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  #1  
Old 2nd March 2020, 05:10 PM
sean sherry sean sherry is offline
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Question Tire pressures

Little Wifey says stick with and put up with the 18 inch Wheels and low profile Tires. Cost reasons switching to 17s But me running 34 PSI in the front did not help. How low could I safely go with up to 110 kph for around 50 Ks once or twice a month ????? Our C200 with seventeens ride very well
Most of the time I'm navigating Sydney's 'orrable traffic.
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Old 2nd March 2020, 06:58 PM
Helmet Helmet is offline
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Default Re: Tire pressures

Maybe wheels isn’t the only difference, the one with 18 inch wheels may also have sports suspension, what model variants are they ?
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  #3  
Old 2nd March 2020, 07:29 PM
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Michel Michel is offline
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Default Re: Tire pressures

Quote:
Originally Posted by sean sherry View Post
Little Wifey says stick with and put up with the 18 inch Wheels and low profile Tires. Cost reasons switching to 17s But me running 34 PSI in the front did not help. How low could I safely go with up to 110 kph for around 50 Ks once or twice a month ????? Our C200 with seventeens ride very well
Most of the time I'm navigating Sydney's 'orrable traffic.
34 PSI on 18 inch tyres is not high, on the contrary it is on the low side.
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  #4  
Old 2nd March 2020, 07:29 PM
sean sherry sean sherry is offline
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Smile Re: Tire pressures

Ah yes I did not think of that... Car is a C250 CGI built Nov. 2110. I guess a
2011 Model I have always felt that any Sports version of a Mercedes spoilt the Car. I will see if I can find the original Specs via the Vin No.
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  #5  
Old 2nd March 2020, 07:33 PM
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Patrick_R Patrick_R is offline
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Default Re: Tire pressures

Sean,
A quick question before I start.
Are you American or schooled in America?

Ok,
My wife has the same issue with 245/45R19 tyres.
They are like fat rubber O rings!
At the recommended pressure of 38 psi it rides like a billy cart, and her top line model, handles like a slot car, and not comfy at all.

Around town, I set them to 30 psi for comfort, but if we do any open road work I put them back to 38. Low tyre pressures produce temperature increase from flexing side walls.
The higher the speed the higher the wall flex the hotter the tyre gets.


Below image:
This is an extreme example of tyre sidewall flex, but the pic really shows it well.
What most people don’t understand is that the tyre has to “grip” the road as it turns, it momentarily stops, grabs the road, then the transmitted power turns the wheel, thus pushing the vehicle forward.
If it doesn’t “grip” the road, it breaks traction (overcomes it’s maximum friction point) or spins



The other issue we have with under inflated tyres are bad tread wear.
She doesn’t do too many k’s so, I haven’t noticed to much of this to be honest, but I do rotate the tyres (front to back only as her tyres are directional and asymmetric)
*please see another post of mine regarding these type of tyres*

Badly inflated tyres look like this, and produce this type of tread wear.



Of course you can go for a smaller wheel & higher profile tyre package to get the ride you are seeking.
Just be careful about the rolling height (that means same tyre revs per kilometre) to ensure correct speedo reading.
If not, a technician may be able to adjust this with a laptop at a dealer or repairer.
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  #6  
Old 2nd March 2020, 08:03 PM
sean sherry sean sherry is offline
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Talking Re: Tire pressures

As past Prime Minister Malcolm Fraser once said 'Life was not meant to be easy " Road Test article when Car was new commented that the Ride was spoilt by the Wheel Tire combination. The spec I found . for the Car for Australia does not mention Sports Suspension. Lousy Roads ? So i can either search for a set of 17s from a C200, same year,( speedo should be ok) or run lower pressure in the City as Patrick suggests. I have a compressor at Home.
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Old 2nd March 2020, 08:13 PM
sean sherry sean sherry is offline
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Thumbs up Re: Tire pressures

No not an American Patrick ,though I have lived and worked there and also traveled widely for Business over the years. But still an Irish man at heart who has lived happily in Aus for at least 50 years This year holds a couple of milestones....
My eighty fifth in April .( no on April fools day ) and our Fifty Fifth Wedding Anniversary in September or so my Wife tells me !!
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  #8  
Old 3rd March 2020, 01:08 PM
sean sherry sean sherry is offline
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Smile Re: Tire pressures

Following Patrick's suggestion I have been running 30PSI on the 18 inch C250. Not wafting like R.R. but quite acceptable on a Car engineered for high Speed Autobahns
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  #9  
Old 3rd March 2020, 03:57 PM
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Patrick_R Patrick_R is offline
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Default Re: Tire pressures

Just remember Sean, not for higher speeds or a fully loaded car.

Just do me a favour after your next drive.
Please put your hands on the sidewalls and see if they seem to be hot or not.
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  #10  
Old 9th March 2020, 03:10 PM
sean sherry sean sherry is offline
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Smile Re: Tire pressures

Hi Patrick, a 4 hour mixed Drive including the last run Home at 100/ 110 KPH Tires just luke warm . Feels fine switching Lanes etc.
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  #11  
Old 9th March 2020, 07:46 PM
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Patrick_R Patrick_R is offline
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Default Re: Tire pressures

If you’re more happier driving the car Sean, your on a winner.
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  #12  
Old 9th March 2020, 09:21 PM
sean sherry sean sherry is offline
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Thumbs up Re: Tire pressures

Yes Patrick, it has taken nearly a year to get everything sorted to my satisfaction Previous owner had to much trust in the Workshop for book Servicing. I am never happy with Cars unless they are running as the designer intended. Both Vintage/classic or Modern.
MG A....3.8 S Jaguar..... 2 Mercedes Sls ...a 1980 107 and a 1965 230.
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  #13  
Old 9th March 2020, 10:23 PM
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SEL_69L SEL_69L is offline
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Default Re: Tire pressures

18" wheels, low profile tyres:-
Running 39 psi front, 41 psi rear; placard suggests 38 and 40.
Drive the car minimum every 3 weeks, but for the longest interval of 3 weeks, check the tyre pressures every time, so they don't develop flat spots from long periods of standing.
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