# 60 to 0 mph



## teucer2000 (May 14, 2002)

My new MR2 does it in 2.7 seconds apparently, about the same as the TT which has much more powerful brakes.....perhaps the TT needs to go on the Atkins diet?


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## kmpowell (May 6, 2002)

Yeah but the new MR2 REALLY is a birds car. No question or debate about that. :-/


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## christtopher (May 7, 2002)

> perhaps the TT needs to go on the Atkins diet?


..perhaps the MR2 needs to loose it's lippy and eyeliner, take off it's skirt and put on a bit of weight and get a tattoo.


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## teucer2000 (May 14, 2002)

Strange...now I've sold the TT I recall that it was the third most popular car for gays, after the Mini and SLK...oh, and Nikki Clarke the hairdresser has one....and God they are so common......


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## Dubcat (Jun 10, 2002)

you drive an MR2 - do you have ANY credibility any more? I think not


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## Carlos (May 6, 2002)

I am no longer a TT owner, therefore am not biased by my current car. Â I am not afraid to criticise the TT when I feel the need.

However, the MR2 is a woman's car. Â If you are a male owner you are definitely a whoopsy. Â This is not a problem of course, but you do need to face up to it. Â :

Now that doubts about your sexuality have gone, the answer to the question lies in the repeated stopping power. Most cars do 60-0 in less than three seconds, so bigger brakes don't make much difference in initial stopping power. Where they do make a difference though is in repeated stopping power. Small brakes might stop you quickly once or twice, but big brakes will be able to do this time and again with less fade. That said, the standard TT brakes are not very good! This is why owners who take their cars on track often upgrade.

In essence the MR2 needs smaller brakes as it is lighter, although two males in the car will tend to weigh more than a male and a female.


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## teucer2000 (May 14, 2002)

Have any of you driven the latest MR2....I reckon that a well driven one would give a 180TT a decent run for its money cross country....it's light weight, good power to weight ratio plus excellent traction means as EVO mag said...'it's a proper sports car'. And before anyone asks, I circuit driven TT's and MR2's so I can make a direct comparison. Don't get me wrong, I still love the TT but there is no way that it is a sports car...it's a boulevard cruiser that combines looks with good performance and four wheel drive security.


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## Dubcat (Jun 10, 2002)

> Have any of you driven the latest MR2....I reckon that a well driven one would give a 180TT a decent run for its money cross country....


If you wanted to brag about having a fast car just go for an evo or scooby - they will blow the pants off of your MR2 AND my TT.

Also - do not drive your MR2 cross country. It does not ahve 4 wheel drive and will get stuck in the mud.



W.


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## teucer2000 (May 14, 2002)

Good advice.....


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## christtopher (May 7, 2002)

Oooo dirty, dirty mud. Get it off me, get it off me I say.


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## Dubcat (Jun 10, 2002)

I re-read my post and now I think it is not immediately obvious that I was joking that you have no credibility because you drive an MR2. In fact looking at the post now I think I come across as a really snobby git  Sorry Tecuer2000 - it wasn't my intention - i was just having a laugh.

W.

p.s. the MR2 is still a girly car though


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## PIPTT (May 6, 2002)

pmsl @ this one, nice work ;D


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## Guest (Jul 29, 2003)

On a totally boring note the 60-0 time, irrespective of the type of vehicle, will ultimately be governed by the coefficient of friction at the tyre/road interface........assuming that any given vehicle has enough braking capacity to achieve a "lock-up" at the speed stated.

Maximum breaking efficiency is achieved when there is 25% slip of the road speed in the speed of the circumference of the tyre.

Newtonian physics will prove that the weight of the vehicle being retarded has nothing to do with the stoppping distance subject to the brakes being powerful enough to reach a "lock-up" situation.

All the above does not take account for the varying types of ABS available. Dependent on the "cycling rate" of a given ABS system will depend on whether or not it lengthens or maintains the optimum mathematical stopping distance.

OH YEAH.........MR2.......ITS LIKE BRITNEY TRYING TO DO PUNK!! ;D ;D


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## teucer2000 (May 14, 2002)

IMHO Britney Spears would look gorgeous doing anything she wants, so I'll take that as a complement. As a point of interest, the girls in the office all prefer the looks of the MR2 to the TT...just goes to show everyone is different.


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## KevinST (May 6, 2002)

> As a point of interest, the girls in the office all prefer the looks of the MR2 to the TT.


I think you've just proved the point they were all trying to say ! :


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## jgoodman00 (May 6, 2002)

> I think you've just proved the point they were all trying to say ! Â : Â


lol


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## teucer2000 (May 14, 2002)

I'm not going to complain if attractive young ladies keep asking for a demo am I?


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## Guest (Jul 29, 2003)

> I'm not going to complain if attractive young ladies keep asking for a demo am I?


With this qualifying statement in mind............
did you consider buying the StreetKa ?


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## teucer2000 (May 14, 2002)

Nope, did think about buying a TT convertible though......then the salesman said Graham Norton had one!


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## r1 (Oct 31, 2002)

> Newtonian physics will prove that the weight of the vehicle being retarded has nothing to do with the stoppping distance


Not true - the mass of the vehicle will change the coefficient of friction...


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## Guest (Jul 29, 2003)

> Not true - the mass of the vehicle will change the coefficient of friction...


Sorry R1....my computer at home is not set up to do equations...otherwise i would post them here....but I AM right.

The equation to determine muu (the coefficient of sliding friction between to surfaces) has no reference in it whatsoever to mass.


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## Carlos (May 6, 2002)

This thread has everything. ;D

This co-efficient of sliding friction...does it depend on the friction caused by the individual surfaces? If so, I guess it could be altered by applying a lubricant? ;D  Sorry, just bringing the thread back on topic


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## Guest (Jul 29, 2003)

> This thread has everything. Â ;D
> 
> This co-efficient of sliding friction...does it depend on the friction caused by the individual surfaces? Â If so, I guess it could be altered by applying a lubricant? Â ;D  Â Sorry, just bringing the thread back on topic


Of course it does...the coefficient of friction is ONLY between the two surfaces in contact....and it is just that...a ratio....and can be effected by temperature, damp, lubricants etc.

It is not however...dependent on mass, or the surface area in contact. Trust me on this...I KNOW THIS STUFF!!

Lubricants........things like spilt hair gel or mousse will defenately affect the stopping distance of an MR2


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## KevinST (May 6, 2002)

but the friction required to stop a really big item in the same distance a s a really small item in the same distance must be greater??

A super tanker traveling at (for example) 20 knots requires a greater distance to stop than a rubber dinghy also traveling at 20 knots... and the tanker must have greater friction on the water as it's wider / deeper ??


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## Carlos (May 6, 2002)

That wasn't the sort of lubricant I was thinking of LapTTop! ;D

Hmm I was going to say "Ah Kev, the supertanker has more momentum, and momentum probably forms part of the equation", but since momentum is mass x velocity, it can't (according to LapTTop).

Big Jon's view is the same as this as well, on his driving day he told me that a fully loaded white van will stop in the same distance as a TT. I didn't really believe him at the time.


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## Guest (Jul 29, 2003)

> That wasn't the sort of lubricant I was thinking of LapTTop! Â ;D
> 
> Hmm I was going to say "Ah Kev, the supertanker has more momentum, and momentum probably forms part of the equation", but since momentum is mass x velocity, it can't (according to LapTTop).
> 
> Big Jon's view is the same as this as well, on his driving day he told me that a fully loaded white van will stop in the same distance as a TT. Â I didn't really believe him at the time.


Big John is right and I am right.......BUT....my specialist knowledge relates to Vehicles and Roads (although laws of physics are constant across the planet in all scenarios, I just have never put them into practice with regards to boats!!).


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## vlastan (May 6, 2002)

> Big Jon's view is the same as this as well, on his driving day he told me that a fully loaded white van will stop in the same distance as a TT. Â I didn't really believe him at the time.


I guess this will be dependant on the breaks that each use.

The had in Top Gear stopping distances for a Porsche and a 4 wheel drive...of course the Porsche will stop a lot quicker.


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## KevinST (May 6, 2002)

OK, what about a 30 ton truck and a Mini (make that a MINI because it's gonna get crushed by the truck  )?? bet they won't stop in the same distance... despite the fact that the truck has a lot more wheels connected to the ground.


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## bluettone (Feb 26, 2003)

OK. Imagine sitting in your car stationary with the brakes on. If you were to get a JCB to try to push the car and move it you have two things stopping you moving:

1. The amount of friction between the brake pads and the disks
2. The amount of friction between the tyres and the road.

Lets assume for the moment that the tyres would start to skid before the brakes let go. In this case, the friction force at the road (F) before the tyres start to slip is ALWAYS (ALWAYS) described by the equation :

F = mu x Rn

where mu = co-efficient of friction and Rn equals the downward force on each wheel.

For any set of tyres and road condition mu is always the same (slick tyres and sticky tarmac has a greater mu than grooved tyres and wet roads).

Also, the downward force on each wheel is always the same (unless the car has more passengers or load).

So the JCB has to apply a force greater than F to move the car by skidding. Obviously when you are actually moving and slowing down the scenario works in reverse but the maximum force the road can exert to slow you down without skidding is still F.

So if this force is always the same why do some cars have better braking distances than others? Well it's all down to our assumption above that the brakes can always apply enough force to make use of the road-to-tyre friction force. The actual force required to stop a car is equal to mass x acceleration (or decceleration in our case). Therefore the quicker we wish to stop, the greater the total force required. If we were slowing down gently, we would never exceed the road-to-tyre friction. If we were emergency stopping, we are likely to use all of it and more (and therefore start skidding). In order to make use of the road-to-tyre friction to the max, we need to make sure the braking force at the disk can always exceed or match the road-to-tyre friction. This is why performace cars have uprated brakes.

You have probably experienced this yourself - you brake harder to stop quicker and more gently to stop slower. Cars with poor brakes can never apply enough stopping power to stop quickly.

So there you go.

Sorry to bore those of you who are not the remotest bit interested in the mechanics of this.

Marco

;D


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## KevinST (May 6, 2002)

Ah ha !!!!

"Newtonian physics will prove that the *weight of the vehicle being retarded has nothing to do with the stoppping distance* subject to the brakes being powerful enough to reach a "lock-up" situation. 
"

"In this case, the friction force at the road (F) before the tyres start to slip is ALWAYS (ALWAYS) described by the equation :

F = mu x Rn

where mu = co-efficient of friction and *Rn equals the downward force on each wheel.*"

Sp, the weight of the vehicle does affect the stopping distance !!


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## bluettone (Feb 26, 2003)

Yes, but maybe not in the straightforward way you might think:

The heavier the car, the more force available for stopping through road-to-tyre friction before the wheels skid.

F = mu x *Rn* (Rn is equivalent to mass of car)

However, the heavier the car, the more force required to stop it for a given rate of decceleration.

F = *mass* x decceleration

So a 10% increase in car mass increases the available stopping force by 10%, but also increases the force required to stop the car by 10%

Marco


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## Dubcat (Jun 10, 2002)

R1 
maybe mass is NOT a part of it - think about it - two objects with similar aerodynamics will both reach the same terminal velocity if dropped from a height, regardless of their mass. That's right isn't it? If it is then it stands to reason that friction is not effected by mass either. I assume you thought mass was a part of the equation because of the downward force exterted by the object due to gravity.
W.
p.s. although intuitively it feels like mass should effect the friction....


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## r14n (Jan 10, 2003)

I'm sensing a bit of friction.

Wheres that wax applicator.


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## bluettone (Feb 26, 2003)

You can trust me I'm an Engineer  :

Mass *is* a factor - both in the force required to accelerate and deccelerate a car and also in the force 'available between the tyre and the road' to stop the car. See the equations above.



Marco


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## Guy (May 13, 2002)

If it is possible to get one or two things sorted so we are on a level playing field.

We are talking about CARS on a normal road fitted with normal tyres.
Not wagons or some types of van tyres (or even super dooper tankers ) Wagons and some van tyres have different compounds to car tyres. Race car tyres are normally much softer and stickier than road tyres, so discount them.

Next, we are talking about sliding friction so the brake (NOT break!) type does not matter one little bit. So all of you having spent lotsa money on brake upgrades for normal road use have wasted your dosh. If you use them on a track you MAY find they are useful though. We are talking about a wheel that is locked and NOT rotating. (ABS kind of puts the mockers on a lot of this discussion as the wheel never locks!) It doesn't matter whether the wheel has stopped rotating because of application of Super Brembos or a thick stick poked through the wheels.

The simplistic system taught to the Police is that â€˜mu equals acceleration rate divided by gravityâ€™. Their arguments in relation to dismissing weight follows along the lines that â€˜(a) the weight at the start of the skid is the same as the weight at the end of the skid, it is not changed so it does not need to be included. And (b) Any weight difference between two objects is counterbalanced by the increase in the area in contact with the road surface as the tyre deforms so the decelleratio rate stays the sameâ€™. These arguments are flawed and not quite right but the results of their computations are normally about right and within the error band the Police use for their presentations.

Weight DOES make a difference BUT it is normally to such a small degree it may be ignored for the NORMAL CAR or car derived van. If you have an overloaded car, it does take longer to skid to a stop BUT there are other factors that come into play, Mr Newtonâ€™s still has it right but Mr Frictionâ€™s rules and Mr Elasticâ€™s plastic tyres and asphalt also come into the playground when braking from 60mph.

Bring on the Wax Wizard - he knows how to stop friction and make it really beautifull at the same time.


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## Dubcat (Jun 10, 2002)

> I'm sensing a bit of friction.
> 
> Wheres that wax applicator. Â


fnar fnar ;D


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## bluettone (Feb 26, 2003)

I absolutely agree - once all 4 wheels are locked, you might as well sit back and relax .....  There's bugger all you can do to shorten your stopping distance.

What upgraded brakes do give you over standard is more braking force per pound of effort on the pedal - meaning you can lock-up quicker 

Marco


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## Dubcat (Jun 10, 2002)

I think the biggest benefit of upgraded brakes is actually a lack of brake fade - i think someone else mentioned that also...


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## KevinST (May 6, 2002)

Well that was fun then wasn't it ;D

BTW - I agree with you that larger brakes on a road car does not improve stopping distance on the initial stop, they only help with the efficiency of the brakes once they have got hot after being used... Mov'it had the very same information on their site some time ago .. was removed last time I looked for it though - wonder if it affected sales


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## Guy (May 13, 2002)

For a road motor, upgraded brakes do 3 things.
1. Â Make money for the seller.
2. Â Look pretty through the spokes.
3. Â Give you something to bore other people about when you talk about them.

For a track motor upgraded brakes do 3 things.
1. Â Work.
2. Â Stay cool enough to work when thoroughly heated.
3. Â Let you stay alive long enough so you can bore other people when you talk about them.

IMHO of course..... Â ;D


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## BigJon (May 7, 2002)

A very simple view, because I am fairly simple:

In the real world of motoring on public roads if the Porsche could stop a lot quicker Mr. Porshce would need to keep an awful lot of rear bumpers in his warehouse.

High performance cars do not get rear ended more often than your avergae family saloon.

As stated by some on this thread, some cars with better brakes might stop in a SLIGHTLY shorter distance but ask yourself where that advantage is realised.

Yep, at the very end of the stop. If the Porsche and Vectra are both doing 90mph and the, whatever it is in the road is 100m in front of them:

They will both hit it very hard.

A good circuit driver WILL need more efficient brakes.

A good road driver just needs to use the eyes and brain. The major factor in stopping distances is the ability of the driver to react, not the brakes.


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## garvin (May 7, 2002)

> I think the biggest benefit of upgraded brakes is actually a lack of brake fade ..............


Absolutely spot on. I find the problem with the 'standard' TT brakes isn't that they aren't any good for the first couple of applications but in 'spirited' driving, where a number of prolonged braking 'sessions' are required in fairly quick succession, they do start to fade and lose 'feel' - it can be quite unnerving


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## Guest (Jul 30, 2003)

Just to show how MASS can be excluded then..............

I would prefer to write your first equation in the recognised international units (at least in this arena of vehicle dynamics) as

F = mu x g x m Â Â (Force=mu x gravity x mass)

Subsitute into this equation the derived Equation from Newton's second law.....

F = m x a (Force = mass x acceleration)

and you get..................

m x a = mu x g x m (mass x acceleration = mu x gravity x mass)

Now...as any basic maths student will tell you, you have mass acting as a multiplying factor on each side of the equation, and as such, it can be cancelled out (and therefore IT DOES NOT AFFECT BREAKING DISTANCES!!!!!!!!!!!!!!!!!!!!!!!!!!!)

We now have....

a = mu x g ( acceleration = mu x gravity)

Whenworking out the deceleration of a braking vehicle (where the brakes are capable of reaching lock up for the speed at which the maths is being applied.....which I believe I stated very early on, but which some of you have failed to read or remember)

We use the eauation......
(at this point please consider sq to mean _squared_)

Vsq = Usq + 2as Â Â Â V is the final velocity
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â U is the initial velocity
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â a is acceleration
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â s is distance

_ where a vehicle is decelerating then "a" is negative
Â where the vehicle is skidding then "a= mu x g" _

therefore

Vsq = Usq -2mu x g x s

This is the final derived equation for working out breaking distances given a specific mu, or, where you have a mu working it the initial speed when the vehicle locked up etc etc etc etc.

AS YOU CAN SEE......MASS PLAYS ABSOLUTELY NO PART WHAT SO EVER IN THESE EQUATIONS.

The tyres do come into play as they heat up........and so does the road surface.....particularly....SMA...Stone Mastic Asphalt.
As this surface heats up through friction with the skidding tyre it has the effect of almost causing the tyre to aquaplane on a layer of molten mastic. This gives a much lower mu. Tyre...in the same way, mutate in their make up at the tyre road interface.
BUT.......the adjustments made for this, are complex, and have very very little bearing on the overall result when applied.


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## bluettone (Feb 26, 2003)

Thanks LapTTop 

In fact, in one of my earlier posts I stated that a 10% increase in mass results in higher road friction but higher force to deccelerate.

I should have recognised this cancelling logic more explicitly.

What fun this thread has been



Marco


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## Guest (Jul 30, 2003)

Can we just get back to the topic of hairdresser's cars now then?!?!?! (all in good humour obviously  )


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## bluettone (Feb 26, 2003)

> Can we just get back to the topic of hairdresser's cars now then?!?!?! (all in good humour obviously Â  )


Yes, was there something you wanted to say about your TTR then? ;D ;D

Marco


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## jgoodman00 (May 6, 2002)

I thought upgrading brakes was also related to feel, i.e. how close you can get the wheels to locking, without actually locking them.

Obviously, with ABS, a lot of this must rely on the functionality of the ABS sensors...


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