Something I've noticed: while backing (coasting) down my driveway (slight grade) my MINI will decrease speed, while my Explorer will increase. This would imply some sort of resistance.
MINI has stock run-flats inflated to 35psi (warm)
Ex has 31-10.5 mud tires inflated to 30psi.
I have also noticed the MINI losing speed while coasting down an incline in other instances, but no comparison with other vehicles.
Is this tire loss, driveline loss, or something else? Should I have the dealer check it out?

 

You might want to jack it up and check how well the wheels turn. Maybe your parking break is sticking a little. Our MINI coasts fairly easily but the only car we have to compare it to is a Honda Insight that could coast for miles.

 

Every vehicle has rolling resistance, without exception. Your explorer is around 1000-1500 lbs more than your MINI, so the force pulling your explorer is greater at the same incline.

If you don't trust that it exists, put your car up on some jack stands and give the free wheels a good push. You'll notice two things:

1) that it take a good amount of push to get them spinning. This is the same force that has to be overcome to get your car rolling in neutral down an incline. It's also the main reason to go to lighter wheels. It will take less force to get them spinning.

2) that the wheels won't keep spinning. They'll eventually stop all by themselves. This shows that the resistance is present. If you have lighter wheels, they'll stop sooner and more readily, since they will carry less momentum from your initial push.

If you are concerned that there may be a problem, do the test with all your wheels, and if one seems to be stopping quicker than the rest, you might have a problem. My guess you are just noticing a combination of factors dealing with the difference in the weight of the vehicles, wheel weights, rotor weights, etc. But you might be having an issue with your brakes pressing on your rotors at one or more wheels, so it's worth performing this simple test.

 

Kapps and Will,
Thanks for the insight. This could also tie-in to the consistent pull to the left that I get. One brake possibly dragging a little.

 

It's a good possibility. Good luck!

 

Do both vehicles have manual transmissions and are you coasting in neutral with both of them?

Newton would disagree with you. F=m*a so the mass of the explorer does affect the force, but not the acceleration (gravity is a constant).

 

Andy,
Yes both are manual trans and coasting with clutch disengaged.

 

do you have your foot on the break?