# How long can a manual transmission car run in coasting on gears?

Let me explain the question:

Consider the scenario - you have been driving at 80 KMPH and now you have lifted off your legs from accelerator. The car continues to run with its kinetic energy (I assume the ECM would cut the fuel off during this period).

My opinion is that the car would slow down gradually from 80 KMPH and at some point it will reduce to say, 50 KMPH where in the gear may need to be downshifted to 4th and so on. So after some time it shall come to a halt.

But I have heard another point from one of my friends on his Hyundai car is that, the car would continue to run after reaching say 50 KMPH (where the 5th gear needs to be downshifted) and it would run until the driver brakes the vehicle.

I was puzzled a bit, thinking how could this happen? If the fuel is cut off or atleast it's at idling level, what could drive the vehicle further? Should the vehicle not stop once all of it's kinetic energy is absorbed?

Can some one help me to understand this?

Relevance
• 8 years ago

If you're in Nuetral the engine is disengeged from the transmission via the plates in the clutch.

The transmissions gears are also disengaged from the drive shaft by way of the dog.

If you've ever broken a drive shaft it will continue to spin via the differential and he wheels.

The only things that come into play are forward momentum and friciton. if you've ever made a pinewood derby car, you knwo there is friction everywhere, but the more intitial speed you have the further you'll go.

I ran out of gas in the fast lane of the Turnpike a while back. teh pickup truck ahd enough mass and forward momentum that I made it more than a mile before a complete stop and jsut a few hundred feet from the rest stop.

• 8 years ago

How long I couldn't tell you but in 5th gear most cars have that as overdrive so there is very little mechanical drag and the momentum will carry the car. Down shifting would most likely slow the car more then just leaving it in 5th. But there are many factors to consider, such as road condition, tires, wheel bearings, suspension.

Source(s): diesel technician
• Truth
Lv 7
8 years ago

ok .. this question is impossible to answer with out some details. first you have to Factor in wind resistance , gravity weight of car , land terrain are you coasting down hill, up hill ,flat land. resistance on the brake size and weight of wheels an tires. once disengage the engine form the transmission you start loosing momentum unless your going down hill . see Newton's laws of motion it will explain in detail.