![]() Then you' ll have to use lap times, and feel to get the ratio dialed in. after racing different tracks, and noting what ratios you use for the length of each, you' ll be able to take "an educated guess" on a ratio to start with. When using the formulas to figure things out, and the rear tires are two different sizes, use the average of the two (add them together and then divide by 2) or true them down to the smaller size.Īs for figuring out which ratio to use when racing at a track for the first time, there is really no substitute for experience. Pretty simple stuff huh? You bet! Use a pair of calipers to measure the diameter of the tire. ![]() (Then switch to a pinion that works with the spur to get as close to a 5.40 to 1 ratio as possible. If the size of the worn tires measures 2.25, and the new tires measure 2.50, and the old ratio was 6 to 1, then figure out the new ratio like this: 6 divided by 2.50 multiplied by 2.25 equals a 5.40 ratio. To figure out how much of a gear ratio change is needed, simply divide the ratio by the old tire diameter then multiply by the new tire diameter and this will give you the new ratio to use. The smaller diameter means you must adjust the gear ratio to maintain the same top speed and performance. All things being equal, tires with a larger diameter may require a smaller pinion and small diameter tires may require a larger one, to maintain the same performance.Īlso, as you run a set of foam tires they naturally wear down in size. The diameter of a tire drastically effects the choice of which ratio to run. Meaning the motor turns over 13.5 times for every 1 rotation of the wheels.Īn important thing to remember, when comparing the ratio you' re using to the ratios other drivers are using, is tire size. Using the 6 to 1 ratio from the 120 spur and 20 pinion, if a gearbox had an internal ratio of 2.25, the overall ratio would end up being 13.5 to 1. The internal ratio is usually listed in the instructions for the car or truck. When using a car with a gearbox, simply multiply the ratio by the internal gearbox ratio to get an overall ratio. This means that for every 6 turns the motor rotates, the wheels rotate 1 time. As an example, a 120 spur and 20 pinion equals a 6 to 1 ratio. To find the gear ratio, simply divide the spur gear by the pinion gear. Grab a calculator, a pad of paper and a pen, there is some simple math that will allow every racer to figure out a gear ratio, overall ratio and how to adjust a ratio for tire wear. Well, figuring the ratio for a car is easy, figuring out what ratio to run is the hard part! Of course it would be nice to always see the values.Gear Ratio Basics: Beginners and experts alike often ask "How do you determine a gear ratio?". To answer the question about the sport transmission gear ratios: I have a capture card and I took screenshots of both the sport and race transmission and the gear ratios of the first five gears are identical (at least for the four cars I mentioned above). I’ve tried that with four cars ('70 Challenger, Dodge Super Bee, '70 Chevelle and Pontiac GTO) and at least for them it works like that. In the Hellcat Challenger, you keep an 8-speed for all upgrades levels…Īssumption: If a car has less than 5 gears, the street and sport transmission will change the transmission to 5-speed and also change the gear ratios. If you go to “Race,” you get a fully-tunable 6-speed in that same car. If you stay below that, you retain 4 gears. For instance, the '70 Challenger goes from it’s stock 4-speed to a generic 5-speed when you go to the “Sport” upgrade. ![]() But in older cars - like almost all the muscle cars in the game - you get a whole new transmission. The differential ratio is set by the ring & pinion gears in the rear differential, which should be tied to the “sport” differential upgrade, not the transmission.) you just get the “stock” transmission with the unlocked rear diff. For most modern cars, yes, you’re correct (And what a stupid thing that is. So you can search for the original gear ratios of the car and hope that they are correct in Forza, check the top speed in each gear and use engine speed, tire dimension and final drive ratio to calculate the gear ratio for each gear or replicate the gears with a race transmission. The gear ratios or the number of gears are not changed, so the cars stock gear ratios are identical to the gear ratios of the “Sport Transmission”. The “Sport Transmission” only unlocks the final drive ratio and reduces the shift time.
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