HI all. Up till a couple of months ago, when I would fill up with fuel, I knew that if I had done 600 klms, i would only have to put in 60 liters of fuel, give or take a liter. Now, I consistantly do 530 klms and i put in 60 liters. Sudden drop! Got new o2 sensor, fuel filter, pump, regulator, air filter, but no joy. Interesting thing is, got it dynoed a week ago, and the tuner stuck the O2 sensor in the exhaust and across the rev range it was running very lean, in a good way. (I run an emanage) See attachment. http://i49.photobucket.com/albums/f274/azkazmagna/HPoldtuneandnewtunesmall30-01-09Med.jpg
So it definitely isn't running rich. The only thing I have done differently is change from my ROH 15 inch mags and standard tyres to 17 inch running 235/45 rubber. Could this mag and tyre change really had made that much difference to speedo? So Am I getting good mileage still but the odometer isn't reading it correctly or something? I entered my details into a tyre size changing calculator and its only 1 kilometer or so out at 100klms. Thanks.

I had same outcome on my Commodore from doing same change, not quite as much as yours but I still noticed a significant different in consumption

Do you think it was actual consumption, or just that the odometer was no longer accurate?

two possibilities, new tyres are putting a lot more rolling resistance against the car, or the weather. I always get better consumption in the winter when its cooler. Could be a combination of both the above.

HI all. Up till a couple of months ago, when I would fill up with fuel, I knew that if I had done 600 klms, i would only have to put in 60 liters of fuel, give or take a liter. Now, I consistantly do 530 klms and i put in 60 liters. Sudden drop! Got new o2 sensor, fuel filter, pump, regulator, air filter, but no joy. Interesting thing is, got it dynoed a week ago, and the tuner stuck the O2 sensor in the exhaust and across the rev range it was running very lean, in a good way. (I run an emanage) See attachment. http://i49.photobucket.com/albums/f274/azkazmagna/HPoldtuneandnewtunesmall30-01-09Med.jpg
So it definitely isn't running rich. The only thing I have done differently is change from my ROH 15 inch mags and standard tyres to 17 inch running 235/45 rubber. Could this mag and tyre change really had made that much difference to speedo? So Am I getting good mileage still but the odometer isn't reading it correctly or something? I entered my details into a tyre size changing calculator and its only 1 kilometer or so out at 100klms. Thanks.

Thats borderline stupid on that AFR you know, id be kicking the tuners ass for that, should be closer to 12 across the range, all it will take is one extra hot day or a bad batch of fuel and pop goes a ring land

Isn't 30 way too low for tyre pressure? For 17s it should be more like 34-36 shouldn't it?

Isn't 30 way too low for tyre pressure? For 17s it should be more like 34-36 shouldn't it?

They usually never check tyre pressure on the dyno mine has like 50 for my power run after the retune

obsiuouy the closer you run to stoich at high load the higher chance of detoantion, but even hicomp engines are safe to run close to 13.0:1 he isnt quite there so i dont see the drama and if the car is tuned in this heat with afr's like that then its unlikley there will be sufficient extremes to cause pre-igntion/detonation othe rthen bad fuel which woul d come regardless of tune, just luck of the draw.

I was looking at the start of the graph to help find your missing mileage, but that tune/graph looks pretty damn good for AFR's, very flat and good mixtures for each load point. As far as tuning goes, this is text book stuff and the tuner knows it well. Much better then most people who call themselves tuners.

I run my tyres at 34psi. I don't think he checked it or put it into the dyno though. Where did my dyno graph go?

i run my standard 215/60/R16 at 36 psi and get even wear. lower profile certainly need higher pressure, read the side of the the tyre and i bet it says 40 psi at least.

Will check those tyre pressures! Mags are Advan AVS model 5 twin spokes, apparently there a light weight mag, so hopefully rolling resistance isn't that increased over my old mags.

the extra rolling resistance would come from wider softer tread (if you changed rubberrings/tyres)

the heat has a big effect, but its likely a few issues rolled into 1. heat, tyres, not driving like a nanna as often

thats about the only difference.

There is always the chance the odometer isnt functioning correctly.

i run my standard 215/60/R16 at 36 psi and get even wear. lower profile certainly need higher pressure, read the side of the the tyre and i bet it says 40 psi at least.
17s still have a lot of tyre, you don't get to the 40s till you hit 18s or 19s...

I run 40psi on my 18s - It's stiff and rough, but I like it.

Thats borderline stupid on that AFR you know, id be kicking the tuners ass for that, should be closer to 12 across the range, all it will take is one extra hot day or a bad batch of fuel and pop goes a ring land

pfft its factory NA not FI. It could run lean and it'd be fine.

17s still have a lot of tyre, you don't get to the 40s till you hit 18s or 19s...

I run 40psi on my 18s - It's stiff and rough, but I like it.

watch your back guys hahaha just kidding

ive run 40psi in my 15's since i started driving my cars. ive had bigger treads but ive always gotten good kms from tyres ive kept on the higher side of the manufacturer specs.

Ive just done 38000km on my front tyres, and now they are going on the back, and i have roughly 25-30000 left in the rears when they go on the front.

Not bad for a set of tyres that cost me 266 fitted and balanced.

Thanks for the suggestions guys. Will keep monitoring it and see what happens.

Cheers.

watch your back guys hahaha just kidding

ive run 40psi in my 15's since i started driving my cars. ive had bigger treads but ive always gotten good kms from tyres ive kept on the higher side of the manufacturer specs.


I was beginning to think I was the only one....I run 40psi (cold) in my 16's and anything less feels a bit too "floaty" for my liking.....

I was beginning to think I was the only one....I run 40psi (cold) in my 16's and anything less feels a bit too "floaty" for my liking.....

I do 40+ in my 17's... cold.. 42psi is the norm

Steve

don't forget that tyre pressures are different when the tyres are cold to when they are hot. i think they can vary by up to about 8psi from general driving.

as has been said, the AFRs of 13 are fine for a natro car. if it was a turbo i would be a bit worried.

the poor fuel economy could be caused by the wider tyres adding extra rolling resistance. it could also be due to the new wheels being heavier, depending on the style of the wheel put on. and heavier wheels means more power is required to accelerate.