sound 8

On my SL63 2013 I have 20 inch rims on the back and 19 inch on the front,
and their black. Now most SL63's have 19 inch all round.
So to keep the gearing correct and the speedo accurate the rear axle
ratio should be different. Now I can't see MB tweaking the odd 63 because
it has 20 inch rims on the back, but aahh you say just change the tyre
profile, BUT they haven't my 20's have 30 profile and the 19 has 30 profile,
and both are 285. So I must presume my car is over geared with a slow speedo. Anybody from MB could throw some light.

VII

The difference is accommodated by software setup, don't sweat it.

crazyfox

Well I m running 22 rear n 20 up front.

okbarnett

do you think mercedes would FU something like that out of ignorance , or on purpose? then you shouldnt have considered paying $150,000 for the car

sound 8

I think the 20 inch rears should have 25 profile tyres, it doesn't matter if
you put 22 or any size wheel as long as you fit the right profile. This can be
done on a tyre/wheel calculator. The gearing is obviously made for a 19 inch
rim, so I guess as long as it is within the law speed wise then they just ignore it. It does mean though slightly slower acceleration.

Thericker

1st I've never seen a single OEM MB "Sedan/Car not talking SUV etc" running a 285 tire up front, somone added those after the fact.. 2nd according to tire size 285/30/20 285/30/19 you're indeed skewing rear gear ratio w/taller gearing & slightly slower acceleration...
http://www.miata.net/cgi-bin/tirescgi

You may even notice overly aggressive ESP cutting your fun while burning out or hard acceleration it'll cut throttle pull timing even add brakes, if the ECU senses anything over 2% size difference from back to front it will indeed do the above.. If your tires/wheels are as described the difference is 1 full inch in diameter or 3.9% you should be running 265/35/19 up front 285/30/20 rear lowering difference to just 3/10 of inch in diameter or 1.6%

sound 8

Thanks Thericker you know your stuff.
So I am left with a problem
without spending a fortune on a new axle.. the only thing to do is fit a 25 profile tyre. Which means a harder ride, unless you can help further.

pigskinplayers

I'm in the wheel and tire biz...here's an easy way to calculate overall diameter ..

section width x aspect ratio with decimal pt = sidewall height

sidewall height x2 = equals actual rubber height top and bottom

then you convert to inches by dividing total by 25.4

finally add rim size.

so 285/30/19

285 x .30= 85.5 x 2 = 171 /25.4 = 6.73 + 19 = 25.73 overall height

265/35/19

265 x .35 = 92.75 x 2 = 185.50 / 25.4 = 7.30 + 19 = 26.30 overall height

This formula gets you close but each manufacturer uses uses slightly different tread depths so a tire can vary a few 10ths.

Hope that helps!

crazyfox

I see. That in fact explain my problem too. Ok I had a wide body n what's the ideal size of wheel n tire? Can I go 20 all around?

Thericker

The 285/30/20 rear is INDEED correct ratio for the rear, your 285/30/19 fronts are CAUSING your specific problem. Change out your front tires to 265/35/19 as I said above & your car will be setup perfectly w/less than 2% diff in diameter from back to front

Thericker

22"s are far too large, go 20" ALL around w/proper tire sizes IE use Calculator link I suplied above, make certain your overall tire diameter doesn't differ by more than 2%

Thericker

Basically same info & WAY easier..
-----------------------------------Tire Size Comparison--------------------------------
Specification---Sidewall--Radius---Diameter--Circumference----Revs/Mile--Difference
285/30-19-----3.4in-----12.9in----25.7in-----80.8in------------784---------0.0%
265/35-19-----3.7in-----13.2in----26.3in-----82.6in------------767---------2.2%
----------------------------------- Back to the Calculator-------------------------------

crazyfox

Thanks . Btw what are you running on thericker? Front n back? Ur car looks really cool!

crazyfox

This might help sound8? Not for wide body.

Thericker

345/25/20 265/30/20 -2% difference

Though I just bought set of super lightweight CCW 18x13 18x10 gonna roll on 345/30/18
265/40/18 The fat front aspect ratio is to make up for giant 345's IE difference is less than 1%

sound 8

WOW my head is spinning with so much info..
However if I bought my car with 285 30 19 and then changed and put
285 30 20 surely this is wrong. Forget the fronts, I thought if you went
up in size you came down in profile. I checked on the calculator you gave me
and a 30 profile on a 20 is much bigger in diameter than a 19 with 30
profile. If I fit 295 25 20 it is almost identical to 285 30 19. Or will the diff
sort out the difference.

Thericker

The 285/30/19 up front is way to WIDE forget the Aspect ratio difference for a second. 285's shouldn't be on front of ANY perf oriented 2 door lux vert.. They're most def slowing you down & killing gas mileage & I'd be surprised if they don't rub on tight turning or over bumps etc.. Best route is 265/35/19

Wolfman

I had the same thoughts when I installed the same wheels as Sound8 on our 2013 SL550.

The rear tire size just seemed wrong. Since I am on our 2nd SL in 3 months I was able to check the car speed via GPS with 19" all around and then with the 19"/20" combo.

Speedo and GPS was the same for me on both sets of wheels.
While all the wheel diameter calculations are correct and should account for a slower speed, I assume that the R231 SL computers recognize the the different rotational speed of the rears and adjust the speedo for that.

After all, it's hard to believe that AMG would cripple their SL65 (stock wheel combo) or their SL63 (forged wheel upgrade) on purpose.
Since nothing is mechanical anymore and wheel rotation data is constantly used for ASR, ESP, active lane assist, etc. there is no reason to think that MB can't add a different wheel rotation setting for the forged wheel package.