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It depends on the weight the truck is designed to haul.

"Most" trucks have 9 or 10 speed transmissions. That is the common denominator in many trucks driving down the roadways today. But, there are 13, 15, 18 and even 21 speed trucks driving down the road as well.

Heavy-haul trucks such as the ones used to haul heavy construction equipment have more speeds because of the sheer weight they are hauling.

Semi's pretty much don't go below at least a 9 speed transmission. Weight is the biggest factor. You can't have a 5 speed transmission attempting to move an 80,000 pound truck. The clutch would burn up the first day you started driving it if the transmission didn't burn up first.

Gearing on trucks is pretty much directly related to the amount of gross vehicle weight the semi is designed to pull. However, the 10 speed is the most common simply because it is more economical when considering purchasing an entire fleet of trucks. You don't go to work for Werner Enterprised (blue trucks driving down the highway) or JB Hunt (yellow trucks) or other large trucking companies and expect to find 18 speed transmissions in them. But, you will probably expect to find an 18 speed in a truck hauling an "Oversized Load" - which could mean it is too big for the trailer or it is too heavy or usually - a combination of both.

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13y ago

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