Why rev match???
When we have modern gear boxes with synchros what’s the point of revving to match the gears? Is a question that i got asked in a debate with my father. According to him it’s completely wrong.
With older transmissions, where you need to double clutch and rev match on downshifts to get the gears to match angular velocities, this is an absolute must.
But with the modern gearbox, it’s plain wring to rev match, or at least according to my dad. Every time he wants to access his car’s power band, and downshifts, he never rev matches and the car sort of violently shakes.
This to me seems like the perfect reason to downshift! But am i the only one who thinks like this besides racing drivers, and tractor drivers nowadays who have transmissions without synchros?
Comments
If you don’t rev match and just let the clutch up, it shocks the drivetrain. I prefer to revmatch for smoothness and because its fun to heel toe.
Why in the world would it be wrong to rev match? You save your gearbox a lot of stress and the ride will be alot smoother, you’ll get to access your power a lot easier and so on and so on…
You don’t need to rev to match the gears on upshifts. That’s what synchros are there for, to speed up the next gear and allow it to mesh nicely with the previous gear.
Rev matching downshifts is important because you are essentially bringing the motor (crank) RPMs back up to speed to match the higher speed of the lower gear. This reduces the stress imparts on the engine by the gearbox and also puts less stress on your flywheel and clutch.
I have though about it some more. And i think it comes down to this just as you said. You do not need to raise the revs of the motor in order to get into the desired gear on downshifting. The synchros do that for you.
What you still need to do though, is raise the revs in order for the clutch plates to match rotational velocities(or RPMs), just as what you said, the crank speed must match the speed of the gear box and that side of the clutch.
My first car had a really worn transmission, so I got used to double clutch down shifting with rev matching. It just got a habit, so I do it in other cars now, even though there is no need for it. And it prevents the syncros from wearing out.
Sorry… but your dad is well, wrong. Rev matching is absolutely essential to avoid damaging your drive train. Aggressively downshifting without rev matching means your jumping from one completely different power band to another. This puts stress on just about everything on the drive train/driveline - your gearbox, your clutch, your drive shafts, prop shafts and even your tyres.
If he’s deliberately doing it to slow the car with the gears (lifting the clutch slowly and gradually) that’s fine, it’s called engine braking. But if it’s drastically changing the physics of the car (jolting/shaking) then he’s damaging stuff.
More info here: http://www.drivingfast.net/car-control/rev-matching.htm
I just went out for a drive with my dad, and indeed what he does for examaple when doing 50km/h in 4th gear, and downshifting to 2nd gear is the slow way of release the clutch without rev matching. So he creates this engine breaking effect.
I can only imagine that this is also horrible for the clutch, as you are pretty much slipping it every time you downshift, after which he applies throttle and gets to the desired RPM range that he needs.
I was pretty shocked that he does this, as he is an engineer himself and has pretty good understanding of a car’s mechanics. As i said in the post, he never rev matched on modern cars, as he only did it on cars with older transmissions that needed double clutching.
But anyways, i’m glad my instincts were correct after all. And thanks for the info :)
I always use heel and toe when driving faster, and rev matching on downshifts to overtake someone as well. But double clutching doesnt make any sense in “recent” cars. Correct me if im wrong.