I have used the search function, but I didn't see a topic on this... so here we go.

Today I spoke to a relative who thinks people generally don't care about tyre pressure. So I'm curious. Do you? What's your tyre pressure, and why? Do you follow the advise given by the manufacturer, do you check regularly, ...?

I'm currently testing 2.7 bar in front and 2.9 at the back, might increase the front to 2.8 or 2.9 too. Anything speaking against that? So far (previously it was about 2) my experience is good, FC seems to be lower (will check the next time I fill up), acceleration is better, gear changes happen earlier, steering is lighter, car feels more stable (even if it is slightly less comfortable).

That being said, maybe we can collect more or less common tips on saving fuel here? What I have heard:

Accelerating fast, but then coasting along gently (try to avoid constant speed changes) should help, I have heard (short bursts of high RPM are ok, staying at a high RPM is not). In other countries I have seen drivers who'd be in 3rd at 50-70 km/h... that's not good. 5th is usually fine with any car, unless you go uphill or need to accelerate fast.

Empty the car. Don't transport stuff you don't have to. The less the car weights, the lower the FC and the better the performance.

Try to glide to a stop (avoid braking). As long as a gear is engaged, but the foot lifted from the gas pedal you don't consume any petrol at all. Try to make use of that at traffic lights for example (of course others will try to overtake you then or cut in... :-/ ).

Anything else I have forgotten? Anything you want to share? Hopefully this is nothing new to all of you, but if yes then maybe it helps.

How high was the FC before you pump up the tyre? What pressure did you have before and now?

They say you should pump up with cold tyres... very funny, how can they be cold here? Or is that valid anywhere, i.e. when it's "cold" here that's when you should pump up? (Cold means you haven't driven for a long time before checking the pressure, for example less than 10 km).

Some say 3 bar for safety reasons, but the sticker on the car usually says less than that (my Xsara about 2.3 and I think the same in the back, for the Kangoo it's 2.6 and 2.9). Others say 0.2 more than the sticker says. What's best for your car?

If the pressure is too low it will ruin handling (dangerous), FC is high and it might also ruin the tyre.

Hm... I thought the engine gets no fuel at all when the momentum of the car is keeping it running. If you are in neutral then the engine needs some fuel to keep it at idle, so press the clutch as late as possible.

Another thing when driving auto... put it into neutral when stopping, depending on the gearbox (robotized manual) it will use up the clutch, and even if not the engine needs more fuel not to stall cause there is a constant load on it.

wow, isn't 130-140 = 1.3 to 1.4 bar? That's very low... (though the Kelisa is also quite light). Big improvement in FC you've got there

Haven't watched it. I suppose it depends on how high/low the pressure was before. If it's way too low it makes a huge difference, if you followed the car manufacturer and then inflate a bit the gain won't be very big (but hey, less FC is less FC).

From what I have read, unless you go above 3.0 bar (300 kpa) it shouldn't get uneven (someone reports 3.5 bar and no uneven wear...) or even get a blowout. What does kill the tyre is too low pressure, because it heats up a lot (high friction). 42 psi is the official value from Renault it seems, but I too am scared to go any higher than that.

If the car gets bumpy and hops around/looses traction, then that is too much. Haven't noticed that though with the Kangoo, but your milage might vary.

Generally you are right, front is supposed to be higher than rear, also heavy load or high speed driving should have higher pressure. Not sure why it isn't that way on my Kangoo (values taken from Continental... they don't have a sticker on the Kangoo), but I can imagine that the rear is supposed to have a higher pressure because it is also a small transporter, thus carrying heavy loads.

Trying to watch the video now, but about the slowing down part wikipedia begs to differ:
http://en.wikipedia.org/wiki/Engine_braking
"Additionally, most modern engines don't use any fuel while engine braking which helps reduce fuel consumption.[citation needed] This is known as DFCO or Deceleration Fuel Cut-Off."


This post has been edited by kadajawi: Nov 30 2011, 09:07 PM

@amduser: Care to explain why that is so with the AT car? I do it too... I mean put it into neutral. I thought there is no direct connection between the gearbox and the engine, only through fluids? That's why there is no wear on the clutch when stopping in D...? At least in a regular auto box. Now you are scaring me

Mythbusters only test at a maximum of 50 mph... that's rather slow, at higher speeds the difference should be bigger.

We'll see how the Kangoo will do when I fill it up the next time. In Germany +0.1 bar meant about 1 liter less per 100 km, but I was driving at an average of 140 km/h there, with sticky winter tyres in summer.

Also modern tyres shouldn't bulge in the center as long as you stay below the pressure they are rated for (usually 3 bar/300 kpa). 3 bar is also what they seem to recommend during secure driving lessons (where you learn what to do in extreme situations like the rear breaking out/car starting to spin etc.).

It depends on the gear you are in. If you do engine braking in 5th gear the effect is very small. I imagine there is little friction in the engine at low rpm, so there is little engine braking, but no fuel has to be burned to keep the engine running. In 1st the braking effect is higher because the rpm is very high then (and never ever try to force in 1st while you are still moving (unless very slow), unless you can somewhat rev the engine in neutral to match the current speed (there is something in modern gearboxes to make that possible, but you will wear out the gearbox IIRC)).

The trip meter on a VW Touran (diesel) told me the FC was 0.00 when not touching the gas pedal, even in 5th or 6th.

On my 2002 Xsara (1.4 petrol) I can also feel the fuel cut off... at a certain point the engine gets fuel again (starts pushing the car) to keep it from stalling, somewhere around 1000 rpm. I guess it differs from car to car, so it's worth trying.
http://www.gassavers.org/showpost.php?p=109296&postcount=14 is particularly enlightening. Depends on the car, carburetors don't do it, but computer controlled fuel injected engines do cut off fuel.

I'll have to search for the sticker again, maybe I'm blind.

@Aaron: I see, so if I pump up the tyre at 0°C (with the actual weather being also around that temperature) and then drive for a while the pressure will be lets say +0.3 bar, and if I do the same thing at 30°C (i.e. in Malaysia) and drive for a while it will still be what was pumped in earlier +0.3 bar?

Haha. I think that it at least to some extend works that way. The friction/movement inside the tyre (which should be higher with with a less inflated tyre) creates heat, regardless of the external temperature the tyre temperature is raised by a more or less similar temperature (given all other conditions being the same (although tyres at low temperatures behave differently, for low temperatures the rubber has to be softer to achieve the same level of grip, but we'll ignore that now)). Hm. Not sure that is important for a normal driver...

Rolling down the windows in Malaysia is not very effective... you just get hot air blown all over you. Ok, not necessarily, but I think aircon makes sense in Malaysia, but it doesn't have to freeze you.

Normally it is also advisable to turn of the engine when stopping (for more than 20 seconds), however you'll lose the aircon...

Btw.: http://en.wikipedia.org/wiki/Fuel_economy-...izing_behaviors Some of the tipps are very dangerous (coasting!) or very annoying to others and dangerous (accelerating hard, then turn off the engine and remain in neutral until you get too slow and have to speed up again), but some things everyone can do.

True... I'll see how the car handles when it's really wet, but I'm hardly above the suggested pressure, so I should be fine. I hope. So far the handling has improved (and in light rain it was fine today), the comfort hasn't really gone south much (it's relatively harsh anyway, whereas the CBU Kangoo is supposed to be overly soft. Weird. At least the car won't easily crash.)

The fuel isn't that cheap considering what people usually earn (though fuel takes a larger part of the earnings in Europe), though cars are a greater part of the equation (not being cheaper than in other countries, usually more expensive, whereas the fuel is 1/4 the price of fuel in Europe).

Besides it doesn't hurt to try to save some fuel, also means less polution and less waste of resources. Don't know about you, but I like the air I breathe to be clean (Shanghai was pretty awful).

You just shouldn't risk your life to lower the FC, I totally agree.

(I think Tracy inspired this thread in her obsession to save fuel Or maybe she just wants a reason to buy a new car. )

Haha, turning off the aircon is a bit extreme.

It's no big deal to quickly engage a gear when in neutral (especially with a manual... I make sure to be in the right gear to pick up speed again, so I just need to let go of the clutch/rev match. I'm only doing that when I approach a traffic light/stop sign or I'm in a traffic jam though).

Not sure about tyre wear. Too low pressure will definitely wear down the tyre very fast, if you want to play it safe and comfortable then by all means use the recommended pressure. That's basically what I am doing (+0.1 bar in front, still way below the limit). In Europe many (including car clubs) recommend +0.2 bar, however the climate is different, so I don't know if one can apply that here (they are also more keen on saving petrol... almost RM 7 per liter now!). I used to drive with +0.1-0.2 bar over the minimum recommended pressure and didn't notice any increase in tyre wear, but I did not really pay attention to it and the recommended pressure is pretty low for that car.

Hypermiling... please don't. That might be a nice hobby/sport (if you are James May), but on public roads?

Btw., somewhere here I've read that some remove their catalytic converter to save a few %... -.-

Ps: My 1.4 uses about 12l/100km... I know I'm accelerating too hard, but that's just too much. How can such a small engine burn so much fuel? Since I've pumped up the tyres the car seems to change gear earlier and the speed is maintained more easily, at least that's my impression so far.

Uuuuuuuuuhm... me. (at least sometimes). 7 seater with only blowers in the front row, so if the 3rd row is supposed to not be in a sauna it has to be arctic winter in the front. Previous owner should have gotten the extra blowers for the rear passengers...

Btw., it's not safe for the driver to be too warm. The brain doesn't work that well when it's hot.

This post has been edited by kadajawi: Dec 7 2011, 11:44 PM

Ok, so first attempt, 12 liter/100 km. Previously around 12.5, but more luggage (7 persons, 4 of them kids instead of usually 2 adults only) on board.

Then now I just filled up, 11.5 liter. Not as good as I hoped for, this time more highway (150 km in Singapore, usually the fastest driver on the road (around speed limit), most of the time 6 adults in the car, again 12.5 is with usually 2), then 150 km in Malaysia with some traffic jams etc. Definitely an improvement, but perhaps not as big as I hoped for. But hey, every bit helps. Handling has improved, even though I have found a sticker that recommends a lower pressure than what the Continental website suggested for the car.

I have noticed that the front tyres were worn out unevenly, probably due to low pressure (the thread pointing away from the car is F1 style now...). Might have to look for new ones soon... sad.gif Maybe eco tyres? But I don't want to compromise on safety...

I made fun of a Hummer with rubber coated rims (i.e. gigantic oversized rims), and it was enough to make him stalk me and talk thrash.

On topic... I have managed to get the FC down to around 10L/100 km, but that was mostly highway etc., usually it is higher. But at least it's a bit lower due to the higher pressure, and the handling is improved.

This post has been edited by kadajawi: Feb 2 2012, 12:37 PM

Pumping petrol at night might be a bit dangerous though, and the temperature difference between day and night in Malaysia isn't that big.

Actually high pressure can help with grip when cornering. A tyre can deform a lot when cornering, so much so that it slips from the rim (ok, you have to be cornering very, very hard). A more pumped up tyre should perform better. Also a with a higher pressure the car should feel more stable, react more direct to steering input. I think grip will only be compromised when the suspension can not keep up with the bumpiness of the road, so the tyre does not have any road contact. A less full tyre might be able to accommodate for the bumpiness and take in these bumps, thus maintaining better contact with the surface.

AFAIK a regular car tyre should not bulge under high pressure (as long as you still stay within the limits, usually I think 3 bar/300 kpa).