Braking vs. Downshifting

Cecil's Columns/Staff Reports
1

The following comes from my brother, who has been in the automotive racing business for some time now. His credentials span wide enough (pit crew engineer of Porsche racing for many years).

He has shown up unexpectedly at my door a few times with a hot new Porsche, and has taken me for a few short (but WOW) rides in the last few years.

He’s addressed the situation of the brake vs.downshift scenario like this:

“In high speed racing, the brakes of the car must absorb most of the HP (in slowing the car) that the engine produced in getting you to that speed in the first place…Now, consider that the engine has an entire cooling radiator to keep it cool, but yet the disks of the wheel have limited “scoops” with which to dissipate almost the same amount of energy (heat).”

Further, he said “So, if you were to try and run an entire high speed professional race using the brakes as your sole source of stopping “power”, then the rotors would heat up and fail to perform (at least fail to perform as well as the other guys who downshift) if not fail altogether during the race.”

Again, further:
“So, the pro racers downshift as well as brake to slow down for the turns, since this is like “free” braking…at least as far as the rotors are concerned.”

Finally, he added:
“The price is that it creates/transfers these braking forces into the engine/clutch/xmission, which reduces the life span of them to near zero. However, since these things get rebuilt after every race, the only “price” is post-race cost, which is sacrificial in pro racing if you think about it”.

Winning is indeed everything…
JJ Richard

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Cecil’s column: “To slow a stick-shift car, should you brake or downshift? (Week of: 27-Feb-98)”

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I’m a downshifter. I feel that I have better control of the vehicle.
The speedometer on my 88 S10 broke at 185000 miles. That was 6years ago.I have not replaced the brakes or clutch. It is all in how you use them. No jackrabbit starts and no screaching stops. There are still plenty of brakes and the clutch is a little weak. So is the engine.It probably has 250000 miles on it now.
I drive heavy trucks the same way.It increases breaking power and like Cecil says,You are ready if you need to get back on it.
I don’t know how race car drivers do it. Mindset and all. But the op failed to mention that brakes are made to cool quickly. Also todays ABS brakes won’t let you lock them up like in days of old.
I guess that it has to do with always being ready for what happens next.

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I forgot to mention that you don’t need to clutch to shift a vehicle. You do it with engine speed.That saves throwout bearings and clutch wear.
Now I hope I’ve waited long enough to avoid flood control

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JWN,

Congrats on your vehichles’ longevity. Given today’s technology (or even yesterday’s technology), I am not surprised to hear that your beloved Chevy truck is still alive and kickin’!

I fully understand your point about “it’s all about how you use it.”, and for the everyday driver/consumer, your downshifting habits don’t seem to pose any life threatening limits on your truck(s).

However, I feel that you fail to realize the full potential of the level of ABUSE that I am speaking of with reference to PRO racing! :slight_smile:

How long do you think your trusty Chevy and its clutch, etc. would last if you were to place demands such as 0 to 150 mph, immediately followed by 150 to 50 mph, then back up to 150 mph, etc, etc, over and over again on it for say, 500 miles, balls to the wall?

Slice it any way you want, slowing down for the next red light via downshifting (even cumulatively over a decade) doesn’t even come close to braking repeatedly from 150+ mph to near zero (as discussed above) for 500 intense racing miles.

My post was simply intended to illustrate that there are at least two (casual vs pro) driving enviroments that must be considered prior to speculating on the “downshifting vs. braking” topic.

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I pretty much agree with what’s been said so far on this subject. I’d like to add one thought though. I live in the mountains, and when it snows we have lots of asphalt based bobsled runs around here. If you have a front wheel drive car, and you try to go down a snowy or icy slope with the drive wheels engaged, you stand a very good chance of doing a 180. I’ve done it myself, and seen it happen way too often. In this situation, you can never tell if the engine is fighting or helping the brakes, and in either case, the braking force on the front wheels is different than on the rear wheels. One bad bump or swerve, the lighter rear end breaks free, and it’s tilt-a-whirl time.
My advice: in this situation, straight shift or automatic, put the car in neutral and ride down with just the brakes. Good day.

7

Picking nits…

JJ Richard wrote:

That’s an exaggeration. Only a small portion of your forward momentum is translated into heat in your brake system. Much more is distributed between your tires and the road. The problem is that your brake system concentrates heat into a small area and is not that efficient at dissipating the heat elsewhere. I’m not disagreeing with your basic premise, just the statement that the energy transfered to your brakes is equal to the energy required to get the vehicle up to speed.
justwannano wrote:

Conventional wisdom has always been that engine braking affords more controlled stopping than regular braking. However, with the advent of ABS, this may no longer be true. I suspect that a modern ABS will give you more control than engine braking for the simple reason that your wheels can lock up during engine braking if you encounter debris on the road (or ice, as TNTruth pointed out), where ABS are designed NOT to lock up.

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JoeyBlade,

You are correct, I sit corrected! :slight_smile:

JJ

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I can shift without clutch? How do I teach myself to do this? Should I just try it? I’ve been driving a standard for years and never even conceived of such a possiblity…

10

Coop,

Yes, you can, if you shift at just the right speeds (for your car). I have a 1990 Honda Civic DX hatchback, and my “perfect” clutchless shifting speeds are:

1st to 2nd: 15 MPH.
2nd to 3rd: 30 MPH.
3rd to 4th: 45 MPH.
4th to 5th: 45 to 50 MPH.

The technique is to get up to the correct RPM in 1st gear (which varies amongst vehicles), and then as you BEGIN to raise your foot from the gas pedal, EASE the shifter out of 1st gear, and gently apply pressure into the 2nd gear position of the stick. If you’re going at the correct speed for the gear change, the shifter will “slide in” to 2nd gear, with an associated “decceleration bump”. Optimally, you want the “bump” to be as close to zero as possible. Work on your speeds to acheive as near a zero “bump” as possible.

To go from 2nd to 3rd, etc, follow the same procedure… I don’t have a tach in my car, so I go by the speedometer.

In fact, should your clutch go out completely one day (only if due to mechanical linkage failure) while you’re out in the “boonies”, you can even start your car while in first gear. Hold the (now useless) clutch pedal to the floor (to defeat the safety switch), and turn the key. The starter will actually lunge your car forward as the engine starts, and once the engine is started, you can then release the key and travel on shifting gears without the clutch as described above. This is a last ditch effort, and should only be used to get you to safety.

Red lights are killers, since coming to a complete halt will kill the engine, thereby forcing you to start all over again. So, plan ahead for lights by slowing down and downshifting (again, same procedure, only in reverse, at slightly different speeds) well ahead of time.

The bad news is that shifting without a clutch (even if you have a good clutch, and just do it when shifting from 2nd on up during everyday use) places stress on the “synchro rings” in your transmission, and will eventually turn your xmission into an expensive paper weight.
Thus, the invention of the clutch in the first place. The clutch is the sacrificial lamb. It’s cheaper to replace a clutch every decade or two than to replace a transmission even once.

Bottom line, it’s nice to know how to shift without a clutch, and you can certainly practice it to get your upshift/downspeeds commited to memory just in case, but you’re way better off using the clutch on a daily basis!!!

Also, get into the habit of taking your foot completely OFF of the clutch (your left foot should always be on the carpet unless you are actively shifting gears) as you climb through the gears. Also, get out of the habit (if you have it) of resting your hand on the shifter as you’re cruising along. The shifter needs to vibrate slightly due to things taking place in the xmission as you drive. Resting your hand on the shifter might make you feel cool, but it isn’t doing your xmission any good…

JJ Richard

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(Discussion below applies to automatics)
I was told that in snowy or icy conditions, putting your car in neutral while braking will lower the time needed to come for a full stop. True enough. I’ve adopted the habit, and extended it to all weather conditions. My stopping routine consists of taking my foot off the gas, wait till my speedometer falls to 10-15 mph, throw the car in neutral, and apply the brakes. Of course, I might nudge the brakes a bit while decelerating to 10-15 MPH, depending on traffic conditions (unless I have to come to a full, quasi-instant stop or major emergency slowdown, in which case I forgo the niceties). All in all, this method slows down wearing of the brakes, as they don’t have to fight the engine as it still tries to propel the car forward.

My Q to the group: Do I really have to wait to decelerate to 10-15MPH before putting the car in neutral? What are the optimal numbers?

More fundamentally, can somebody defend my practice? It’s second-nature to me now, and I have had passengers think that I’m out to lunch.