tyre speed rating

Normally stiffer sidewalls.

They overheat.

Obviously none are lost due to processor marking, however, talking about tyres, it would not be improbable for a manufacturer to downrate tyres, ie simply produce one V or W rated tyre, but then mark different batches at different speed ratings, thus giving them an excuse to sell the same size tyre at various prices, with the V or W ones at a significant markup, supported by the price of the "lower" speed tyres. The manufacturer gains in simplicity of production, but may lose out on material costs, however I am sure the markup more than covers it. Note I am not talking about a sub standard manufacturing process, I am talking about top level manufacturers like Michelin, Goodyear, Pirelli etc.

"DavidR" gurgled happily, sounding much like they were saying:

Quite simply, the fact that the entire construction of the tyre differs.

Years ago I used to buy tyres of known makes that had 'remould quality' branded onto the side, they were (as far as I could see) defective in appearance or the markings were wonky, rather than actually faulty. I don't remember any failing.

My Mondeo handbook says that the speed rating H, V, W or Y depends on the engine (1.8). I had V fitted.

I have had various cars of around 100bhp over the years and seen the range from S to V. Speed rating alone cannot be a factor. Power is defined in physics as force x speed so speed and load rating need to be taken in combination.

You decided to post a response mentioning "maximum accelleration, braking, cornering" so I asked you to expand on your answer. Rather than getting narky I suggest you should become more informed before the next occasion you decide to pass on your "knowledge".

Unlike you I have not made any silly assertions. If I knew definitively I could have simply replied directly to the OP's question and bypassed you.

Here's a suggestion. The speed rating is the speed at which the tyre will survive for at least 10 minutes at its rated load and pressure at 25C ambient.

So there you have it. Power and energy. But the sums still don't make sense for having a surplus speed rating.

good for you.

Indeed. Which generally reduces comfort.

So it appears, as I put in another post. But this leads further... Two tyres of the same nominal size will have the same surface area for heat dissipation. So for the high speed tyre to run cooler it must have a lower rolling resistance - which generally reduces grip.

More and more I'm convinced that whatever is stamped on the outside, nothing changes on the inside.

Finding definitive answer involving tyres and VW is a challenge!

My 08 Touran was supplied with Continental 94V rated tyres. I replaced them with Bridgestone 94V as they last much longer, but before I did so I wanted to know why my neighbour's identical spec (but 57 reg) Touran was fitted with 91V tyres.

I asked my local dealer, the supplying dealer and VW customer services all of whom confirmed mine should have 94V and his 91V but couldn't say why and unhelpfully just said "replace with what's on the car!"

"Doctor D" gurgled happily, sounding much like they were saying:

I suspect they found that the lighter-rated tyres wore more rapidly, so increased the load rating (615kg to 670kg per tyre) for new cars.

Parkers suggests Touran GVW is about 2200kg, so there's not a _heck_ of a lot of headroom on the 91s, given that weight distribution will never be

Thanks Adrian. Makes sense, far more helpful than VW customer services or a dealership!