shanusanus

Hi all - well finally did it - changed my 18" 235/50 ZR18's to 19" AMG 63 Titanuim 245/40 19" front and 275/40 19" rear. Im Very happy with them - pics attached!

Ride is good and I get over speed bumps with Air Setting 1 otherwise I get wheel arch rub.

HOWEVER - Since changing the wheels the damn Cruise Control will not engage over 40mph. At 40 mph everything works. However any speed setting I try over 40mph it just flashes the speedo ring and doesnt set.

Now, I'm not too sure but me neighboor feels it may need the cluster calibrating to let it know that ive changed wheel size. IS this true and if so how do we do it? Ive checked the handbook but nothing letting me know why its flashing the speedo rev lights and not setting. I dont get the Cruise Error the book states - it jut flashes the speedo and doesnt set the speed I want - anything over 40mph.

HELP

Jud Chapin

Nice looking wheels! Sorry, can't help with your cruise problem.

lexlyf

If you have the in dash Command Unit, there is a setting to recalibrate for tire size. It is in the navigtion set of menus.

raymond g-

i dont think any amount of recalibration will do the trick here. if you had
studied the tire specs prior to purchase, you will see that the rolling circum-
ference differs vastly between front and rear. accordingly the front tire
will be rolling 755x per mile, whereas the rear is rolling 729x per mile.....a
difference of 188' per mile....3" per revolution. that's extremely bad.
are you sure of the tire specs you posted? if so, why did you select these
tire sizes?

your rears should be 275-35....or, your fronts 245-45.

because the differential in rolling rubber per mile has exceeded the tolerance
limits of the cruise control, it shuts down.

BlownV8

Yep, you are running the wrong size tires.

shanusanus

OK so at present im running 275\40 at rear - if I drop to 275\35 then all is ok?I dont pretend to understand how you work this out though but anyway - would 275\35 at rear solve my prob - thats assuming I keep 245\40 at front?

BlownV8

Yes, that should get everything spinning close enough to stock.

raymond g-

http://www.miata.net/garage/tirecalc.html

enter your front tire specs in the left side. enter your rear tire specs on right
side. compare circumference and rolling data. if the rolling speed/distance
of your front end is greatly different than the rear, the cruise control freaks
out. if you have 4matic, it may also help shorten the lifespan of the power
train and/or cause accelerated tire wear.

it doesn't matter what size your wheels are; it's somewhat irrelevant. but
what is crucial is the tire, since that is the part touching the ground. using
the above calc engine, as long as you keep the tire's rolling distance close
to OEM, the speedo/odo will be reasonably accurate. if you dont care about
the accuracy of the gauges, at least keep the rolling distance of front/rear
tires the same (or within an inch) so that the cruise control and 4matic
systems remain functional and good health.

shanusanus

Thats a great site - thank you so much for that - so I guess im off to get some 2 new rear tyres!! typical

shanusanus

Whats the tolerance range for a CL ?
I mean if I go 245\40 ZR19 front and 275\35 ZR19 rear then that site shows everything good :

Circumference :83.9 \ 83.5 in
Rev\Mile :755.0 \ 759.0

Non Stock 0.5% too fast so 60mph will be 59.7mph.

But is that within OEM range for cruise control to work? Only reason I ask is that I had 235\50 R18 on before and that gave these results:

Circumference :85.6 \ 85.6 in
Rev\Mile :740.0 \ 740.0

Non Stock 0.0% so 60mph will be 60mph.

With regards to Circumference and Rev\Mile thats approx 2 in difference on Circumference and 15-20 diference on Rev\Mile. Is that OK?

vraa

The problem was the sheer fact that your rears and fronts were rolling at very odd speeds because of your odd tire sizes.

As long as you keep the ratios correct (meaning your overall rolling diameter) as close as possible, you'll be okay.

57.44 cm is your OEM front and rear diameter.
With your current setup it went to
58.06 cm in the front
and
59.26 in the rear

As you can see, you're rear is far too high. How wide are your rims?

I think regardless:
That should be correct. So I think you need thinner rear tires.
That would put you at
57.88 cm diameter, much better.

shanusanus

This has all been a rather stressful ordeal

So now I have 5mm spacers on each side to stop the slight rubbing I was getting. But now im 5mm outside the wheel arch at rear - wonder if this will pass MOT now?

And to solve the cruise control issue Im having to buy 2 new rear tyres 275 35 ZR19 - man how annoying is this - just to get some nice wheels

My whole body is aching after taking the wheels off - on - off - on -off - on so many times to try different spacers - im well knackerd

beacham

hi mate, i feel for you on this one. if your going to change the rears why not get a narrower tyre so you no longer need spacers and dont have any rubbing issues. i have 20's on mine and run 245 front & 255 rear this is what the wheels come with and cause me no issues at all.

shanusanus

Hi Beecham - the logical thing would be to narrow the tyres but 1 thing: the alloys themselves are 265mm wide so I cant go narrower than them can I?

As it is I've ordered 2 X 275 35 ZR19 Bridgestone Potenza so I guess we'll try them - I just have that 5mm either side of the wheelarch now! Im just wondering if the lower tyre wall size will let me get rid of the 5mm spacers ?!?!

who bloody knows - im just well tired now!

raymond g-

http://www.1010tires.com/WheelOffsetCalculator.asp

http://www.alloywheelsdirect.net/inf.../mercedes-benz

shanusanus

OK so im thinking these now:

Keeping my 245 40 ZR19 Front and putting 255 40 ZR19 Rear.

That way I hopefully reduce the rubbing on the rear wheels. Ive checked the above website and found the following:

Front Tyre:
Diameter : 26.7in
Circumference : 83.9 in
Revs\Mile : 755.0

Rear Tyre:
Diameter : 27.0in
Circumference : 84.9 in
Revs\Mile : 746.0

It seems that there is an inch difference in Circumference - would you think this is tolerable - esp getting the cruise control working?

Im trying to only have to buy 2 new tyres - rather than having to change all 4

Do you think this would be ok now?

shanusanus

Ok so this morning I take off the rear wheels - remove the 5mm spacers and just out of interest pop the wheels on - what ya know - no rubbing at all!! So my 275 40 R19 seem ok now from a rubbing point of view - work that out!! Maybe it was the brake discs touching the pads I could hear?!?!

But of course I still have the Cruise Control issue so I've ordered 2 new rear tyres in 255 40 R19 size - that should solve my Cruise issue as they are within 1" circumference comparison and also should solve ANY rubbing that MAY have occured. Fingers crossed!.

BTW - anyone here had Bridgestone Potenza REO40 tyres? Dont know much about them but after all my spending recently I had to go with what I could afford now. I Did want Continental Sport 2 but too much for me to spend right now. )

raymond g-

in all the threads, i may have lost sight of some specs. i know you're wanting to
resolve this as soon as possible, but i think you're making a decision and ordering
a little too quickly. give folks here full specs and a chance to respond so that
you're not chasing for a solution in circles.

- i dont think you've posted the full specs for your new rims yet. it would help
me to know the full specs on your old rims as well.
- given a specific set of rims, each has a range of tire sizes it can safely use
- i'm just being overly cautious given your lack of experience and that you're
making a big jump from 275 to 255 on same set of rims....only to realize that
i dont recall seeing the specs on your rims to begin with.
- i'm presuming you're trying to get shoes for your CL500, right? which yr?
in my experience with 210 models, different years may have limits on tire size
and rubbing issues.

(the circumference of your new idea seems within tolerance though)

mclarenm8d

I agree with Raymond's post here, we need more info. IMO, I can't see how anyone would like a 255 rear tire on a CL (FYI, I'm working on trying to find a combination to get a 305 under my CL55 with 275 fronts).

The root cause is that the rear tires were way too tall - this freaked out the cruise control, plus the CL can't easily take an increase in tire height without tire rub if the offset and tire width are held constant.

We would also need to know the width and offset of the rear rims. Fronts seem to be okay for you.

shanusanus

Ok full details here :

Rear Rim size 19" 9.5J. Rim width is 265mm Offset is 35
Front Rim size 19" 8.5J. Rim width is 245mm Offset is 35

I did have 18" wheels with 235\50 ZR18 all round. I do not know the offset and I dont know rim width size - but as I say they had 235\50 ZR18 all round.

I took advice from a local tyre person that 275\40 r19 is what I needed in rear. Obviously this caused the Cruise Control issue and I here ubbing - but strangly is sounds like a metal rubbing (like brake discs) rather than rubber rubbing.

That site you suggested shows I could go 275\35 R19 and that would solve my cruise control issues BUT I also wanted to stop the rubbing sound which I beleive is on the inner wall side of the tyre - possibly on the air suspension tube?!?! although as above - today I think it may be the brake discs rubbing on the pads causing the noise! In any case I still though narrower tyres would be best now so bought 255\40 R19 which according to the site you gave me shows they are 1" circumference difference so should be ok with the cruise control now.

As for going from 275\40 to 255\40 - Ive called 3 tyre shops and they al say that if the rim is 265mm (9,5J) then 255 OR 275 will fit fine. Are they wrong with this information?

raymond g-

- definitely the lower aspect ratio tire in the rear is important.
- i wasn't aware of the rubbing, so of course, the degree of rubbing, the
exact location, etc all helps to isolate the cause, ergo the solution required.
- ....natch, it helps to be certain if it's a disc/rotor rub or suspension
- for a 9.5" wheel width, the 255 seems very acceptable...no worries. you
hadn't reported the width earlier so I was concerned in case the rear was
something like 10"

sounds like you're on your way to solving this. anyone else...feel free to
jump in.