RF5BPilot

"Rev Matching" has become a widely used term in recent years and I could never figure out why we needed the term since we already had "double clutching."

Watching a Bondurant video the other day, I finally figured out that they're different.

3 Options for Downshifting

1. No technique downshift
Actions: Push in clutch pedal. Shift to lower gear. Let out clutch.
- Good for changes when you're going slowly. For example, you've slowed down for traffic, the engine and trans are already at near idle and you're going just fast enough that you don't want to shift into first. You can put it in second and just move on. Simple. Takes essentially no practice or training. (When I buy a used car with a manual transmission, the first thing I want to see is how the previous owner drives the car & trans.)
- Bad for most instances in that increases wear on synchros and the clutch. Can also jerk the rear end loose when you need the traction in a high-performance corner.

2. Rev Matching.
Action: Push in clutch pedal. Shift to lower gear. Blip the throttle to increase the engine rpms. Let out clutch.
- Good for high performance driving. Slightly faster than double clutching. Goal is to get the engine close the rpm's that it will be running when you let out the clutch. Reduces clutch wear. Makes a smoother transition to keep you from losing traction in the rear when you engage the clutch.
- Bad in that it has higher wear on syncros (because you have already shoved the stick into the lower gear before blipping the throttle).

3. Double Clutching
Actions: Push in clutch. Shift into neutral. Let out clutch. Blip the throttle to increase the engine and transmission to close to what it will be in the lower gear. Push in clutch. Shift to lower gear. Let out clutch.
- Good in that it reduces wear on both the syncros and the clutch. Makes a smoother engagement (like rev matching) to maintain traction. Will save you money over time with less servicing and wear on the transmission and clutch. There are older transmissions that require this. But all transmissions benefit from it.
- Bad - takes a little more practice to do it quickly and well. Takes a fraction of a second longer to do it than rev matching--realistically, only relevant to professional racers.

JDS968

Odd, I learned to time the rev match by blipping the throttle as soon as I get the lever out of gear, rather than shifting first and THEN blipping the throttle while waiting to clutch out.

Of course, I learned to rev match on a 968 which doesn't like to be slammed rapidly from one gear to another, so there's ample time for that.

S4ordie

How I learned and how I drive in performance situations. Why would this be much different than rev matching in terms of wear or potential damage.

alordofchaos

^ ^ ^ +1, though I would say I am blipping the throttle as the clutch pedal is at or very near the bottom of the travel, so that when I release, the rpms match for the speed/gear
Also, twice the wear on the clutch throw-out bearing, if you are worried about that kind of thing.

I wouldn't consider rev-matching a separate way of shifting, just something taht you do whenever you shift. As an example, once in a great while, I shift gears without using the clutch by rev matching.

Bill51sdr

I self-taught heel & toe (rev matching) on my first car. It was a POS Fiat 128 and I had to use this method to keep the damn thing from stalling out in between shifts.

Double clutching seems like you are adding an extra step to the heel/toe process to accomplish the same result..

Yabo

I want to see someone heel-toe-double-clutch... FTW

JDS968

I think you guys are conflating two different things here.

Heel-and-toe is a procedure to combine heavy braking with rev matching a downshift specifically to keep the engine in the powerband at corner entry.

Double clutching is just punching your left foot in twice instead of once. It could be used for any shift, whether you're upshifting, coasting, braking hard, whatever. It could be combined with a heel-and-toe downshift just like you would for a single clutch heel-and-toe downshift.

GTgears

My favorite video to post whenever this topic comes up...

mark kibort

its really a bit more complicated than this and there is one more option

yes there are 3 styles as laid out. all having to do with letting the clutch out in a high performance situation and not upsetting the car, one (#3) has to do with making the shift easier on the transmission by spinning up the layshaft in the transmission as you let out the clutch in neutral, rev the engine up and then select a gear, then letting the clutch out again. (AKA double clutch)

However, the reality is , if you drag the clutch slightly (not pressing it in all the way) you get the same effect as double clutch when you blip the throttle and that's what alll the GOOD racers do when they shift. the point here is, it doesnt take much dragging force on the clutch to rev up the lay shaft in the transmission while not effecting the job that the synchros do . you might notice if you downshift on a decel, you can blip the throttle and barely use the clutch, if at all and it slips out of gear to neutral... So, this means, you need very little clutch to get it into neutral, a quick blip as you pass through and then full clutch as you engage the gear. this makes for a near no wear situation for a downshift, AND with rev matching, creates no disparate forces on the rear wheels when letting the clutch out to upset the car. win win.

so, i would say, dragging the clutch is the best over all way to downshift. same effect as double clutching, but much easier and doesnt waste any time.

mark kibort

I dont think there is confustion about that. heal toe just allows, as you say, the brakes to be involved too.

makes little sense for upshifting, as naturally the RPM fall at rate that usually matches the RPM for the upshift in the time it takes to actually make the upshift

downshifting, the RPM between shifts would naturally fall and you want it to be usually about 30-40% higher. so, you blip the throttle. do this with dragging the clutch through neutral, even very quicly, and you effectively, "double clutch" without having to push the clutch in and out twice through neutral.

mark kibort

it really wouldnt make any difference if you push the clutch all the way to the floor, but dragging the clutch through neutral , blipping and then shifting will give a mimial sycnhro wear shift. (the double clutch effect) otherwise when the clutch is put in, the engine is separated from the transmission , totally. it wouldnt matter when you blipped.

actually, you want a little less clutch depression as you blip, through neutral, to spin up the transmission , that way you get the best of both worlds. reduced synchro wear to speed up the layshaft. (the engine does this with the dragging clutch) and engine matched RPM to road speed, so no upsetting the car when released. with out rev matching, you wear synchros, you wear the clutch and you wear the tires and upset the car if you release quickly.

noturavgm

One of my favorite vids if you've never seen it. Brocky single clutches 5-4, and doubles 4-3, and 3-2. Nice and smooth with mechanical empathy for a long race. All with one elbow on the door

Deadeye

Watching the NASCAR race at Road America last week they had a camera pointed at the feet of one of the experienced road course drivers. He was left foot braking and blipping the throttle to down shift with no attempt to use the clutch at all. I assume this is tough on the gearbox, but is this a common practice in these cars or just the road courses?

mark kibort

Nice!!

mark kibort

You can do this with dog gears. they are designed to just grab and are strong enough as well. The only downside is that if you get it wrong,its not so much a problem with the gear box being damaged, as it is to have the rear tires lose grip because of disparate rotation vs road speed.

im sure all of us have done this with our street cars. knowing the RPM, the street transmissions allow for no clutch engagement. upshifts are a lot easier than downshifts.