Mercedes-Benz Forum banner

1 - 12 of 12 Posts

·
Premium Member
Joined
·
440 Posts
Discussion Starter #1 (Edited)
Would someone who understands wheel alignment terminology please check my conclusions below regarding rear wheel toe-in.

I have now worn out two sets of rear tyres and decided that the rear suspension parts were stuffed, so have ordered replacement parts. While waiting for the parts to arrive I was contemplating the rear alignment specs.

At the last fitting of my new Rear Tyres (265/40 R18 97Y) the very reputable Tyre Company set the Rear Total Toe-in to 9.5mm, and according to them the specified range for my car is 6.7mm to 13.1mm. I immediately drove back and complained because I noticed;
  • I could smell burning rubber when I drove home.
  • The rear wheels look ridiculously toed-in.
  • The back edge of the rear wheels stick out beyond the mud guard.
  • The back of the car skates sideways slightly whenever a rear wheel jumps off the road when going over a pothole.
The Tyre Company double checked and assured me that they were correct. I then took the car back after 2,000Km and they checked again and said all was well. (The rear cambers were RL -1 deg. and RR -2 deg. 25 min. The planned new camber struts should bring these closer to spec. 1 deg. 26 min. +/- 30 min.)

Now after 11,000Km the rear tyres have worn through the steel on the inside edge. (I know the tyres are unsafe but we had to finish a 900Km journey and I did not notice the bad wear until doing another job on the car.)
W220 Rear Tyres with Worn Steel Showing.jpg

I used WIS to determine the specified Rear Total Toe-in (for W220, not engine 275, not USA, not 4MATIC).
W220 Rear Toe In Specification.jpg

WIS recommends measuring the rear vehicle level using an inclinometer (086a) on the rear half shaft.
Inclinometer on rear half shaft.jpg

I have discovered an app for a smart phone which also does the inclinometer job. This diagram shows how.
Smart Phone Inclinometer App on rear axle.jpg

The preferred rear vehicle level is -1.9 deg. with a tolerance of +/- 1.0 deg.

The problem is to convert the specified Total Toe-in angle to mm. Later edit after I was alerted to a wrong assumption on my part. See more accurate diagram at Post 7.

I developed a spread sheet to convert the Total Toe-in angle to mm and produced these results. Later edit after I was alerted to a wrong assumption on my part. See more accurate diagram at Post 7.

Here is the maths I used. Later edit after I was alerted to a wrong assumption on my part. See more accurate diagram at Post 7.

To summarise; Later edit after I was alerted to a wrong assumption on my part. See more accurate summary at Post 7.

As always any comment and advice is much appreciated.
Regards,
Brian
 

·
Registered
Joined
·
145 Posts
1) You may mix the toe in with camber.

2) The rear axle may not perpendicular to the rim at all via c/v joint.

3) It is true to me measuring the difference between the edges ( diameter ) instead to the centre ( as radius). So effectively, the toe in in mm will be doubled from 4 to 8 mm.
 

·
W220 Moderator
Joined
·
1,129 Posts
THis may help with "Target Values". MB dealer printout from my last alignment in Nov.
 

Attachments

·
Registered
Joined
·
2,387 Posts
Well, I am confused.

"The rear wheels look ridiculously toed-in.
The back edge of the rear wheels stick out beyond the mud guard.
The back of the car skates sideways slightly whenever a rear wheel jumps off the road when going over a pothole."

All of that strongly suggests very excessive toe in.

Yet, from the tire wear, you appear to have very excessive toe out, not toe in. Toe in has the front of the tires closer together than the rear of the tires. It is common for the front wheels to have toe in, the rear wheels to have toe out, on a rear-drive vehicle. Excessive toe in will wear the outside edges of the tires, excessive toe out will wear the inner edges of the tires.
I have not investigated the MB specs, but toe is commonly measured as the difference between the distance between the front edges of the tires and the rear edge of the tires. That difference is commonly around 6-8mm. I don't think that you would easily see 9.3mm total toe, and I would expect a rear-drive car to have toe out, not in.

My understanding has been that the rear toe is only very minimally adjustable on the S Class cars. Do you have bent parts? The wrong parts?

The angle of the half-shafts will show camber, not toe. Camber is the angle you see from behind the car. Toe is the angle you see from above the car. Excessive negative camber (top of the tires closer together than the bottom of the tires) will wear the inner edges of the tires, but I can't imagine camber wearing the edges as sharply, and as much, as the photos show.
 

·
Registered
Joined
·
190 Posts
Wallyp, I agree with everything.

Brian, there is something very wrong with the very reputable Tyre Company. Rear wheel drive cars usually have slight toe-in at the front and slight toe-out at the rear. As wallyp says, your tyres indicate serious toe-out. Perhaps the technician confused a toe measurement taken at the front axle to be the toe measurement taken between the front and rear of the wheel.

The handling would have been very strange. I expect it would have felt increasingly unstable at high speed. It must have been quite unpleasant to drive.

The alternative is that there's a worn bush or ball joint somewhere.

Most models of the W220 are a little unusual in that the front and rear tracks are exactly the same, so if your wheels have the same width and offset (like mine and many others) then when the steering wheel is exactly straight ahead, the front and rear wheels will be exactly in line with eachother if the toe is zero. That's a pretty good starting point by the way.

(I have 275/30/20's all round, which are incredibly sensitive to everything - toe, camber, ride height, roundness, balance, tyre pressure, bearings, bushes, ball joints, kerbs and pot-holes - but are amazing when everything is right).

Nick
 

·
Premium Member
Joined
·
440 Posts
Discussion Starter #6 (Edited)
1) You may mix the toe in with camber.

2) The rear axle may not perpendicular to the rim at all via c/v joint.

3) It is true to me measuring the difference between the edges ( diameter ) instead to the centre ( as radius). So effectively, the toe in in mm will be doubled from 4 to 8 mm.
1) Definitely not true.
2) Agree.
3) Thank you. That is what I was getting wrong. I will redo my diagrams and calculations.

Thanks for the reply, Brian
 

·
Premium Member
Joined
·
440 Posts
Discussion Starter #7
I didn’t want to open a can of worms with my post but thanks for the comments.

Dalplex alerted me to my mistake in the original post so I have done some more research and am closer to the truth.

My starting point was the M-B specified Total Toe-in Specification for my car which is (at rear axle level -1.9 deg.) an angle of 41 min. (+/- 14) min.)

I had to convert the toe-in angle to a toe-in distance in mm because that is what is shown on my wheel alignment print out.

Toe is the angle of the wheels with respect to the vehicle’s centreline. Toe-In (Positive Toe) is where the front of the wheel is closer to the geometric centreline than the rear of the same wheel.

Reference Wikipedia, toe can be measured in linear units (ie a distance in mm), as the difference in the distance between the front of the tyres and the back of the tyres, or as an angular deflection (ie in degrees or minutes).

Consequently I should have calculated the total toe-in mm as the distance between the front tread and the rear tread on the same wheel, where-as I calculated the total toe-in mm as the distance from the wheel straight ahead (parallel to centreline) position.

I will now reproduce the diagrams with the correction.

Here is the Corrected Total Toe In Angle to mm diagram.
Corrected Total Toe In Angle to mm Diagram.jpg

Here is the Corrected Total Toe In Maths for 669mm Diameter diagram.
Corrected Total Toe In Maths for 669mm Diameter v2.jpg

Here is the Corrected Total Toe In Angle to mm Results for 669mm Diameter.
Corrected Total Toe In Angle to mm Results for 669mm Diameter.jpg

And here is my new summary; the specified Total Toe-in for my car (at a vehicle level of -1.9 deg.) is 41 minutes which corresponds to a Total Toe-In of 7.98mm.

At my last wheel alignment the Tyre Fitting Company specified Total Toe-In as 6.7mm to 13.1mm which averages at 9.9mm.

So it looks like a rear total toe-in setting of 9.5mm is very acceptable.

Regards,
Brian
PS I will go back and edit the original post and delete the wrong diagrams.
 

·
Premium Member
Joined
·
440 Posts
Discussion Starter #8
Thanks wallyp and welwynnick,

I have corrected a wrong assumption on my part which makes the Wheel Alignment Company's settings look much better.

The worn through steel on the inner edge does look like excessive toe-out, but be assured the wheels do have 9.5mm toe-in.

It looks like what caused the inner strip of both rear tyres to wear are worn rear camber struts and rear torque struts.

I have spent the morning under the car checking for any slack in the rear suspension components. I used a long adjustable spanner and measured the amount of movement (distance the end of the spanner moved) as I twisted each suspension component.

  • Component, RR, RL
  • Camber Strut,15mm, 10mm
  • Torque Strut, 20mm, 30mm
  • Track Rod, 15 - 20mm, 15mm
  • Thrust Arm, 2mm, 2mm
  • Tie Rod, Nil, Nil
I will now go ahead and order all new components.

Regards,
Brian
 

·
W220 Moderator
Joined
·
5,531 Posts
Hi Brian,

Take this with a pinch of salt, because I have not looked up MB specs on this !!

However,

~ 1.5 Degrees Camber sounds quite acceptable, but 9.5mm Toe In ????????????????????

I suppose that depends how and where it is measured, and what measuring equipment is used :dunno:

But on a "Normal" Set of Laser Tracking Gauges like mine, I'd expect the Front Wheels to be almost Parallel, just a touch of Toe in, and Rears just a touch of Toe Out, like most RWD Vehicles :dunno:

Like you say, your corrected figures indicate ~ 41 min , so like 2/3 of a degree, yeah that sounds much better :wink

Oh, and finally, my experience of watching other Garages, Tyre Bays etc attempt any Wheel Alignment shows that none I've ever seen actually know what they are doing, and if they do, they do not check the Calibration of their Gauges, rendering the Figures Measured useless :rolleyes:

HTH,

Cheers Dave
 

·
Registered
Joined
·
956 Posts
Ricebubbles:
I had rear tire wear like yours long time ago on my "end of life" tires, that just very rapidly got worse.
Wheel alignment checks were reasonable, but the right chamber eccentric bolt was seized, and the mechanic would not try to make it perfect, from experience it would most likely break.
But 220 rear suspension is a tire eater.

Nice to hear from you!
 

·
W220 Moderator
Joined
·
5,531 Posts
Hi,

They don't wear Tyres when all arms are good and alignment is spot on, staggered wide set ups do a bit, but not terrible ;)

I find in UK that our MOT Testers can't fail on some types of worn bushes, hell I don't think they can actually feel them unless they are really hanging, so owners just keep on driving with shagged rear end !!

According to my local Tester, a Bush where the Bolt goes all the way through with Chassis / Subframe both sides can have no rubber left, yet they still can't fail it, because the Arm cannot actually fall off :frown

Yet another tester, who is IMHO really Anal, will fail a Bush which is perfectly OK, just a few slight perish marks on the rubber............. :dunno: ..............

What I do know is that there is no "Consistency" in the UK Annual Test, it is all "In The Opinion Of The Tester" DOH !!
Some testers are absolute "no nothings" ;)

Cheers Dave
 

·
Premium Member
Joined
·
440 Posts
Discussion Starter #12
THis may help with "Target Values". MB dealer printout from my last alignment in Nov.
Hi Ex-FEd,

Your attachment is very pixelated and hard to read but I have made out that your rear toe-in specifications (target values) for your 2006 US W220 S500 are;
total toe-in 42 minutes at a rear axle level of -0.4 degrees.

This compares well with my 2003 Update EU spec'd (Australian Delivered) W220 which are;
total toe-in 41 minutes at a rear axle level of -1.9 degrees.

Your results give me confidence that I have assumed the correct specification values for my car.

It is interesting that the preferred rear end ride height levels are different for different countries, with your US W220 sitting closer to the ground than my EU spec'd car.

It also confirms a large degree of toe-in is specified and not parallel or even toe-out as suggested by some posters. By large I mean that 41 minutes of angle is the same as 8mm of linear toe-in (as measured between the front tread and the back tread of the rear tyres.

Regards,
Brian
 
1 - 12 of 12 Posts
About this Discussion
11 Replies
7 Participants
ricebubbles
Mercedes-Benz Forum
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!
Full Forum Listing
Top