How driving at low RPM affects the clutch in different gears.

[shane92w]

Hi there,

 

I drive an 07 Skoda Fabia VRS. 

 

In relation to minimising the stress going through the clutch whilst driving, I've been told by quite a few people that driving in 6th gear at low RPM, say 1500 RPM for arguments sake, is bad for the clutch, and its not as bad to drive at low RPM in lower gears. If this is true why is this so? Does the total weight of the 6th gear assembly weigh more that the 1st gear assembly?

 

I thought it would only affect the clutch if you were to accelerate harshly at low RPM, and that this isn't a good idea in any gear but it would be worse for the clutch in 1st gear than in 6th because 1st gear accelerates faster i.e. produces more torque.

 

Any thoughts would be appreciated,

 

Thanks.

[silver1011]

The clutch is the least of your worries, this type of driving style (encouraged for improved fuel economy) also has implications on the life of dual mass flywheels (DMF's) too.

[softscoop]

To accelerate from 1500rpm in a low gear requires far less effort from the engine than accelerating from 1500rpm in a higher gear.

 

The engine will actually produce more torque in higher gears as it has to overcome greater forces to continue acceleration compared to lower speeds.

 

This is why HP vs speed is not a 1-1 relationship.

 

A car to do 100MPH does not need much HP. To make the same car do 200MPH requires a lot more than 2x the HP.

http://www.physlink.com/education/askexperts/ae462.cfm

[KenONeill]

More to the point, the low mechanical advantage at low revs in a high gear stresses the dual mass flywheel, and causes it to wear faster!

[countryboy]

Driving at low revs in a high gear is more stressful for a clutch and drivetrain when you put your foot down as you don't get the mechanical advantage in the lower gears to accelerate the car, also a faster turning shaft can transmit more torque than a slow turning one. That is why on tractors there are 2 standard power take off (PTO) speeds, 540 and 1000 rpm, you can only use the 540 rpm PTO setting for implements needing no more then 65 hp. The same true for car transmissions.

Ian

[shane92w]

Thanks for the comments folks, I have a better understanding of this area now. I'll be mindful of this next time I'm thinking I could get away with 6th gear for fuel efficiency, a flywheel is more expensive than some diesel!

[XLBaconDoubleCheese]

Being in the correct gear will save you fuel too, low revs and trying to pull away will result in chucking loads of fuel in for little gain, so it's win win!

[countryboy]

A diesel, in fact any engine, will produce it's best efficiency when running around peak torque, that is when you get the most bang for your buck, irrespective of absolute fuel consumption.

Ian

[Delberthot]

I'm having a look around the internet but haven't been able to find anything as yet:

 

Around about Christmas I will be going from a normally aspirated 1.8 Honda Civic to a 1.2 105PS Rapid. This will be my first turbo charged car.

 

I would like to drive as economically as possible but want the car and therefore the engine to last around 10 years (more if possible) which will be roughly 110000-120000 miles at the 10 year mark.

 

At the moment if I am accelerating gently in traffic I'll normally change into 4th at 30mph, 5th at 40 and 6th at 50. If I want to accelerate quickly or overtake then I will always change down to the appropriate gear.

 

From reading this thread trying to accelerate quickly in a high gear will cause premature wear on the engine and reduce fuel economy so is there a fool proof way to know what I should be doing at what point when I get my new car?

 

i.e. what speed should I be in for each gear or should I look at the peak torque figures as mentioned above for each gear and go for that?

[XLBaconDoubleCheese]

It's more a diesel issue with the extra torque they produce so doubt you'll have any issues in your 1.2 tsi