Braking with the gears what ridiculous practice

stumpjumper

if i may add my 5p (it might be a long post so it's a bit more than tuppence worth )

part of this discussion comes down to different cars.
I have a SAAB and a Mazda MX5 - both require different driving techniquies.

engine braking in the SAAB is almost non existant - indeed the Citroen C4 i had before that had virtually no engine braking at all... changing down the box bearly affected your speed. where as in the MX5 there is marked engine braking.

first off... where does this idea of excessive wear on the transmission come from? having the engine slow the car down does not wear the gearbox and clutch any more than using the engine to speed up the car.
the clutch is simply a brake - it only wears when the gearbox and engine are spinning at different speeds. if you rev match then there is no wear on the clutch.
what this means is if, as you change gear, blip the throttle to raise the revs so that as you bring the clutch in the engine is already at the correct speed for the new gear. the clutch is not needed to do any work to match the speed of the gear box and engine, and no wear has occoured.

to add to the debate - if i am approching traffic lights that are on red (in the MX5) and i am in, say, 5th traveling at 30mph - this is pretty close to idle, so i down shift to 4th, blipping the throttle as i go, and now i am travelling in 4th, my foot is off the throttle, but i'm not pressing the brake.. and the car is slowing. as my speed drops i will then drop to 3rd at about 20mph... at this point if the lights change then i am in the correct gear to increase my speed back up to 30mph. where i can then shift back to 5th. if the lights are still red then depending on my distance to the line and the traffic infront of me i will shift again down to 2nd at about 10-15mph, and begin to brake to the line, and shift into 1st.
this ensures that at any point i am in the right gear for my current speed, i am rev matching so i'm not wearing the clutch, nor the gearbox, as its only doing the same work as it would be accellerating me.

often i will use the old technique of double declutching - where i press the clutch once, and move into neutral, blip the throttle, dip the clutch and into gear. Sounds alot writting it out, but in reallife that action takes about the same time as changing normally, but i am reducing wear on the gearbox syncromesh as i am matching the spinning of the gears rather than relying on the mechanical device which does wear.

this is also helpful if the clutch stops working (which has happened to me - the hydralic line on the clutch got a leak and wouldnt always release the clutch) meaning you can effect a gearchange without the need for declutching.

the big thing is i try to read the road ahead so i dont need to change gear mid corner - i want to set the car up for the corner before i enter it - so i do all my braking and get in the correct gear in a straight line first.

and i certainly use engine braking on a descent - on a closed throttle your engine isnt using any more fuel, indeed on some modern engines when you let off the throttle on a long descent and coast down in gear the fuel system almost shuts down so is not using any fuel (or very little).

Pew_Pew_Pew_Lasers!_ wrote:

And when somebody changes gear mid corner to effect engine braking a FWD will be more likely to lose traction at the rear than at the front.

the main reason for this is what is called lift-off oversteer - the act of lifting off the throttle mid corner in a FWD car mean a braking force is applied to the front wheels - causing weight to transfer to the front, and unweighting the rear end - usually what happened is that the driver went into a corner a bit too fast, and the front tyres couldnt cope and the car would understeer away from the corner... the driver then panics, lifts off the gas... causing a braking action on the front wheels.. which causing the weight transfer, increasing grip on the front wheels and reducing at the rear, this then means the car turns in better... and the back end can not resist the increase in lateral force... and breaks away - causing the spin - pugeot 205s and SAABS where quite famous for this charatoristic. the best way to deal with this situation is left foot braking while keeping your right foot on the gas.

i think to sum up... is that i will use both engine braking and normal braking where nesscessary - i will use things like heel and toeing and double declutching to make the change of gear as smooth as possible.

so give an example...
travelling on the motorway, i'm behind a lorry which is travelling at 56mph. I'm crusing in 5th, and there is a long line of traffic currently overtaking me and the lorry. now i know in 5th i dont accellerate very quickly, but i can in 3rd or 4th.
now i spy a gap coming up thats safe to pull out into... i will double declutch, to bring the revs up while changing down either straight to 3rd, or to 4th depending on how quick i need to accellerate. my aim is to change down the gearbox, but make it as smooth as possible so if my passenger had his eyes closed he wouldnt notice anything other than the change in engine note.

and if i may - what was that about doing too much at once?
http://uk.youtube.com/watch?v=yyVHj3sHVHQ