Using a clever formula, Forbes created a list of vehicles with a sales value below its suggested retail value. Unfortunately, it misses one piece — why these vehicles suck. That's why we've created an index to explain it.

Click next to see what that index is and how we'll present these ten vehicles.

This list takes the actual market value of the vehicle (i.e. what it actually sells for after rebates, mark-downs, et cetera) and compares it to the MSRP. Because there are now so many vehicles like this, they've combined it with the J.D. Power & Associates APEAL survey scores and Consumer Reports satisfaction numbers to narrow down the list to ten. How we did that below.

We generally agree with their choices (though, they tend to take the highest MSRP possible) and, in order to help out our friends at Forbes, we've decided to augment the scores with data from the Jalopnik Average Zero Transaction Evaluation Key Value Index, or A.Z.T.E.K. Value Index for short. This index is a measure of the factors contributing to the undesirability of a vehicle. Click on any of the photos to see the Forbes Value and the additional Jalopnik A.Z.T.E.K. Value Index.

Pontiac G6 Coupe
Market Value: $21,943
MSRP: $24,610
Difference: -10.8%
Jalopnik A.Z.T.E.K. Value Index: 27
Reason: Neither as sporty as the Nissan Altima 3.5SE coupe or as well-appointed as the Honda Accord Coupe, the G6 Coupe is a rather attractive face of a dying brand. Even without the Pontiac badge weighing it down, the G6 would be competitively priced if the car itself was at all competitive with other cars in the segment.

Chevrolet Colorado
Market Value: $22,004
MSRP: $24,745
Difference: -11.1%
Jalopnik A.Z.T.E.K. Value Index: CCC+
Reason: Wait, they still build the Chevrolet Colorado? The last Isuzu passenger vehicle still sold in the U.S., the Colorado is the biggest also ran for true Chevy fans unable to buy a far superior product from, well, just about anyone.

Ford Ranger Supercab
Market Value: $18,145
MSRP: $20,405
Difference: -11.1%
Jalopnik A.Z.T.E.K. Value Index: 0.0589
Reason: The Ford Ranger features a "Supercab" with all the heroic ability of Jimmy Olson. Though we not-so-secretly like the Ranger for its straightforward nature, you'd have to be insanely generous to pay full price for this antiquated two-passenger truck.

Pontiac G6 Sedan
Market Value: $18,766
MSRP: $21,165
Difference: -11.3%
Jalopnik A.Z.T.E.K. Value Index: D+
Reason: You know what's less valuable than a Pontiac G6 Coupe? A Pontiac G6 sedan. The coupe may not be the best mid-size two-door, but at least it has some unique style and verve. To be fair to the G6, a lot of people are surprised at how competently it performs — when they rent one.

GMC Canyon
Market Value: $22,749
MSRP: $25,830
Difference: -11.9%
Jalopnik A.Z.T.E.K. Value Index: 0.0000459
Reason: All the reasons you're not buying the Colorado, except add a brand few people remember exists and add a $1,000 to the price.

Jeep Wrangler
Market Value: $24,513
MSRP: $28,815
Difference: -14.9%
Jalopnik A.Z.T.E.K. Value Index: *****
Reason: As great as the Jeep Wrangler is, it's a special kind of insanity that makes anyone thinks $28,815 for one is a good idea. Granted, you'll be able to grab a cheap one MSRPing at a much lower rate, but a fully loaded Wrangler starts pushing into ridiculous rates. As much as we love the simple, straightforward Wrangler, most people are demanding a roof.

GMC Envoy
Market Value: $25,709
MSRP: $30,625
Difference: -16.1%
Jalopnik A.Z.T.E.K. Value Index: Fuzzlebum
Reason: You know what people aren't buying? SUVs. Especially not with an old platform and dated design. It's all about the MPGs baby.

Dodge Caliber
Market Value: $16,490
MSRP: $20,295
Difference: -18.7%
Jalopnik A.Z.T.E.K. Value Index: 7/10
Reason: It's rare a non-Chinese automaker creates a new vehicle that debuts two generations behind the competition, but buying a Caliber is like buying a rotary phone. It looks old. The interior is cheap. The engine is found in, essentially, every other vehicle on the planet. The only intriguing model is the SRT4 and even that is so scary to drive the only intrigue is how long you'll have before you sell it.

Dodge Durango
Market Value: $22,649
MSRP: $28,130
Difference: -19.5%
Jalopnik A.Z.T.E.K. Value Index: ü
Reason: Remember how we said it's rare for an automaker to create a new vehicle that debuts two generations behind the competition? It's not rare for Chrysler. The under-designed, oversized Durango was reworked just in time for the Carpocalypse and sold as poorly as a new SUV might. Even better, the milquetoast hybrid Durango was so great they discontinued it only months after they released it. Hard to believe they went bankrupt...

Mercury Grand Marquis
Market Value: $22,793
MSRP: $28,985
Difference: -21.4%
Jalopnik A.Z.T.E.K. Value Index: 1,959,039,098
Reason: Built on a platform older than the average blogger, designed to emulate old age, gigantic, and generous with the fuel use, the Mercury Grand Marquis is the car Ford used to build, which is why only people old enough to remember the days when Henry Ford I ran the company are the only people who actually buy one. Also, you don't have the advantage of looking like a squad car and having everyone around you slow down.

Send an email to Matt Hardigree, the author of this post, at matt@jalopnik.com.