tyres that fit the 18s on a 4200

[Budapeststu]

Hi All,

It's been a while and I have a question that relates to my ongoing plan to get back into Maser ownership. I have a set of winter tyres for my SL55, which are 255/40 R18s all round. I'm wondering if anyone can confirm if these would fit the 18" rims of a 4200?

I have 18" rims on the SL and the front/back sizes for the summer tyres are similar to what I had on the Maser (currently 255/40 R18 on front 8.5J and 285/35 R18 on rear 9.5J).

It's £1,000 a set for good winter tyres and if I'm going to come back into the fold it'd be a big help if I don't have to buy another set of winter rubber.

Any thoughts?

Stu

 

[Emtee]

Hi Stu,

Here are the standard 4200 tyre sizes...

Front - 235/40/18

Rear - 265/35/18

You might be okay with the fronts running 255/40/18's as you're oversizing, but not sure about undersizing the rears?

 

[Budapeststu]

Hi Miles,

Good to hear from you. The Merc has 285's for the summer and the 255's go on just fine. I was sceptical but my tyre place here said they'd be fine. I'll check on the wheel dimensions with my tyre dealer but as I think only the profile of the tyres is really critical and there's 5mm difference at the back only then I think I'll be ok. If I have a definitive answer I'll let you know.

Stu

 

[Emtee]

Hi Stu,

Hope all is well with you?

Let me know how you get on? I'd be interested to know how far you can vary from the prescribed sizing? If they're okay, I assume you'll have exposed wheel rim and will need to be extra careful in those slippy conditions?

 

[rotorheadcase]

Going down in tyre width at the back and up at the front will induce more oversteer. You can dial some of this out with a wheel alignment but honestly you are better off getting the correct tyres.

10 mm a side at the back may not seem like much but combine that with an increase of 20 mm a side at the front and you can come unstuck on a slippery roundabout or turn in the blink of an eye. Use the 255s at the back by all means but get a pair of 225s for the front to balance this out.

Regards,

Neil

 

[ENZ525]

Think it is also worth mentioning that the profile, ie, the 35 or 40, is a percentage of the width,
so this will also make a difference on the overall rolling circumference.
Using 285/35/18 and 255/35/18 as examples, this gives 1980.56 vs 1917.22 mm,
or a -3.2% difference on the rear...(with the speedo showing 70mph you are actually doing 67.76)
For the 235/40/18 vs 255/40/18 the numbers are, 1945.88 vs 1994.13 mm,
or +2.48% on the front... (with the speedo showing 70mph you are actually doing 71.74).

 

[rotorheadcase]

Good point Enzo, I had forgotten to mention aspect ratio. The rears are close but the fronts are well out and may cause problems with the ABS and/or traction control.

Regards,

Neil

 

[Budapeststu]

Hi All,

Thanks a lot for the advice, I certainly take Neil's point on the front tyres re going for a wider tyre than the current one. Now I see that on the Merc the fronts are the same width/profile and only the backs are more narrow. I don't know if the Merc's electronic suspension is set up to deal with different sizes of winter/summer tyres at the back but this is certainly the official size I was advised of.

Miles, I'm doing very well thanks, all the better for being back here on the forum. The 255's on the back of my SL looked fine and there was no exposed rim to speak of. I don't know how that works either but they fit just fine and I drove the car for 6 months in snow and ice with total confidence. Any Maser owner will surely appreciate that if I feel safe driving a rear wheel drive car with 500 BHP in snow and ice then the tyres must be serving me well.

I hope to be back with a Maser soon. I'll keep you all posted on my progress.

 

[safrane]

Think the wrong tyres will also throw the ASR/MSP into a wobble.

 

[Emtee]

After hearing that a few of the US owners ran over-sized tyres to protect their rims, I did the same with my 4200 and had no issues. I used the details below to settle on the nearest best size. I'd be wary of a mixture of over and under sizing though.


Rear standard.

265/35/18 - Overall tyre diameter of 643mm. Circumference of 2019mm. 797 revolutions per mile.

Options.

275/30/18 - Overall tyre diameter of 622mm (a difference of -21mm or -3.27% against standard). Circumference of 1955mm. 823 revolutions per mile.
275/35/18 - Overall tyre diameter of 650mm (a difference of +7mm or +1.09% against standard). Circumference of 2041mm. 788 revolutions per mile.

285/30/18 - Overall tyre diameter of 628mm (a difference of -15mm or -2.33% against standard). Circumference of 1973mm. 815 revolutions per mile.
285/35/18 - Overall tyre diameter of 657mm (a difference of +14mm or +2.18% against standard). Circumference of 2063mm. 780 revolutions per mile.

Front standard.

235/40/18 - Overall tyre diameter of 645mm. Circumference of 2027mm. 794 revolutions per mile.

Options.

245/35/18 - Overall tyre diameter of 629mm (a difference of -16mm or -2.48% against standard). Circumference of 1975mm. 815 revolutions per mile.
245/40/18 - Overall tyre diameter of 653mm (a difference of +8mm or +1.24% against standard). Circumference of 2052mm. 784 revolutions per mile.

255/35/18 - Overall tyre diameter of 636mm (a difference of -9mm or -1.4% against standard). Circumference of 1997mm. 806 revolutions per mile.
255/40/18 - Overall tyre diameter of 661mm (a difference of +16mm or +2.48% against standard). Circumference of 2077mm. 775 revolutions per mile.


One of the calculators I used advised no more than +/-2.5% variance in diameter.

 

[rotorheadcase]

Nice summary there Miles. No harm at all going +1 on the width, provided that you do exactly as you have done.

Regards,

Neil

 

[Fat Arnie]

Bear in mind that any two tyres of a given size, if from different manufacturers, or even ranges, are not necessarily the same size.

For example I used to run Avons on my Caterham, there were ACB10's which were marked 245/45/13 and had an actual section width of 221mm, 561mm dia and CR500's which were marked 205/55/13 and had an actual section width of 230mm on 554mm dia.

The above is an extreme case, but shows that variance between brands.

The traction control will be marginally upset by diameter changes, but not in a sufficient manner to be detected by any of us in terms of change to slip angles.

If you want more grip, dont look to change sizes, look at the compound.

The two tyres I mentioned above were 2 secs per lap apart on circuits like Brands GP, this being down to compound.

Good tyres are not those fitted OEM, and the Japanese make some very good tyres such Toyo Proxes T-1. They wont last anything as long a Pirellis, but will give MUCH more grip as they are much softer. Less wheelslin, more lateral grip, less understeer.

If the 4200 has adjustable spring platforms like the 3200s, corner weighting the car will also massively enhance handling.

 

[rotorheadcase]

All good points Arnie, but the original post was concerning winter tyres, in which case Proxes are like proverbial ice skates. The Yoko Advans on my AWD Porsche are diabolical in the wet but give me an extra 3-4 seconds a lap on a dry warm track. For R spec tyres temperature is critical, as you know.

Corner weighting is a very good idea but not many places do it correctly or can be bothered to take the time.

Regards,

Neil

 

[Fat Arnie]

Oh, I failed to pick up on the winter tyres bitany.

Main point however is that the size variation between brands is very significant.

I would also suggest that if you take one of these cars near conditions that require road salt, it will start to personally decompose rather rapidly compared to most other cars.

I'd buy a winter shed instead.

 

[davy83]

Any one tried a 285/35/18 on the rears? Does this protect the rims a bit better? I have noticed how the rim looks like it will hit the kerb before the tyre which does not seem right to me.

 

[Parisien]

Vredsteins protect the rim better........but always avoid potholes at speed due to re-inforced sides......


P

 

[rotorheadcase]

285/30 would be a better match, the 35 aspect ratio would probably throw out the ABS/ASR.

Regards,

Neil

 

[davy83]

Why would 2% larger diameter be worse than 2% lower diameter for the ABS/ASR? Must be the same more or less? I am thinking the walls are low enough without making them any lower? potholes, ride quality etc? I am also thinking I quite like these Falkens that some one on here recommended that I put on the front and they don't come in 30 profile.

 

[rotorheadcase]

My understanding is that the ABs is more tolerant of lower diameters because tyres if not checked, deflate over time not inflate and the manufactures need to account for people who did not check tyre pressures routinely.

Neil