Game Breaker / Forza

General

• Vehicles with AWD often delve into this, due to the lateral grip bonus and an amazing launch. In Forza Motorsport 2, only manufacturers with AWD cars could allow AWD swaps, and even then they are only included in specific engine swaps, but future games would open the swap to almost every other car (with hybrids and electrics being some of the exceptions). The strongest examples are easily Audis, Mitsubishis, Subarus, Fords and especially Lamborghinis, which usually have some of the best cars in the game.
• The PI system is not a perfect one: for instance, two cars with very similar power (and torque)-to-weight ratios could have different PIs just because the engines are different. An example is Chevrolet's LS3 engine (Which has been given Serial Numbers Filed Off treatment and appears as simply the "6.2L V8") in Horizon 3 and 4, which is considered a PI-efficient engine. Another example are all kinds of upgrades (such as AWD swaps, installing centrifugal chargers or increasing the tire width) that substract PI instead of increasing it.
• The Aston Martin DBR9, Alfa Romeo 33 Stradale, Shelby Cobra Daytona, Ford GT (new and old), McLaren F1, Ferrari 250 GTO and Porsche 906 have consistenly been strong cars on almost every game they appeared.

Forza Motorsport

• The Honda CRX in the first game falls into this due to improperly set drag values.
• In a sense, modification, as in Forza Motorsport 3 and previous games, the AI never has upgraded cars.
• Things can get deliciously broken when you take a car that technically qualifies for a given race but which no human judge would allow entry. An example, the French Elite Invitational in Motorsport 3. Usually this is the stomping ground of Peugeot and Renault hatchbacks, but things get interesting if you're bastard enough to bring a Bugatti, or even more, a Peugeot 908 LM! Even better, at driver level 20 the game gives you a Veyron for free.
• Due to how Motorsport 3 calculates a car's Performance Index (in other words, how "fast" a car is going around a track), All-wheel-drive drivetrains cause your performance index to actually go down, since it adds about a hundred pounds to the car. However, this allows players to then install huge engines, or cut weight from the rest of the car. What effectively happens is online play gets dominated by AWD Audi A5s, Dodge Vipers with AWD drivetrains, and AWD Volkswagens
• As of Motorsport 4, these problems have been fixed; AI can be allowed to upgrade their cars, events now have an upper PI limit, and AWD cars/conversions grant more PI rather than less.
  • However, upgraded muscle cars are tremendously fast for their class. As a result, a few muscle cars have been banned from setting leaderboard times while the problem is addressed.
  • Rivals mode is very easily abused. By continually going only a fraction faster than your previous effort you will collect many more bounties than if you set your fastest time straight away. History repeats itself with Motorsport 5.
  • Moreover, performing RWD swaps on cars (like making a Honda Civic, normally FWD, into a RWD Car) causes a massive performance index number drop in cars without any real drop in performance - allowing you to slap on weight removals, turbochargers, and bigger tires without much of a PI increase from the stock car.
  • And there's a nice bug that allows you to turn any turbo/supercharged car into an NA car
• Meet the Lamborghini Sesto Elemento! Italian for "Sixth Element" which means almost the entire car is made from carbon fiber and shaves as much weight as possible with a lack of proper paint, minimal interior and a lack of proper seats, just cushions arranged in a seat-like shape. It weighs 999 kilograms.
• Forza Motorsport 5 gives the Lotus E21 Formula One car. At first it was the most expensive car in the game, and for good reason: one, it's quick and astoundingly fast; two, it starts very quickly off the line even without driving aids; three, its handling is wonderfully touchy, you can pretty much handle many corners throughout the game almost flat-out. Even better, it is now available as a gift from Turn 10 after the economy update. Yes, this car is pretty much a huge load of badass-ness.
  • Another game-breaking car in 5 is the Mazda 787B, one of the game's LM Prototypes. Available only for those who buy the VIP membership - which costs just a couple bucks - this car set world records on pretty much every track in the game in its class. It surely isn't brilliant if stock, but with the proper tune-up, this car pretty much blows every other car in its class behind biting the dust.
• Motorsport 6 added in the 2014 Audi R18, just as good as the 787B, and if that wasn't enough, one of the monthly packs added the Toyota TS040, which is far more broken than the other two cars.
• Niki Lauda's Ferrari 312 T2 is hegemonic in the R-class lap time rankings as it is one of the quickest-accelerating and one of the nimblest cars in the game.
• One of the best R and S-class cars in Motorsport 7? The Lotus Elise GT1, which is included in a DLC pack.

Forza Horizon

• Forza Horizon:
  • The first Horizon gives us the Pagani Zonda R. Fast, easy to handle, and even gorgeous.
  • The Radical SR8 RX is a viable alternative where you sacrifice top speed for a lower-than-average price for its class.
  • Another example, other than the Pagani and the Lamborghini, is street races. They can net you at the very least the same amount of money if you place first in the final few Festival races (the ones where's also Darius Flynt), and from that point on, the last few of the street races give you 50-60k credits. And it only gets better if you (ab)use the Hard Mode Perks.
• Forza Horizon 2:
  • The Lamborghini Veneno is unquestionably the best car in Horizon 2, and appears almost ubiquitously at the top of the S2-class leaderboards. Lightweight? Check. All-wheel-drive? Check. Extremely powerful engine? Check. Unthinkable agility? Super check!
  • Supercars and hypercars in general dominated Horizon 2 thanks to the fact that there was little penalty to going offroad in an unsuitable car in this game, so you were often better off just using a Ferrari for everything rather than being more selective. Horizon 3 onwards moved to address this by making it much tougher to control your car across open terrain if its not built for it, along with implementing a wider range of specialist offroad vehicles for that purpose.
• Forza Horizon 3:
  • Who said you cannot farm in the Outback? Horizon 3 is smashed so much that it's easy to find all the Drivaters congregating around the airfield (making for near miss and head to head, as well as bounty and photo shoots) accessible from the start. It's a long stretch of road that allows for high speed racing and drifting in a half decent car, foliage and hills on either side for jumps and wreckage, and it's just south of a festival you can unlock early on making for easy access to spend the cash skill points and XP that had been pouring down even more than the game usually generously gives out. Once you get Byron Bay built up it unlocks the Goliath track, a 10-15 minute per lap marathon where depending on your car and setup where you can easily bag a hundred thousand dollars, 4-5 skill points, and multiple wheelspins per lap.
  • Due to the way PI is calculated in Horizon 3, where grip-based upgrades yield bigger penalties than power-based upgrades, almost every single leaderboard car is a powerbuild (read: huge horsepower, minimum grip to keep it on the floor), which paved the way to lots of twin-turboed V12 AWD swaps. Some of those cars are the Mercury Coupe, the Holden Torana, but other cars like the Nissan GT-R 2012, Lexus LFA or the Centenario are also strong cars.
• Forza Horizon 4:
  • The Hot Wheels Bone Shaker and the Top Gear Track-Tor were so broken in A and B class respectively that they were banned from Rivals and Online Adventure in Update 16. Current offenders are the Shelby Monaco KC, Plymouth Atomic Punk, Peel Trident, Pagani Zonda Cinque, Shelby Daytona, Alfa Romeo Giulia TZ2 and 155, Ford GT '05, or the Chevrolet Nova Super Sport FE to name a few.
  • The Mosler MT900S is essentially the Infinity -1 Sword of the game: the second fastest car in the game, amazing handling and no wet penalty. It's also one of your most reliable choices to smash any PR Stunt in the game; even the toughest Seasonal PR challenges become a complete joke with this thing. Oh, and you get it as a gift in the game's inbox, so you already have it from the moment you make it to the Festival.
  • The Series 8 update introduced the Ferrari 599XX Evoluzione, which has immediately gained fear among players for being the single fastest car in the entire game: matter of fact, it is the only car able to break the 500 km/h barrier when fully upgraded. No shocker, it blows every other car out of the water in speed-centric tracks, and also has enough handling and acceleration to make it viable for more corner-heavy circuits.
    • And as if that wasn't enough, it's also one of the most common Hard-to-Find cars, being usually in rotation as Seasonal Event rewards or, since it was added in the Backstage, just as easy to get 50% in a season and redeem it.
  • The route creator in Horizon 4 is utterly exploitable thanks to a major flaw in the AI's pathfinding: The AI will always follow the exact route created by the player instead of finding the shortest path between each checkpoint. This means that players can create routes that will deliberately send the AI cars off course while the players take shortcuts, making Unbeatable difficulty a trivial matter. It can be exploited in the Weekly Forzathon Challenge to complete N races of a certain discipline (or a race in the Goliath) in a matter of seconds.
  • If skill point grinding or car mastery farming or maybe wheelspin unicorn car and item mining is your thing buy Margaret Thatcher's beach cottage. It has several nearby options to do all three, take your pick. If your car is competitive then there's farmland just outside (where the Fortune Island departure point is) for lazy drift and wreckage points and easy gain. Any car can jump the sand dunes and cliffs up ahead for easy, if risky, massive gain. And for the outright daring there is about five miles of four lane highway close by: speed skills, daredevil skills, near miss and wreckage skills, drift skills, where a skilled played can get scores into the hundreds of thousands (although the game caps your SP gain at 10 per skill chain, which translates to 500,000 points per skill chain). It becomes even easier with an upgraded Drift- or Skill-Boosted Forza Edition car like the BMW M6 FE, Caterham Superlight FE, or the Renault 5 FE.
    • The Renault 5 FE itself is one of the best choices, if not the best, for skill farming. It has excellent off-road performance, versatile handling that can accommodate both drifting and high-speed precise cornering, respectable speeds with the capability of being tuned to S2 class, and a small physical profile that makes it easier to weave through traffic or tight spaces. Furthermore, it is accessible for a relatively low price on the auction house (avg. ~80,000 CR) if you did not obtain one already through wheelspins. Its skill boost affects ALL types of skills, and its car mastery board is also designed to take advantage of this with many perks that further increase skill point values.
  • Wall-riding (that is, hugging walls instead of taking a turn like it was supposed to be taken) in Horizon 4 causes such a low drop in speed that it's always better than taking a clean turn. It doubles as a Scrappy Mechanic as it's not looked at favourably at higher skill levels. Thankfully, in the Series 9 update, Playground added slowdown and ghosting penalties for wall-riders and high-speed rammers in online races.
  • Either of the Peel three-wheel microcars can be made to completely trivialize any race against Drivatars by exploiting the way the game calculates Performance Indexes. If you tune and tweak one so it can get to a higher top speed, but not too high so that it still has a PI of 100, AI drivatars will be matched to the cars base stats, meaning unmodified Peel's and other cars that struggle to even hit 50 mph.
• Forza Horizon 5:
  • The Lamborghini Sesto Elemento Forza Edition has quickly gained infamy as the absolute best car in the entire game if fully upgraded. It may not reach the speeds of the Koenigsegg Jesko or Bugatti Chiron (or even Hennessey Venom F5 as of Hot Wheels expansion), but what really elevates this car into Game-Breaker territory is its insane handling, almost feeling like you're driving on rails. Not only that, it also has a Skills Boost by virtue of being a Forza Edition car, making it a great choice to grind for Skill Points as well.
  • During the game's first week, the Willys Jeep was overused but not for performance reasons; players noticed that the 40,000-credit military car has the free Super Wheelspin skill and requires only 5 skill points^note 1 point each for the starting 7000 EXP perk and the perk to the right, and then 3 more points for the free Super Wheelspin itself. Players have thus been buying Willys Jeeps en masse to farm as many Super Wheelspins as possible. It was thus not surprising that in the game's first major patch, the Super Wheelspin perk was removed from the Car Mastery tree of not only the Jeep, but also the C8 Corvette Stingray and A90 Supra, both of which, pre-patch, also had a Super Wheelspin perk accessible with only 5 skill points.
  • The Hot Wheels Bone Shaker returns from Horizon 4, and so too does its dominance in A-class road racing. Unlike in the prior game, though, it is once again available for use in Horizon Open. General improvements to A-class cars overall mean it isn't at the same overwhelmingly broken level it was in the last game^note Examples of cars that really give it a run for its money in A-class include the Nissan Skyline GT-R R34, the Honda NSX-R GT and the Car Pass-only Subaru WRX STI S209 for Road racing; the Bone Shaker is also dominant in Dirt racing, but is outgunned by the Mercedes-Benz X-Class, International Scout 800A and Toyota Tacoma TRD Pro in Cross Country., but it is very close to it; it's still plenty capable of carrying a mediocre driver to high placings, and a skilled driver far ahead of the pack. Not only that, unlike with 4, it's also readily available for everyone to purchase in the Autoshow at 150,000 credits.
  • Update 6 added a drift transmission as a new upgrade for all cars in the Tuning Shop. Even though it is clearly meant for drift builds, it gained unlikely usage through Good Bad Bugs on two cars in particular: the RAESR Tachyon Speed and the Jaguar I-Pace. The former in particular became extremely infamous as the default gear ratios for the drift transmission, when installed in the Tachyon, reduced the car's top speed from 390 kph all the way down to a mere 32 kph, which in turn tanks the car's PI rating like a rock from S2 all the way to the middle of A-class. The car's original top speed could then be restored by adjusting the gear ratios. Predictably, this completely broke A-class road racing in a way that the Bone Shaker could only dream of, as it was akin to bringing a hydrogen bomb to a knife fight. Playground addressed the issue by temporarily stopping A-class Horizon Open races and banning both the Tachyon and the I-Pace from online races and Rivals as the latter dropped its PI class from A to B with the drift transmission installed. A-class Horizon Open races were re-opened soon after, though from this point on, all electric vehicle introduced from Update 7 and on do not have access to the drift transmission.