[ROVERNET - UK] P6 Design & Rear Suspension Function

[Glen Wilson]

Vern Klukas wrote:
> Body roll has very little to do with road holding (and, btw, has 
> nothing to do with a car overturning, that is dependant on lateral 
> roadholding, the track width and the car's centre of gravity), and I 
> would suggest that it was the driver lifting in the P6 that allowed 
> you to pull ahead. When the boys and I would take customers cars out 
> for "road tests," I never had trouble keeping up to a SD1 in a V8 P6. 
> In a 4cyl P6, the SD1 would walk away on the straights but I could 
> stay with him on the twisty bits.

I'm not arguing the mechanics of the thing with you, Vern, because I 
think you know a lot more about that than I do, but when a car is 
leaning heavily and the tires are losing grip, you've reached the limits 
of the the car's roadholding ability. I've owned a couple of French 
cars, so I know what you mean about body roll vs roadholding.

Also, the twisty bits are not the same as the freeway on/off ramp I 
specified. The ramp is more like a skid  pad than a road course.
>>
>> So, I'm not knocking the P6 suspension, but I'm not sure that all of 
>> the complexity bought you all that much for all of the expense and 
>> service hassles. The SD1 had a well-located live axle that wasn't all 
>> that different from what was installed under Volvo sedans up into the 
>> 90's.
>
> Beg to differ there, the SD1 was much more sophisticated than Volvo's 
> approach
>
Well, then, you're making my argument for me. I don't know how 
sophisticated it was, but it was a whole lot simpler than the P6 rear 
suspension. The SD1 rear suspension only has about ten moving parts to 
it, if you include all of the bushings. It couldn't have been expensive 
to manufacture (or it wouldn't have been on the SD1 in the first place), 
and it is simple to service.
>>  The complexity made it more difficult and expensive to service due 
>> to the time it took to do things like setting the valve clearances 
>> (on the 4-cyl)
>
> But how often do you set the valve clearances on a 2000?

Isn't once enough? Would your design choice be an engine that 
necessitates the removal of the cylinder head (often more than once 
according to posters on this list) in order to adjust the valve 
clearances? And, of course, Rover manufactured a special jig for that, 
too. Who wants an engine where a wrench, a screwdriver, and a set of 
feeler gauges is all you need to do the job? No fun in that. Then 
there's the cost of the cylinder head gasket.

The 4-cyl valve clearance snafu speaks volumes to what sort of 
priorities Rover had.
>
>> or servicing the rear brakes, to say nothing of having to source 
>> front shocks that are valved in reverse to every other car on the road.
>
> Total red herring there Glen. The same can be said for any part of any 
> car, that is unique to that particular model.

Red herring fallacy <http://en.wikipedia.org/wiki/Red_herring_fallacy>, 
a logical fallacy in which one purports to prove one's point by means of 
irrelevant arguments

Not at all. Shocks are a routine service item that can be sourced from a 
variety of vendors located around the corner. Since most shocks, at the 
time, fit several different vehicle, they were more likely to be stocked 
and would be priced lower. Maybe these things were readily available in 
the UK, but not in the USA.

The argument was that the design made the cars inherently difficult and 
expensive to service compared to other cars. This was true in the home 
market, but it was doubly true in the American market where they hoped 
to sell a lot of cars. If you went to someone other than a Rover 
specialist (ka-ching!), the shocks wouldn't be readily available, and 
the local master mechanic wouldn't have the tool to adjust the pistons 
out of the rear brake calipers. To adjust the valve clearance, the 
mechanic would have to order a head gasket set from Rover and then be 
willing to take on the liability for removing and reinstalling a 
cylinder head. Of course, that wouldn't be so bad because he'd be 
charging you $300 to adjust your valve clearances, anyway, due to the 
inherent issues designed into the engine by Rover engineers and approved 
by Rover management.

Volvo service would have laughed out loud at such silliness. And Volvo 
sales may well have pointed out that the P6 you were considering would 
be off the road for two days and cost you hundreds of dollars for what 
were simple and inexpensive operations on other cars such as the Volvo.

Vern, I love the P6, too.  But it's pretty hard to argue that Rover 
thought through the service issues or the associated costs or the 
inconvenience to the owner.  If they thought these things would fly in 
the mass American market, then they must have been truly naive or just 
bloody headed.

Glen