4 new tyres = - 15% economy?

Hi All,

This looked like the best place to put this: looking for either advice or to put mind at rest.

Replaced the standard Continental Contact Sport's the other day with 4x Goodyear Eagle F1s. They are 235/35/19s.

The Continentals had about 2-3mm tread all round and it's getting cold and greasy round here so I thought best to change them.

My economy seems to have plummeted. To Hull and back from here (York) I would normally get around 41mpg, but lately 3 consecutive runs have been <37mpg. It seems to have a high rolling resistance.

For example, there's a fairly steep hill from Hull to York and before in neutral it would just run away with itself, 50 at the top, 80 at the bottom, now it'll actually slow down at points down the hill.

When I got the tyres fitted they lost pressure (about 3psi) a few times but now they've stopped that. I've put them at 39 and 36 (front/rear).

My tracking measurement was +0.5mm on the fronts. I haven't had it perfected but can do.

The old tyres were fairly worn but not bald and obviously new ones have standard 8mm tread or whatever it is.

Is this normal? Is it just because the F1s have more grip and therefore drag more? Or is it a just a "run in" period with new tyres. Do they need more pressure?

Any thoughts appreciated. Tag your buddies.

allanmb said:

Which F1s did you get? I wouldn't expect that much of a difference in fuel economy. Has the fitter changed your tow/tracking correctly? I had a fitter put the opposite on mine and my tryes wore down within a 1000 miles!

I would also say that I used to run my 19s with 42 PSI on my A4. I think you could put a bit more air in yours. Also, losing 3PSI a few times is not normal in my experience

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They are symmetric 2s. I haven't had any wheel alignment done. Thinking I should do it - a place near me does four wheel alignment for £35 (Audi = £100).

I'll try adding a few more PSI to them. It says 38/35 on the inside of my door. Your A4 will have weighed more than my S3 though I guess - particularly if a bigger engine? Edit: just looked it up: recommended is 42/39 on my tyres for a normal load, and lots of people online running 44 all round... Will have a play!

allanmb said:

The difference is nowhere near that between a worn tyre and a new tyre. A new tyre radius would be 324mm. Worn down to 2mm tread, the old ones would have been 318mm (6mm of wear). That's not even 2% difference. Assuming the OP was getting exactly 41mpg with the old wear then the new ones would report 40.25mpg.

To the OP. Are you using the DIS to get your consumption figures? Or are you doing top ups? One thing to note is that it is now cooler and damper so this will affect the economy especially if you have a turbo. If you have a diesel it is also possible that your filling station has switched over to winter diesel which also affects economy by a fair margin

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I did the maths on this also and I agree with your thinking. I am using the MPG on the dashboard yes, but the change in MPG was exceptionally stark and obvious and I've not been booting it. It's S3 so it's petrol. The funny thing is it doesn't feel any slower accelerating which I'd expect, I'd almost say the DIS was lying, maybe I should do a top up test.

It's booked in on Monday at Audi but the tyre pressure have stopped messing me about...so far. I'll get the tyre place to check the fit and rebalance them too.

Thanks for replying.

desertstorm said:

Title is a little miss leading if you were getting 15% less economy and you used to get 41mpg then 41 x 0.85 = 34.85 mpg
At 37mpg you have dropped about 10%. 41mpg x 0.9 = 36.9mpg.The F1 asy 2 always came out well in tyre reviews for rolling resistance.
As you said it's getting darker and colder, the car takes longer to warm up and are driving around with lights, seat heaters and other electrical loads on. Along with the small change in gearing and increased weight of the new wheel tyre combination this will also have an impact.
Have you had the tracking changed since the new tyres have been fitted ?

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There have been some runs around 35.6-36. But anyway, I was running them at too low of a pressure. I was running 38-35ish but they should be at 42-39ish according to inside of door. When I got it back from Audi last week it was 35 all round! Rollseyes

I also noticed that F1s ASY2 got a top score on rolling resistance.

I haven't had tracking done yet, but had it measured at 0.5, I think tolerance is 1.3+/-1.3. (0.0-2.6)

Anyway I got home through the city last night at 32mpg after pumping them up which bowled me over, normally get like 25 in the city lol and that's without heavy footing it - so thanks for those questioning correct tyre pressure. Driving to Hull tonight and will check before leaving and drive normally and get a figure out of it.

Just gonna check the pressures over the weekend and see if they go down. Obviously if they do ball into Audi Monday AM and start snappin' necks and cashin' cheques.

The saga continues. Last night set it to 42-39 before a normal eco drive to Hull (Average speed) and thought the wheels were going to explode. By the time I got to Hull with some temp they were 44-40 and had some understeer on a damp road. Dropped them to 41-38 on arrival and not driven it since last night. I used to run previous at 38-35 whcih was comfy but rubbed the outside a bit. It says 41-38 on inside of door so I think I'll put in 39-36 and see how we go. Pressure's still dropping but thinking it could be paranoia. It's booked in at Audi on Monday. Also there's a chunk missing from drivers side front - very smooth and clean cut, almost like from a blunt chisel...I don't park on drivers side and its not rough - think Audi took a chunk out of it. It's between rim and tyre which is why I haven't noticed it before.

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