14" and 15" rim wheel alignment specs 116 Vs 126

[goldacre]

Hi folks, some time ago i put on the late model W126 15" rims and some decent tyres (Turanza 225/60/15) on my 450 SEL (4.5) and had the wheel alignment done (digital one) and the specs set where as record for a 1979 450 SEL. After some decent driving both front wheels are showing noticeable toe in wear (inner part wearing too quickly and both tyres show even wear to each other), the cars rubbers in the suspension are good and new tie end rods were put in prior to the alignment and the driving i do is country miles so the wheels have had a comfortable run (no curbing and the like).

Questions are:
1) should one use the wheel alignment specs for a late model W126 Merc which had these 15" rims on them?
2) is there any fundamental differences in suspension set up (layout less the hydro stuff) alignment specs between the 6.9 with 15" rims compared to the 4.5 with 14" rims?
3) any other leads and/or ideas?

Many thanks

G

[oversize]

The W126 wheels have an offset of ET25 vs the W116 of ET30.  6.9s and 450s used the same diameter wheels but the 6.9 used a wider wheel (6.5" vs 6").  Changing the offset can affect the scrub radius and affect all manner of handling characteristics.  However when modifying a car you have to look at the individual car's needs and intended use, not what the manufacturer suggested.

In the absence of specs racers use infra-red thermometers to check tyre temperature and make the necessary adjustments to the front end as required.

Do you know the difference between toe and camber?  Excessive toe out creates accelerated wear with feathered edges on the inner tread blocks.  Excessive negative camber causes accelerated wear on the inner shoulder of the tyre and the tread wear is smooth in both directions.

[TJ 450]

I would be double checking the condition of the control arm bushes and ball joints, I thought they were reasonable on my 6.9 until I replaced them... it feels like a new car now.

Are there any knocks, or is the steering lacking precision?

Alignment specs shouldn't be any different between the wheels, as they will have about the same rolling diameter. They will be different on the 126, as the suspension setup is quite different.

Normal wear patterns on the 116 front tyres show more wear on the inner shoulders.

Excessive negative camber can also be due to collapsed inner upper control arm bushes (unlikely).

Tim

[TJ 450]

Also, the regular 450 has the same 6 1/2" wheels as the 6.9 from the factory.

Check the condition of the tie rods, drag link and idler arm bushings if you think the toe is incorrectly set.

If anything is slightly worn, it wouldn't hurt to replace them all at once with Lemfeorder parts...

Tim

[ptashek]

Could this not also be caused by doing alignment without the push-bar used to load the front axle, as suggested in the workshop manual?

[goldacre]

Hi folks, thanks for the feed back, responses as follows:

The W126 wheels have an offset of ET25 vs the W116 of ET30.  6.9s and 450s used the same diameter wheels but the 6.9 used a wider wheel (6.5" vs 6").  Changing the offset can affect the scrub radius and affect all manner of handling characteristics. 

Cool, will investigate this when i get one of the rims off the car as have purchased a set of disk brakes that need putting on rain permitting  The late model W126 are said to be a direct fit according to Tom at the Classic Centre and was a very popular upgrade they did but have just been told they no longer
have the new W126 rims in stock, all sold out and none left apparently, bummer 

Do you know the difference between toe and camber?  Excessive toe out creates accelerated wear with feathered edges on the inner tread blocks.  Excessive negative camber causes accelerated wear on the inner shoulder of the tyre and the tread wear is smooth in both directions.

Just jumped online and did some research on the toe and camber and found the following:

One Side Wear -
When an inner or outer rib wears faster than the rest of the tire, the need for wheel alignment is indicated. There is excessive camber in the front suspension, causing the wheel to lean too much to the inside or outside and putting too much load on one side of the tire. The car may simply need the wheels aligned, but misalignment could be due to sagging springs, worn ball joints, or worn control arm bushings. Because load has a great affect on alignment, be sure the car is loaded the way it's normally driven when you have the wheels aligned; this is particularly important with independent rear suspension cars.

this fits my wear pattern and equal-distance to by fact they both show the same level of wear so perhaps an issue with the original alignment?

I would be double checking the condition of the control arm bushes and ball joints, I thought they were reasonable on my 6.9 until I replaced them... it feels like a new car now. Are there any knocks, or is the steering lacking precision? Normal wear patterns on the 116 front tyres show more wear on the inner shoulders. Check the condition of the tie rods, drag link and idler arm bushings if you think the toe is incorrectly set.

steering is spot on from the feel of things, no complaints here, good to know its a normal occurrence for the W116 although the klm i drive are bugger all which is cause for concern, at this stage looking at the camber issue as this fits the wear pattern. have actually just replaced the drag link, one of the easier jobs this week  the tie rods are brand new but everything else is original.

Could this not also be caused by doing alignment without the push-bar used to load the front axle, as suggested in the workshop manual?

i tackled this by getting my mate to sit in the drivers seat to add normal driving weight, the dog only weighs 6 kilos but they put her on the passenger seat anyway  i have heard of the rod method, no idea how it works or if any wheel alignment dealers use it 

Many thanks folks, have a few places to look at, we have a full on wheels and tyre dealer in our town to may take down for another check and service, especially after replacing the drag link.

G

[Mforcer]

The W126 wheels have an offset of ET25 vs the W116 of ET30.  6.9s and 450s used the same diameter wheels but the 6.9 used a wider wheel (6.5" vs 6").

From memory, I think the ET30 vs ET25 was the difference between the 6" and 6.5" rims. My AMG 16x7.5 rims have a lower offset, et17 and I haven't noticed any issues with uneven tire wear.

[goldacre]

Halfway through putting on new front disk  (if you don't have a vice handy place the disc assembly onto the front wheel you took off and place bolts for wheel through the rim reverse stye to secure the disk assembly in place then you will have an anchor to undo the freakingly well secured hex bolts holding the disk to the hub!) 

OK, checked the steel 15" rims and they are 7" rims with an ET of 25 (ET25) for the uninitiated the following link/info explains what the flip is ET?

http://www.wheelsrus.com.au/blog/tech/wheel-101-wheel-terminology-explained/
What does Offset mean?
The distance between the centreline of the wheel and the plane of the hub-mounting surface of the wheel is known as the wheel offset.
The offset can be either positive or negative, and is typically measured in millimeters. Offset has a significant effect on many elements of a vehicle's suspension, including suspension geometry, clearance between the tire and suspension elements, the scrub radius of the steering system, and visually, the width of the wheel faces relative to the car's bodywork.
Offset is usually stamped or engraved into the wheel and is measured in millimeters of 'ET' [ET is the short form of the German word 'Einpresstiefe' which literally translates as 'insertion depth'. (LOL!!!!  ) An example would be "ET45″ for a 45mm offset.
Zero Offset wheels have their mounting face even with the centreline of the wheel and are by definition "ET 0″.
Positive Offset wheels have their mounting face toward the front face of the wheel.
Negative Offset wheels have their mounting face toward the rear of the wheel.
The easiest way calculate wheel offset is as follows:
First, measure the overall width of the wheel (remember, just because a wheel is 18×7.5, does not mean that the OVERALL width is 7.5". It means that the measurement between the outboard flange and the inboard flange is 7.5"). Next, divide that width of the wheel by two; this will give you the centreline of the wheel.
Overall width/2 = Centreline
After determining the centreline, measure from the hub-mounting surface of the hub to the edge of the inboard flange (if the wheel were laying flat on the ground – face up – your measurement would be from the ground to the hub-mounting surface). This is your back spacing.
Back spacing – Centerline = Offset

G

[ptashek]

Could this not also be caused by doing alignment without the push-bar used to load the front axle, as suggested in the workshop manual?

i tackled this by getting my mate to sit in the drivers seat to add normal driving weight, the dog only weighs 6 kilos but they put her on the passenger seat anyway  i have heard of the rod method, no idea how it works or if any wheel alignment dealers use it 

MB does, and other shops that have seen a W116 before tend to remember.
It's used to simulate driving conditions on the front axle, basically pushing the wheels out as they would be when the car is driven. Or so I understand it reading the manual. 

[TJ 450]

When I've installed new discs in the past, I've bolted it (the hub) onto a wheel... that gives you lots of leverage, but it's still a challenge for sure.

Tim