Downshifting certainly can help you to slow down. However, the brakes are more than adequate to slow the car to the limit dictated by the ABS, which is dictated by the grip of the tires. You can use the engine to assist in slowing, but (a) it gives no advantage over the brakes, and (b) you're better off putting the wear on brake pads than the motor.

I like the point about smoothness, but, speaking for myself, I can apply stopping power much more smoothly with my brake pedal than by downshifting.

To my knowledge, race car drivers do not use the motor to brake the car. They use the brakes to slow the car and heel/toe downshifting to avoid braking the car with the motor. I have no idea why truckers downshift, and I'm not sure what percentage do vs. don't. Maybe the brakes on trucks have different issues than those on cars??? Keep in mind that a lot of things people do while driving are based on (1) misinformation, (2) tradition, or (3) my father told me to do it that way. Some examples:

>>Putting premium gasoline in a car rated for 87 octane. Myth: it's good for my car, or it gives me more power. Truth: Higher octane simply gives more resistance to knock. If your car doesn't knock with 87, then higher octane gas does you no good.

>>Stepping on the gas pedal while starting the car. Good if you have a carburetor, but not if you have fuel injection.

Maybe some truckers downshift because that's the way they were taught to do it a long time ago?

 

1.) I agree that I dont know what race car drivers do, I would love to ask one
2.) Truckers have exhaust braks/jake brakes that when you down shift that is the crazy noise the trucks make and truckers can get fined HUGE money for doing it in the city. I always thought it was because it helped save money on breaks and didn't affect gas mileage to much. But again that could be the driver of the myth and really it is doing that.
3.) I put premium in my car if I am going on a long trip on the highway, I believe that it clears out some of the carbon and allows the engine some time to clean up, because of the extra refining time the gas tends to be cleaner. I think anyways but again could be a myth thing. But i totally agree with you on the my car has more power yo if I put 103 octane into my civic.
4.) I cant agree with you more that there are probably more ficitons/myths than fact about cars than actual engineered truth. Maybe that would be a good TV Show to start.

Long story short I agree that if you can brake PROPERLY that you shouldn't NEED to downshift, but I know that most people (myself included) cant drive my machine to its limits safely. I just know what I have learned on the seat of a bike, and I KNOW for a fact that downshifting helps slow you.

 

If I were a driving instructor . . .

I would tell every student to take his/her car to a nice straight, quiet road, wait until there is nobody behind him, get to 60 MPH, then brake as hard as possible. Repeat frequently, and learn how the car reacts. As time allows, practice different degrees of braking.

I can make people's heads spin by hitting the brakes in my 944 and Boxster.

Also, in my ideal world every driver's ed class would make use of a skidpad to teach drivers how to deal with oversteer and understeer.

 

I've been told by more than one tech that using the engine to brake is just stupid. By downshifting into a lower gear it was explained to me that it puts stress on the clutch and engine... which would you rather replace, 60 buck brake pads or new clutch for 600-1200 bucks? I'll take the pads, thank you very much.

 

I dont know about putting higher octane than the recommended octane from the manufacturer.

The engine was designed for that octane. Therefore higher purity gas can ignite to early, or lower purity gas can ignite to late.

This would mess up the timing? And actually decrease your hp or engine output.

I always put the recommended fuel grade.

 

Octane...look it up. Will not cause pre-detonation!! unless you have a 12:1 compression ratio, then will need higher octane. Octane is a gasoline rating given to its resistance to pre-detonation! Therefore a higher octane rating will have more resistance to ignite prematurely due to compression heat.

The lancer engine is 10:1 compression and will work fine with 87,89,91 octanes, hell you could add an octane booster if you want, it won't do a thing. No way can higher octane harm it or prevent it from fully igniting. A spark will ignite the gasoline fine...its a hot spark. I would run a good 87 octane quality gas with necessary detergents in to to help keep your engine "clean". Personally I run 89 octane because some gas station will only put the better detergents and such in the high grades.

If you notice in the manual it states a "MINIMUM" of 87 octane, you can go higher if you wish. But until you can play with advancing spark timing, there is not really a need.

I know this is off topic so I will flag myself but I wanted to clear this up for the non-gear heads!

 

my F4i had a decrease in performance when I put 93 in (89 recommended). I think it was because it wasnt compressed to its critical point enough and not all the fuel was burnt. I was running about a second slower and the powerband felt more jerky

Sorry Ill stay on topic too.

 

Let's just accept that people have been arguing about the gains/losses with higher octane for years. There is never going to be an exact answer.

So let's move on.

 

Over the past few minutes I wrote something for another thread, and it got me thinking about this one again.

BMW and Acura have recently been setting up their sequential automatic transmissions so that a command to downshift is followed by a "blip" of the throttle to rev the engine. I think other makers (maybe Ferrari and Porsche) are doing this, too. So, a command to downshift results in the following sequence of events:
1. Command
2. Disengage transmission from engine
3. Rev engine
4. Engage transmission in lower gear

This is done specifically to prevent the engine from slowing the car while executing a downshift. Basically, the computer does the automatic equivalent of a heel-toe downshift in a manual.

On another note, while I have never spoken to a professional driver about the downshifting issue, in over a dozen outings at Summit Point with Porsche Club and many autocrosses, I have never even heard the idea of downshifting to slow the car mentioned. Rather, PCA instructors specifically teach drivers how to properly use brakes to their limits, and (when the driver is ready) how to do a heel-toe shift to avoid slowing the car with the motor.

Sorry if I'm beating a dead horse , but I find the issue of the sequentials that do the throttle blip to be interesting. I wonder how this would apply to a CVT???

 

After all this info, I too, am curious that about the CVT.
I have heard both sides that you should and shouldnt downshift except for quick accleration purposes.
Funny thing is on the CVT, the car does downshift under sport mode. While the car slows down, you are watching your gears downshift on it's own.
What does this mean compared to what we are all reading here?

I am under the impression that you can downshift as long as you are downshifting on the right speed and on the right RPM.
When people are upshifting, some people who are not the best at shifting, choose a RPM mark to shift. EG, on 1st gear some people who are not real familiar with manual trannies, shift when they get to, say, 3500 rpm and on the second gear, the same on the next and so forth. When downshifting, some people are looking at the speed. ANd choose a point of downshifting.

I have heard numerous ways of shifting.
Even if you were to GOOGLE, 'Manual Shifting Instruction,' quite a few do recommend downshifting while others do not.

I have downshifted before and I have used strictly my brakes. But I don't downshift until the car is already slowing down to like 25-35 mph. Depends on what speed I was maxing before i decided to downshift.
e.g. 60mph and I would use the brakes to like 35-40mph and THEN i would start to downshift. There is no shock, it's just smooth.

But since, everyone is throwing in their change, so am i.
I could be doing it completely wrong. And if I am, I hope someone corrects me.

 

It is very simple: DO NOT DOWNSHIFT FOR THE PURPOSE OF SLOWING YOUR CAR!!! Slowing your car is what your brakes are for.

Of course, when you slow down you will at some point want to shift to a lower gear. That is for when it is time to ACCELERATE again. Not for slowing down! Most of what I am about to say I have said in previous posts, but here's a summary:

1. When casually slowing to a stop (e.g., approaching a red light with plenty of room to stop), put your shifter in neutral and coast to a stop using your brakes only to stop the car.

2. When needing to stop in an emergency (e.g., a deer or child runs in front of your car), keep both hands on the wheel and step on the brake as firmly as possible (assuming you have functional ABS). The ABS will limit the brakes to what the tires can handle under the given road conditions. I will emphasize again, KEEP BOTH HANDS ON THE WHEEL! If you try to downshift the car under such circumstances (1) Why are you screwing around with the shifter when you should be giving your full attention to the crisis ahead? (2) Downshifting will NOT give you any more usable stopping power than the brakes will give you!!! This is really a simple matter of physics. If you don't believe me, then find an empty road somewhere and make a chalk line. Approach the chalk line at 40 MPH and hit your brakes as hard as possible. Mark the point at which you stop. See how controlled you are as you stop. Then go back and approach the line again. Attempt to stop the car as fast as possible by downshifting. Check the distance, and check how much control you have over the car. I hope you don't toast your motor on the second run .

3. When making a turn, use the brakes to slow your car. Once your car has slowed to an appropriate speed, then downshift to a gear appropriate to the speed. If the car lurches upon executing the downshift, then you went into too low a gear. Use a higher gear for that speed to avoid lurching the car with the motor. If you are doing serious driving (e.g., on a track or autocross), then learn how to heel-toe. This allows you to brake for the turn, shift into a low gear, and rev the motor to avoid lurching the car, all at the same time. The advantage of the lower gear is to have more torque to accelerate through and out of the turn.

4. When descending a steep hill, use a lower-than-normal gear to MAINTAIN a reasonable speed. However, you should still avoid using the motor to slow the car from that speed. If you need to slow or stop, use the brakes!

Here's an analogy to consider: You're going to take up skateboarding. A friend recommends that you wear a helmet every time you ride the skateboard. You are concerned that you might take some spills and scuff up a $100 helmet. So, you decide not to wear the helmet. Well, you'll save yourself from scuffing up the $100 helmet, but increase the possibility of suffering a serious head injury.

When it comes to my car, I am perfectly happy to use the brakes to stop my car, figuring that I may have to replace $80 worth of brake pads every 50,000 miles instead of every 70,000 miles. I'll do that rather than risk damaging my motor or transmission by using the drivetrain to slow my car!

If Ferrari, Porsche, Acura, and BMW figure you should not slow the car by downshifting, then I think that's pretty good advice .

 

If, when you release the clutch, it is smooth and there is no lurch, then you have shifted into the appropriate gear, and you did not use the motor to slow the car. That's good.

If you release the clutch and the car lurches, then you should have gone into a higher gear or further slowed the car with the brakes. (Or, if you want to accelerate in a hurry from the slowing, you could get on the throttle (as in a heel-toe) to "rev-match" the car prior to releasing the clutch and accelerate smoothly from a lower gear.)

 

On the other hand, if you expect to come to a stop, then why are you downshifting at all??? If you expect to come to a stop, then its neutral and off the clutch until you are ready to go again.

Rant finished! I need a beer.

 

lol

Uh. I am speaking mostly of the CVT.
I should have specified that.



and
I think i got YOUR point.
No downshifiting.
Use brakes. That's what they are their for.
Dats no good.
Right?

Cool
Have one on me.

These lil icons are so funny.




P.S. You had 2 Porcshes? lol damn

 

Back in '97 I paid $6,500 for my '86 944, and in '04 I paid $29,000 for the '99 Boxster. So, between the two cars I paid less than many people pay for a new SUV.

Despite not having much power, the 944 was a great car. Over 10 years it never let me down on the road, although it did put me in a bind once when the clutch failed going into turn 3 at Summit Point . Given that the clucth had 230K miles at the time, I can't really fault it . Over those 10 years I did have my share of issues though: failed motor mounts, leaking power steering hoses, failed clutch slave cylinder, etc. Fortunately, I could do a lot of the work myself and that saved a lot of money. It seems to me that most mechanics see "Porsche" and the dollar signs in their eyes light up!

I bought the Boxster with 17,XXX miles on it, so it was practically a new car. It is not my daily driver, and it just crossed 30K miles a month or so ago. It's a really sweet car. Still not a power hog, but really a joy to drive. It's a lot of fun in an autocross, but I'm still debating whether or not to track the car. I'm tall and don't fit in the car with a helmet on and the top up (I can autocross with the top down). Also, my head sticks up above the roll bars, and Porsche Club would make me modify the car to track it. Furthermore, if I killed the 944 on the track it wouldn't have been that big of a financial hit. If I were to have a serious incident on the track with the Boxster, that would hurt (in the wallet and possibly in other ways).

Back on topic, on the way home from work last night I did some experimenting with my Lancer . On a wide, dry, two-lane road with no other cars in sight, I took the car to 60 MPH and stomped the brakes. The ABS kicked in immediately, and the car decelerated dramatically but under control. The rear end did fishtail a tiny bit (probably not more than 15 degrees of its axis), but nothing in any way frightening. I repeated this experiment a second time with the same result. Being a scientist (a PhD in biology), I was temped to do the other part of the experiment: stopping the car from 60 with downshifting. I quickly decided not to do this part of the experiment, though, for two reasons: (1) I bought the Lancer on July 13 and it now has 2200 miles on it; I really don't want to toast the drivetrain at this point. (2) The fact that the ABS kicked in immediately proves my point that downshifting would provide no added benefit. Short of steering the car into a wall, a tree, or another vehicle, you simply cannot slow the car at a rate greater than what the ABS will allow. Since the brakes take you to that limit instantly, that's the end of the story.

I'll go back to something Cosworth said previously about the tires and the analogy of pushing someone over. It is an interesting take, but the analogy does break down. First off, let's simplify the situation and assume the car in question is always traveling in a straight line (we'll take spins, etc. out of the picture). In a normally functioning car, tires are what limits the ability of the car to decelerate. That's just the way it is. This is clearly demonstrated by the fact that stepping on the brakes can easily lock up the wheels (in a non-ABS car) or kick in your ABS. If you put old VW Beetle brakes in a car with Dodge Viper sized wheels and slick tires, then that would change. I imagine you could not lock up the wheels in such a car. But, in normal cars, the friction between the tires and the road limits how fast you can stop.

Consider a car that is moving forward in a straight line and braking, the force of the road acting via friction on a tire on the right side of the car turns the wheel clockwise. The brakes act on the rotors to oppose the force exerted on the wheel by the road. At the point when the force of the brakes exceeds the force exerted by the road, the wheel stops turning and skids (the job of ABS is to reduce force exerted by the brakes just before the point where the wheel stops turning). Cosworth's pushing analogy breaks down because the wheel doesn't care how smoothly or "unsmoothly" we get to that point. Rather, it's basic physics. If the force from the road is greater than the opposing force from the brakes, then the wheel turns. If the force exerted by the brakes is greater, then the wheel locks. That being said, a person in a non-ABS car is more likely to pass that limit when braking in a panic than when braking smoothly, but the limit doesn't change. Conversely, if I wanted to, I could lock the brakes on my 944 perfectly well by braking smoothly to the point where I exceeded the traction limit of the car. After some practice, I got very good at hitting those brakes really hard without hitting that limit. A car with ABS simply cannot be "pushed over" as the ABS will prevent the car from reaching the traction limit. (Actually some cars, like my Boxster, will allow the wheels to lock a little bit.)

OK, so my full-time job is as a biology teacher. Being a car nut and a teacher, I get into this sort of thing .


Back to work