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Author Topic: Sensitivity to cross winds  (Read 2785 times)
Jon Weywadt
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« on: June 04, 2009, 01:04:59 pm »

Tuesday I was out driving around in some strong gusty winds. It seemed to me that the Murena was rather sensitive to the cross winds. Has anyone else had similar experience? Huh It could be because it is a very light car, or pehaps my front-end alignment needs to be checked.
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Matranaut par excellence Cool
Matra_Hans
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« Reply #1 on: June 04, 2009, 02:09:29 pm »

Hi
The basic principles:
The Murena has a very low wind resistance. The lower wind resistance a car has the less stabile it will be.
The Murena has almost 60% of the weight on the rear wheels: again this makes the car less willing to drive straight.
The correct tire pressure is very important for the Murena’s stability and driving dynamics, and it is very important that the front tires are narrower than the rear tires (as original) Many Murenas have been fitted with same size tires front and rear.

In general I will say that the Murena is not a car for cruising at high speed at the motorway, but it is a car for driving (relatively) fast on small and twisted country or mountain roads.
On the other hand: I have been driving up 180 km/h in strong winds without too much trouble. (Yes I know it was too fast, but I had to follow another Murena driver).

Hans
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Anders Dinsen
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« Reply #2 on: June 04, 2009, 04:27:57 pm »

You forgot one basic principle in your list, Hans: Sensitivity to side winds depends on how much offset there is between the centre of gravity in the longitudal direction, and the centre of the wind pressure on the side of the car.

And in this respect, the Murena is far better designed than most other cars, as the 60/40 weight distribution corresponds roughly to the distribution of side surface area.

Add to this that the car is low, so the side area is smaller than most other cars.

But the light and very direct steering and superb feedback from the road can probably make you FEEL that it is somewhat unstable.

/Anders
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Titus
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« Reply #3 on: June 04, 2009, 11:46:11 pm »

I fitted new rear tyres for the trip to Romorantin (Yokos, thanks Anders). I had not really noticed a problem with cross winds before the French road trip.

On the way down to the UK ferry port I overtook for the first time and the car felt scarily unstable. I have had the trailing arms refurbed resulting in uneven camber between the two, but within tolerence. I thought the camber was the problem.

Driving in France I felt the cars instability with every km. I hadn't noticed the trees moving with the wind until it was pointed out to me. Although the sun was glorious the cross winds were strong. So this was considered as to why the car was not performing as expected.

After many km. to Romorantin the UK convoy returned via Le Mans where we some what opened up the performance of the cars to lap the circuit. Cross winds were still in evidence but the Murena had settled down to drive without any concerns.

The final leg home resulted in the car driving well with the cross winds still in evidence. I can only conclude that the new Yokos just needed bedding in.

That's my experience. Hope it helps.
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Anders Dinsen
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« Reply #4 on: June 05, 2009, 08:28:14 am »

The final leg home resulted in the car driving well with the cross winds still in evidence. I can only conclude that the new Yokos just needed bedding in.

Interesting..., and not unlikely. Having just completed a 'test drive' with my refurbished rear shocks, I'm actually a little surprised how much the rear shocks mean to the stability of the car. And this was mostly in straight line driving (city, country and motorway), since the roads are quite wet this morning.

The 'worst' thing about the Murena is the light steering where you feel the road and any slight instability of the car. This is it's 'race car heritage', I think Wink

/Anders
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
suffolkpete
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« Reply #5 on: June 05, 2009, 09:14:37 pm »

I think that most handling and stability problems are a combination of factors, shocks, tyres, steering joints, wheel alignment etc.  The light front end and "fast" rack certainly don't help.  I had one or two exciting moments driving to the Wobbly Wheel in heavy rain, although overtaking a convoy of five Triumph Stags perhaps wasn't such a good idea  Smiley  I put it down to the cheap rear tyres, and the fact that they're the wrong size, 185/70 instead of 195/70.  Titus's experience could be down to the fact that the weather was cooler on the return trip and perhaps the tyre pressures were a bit lower.
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