Why use 6th gear?

March 14, 2006 11:35 AM

Just bought a Renault Laguna 1,9Tdi Diesel. My first Diesel and it has six gears - I am not used to the 6th gear - not sure it makes much of a difference between 5th gear - should I always be aiming to get it into 6th gear - is this to do with fuel efficiency?
posted by calvinorr to travel & transportation (10 comments total)

Yes, on the freeway you'll want to use 6th for cruising. In higher gears the engine runs at lower rpms for any given speed, less revs means less gas. Took me a while to get used to sixth in my RX8 but now it's second nature.
posted by zeoslap at 11:41 AM on March 14, 2006

The sixth gear is mostly there to convince car snobs that diesels can be fun and sporty. You should also get better fuel economy if you run the car in sixth gear. If the engine speed is low, you may have little or no acceleration in sixth. In that case, you need to downshift to fifth or fourth in order to accelerate and pass another car.

If you shift slowly, you may want to stick to 5th - that way, you can always accelerate out of danger, such as when someone to the left or right of you tries to change lanes into you without looking. If you can make quick gearchanges, then try to be in sixth as much as possible.
posted by b1tr0t at 11:45 AM on March 14, 2006

Turbodiesels typically have more low end torque than a comparable gasoline engine, since they don't rev as high. So you should be able to put that 6th gear to use.

Also, what they said.
posted by kableh at 12:13 PM on March 14, 2006

I drive a VW TDI and would love a sixth gear. It could really use it at high speeds—above 85 the engine and RPM count really seem to scream for one more shift.

Use it, so I might live vicariously through you. It will absolutely save you diesel and likely treat your engine better in the long run.
posted by symphonik at 12:24 PM on March 14, 2006

Cheers, what a great response.
posted by calvinorr at 12:59 PM on March 14, 2006

Could I piggyback on here with a small shifting question? I am acclimating (slowly) to driving on the crazy-assed hills here in Seattle, and sometimes I accidentally shift, say, into second gear going up, when I really need to be in first. If I can't switch back fast enough, I have to jam on the gas to get going. How much am I killing my car when this happens?
posted by astruc at 1:31 PM on March 14, 2006

astruc, bad piggybacker!

That being said -- yes, it's probably not the best to lurch up the hill in an inappropriate gear. I can't imagine you'll ever have a point where you can't realize your error and shift back into first quickly. Try to switch to the correct gear, not because of potential transmission damage but because you might stall the vehicle, and you may have learned by now how bad that is on a steep uphill grade.

However, in the time that it will take you to get used to the hills, you won't do too much damage. Just don't let it go on too long. San Francisco is very similar, and I adjusted to that fairly quick.

Transmissions are usually sympathetic to drivers learning new terrain, though I suppose it depends on what you're driving.
posted by symphonik at 1:58 PM on March 14, 2006

The trick to safely traversing Seattle's hills is to shift late. Let the revs build before you shift.

That having been said, the situation can be completely different when the pavement is wet. It is very easy to slip in the rain if you manage to send too much power to the drive wheels. In that case, you actually do want to shift up to second and give it plenty of gas. You will waste a little fuel, but you won't damage the engine.

If you want to get to know your transmission well, try turning the radio completely off for a few days. If the weather allows, roll your windows down. As you drive, pay attention to the following:
1. what sounds is my engine making, and how does that sound change as I drive?
2. In any given gear, does my car have an easier time accelerating at low or high RPMs? Is there a range at which acceleration is particularly good or bad? (remember these ranges, they are very important)
3. What sounds do my tires make?
4. Pay attention to the road surface WHILE looking straight ahead (don't look directly at the ground, follow the ground texture with your peripheral vision). When you roll over road imperfections, what do you feel in the steering wheel, pedals, and seat?

There aren't any generally correct answers, but if you pay attention to these things you will quickly develop more control over your car.
posted by b1tr0t at 3:34 PM on March 14, 2006

b1tr0t, thank you so much for the suggestion about wet pavement. I have been having definite problems with my wheels skating and was wondering how to correct. And symphonik, thank you too.
posted by astruc at 5:14 PM on March 14, 2006

The danger of flooring the engine at low RPMs is referred to as lugging and you generally want to avoid it if at all possible. I would say that this only applies if the RPM is less than 1500 (assuming a four cylinder.) You really don't want to open the throttle and lug the engine at the very low RPMs, but as long as you're still putting along at say 1000 - 1500 RPM or more I would no longer consider that lugging. But really you should quickly switch to first in those scenarios, if you happen to hit second accidently.

/a San Francisco stick shift driver
posted by Rhomboid at 6:47 PM on March 14, 2006