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Mpg Drop Since New Tyres Fitted :(


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#1 Grumpy Cabbie

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Posted 19 March 2010 - 05:53 PM

The tracking was out on my car and it started to chew the inside edge of my tyres, until they were getting borderline illegal at 12.5k miles. The outside edge was ok and had about 3mm. I do loads of town driving and normally expect 17k miles out of a set of front tyres! But 12.5k is low even for me :(



Had the main dealer do the wheel allignment and replaced the tyres with like for like Bridgestones. They matched the price of a local tyre warehouse so the cost was very good.



However, I have since noticed that my fuel economy is down by about 3-5 mpg on average! I checked the tyre pressures and noticed they had only pumped them to 31 psi not 37. Not a good start so I pumped them to the correct psi and hoped that would improve the fuel economy. It hasn't.



I'm now halfway through my second tank of fuel since the new tyres and the trip computer is at 48 mpg (works out 45 mpg true) when I normally get about 51 mpg (48 mpg true). (I have a lead right foot )



I though maybe they hadn't adjusted the tracking correctly but the car handles fine, holds a straight line and actually takes corners better. Could it have been that the car was running on the inner edge of the old tyres with the allignment out and as such this gave less resistance and better mpg? It did tramline a little in the wet just before I changed the tyres. Or do new tyres take a little time to wear in?



Any advice appreciated

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#2 timberwolf

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Posted 19 March 2010 - 06:39 PM

Yes, there is a small mpg hit with new tyres for the first few 1000 miles. Curiously, the OEM tyres fitted at the factory don't seem to have this mpg penalty.

#3 Grumpy Cabbie

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Posted 19 March 2010 - 07:35 PM

Yes, there is a small mpg hit with new tyres for the first few 1000 miles. Curiously, the OEM tyres fitted at the factory don't seem to have this mpg penalty.



But how?

I've put on the Bridgestone B250 or whatever it is. It's the same as the ones already on the car. How come the OEM tyres are ok yet these new ones aren't?

Very strange.

#4 timberwolf

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Posted 19 March 2010 - 09:46 PM

AIUI the brand/model name of the tyre is just a name - it doesn't tell you what ingredients or percentage of each ingredient went to make up that tyre. Tyre manufacturers change the quantities of the ingredients over time, to vary the properties of the tyre such as the wear characteristics or road grip. So you may have had brand/model and were really happy with it, and then buy what you think is the same tyre a few years later but the manufacturer has changed the blend. Who knows, tyre manufacturers may sell the same brand/model in different countries, but vary the ingredients based on regional preferences?

Or maybe the tyres just enjoyed the sea voyage from Japan, and happy tyres have lower rolling resistance :P

#5 Ancient Nerd

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Posted 19 March 2010 - 11:59 PM

Hi GC,

That tyre wear is really bad. I've done just over 15,000 and there is no visible wear. I'll check, because there must have been some. Tyres are Michelin Primacy.

The previous Gen II Prius is still in the family. I passed it on at just over 40,000 miles, still on its original tyres. The fronts were replaced at around 45,000. The original rears are still on the car (now on the front) and still going at 55,000.

A lot of the miles are done on minor roads in fairly bad condition, so they've done a few potholes etc. in their time.

Do you go over many of the square speed bumps that are around the same width as the car. These are tyre killers and will cause the damage you describe. To save your tyres, you need to take one wheel over the centre of the bump. Unfortunately, that kills the suspension instead. It's also uncomfortable, which I guess you really don't want.

Anyway, better luck with the new ones.

#6 Sagitar

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Posted 20 March 2010 - 01:15 AM

The tracking was out on my car and it started to chew the inside edge of my tyres, until they were getting borderline illegal at 12.5k miles. The outside edge was ok and had about 3mm. I do loads of town driving and normally expect 17k miles out of a set of front tyres! But 12.5k is low even for me :(



Had the main dealer do the wheel allignment and replaced the tyres with like for like Bridgestones. They matched the price of a local tyre warehouse so the cost was very good.



However, I have since noticed that my fuel economy is down by about 3-5 mpg on average! I checked the tyre pressures and noticed they had only pumped them to 31 psi not 37. Not a good start so I pumped them to the correct psi and hoped that would improve the fuel economy. It hasn't.



I'm now halfway through my second tank of fuel since the new tyres and the trip computer is at 48 mpg (works out 45 mpg true) when I normally get about 51 mpg (48 mpg true). (I have a lead right foot )



I though maybe they hadn't adjusted the tracking correctly but the car handles fine, holds a straight line and actually takes corners better. Could it have been that the car was running on the inner edge of the old tyres with the allignment out and as such this gave less resistance and better mpg? It did tramline a little in the wet just before I changed the tyres. Or do new tyres take a little time to wear in?



Any advice appreciated


That's a bummer. I have heard of tyres needing "running in" but have never associated it with rolling resistance. It's possible that the material needs time to cure and will perform better when it has hardened up a bit in use.

The corner wear that you were getting I would have blamed on "scrubbing" in corners and that ought to give reduced mileage performance. I would expect mileage to get better from sorting out the geometry.

I have just put back my summer tyres and my mileage is improved a little I think, but that is probably down to the temperature change.

I would be wary of making judgements in the short term, so many things can affect mileage from day to day.

I hope it gets better for you.

#7 Grumpy Cabbie

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Posted 20 March 2010 - 08:32 AM

Hi GC,

That tyre wear is really bad. I've done just over 15,000 and there is no visible wear. I'll check, because there must have been some. Tyres are Michelin Primacy.

The previous Gen II Prius is still in the family. I passed it on at just over 40,000 miles, still on its original tyres. The fronts were replaced at around 45,000. The original rears are still on the car (now on the front) and still going at 55,000.

A lot of the miles are done on minor roads in fairly bad condition, so they've done a few potholes etc. in their time.

Do you go over many of the square speed bumps that are around the same width as the car. These are tyre killers and will cause the damage you describe. To save your tyres, you need to take one wheel over the centre of the bump. Unfortunately, that kills the suspension instead. It's also uncomfortable, which I guess you really don't want.

Anyway, better luck with the new ones.



I hear what you're saying about tyre life but as a cab in town you'd be lucky to get more than 20k. It's all the bad things concentrated in short trips. Pulling out of junctions (not even quickly), three point turns, start stop x 1000 each day etc. If I just did airport runs then I'd expect 50k but some of our drivers with heavy diesel engines think 12k out of a set of tyres is good!

And don't get me started about speed bumps! lol

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