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Caravan Tyre Pressure And Wheel Nut Guide
The Caravan Handbook typically provides the recommended tyre pressure for the original tyre size installed on the caravan when it’s loaded to its Maximum Technical Permitted Laden Mass (MTPLM). Since the weight inside your caravan can vary, or if you have an older caravan, the tyre size may have been modified. Therefore, it’s valuable to understand how to determine the appropriate tyre pressure based on the markings on the tyres currently equipped with your caravan.
It’s essential to be able to interpret the information displayed on the tyre sidewall. Here’s a typical example of such a code:
245/75R 16 120/116 S
The number on the tyre sidewall is broken down as follows:
- The first part represents the tread width, measuring 245 mm in this case.
- The second number is the Aspect Ratio, indicating that the tyre’s sidewall height is 75% of its tread width.
- The letter “R” signifies the tyre’s construction type, which is radial in this instance.
- The following number “16” indicates the rim diameter, measured in inches.
- The subsequent number “120/116” corresponds to the load rating, which I’ll explain further shortly.
- Lastly, the letter “H” denotes the speed rating of the tyre.
Regarding the load rating, it can vary from 60 to 130, which translates to a maximum load capacity per tyre ranging from 250 Kgs to 1900 Kgs. The crucial first step is to ensure that the tyres are rated to support the Maximum Technical Permitted Laden Mass (MTPLM) of your caravan. To determine this, we need to consider the load index ratings.
| Load Index | Kg’s | Load Index | Kg’s | Load Index | Kg’s |
|---|---|---|---|---|---|
| 60 | 250 | 83 | 487 | 106 | 950 |
| 61 | 257 | 84 | 500 | 107 | 975 |
| 62 | 265 | 85 | 515 | 108 | 1000 |
| 63 | 272 | 86 | 530 | 109 | 1030 |
| 64 | 280 | 87 | 545 | 110 | 1060 |
| 65 | 280 | 88 | 560 | 111 | 1090 |
| 66 | 300 | 89 | 580 | 112 | 1120 |
| 67 | 307 | 90 | 600 | 113 | 1150 |
| 68 | 315 | 91 | 615 | 114 | 1180 |
| 69 | 325 | 92 | 630 | 115 | 1215 |
| 70 | 335 | 93 | 650 | 116 | 1250 |
| 71 | 345 | 94 | 670 | 117 | 1285 |
| 72 | 355 | 95 | 690 | 118 | 1320 |
| 73 | 365 | 96 | 710 | 119 | 1360 |
| 74 | 375 | 97 | 730 | 120 | 1400 |
| 75 | 387 | 98 | 750 | 121 | 1450 |
| 76 | 400 | 99 | 775 | 122 | 1500 |
| 77 | 412 | 100 | 800 | 123 | 1550 |
| 78 | 425 | 101 | 825 | 124 | 1600 |
| 79 | 437 | 102 | 850 | 125 | 1650 |
| 80 | 450 | 103 | 875 | 126 | 1700 |
| 81 | 462 | 104 | 900 | 127 | 1750 |
| 82 | 475 | 105 | 925 | 128 | 1800 |
Another important piece of information we need from the tyre is the Maximum Tyre Inflation Pressure and Load. This information is typically found below the tyre data in small text on the sidewall. It’s usually displayed as something like “MAXIMUM LOAD 1400 Kg’s MAXIMUM PRESSURE 80 PSI,” and it might also provide the pressure in bar units.
Referring to the table mentioned earlier, you can cross-reference the load rating code number to determine the maximum permissible load that the tyre can handle. Using our previous tyre data example, a load index of “120/116” indicates that the tyre’s maximum load capacity is 1400 Kg’s for a single tyre or 1250 Kg’s for a dual tyre setup. Keep in mind that these values are per tyre. So, on a single axle, both tyres can collectively carry a maximum load of 2800 Kg’s (SINGLE) or 5000 Kg’s (DUAL).
However, it’s important to note that the tyre industry generally recommends not exceeding 90% of the tyre’s load index rating. In this case, the maximum axle weight would be 2520 Kg’s (SINGLE) and 4500 Kg’s (DUAL).
Now that you have the Maximum Technical Permitted Laden Mass (MTPLM) of your caravan and the maximum pressure for your tyres, you can calculate the correct tyre pressure. Divide the maximum tyre pressure figure by the maximum weight in the table above. Then, multiply this result by the actual load you plan to place on the tyre. For a single axle caravan, this would be half of the MTPLM, and for a twin axle caravan, it would be a quarter of the MTPLM. The resulting figure should be the appropriate inflation pressure for each tyre.
Calculating the tyre pressure for a single axle caravan:
tyre Details: 245/75R16 120/116 S
Maximum Inflation Pressure: 80 PSI
Caravan Weight: 2000 Kg’s
To determine the correct tyre pressure:
Start by dividing the maximum pressure for the tyre (80 PSI) by its load rating (1400 Kg’s):
80 / 1400 = 0.0571428 (Max Pressure for the tyre divided by load rating)
Next, multiply this result by half the weight of the caravan (since it’s a single axle caravan):
0.0571428 x (2000 / 2) = 57.1428 PSI (Inflation factor times half the weight of the caravan)
So, the appropriate tyre pressure for your single axle caravan is 57.1428 PSI.
Calculating the tyre pressure for a twin axle caravan:
tyre Details: 245/75R16 120/116 S
Maximum Inflation Pressure: 80 PSI
Caravan Weight: 3500 Kg’s
To determine the correct tyre pressure:
1. Begin by dividing the maximum pressure for the tyre (80 PSI) by its load rating (1250 Kg’s):
80 / 1250 = 0.064 (Max Pressure for the tyre divided by load rating)
2. Next, multiply this result by one-quarter of the weight of the caravan (since it’s a twin axle caravan):
0.064 x (3500 / 4) = 56 PSI (Inflation factor times one-quarter of the weight of the caravan)
So, the appropriate tyre pressure for your twin axle caravan is 56 PSI.
Additional Tip: When checking tyre pressures, keep in mind that the inflation pressure of a hot tyre is typically about 4 PSI higher than when it’s cold. If you find that your tyre pressures are more than 4 PSI higher when hot, then the cold inflation pressure is too low. Conversely, if the hot inflation pressure is less than 4 PSI different from the cold pressure, the cold pressure is likely too high. This guideline is based on the principle that for every 10-degree Fahrenheit change in temperature, the tyre pressure changes by 1 PSI.
Speed Category
A speed symbol is a graphical symbol that signifies the speed category at which a tyre can support a load consistent with its Load Index, all within specified service conditions.
A speed category is a specific classification assigned to a tyre, indicating the highest speed at which the tyre is approved and rated for safe use.
| Speed Symbol | Speed Category (kph) | Speed Symbol | Speed Category |
|---|---|---|---|
| A1 | 5 | J | 100 |
| A2 | 10 | K | 110 |
| A3 | 15 | L | 120 |
| A4 | 20 | M | 130 |
| A5 | 25 | N | 140 |
| A6 | 30 | P | 150 |
| A7 | 35 | Q | 160 |
| A8 | 40 | R | 170 |
| B | 50 | S | 185 |
| C | 60 | T | 190 |
| D | 65 | U | 200 |
| E | 70 | H | 210 |
| F | 80 | V | 240 |
| G | 90 | Z | Over 240 |
Torque Setting Recommendations for Various Wheel Nut/Stud Specifications:
Please be aware that each manufacturer may have a unique torque range, so it’s crucial to consult your owner’s manual for specific instructions. Nevertheless, here are some general recommendations:
1. Use an Impact or Rattle Gun with Caution: If you choose to use an impact or rattle gun, it should only be employed to quickly secure the wheel nuts for efficiency.
2. Avoid Final Torque with an Impact Gun: It’s important to note that an impact gun should never be relied upon to achieve the final torque setting for the wheel nuts. This should always be done manually to ensure proper and safe tightening.
Torque Setting Guide
| Wheel Stud | Foot Pounds | Newton Metres |
|---|---|---|
| 7/16″ studs | 80 ft-lbs | 108 Nm |
| 1/2″ studs | 100 ft-lbs | 135 Nm |
| 9/16″ studs | 140 ft-lbs | 190 Nm |
| 5/8″ studs | 175 ft-lbs | 237 Nm |
| 10mm studs | 50 ft-lbs | 68 Nm |
| 12mm studs | 100 ft-lbs | 135 Nm |
| 14mm studs | 154 ft-lbs | 209 Nm |
Important Note:
- Wheel Nut Re-Torquing: It is absolutely essential to re-torque wheel nuts after an initial break-in period, in accordance with the trailer/caravan manufacturer’s specific instructions.
- Re-Torque Schedule: If the manufacturer hasn’t specified a re-torque schedule, we recommend checking the wheel nut tension after the first 100 kilometers of operation.
- Authorized Service Provider: We strongly advise having the re-torque procedure carried out by an approved tyre dealer, trailer dealer, or a similarly qualified agent.
- Inclusion in Owner’s Manual: If not provided by the approved dealer or agent, we recommend incorporating these re-torque recommendations and procedures into your trailer/caravan owner’s manual.
- Proper Nut Torque Sequence: Ensure that the correct nut torque sequence is followed to accurately and centrally position the wheel on the trailer or caravan’s hub.
To determine the correct tyre pressure for a single axle caravan:
Start by dividing the maximum tyre inflation pressure (80 PSI) by the tyre’s load rating (1400 Kg’s):
80 / 1400 = 0.0571428 (Maximum tyre pressure divided by load rating).
Next, multiply this result by half of the weight of the caravan (which is 2000 Kg’s, so half is 1000 Kg’s):
0.0571428 x 1000 = 57.1428 PSI.
The appropriate tyre pressure for your single axle caravan is 57.1428 PSI.
| Stud Size | Lug Nut Type | Torque Specifications | Wheel Size & Type | Wheel Material |
|---|---|---|---|---|
| 1/2″ | Coned | 90-120 ft.-lb | 15″ | Steel |
| 1/2″ | Coned | 90-120 ft.-lb | 16″ | Steel |
| 9/16″ | Coned | 120-140 ft.-lb | 16″ | Steel |
| 5/8″ | Coned w/Wheel Clamp Ring | 190-210 ft.-lb | 17.5″ single or 16″ Dual | Steel |
| 5/8″ | Flanged Nuts (Non-Rotating Flange)* | 275-325 ft.-lb | 17.5″ single or 16″ Dual | Steel |
| 5/8″ | Flanged Nuts (Non-Rotating Flange)** | 190-210 ft.-lb | 17.5″ single or 16″ Dual | Steel |
| 1/2″ | Coned | 90-100 ft.-lb | 15″ | Aluminium (Alcoa) |
| 1/2″ | Coned | 90-100 ft.-lb | 16″ | Aluminium (Alcoa) |
| 9/16″ | Coned | 120-140 ft.-lb | 16″ | Aluminium (Alcoa) |
| 9/16″ | Coned | 130-150 ft.-lb | 17.5″ | Aluminium (Alcoa) |
| 5/8″ | Coned | 140-160 ft.-lb | 17.5″ | Aluminium (Alcoa) |
| 5/8″ | Flanged Nuts (Non-Rotating Flange)** | 150 ft.-lb | 16″ | Aluminium (Alcoa) |
Important Note:
1. Piece Nut with Non-Rotating Flange: This refers to a single-piece nut design with a stationary flange.
2. Piece Nut with Rotating Flange: This indicates a two-piece nut with a flange that can rotate.
Please be aware that the torque specifications provided here are general guidelines. It is crucial to consult your trailer or wheel manufacturer for the specific torque values suitable for your application. The information above has been compiled from various sources and may not be appropriate for your particular situation.
Always adhere to the recommended torque sequence and torque values as specified by the trailer or wheel manufacturer. Furthermore, after installing any wheel, it is imperative to re-check and ensure the correct torque at 10 miles, 25 miles, and 100 miles following the wheel’s installation. This helps maintain the safety and integrity of your setup.
