Why can't you tow the SE on a dolly with the front wheels off the ground?

[Carsten Haase]

I learned the hard way when I was a teenager driving too fast in the snow that you shouldn't downshift to slow down in a FWD car. As soon as I did that, the rear end happily came around on me. This was before the days of stability control too.

Cars have proportioning valves that control how much fluid pressure is applied to the front versus the rear. No stock car just applies the front or the rear brakes so I have to conclude that there is a small amount of rear braking on regenerative braking. Maybe I'm wrong too. I know I would design it to be safer and apply the rear brakes on decel.

Any car can spin around on any surface with the right inputs (aka trail braking if done intentionally lol).

Everything I've read and experienced says too much rear brake leads to instability, too much front brake leads to understeer. Rear brakes help reduce stoping distance but don't improve stability.

• "Warning - having too much rear bias can make your car very unstable."
• "too much rear brakes will tend to cause the car to spin; too much front and car will not turn in."
• "Oversteer is caused when the rear wheels lock up first; understeer is the opposite and occurs when the car is front biased"
• "When braking, weight transfers from the rear to the front. This increases traction in the front and reduces it in the rear. If the brakes had a 50/50 balance, the rear wheels would lock up first. This could cause a dangerous spin... NOTE: OEM brake systems are often designed with 5-10% additional front bias. This increases stability but slightly increases stopping distance."

More anecdotal evidence:

I have an annoying squeak coming from the rear brakes when turning right. The slightest amount of brake pressure makes the squeak stop but I have to press the brake pedal, regen alone won't do it.

I've intentionally tested stability on straight black ice. Any brake application triggered the very noticable ABS pulsing to prevent lockup but regen only resulted in perfectly smooth (stable) stops thanks to the precise electric motor control

 

[revorg]

... but regen only resulted in perfectly smooth (stable) stops thanks to the precise electric motor control ...

Good to know.

 

[Carsten Haase]

Back to the original topic of this thread...

ICE MINIs allow for dolly towing but the BEV doesn't even though the rear is basically identical.

My guess is that MINI decided there was an increased risk of battery puncture from road debris with the car angled upwards behind another vehicle and it was better to ban dolly towing than deal with the potential negative media attention from an EV fire.

 

[Wreckless117]

To overcome that, you put the car in neutral but that means the car is on. Then, you have to deal with the regenerative braking. It engages the rear brakes with one pedal driving. It wouldn't be safe to have 100% of the braking force to be on the front because in wet conditions, the rear end would get very unstable and want to come around. Check your rear wheels for brake dust to see this. My rear wheels always get dirtier than the fronts.

So it is probably the combination of the parking brake and regenerative braking. That is my guess.

I just posted this in another thread as well, but Regen does not use friction brakes at all.

To test I literally unplugged at 100%, pulled out the garage, immediately went to about 55mph down my road and then just let off, full Regen to a stop, parked and checked the temps and touched the rotors. Regen does not use friction brakes.

DSC on the hand does, and that is why everyone is seeing brake dust, especially more so on the rear wheels.

Neat trick, wash your car, and then fully disable DSC for a week, boom no brake dust.

As far as where the energy goes I do not know, possible that do to the mini only using a certain percentage of battery vs true capacity and it can actually take the extra charge. Not like your gonna over charge it with Regen to begin with...

 

[SameGuy]

To test I literally unplugged at 100%, pulled out the garage, immediately went to about 55mph down my road and then just let off, full Regen to a stop, parked and checked the temps and touched the rotors. Regen does not use friction brakes.

Regen doesn’t fully regenerate the amount you used to pull out of your driveway and bring it up to 55, so you made room for those electrons!

 

[Wreckless117]

Regen doesn’t fully regenerate the amount you used to pull out of your driveway and bring it up to 55, so you made room for those electrons!

Lol exactly

 

[FrankinCarp]

Lol exactly

It is all about the Law of Conservation of Mass and Energy. A significant amount of energy is consumed in accelerating and driving at any speed. The regeneration from slowing to a stop, even on a downhill, is not likely to return as much to the battery.


Mike Wazowski [emoji1063]
[emoji4]& [emoji23] for more [emoji298]️[emoji298]️

 

[Carsten Haase]

As far as where the energy goes I do not know, possible that do to the mini only using a certain percentage of battery vs true capacity and it can actually take the extra charge. Not like your gonna over charge it with Regen to begin with...

I responded to the other thread with the manual section that does say brakes are sometimes used during regen.

The problem with regen at high SOC isn't that you're going to over charge the battery, it's the C rate. Fully charged batteries (or cold batteries) do not like high current and full strength regen sometimes goes over what they're able to accept. MINI decided to avoid limiting regen (like Tesla used to) to create a consistent driver experience by blending in the brakes. Tesla now does the same thing as well

 

[GetOffYourGas]

I responded to the other thread with the manual section that does say brakes are sometimes used during regen.

The problem with regen at high SOC isn't that you're going to over charge the battery, it's the C rate. Fully charged batteries (or cold batteries) do not like high current and full strength regen sometimes goes over what they're able to accept. MINI decided to avoid limiting regen (like Tesla used to) to create a consistent driver experience by blending in the brakes. Tesla now does the same thing as well

Chevy hasn’t made this leap. My Bolt definitely does not slow as quickly with a full charge. It’s actually unnerving at first if you are used to always having one-pedal driving.


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