Will be getting new tyres on my octavia this week sometime. 

 

Since ive only recently bought the car i want to make sure im getting the right size as i know you can use slightly different spec etc

That is the OEM spec, yes. Should be a data label on the inside of the fuel flap as well, from memory? Or maybe that’s just pressures. 

Pretty sure it will list the tyre spec along side pressures as the pressures vary by tyre size.

 

Also, haven't looked it up - but almost certain the factory spec is a Y rated tyre. Academic really in practical terms but it is the law not to replace a lower speed rated tyre unless it is a winter tyre or a temporary space saver spare... 

16 hours ago, TheClient said:

Pretty sure it will list the tyre spec along side pressures as the pressures vary by tyre size.

 

Also, haven't looked it up - but almost certain the factory spec is a Y rated tyre. Academic really in practical terms but it is the law not to replace a lower speed rated tyre unless it is a winter tyre or a temporary space saver spare... 

never heard of that law before?

8 hours ago, ApertureS said:

never heard of that law before?

Well for starters, fitting a lower speed rated tyre is an adverse undeclared mod. Which may render your car uninsured. Its a fairly objective test - tyre is mfr speed rating or it is not. All that needs checking is the tyre plate.   Driving uninsured is.... against the law. 

 

I'll let you paw over the uk statute books and see what you find as far as tyre load index and speed ratings and going below mfr specifications. In many other jurisdictions such a departure,  is also explicitly illegal. 

 

More to the point, load index and speed index are both indications of the tyre structural integrity and strength. Would it be a good idea to fit lower index or speed on the basis you know better? You run lighter loads, you don't drive at 160mph etc.   For me, I'd stick with the mfr spec and avoid the hassle, risks, legal aspects.....just my opinion of course.  

12 hours ago, ApertureS said:

never heard of that law before?

Well called that man! 👍

 

You created some impressive backpedalling!

Tyres - Load index and speed rating (question and answer session)

 

Question 1

My maximum axle load is 1,230kg. Can I use tyres with a 91 (615kg) load index?

Answer 1

Yes

 

Question 2

My car's top speed is 150mph (240km/h). Can I fit tyres with a speed rating of V (150mph) (240km/h)?

Answer 2

Yes

 

Question 3

My car's top speed is 150mph (240km/h). Can I fit winter rated tyres (tyres with the 3PMSF symbol are winter rated, so include all-season tyres) that have a speed rating of H (130mph) (210km/h)?

Answer 3

Yes

 

Edited 14 November, 20232 yr by Carlston

Q1 and Q2 are to a large extent out of an individual's hand, so far as assement is concerned,  as they are already defined on the vehicle fitment plate for tyres, which factors the vehicles load and other inputs already for you.

 

I don't think you can argue with what is already plated on the vehicle explicitly.

 

And if you go outside manufacturer fitted specification you are running an argument with an insurer for sure and one which is quite obvious.  Amongst other enforcement organisations, depending on the  jurisdiction being referenced in countries where it may be illegal, if you were to travel cross border for example

 But if you want to... put some s rate retread tyres on your vrs. They still have a rating to 180 kph well in excess of legal road speeds in uk. 

Car insurance is based on risk, and ultimately it's a UK court that decides what an insurance company can use to wriggle out of paying a claim. Claiming a 150mph car needs 186mph tyres won't cut much mustard with a UK judge.

 

If a car's top speed is 150mph, it doesn't matter whether V, W, or Y rated tyres are fitted because the risk is the same.

 

Similarly, if a gross axle weight is 1,230kg it doesn't matter whether load indexes of 91(615kg), 92(630kg), 93(650kg), 94(670kg), 95(690kg), etc, are fitted as the higher load indexes don't reduce the risk.

 

Car manufacturers will often over-specify a tyre because that just happens to be what the tyre company is making in that size. Skoda might say to a tyre manufacturer that they would like a V speed rated 225/35R19, but the tyre manufacturer might say they can only offer that size with a W or Y speed rating. This happens a lot with wide, low-profile tyres, ie. the car ends up with over-specified tyres.

 

If you have a look at mytyres, you won't see any 225/35R19 summer tyres with a speed index less than W (168mph). So if you ordered an Octavia MK3 with a top speed between 130mph and 150mph, you would get tyres that were rated for at least W (168mph). These W rated tyres aren't safer than V speed rated tyres for this car, because the top speed isn't more than 150mph. So if a tyre manufacturer did start making V speed rated tyres in this size and you fitted them, it wouldn't increase the risk. Therefore, it wouldn't be a significant modification and wouldn't need to be declared to the insurance company.

 

In some European countries there are strict laws that mean you have to keep to the tyre and rim specifications that are shown in the CoC (Certificate of Conformity). These strict European laws don't apply to the UK.

 

Edited 14 November, 20232 yr by Carlston

I have the C of C for my MINI Electric & it is for 205/45 R 17 W 88 on 7,0 J x 17 ET54 the car came with.   The cars limit is 94 mph with up to 168 mph (max) tyres. 

 

The thing is the tyres they came with were Goodyear Eagle F1 tyres which were rubbish in the slights of a damp surface even at UK NSL of 60 mph.

On 14/11/2023 at 16:30, TheClient said:

Well for starters, fitting a lower speed rated tyre is an adverse undeclared mod. Which may render your car uninsured. Its a fairly objective test - tyre is mfr speed rating or it is not. All that needs checking is the tyre plate.   Driving uninsured is.... against the law. 

 

I'll let you paw over the uk statute books and see what you find as far as tyre load index and speed ratings and going below mfr specifications. In many other jurisdictions such a departure,  is also explicitly illegal. 

 

More to the point, load index and speed index are both indications of the tyre structural integrity and strength. Would it be a good idea to fit lower index or speed on the basis you know better? You run lighter loads, you don't drive at 160mph etc.   For me, I'd stick with the mfr spec and avoid the hassle, risks, legal aspects.....just my opinion of course.  

That is a lot of words about a law that you’ve not been able to quote?

 

If you made the statement why not just quote the statute and section?

 

Not once did I say I would or wouldn’t do things a certain way - Never did I say I would fit lower rated tyres - just asked you to cite your sources if you’re going to give people legal advice.

 

fitting a different brand of oil filter or air filter is also technically an undeclared modification, fitting a different brand of tyre is also an undeclared modification from factory specification.

I don’t remember the last time I even saw a tyre below a V speed rating for sale (in larger sizes like 17’’ up) which is rated for up to 149mph which 99% of cars won’t even get to 60% of their tolerance.

 

It was a simple question of you made a statement quoting a law, so state the law.

 

edit:

 

something else to add - no vehicle is ‘plated’ with tyre sizes. A sticker in the door jam or fuel cap is not a plate. A ‘plated’ label is a legally required plate attached to the chassis which contains legally required information such as vin, load ratings and other vehicle data. A tyre pressure sticker comes in lots of different flavours and most do not state any tyre weight or speed sizes.

Edited 16 November, 20232 yr by ApertureS

TheClient usually posts very good advice and I hold him in the same esteem as yourself, both people with a lot of current, relevant hands on experience to share.

 

Its a human nature thing, I have noticed some posters when challenged become extremely verbose and diversionary rather than just accepting their advice can not be backed up, one in particular is dreadful!

 

In my country is illegal to fit any tire other than those sizes homologated for the vehicle, the Gendarmes or the insurers dont give a flying 4x unless its clearly dangerous or has caused an accident, the poor CT testers have to do the enforcement but there is no gain for them as they are not allowed to do anything other than test, no repairs, tyre fitting etc.

 

The tyre fitting places make a fortune from it and frequently lie in doing so insisting that 2 or even 4 tyres are fitted after a puncture, that an identical make, type and size of tyre cannot be fitted on its own because the tread pattern has changed and that all 4 must be replaced etc.

 

Something interesting that I learned regarding the tyre ratings is that the maximum speed and load, lets say 160mph and 690kg is not continously rated at those figures, it has to support that load at that speed with the correct pressure for 10 minutes (not certain of the time) on the test rig without going above a maximum temperature.

 

I have a 2500kg tipping trailer still on the 30+ years old OE fitment tyres which are 95/93L rated, 93 being the applicable one for twin axle, so 650kg x 4 at maximum 75mph is deemed safe for a maximum of 10 minutes.

 

Given those tyres have regularly carried double that for 30 years and have impressive sidewall cracking its safe to say there is a big margin of safety, I only travel a maximum of 10 miles laden and at slow speeds, I would not take it on an autoroute journey even unladen with L rated tyres, there is no question of their load carrying capacity, just one look at them tells you that, they look like dumper truck tyres but it was a bit of a shock to find their 75mph speed rating knowing that it is only for 10 minutes.

 

Please check the 10 minutes I quoted, it may be longer, also what temperature bearing in mind what the ambient temperatures might be.

It might help to know how the speed rating for a given tyre is determined, when making a buying decision that involves a choice of speed rating.

My car came with W rated tyres, which when I replaced them, I changed to Y rated tyres.

I did this as I assumed, rightly or wrongly, that the Y-rated tyres would be better-made and more resistant to blow-outs than W rated tyres.

But I did this based on an assumption, not on any actual knowledge of how tyres actually achieve a speed rating.

A blow out is either a catastrophic puncture or a tyre that has overheated and had a catastrophic structural failure through running at too low a pressure or in very rare cases like my tipping trailer through exceeding both the load and speed ratings for a sustained period.

 

I doubt that a higher speed rated tyre would help you in any of the above except the last and there are very few of us that would willingly put themselves in that situation.

 

Blow outs were a frequent occurrence before the introduction of tubeless tyres, I suffered a blow out on a tubed trailer tyre and don't wish to repeat the performance, I read a 60's Readers Digest article on the new invention of "puncture proof" tubeless tyres, they were not puncture proof in the way we think of a puncture now but back then a puncture when driving could be catastrophic, they described a test where the vehicle drove over a plank of wood with nails sticking up and the tubed tyre deflating immediately and the tubeless one "self sealing" in their words around the nails and deflating in a slow and controlled manner giving adequate warning to the driver to slow to a stop safely.

 

Well that would have worked with 1960's drivers whose senses had a connection to their vehicles responses, that has by and large been lost on todays generation who have never known anything other than driver assistance systems.

 

 

Data from fuel flap is just for pressures but indicated wheel sizes gives approx.idea what's permissible. Main idea there is "wheel with X size must have Y bar".

Exact list of OE tyre/rim/car combinations is in service manual.

Example? My Fabia mk1 had pressures on fuel flap for R13 wheels too.

But (due to exact engine power and front brake size) min was R14- and R13 can be installed only on rear (drum brakes), haha.

---------

What you see on fuel flap (or B-pillar) of any car: this model CAN have those wheels but it's not said that for exact car all wheels can be installed.