r/performancedriving • u/guerreroTX • Jun 22 '20
Top speed driving
Hello everyone,
I am from the U.K and next week I will be driving across Germany, where in most parts of the motorways there is no speed limit.
I own a Mercedes CLK from 2004, it’s capable of going 142 miles an hour. I look after the car, also the car was recently checked by a mechanic covering all aspects of the car( suspension, chasis, etc).
I am a safe and responsible driver and I would like to see how my car performs over 100 miles an hour. I have driven before in Germany and I understand how driving works there. From a mechanical point of view, is it safe for me to drive at top speed?
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u/Beeblebrox237 Jun 22 '20
As long as your mechanic has cleared it then you should be fine. I've found German cars to be incredibly easy to drive at speeds in excess of 120 mph.
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u/rvbjohn Jun 23 '20
Id do it for like ten minutes and maybe pull off and check things the first go if itll make you feel better. Aside from that it should be fine.
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u/epyon22 Jun 23 '20
Couldn't find a clip but remembering Jeremy Clarkson from top gear about to lower the wing on the Bugatti Veyron and doing some high speed "checks" in Series Seven, Episode Five.
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u/guerreroTX Jun 23 '20
So, I done it and it was a smooth ride. Weather was good, not much traffic. I was driving on my own and checked all tyres any suspicious damage. The tyres’ speed rating and load rating wasn’t a problem either, apparently they can go up 168 miles an hour. I also made sure I had just the right amount of air in all tyres. After reaching 200km an hour it gotten louder than usual, but the car stuck to the road and was stable, even at 230km an hour (142, top speed). Thanks for your help guys.
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u/zzpza Jun 23 '20 edited Jun 23 '20
It's good that you've had the car checked out by a mechanic. But, the mechanic isn't going to be in the car when it's doing these speeds, you and your passenger (if present) will be. It's ultimately your decision if it's safe, but you can take on board that the mechanic said.
The single most important factor (IMHO) is your tyres. First and foremost, check their speed and load ratings. Never exceed the speed rating of a tyre, it's asking for trouble. And trouble at the top end of your tyres performance can be terminal for the occupants. You will find the correct load rating from the vehicle handbook. If the speed rating is fine but the load rating is too low they will overheat and fail.
Next is tyre pressures. The front and rear will have different pressures, and this will also depend on the amount of luggage in the vehicle. Do not overload the car, as this will overload the tyres. Do not under inflate the tyres as this will cause a reduced contact area and also excess flexing, resulting in a loss of grip and the tyre overheating. Do not over inflate the tyres either as this will result in loss of grip (reduced contact area again). Both over and under inflating will also prematurely wear a tyre. It's possible to make a brand new tyre illegal to use in less than 100 miles if it's not been correctly inflated. Do not assume it's '30 psi all round'.
Next inspect the tyres for damage. Look at both the outer facing side and inner facing side of the tyres. Get your head underneath the car (or jack it up and take each tyre off in turn) and check the inner side wall for damage that wouldn't normally be visible. Cuts, bulges, and gouges are dangerous, and the tyre should be replaced. Same on the outer sidewall. When replacing tyres on a performance vehicle they should always be replaced as a pair (front pair, or rear pair), or as a full set. A blowout is the last thing you want.
Next is the tyre tread. Check the tread on all the tyres. If you have 2.0mm or less you should change them. Getting the maximum life out of your tyres is fine if you're sticking to normal driving speeds, but not when you're going to be pushing the vehicle above 100MPH for extended periods of time. Imagine hitting standing water at 120MPH with near bald tyres.
Are there any problems you know about with your tyres such as a slow leak? If so, get them replaced. If that slow leak turns into a fast leak at high speed you are in serious trouble.
I'm going to assume you've had a recent suspension alignment and the tyres are correctly balanced, with no loose weights. If not, get that done.
Finally, buy a tyre pressure gauge and a tread depth gauge. Assuming you've done all the above and are happy that your brakes are in good condition, with lots of life left in the discs and pads, go gently up to a speed you're happy with between two rest stops on the Autobahn. No more than 10-15 minutes at high speed. Stop and check your tyres again. Look at the surface, is there any feathering or excessive scuffing on the edges. How hot is the tyre? Are the pressures still holding up?
If after all this everything looks good (and it's not raining or any other bad weather conditions, you're not tired or distracted, etc) than go for it. Just stop every couple of hours and check your tyres.
Edit: typos