I had recently posted (What did you do to your XJS today?) about the new brakes (including all rotors) on my ’94 kitty, along with brand new tires. Just as I stated in that post, at time of replacement of the old Pzeros, I was hoping for tires that would improve ride comfort. The handling gain from the 17” Revolvers had come at the expected loss of ride comfort and it is my understanding that the Pirelli’s only made this loss worse, as ride comfort is not necessarily Pirelli’s strength. So, since it was time to replace the old and tired (no pun) Pzeros, it was time to try to offset the Revolvers’ ride loss by finding a better ride tire and, luckily, I was given what may just be the best tip: Continental Extreme Contact DWS06 tires on the exact spec as the Pzeros were, meaning 235/50 R17. The ride improvement is simply amazing and exactly what I needed; I couldn’t be happier.

But that was not all of what these tires have resolved. Something else has happened after the tire replacement that I cannot really understand and which is the reason why I’m writing this. Some here may remember that I have previously complained about my face lift XJS’ rather poor power steering assist, as compared to, say, my old XJ12 (extremely light) or my current XJR (just perfect). I know that pre-face lift XJS cars are very different to mine with much better power assist. I have even kept those Pirelli Pzeros way over inflated to get decent steering when moving slowly or from stopped. But, guess what… after this recent tire replacement this problem has totally gone away and my steering now feels just like on my XJR. I have done absolutely nothing else to the car that could affect this condition. So, how can this new Continental rubber contribute to a much lighter steering effort? The tires have a kind of “cute” tread pattern, as in not the usual longitudinal tread pattern, but rather an area with a sort of a “mesh” cross pattern and I could see a little bit of help from the tread pattern, but not really as much as I’m benefiting from. Or, could it rather be that these Continentals are actually the "norm" and that it was the Pirelli's tire design that was all along creating this heavier steering problem on my XJS?

Anybody here that may know something about these tires that I don't?
It is no longer a problem, just curiosity.

Cheers,

 

My opinion.

Jacking the car to remove/replace the tyres, has extended the suspension to FULL down. This has "twisted" the balljoints into a position they will NEVER see with any style of driving.

This has had the result of grease being "dragged" into the working point of the joints, and thus lubed what MAY have been tight/dry joints.

This is exactly what I have had with the X300 and the Black S Type. I relented with the X300 and fitted new balljoints WITH grease nipples. No such luck with the S, so I fitted my own grease nipples to the lower joints. Both these joints took some serious amounts of grease, and the difference in the cars was the same as you just scribed.

Greasing these joints once a year has kept this problem at bay.

 

Interesting, I would've never thought of this, but somehow I have difficulty putting together ball joint lubrication with steering operation effort, especially considering the fact that steering has power assist. Besides, this is not the first time that this car has been on a lift, including that very ocassion when the Pirelli's were installed in the first place, so I'd ask why didn't this rather happened before, in those ocassions? But, still, you may be correct on this, although if this was the case, wouldn't this be a far more common driver's experience, meaning that drivers' steering effort gripes get "fixed" without explanation after a car was lifted for an oil change?

Thanks for your response!

l'd really like to hear a couple more opinions.

Cheers,

 

I only wish I could get the steering on my 89 XJS to not be so light. I barely get any feedback from the pavement at all. I'm hoping poly bushings will have some effect when I finally get around to doing those modifications.

Jess

 

The tread design really does affect the steering feel. I had a new '90 Civic that went from nice steering effort to heavy with a tire change. I lived with it for several years until replacements were needed which cleared up the problem. I guess this is why I see nearly new sets of tires for sale on CL. It's helpful when forum members post their experiences with their tire selections.

 

Now this here sure makes sense and it seems to be the obvious answer, confirming my own suspicion and since nothing else was done to the car (of course, except for new brakes). I just couldn't believe the degree of improvement experienced, but .l'll take it...

Cheers,

 

This is exactly the way my old XJ12 (Series II) Steering felt like, I could turn it with my pinky, but road feel was poor. Putting poly bushings made it dangerous, as in over sensitive to the point of totally losing control of the car at 70 mph on an LA freeway; took them right out and installed new stock bushings and it was back to normal. I've never had an explanation for that incident.

Cheers,

 

So you suppose the hidden fix crept in?


At times it seems that removing a part and replacing it
fixes things. And, that the replacement part had nothing
to do with it?


Was driving to market the other day. it seemed that the steering went tight. NO PS?? First thought, engine quit! coasted to the side. Not sure. Off with the key, put trans in park, crank, engine fired right up. Been just fine since. Did engine quit? Or did the PS take a break???
I don't know??? Should've observed a bit more...


Carl

 

I agree with others this has zero to do with tires and all to do with the suspension being flexed. I don't know that I would go so far as to make a guess about grease creeping around, but yeah.

 

Jess what tire Pressures are you running?... what tires ? and how old? and are they a HIGH MILAGE TIRE?


A High Mileage tire will have a harder compound ... old tires will become HARD... as new tires for us made an undrivable car in the rain now completely manageable... in the rain and dry...
yes I can still break them loose if I really try...


if you find you have been running you tires with to higha pressure it will lighten the steering effort.... (caution do not lower the tire pressure below what is recommended on your door...)


I run mine a little higher for High speed on the freeway and for gas mileage...

 

Different tires can result in very different driving characteristics. Tread design and compound, sidewall height, sidewall stiffness, size of contact patch, fit of tire onto the wheel....all these things (and probably others) can contribute to steering effort, steering "feel', responsiveness, etc

I'm never surprised if someone reports a very different feel after replacing tires

Cheers
DD

 

Mine are Cooper Cobras, 235/60-R15. Three of the tires are about 2 years old and one of them is about 4 years old. The only reason I'm running Cooper Cobras is the car came with them when I bought it 4 years ago and one of them was dry-rotted. Let me clarify: All four had issues, we just didn't know it at the time. Turns out the other three all had tread separation down the midline of the tire, and we replaced them at that point. We then had to replace another one of those three when it arrived from Cooper in a state I can only describe as "deformed."

However, at the time we replaced the first one, I only knew about the one dry-rotted tire, so we replaced it with an identical match. If I had to do it all over again, I would go back to the stock tire size (215/70-R15) because the selection is vastly superior. On the 235/60, I can only pick between one BF Goodrich tire and the Cooper tire. The Coopers ride well enough, they're quiet, and they seem to offer reasonable dry handling, but they are iffy in the rain and not a performance tire in my opinion, and the failure/defect rate is too high. I'd rather have Yokohama AVID Ascend tires on this car but I'd have to step back to 215/70 to do it. At the time, cost would have been a factor. Right now, the Cobras still have most of their tread on them and I'm planning an upgrade to 17x8 rims, anyway. No point in changing out the tires again this close to doing the suspension/wheel changes.

I run them at about 32 psi.

Jess

 

But how would that make sense when the car has been on a lift several times, as in "suspension being flexed" during the ten years since those Pirelli's were installed, yet the heavy steering issue was never affected. It is just too much of a coincidence that the minute l drove off with the new Continentals the years old too heavy steering problem went away like by a miracle from the Holy Spirit. What else can possibly explain what happened?

 

I agree with you Force, it is the tyre change that has done it. The evidence for it is utterly overwhelming! Static and low speed friction is greatly affected by carcass compound and tyre tread block design. There used to be a tyre in the UK that looked like the tread blocks were separate elongated sugar cubes, and at tickover they could stall a power-steered car when lock was wound on! So your experience is not at all unusual.
Greg

 

I think it was just me, an over reaction. The GM PS pump, the Jaguar rack and the present B. F. Goodrich "T' tires off just a tad of added steering input before responding. A non-issue. All is just fine.


Related, sorta: Power steering fluid coolers on some GM cars, but not others. Why? My idea. The earlier version had the reservoir integral with the pump. The later version used a remote reservoir. My LT1 transplant has the latter. No cooler needed. The lines and reservoir fulfill that function.


Jaguar relevance: Jaguars use GM PS pumps.


Carl

 

Speaking of which, I am used to the "standard" P/S pump, meaning the typical kind of round assy with a flat back wall (with ports/hoses) a pulley out front and an oil filler opening with a twist cap at the top. But this is not even close to what I have on my 4.0L face lift. The only obvious item that I see is the separate reservoir next to the coolant overflow tank. Frankly, I have no idea how this pump generates pressure.

Some time back, when I didn't know why my power steering assist was so poor I was contemplating to, maybe, change to a different pump, like perhaps one from the pre-face lift cars that have plenty of power assist, but since the pumps are physically so different I kind of left it alone. Luckily, the problem was just resolved with the new Continental tires.

Would anybody have a quick description of how the 4.0L face lift P/S pump works?
Thank you.

Cheers,

 

I recall that it's driven from the 'auxiliary shaft'....which I think is driven by the timing chain. If not the chain itself then a gear system running off the timing chain.

The pump itself is a 'vane' type pump

Cheers
DD

 

Neat. Separate reservoir adds the cooling feature. No belt to
squeal.


The old style and familiar GM pump has a valve on top. Variances in springs and orifice sizes can alter the assist.


Add wheel alignment to the mix. Alters steering stability big time.
Wheel offsets and diameters change things a lot. Caster, king pin angle, camber...


Carl

 

Makes sense, all internals with no pulleys or belts in view.
So, would this vane type then be similar to the way traditional 15 psi fuel pumps work? This would make it hard for any attempt at altering pump pressure, and even for replacement with any traditional style pumps.

Cheers,

 

Wow! Never saw it this way, but you're totally right in regards to belt issues (squeal, wear, damage, replacement cost, etc.) and also true with the extra cooling.

How does steering stability manifest itself, example?

Cheers,