A blowout is a catastrophic tire failure that can create significant damage or even loss of life. Tires can fail in other ways, too, that may result in anything from a nuisance to vehicle damage. Tread separation can fling heavy pieces of rubber and steel threads at your rig. Slow leaks can create a risk of under-inflation, a major source of tire failure, if not detected and corrected.
Proper tires selection can also have a major impact on handling and ride. For instance, tires with a heavier than necessary load rating can cause a harsh ride which can contribute to frame problems on mid seventies Airstreams. Sway and stability problems can be aggravated by tires that are under-inflated or have excess sideways give.
One of the more important maintenance issues in keeping your rig safe and comfortable is in the selection and maintenance of tires. It is not likely that they will wear out due to loss of tread but rather will need replacement after five to ten years due to aging of the materials. Know what size, type, and ratings for tires are needed for your rig. Make sure you equip your rig with proper tires, put your tires on your 'always check' list, and be able to read your tires to check and verify.
Tires are what keeps the hard parts of your rig from touching the ground. They use air contained by flexible rubber to provide a pneumatic cushion between your rig and the ground. By knowing the footprint of your tires on the ground and the air pressure in the tires, you can determine how much weight each tire supports. If you look at the side of your tires, you will see all sorts of sets of numbers and letters. These will tell you everything you might want to know about the tire if you can figure out the code.
Tire labeling schemes have been undergoing change through the years. Here is a summary of the more common systems courtesy http://www.trailertires.com/
THE NUMERIC SYSTEM - (4.80 X 8) mostly used on smaller trailer tires, indicates the tire section width (4.80"), and the rim diameter (8")
THE ALPHA NUMERIC SYSTEM - (B78 X 13 C) common on 13"-15" trailer tires, indicates air chamber size (B), the 'Aspect Ratio' (78), the rim diameter (13"), and the load range (C)
THE METRIC SYSTEM - (ST205 75D 15) currently being phased in by trailer tire manufacturers, indicated the tire application type (ST-special trailer), the section width (205mm), the 'Aspect Ratio' (75), the construction type (D= bias ply), and rim dia.(15")
Note the confusion in measurements. Some things in inches, others in millimeters. The toss in indices in both letters and numbers and acronyms or codes for tire type, purpose, style and other attributes and you have a real zoo of cryptographic sidewall legends.
Tires are just one component of a complete system. Axles, breaks, bearings, hubs, rims, and all the rest have to work together as a system to provide safety for the load, speed, and use of the vehicle. Tires need to fit on their wheels and inside a vehicle wheel well. They need to be able to support their share of the load and operate at the desired speeds. A tread design will need to be matched to road conditions.
The load a tire can safely carry is one of the most important characteristics to consider in choosing a tire for an application. It the dimdarks (way back in the dim dark past) it was measured by the number of layers or plies of material in the tire. Then that got confused because stronger materials and techniques made it possible to manufacture tires that could carry larger loads with fewer plies so a Load Range letter was used to indicate how much load a tire could support. Finally a load index rating was developed that provides a numeric index to a load capabilities table. Passenger car tires with a 4 ply rating have a Load Range of "B" and a Load Index of less than 100. Light truck tires have load ranges of C, D, or E for ply ratings of 6, 8, or 10 and load indexes of 104, 110, or 116 respectively.
A speed rating for tires is really a measure of the heat handling capabilities of the tire. As the tire rolls down the road, it flexes the sidewalls and tread to keep enough surface on the road to support the load. The flexing creates heat. The faster the flexing the more the heat. Faster flex is a result of higher speed. So higher speeds mean that the tires generate more heat. Tires have a speed rating letter index that provides information about the tire's heat handling capability.
There are three tire application types commonly found. These are passenger, light truck, and special trailer. They will be noted by a 'P,' "LT," or "ST" in front of the tire size.
" In order to properly select passenger tires for use on light truck vehicles (mini pick-ups, mini-vans, recreational vehicles, SUV's, full-sized 1/2 ton pick-ups and vans), the load capacity of the passenger tire at any inflation must be reduced by 9% and the maximum load capacity molded on the sidewall must also be reduced by 9%." - http://www.tiresafety.com/size_class/size_nav4b.htm
Perhaps the number one cause of tire failure is lack of pressure in the tires. This causes them to flex a lot more when going down the road and this generates heat and it is the heat that kills the tires. When checking tire pressure, err on the high side. Running at maximum rated cold pressure may cause a bit of extra wear in the center of the tire but it will be safer than running without sufficient pressure.
One way to make sure you have the proper pressure is to check them before you start on a ride on a day without any extreme weather. Then check the pressure twenty miles or so down the road. If the pressure in the tire has gone up more than ten percent or so, you didn't get enough air into them in the first place (heat makes the pressure rise more than it should). So add air if the pressure after twenty miles or so goes up more than ten percent. If you have an infra-red non contact thermometer (Radio Shack or some tool places for under $50) you can check tire temperature as another indicator of proper pressure. The tire temperature shouldn't get more than thirty degrees or so above ambient air temperature.
Tires can fail for other reasons besides not having enough air in them. Make sure you have the proper tires for your rig and that they are the right size for your rim and wheel and well. Make sure the tires are not overloaded and that your rig load is properly loaded to distribute weight as evenly as possible to all wheels.
Inspect the tires at each stop to make sure that they are still there and that there are no obvious signs of trouble such as tread separation, bubbles, gashes, artifacts picked up on the road (like nails or bolts), or any other source of potential problem. Give them a slight kick or thump to make sure they still have good air pressure. Check the temperature of the tire and the hub to make sure they aren't getting too hot. In these checks, compare the tires and hubs to each other and look for anomalies. If one tire or hub is significantly different from the others in feel, appearance, or temperature, be sure to find out why before you get back on the road.
(no endorsement implied or given – for your use only at your own discretion and best judgment – and all the other usual or unusual liability avoidance warnings and caveats)
http://www.coopertire.com/tire_cooper/info-sidewall.html – how to read the encyclopedia of information embossed on your tire and what it means
http://www.tires101.com/ - “Here you'll find all the technical information you need to purchase, maintain and understand your automotive tires and wheels.“ -- http://www.1010tires.com/tiretech.asp – tire size calculator
http://www.volvotuning.com/tires.html – Volvo performance site information about reading your tires and understanding the ratings.
http://www.kelly-springfield.com/auto/tire_school/ - Kelly Springfield Tire School for light truck and auto tires. “Tires are an important part of your vehicle and is an important decision to make. Tires are designed to deliver different performance for different vehicles and different owners. The Kelly Tire School offers you a chance to understand tires and be confident in your purchase. “
http://www.tyres1.com/tech_main.html – more on understanding ratings and terminology
http://www.toyo.com.au/tech_info.html - Technical Information Bulletins - Tyre Issues and Information from Toyo's New Technical Centre, Itami, Japan.
Autopedia . see RV Tire and Safety page - “From here you will be able to learn just about everything there is to know about tires for your car, truck, sport utility or RV.”
Goodyear RV – homepage for Goodyear Tires RV information
http://truckus.webmichelin.com/index_rv.htm – Michelin RV Tires page
http://www.tirerack.com/ - a source for tires on the web that someone on a forum seemed happy with (but use your own judgment!)
http://www.rma.org/ - Rubber Manufacturer's Assocation – a tire safety quiz and information about tires in terms of manufacture and disposal.
http://www.smartire.com/fl/ - a company that makes remote tire sensors so you can watch pressure and temperature from the driver's seat.
http://www.insta-chain.com/index.html – interesting automatic chain system for those who get out in winter weather a lot.
http://www.tirerack.com/tires/tiretech/general/pressure.htm – a whole page on tire pressure! And a lot of links to other pages on handling blowouts, hydroplaning, pull, and other good information for tire enthusiasts and worrywarts.
Note: there are a lot of facts, assumptions, and calculations that are used to provide the information presented here. The intent is to provide 'back of the envelope' accuracy and not engineering or science level accuracy. There may also be cases of teaching license taken, such as the water and electricity analogy. However, errors or miscalculations may lead to misinformation or some analogies may mislead. If you see something you think should be corrected, please let us know - email rvtech@SierraNevadaAirstreams.org
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