Unsprung Weight

[TeryT]

Well thanks again Mr. Thai! And thanks for creating this here forum - GREAT RESOURCE!!!

Now as to the LT tires increasing unsprung weight - agreed. As to this unsprung weight specifically slowing the vehicle down - whether the additional weight is sprung or unsprung would make no difference to fuel economy. It's still weight that has to be moved around regardless.

Maybe you could answer one question I've not had adequately explained. How does independent suspension provide more unsprung weight - which is supposedly better for towing? (Somehow I just bet you have a link for this somewhere! LOL)

 

[Thai]

Sprung and Unsprung Weight

"Sprung" weight is a term used to describe the parts of an automobile that are supported by the front and rear springs. They suspend the vehicle's frame, body, engine, and the power train above the wheels. These are quite heavy assemblies. The "unsprung" weight includes wheels and tires, brake assemblies, the rear axle assembly, and other structural members not supported by the springs.

Unsprung Weight is a term used to describe that part of a vehicle's mass that is directly connected to the wheels, and not isolated through the suspension.

Because this part of a vehicle is in direct connection to the road and therefore subject to all of its imperfections, it is important that this weight be as low as possible, or at least much lower than the weight of the sprung part of the vehicle, in order that the wheels maintain optimal contact with the road surface. The greater the unsprung weight, the greater the inertia of the suspension, which will be unable to respond as quickly to rapid changes at the interface between the road and wheel. Unsprung weight can be reduced by using light alloy wheels, independent rear suspension (where the weight of the differential is not part of the unsprung weight), and front-wheel drive.

The classic design of rear-wheel drive through a live axle gives quite a high unsprung weight, which is one reason why it has fallen out of favour in the last 20 or so years.