learn how to downshift with rev-matching.
while the clutch is in, blip the throttle to where it will be when you engage the gear (usually +~500rpm per gear downshifted). if you do a straight downshift, you’ll notice that the car will jerk (due to the difference between driveline and engine speeds matching up) and the revs will jump up. rev matching makes for a much smoother downshift and is easier on your transmission and synchros.
the actual act of shifting should be really gentle- the gears should almost put themselves into place if all your rpm’s are matched properly.
Yes, but truck brakes are marginal at best. Air brakes work differently than the hydraulic brakes in cars. (Although I couldn’t find out on HowStuffWorks). I believe that if the air pressure drops too low, the brakes stop working. So any small leak in the system can degrade braking performance.
I believe on power brakes there is milliseconds of delay before brakes can provide maximum braking power. I don’t believe you can downshift that fast. If you should happen to stall you car in an emergency stopping situation by downshifting too late, then of course your power brakes stop working in short order. I would be surprised if there is any measurable difference in stopping a car whether you downshift of not. Given that you are not putting your full attention to braking, it could even possible take longer to stop a car while you are downshifting. Granted if your brakes are not properly maintained, then yes, downshifting would provide a great amount of help.
I suppose this whole downshifting to decelerate debate should be put to a scientific test.
Logically, the benefit of downshifting while braking should be minimal. Cars on sale in the US market today can stop from 80 mph - 0 (115 ft/sec) within 150 - 270 feet using brakes alone.
How long would it take to slow a car from 80 mph - 6 mph using engine braking alone? It’s no contest. Engine braking could theoretically help a little, but how much and why risk killing the engine or dividing your attention? (Dilbert)
I used to downshift to decelerate all the time because it sounded really cool and those 1st gear downshifts can slow the car in a hurry without activating the brake lights. (don’t ask)
On my current vehicle I ran some tests and noticed that aggressive downshifting yielded a 10% loss of gas mileage per tank and who knows how much I shortened the life of the clutch and valvetrain.
True, but don’t be afraid to rev it when needed, though. Going uphill, accelerating, all could be decent reasons to keep the revs up. Most petrol engines can safely go to 5,000 to 5,500 RPM for a while. And revving a little whilst accelerating isn’t bad either: a car that’s always shifted at 3,000 RPM will drive like a ‘lazy’ car, of that makes sense. A lively driver makes for a lively engine. Hell, if I drive to my yearly winter holiday in France, most of the while my 1400 cc engine is between 4,750 and 5,000 RPM on the French highways, for hours on end. We’re talking a 1,000 kilogram car, three occupants, a shitload of luggage, and a luggage box for the skis and snowboards. No problem whatsoever, with a puny 75 BHP to tag it all along.
Good intention, but it needs elaboration. True, this is not about driving a manual per se, but: make sure you’re at sufficient speed when you move over in the other lane to pass. Accelerate in third (for most cars) whilst behind the other car, closing the gap. Pass in fourth. Upshift to fifth after moving right again.
When was this? Sure, “overdrives” were common in the late 70’s, but I know of no moders cars (except automatic transmissions) that still have a full-overdrive 5th. Most if not all modern manuals reach top speed in 5th - or sixth, as the case may be. It is true that fifth will give you the best mileage on the highway, even if it’s not an overdrive: it still produces less revs at the same speed than driving in 4th.
Eh? How on earth would it fry the electronics? You’re just mimicking the starter engine (which won’t work, mostly because your battery died for whatever reason) by making the engine turn with the iginition on. Maybe there is some drivetrain wear from popping the clutch in second (first will just STOP the car whilst push-starting), but it can’t be a lot - and push-starting is rare anyway. How would it have any effects on the electronics of a car? When it starts, it starts and runs. That’s it. I’ve never heard a manufacturer or expert advise against this practice.
Funny then that all road side assistence services I’ve ever encountered will gladly jump-start your car if you’ve run out of juice. Surely, they would tow you and charge you more money if they possibly could.
I’d be interested in seeing a cite on that (that isn’t referring to trucks). I believe the experts are pretty much in agreement that downshifting is unnecessary for slowing down your car. The only exception is if you are applying the brakes on a long downhill stretch and there is danger of them overheating. Brakes can fade if you get them really hot - but that doesn’t happen under normal conditions.
You will wear out your thowout bearing and/or clutch and/or syncros sooner than necessary, and there is no reason to do so, since the brakes will stop the car just fine. Replacing brake pads costs only a fraction of a new transmission. Look at it this way: the clutch and transmission parts have a finite life; if you shift gears X number of times more than I do because you are downshifting at every stop, doesn’t it stand to reason that you will wear out those parts that much faster?
I had this argument with a friend. He liked to downshift through all the gears, all the way down to first, at EVERY stoplight. He said he did it to save wear on his brakes. I told him it would cost him more in the long run, but he didn’t believe me. Sure enough, his throwout bearing failed last spring, and he had to pay for a new clutch. And that’s not cheap.
BTW, overheating and fading is the reason race car drivers use engine braking: they make emergency stops at every corner. A Formula One car can take it, but your “average” Porsche 911 with super-powerful Brembo brakes will experience fading - let alone a lesser car. And once the brakes fade, engine braking DOES help a bit.
Of course, on the road this doesn’t apply, unless you brake full force at every traffic light.
Also, a car with ABS per definition has four disk brakes. No drums and ABS.
Now I’m going to ask a pretty naive question… What is downshifting, and how do you do it?
My 2c on the downshifting thing…
Yes, the experts are in agreement that downshifting a modern car to slow is unnecessary and potentially expensive in the long term, however it’s also fun.
In the real world, whether I use braking only or a combination of braking and downshifting depends on the conditions. It also depends on my mood (am I the first to admit this?).
If I’m in a “sensible mood”, I’ll still downshift sometimes if the conditions warrant it, but I will use lots of braking, and might bypass some of the gears. Maybe from 5th to 3rd only, all the while making the brakes do most of the work (Before someone jumps in here, I’m talking about dropping to 3rd at a reasonably appropriate speed, not when I should be dropping to 4th), then more, stronger braking, and clutch in -still in 3rd -just before the engine starts to lug as I roll to a stop.
If I’m in the mood for enjoying my car, I’ll more aggressively shift down through all the gears relatively early (just as I’ll shift up relatively late), and rely the brakes a little less. I do this in the full knowledge of the potential costs on the drivetrain compared to the cheaper brake overhaul. I weigh this factor against the enjoyment I’m getting out of the car. Hey, it’s my car. This is different from person to person. Indeed, it’s different from day to day for one person depending on mood, so I don’t think there is a “correct” method.
Assuming I’m feeling sensible and boring:
Scenario 1 In good weather and traffic conditions, I’m coming along a flat road at an appropriate speed and there is a set of traffic lights 200 metres (or yards or whatever) away. They flip red, and I know they’ll be red for awhile. I won’t engine-brake. I’ll leave it it 4th or 5th or whatever I’m in, and just gently brake the car up to the stop line at the intersection just as I would in an automatic. I’ll leave the clutch engaged until I’m down to about 20km/h.
Scenario 2 The same piece of road and weather conditions as above, but when I first notice the traffic lights at a distance, they have already been red for an unknown amount of time, and may go green suddenly. I’ll downshift through all the gears, but I’ll do it gently, and rely on the brakes primarily.
Scenario 3 The lights are on the other side of a curve so I can’t see them until late. It’s raining, and it’s evening rush hour. I’d downshift early (but not too early -don’t want to lose traction) to enable me to be in a lower gear than usual for the speed (I may even have to rev it up slightly). Then I can let the engine slow me down as required (not the clutch), and I also have plenty of potential acceleration which may be needed on a busy road when people are doing erratic lange changing etc.
Downshifting is changing to a lower gear to slow the car down.
If, for example you’re doing say, 40mph in 4th gear, and you shift into 3rd, your car will slow down (and your engine will sound briefly louder because it is taking an extra load).
TheLoadedDog, you drive exactly like me.
So, are speeding tickets expensive down under? 
Now to add another question… what is the correct way to brake? Under normal driving conditions, say…
Do you just let off the gas and let the engine start pulling the car slower and then press the brake, or do you push in the clutch and use the brake?
Just let off the gas, and apply the clutch when the engine starts to near its stationary revs. Say, you’re in fifth, and you brake for a traffic light. Just let it in gear, and engage the clutch when you’re doing 15 MPH or so. Maybe 20, depends on your gears. But you’ll know it when you hear it. If you have a rev counter: deploy the clutch when it drops below 1200-1500 RPM.
I’ve probably driven a manual transmission fewer than twenty times in my whole life, so I haven’t really formed an opinion on the whole downshifting thing.
But I do remember that Cecil wrote about it a few years back…
So when you’re stopped at a stop light, do you put the car in neutral, or keep it in first with the clutch down?
I told you I had a bunch of questions!
Ah, that’s a whole 'nother debate there, my friend.
The Experts say it’s best to leave the car in neutral, as keeping it in first will wear the clutch faster (more specifically, a particular thingamajig within the clutch that I forget right now:)). I never bother, and leave it in first. Well, unless I’m in a traffic jam, or the bridge just opened or something.
I doubt the wear on the clutch from leaving it in first is significant compared to, say, riding it all the time, or perhaps from shifting badly (with too much revs, and/or with a sudden pop when shifting gears).
I speak of the US market, I presume Coldfire speaks of the European market. In the US we have this annoying federal regulation known as CAFE that requires all cars sold by a manufacturer to achieve an overall average of 28 miles per gallon on the highway. The only way to achieve this goal (among other things) is for the highest gear to be super lazy and super-overdrive. A manual transmission fourth gear ratio in the States of 1.0 or less is common and a fifth gear ratio of 0.70 or less is very common. Ratios of 30 or more mph/ 1000 rpm in fifth gear are common here. In a four cylinder application, to combine such tall gearing with low torque and a narrow powerband gives a situation where acceleration in fifth is, let us say, leisurely. The gearing is usually so tall that the car does not have enough torque to achieve the torque peak or horsepower peak, let alone redline.
For example, at 3700 rpm, the car is making 100 mph in fifth but the engine is only making 70 bhp at 3700 rpm and still 1800 rpm short of horse peak. Aerodynamic drag exceeds bhp and the car stops accelerating. Downshift to fourth, revs jump to 4,500, smack in the middle of the powerband, and the motor pulls cleanly to 5,000 rpm and 110 mph. Therefore top speed is often achieved in 4th (it’s usually closer than my example) which is geared such that it can almost always approach the redline. More important than the relative top speeds, acceleration in fourth is always orders of magnitude quicker than in fifth.
Porsches and Ferraris are different, of course, and these will usually pull to the red in the highest gear even in the US because they are geared for top speed, not top fuel economy. Porsche and Ferrari owners in the US also pay “gas guzzler” penalties.
I would have to surmise that a VW Golf sold in Europe would be geared quite a bit shorter than one sold in the US: Europe has no CAFE rules and top speed is quite a lot more important in Europe than here.
Regarding whether to drive with brio or to drive like a grandfather, it’s a preference or a style more than anything else. If your goal is to minimise overall driving cost, shifting at 3,000 rpm is no crime. If you’re trying to maximise fun or get somewhere as fast as possible, “drive it like you stole it.”
Yeah, 'cept I’m supposed to spend most of the time on the left side of the road. 
Dunno mate. The cops have never caught me.
The only time you are going to need to downshift is if you reduce your speed so that you are going too slow for the gear you are in (called “lugging” the engine). Let’s say for example, you are going 45 mph in 4th gear, and you turn a corner. You have to slow down to make the turn, so you don’t want to leave it in 4th gear. So you downshift to 3rd (or even 2nd) before you get to the turn. But if you just jam it into a lower gear without matching revs like kryptonite2 explained (also called “double clutching”), your car isn’t gonna like you as much. And really experienced drivers will do some “heel & toe” where you actually get your foot half on the brake and half on the accelerator, so you can slow down for the turn AND match revs at the same time. But that’s getting into the “don’t try this at home” category. However, I think it’s a good idea to at least learn how to double clutch. It takes a lot of practice.
If you are coming to a stop (not just slowing down), you don’t need to downshift. Just put on the brakes, and put it in neutral when your speed is low. You don’t have to hit the clutch as soon as you hit the brakes - wait until you’re almost stopped, then depress the clutch. But don’t wait so long that you stall the engine. I leave it in neutral when I’m stopped, but I guess you could leave it in gear with the clutch in if you really feel the need.
Lucky dog.
Lorzenzo, I was not aware of the CAFE rules. So, are you saying that to achieve an average of 28 MPG for all models in a range, manufacturers gear their (less sold) manual four cilinders to get great mileage, so they can still ge away with selling 5 liter V8’s that do 10 MPG?
Still, I’m not sure if a brand like Volkswagen would be affected, or any European manufacturer for that matter. Four cilinders are more common with European brands, and 28 MPG is hardly a record number: it corresponds to 1 liter per 11.91 kilometers, something about 95% of all new European cars will be able to achieve at regular highway speeds. So, in short: I don’t think that American Golf is geared any differently than its European counterpart.
FWIW, my car willredline in 4th, but it will lose the fight against friction in 5th. Your story about torque bandwidth is valid, of course: with a full load and going uphill, I find myself cruising in 4th on highways for minutes on end sometimes. 5th will just mean the speed drops, and 4th means it will maintain it.