[prash2606]

Hello BHPians,

This is my first post and it comes with a curiosity for which I believe I couldn't find an answer in the posts. Please pardon me if a response already exists.

Query: At times I've observed that the top speed mentioned on the car speedo meter is northwards of 180kmph even in a hatch back or a <10lacs sedan, however, the tyres provided by manufacturer may not be a suitable match for those speeds, even though the car is not capable to climb up to those theoretical speeds mentioned on the meter. Has anyone come across such scenarios on any make/model and if yes, then can we legally pull up the dealer/manufacturer to provide the tyres more suitable for such acclaimed theoretical speeds?

[Amrik Singh]

Suitability or adaptability of Tyres cannot be related to the Car only. Another factor is the Road and Temperature. The road surfaces are of different types. The manufacturers test their products on their own tracks which are not exactly the same elsewhere. So any attempt to hold them liable for this anomaly will probably fall flat.

[Dr.AD]

Originally Posted by prash2606

Query: At times I've observed that the top speed mentioned on the car speedo meter is northwards of 180kmph even in a hatch back or a <10lacs sedan, however, the tyres provided by manufacturer may not be a suitable match for those speeds, even though the car is not capable to climb up to those theoretical speeds mentioned on the meter.

The top speed marked on the speedometer has no meaning. That is not the top speed of the car. Forget the tyre speed rating, the car itself is often not capable of reaching that speed. The car manufacturer does not even claim that the car will reach that speed. They provide car's rated top speed in the spec sheet, which is often a number much below the top marking in the speedometer dial.

The OEM tyre choice will usually have a speed rating of more than the rated top speed of the car, as per the spec sheet of the car. And thus, there is nothing wrong with this practice. The top number on the speedometer has no bearing on this equation, and has no meaning as such.

[Jeroen]

Other members have already explained how this works. Cars just don’t reach the maximum speed of the speedometer. But they do have a maximum speed obviously. And it would be safe practice to have tyres fitted that are suitable for that speed.

Whether that is a legal requirement in India I don’t know, I am sure other members will chip in. In some countries it is a legal requirement in some it is not.

In my home country it isn’t anymore. We did away with that requirement many years ago. So my Jaguar can do speeds in excess of 265 Km /h. So I like to have the appropriate speed rated tires, just because occasionally I have been known to hit that speed on the German Autobahn.

I am not sure why the Dutch government did away with this rule. I am a liberal at heart, so the less rules and regulation and keeping people responsible for their own actions is great. But most people would not have a clue there is even such a thing as a speed rating for their tires. Ensuring with a simple rule/law that the speed rating of the tires need to match the car maximum speed seemsvery simple and straightforward to me. Almost impossible to make mistakes.

But I could fit much lower speed rated tires and save myself an awful lot of money. Up to my own discretion and responsibility. I do know that certain insurers require the speed rating of the tires fitted to match the maximum speed of the vehicle. Usually, on super cars and so on.

Irrespective it is advisable to have all four tires the same speed rating. If you have two sets with a different speed rating, put the ones with the lowest rating on the front wheels. That will ensure you will have the best grip on the rear wheels.

Jeroen

[dhanushs]

Apart from what others have mentioned above..

Originally Posted by prash2606

... then can we legally pull up the dealer/manufacturer ...

Sorry for going off-topic, but, may I ask why you are so eager to get into a legal battle?

even though the car is not capable to climb up to those theoretical speeds mentioned on the meter.

You have yourself mentioned that you know the car wont reach those speeds, but, I was wondering why you wanted to get into a legal battle, just cos of a number in an instrument console.
Wondering what would be the purpose?

[prash2606]

Dear fellow BHPian,

To clear the air, I have no intent of any legal action. This is pure plain out of curiosity. To simplify, I'm asking if such a mismatch exist (speedo mentioned topseed vs stock tyres provided), can we pull up the dealer to provide the tyres more suitable for those theoretical speeds. Please understand even if the car is not able to reach those mentioned speeds and if a mismatch exist, I think we have an argument, either with dealer or the manufacturer. There should be a reason why those speeds are mentioned on the speedo.

Hope this makes sense.

[fhdowntheline]

Another important point is that the tyre may be used by other cars which have different speed capabilities. For example, a V rated tyre on a Linea has a different implication than say if it is fitted on a Ciaz.

[Sankar]

Originally Posted by prash2606

Query: At times I've observed that the top speed mentioned on the car speedo meter is northwards of 180kmph even in a hatch back or a <10lacs sedan, however, the tyres provided by manufacturer may not be a suitable match for those speeds, even though the car is not capable to climb up to those theoretical speeds mentioned on the meter. Has anyone come across such scenarios on any make/model and if yes, then can we legally pull up the dealer/manufacturer to provide the tyres more suitable for such acclaimed theoretical speeds?

The car manufacturer always fit a tyre with a speed rating that is rated for the maximum speed vehicle is capable of doing (not the speedometer max value).

For eg:
1) Most Maruti Suzuki 1.2K engine cars will do a true top speed of 175KPH, the Apollo tyres fitted as OE are T rated which is good for 190KPH. The numbers printed on the speedometer may go beyond 200 but it is irrelevant.

2) Innova Crysta will do a true top speed of 180KPH and the bridgestone tyres fitted as OE are H rated which is good for 210KPH. Highest value on the speedometer is 200.

For any new car you can find out its manufacturer specified true top speed (from the specifications or other sources) and find the speed rating of the OE fitted tyre (which is usually there on the tyre itself - T, H, V, W etc) and check if they are under or over rated for the speeds capable. Don't go by max numbers displayed on the speedometer and compare that to the OE tyre its pointless.


https://www.uniroyal-tyres.com/car/t...-speed-ratings

[Jeroen]

Originally Posted by prash2606

There should be a reason why those speeds are mentioned on the speedo.
.

There is a bit of a historical technical reason to it, but mostly just PR these days.

In the old days speedo used to be quite delicate instruments. A coil through which a current was put, created a magnet force. That would twist a metal rod inside the coil to which the speed indicator handle was attached. There was also a spring attached. More current, more twitching against the force of the magnetic field etc. Very simple, but effective. However, these are somewhat delicate instruments and needed to be carefully calibrated. However, accuracy of these kind of instruments deteriorates as function of the scale. The higher up on the scale the less accurate. So that is why the scale goes up to a much higher speed then the car is capable off. It keeps the speed dial in the more accurate part of the scale. Of course, speedometer are calibrated such that they always over indicate as well.

Also, manufacturers would standardise the speedometers across a range of cars with different engines. The speedometer had to fit the car with the highest maximum speed as well as the lowest maximum speed. Somin some cars the difference between max speed on the dial can be quite different from the speed the car is capable off.

Nowadays, any of these arguments is less relevant, or to a lesser extent. A lot of these high speeds are just another PR gimmick!

I remember when I was a little boy, my mates and I would stroll along the neighbourhood streets with a little notebook. We would peek inside each car and note the maximum speed of the car. Man, you would be so proud when your dad car had a higher speed on the dial than your friends!

These days people called marketeers look at what little 8 year old boys like and model that into their cars. That is progress, completely useless professions.

Jeroen

[Dr.AD]

Originally Posted by prash2606

This is pure plain out of curiosity.
...
There should be a reason why those speeds are mentioned on the speedo.

If you are just curious about how the maximum number on the speedometer is decided, then there are a few reasons. In addition to standardization across different car models (and across different geographies/countries), and accuracy, as mentioned by @Jeroen, the other important factors are aesthetics and psychology.

Aesthetics or simply design of the dial plays a big role in choosing the scale and the markings within the scale. Further, psychology of interpreting the position of needle at driving speed plays a critical role too. Most speedometer dials are designed such that during usual highway speeds, the needle is somewhere in the "top dead center" position (or somewhere in the middle of the scale). This looks beautiful as well as conveys a message that "all is well". If at that regular driving speed, the needle is already pointing towards the top end of the scale, it would sort of give a message that something is getting pushed too high, and a message of danger, which would not be correct. This is why having an extra headroom on the scale helps by keeping the needle in the middle portions during regular driving.

The psychological and aesthetics aspects are carefully considered by the design team before choosing the dial design, including the scale and the markings on the scale. This is true for most measurement devices, and not just for car speedometers.

Here is one article that explain this: https://www.businessinsider.in/tech/...w/61756995.cms

Thus, there are several considerations in choosing the top markings on the speedometer (or for any other measurement scale for that matter), and there is neither implicit nor explicit assumption that that is the achievable top number for whatever is being measured. The car manufacturers most certainly do not claim that to be the top speed. They explicitly mention top speed as a separate number in the spec sheet, and that is always a lower number than the speedometer dial's maximum number.

Now just for the sake of arguments if you want to challenge the car manufacturer for putting a specific max number of the speedometer, why bring tyre in the equation? The tyre is not the limiting factor. You would have to challenge them on why the engine and the aerodynamics (the two primary factors deciding the top speed - not the tyre!) are not made good enough to reach that speed. These two are the factors that limit the top speed. The OEM tyres are usually with a speed rating higher than the top speed limited by the engine and the aerodynamics of the car. Thus, the tyres are not the limiting factors, even if you want to argue just for the sake of arguments.

[Brumby]

Any analogue gauge (pressure, temperature, charge, speed etc) cannot have it's max. scale reading as the reading that it will read normally. The analogue gauges read best and most accurate values between 10 O'clock to 2 O'clock position, for car speedometers, that is the range where the car will perform the best without stressing the components or with lower efficiency.

Exceptions for the speedos designed and laid out in oblique or other directions.

So the mid-scale range is the most suitable for operation (local regulations my prohibit even that, specially for high end cars).

For tyres, no car has tyres which are under-rated for the maximum speed that can be done on that car (stock condition). Exceptions will always be there.

Theoretically, if there is a straight steep infinite slope, a car going down the slope with can exceed its maximum speed and the speed rating of the tyres.

The manufacturers have a safety factor which means the tyre will not disintegrate the moment you reach the rated speed, it can sustain slightly higher speeds for may be a few minutes.

Any person driving a vehicle has a responsibility to know his vehicle well and must drive only when he is sane and understands the limits of the vehicle.

Cheers

[Vineelvatsav]

This is a bit off curiosity spark, really wanted to know what am I missing.
I have a Nissan Micra XV CVT, which has a top speed of 155 kmph, though I could only max out at 150 kmph, considering the ideal situation my OE tyre should have the speed rating of Q (160 kmph), considering wear and tear, high temperature of India etc which leads to my assumption that 20% excess of that should be considered and be rated T (190 kmph) but why is it rated H(210 kmph), since T rated tyre is cheaper can I go with those??
This is the tip of the iceberg I also have a 2017 Mercedes GLE 250d which has a top speed of 210 kmph, considering ideal situation again, OE tyre rating should have been H (210 kmph) again assuming 20% it should have been W(270 kmph) but why is it Y (300 kmph)? Y tyres are softer as per my understanding, which as per my understanding have less life.
Is there something else to all this?
I get that higher speed rated tyres have better grip, how useful is that. Is this a ploy by tyre manufacturers to sell more tyres? I just don’t get it.

[Samfromindia]

Ford Ecosport TDCi Top Speed

Speedo Limit: 220KMPH
Real World: Speedo = 180KMPH / GPS 172KMPH
Tyre: MRF ZV2K 92H = 210KMPH rated

https://www.team-bhp.com/forum/tyre-...ml#post4624740 (Ford Ecosport : Tyre & wheel upgrade thread)