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  #16  
Old 9th July 2013, 10:05 AM
BenzBoy BenzBoy is offline
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Default Re: Tyres

Quote:
Originally Posted by SEL_69L View Post
The standard tyre on a 6.9 is a 215/70/14.
Yes - and Mr Oversize's point is that this size is currently available only in S rated. Thus the discussion about ratings and insurance. So when your tyres wear out what will you do?
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  #17  
Old 9th July 2013, 10:40 AM
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Default Re: Tyres

Buy a cheap set of W126 wheels with the same offset as for the 14" Bundts, and fit 215/65/15H tyres.

215 /65/15H is the standard specification for a Toyota Tarago, and these tyres are about $120 cheaper per corner than the 215/70/14 Michelins as fitted as original equipment on a 6.9

215 tyres instead of 205 or 195 tyres, would go quite nicely on a 450 SEL, and no problem with a collapsing suspension, either!

Last edited by SEL_69L; 9th July 2013 at 05:43 PM.
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  #18  
Old 9th July 2013, 01:43 PM
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Default Re: Tyres

96 is a load rating commonly seen for passenger car tyres.
Such a tyre is rated to carry a maximum load of 710 kilogrammes.
That is the load rating for the tyres currently fitted to my car.
For a 6.9, which is very heavy in the front end, and that is not too much of a safety margin.

The empty weight of a 6.9 is 1935 kilogrammes.
Fully loaded, with 4 x 100 kilogrammes of people, 150 kilogrammes of luggage and 80 kilgrammes of fuel, that maxes out at around 2,500 kilogrammes.

I have never had my car fully loaded, but even when there's just me in it, there is still not much less weight over the front two tyres.

The implication for me (and for others), is that the tyres MUST be replaced when their legal age has been reached. If my memory serves me correctly, that is seven years, from the date noted on the tyre.
If that period is exceeded, high speed tyre failure is risked. Insurance companies may well 'cop out' in the event of an accident, due to tyre failure.

For the record load ratings are:
70: 335 kgs per tyre
80: 450 kgs per tyre
90: 600 kgs per tyre
100: 800 kgs per tyre.

You can interpolate between these for your own application.
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  #19  
Old 9th July 2013, 11:37 PM
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Default Re: Tyres

I have just found another VERY GOOD reason for not increasing the tyre width beyond 225mm:
You can't store the spare tyre in the boot wheel well, and lower the boot floor lid onto the spare tyre, so that the lid sits flush with the boot floor, if the tyre width exceeds 225mm.

I would find that annoying.

It also implies that you can't go less than a 60% profile, unless you leave the tyre outside diameter too small. Another impliction is of benefit to the suspension: the bushes in the suspension don't receive an overly harsh time, with low profile tyres.
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  #20  
Old 9th July 2013, 11:51 PM
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Default Re: Tyres

The Tyre and Rim Association of Australia lists a 215/70R14 tyre at 658mm rolling diameter.

In Victoria tyre age has no bearing on legality. They only have to be free of any apparent defects that may make them unsafe (including significant stress cracking).

The correct load rating for a 6.9 is 1610lb (or 730kg) as stated on the placard; that's for each tyre. 730kg x 4 = 2920kg.

Bearing in mind the max GVM of a 6.9 is 2420kg and the curb weight is 1935kg, it gives you a luggage capacity of 485kg. Curb weight (DIN 70020) includes and full tank of fuel and a 75kg driver.

Above 2420kg and you're actually exceeding the GVM of THE VEHICLE (not the tyres). The manual goes on to say max. axle load is 1245kg (front) and 1175kg (rear), which is 622.5kg (f) and 587.5kg (r) on each side . That's the max. mass on each side of each axle, not the minimum load rating of the tyres.

If you did equate that max. mass to a tyre load rating, you'd get 92 and 90 respectively. There's a large safety margin when MB specified 97, so really 96 is more than sufficient. However, convincing an insurance company is not an easy task; they have their policies and no discussions shall be entered into, unless they offer tailored policies.

Even on standard tyres, if you turn the wheels of a 6.9 and the suspension collapses, you'll wreck the guards. It's the same with any car if a spring breaks with the wheels turned. Tyre width isn't an issue as long as wheel offset is between et11 to et30 and they don't rub, foul or protrude.

I wouldn't be changing to 15s as I have no doubt you'll have similar problems sourcing tyres with the correct specifications. Even 16s are a problem and 17s aren't that popular either. 18s are the best (but expensive) and you risk a harsh ride and suspension bushes failing prematurely. Plus finding 18" wheels in the correct offset has been extremely difficult (but not impossible).
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  #21  
Old 9th July 2013, 11:57 PM
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Default Re: Tyres

Quote:
Originally Posted by SEL_69L View Post
I have just found another VERY GOOD reason for not increasing the tyre width beyond 225mm:
You can't store the spare tyre in the boot wheel well, and lower the boot floor lid onto the spare tyre, so that the lid sits flush with the boot floor, if the tyre width exceeds 225mm.

I would find that annoying.

It also implies that you can't go less than a 60% profile, unless you leave the tyre outside diameter too small. Another impliction is of benefit to the suspension: the bushes in the suspension don't receive an overly harsh time, with low profile tyres.
Why even carry a spare?? In Victoria you don't need one to be legal unless you're a taxi who needs a full size spare. Get roadside assist, keep the car light and save fuel.

If you do insist on a spare go for one that fits in the boot and treat it as a space saver. 80kmh max when fitted unless all your other tyres are the same. That's what I'll be doing since my rear tyres will be wider than my fronts and I can't choose which tyre might go flat....
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  #22  
Old 10th July 2013, 09:59 AM
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Default Re: Tyres

Thankyou for the more detailed information regarding weights than I guesstimated.

It is possible to know the exact safety margin for 96 load rated tyres fitted to the front of a 6.9, with the info. you have provided. It is also worthwhile to know that the correct load rated tyre for the front of a 6.9 is 97.

15" wheels from a W126 are perfectly OK to use on a 6.9, because the width and offset are exactly the same. If you have the same wheel offset as for 14" Bundts, the geometry for zero offset steering is maintained. The fitting of 15" wheels opens up the range of good quality tyres that may be commonly available. This also means cheaper tyre prices.

Original equipment tyres for the later model Toyota Taragos are nearly identical to the tyre requirements of a 6.9, with W126 15 slot wheels.
Toyota Tarago: 215/15/65 96H
6.9: 215/15/65 97H


With zero offset steering, the axis of the kingpin passes through the middle of the contact patch of the tyre on the road. If that is not maintained, the steering becomes heavier, and tyre wear under cornering conditions is biased to one side of the tyre. It is easy to identify a vehicle equipped with zero offset steering. The front wheels LOOK to be way off vertical when the steering wheel is on hard left or right lock. Almost all current production cars have some element of zero offset design approach in the steering geometry.

Last edited by SEL_69L; 10th July 2013 at 11:39 AM.
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  #23  
Old 10th July 2013, 08:15 PM
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Default Re: Tyres

The safety margin on the front is the difference between the maximum GVM on each wheel and the minimum load rating on each tyre in kg. Same with the back. So that means:

Front

97 (730kg) - (1245kg/2) = 107.5kg each side

Rear

97 (730kg) - (1175kg/2) = 142.5kg each side

So basically MB provided tyres on the front that can carry 107kg more than the capacity of the vehicle on each side and 142kg on the rear.

Doing the same with 96 rated tyres your get 20kg less:

Front: 87.5kg

Rear: 122.5kg

Just remember that's the SAFETY MARGIN, not the payload you can carry above the kerb weight
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  #24  
Old 10th July 2013, 08:52 PM
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Default Re: Tyres

Quote:
Originally Posted by SEL_69L View Post
With zero offset steering, the axis of the kingpin passes through the middle of the contact patch of the tyre on the road. If that is not maintained, the steering becomes heavier, and tyre wear under cornering conditions is biased to one side of the tyre. It is easy to identify a vehicle equipped with zero offset steering. The front wheels LOOK to be way off vertical when the steering wheel is on hard left or right lock. Almost all current production cars have some element of zero offset design approach in the steering geometry.
That would suggest you can't use anything other than et30 on a W116. However AMG offered wheels with et11 and personally I'll trust their judgement. More than that and I believe it's likely you'll strike problems. Most modern MB wheels have very high offsets (above et30) and they cannot be fitted without spacers as they rub on the inner guards. In Victoria spacers are illegal unless they're original equipment
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79 6.9#5541 (Red Bull)
78 6.9#4248 (Skye)
79 6.9#3686 (Moby Dick)
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  #25  
Old 10th July 2013, 09:11 PM
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Default Re: Tyres

Even though the payload has been determined to be 485kg, that doesn't mean you could put all that in the boot, because the maximum GVM isn't evenly distributed front to rear. If you convert to percentages it's a little clearer:

2420kg total (100%)
1245kg front (51%)
1175kg rear (49%)

So if you distribute the payload in the same way you get a payload of:

Front: 247kg
Rear: 238kg

Bearing in mind it'd be rather difficult to add 247kg over the front axle since there's no-where to store anything, it leaves you adding no more than 238kg into the boot. Or 2 x 75kg mates in the back seat and 88kg in the boot. Or 3 x 75kg mates in the back seat and 13kg in the boot!

All very mathematical and it sounds very interesting, but in practice if you add 10kg to the boot, some of it will be carried by the front wheels. It all depends where the weight's positioned in relation to the rear axle. That fact adds so many variables that the only way to know for sure is to run the car over a weighbridge, one axle at a time. I'd love to try it one day....
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79 6.9#3686 (Moby Dick)
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Last edited by Oversize; 10th July 2013 at 09:15 PM.
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  #26  
Old 11th July 2013, 06:08 AM
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Default Re: Tyres

What fascinating discussion and facts being propagated. Some of it probably goes over my head to some degree, but I nevertheless would like to give credit where due - and, in this instance all very much deserved.

To get back to simplicity, there is a question I would like to pose: Some little while ago, one of our esteemed TK members had some 215.70.14 Maxxis fitted, with the appropriate (?) white wall band on the outside - I would respectfully suggest a definite improvement in appearance (!). However, what method or material would be useful in cleaning the white band ? Any suggestions would be welcome. BTW, those Maxxis seem to work and perform well, and they're not too bad in the "Looks" department. Regards. Styria
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  #27  
Old 11th July 2013, 07:23 AM
BenzBoy BenzBoy is offline
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Default Re: Tyres

I use White Magic - http://www.whitemagic.biz/
Cut off a small strip and using the same carwash as for the rest of the car, simply wipe around the whitewalls a few times. After you have done it a few times the whitewalls will be whiter than if you used solvent.
It's dead cheap and dead simple.
Regards,
Brian
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  #28  
Old 11th July 2013, 07:23 AM
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Default Re: Tyres

Quote:
Originally Posted by Styria View Post
There is a question I would like to pose: Some little while ago, one of our esteemed TK members had some 215.70.14 Maxxis fitted, with the appropriate (?) white wall band on the outside - I would respectfully suggest a definite improvement in appearance (!). However, what method or material would be useful in cleaning the white band ? Any suggestions would be welcome. BTW, those Maxxis seem to work and perform well, and they're not too bad in the "Looks" department. Regards. Styria
I was unaware that Maxxis tyres were available with a white band!

Nevertheless, The best way I found to clean the whitewalls of my late Queen of Sheba was plain old thinners...
No scrubbing and no hard yakka.
Just pour some on a rag and wipe seriously et voila!!
I used to clean four tyres in less than 15min.
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