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Discussion Starter · #1 · (Edited)
Having recently replaced the old brittle tyres with new Pirelli Scorpion Verde 235/70 R16 on my '95 RRC, I am noticing slightly lighter steering which is a bonus, but also a lot of vagueness and play on centre, especially at highway speeds.

I drove from London to Burgundy yesterday and had trouble keeping the car tracking straight as there are about 2 inches of play in the steering wheel when it is centred. I have gotten used to it but it is pretty annoying as when a big lorry goes past, it's is enough to upset the direction of the car and due to the vagueness, I have to pogo the car left and right until it centres again.

Any ideas as it didn't happen as much with the old tyres although I had an alignment done with them and not with the new ones. I'm hoping that it is not the steering box as I know that is expensive.

Another thing to add is the shakiness above 70mph which becomes really pronounced at about 80mph which makes reaching 130kph highway speeds in France impossible but at least I'm getting about 300 miles per tank 馃槈.
IMG_2131.jpeg IMG_2044.jpeg
 

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With quite a few links in steering system it's worth checking through to assess each joint initially by placing your hand onto each joint and getting someone else to wobble steering wheel and let you evaluate.

First link from steering arm drop link to the front wheel on opposite side, both ends.

Second link behind axle "drag link" that connects the two opposite wheels together, both ends.

Then the static "panhard rod" that connects from chassis one side to axle on other side, this one provides the lateral location for the axle that resists the steering input. Although it doesn't move when steering (at least it shouldn't) if there's play in this it will give that centre slack as the axle first tries to move across the vehicle before the wheels effectively turn and give you a vague response as this has to move back the other way to go into opposite turn.

Obviously each joint should be free of slack to operate effectively, so you can audit without any tools easily and give a primary assessment as to it's general health.

Vibrations, what front tire pressures have you got set ?
Also which front shock absorbers are fitted ?
 

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Discussion Starter · #3 ·
Hi Nigel, I鈥檒l try and give that process of elimination a go.

I recently removed the EAS and put in OME shocks and Bilstein dampers as I was advised they would offer the most compliant ride.

I鈥檒l check tyre pressures today as they were inflated by that garage who installed them. What are your recommended pressures?
 

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I use Bilstein dampers too, but have experienced elements I don't want in some others so all good from that point ov view.

Pressures, as a start point 26 front and 32 rear as presume you've a luggage payload with you. It's that front setting that can give you some effects especially if it's significantly higher than ideal.

I've different tire to yours and so use pressure specific for them which I calculated after weighing the car to get final figures.
If you wanted something more specific to use then post the tire's full size and load spec (the 102H type figure) also it should have written on the sidewall a maximum kg @ x psi data which is needed to calculate against vehicle weight to give more accurate reading.
 

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I use Bilstein dampers too, but have experienced elements I don't want in some others so all good from that point ov view.

Pressures, as a start point 26 front and 32 rear as presume you've a luggage payload with you. It's that front setting that can give you some effects especially if it's significantly higher than ideal.

I've different tire to yours and so use pressure specific for them which I calculated after weighing the car to get final figures.
If you wanted something more specific to use then post the tire's full size and load spec (the 102H type figure) also it should have written on the sidewall a maximum kg @ x psi data which is needed to calculate against vehicle weight to give more accurate reading.
Speaking of tire pressures, and sorry I'm not trying to hijack the thread, how did you resolve your tire pressures? I have larger than stock tires, with greater load capacity, however the calulation I did even ith the extra weight on the car suggested incredibly low pressures, which while correlating to the greater load capacity are clearly too low to be safe or functional on the road. For example, even accounting for the extra weight on my car, the calculated tire pressures for 245/75's based on the pressure of stock 205/80's (26F and 38R) is 16psi front and 25 psi rear, which is obviously unrealistic. I've kept the 26psi front the same (despite the larger tire) but dropped the back down to about 30, since 38 psi in a 245/75 makes ith WAY too stiff. It still doesnt feel like they're inflated correctly though. Also, I always wondered why the huge disparity front and rear? I imagine the weight distribution (with standard load) is fairly even, no?
 

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Weight distribution I've gone as follows;- it's more or less a front "mid engine" layout as principle motor mass and gearbox is within the wheelbase (front axle under front two cylinders) with payload area cantilevered past rear axle and containing fuel load plus spare wheel etc.
In addition, tow bar loading is also significantly cantilevered too if using that.

My tire assessment for which I ignored original to see what free calculations would give, my carcasses are rated at 1150kg @ 50 psi stated on sidewall and should support maximum of 4600kg @ 50 psi.
Weighed vehicle @ 2050 kg with half tank of fuel to give median baseline, which gave 44.56% of the 4600kg maximum.

44.56% of 50 psi is 22.3 psi to carry empty vehicle total weight which looks sensible and a reality check.

Then added 500kg as average 4 passenger plus general luggage payload, making 55.43% of total tire capacity, and 27.7 psi for this status.

Considered that when loading with passengers and load bay none of the extra mass is directly over front axle ( it doesn't vary that end particularly) so added a compensatory factor to recognize this, made adjustment to 25 psi front and 28 rear as a baseline final general use figure.

For really full loading I take the rears up to 32 psi in compensation, but that is 4 pax and packed to the roof with holiday kit.

Checked temperature on long runs when brakes not used much to influence to asses if any significant discrepancy, and all in balance when using my baseline data so use that permanently.
 

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Discussion Starter · #7 ·
@RRLondon, this makes a lot of sense and after your advice from the earlier post, I did the simplest thing and checked all the pressures which I was hoping would have been accurately filled by the mechanic, but alas, they were way off.

FR 1.6bar, FL 1.8bar, RR 2bar RL 1.8bar.

I went with the (probably outdated) recommendation in the manual of 1.9 bar on the fronts and 2.6 bar on the rear. I also have a rear bike rack + ebike and a boot full of luggage but just me alone in the vehicle.

Todays' drive was markedly better by about 50% when it comes to the on centre vagueness, although it is still there. It did allow me to push it a little faster but that yielded to pretty unpleasant shuddering at about 75mph, so I ended up keeping it below that to eliminate the problem.

The tyres have 106H stamped on them.

IMG_2155.jpeg
 

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Discussion Starter · #8 ·
A quick update on the steering after another 1000 miles through Italy, of which about 200 have been on rough dirt roads.

Whether it is a combination of improving the tyre pressures as well as getting used to the vagueness, there seems to be less of it as well as far less shudder. I'm no expert, but I'm wondering whether some of the off-road driving has also loosened up some of the linkages thereby aiding the issue a bit.

A couple of new gremlins have cropped up:
  • The HVAC fan seems to switch off when on setting 4 after working for about 3-5 minutes, but when I knock it down to setting 3, it will stay on constantly. The good news is that the AC is keeping up with the 37C heat in Italy.
  • Occasionally the car will die whilst performing parking manoeuvres on full lock but not always.
  • The transition between gears is a little rough when accelerating up to speed on the motorway and sometimes also when decelerating. (This isn't new, but thought I would mention it)
 

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Good that you've experienced a more calmed drive with a little optimisation.

That vibration, I'm assuming it's front end of vehicle and showing through the main structure as specifically different from the steering wheel oscillation around it's axis ? An important distinction from analysis point of view.

To experiment a little further with some concise steps to assess;- if you go downward on front tyre pressure in 2 psi increments and give each step some time to gain experience, then it's a possibility you can get a positive response. This is essentially to fault find and not necessarily set out to run without good reason at arbitrary lower pressure. Look at 22 psi (1.4 bar) as practical minimum for research purposes.

What this does is alter the spring rate (tyre is essentially a huge undamped spring) to see if you've got a crossover in cadence of tyre carcass frequency and that which you shock absorbers are able to impart detailed control.

Also acts as a slight damper on steering input to allow natural suspension geometry to keep response calmer.
 
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