At AutoNetTV we love doughnuts. So let’s pretend you have three doughnuts right in front of your for our discussion of upsizing wheels and tires. Hey, don’t eat them now – your going to need them later.

Many people want to accessorize their car – you know, make it theirs. One of the easiest ways to get a custom look is to get some new wheels. There are thousands of wheel designs out there to get you the look you want. And for many, that look includes bigger wheels. It used to be that cars came from the factory with 15 or 16 inch wheels. Now 16, 17 and even 18 inchers are standard. And the factories are offering optional wheel packages up to 20 inches or more.

So let’s talk about what to consider when you want to upsize your wheels. It’s not exactly a do it yourself project, so you need to know a thing or two before you get started. The most important term to know is rolling diameter. The rolling diameter is simply the overall height of your tire. Unless you want to modify your suspension, you’ll want to keep your rolling diameter the same when you upsize your wheels.

Let’s think about those three golden doughnuts in front of you. They’re all about the same size. So if we pretend they’re tires, they would have the same rolling diameter. The doughnut hole is the size of the wheel. Now pretend we’ve made the hole bigger on some. That’s like having a bigger wheel – but the rolling diameter is the same.

It’s important to keep the rolling diameter the same for several reasons. First of all, if the tire is bigger, it might not fit in the wheel well. Next the speedometer, odometer and anti-lock brake system are all calibrated for the factory rolling diameter. In order for your anti-lock brakes to work properly, the rolling diameter must stay within 3% of the factory recommendation. If you ignore that, you run the risk that your anti-lock brakes won’t work properly.

Some cars today have electronically controlled suspension that will be negatively affected by changing the rolling diameter. Let’s think about the doughnuts again. You see, as the size of the wheel gets bigger, the sidewall gets shorter. The tire holds less air, so the sidewalls are made stiffer to compensate.

Low profile tires from top manufacturers use special compounds that give the sidewall the strength it needs without compromising ride quality. As you increase your wheel size, you’ll typically get a slightly wider tire. This means that you have a larger contact patch. The contact patch is part of the tire that contacts the road. Because there’s more rubber on the road, the vehicle will handle better. And braking distances will be shorter. A lot of people with trucks or SUV’s love the extra control.

You do have to watch out that the contact patch isn’t so big that the tires rub in turns or over bumps. What we’re talking about here is fitment. Your tire professional can help you get this right. He’ll install your new wheels, add spacers if needed to make sure your brakes fit inside your new wheels, and get you rolling.

Also, if you drive off-road a lot, you may need a higher profile tire to protect your new rims. And make sure your new tires have the load rating you need if you tow a trailer or haul heavy loads. Again, your tire professional knows how to help.

And don’t forget about tire pressure. If you have larger rims, your new tires will hold less air and they’ll need to run a slightly higher pressure. Forget that and you’ll wear your tires out fast. Finally, get an alignment after you get your new shoes. AutoNetTV wants you to safely have the look you want.

We all know that under inflated tires wear out more quickly. Under-inflation is also a major cause of tire failure. More flats, blow outs, skids and longer stopping distances are all results of under-inflated tires.

It’s hard to tell when a radial tire is under-inflated. If your manufacturer recommends 35 pounds of pressure, your tire is considered significantly under inflated at 26 pounds. The tire may not look low until it gets below 20 pounds.

Uncle Sam to the rescue! A new federal law requires manufacturers to include a Tire Pressure Monitoring System – or TPMS system – in all vehicles by the 2008 model year.

Some 2006 and 2007 models already have TPMS. The system is a dashboard mounted warning light that goes off if one or more of the tires falls 25 % below the manufacturer’s pressure recommendations.

The law covers all passenger cars, SUVs, mini vans and pick up trucks. The system must also indicate if it has a malfunction. This technology has been used by race cars for years. They are able to head off problems from under inflation by closely monitoring tire pressure on the track. It’s up to your car’s manufacturer to determine which of many TPMS systems available they’ll use to comply with the law.

Obviously, all of this doesn’t come free. Government studies have estimated the net costs. Of course, the TPMS system itself will cost something. Maintaining the system will have a cost, replacement of worn or broken parts and tire repair cost increases. The net cost is estimated to be between $27 and $100.

The costs are partially offset by savings in fuel and tread wear. There is also a saving in property damage and travel delay. Also, the government predicts fewer fatal accidents. They estimate there will be between $3,000,000 to $9,000,000 for every life saved.

Your safety has always been a concern of your service center. They want you on the road and accident free. They’ve traditionally provided things like tire rotations, snow tire mounting and flat fixes at a very low cost. They’ve been able to quickly and cheaply provide the service, and they pass the low cost on to you as an expression of their good will. That’s why they’re concerned about how you’ll perceive the changes that this new law will force.

Every time a tire is changed: taken off to fix a flat, a new tire installed, or a snow tire mounted, the service technician is now going to have to deal with the TPMS system. Sensors will need to be removed and reinstalled. The sensors will have to be re-activated after the change. And, unfortunately, the very act of changing the tire will damage some sensor parts from time to time – it’s inevitable and can’t be avoided.

Even a simple tire rotation will require that the monitor be reprogrammed to the new location of each tire. When a car battery is disconnected, the TPMS system will need to be reprogrammed. TPMS sensor batteries will need to be changed and failed parts replaced.

And the service centers themselves will need to purchase new scanning equipment to work with the TPMS sensors and to update expensive tire change equipment to better service wheels equipped with the new monitoring systems.

Service technicians will have to be trained on many systems and new tire-changing techniques. All of this adds up to significantly increased cost to the service center to perform what was once a very inexpensive service for you. So when you start so see the cost of tire changes, flat repairs and rotations going up, please keep in mind that it’s because of government mandated safety equipment. Your service center just wants to keep you safely on the road – and it’s committed to do so at a fair price. The effects of the new law will take some time to sort out, but it will help you avoid the most common vehicle failure, and possibly a catastrophic accident.