Instability in crosswinds

Ian Donkin · Post by **Ian Donkin** » Mon Jan 31, 2005 4:28 pm

Went for a blast around the moors of the Peak District yesterday and not for the first time was blown all over the road whenever exposed to strong crosswinds. Whilst sometimes this can be 'amusing' it calls for absolute focus of the mind and I really think I need to do something about it.

My '72T runs on 195/65's, has new shocks front and rear, new track rod ends (full comp re-alignment afterwards), but no anti-roll bars whatsoever. I'm also assuming it is on standard rate torsion bars. From the way it crashes through potholes, I suspect the front 'a'-arm bushes could do with replacement.

I'd be interested to hear your thoughts on what course of action I should undertake - I've read about Weltmeister replacement bushes, but am concerned they may be very noisy and make the ride even more harsh.

Also your thoughts as to whether a front anti roll-bar would help reduce the instability. My preference would be towards mild understeer rather than oversteer - the later always being available in abundance in an early (or is that any) 911 if you abuse it!

Thanks in advance.

Luke · Post by **Luke** » Mon Jan 31, 2005 4:39 pm

Ian, I have welmesiters on the front of mine plus antiroll bar, however it still get buffeted in a big cross wind, it's just a fact of nature.

The welmeisters are good but do tend to squeak a bit unless you install a means to regrease them (i.e.) a grease nipple) I can talk you through fitting them if you need it, I replaced all the front suspension on my car last year

Luke · Post by **Luke** » Mon Jan 31, 2005 4:43 pm

btw, there is no OEM bush replaecment for the fornt to my knowledge, you have 2 basic choices, poly bushes, or oh so sexy Elephant racing poly-bronze bushings

Gary71 · Post by **Gary71** » Mon Jan 31, 2005 4:52 pm

Unfortunately a lot of it is aerodynamics, not much you can do there without compromising the shape.

My T has the same set up, but with 'S' front and rear rolls bars. It's still just as affected by crosswinds. Certainly giving the car a natural understeer bias by adding a front ARB and not the rear would improve stability at the expense of agility.

Increasing toe in on the rear would firm the steering response and make it feel less 'vague'. However you would already be using some of available slip angle before breakaway. So it's a double edged sword that one.

I'm in the process of replacing my rear suspension bushing (just with O.E rubber) so the geometry I set on the rig has some chance of staying there whilst driving. The bushes looked original and were completely shot.

The aero problem has been one area I've been looking into. The long term plan involves a 964 engine lid lift mechanism and the standard grille...

Lightweight_911 · Post by **Lightweight_911** » Mon Jan 31, 2005 5:26 pm

What is your front/rear ride height like ?

As an approximate guide, on level ground & ideally with 3/4 tank of petrol, measure from the ground to the centre (highest point) of the wheelarch - fronts should be 25.5" & rear should be 25".

Lowering the F&R by approx 1" makes a significant improvement.

Ian Donkin · Post by **Ian Donkin** » Mon Jan 31, 2005 6:01 pm

Thanks for the contributions guys although I had hoped it was my car, not an inherrent feature of the early cars

.

Andy - just measured and my ride heights are already a low 23.75" rear and 24.75" front (that's how it was when I bought it) - it also has the 's' profile front spoiler.

There's also no play in the bearings (adjusted two weeks ago) or steering, so I guess I'll have to start with the bushes and see where I get to. Might as well use the opportunity to get the front arms powder coated, so it could be a couple of weeks before I can complete the job.

I'll try and take some piccies of progress.

Lightweight_911 · Post by **Lightweight_911** » Mon Jan 31, 2005 8:52 pm

What tyre pressures are you running ?

tanick · Post by **tanick** » Mon Jan 31, 2005 9:08 pm

Anyone know why Porsche don't make replacement bushes? I need to sort out my suspension but guess I can't powdercoat the arms without replacing the bushes and I've been advised to keep the car stock when it comes to the bushes to stop it getting too hard. New arms ( with the bushes) are £150 each. There must be a better way??

Ian Donkin · Post by **Ian Donkin** » Tue Feb 01, 2005 10:34 am

Andy

Tyre pressures are 29 rear, 26 front - I'm sure that's what is on the tyre pressure plate mounted on the engine shut panel.

Just for clarity on the instability - 'slightly over' 70mph on two lane section of road over the moors, big gust of wind puts half the car in the other lane

.

On Sunday over the Strines I had to 'hold on tight' (and back off) as it was trying to push me towards the ditch on the nearside.

Also, thinking more about it, could the 'crashing' noise I get over bumps be more related to the ball joints and upper shock mounts than the 'a'-arms (although I'm going to replace these bushes anyway)?

I can see this getting more expensive....

gav p · Post by **gav p** » Fri Feb 04, 2005 4:29 pm

Ian,

Mine gets blown around quite a bit. I'm sure it is bush wear with my suspension which is exaggerating the effect, rather than purely being a feature of the design. After all, the later '70s and '80s cars have basically the same suspension design and bodywork shape in side profile, and are capable of far greater top speeds than my '69. If the cross-wind problem was an intrinsic design fault you'd think that the average 3.2 carrera or 930 would be almost undriveable anything near their limits on a blustery day!

How are your rear susp. bushes? In my case, I know that the rear suspension arm bushes are completely shot, so theres problably half a degree of movement in the toe-in/toe-out at the rear wheels... effectively rear wheel steering!! Cant be helping...