Braking downshift and rear tires lockup
 

I got my BRZ a few weeks back and don't know whether I'm doing something wrong or otherwise. So if anyone can help it'll be great. Say I'm driving along a straight road at 80km/h (50mph) and am going into a slip lane for a 90 degree turn into a suburban street. I'll downshift down to 2nd gear and as I release the clutch (from 3rd to 2nd), the rear tires chirp (or slightly lockup). I'm tempted to ease of the clutch slower but then I'm worried about riding the clutch.

Slightly getting worried about how all this affects the life of the transmission/clutch :(

Can someone explain to me what's going on? and how can I avoid this?

EDIT for clarification:

What's happening is I'm travelling at50mph but as I'm going into the slip lane I am braking to the the appropriate speed of the turn about 30kmh or 18.6mph. Once I get to around 20mph I downshift to 2nd and that's when the chirp (lockup) occurs. I'm not shifting to 2nd at 50mph lol. I'm shifting to 2nd at 18mph just before the turn.

Do u blip the throttle by heel and toe to match rev when releasing clutch?

If u dont, try it.

Sounds to me like your not matching revs before you downshift.

Dang beat me to it.

I've had the same chirp (lockup) issue everytime I downshift but have since learnt how to rev match and now its fine. Still not perfect but getting there in terms of rev matching.

Haven't tried heel and toe to rev match going from 3rd to 2nd. Will have to get used to heel and toe'ing first. But question is, is it a must to heel toe and rev match and downshift in this car?

Heel toe will really only help on the track or when you have to down shift while braking. It is a VERY useful skill. I still suck at it. When I move my heel over I slam the brakes harder and it makes for a very sloppy shift.

It's not a must but your clutch will last a lot longer, your passengers will have a more comfortable ride and most importantly you will have a nice feeling of accomplishment in the fact that you're doing something well.

There's a saying in the Miata camp supposedly by the owner of Mazda: "Being one with the horse". It's the same with your car when you perform well. All it takes is practice, practice and more practice.

Another way to execute a heel toe downshift is to blip the throttle with the blade of your foot while using the ball of your foot to brake. It also helps to practice rev match downshifting (no braking).

Heel toe is very difficult to do right, especially with these pedals, but once you get it down it is a blast! There are pedals you can buy that move the throttle closer to the brake on this car making it easier to reach both.

Just a tip, its not really using your heel and toe, more of toe and side of your foot. At least thats how I do it. Check out youtube, there is a number of videos that will show you how to do it.

Why change into 2nd at 80kph in normal driving?
That's taking it up to 6,000rpm and certainly needs rev matching to save loading the clutch and transmission. Try using 3rd instead which will still take the engine up to over 4,000rpm and give good engine braking without so much load on everything. It's probably the right gear for the turn too, it's very flexible if you're just cruising.

What you doing is a drift technique called shift lock. Try downshifting at a lower rpm.

Sounds like 5th to 2nd;sure you were in 3rd?

Beat me to it :P

You’re doing something wrong, mate. ;)

I’ll bet they do. And you’re correct, you’re momentarily locking up your tires, which is to say they’re skidding. A tire that’s skidding like that has little to no directional control. Do that in the wet (it rains in Australia from time to time, right?) and while initiating a turn … and you’re likely to find yourself spinning around and quite possibly crashing. People do this all the time in the city and while the speeds are generally low, what happens is that they slap a curb sideways with the wheels and fold them under. Typical repairs are in the neighborhood of $5000 US and up. More if you flip your car on its head. You’ll be unhappy.

You’re changing down too soon and to a gear that’s too low. Change into second gear to go around a turn at 10-20 mph, perhaps. Use third gear, otherwise; it's good for 23–83 mph @ 2000–7400 rpm.

When you change down into second gear at 50 mph, while abruptly engaging the clutch you’re sending a shock through the drivetrain, the engine is acting as a brake on the drive wheels because it cannot instantly spin up to almost 6100 rpm at 50 mph, causing the rear wheels to lock up momentarily … and this is a scenario leading to a crash real soon now, especially in the wet.

Stop doing that.

Cruising along at 50 mph, an appropriate gear would be fifth or sixth gear.

Don’t change down into the next lower gear until the revs in the current gear are around 2500 or lower.

The tachometer (tach) will tell you this. That’s why God gave us tachometers for our sports/GT cars. They’re very important, even more so than speedometers. We need speedometers largely to avoid confrontations with The Law. The tach is for driving the car properly, keeping the engine in the appropriate rev range and power band as required.

By the way, before I forget, Sierra is an unusually knowledgeable fellow and you could learn a lot from him, AND he’s a fellow Aussie, I believe.

Exactly. Excess clutch wear is the inevitable result of “dragging” the engine up to 6100 rpm by slowly engaging the clutch. You MUST do that anyway, if you insist on changing down to any gear that zings your revs (rpms) up to 6000 rpm or even 4500 rpm. It’s too much and runs the risk of locking up the rears (tires). You don't want to do that. Not so much because it's abusive to your fine car, but because it's dangerous.

You MUST slowly engage the clutch, however, regardless of the wear issues, BECAUSE YOU’RE GOING TO CRASH OTHERWISE! It’s just a matter of time…

Crash repairs will easily exceed the cost of clutch disk replacement.

You should be worried, yes. What you’re doing is not only dangerous, skidding your rear end, it also subjects the clutch and entire drivetrain to unnecessary wear.

You CAN change down at higher rpms, but then you must learn to rev match properly. That’s why rev matching was “invented.” Precisely to avoid this problem and allow one to SAFELY change down through the gearbox at higher rpm while largely eliminating clutch wear (when done skillfully).

Heal and toe (sometimes a misnomer) is simply rev matching while SIMULTANEOUSLY braking. This is a technique for going faster, basically, and not running the risk, once again, of locking up those rears when charging into a corner.

Yes, there’s a lot to learn, but you can do it despite the initial awkwardness everyone experiences. It’s challenging, fun, and as Whaap alluded to, eventually you will “become one” with your machine.

It is immensely satisfying.

Keep working at it. And buy some good books on driving. Frankly, most of the youtube videos I’ve seen are poor at best. Do a search on “Skip Barber.”

Better still, find a good racing-oriented driving school at a local race track if you have such things in your area. It would be money well spent. I’d recommend that before buying hardware for your car.

I must run, now.

I hope this has been at least a wee bit helpful. :)

TL;DR - Either rev match, or shift to 2nd at a lower speed. Maybe drop to 3rd first. Brakes are cheaper to replace than your clutch, and you're only DD'ing, so no need to engine brake that harshly when you can simply use your brake pedal instead, then downshift at a more appropriate speed.

Holy cow!! If you keep driving like this you'll wear out your synchros, clutch, engine mounts, tires, and who knows what else. Stop that immediately! Read Porsche's post. Then read it again. Then try to apply it to your driving.

If the transmission was designed to be the primary force in slowing the car it would be gigantic like ones found in big trucks. There's a reason your car has brakes man, use them.

Use the drivetrain togo, the BRAKES to slow.

Why coming into a 90* turn so hot anyway? You've got to almost stop to take the corner, use more brake coming off the highway to scrub speed off and downshift only when your speed matches the lower gear.

Everything Porsche said is dead on.. follow it and you'll have a much more pleasant experience as well as a car that lives to tell the tale. ;)

Which is torture on your drivetrain. Mechanical sympathy is imperative to your car lasting to the end of its warranty period. This video taught me a lot:

[ame="http://www.youtube.com/watch?v=qbwu83MO3ts"]The Drift Bible by The Drift King - Best Motoring International Vol. 09 - YouTube[/ame]

Also worth noting -- you can do a rev-matched downshift without heel & toe action. More like just toe action. To gradually slow down you can do just the toe part. Simply blip the throttle, downshift one gear, and let engine braking slow the car. Once the revs falls and it's comfortable to downshift into the next gear, do it. Sometimes heel and toe driving is suited to more purposeful inputs rather than casual driving. But there's still a benefit to rev-matched downshifts because they are smoother, safer, keeping you better in control of the vehicle as a whole. Really they are the only way to downshift correctly, anywhere, ever.

Learning this stuff takes time. Be patient and reward yourself with ice cream often. (It'll give the clutch time to cool off, mr. clutchdraggerdownunder! :D )

I should probably make myself clear before everyone says I'm destroying the car by shifting to 2nd at 80kmh or 50mph...or before I'm notorious as mr.clutchdraggerdownunder

What's happening is I'm travelling at50mph but as I'm going into the slip lane I am braking to the the appropriate speed of the turn about 30kmh or 18.6mph. Once I get to around 20mph I downshift to 2nd and that's when the chirp (lockup) occurs. I'm not shifting to 2nd at 50mph lol. I'm shifting to 2nd at 18mph just before the turn.

I should've been more clearer in my opening post.

Then just rev match and let it out easier.

JDM

Check the reflexes in your left foot, or have your doctor do it.

Something about your story/scenario is not making sense, unless you are jack-hammering your clutch pedal and not reading your gauges correctly. Downshifting to 2nd at ~ 18 mph will not lock or spin the rear wheels unless you are on ice.

Unless you're into the turn at 30kph when you drop the clutch it makes no sense that it's chirping the tyres? I would select 3rd just before the turn which will be more 'serene' for normal driving, better on fuel and able to quickly get you back up to whatever the speed limit might be.

For what it's worth I don't find braking exciting unless i'm stepping on it a bit.
What I do enjoy, if no traffic is following and time doesn't matter, is trying to judge when to start slowing for an intersection or turn from 110kph without using the brakes. It makes a difference to fuel consumption to ease down to say 80kph then back right off down to 60kph, into 4th and then 2nd just before you get there ready to use that saved up fuel for a good quick squirt through the gears back up to cruising speed.

You really shouldn't be locking up the rear tires even if you thew it in gear and didn't even touch the gas to match the revs. Sounds odd. I'd recommend learning to match revs though as it can make certain components last longer.

If you can, get some vid of the scenario when you have a chance so we can see and hear what's going on. I think there's quite a bit lost in text here that we need to know to help you better.

How about you have your car in sports mode then break hard for the corner and then down shift the car will rev match automatically and you can then power out of the corner. All you need is a auto transmission on your BRZ!


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You wanna learn how to heel toe shift without damaging your car? Go buy a G27 wheel and go buy a PS3 and GT5. Bingo! Thats how I learned it, now I can easily rev match without using my real car as the learning tool. :)

Had a mate sit in the car to give me pointers. Turns out that I was releasing the clutch too quickly. When I was shifting from 3->2 there was a mismatch of engine speeds between the transmission and engine. When the clutch is suddenly engaged, one of these components (engine or transmission) has to play catch up so the rear tyres lock up or more accurately drag along the road.

See? What did I tell you? ;)

Yes.

Engine.

When you de-clutch, the revs drop towards idle speed of course. When you engage a gear, the rear wheels are now “driving” the input shaft and, thus, the clutch disk at the rpm determined by the road speed and gear ratio.

The clutch disk is spinning much faster than the flywheel which is connected to the engine. Abruptly clamping them together creates a shock and the slower one is suddenly dragged up to the same speed of the faster one.

Yes. Since the engine, via the flywheel, cannot speed up instantaneously to match the rear wheels, the drive wheels, rear tires here, are slowed dramatically and are literally dragged down the road, protesting loudly. The rear wheels are not actually locked up, they are skidding though, but it’s just easier to describe it that way since the dynamic effect is largely the same.

You’re very unlikely to crash doing this at 18 mph. Your tail end might twitch a bit, but if the car did start to go sideways on you, it would scrub off speed so fast that you’d be unlikely to loop it or hit anything.

ANY TIME you chirp the rear wheels under deceleration, you’ve done it wrong, mate. ;)

At low speeds, this is just poor driving, "sloppy," you know, and hard on the machinery. At high speeds it can be dangerous and can even prove to be fatal in the ensuing crash.

It is difficult to cover all the details while writing a description, and I’m too lazy to do a thorough job of it. I can do better talking to you in person. I'm lazy, I tell you!

Are you getting a handle on this business, now? :)

And you youngsters out there who are reading and trying to learn on this forum… is this making sense to you, too?

Any questions? :)

Love your explanations Porsche. That was a really thorough explanation and you say that's lazy? I can't imagine what the explanation would be if you weren't lazy, it'd be so informative and epic :)

I'm definitely understanding what's going on, now just need to put it to practice.

On a separate topic, would love to talk to you about NA builds but we'll leave that to next time.

Thanks.

I strive to be helpful ... not combative.

It's always nice when someone takes the time to recognize my efforts. It's good to be appreciated. :)

Came here to suggest 3rd as well. I bet he doesn't even need the clutch to engage 3rd smoothly at 18mph.

ABS kicks in because of the road? Just a thought...

This whole thread I've been bonking my noggin wondering how to lock the wheels at that speed...of course he would be just spinning them.

Totally deadly at higher speeds. First week I had the car, I accidentally shifted into 1st while being over eager in some local twisties; as soon as I started to let the clutch out I knew my mistake, but the car got sideways instantly. Clutched in and shifted to the right gear, correcting the steering wheel at the same time. Scary stuff. Don't play around not knowing what you're doing.

2 words: Rev match