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.

There is very common on your steering feels,
If your steering feel very heavy and hard foot the car won't runs and the will force to runs and drink more fuel.

This post has been edited by kimsim: Nov 30 2011, 07:40 PM

deleted...that awesome fc was becos of low oil quantity..not becos of i pumped the tyres..

This post has been edited by megat89: Dec 12 2011, 02:47 PM

what car u driving?

wow, RM40-RM45 (if RON95 = 21L -23L) can go 480KM, that mean 28.85 - 20.8 KM/L), may I know what car are you driving?

kelisa 1liter manual like 80% highway, 20% city, average speed 90-100kmh..

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.

before i pumped in,the tyre pressure was averaging about 130-140kpa..and that time rm40 can last for about 370km..i always follow the sticker..never try more or less than that..ohw, yeah another thing i forgot to mention, the good fc that i achieve also because that time my engine oil was quiet low..

This post has been edited by megat89: Nov 30 2011, 08:18 PM

Yes to glide to slower, using road and air friction ... not gliding to a complete stop, that will be too slow/long

No petrol consume is when your engine is not running at all.... not pressing on gas pedal you engine is still at the idle RPM.

Well if you watch Mythbusters, the savings induced by overinflating a tire is negligeble although it does reduce rolling resistance by abit, but only a very slight amount. And if you do overinflate your tire, you have a higher chance of getting a blowout. 42psi is definitely overinflated plus you also get uneven tyre wear towards the middle since your tire expands more than usual now.

And your front is supposed to be pumped slightly higher than the rear since the front is where your engine is and the tire have to support more weight.

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

The improvement in FC he got is most probably due to other factors.



fast forward to 4:50

Well my usual practise is if i know i'm going to come to a stop, i'll put my gear to neutral and cruise to a stop. As long as the engine is running at a higher RPM, it will consume more fuel anyway. Its impossible that the engine is consuming zero fuel eventhough you've released the throttle. Don't forget, the engine is still running, it isn't turned off.

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

put your gear to neutral while your car is moving is not recommended

if you are driving AT car, this is not recommended as well because engaging to neutral gear while the car is moving can cause excessive wear to the gearbox

@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

well, the fact that it says 'citation needed' means theres no source. Don't forget, Wikipedia is not 100% accurate.

did a quick google and came up with this

http://www.gassavers.org/showthread.php?t=6651

It may be true that if you use release the throttle completely and use engine braking(on a manual) it might cut off the fuel depending on the car, but you have to do it at the very last minute. Engine braking is quite strong if you're on a manual box'

If i remembered correctly, the Kangoo does have the sticker somewhere near the door area. I remembered if not mistaken its on the door itself instead of the door frame. My friend have a Kangoo and i helped him pump his tire up last time.

About the video, i just posted the vid in my post above. Pretty informative.

Well, I'm on a Manual, so yeah...

nope.. this is actually true.. according to laws of physic.. when u already drive the car for a period of time.. the friction btw the tire and the road create heat.. and when heat is applied to the air in ur tire.. the air expands.. and that is why when ur car is on a hot day or already drive for a period of time..

it is recommended that u don pump air to it.. as the measurement of the air is not the same as compared to cold air.. this is true yo... =)

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?

not sure either bro... now i am curious... @.@

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...