Free wheeling, Prius vs Cmax

[homestead]

We drove over the Oregon coast range last week.  On the downhill side with several miles

of downhill I was coasting along in-gear and I noticed a older prius (2009?) in front of me.

We were going about 60mph for a few miles downhill and I noticed that I had to brake

a couple times to keep from getting too close to the prius.  I was surprised at the time

because I figured the prius would have a lower drag coefficient.  The prius wasn't braking

like I was.  Later on I thought it was possible that I had maxed out my high voltage battery

which would have give me less resistance but since we were on the same road at the same speed

the prius should have been maxed out too.  So the question is which car should win the

downhill coast, Prius or C-max?

[dicko]

Who cares?  You have a C-Max so enjoy it.  Don't worry about Prius'.

     -Dick-

[homestead]

Who cares?  You have a C-Max so enjoy it.  Don't worry about Prius'.

     -Dick-

No worries, I come from a scientific background so I enjoy thinking and discussing topics

about rolling resistance, drag coefficient, braking regeneration, etc.  After thinking on this

some more I believe I was gaining ground on the prius because of the weight difference in the

cars.  The C-max weighs a few hundred pounds more than the prius.

[livesmith]

We drove over the Oregon coast range last week.  On the downhill side with several miles

of downhill I was coasting along in-gear and I noticed a older prius (2009?) in front of me.

We were going about 60mph for a few miles downhill and I noticed that I had to brake

a couple times to keep from getting too close to the prius.  I was surprised at the time

because I figured the prius would have a lower drag coefficient.  The prius wasn't braking

like I was.  Later on I thought it was possible that I had maxed out my high voltage battery

which would have give me less resistance but since we were on the same road at the same speed

the prius should have been maxed out too.  So the question is which car should win the

downhill coast, Prius or C-max?

 

There are a number of variables we don't know...  Here are the pieces off the top of my head:

 

-Yes, the Prius should have a better drag coefficiency and go through the air better.  It gets better mpg so that all works together.

 

-As for coasting though, he may have been in B mode(same as L in the C-Max) which would be using his ICE to slow him down a bit.

 

-I don't know how the standard non-braking regen in a Prius compares to the same in the C-Max.  I had a 2004 Prius(which would be the same as the 2009).  Can't say I'd tell a lot of difference in non-braking regen...

 

-If the Prius Battery was topped off, the ICE would definitely be spinning, but not sure that I recall any added drag from it if it's not braking or in B mode...

 

 

Then there's just the usual every car potential differences...  Tires(different resistances), brakes(possibly dragging), etc...

[Adrian_L]

Who cares?  You have a C-Max so enjoy it.  Don't worry about Prius'.

     -Dick-

 

Should we run all our potential questions past you to see if they meet your approval?

 

If a topic bores you or you have no interest, move on,  Dick.

Edited May 26, 2016 by Adrian_L

[cwstnsko]

At the top of a hill, a heavier car has more potential energy than a light car.  All other things being roughly equal, the heavier car will gain speed faster than the lighter car.  650 lbs of additional weight should be more than enough to overcome the difference in drag coefficient.

[stevedebi]

No worries, I come from a scientific background so I enjoy thinking and discussing topics

about rolling resistance, drag coefficient, braking regeneration, etc.  After thinking on this

some more I believe I was gaining ground on the prius because of the weight difference in the

cars.  The C-max weighs a few hundred pounds more than the prius.

It is fairly simple. For one thing, we don't know what the Prius was doing. It may well have been in their "B" mode, which is similar to our "L" mode, causing more regen.

 

You do know that there is a switch on the shifter that puts you in "hill mode"? It increases the regen slightly.  If you need more braking, shift to "L". Note that the engine may come on and spin up to fairly high RPM, but it is not using gas - the car is using the engine as a brake when the HVB gets full.

 

I own the Energi version, but I believe both the hybrid and the Energi have the same modes.

[homestead]

It is fairly simple. For one thing, we don't know what the Prius was doing. It may well have been in their "B" mode, which is similar to our "L" mode, causing more regen.

 

You do know that there is a switch on the shifter that puts you in "hill mode"? It increases the regen slightly.  If you need more braking, shift to "L". Note that the engine may come on and spin up to fairly high RPM, but it is not using gas - the car is using the engine as a brake when the HVB gets full.

 

I own the Energi version, but I believe both the hybrid and the Energi have the same modes.

I have tended to avoid using "hill mode" because I thought since the ICE was slowing down the descent that the

maximum charging would come by using the brakes alone.

[Adrian_L]

Anybody notice a "clunk" sound from the transmission when coming to a stop with the hill mode on?

[livesmith]

I have tended to avoid using "hill mode" because I thought since the ICE was slowing down the descent that the

maximum charging would come by using the brakes alone.

 

To my knowledge Hill descent uses whatever is available to make sure you don't exceed(much) your set speed.  Basically reverse cruise control.  

 

So, I'd advise using L mode first on bigger hills.  That one shouldn't use any friction braking at all.  Hill descent will use friction brakes if you are exceeding the set speed and it can't use any more regen.(not sure if it will spin the ice like L mode or not...)

[stevedebi]

I have tended to avoid using "hill mode" because I thought since the ICE was slowing down the descent that the

maximum charging would come by using the brakes alone.

No, the hill mode and "L" engage the regen, that is all. When the Hybrid gets to full HVB, it will shed energy by engaging the ICE (but not burning fuel), as discussed previously.

[homestead]

What what speed are you guys putting it into low going down hill to slow your acceleration?

How does the engine/trans respond to that?  Noticed around town if I accidentally put it in L

instead of drive the engine really howls at low speed.

[plus 3 golfer]

What what speed are you guys putting it into low going down hill to slow your acceleration?

How does the engine/trans respond to that?  Noticed around town if I accidentally put it in L

instead of drive the engine really howls at low speed.

You can shift to low at any speed.  IAlso, ICE may engage when using hill assist..  I use it all the time to avoid friction braking in the mountains. Put the rpm gauge up in myview as you shift to low.

 

Remember, the C-Max uses planetary gearing not fixed gears.  So, ICE rpm may be "regulated" by rotating the generator as a motor.  I'll run / record some tests on vehicle speed and ICE rpm when shifting to low.  From the owner's manual:

 

Low (L) • Provides maximum engine braking. • The transmission may be shifted into low (L) at any vehicle speed. • Is not intended for use under extended or normal driving conditions and results in lower fuel economy

Edited May 27, 2016 by Plus 3 Golfer