We have all seen vehicles with lifted suspensions and big tires and wondered, “How does that even move?”
Those who have installed a lift kit along with larger tires may wonder why their vehicle takes off so slowly. It is most likely because the factory installed stock gear ratio is too high.
Changing your Gear Ratio is essential for gaining back lost power!
High vs. Low Gear Ratio
Most vehicles are set up by the manufacturer for maximum fuel economy, which use a high gear ratio, 3.42 or 3.08 for example. If you are using your vehicle for towing, it would generally have a low gear ratio like 4.10 or 4.30.
Ratio is how the pinion gear relates to the ring gear. In a 3.42 ratio, the pinion has to travel 3.42 revolutions compared to the ring gear’s one rotation. This situation is ideal for everyday driving, not towing. Comparatively, a low ratio like 4.30 would be 4.3 revolutions for every one ring gear rotation. This is much better for vehicles that are used for towing.
Let’s say you have a Jeep with 3.21 gears and a 30 inch tire. At 70 miles per hour, your RPM is about 1750 RPM. Now, put on a 35 inch tire. This will decrease the RPM to 1500 RPM. This causes the engine to never reach overdrive. However, if you change the gear ratio to 4.10 (a low ratio), the RPM goes to 900 RPM. This is a little over factory settings, but it is because you are turning a heavy 35 inch tire. Now, the engine can go into overdrive without lugging the engine. This will help decrease the stress on the engine and driveline.
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