Discussion
From another thread. Some members suggest that special licences for competent motorists should be considered. That would include raising permitted speed to those who have those licences to 100mph.
This poses a question that I ask those people who I drive with at speeds of 100mph.
Q. If 2 similar cars travelling in the same direction, one at 100mph and the other at 70mph have to brake at exactly the same time to deal with an emergency incident that requires them to stop. How fast will the 100mph car be travelling when the 70mph car comes to a halt?
For the sake of DucatiGary. The 100mph car is not a Porsche SSS3 car with 24 pot calliper brakes, twin turbo ABS and a parachute attached to the rear spoiler operated by a button on the steering wheel.
This poses a question that I ask those people who I drive with at speeds of 100mph.
Q. If 2 similar cars travelling in the same direction, one at 100mph and the other at 70mph have to brake at exactly the same time to deal with an emergency incident that requires them to stop. How fast will the 100mph car be travelling when the 70mph car comes to a halt?
For the sake of DucatiGary. The 100mph car is not a Porsche SSS3 car with 24 pot calliper brakes, twin turbo ABS and a parachute attached to the rear spoiler operated by a button on the steering wheel.
Mg6b said:
For the sake of DucatiGary. The 100mph car is not a Porsche SSS3 car with 24 pot calliper brakes, twin turbo ABS and a parachute attached to the rear spoiler operated by a button on the steering wheel.
its a valid point though and sways the overall outcome.a 997 TT will stop much quicker from 100mph to 0mph than a wonky vectra will stop from 70mph to 30mph.
fact.
and therefors HAS to be taken into account or this thread is worthless.
DucatiGary said:
Mg6b said:
For the sake of DucatiGary. The 100mph car is not a Porsche SSS3 car with 24 pot calliper brakes, twin turbo ABS and a parachute attached to the rear spoiler operated by a button on the steering wheel.
its a valid point though and sways the overall outcome.a 997 TT will stop much quicker from 100mph to 0mph than a wonky vectra will stop from 70mph to 30mph.
fact.
and therefors HAS to be taken into account or this thread is worthless.
Mg6b said:
tribbles said:
Does it actually make a difference as long as the deceleration was the same? (The only variable would really be time).
The deceleration cannot be the same because the faster car has greater force to overcome comparative to weight due to its velocity when the brake pedals are applied at the instant braking is actioned. Therefore will not be decelerating initially at the same rate as the slower one.Brakes would be less efficient at higher speeds, but how their efficiency changes depends on what the car is (so would be a difficult value to factor in - especially as the faster speed would bring the brakes to temperature quicker [but then could go over temperature]).
But assuming the deceleration amount was the same, then the actual deceleration amount wouldn't affect the faster car's speed when the slower one had stopped.
so in another thread somone posted stuff that was pretend make up lets play posts trying to get factual real life situations mixed up with pretend things and trying to use the overall outcome as a reason why we shouldnt be allowed to drive at 100mph.
i think some people could see through it though . . . . .
'twas smart, that.
i think some people could see through it though . . . . .
'twas smart, that.
time2react said:
You would also have to factor in the drivers reaction times.
My calculations were for identical reaction times from the drivers (0.67secs), able to achieve the same rates of deceleration (8.5ms-2). As I said, where the 70mph vehicle comes to rest (for arguments sake stopping at the problem) the 100mph vehicle would still be doing 77mph at that position as it passed (or hit) the problem. If it had been doing 140mph it would still have been doing 128mph (using the same reaction times & rates of deceleration).Edited by vonhosen on Monday 7th January 22:54
vonhosen said:
time2react said:
You would also have to factor in the drivers reaction times.
My calculations were for identical reaction times from the drivers (0.67secs), able to achieve the same rates of deceleration (8.5ms-2). As I said, where the 70mph vehicle comes to rest (for arguments sake stopping at the problem) the 100mph vehicle would still be doing 77mph at that position as it passed (or hit) the problem. If it had been doing 140mph it would still have been doing 128mph (using the same reaction times & rates of deceleration).Edited by vonhosen on Monday 7th January 22:54
If you could see there were no apparent problems or hazzards, would exceeding 70 still be out of the question? Of course we can stop quicker at lower speeds, but that doesn't mean it's not safe to do the 100 where appropriate, which is where the original Q is leading.
tribbles said:
Mg6b said:
tribbles said:
Does it actually make a difference as long as the deceleration was the same? (The only variable would really be time).
The deceleration cannot be the same because the faster car has greater force to overcome comparative to weight due to its velocity when the brake pedals are applied at the instant braking is actioned. Therefore will not be decelerating initially at the same rate as the slower one.Brakes would be less efficient at higher speeds, but how their efficiency changes depends on what the car is (so would be a difficult value to factor in - especially as the faster speed would bring the brakes to temperature quicker [but then could go over temperature]).
But assuming the deceleration amount was the same, then the actual deceleration amount wouldn't affect the faster car's speed when the slower one had stopped.
Impossible to state accurately as all variables not known. However it will be doing approximately 30MPH, with both cars shedding speed at a constant rate.
In reality the 100MPH car will shed speed at a higher rate initially, due to wind resistance, but may shed speed at a lower rate towards the end of the run due to brake fade.
In addition the mechanical grip generated by the suspension and tyres may vary over the speed range.
In reality the 100MPH car will shed speed at a higher rate initially, due to wind resistance, but may shed speed at a lower rate towards the end of the run due to brake fade.
In addition the mechanical grip generated by the suspension and tyres may vary over the speed range.
Von is not far out. He has used calculations to find the speed.
With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
Mg6b said:
Von is not far out. He has used calculations to find the speed.
With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
Von answered a different question. My answer is the correct one to the question as posed.With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
s2art said:
Mg6b said:
Von is not far out. He has used calculations to find the speed.
With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
Von answered a different question. My answer is the correct one to the question as posed.With small variations such as road surface braking effort and other minute differences, the faster car will be travelling in the region of 70mph.
Thats pretty fast when you need to stop in the same distance that the first car managed to do so.
You may well scoff at these facts but this is reality. Ask Rob Gravet. He does a fairly good demonstration of this on his car course!
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