Expert
Posts: 5870 Location: western PA
Boy, now I'm confused. I think.I've been told any number of times, the number one reason for tire failure is under inflation.I have an F-350, load range E tires. When running empty I run them at 50 lbs. When I drop the trailer on it though the rears get 80 and the fronts get 70. The trailer stays at max all the time because it is usually loaded if it is hooked up. I've had great success with this plan and my truck tires usually run 70k before I need to replace them. I've started replacing the trailer tires every 5 or 6 years no matter how they look. I had a fender destroyed by a tire that looked fine, no cracks and plenty of tread. That repair cost more than four new tires would have. So never again.
The reason for your success is what you have learned and practised. Higher pressures under a load. I also DITTO Paul, max inflation all the time.
Posted 2013-09-23 12:12 PM (#154914 - in reply to #154897) Subject: RE: Tire pressure
Veteran
Posts: 136 Location: Watertown, TN
I have to admit, the truck is parked in a shop that includes a 6HP, 80 gal. compressor so it is easy for me to adjust tire pressure. If not for that, I would be right there with Paul and keep them pumped up all the time. I DID develop the habit years ago of checking the tire pressure on everything before a trip. That is something I would highly recommend. Tire gauges are pretty cheap in the grand scheme of things.
Tire pressure
I've been told any number of times, the number one reason for tire failure is under inflation.I have an F-350, load range E tires. When running empty I run them at 50 lbs. When I drop the trailer on it though the rears get 80 and the fronts get 70. The trailer stays at max all the time because it is usually loaded if it is hooked up. I've had great success with this plan and my truck tires usually run 70k before I need to replace them. I've started replacing the trailer tires every 5 or 6 years no matter how they look. I had a fender destroyed by a tire that looked fine, no cracks and plenty of tread. That repair cost more than four new tires would have. So never again.
I've been told any number of times, the number one reason for tire failure is under inflation.I have an F-350, load range E tires. When running empty I run them at 50 lbs. When I drop the trailer on it though the rears get 80 and the fronts get 70. The trailer stays at max all the time because it is usually loaded if it is hooked up. I've had great success with this plan and my truck tires usually run 70k before I need to replace them. I've started replacing the trailer tires every 5 or 6 years no matter how they look. I had a fender destroyed by a tire that looked fine, no cracks and plenty of tread. That repair cost more than four new tires would have. So never again.