R129 sl280 - high consumption, wrong tyres?

olivier_wery

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R129 SL280 N reg 58k miles
Hi everyone.
I bought a couple of month ago an N-reg SL280, in a lovely v dark green, cream leather. It's a v nice car by my own standard (it's also my first merc...), but I am having a bit of an issue with the gas mileage... Now... I never expected this car to be economical, but this is worryingly high considering I tend to run it very smoothly.
I am wondering if the tyres could have something to do with it...
I have inherited some beautiful but ludicrusly large 265/18 wheels and tyres. Though they do give a stance to the car, they make the ride harsh, and I guess the consumption higher than what it could be...
Would someone know the average gas mileage you can potentially return with this car, and what tyre size it should be equipped with? I have received from another member an owner's manual, but for the SL300 and SL500. For the 300 it states 225/555 ZR 16, which seems more in tune with the engine power overall speed of the car....
Thanks in advance for your help
Olivier.
 

100%Bitch

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What MPG are you getting?
 
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olivier_wery

olivier_wery

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Around 17/18mpg...
 

SQ_W211

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I have 255/35/18 at the back of my CLk and didnt see any MPG increase.

You should check the tyre pressure from time to time as that makes a huge difference. I had 28psi all around and never use to hit over 37mpg on a run and then I filled it up to 32psi which showed an increase of 40.8mpg so 3mpg with just right pressure in tyres
 
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olivier_wery

olivier_wery

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Thanks Amo. How can I find what pressure I am meant to put in these tyres... would any tyre fillter know this?
 

hairyg

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R129 (1994) SL320
I have a 1994 SL320 on its original wheels and they are 225/55 16. I run with 29psi in the front and 34psi at the back. On mine, the tyre pressures are shown on the inside of the petrol filler cap. These are only right for the standard wheels and tyres, of course

MPG depends on how I am driving but I always get better than 20mpg even when I get enthusiastic.

The 280 is known for being thirsty as the engine is quite small for such a heavy car but I would expect better than you are getting if you are driving gently.
 

SQ_W211

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Thanks Amo. How can I find what pressure I am meant to put in these tyres... would any tyre fillter know this?

The manufactures recommendations are listed on the door sill but they are only for factory tyres. If you change then you should check with your local tyre shop. I have 225/40/18 at front and fill them to 30 - 32 and 255/35/18 at rear and i use 34psi on the back.

It seems that your are getting very low fuel average for your engine size, you should get it looked at from your local indie to see for any obvious issues which might have a negative impact on fuel consumption.
 

television

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The same pressure is used no matter what the wheels or tyre size is,,it is a weight issue. I ran my 129 with 31 in the front and 33 in the rear,,as AMO it can make a big difference to the fuel consumption
 

Quick Silver

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I get around 25 mpg in my SL 300 in urban driving , short town journeys it will drop to around 18 mpg but on a long run driven sensibly can squeeze a tad over 31 mpg . I did a RETURN journey up to Bourton on the Water yesterday a total distance of 290 miles and returned 24mpg overall and I wasn't hanging around either .

Does your gearbox have a switch with S (sport) and E (economy) position as this makes quite a difference and is it a 4,5,or 6 speed box as this will also make a difference, the older models have less gears and tend to be less frugal

The 129 SL was never designed for economy but as a high performance touring car and it is also a very heavy car even without the hard top . It weighs a total of 2080kg x 2.2 = lbs divide by 1760 = tons.
 

turbopete

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I get around 25 mpg in my SL 300 in urban driving , short town journeys it will drop to around 18 mpg but on a long run driven sensibly can squeeze a tad over 31 mpg . I did a RETURN journey up to Bourton on the Water yesterday a total distance of 290 miles and returned 24mpg overall and I wasn't hanging around either .

Does your gearbox have a switch with S (sport) and E (economy) position as this makes quite a difference and is it a 4,5,or 6 speed box as this will also make a difference, the older models have less gears and tend to be less frugal

The 129 SL was never designed for economy but as a high performance touring car and it is also a very heavy car even without the hard top . It weighs a total of 2080kg x 2.2 = lbs divide by 1760 = tons.

or if you want to work in euro's, almost 2.1 tonnes!
 
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olivier_wery

olivier_wery

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R129 SL280 N reg 58k miles
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Hi there thanks for the info, it is the 4 gears, and i have managed to return 28 mpg on a London - Brussels and back on E setting (though S is so much more fun.... :shock:)

I will recheck the pressure.

I have to say I find the car quite harsh on these wheels still, but it looks soooooooooooo good.... Don't know what to do... still tempted to revert to original size... Has anyone got an opinion?
 

television

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The 17" wheels are the best all round on the 129
 
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olivier_wery

olivier_wery

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In which size? 235 - 245???
 

Alex M Grieve

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I get around 25 mpg in my SL 300 in urban driving , short town journeys it will drop to around 18 mpg but on a long run driven sensibly can squeeze a tad over 31 mpg . I did a RETURN journey up to Bourton on the Water yesterday a total distance of 290 miles and returned 24mpg overall and I wasn't hanging around either .

Does your gearbox have a switch with S (sport) and E (economy) position as this makes quite a difference and is it a 4,5,or 6 speed box as this will also make a difference, the older models have less gears and tend to be less frugal

The 129 SL was never designed for economy but as a high performance touring car and it is also a very heavy car even without the hard top . It weighs a total of 2080kg x 2.2 = lbs divide by 1760 = tons.

Sorry to be a bit late on this. I have an SL 500 pretty much identical to Quick Silver's car, which returns much the same fuel consumption.

I get the impression that it takes a certain amount of energy to achieve the performance and that can come from a smaller engine working harder, or a larger lazier engine - but they use the same amount of fuel.

I had a long trip around France in convoy with an R 107 300SL - I followed him as I was sure I could catch up if necessary. He used more fuel than I did.

I generally get 24.5 overall, 25.5 touring.
 


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