Maths bods, real speed at 7300rpm?

[AdamT]

Took the R turbo out for an early morning blast, (as one does ) and the conditions were perfect. This was the first time I have it sitting at absolute top speed for what seemed like a very long time . We recently swapped the ruf 19s, for turbo 18s, and I was hitting the limiter at 7300rpm, the speedo was indicating 213...

Could any maths bod calculate the exact speed? The wheels are standard turbo 18s, 295/30 tyres (quite worn, maybe 3mm of tread) The gearing is standard 996 turbo also.

Thanks, i have a feeling it was a real 205/206mph...but dont know how to calculate it.

Video will follow in a little while

best,
adam

[mbutchers]

Sounds very exciting Adam - To work this out, you will need gearing ratio, final drive ratio, and rolling circumference of the tyre. Unfortunately, to give a finite answer would be very difficult, the tyre is likely to 'grow' at such high speeds, which would quite likely give rise to some inaccuracies.

[AdamT]

This is what i was afraid of, i dont really know where to start...I also increaded the tyre pressures, which im sure would make some difference too.

thanks though,

best
adam

[ArticM]

AdamT said:

This is what i was afraid of, i dont really know where to start...I also increaded the tyre pressures, which im sure would make some difference too.

thanks though,

best
adam

why dont you borror a friends tom tom and use a gps speed to calibrate ?

[br d]

AdamT said:

I was hitting the limiter at 7300rpm, the speedo was indicating 213...

AdamT said:

295/30 tyres (quite worn, maybe 3mm of tread)

Scary stuff.

brad

[AdamT]

br d said:

AdamT said:

I was hitting the limiter at 7300rpm, the speedo was indicating 213...

AdamT said:

295/30 tyres (quite worn, maybe 3mm of tread)

Scary stuff.

brad

Well they come with 5mm new (pilot sport cups), and were thoroughly checked by myself before the run, whilst increasing the pressures to michelins recommendations (ruf put me in contact with one of the heads of cup tyre development as i wanted to know as much as possible before running the tyres so fast)

Not scary, fun

[thegoose]

If it's dry - Low tread = reduced tyre shuffle = more planted.

[markbe]

AdamT said:

Took the R turbo out for an early morning blast, (as one does ) and the conditions were perfect. This was the first time I have it sitting at absolute top speed for what seemed like a very long time . We recently swapped the ruf 19s, for turbo 18s, and I was hitting the limiter at 7300rpm, the speedo was indicating 213...

Could any maths bod calculate the exact speed? The wheels are standard turbo 18s, 295/30 tyres (quite worn, maybe 3mm of tread) The gearing is standard 996 turbo also.

Thanks, i have a feeling it was a real 205/206mph...but dont know how to calculate it.

Video will follow in a little while

best,
adam

Hi Adam, standard gearing for turbo is 28.8mph per 1000 on 295/30-18"
So allow a little off for tyre wear and a little for tyre expansion, tyre pressures make no difference, would not try it at 15psi mind!!!

SO speed attained subject to accurate rev counter and limiter....

...........210.MPH.

Well done Adam.

Ps, time to change those tyres.

Mark.

[welshnobby]

markbe said:

...........210.MPH.

.....back of the net

Adam, that is impressive stuff. You will probably get the usual bores who chastise you for achieving these speeds on the public (german 'bahn) road, but i think you have already displayed the caution that you employ before entering into such a high speed run...i.e. going to the effort of speaking to michelins development bods. I'm sure that this run was done as safely as possible and probably more safe that someone blatting up to 120mph on our crowded motorways with improperly inflated worn tyres and low on oil etc. I tip my hat in your direction. It is what the cars were engineered to do, so why not do it?

Now, pop out and buy some Braso to polish those pendulous balls of yours!

[br d]

I've been on forums where Adam is getting slagged off for going too fast and I don't want to be associated with that crowd, it's very obvious he knows he stuff and understands his cars far better than I ever will. And yes he is driving within the law on these autobahns. All the same, other users are on the roads too and at over 200 mph no tyre is 100% safe, certainly not a worn one and that is why I think it sounds scary. If that makes me a 'bore' then so be it.

And as for this:
"and probably more safe that someone blatting up to 120mph on our crowded motorways with improperly inflated worn tyres and low on oil etc."

Probably more safe than that? I should hope so.

Good luck to you Adam, I know from reading your posts you are a responsible driver but FFS don't do it so often you get blase about it. Even the slightest error at that speed doesn't bare thinking about.

brad

[graeme36s]

Adam you are a very, very naughty boy. I only managed 330kph in a Veyron before a diesel Mondeo intervened. You have been chastised

[Bodo]

br d said:

And yes he is driving within the law on these autobahns.

Nope. You are advised to drive no more than 130km/h by German law, unless restricted by a lower speed limit.

[br d]

Bodo said:

Nope. You are advised to drive no more than 130km/h by German law, unless restricted by a lower speed limit.

Could you clarify that Bodo? That statement seems oxymoronic to me. A law is a law and advice is advice.
If you are 'advised' to drive at 130kph that doesn't mean you legally have to.

Not having a dig, I'm genuinely interested in how that works.

brad

[AdamT]

br d said:

Good luck to you Adam, I know from reading your posts you are a responsible driver but FFS don't do it so often you get blase about it. Even the slightest error at that speed doesn't bare thinking about.

brad

Brad,

You got that right, honest to god that would be scary...

[bcnrml]

welshnobby said:

markbe said:

...........210.MPH.

.....back of the net

Adam, that is impressive stuff. You will probably get the usual bores who chastise you for achieving these speeds on the public (german 'bahn) road, but i think you have already displayed the caution that you employ before entering into such a high speed run...i.e. going to the effort of speaking to michelins development bods. I'm sure that this run was done as safely as possible and probably more safe that someone blatting up to 120mph on our crowded motorways with improperly inflated worn tyres and low on oil etc. I tip my hat in your direction. It is what the cars were engineered to do, so why not do it?

Now, pop out and buy some Braso to polish those pendulous balls of yours!

Agreed!!

[AdamT]

br d said:

Bodo said:

Nope. You are advised to drive no more than 130km/h by German law, unless restricted by a lower speed limit.

Could you clarify that Bodo? That statement seems oxymoronic to me. A law is a law and advice is advice.
If you are 'advised' to drive at 130kph that doesn't mean you legally have to.

Not having a dig, I'm genuinely interested in how that works.

brad

This is an interesting thought,

My understanding was that if you are involved in an accident on a de restricted autobahn. And it was proven that you were travelling at a speed greater than 130kmh, then it is "your fault" as it were.

But I think im wrong on that one.

Have overtaken many polizei cars at speeds above 130kmh, and never seemed like a problem. I think they will stop you if your speed is wreckless, i.e if theres too much traffic, weather conditions etc...

My friend who was with me took a video, so am looking forward to seeing it.

best,
adam

Edited by AdamT on Monday 28th May 16:30

[Bodo]

br d said:

Bodo said:

Nope. You are advised to drive no more than 130km/h by German law, unless restricted by a lower speed limit.

Could you clarify that Bodo? That statement seems oxymoronic to me. A law is a law and advice is advice.
If you are 'advised' to drive at 130kph that doesn't mean you legally have to.

Not having a dig, I'm genuinely interested in how that works.

brad

I agree, it sounds oxymoronic without further explanation. The term I'm referring to here is Richtgeschwindigkeit, which basically means 'reference speed', and is defined by law.

Wikipedia said:

The Richtgeschwindigkeit (German for reference speed) is a legal term in Germany describing a recommended speed for roads without a speed limit that should not be exceeded even with fine road, traffic, view and weather conditions.

Exceeding the target speed is neither a felony nor a misdemeanour. However, an increased liability in the case of an accident may result from driving faster than the recommended speed, due to an increased danger of operating the vehicle.

In Germany, the Autobahnrichtgeschwindigkeitsverordnung (directive on reference speed on motorways), introduced in 1974, recommends a speed of no more than 130 km/h (about 80 mph) for autobahns and roads similar to autobahns (lanes separated by a median or at least two lanes per direction), provided there are no traffic signs posting a lower speed limit present.

I'm welcoming this, since it emphasises what should be a given anyway: you takes a certain risk, you are responsible when it goes wrong. So I would rather say that Adam does not drive within the law, but not outside either, as long as no incident provokes the question being asked

[AdamT]

Bodo said:

br d said:

Bodo said:

Nope. You are advised to drive no more than 130km/h by German law, unless restricted by a lower speed limit.

Could you clarify that Bodo? That statement seems oxymoronic to me. A law is a law and advice is advice.
If you are 'advised' to drive at 130kph that doesn't mean you legally have to.

Not having a dig, I'm genuinely interested in how that works.

brad

I agree, it sounds oxymoronic without further explanation. The term I'm referring to here is Richtgeschwindigkeit, which basically means 'reference speed', and is defined by law.

Wikipedia said:

The Richtgeschwindigkeit (German for reference speed) is a legal term in Germany describing a recommended speed for roads without a speed limit that should not be exceeded even with fine road, traffic, view and weather conditions.

Exceeding the target speed is neither a felony nor a misdemeanour. However, an increased liability in the case of an accident may result from driving faster than the recommended speed, due to an increased danger of operating the vehicle.

In Germany, the Autobahnrichtgeschwindigkeitsverordnung (directive on reference speed on motorways), introduced in 1974, recommends a speed of no more than 130 km/h (about 80 mph) for autobahns and roads similar to autobahns (lanes separated by a median or at least two lanes per direction), provided there are no traffic signs posting a lower speed limit present.

I'm welcoming this, since it emphasises what should be a given anyway: you takes a certain risk, you are responsible when it goes wrong. So I would rather say that Adam does not drive within the law, but not outside either, as long as no incident provokes the question being asked

Yeah thats what i had heard of, thanks for the reference,

best,
adam

[carylwills]

In a dull moment on a wet Bank Holiday Monday I got out my slide rule

Assuming the following:

Tyre is a 295/30ZR18 94Y Michelin Pilot Sport CUP the outside diameter when new is 25.2" (from Michelin Data Sheet). These tyres only start with 6mm of tread. If there was only 3mm tread left then the diameter of the tyre will be 25.2" - (2 * 3mm /25.4)" = 24.96"

RUF 996 Turbo R gear ratio in 6th is 0.75:1 and Final drive is 3.44:1 (From RUFs' web site)

Assuming there is no increase in tread diameter due to centrifgal force acting on the tread. There probably is a bit, but I have no idea what it is and it would tend to make the velocity greater not less.

So lets work out the number of times the tyre goes round in one hour and then multiply that by the distance travelled in one revolution and convert to miles. This will give the speed in miles per hour.

Number of wheel rotations per HOUR = (7300 * 60) / (0.75 * 3.44) = 169767.44 RPH

The distance travelled in MILES due to 1 revolution of the wheel = Wheel dia * pi / number of inches in a mile (12 * 5280) (there are 12 inches in a foot and 5280 feet in a mile).

Distance in 1 rev = 24.96 * pi / (12 * 5280) = 0.001237597 miles

Therefore speed in MPH = 169767.44 * 0.001237597 = 210.104 MPH

WOW!!!

[AdamT]

carylwills said:

In a dull moment on a wet Bank Holiday Monday I got out my slide rule

Assuming the following:

Tyre is a 295/30ZR18 94Y Michelin Pilot Sport CUP the outside diameter when new is 25.2" (from Michelin Data Sheet). These tyres only start with 6mm of tread. If there was only 3mm tread left then the diameter of the tyre will be 25.2" - (2 * 3mm /25.4)" = 24.96"

RUF 996 Turbo R gear ratio in 6th is 0.75:1 and Final drive is 3.44:1 (From RUFs' web site)

Assuming there is no increase in tread diameter due to centrifgal force acting on the tread. There probably is a bit, but I have no idea what it is and it would tend to make the velocity greater not less.

So lets work out the number of times the tyre goes round in one hour and then multiply that by the distance travelled in one revolution and convert to miles. This will give the speed in miles per hour.

Number of wheel rotations per HOUR = (7300 * 60) / (0.75 * 3.44) = 169767.44 RPH

The distance travelled in MILES due to 1 revolution of the wheel = Wheel dia * pi / number of inches in a mile (12 * 5280) (there are 12 inches in a foot and 5280 feet in a mile).

Distance in 1 rev = 24.96 * pi / (12 * 5280) = 0.001237597 miles

Therefore speed in MPH = 169767.44 * 0.001237597 = 210.104 MPH

WOW!!!

Thanks for breaking it down like that Pretty darn interesting.

One thing though, do you know if the data for the gear ratios was for the Ruf longer sixth gear or the standard 996 turbo 6th (which is the one we have)

thanks again,

best
adam