Braking power?

  • Thread starter Thread starter azausa
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azausa said:
Just saw this post on FB -> https://www.facebook.com/groups/electricMINI/permalink/2994782157437065/

It raises the question of the braking power of the SE in certain situations where you have to step on the brakes hard to avoid an accident.
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Because I've never been Facebooked, can you tell me if more than one Facebooker has reported problems with panic stops in their MINI Cooper SEs?

Has anyone on this forum reported any problem with panic stops? I can't remember one complaint or even a concern. The SE is about 400 lbs heavier than its ICE counterpart, so it will take longer to stop from the same speed, but nothing alarming.
 
Here is the post -> “Does anyone else feel that the brakes are not so good on the mini? I have owned sports models of every car I have bought and they generally have bigger brakes than the regular cars and stop on a pin. The regenerative braking is awesome and very effective, but both myself and my wife have had to stand on the brakes hard a few times, a child on a bike for her today in a 50km zone went straight across the road in front of her for example and the brakes really feel low on power in that situation. Also if you are doing Vmax and stand on them they are not that good. The disk size is really small IMO”

Also very interested if anybody has encountered this?
 
Its a firm pedal, but stops well/confidantly for me. I've had some emergency stops, don't think I've slid a tire. It does coat the wheels with more brake dust than I'd expect, however. If there was a brake problem I would think it would have shown up in one of those track tests, you know the ones where they overheat the batteries.

Do they put different brake hardware on the SE than the ICE version?
 
Rotor size doesn't have much to do with stopping power, it only helps with brake sensitivity/control and heat. If you can lock the wheels, that's all the stopping power you're going to get.

If they had to "stand on the brakes" that's likely an issue with the vacuum booster and not the actual brakes.
 
Only had to brake seriously in earnest once since I acquired the SE, and they worked just fine. (And if Facebook said the sun was shining, I'd take my umbrella. Completely unneeded use of bandwidth.)
 
ColdCase said:
Do they put different brake hardware on the SE than the ICE version?
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The SE has the "S" brakes, which is why you can't put 15" wheels on it (brakes are too big). I hate having to use my friction brakes, but when I'm forced to for sudden stops I feel they work just as well as my previous 2015 S Hardtop's brakes. The SE actually should brake a bit better, since the regenerative brakes would kick in as soon as you move your foot. Unless the person was doing two-foot braking, maybe that's the issue? If you keep your foot on the go pedal the SE will go forward quite easily.
 
insightman said:
The SE is about 400 lbs heavier than its ICE counterpart, so it will take longer to stop from the same speed, but nothing alarming.
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Not entirely true... The braking force = the tyre coefficient * normal force. So:

Fb = k . Fn

Fn = normal force which is the weight * g, so

Fb = k . mg

The deceleration due to the force is governed by:

F = ma => a = F/m = k.mg/m = kg.

So the deceleration is proportional to the tyre coefficient, and not the weight. *However* in the real world, tyres have a maximum energy they can tolerate, and we have weight transfer. If you put too much energy through the tyre, it will slip as the rubber deforms and/or melts. Weight and/or weight transfer means that the tyre could end up trying to dissipate too much energy and it slips.

So, the ICE car is lighter, which puts less energy through the tyre, however the ICE car has a weight bias to the front (something like 65:35 from memory) whereas the SE is more neutral. This would mean as you brake, you put more stress on the front in the ICE car. So there are 3 likely outcomes:

1) The tyres can handle both the extra weight and extra weight transfer - same stopping distance.
2) The extra weight of the SE means the tyres can't handle as much deceleration - the ICE stops sooner
3) The extra weight over the fronts of the ICE car means the tyres can't handle as much deceleration - the SE stops sooner.

I personally believe 1) to be the correct outcome. With the same tyres and wheels, on the same road, the ICE and SE cars should stop at the same distance.

PS. we ignored ABS, and assume the braking force is enough to lock the tyres if ABS wasn't available. You could also argue that as the brake pads on the SE are always newer, having never been used so they would be more efficient ;)
 
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Passing thought: perhaps due to the quietness of an EV, the FB poster was driving faster than they realized, thus requiring them to brake harder than they're used to?

Anyway, C&D reports a 70-0 stopping distance for the SE of 169 ft:

https://www.caranddriver.com/reviews/a30689865/2020-mini-cooper-se-drive/

The S was tested to stop in 158 ft:

https://www.caranddriver.com/mini/cooper-hardtop-convertible

(Yes, I know the link says convertible, but the article seems to be generically about all S models.)

Most other tests seem to be for 60-0 distance, so it is hard to compare, but top 10 supercars tested by C&D can come to a halt in about 130-135 ft.
 
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For comparison C&D tested an MX5 Miata club at 170 ft. A cooper S ICE with what looked like 18 inch rims (they didn't mention the tyres) took 158ft. Different wheels/tyres means different braking ability, but even then 11 feet is less than a car length from 70mph.
 
vader said:
For comparison C&D tested an MX5 Miata club at 170 ft. A cooper S ICE with what looked like 18 inch rims (they didn't mention the tyres) took 158ft.
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Interesting, that must be the fat that made its way into the summary article I linked.

I also came across a recent test of the new Civic (base model): 174 ft, down 4 ft from its predecessor.

Seems like many cars are rather similar on this measurement, with other factors - modulation, fade, etc. - being the real differentiators.

(I once test-drove a Chevy Bolt - it seemed to stop just fine, but the regenerative and mechanical brakes seemed poorly blended, making the brake pedal feel a bit clunky )
 
vader said:
For comparison C&D tested an MX5 Miata club at 170 ft. A cooper S ICE with what looked like 18 inch rims (they didn't mention the tyres) took 158ft. Different wheels/tyres means different braking ability, but even then 11 feet is less than a car length from 70mph.
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From some press photos, the ICE cooper S shown in the C&D pictures comes with 205/40R18 Pirelli Cinturato P7 tires. These have an AA traction rating so they're likely more grippy than the SEs A rated tires
 
insightman said:
Has anyone on this forum reported any problem with panic stops? I can't remember one complaint or even a concern. The SE is about 400 lbs heavier than its ICE counterpart, so it will take longer to stop from the same speed, but nothing alarming.
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Just a couple of months ago, in a thunderstorm (rain), I was driving my 2021 MINI SE in the far right lane on a freeway frontage road, perhaps doing 40 mph. An idiot in a Caddy SUV exited the adjacent freeway at a high rate of speed (I estimate ~60 - 65 mph) and immediately, without any signal or other deference to frontage road traffic (me!) crossed all 3 lanes of the frontage road very quickly, so she could turn right immediately on the very first street intersecting the frontage road near the freeway's exit ramp. I was forced to slam on my brakes to try to avoid hitting her, but ended up nearly stopping but still lightly impacting her right rear side. Not much damage to my SE (except for the right front tow-hook mounted license plate & frame), thankfully.

She turned anyway and ran away on the side street at speed, but I gave chase and took photos with my smartphone of her rear plate number and reported the incident to the local police.

Even in the rain, I felt my MINI's brakes and Hankook tires performed superbly in slowing and almost stopping the MINI in the (for me) emergency situation. I have no concerns whatsoever about their performance when needed for sudden stopping.
 
Texas22Step said:
Just a couple of months ago, ...

Even in the rain, I felt my MINI's brakes and Hankook tires performed superbly in slowing and almost stopping the MINI in the (for me) emergency situation. I have no concerns whatsoever about their performance when needed for sudden stopping.
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Which Hankook tires do you have? I bought a set of take-off Mini wheels and tires to use for "winter" (pretty mild up here) and they have Hankook A/S tires on them that are not very well reviewed for wet and winter.

Rob
 
Teddydogno1 said:
Which Hankook tires do you have? I bought a set of take-off Mini wheels and tires to use for "winter" (pretty mild up here) and they have Hankook A/S tires on them that are not very well reviewed for wet and winter.
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It will be a few days before I can post that info for you, as I am on travel (by air) right now so I cannot look at the tire sidewalls to see & report those details to you.

It is, of course, impossible for me to determine how much the tires alone contributed to my own experience in the incident vs. the brakes themselves, or vice versa. But the combination of those two (tires & brakes), especially in the rain situation I experienced in my SE, was satisfactory.
 
The FB poster must abe comparing the SE to a more expensive sports car that has better brakes, wider tires, or both. I've never owned one of those cars and think my SE's brakes are great.
 
Texas22Step said:
It will be a few days before I can post that info for you, as I am on travel (by air) right now so I cannot look at the tire sidewalls to see & report those details to you.

It is, of course, impossible for me to determine how much the tires alone contributed to my own experience in the incident vs. the brakes themselves, or vice versa. But the combination of those two (tires & brakes), especially in the rain situation I experienced in my SE, was satisfactory.
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OK, back home now! UPDATE to post #17 above: The OEM tires on my 2021 MINI SE are Hankook Ventus S1 evo 3 K127, size 205/45R17. See details at https://www.hankooktire.com/global/tires-services/passenger-cars/hankook-ventus-s1-evo3-k127.html. These are summer tires (but suit our needs well year-around here in Texas).
 
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