Automatic Crawling Speed

[PsYTraNc3]

Would you like to have a crawling drag race sometime? I have a feeling diesel would win against petrol though.

Should be fun!
Right foot out the window to ensure that neither of us are cheating

 

[Rouxenator]

I'll put both feet out since I have a real automatic

 

[SykomantiS]

This is more applicable to dual clutch transmissions, which is not technically automatic. In fact, if you have a DSG, DCT, or whatever your manufacturer calls it, you shouldn't be standing on the brake pedal with your gears engaged because your clutch would still be engaged. But this is a bit off the actual topic.

So... How do you go about then standing at a red light? Most of these dual clutch ransmissions have an auto mode, no? So how does it work then?

I thought petrol, therefore power, could only be "issued" with the accelerator. I thought there may be a "leak"

As mentioned, there is still air and petrol flowing when the engine is at idle.

That's when you'd want to own a Merc with the 7G tronic transmission...2 reverse gears

Yep, same with our Rexton- uses an older version of the Merc 5 speed auto box. Has 2 reverse gears.

My civic (2.2 turbo diesel, manual) would crawl at around 9km/h in 1st, 16km/h in 2nd, can't remember 3rd, think it's something like 25km/h. In 1st (and 2nd to a certain degree) inclines are more or less 'n non-issue. It just goes, no problem.

The Rexton (2.7 turbo diesel auto) is also around 10km/h in 1st, can force it to pull away in 2nd, but I've never bothered to check the crawl speed.

 

[Rouxenator]

The Rexton (2.7 turbo diesel auto) is also around 10km/h in 1st, can force it to pull away in 2nd, but I've never bothered to check the crawl speed.

\
Never thought of that. My transmission has a snow mode which lets the car pull away in 2nd/3rd depending on the conditions. I wonder if that will affect the crawl speed.

 

[SykomantiS]

It will. I've used it in the rain once or twice.
Quite cool actually. Pull away is obviously slower, but f*** me, once you hit boost in 2nd I could swear it flies off the handle faster than 1st (which I assume has torque limiters in place), and then just completely lose all rear grip- which is why I guess there is such a thing as throttle control and restraint...

 

[Rouxenator]

My mom's W203 has that same 5 speed autobox, never tried the winter mode though... My autobox is an old school 4 speed with very tall gears.

 

[USZA]

So... How do you go about then standing at a red light? Most of these dual clutch ransmissions have an auto mode, no? So how does it work then?

Auto mode is the default mode, and then it has a mode in which you can change gears manually. Irrespective of mode, my manufacturer advises that you put it in neutral and engage the parking brake ala K53, which makes sense if you don't want the clutches to wear out.

 

[Sinbad]

This is more applicable to dual clutch transmissions, which is not technically automatic. In fact, if you have a DSG, DCT, or whatever your manufacturer calls it, you shouldn't be standing on the brake pedal with your gears engaged because your clutch would still be engaged. But this is a bit off the actual topic.

Incorrect.
The dsg has the clutches disengaged when you have your foot on the brake. It reengages them the moment you lift off.

Try putting your handbrake up then releasing the footbrake. You'll feel the car start to pull forward (back will dip a bit against the handbrake and the instantaneous fuel consumption will increase) for about 2 seconds, then it will disengage again so as not to drag the clutch.

 

[USZA]

Incorrect.
The dsg has the clutches disengaged when you have your foot on the brake. It reengages them the moment you lift off.

Try putting your handbrake up then releasing the footbrake. You'll feel the car start to pull forward (back will dip a bit against the handbrake and the instantaneous fuel consumption will increase) for about 2 seconds, then it will disengage again so as not to drag the clutch.

Thanks for clearing that up - didn't know the part about it disengaging.

Was just following the manufacturer's recommendations of not standing on the brakes. Anyway, the brakes last longer by not standing on them.

 

[Sinbad]

Thanks for clearing that up - didn't know the part about it disengaging.

Was just following the manufacturer's recommendations of not standing on the brakes. Anyway, the brakes last longer by not standing on them.

Lol
no.
There's no friction when the car is stationary and thus no wear on brakes....

 

[Priapus]

2.0 T - 6 speed - +-10/kmh while crawling.

Agreed, if I wanted to ruin my average consumption I'll do so by flooring it every time I pull away for a stop. I like how it hits 39.8l/100km under hard acceleration

Mine shows something silly like.. 99l/100km when I floor it from a set of lights.

Thanks for clearing that up - didn't know the part about it disengaging.

Was just following the manufacturer's recommendations of not standing on the brakes. Anyway, the brakes last longer by not standing on them.

Erm.. what?
While car is stationary its not.. moving.. so.. no friction on brake pads... no wear and tear?

 

[USZA]

2.0 T - 6 speed - +-10/kmh while crawling.




Mine shows something silly like.. 99l/100km when I floor it from a set of lights.



Erm.. what?
While car is stationary its not.. moving.. so.. no friction on brake pads... no wear and tear?

Erm? Did you read the rest of this thread?

 

[XennoX]

Just doubled checked the speed: 8km/h with and without aircon. 320nm seems to be more than enough torque for it to not make a difference

This may come as a surprise to you, but your car isn't producing 320 N·m when it's crawling.

 

[kanzen]

This may come as a surprise to you, but your car isn't producing 320 N·m when it's crawling.

You're right...it's only from 1400rpm

 

[ice_cubes]

tested mine yesterday +- 10km/hr petrol