CX-5 Deceleration

C

Col Hennessy

Member
:
CX5
Has anyone else noticed that when you take your foot off the accelerator and cruise to a stop there seems to be an apparent breaking similar to what you feel when the cruise control hold you on a speed as you descend a hill. After reading the manual, I thought it may have had something to do that fancy traction option that is fitted (presumably for icy roads). However I let the car come down a slight slope with and without the traction option and there was no difference. There is a perceptible breaking sensation.
 
I think what you feel is the trans downshifting.
 
halfast3 said:
I think what you feel is the trans downshifting.
Click to expand...

I agree. And it's good to be aware that downshifting behavior is affected by two things that I am aware of;

1)The speed of the vehicle
2)Whether the brakes have been applied after releasing the accelerator

This means if you are coasting up a hill (and therefore don't apply the brakes) the transmission will hold a higher gear for longer compared to a deceleration of the same rate down a hill (in which it is necessary to apply the brakes).


That can be used to your advantage. If the light ahead turns red before you arrive, braking a little as soon as you release the accelerator can effect a downshift which causes you to approach the red light in a lower gear. This is free energy in a modern vehicle because the momentum is used more effectively to keep the engine turning over and less fuel will be consumed. This assumes the engine is hot because a cold engine will inject fuel anyway during engine braking to keep the catalytic temperatures high enough to function properly.
 
I figured this was from how the skyactive charging system works. The alternator free wheels until deceleration...
 
It's just engine braking. Common practice when driving a manual, modern autos now employ it. The torque converter stays locked up until very low speed which helps it feel more responsive should you need to accelerate.
 
It's good for decelerating near a speed trap too so you don't go by the cop with your brake light on.
 
craigo said:
It's just engine braking. Common practice when driving a manual, modern autos now employ it. The torque converter stays locked up until very low speed which helps it feel more responsive should you need to accelerate.
Click to expand...

This.

Other cars tend to unlock the torque converter and coast like it's in neutral when the driver lets off the throttle. The CX5 doesn't do that. It's a slightly weird sensation at first if you're used to driving an automatic, but coming from a manual car it feels normal.

If you don't want to engine brake so much when coming off the throttle and want to coast more, I found that you can press the throttle ever so slightly and the car will just coast and not slow itself down so quickly. It's almost like driving an electric car with a strong regen setting. It's kinda cool because you have more control of your speed with just the throttle and not have to rely on the brakes for small changes in speed.
 
craigo said:
It's just engine braking. Common practice when driving a manual, modern autos now employ it. The torque converter stays locked up until very low speed which helps it feel more responsive should you need to accelerate.
Click to expand...
It feels like the car is in a higher RPM range that it should be. It seems to me that the car is using more fuel when coasting down hill or coming to a stop.
 
mtvon2 said:
It feels like the car is in a higher RPM range that it should be. It seems to me that the car is using more fuel when coasting down hill or coming to a stop.
Click to expand...

RPM does not necesarily equate to fuel consumption. Engine braking, in fact, costs less fuel than leaving it in neutral. The reason being that your own kinetic energy is being used up to keep the engine turning (thus the slowing down) instead of using fuel.
 
vroom said:
RPM does not necesarily equate to fuel consumption. Engine braking, in fact, costs less fuel than leaving it in neutral. The reason being that your own kinetic energy is being used up to keep the engine turning (thus the slowing down) instead of using fuel.
Click to expand...


Not totally sure about this, but the ECU might cut the fuel off entirely.

This generates a fair amount of posts. I wonder if mazda is more aggressive with engine braking than others.
 
For a car with an automatic transmission, the CX5 has had the most engine braking effect I've felt before. The only thing that comes close is a car with a manual transmission.

It was a bit strange at first, but you get used to it.
 
craigo said:
Not totally sure about this, but the ECU might cut the fuel off entirely.
Click to expand...

Yes, most modern fuel injected cars do, but don't take my word for it. Here is a quote from the almighty Wikipedia:

While coasting with the engine running and the transmission in gear, most cars' engine control unit with fuel injection will cut off fuel supply, and the engine will continue running, being driven by the wheels. Compared to coasting in neutral, this has an increased drag...

Also, while coasting in gear, my Canadian CX-5 indicates 0.0 Liters/km. An American model would probably indicate something like 99.9 MPG since it can't indicate infinity!
 
vroom said:
Yes, most modern fuel injected cars do, but don't take my word for it. Here is a quote from the almighty Wikipedia:

While coasting with the engine running and the transmission in gear, most cars' engine control unit with fuel injection will cut off fuel supply, and the engine will continue running, being driven by the wheels. Compared to coasting in neutral, this has an increased drag...

Also, while coasting in gear, my Canadian CX-5 indicates 0.0 Liters/km. An American model would probably indicate something like 99.9 MPG since it can't indicate infinity!
Click to expand...


Yep, that is exactly what it reports.
 
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