WITH SUMMER IN FULL SWING,

many people are gearing up for that great American tradition: the summer road trip.

If you're planning on renting your ride, you're in luck. We've got the scoop on how to get a rental car on the cheap.

1. Book Early...or Late
Knowing precisely when to book your car as a strategy for getting the cheapest rate is a bit of an art form. If you're heading to an area that has a glut of cars, your best strategy might be simply to book at the last minute.

For example, folks heading to Las Vegas on July 8 can get an economy rental from Dollar Rent-A-Car (airport pickup) for a weekly base rate of $81. Later on in the month, the same rental would set you back $100.

Of course, you could wait until the last minute, only to find that your summer road trip will involve two (manually pushed) wheels, not four. So plan further ahead if:

• Your travel dates coincide with a holiday or special public event that brings in swarms of out-of-town travelers (such as a college commencement ceremony or local festival).
• You're traveling to a hot destination during a peak travel period (such as Nantucket during the summer).
• You have specific vehicle needs, such as enough space to fit seven passengers or a model that can handle rough terrain.

2. That Free Upgrade May Cost You
Major car rental companies will give you a wide range of driving options, from economy or sub-compact up to luxury or premium. Keep in mind, upgrades won't necessarily get you a better car, says Phil Reed, consumer advice editor for Edmunds.com. You're really paying for additional room. So if you're piling three kids and a dog into the backseat, an upgrade may be well worth the added dough. If, on the other hand, you're planning on impressing friends and family, a simple upgrade from economy to midsize isn't likely to turn them green with envy.

And don't forget, with gas prices where they are, even a free upgrade might not be a good deal for a single driver.

3. Pay Only for the Insurance You Need
It's one of life's great perplexities: Do you need to buy the rental company insurance or don't you?

What you do need is to make sure you have both collision and liability coverage. (The first covers the car itself, the later covers things you hit.) To find out which you need to buy, do your homework ahead of time.

Start by calling your auto insurance company, suggests the Insurance Information Institute, an organization that studies insurance. Generally, the coverage and deductibles for your own car will apply to any vehicle you rent. Assuming you have full coverage on your regular car, you shouldn't need a collision-damage waiver or liability insurance. Still, you should go over the details of your policy with your agent to make sure. Be specific about where you'll be traveling and for what purpose (business or pleasure).

Even if you're insured, you might need extra collision coverage if:

• You don't have full comprehensive or collision insurance on your car.
• Your rental vehicle has a value higher than that of your own car.
• The state you'll be traveling in requires more or different coverage from that required by your home state.

If you don't have your own auto insurance policy, call your credit card company. Be sure to get details about coverage limits and exclusions, and ask that the company send you a letter spelling out their coverage. Not surprisingly, higher-level cards, such as platinum, might offer better coverage than standard cards. At the minimum, you'll need the liability insurance offered by your car rental company. But check with your credit card company regarding collision coverage before opting for the rental company's plan.

Finally, call your homeowner or renters insurance company. Your policy should cover personal property kept in your rental car. It's worth asking about the extent of your coverage if you're traveling with expensive items such as jewelry or electronics, or if you plan to purchase pricey items during your travels.

4. Shop Around

As one might expect, prices vary widely based on the location, travel dates and type of car you want. Even so, there are two considerations that could get you lower prices.

First, don't write off local companies. Though they don't always offer the best deals for short-term rentals, they're usually more open to negotiation. If you really want to stick with a particular well-known chain, don't be afraid to ask if it'll meet or beat another vendor's lower price.

Do a quick Internet search for companies in your area. Try the yellow pages at Anywho.com. Another good site for low rates from independent companies is Car Rental Express. The site finds you the cheapest rates from among more than 100 consumer-rated companies.

If you want the best price for big chains, and don't care which you're renting from, you might check out Hotwire.com or Priceline.com. Both sites partner with various big-name car rental agencies, but won't tell you who you're renting from until the transaction is complete.

Next question: On-site location or off the beaten path? Consumer Reports recommends you rent off-site if you're looking to save money. You'll pay a surcharge to any company located on airport grounds (the airport charges them for use of grounds and services). However, the higher price might be worth it if you can't easily reach off-site rental companies or your travel arrangements are tight.

If you're traveling to Orlando in late July, for example, you can get a shuttle to the U-Save counter and pay a base rate of $98 per week for an economy car. Or you can rent directly from one of the car rental companies at the airport the lowest rate is $202.85 per week for an economy car from Dollar Rent-A-Car.

5. Look for Discounts
To lower your bill, first check your wallet: AAA, AARP and many professional organizations offer discounts on car rentals to their members. Some of these deals are standing benefits that come with membership, while others are special promotions. Check with your organization and the rental company to make sure you aren't missing a deal.

Join AARP, for example, and you'll get enhanced primary liability insurance and discounts of up to 30% when you rent a car from National Car Rental. And last year, Avis ran a promotion for AARP members that offered customers a choice of a free tank of gas, a free upgrade or $25 off a weekly rental.

If you tend to rent regularly from a particular company, another option for discounts is to join the company's preferred renter club. You won't always get lower rates, but you might get perks like express check-out, access to special services or a better selection of vehicles. Many of these programs have an annual membership fee, however, so don't sign up unless you're a frequent renter.

6. Exit Strategies
When you're on the last leg of your trip, don't just drop off your vehicle and go. Talk to the attendant checking in your vehicle. Make sure you're credited for arriving with the required amount of gas (assuming you have). And be sure to check for the possibility of surcharges, like vehicle damage or not returning the car on time.