Top Speed

[Locoshaz]

Hi guys,

Not sure if anyone can help but here goes......I have a 2001 CLK 200K. It's nice and quick and accelerates to around 90-100mph easily. However, after that, if i try to go any faster it feels as though it's going to take off. The front ends feels very very light and i'm not all that comfortable going when you get a slight bend in the motorway as it feels like the back end might swing around.

Now i know i shouldn't be going that fast, but i just want to know why it won't go any faster. I thought Mercs were supposed to be able to cruise at high speeds? Not that i drive at those speeds all the time. I am very responsible but i just want to know why it feels like it does. Could it be a suspension problem?

Thanks,

Ls.

Ps, it's done 130,000 would that be a likely factor?

 

[Blobcat]

There are quite a few threads around on high speed stability, tyre pressures are suspension settings can have a large effect on high speed handling.
I would check that your tyres are at the correct pressure and that your suspension is not worn out. Have you had any bushes changed?
I have taken mine up to a genuine 145Mph in Germany and it was as solid as a rock. My wife was not complaining and my son never even notice (sat watching DVD's in the back)

 

[Locoshaz]

Thanks for that. I have been informed by a mechanic that it could be something as simple as aero dynamics. He said that when you're travelling at high speeds, air rushes underneath the car and that's why it feels light when steering. He said that a front splitter should cure the problem as it will force the air to run above and either side of the car as opposed to running underneath it.

Has anyone else got any theories on the subject?

Cheers,

LS.

 

[turnipsock]

Forcing air to travel over the top of the car will provide even more lift.

Unfortunatly, cars are basically wing shaped.

 

[Alfie]

Hi guys,

Not sure if anyone can help but here goes......I have a 2001 CLK 200K. It's nice and quick and accelerates to around 90-100mph easily. However, after that, if i try to go any faster it feels as though it's going to take off. The front ends feels very very light and i'm not all that comfortable going when you get a slight bend in the motorway as it feels like the back end might swing around.

Now i know i shouldn't be going that fast, but i just want to know why it won't go any faster. I thought Mercs were supposed to be able to cruise at high speeds? Not that i drive at those speeds all the time. I am very responsible but i just want to know why it feels like it does. Could it be a suspension problem?

Thanks,

Ls.

Ps, it's done 130,000 would that be a likely factor?

Aerodynamics play a huge part in vehicle stability.

Basically as the air rushes under the car it does so at a higher speed then the air above the car (less distance to travel). As Air travels faster across a surface its pressure drops. The faster the air moves, the lower the pressure. therefore we end up with a higher air pressure below the car than above it. This causes the two to try and equalise thus resulting in the car being lifted. This is the basic principle of flight!

Cars which can lessen this imbalance or indeed reverse it (formula 1 cars) are pushed onto the road as opposed to lifted from it.

 

[jberks]

Ps, it's done 130,000 would that be a likely factor?

In a word, Yes - the suspension isn't going to be quite as responsive as it used to be, though I imagine still perfectly adequate for normal use.
There are lots of factors, including head and side winds, certainly my E was rock solid on the 2 occasions I've strayed above 100 but the opportunties here and the consequences mean that I tend not to.
If you want to tighten things up, there are loads of options, from a deeper front splitter to uprated suspension and wheels.

 

[jon_harley]

Basically as the air rushes under the car it does so at a higher speed then the air above the car (less distance to travel). As Air travels faster across a surface its pressure drops. The faster the air moves, the lower the pressure. therefore we end up with a higher air pressure below the car than above it. This causes the two to try and equalise thus resulting in the car being lifted. This is the basic principle of flight!

Well, it's one of them, but flight isn't that simple. You can also get lift just from the angle a surface hits the air at: if it pushes air downwards, there's an equal and opposite reaction pushing the surface (eg wing) upwards.

What isn't in dispute is that with both effects (pressure differences and airflow deflection), a major factor influencing the aerodynamic is the drag produced by the shape. F1 cars do have to minimise lift, but they are also designed to minimise drag. I suspect that drag would be one of the major factors affecting acceleration over 100+ in road cars.

 

[blassberg]

Basically as the air rushes under the car it does so at a higher speed then the air above the car (less distance to travel). As Air travels faster across a surface its pressure drops. The faster the air moves, the lower the pressure. therefore we end up with a higher air pressure below the car than above it.

you say that "air rushes under the car it does so at a higher speed then the air above the car"
but I think you contrast that with the the faster air above = lower pressure (cf monsieur benoulli I believe) which I agree with

 

[blassberg]

I would get the shocks checked out

 

[television]

The effect of passing air through a venturi speeds the air up. as since the volume of air has to pass through a certain size hole, the only way it can do it is by going faster. Its the reason why the wind allways apears to be blowing when amoung tall buildings close together.

Why not veiw some wind tunnel sites on the net, where you can see the effect of drag as well.

malcolm

 

[jberks]

you say that "air rushes under the car it does so at a higher speed then the air above the car"
but I think you contrast that with the the faster air above = lower pressure (cf monsieur benoulli I believe) which I agree with

That's it. A car is shaped like a wing - flat underside and curved upper side, so the air travels further over the top than the bottom, hence faster and so at a lower pressure, causing the pressure above to be lower than that below, and so generate lift.

A diffuser forces air away from the underside of the car, causing less air molecules psi to be under the car and hence lower air pressure. If done in sufficient volume, the pressure below the car is lower than that above, and you have downforce.

I knew my flying lessons would come in handy somewhere!
Still think it's probably the shocks though!

 

[Parrot of Doom]

The discussion about aerodynamics is irrelevant to this problem (no offence intended). The car was designed to travel at these speeds safely. Since it appears not to be doing so, something may be faulty.

I'd check tyre pressures and all suspension bushes.

 

[stumpy]

Aerodynamics are not irrelevant. Does the car have any underbody panels / fairings or aerodynamic devices that have come adrift? The reason I ask is that my car has a small splitter under the nose of the car which gets smacked off when going over speed humps. I only realised what effect it had when doing about 140 and the nose rose up visibly. Just a thought.

 

[Flying Scot]

Aerodynamics play a huge part in vehicle stability.

Basically as the air rushes under the car it does so at a higher speed then the air above the car (less distance to travel). As Air travels faster across a surface its pressure drops. The faster the air moves, the lower the pressure. therefore we end up with a higher air pressure below the car than above it. This causes the two to try and equalise thus resulting in the car being lifted. This is the basic principle of flight!

Cars which can lessen this imbalance or indeed reverse it (formula 1 cars) are pushed onto the road as opposed to lifted from it.

well how about that i guess you are in Australia and that is why the cars dont fall off the world :lol: here in the UK the air goes faster over the longer distance the TOP and you are simplifying Bernoulli's principle to a great extent

perhaps you could explain to me how an aeroplane with a symetrical wing manages to get off the ground

 

[Flying Scot]

BTW i dont really seek a reply as to how a symetrical winged plane manages to fly.

Also Bernoulli is pure (and simplistic) theory and largely discredited now in both aero and hydro dynamics

For Bernoulli's Principle to apply, the fluid is assumed to have these qualities:

The fluid flows smoothly - The fluid flows without any swirls or eddies - There is no flow seperation in the fluid - The fluid has the same density everywhere like water it is incompressible.

So in fact Bernoulli's Principle has little to do with planes or cars even F1 cars which you may have noticed use BIG wings front and rear to generate 'downforce' and there it is angle of attack and area that matter more than the aerofoil section which is designed to minimise drag not create the downforce.

Back to the listed problem sounds like a tyre/suspension issue OR back to the mindset of the driver who complains of a 'feeling' of the front end going light then worries about the back end letting go - the two dont compute - the first one would give understeer the last oversteer - sounds like the driver is at his limit not the car.

 

[Locoshaz]

Flying Scot, let me assure you, i'm nowhere near my limit. Having floored a Calibra to 140mph i think it's strange that a Merc can't get any more than 110 without the front end feeling as though it's going to lift off. When i talk about the back end letting go it's when there is a slight bend in the motorway. Just because something doesn't compute with you, doesn't mean it isn't so.

Thanks to everyone else for the positive replies. I'm going to get the suspension and bushes checked out from a garage soon.

LS.

 

[KevinFuoco]

Well i got a MB 190E 1989 and i can easy go up to 154mph.
Its maybe an old babe but she can fly.
Shes so gorgious on the highway.

 

[jberks]

Well i got a MB 190E 1989 and i can easy go up to 154mph.
Its maybe an old babe but she can fly.
Shes so gorgious on the highway.

2.5 16v Cossie I assume. The normal 190E 2.0 was only good for about 120!

 

[Flying Scot]

well he has an Italian speedo in the car

BUT i thought "speeding" was a banned topic yes no maybe? and that speeds over 70MPH would automatically end up as ***MPH a bit like trying to use a swear word here

 

[FELLOW]

Light speed

The first Q to ask is are you used to driving at high speed. U describe the 200 as quick - that it is not unless heavily modified. My friend had one and it cruised well over the ton but remember it has no supercharger and will not get anywhere near 155 mph - more 128 when flat out.

All cars feel slightly lighter at high speed - does yours feel different to say a BMW or Mondeo - remembering the Merc is rear wheel drive with no torque steer effects.
The tyre are a good place to start. Check the speed rating letter on them - has someone previously fitted low speck ones to sell the car on then next the tyre pressure - increased for high speed driving.

Q do you get any shudder or vibration.

The CLK feels different to a small car (hot hatch) and those with active suspension or front wheel drive - but CLK's are basically autoban cruisers as anyone will now who has thrown one down a country road and felt their botton slide on those big leather armchairs.

The bigger engined CLK's V6 320 to V8 430 will happily cruise at 120-140 mph (I've set the cruise at 125 before) without feeling light and you will easily be able to whisper to your passenger. Pushed up to the limiter they are still stable ---> passed 155 ----> not really suited to UK roads ----> too much speed to loose is someone makes an unexpected move ----> save for the brave in Germany or the track.

PS caught over the ton means loosing your license and I assume we can talk about speed as we are in Europe and we could be talking about belting down a German motorway not the A66