D2 S8 20" Wheel ABS Sensor Repair

[Markiii]

Interesting. 2 questions.

What was the problem you were fixing?

Why is the 20" wheel one difference?

[MikkiJayne]

D2s which had factory 20" wheels have steel struts with larger wheel bearings whereas the non-20" FL cars have alloy struts. The ABS sensor for the steel strut is unique and genuine only so heinously expensive.

[Markiii]

By strut do you mean hub?

[MikkiJayne]

If you like yes. I call the bit that the control arms bolt to the strut or upright, and the turny bit the hub, but they are generally interchangeable Technically upright is probably more correct since its double wishbone rather than macpherson strut.

[Nognar]

It was being replaced as it had failed, thrown a code and was no longer sending a speed reading.

[Markiii]

Originally Posted by MikkiJayne

If you like yes. I call the bit that the control arms bolt to the strut or upright, and the turny bit the hub, but they are generally interchangeable Technically upright is probably more correct since its double wishbone rather than macpherson strut.

Yes upright, that's what I meant. We got there eventually

Must check what mine are

[HPsauce]

Originally Posted by MikkiJayne

D2s which had factory 20" wheels have steel struts with larger wheel bearings whereas the non-20" FL cars have alloy struts.

So there's obviously a reason for this, but what is it and what are the downsides of fitting FE 20" wheels to a car with non-FE alloy suspension?

Or were they just using up the stock of some suspension variant made maybe for the armoured vehicle or some other rare special option?

[MikkiJayne]

I honestly don't know. It is totally counter-productive to handling and ride comfort to fit heavy 20" wheels and then to couple them with even heavier steel uprights which weigh 5Kg more each than the alloy ones. They were specially produced for the 20" cars rather than something which needed using up and are available in both Brembo and HP2 brake fitment.

I can only surmise that something in the load calculations suggested that the alloy upright would not take the stresses of the 20" wheel (or for that matter the 3.3 V8 TDI) and so they designed new uprights from steel instead, and put the larger 92mm bearing in them.

The lower arms are also different for the steel struts - the lower rear has a different inner bush. Possibly stronger?

People have been running 20" wheels with alloy uprights for many years and they are absolutely fine. Whatever calculation it was, there is clearly a substantial safety margin in the alloy stuff. Its probably an extreme use case which no one will ever actually encounter.