Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Hi Forum,

Have just returned home from buying a 2013 GTC, 60 miles from home.

Called in with my local tyreshop as I was passing to check/top-up tyre pressures. As I was there owner glanced over and took a closer look at the tyres and shook his head.

He told me the tyres shouldn't be on that car!

While they are the correct size, and tread & condition legal, he showed me on google, that they are for 4 x 4 & SUV vehicles. Also rear axle has mixed brands.

I bought car from dealer and called him to tell him what I'd just heard, and he told me they are perfectly safe and that the tyreshop are just trying to con me into buying new tyres.

Front is 2 x Michelin Latitude tour HP 235/50/18

Rear is 1 x Michelin Latitude tour HP, & 1 x Avon ZX7 235/50/18

What are your thoughts, am I worrying now about nothing?

Thanks for reading.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - _ORB_

What are the speed ratings

IE 97v or somesuch?

They are good tyres for luxury suv/crossovers going offroad, gravel tracks etc.

for the rears if they are the same spec, I am not sure it is illegal if they are both 97V (if that is what yours are.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mcb100

Have a look on Michelin's website - they're a road orientated tyre intended for SUV's and 4X4's. If they're the right size, load and speed rating they'll work, but not as well as a tyre intended for a medium sized hatchback. Avon seems to be the same story.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Yes, all 4 are 97V

So I can relax, as V is up to 149mph (which I won't be going anywhere near to)?

Just concerned car might start aquaplaning on a wet motorway!

Edited by mikert on 25/09/2020 at 11:48

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Pinstripe

Just concerned car might start aquaplaning on a wet motorway!

Wide tyres are more prone to aquaplaning. Worn tyres are more prone to aquaplaning. GTCs have relatively wide tyres (235/45R18 or larger).

I wouldn't be surprised if SUV tyres with knobblier and possibly deeper treads would work better in an aquaplaning situation than regular tyres because a 4x4 tread pattern gives water more escape routes out from under the tyre.

No tyre excels in all situations. Tyres that are great in the wet are often mediocre in the dry because more gaps in the tread allow water to escape. But those same gaps in the tread means less rubber touching the road when there isn't water needing to get out from under the tyre.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mcb100

They'll be a stiffer construction to 'prop up' a heavier car, leading to a potentially firmer ride, and maybe a harder rubber compound, compromising wet grip but decreasing wear.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Planning to set PSI at mid range between recommended & eco (as on b-pillar) which is 2.5 bar (36psi), Do you reckon I should stick to lower end of suggested range?

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Bromptonaut

Do they meet the criteria for size, speed rating and load category per the car's handbook and any tyre information displayed on (eg) door frames?

As others say these seem to to be oriented to the 4*4/SUV market. Michelin's website suggests they have some Mud/Snow capability. Other sources suggest they will have stiffer sidewalls which may mean a firmer ride.

Could it be so firm as to be dangerous?

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Well the size is correct as per door pillar (only 1 size there) Can't find anything in booklets regarding speed ratings though.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mcb100

Put your registration into someone like Black Circles' website, and it'll find the correct width/diameter/load/speed rating for your car.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Already tried black circles, and kwikfit. Size is correct, speed rating default is "any"

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Andrew-T

Being simple-minded, I would suggest that there is no single brand of tyre that is the only correct choice for your vehicle. As with oil, several brands will be suitable provided you get the correct size and rating. You would need to be a specialist driver of some sort to tell the difference between those. Usually, as with many things, you get what you pay for in terms of performance and durability.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - RT

There's no official classification for "4x4" or "SUV" tyres - we use the same as ordinary car tyres although in different sizes and load ratings - I suspect the tyre "fitter" has a lack of knowledge of tyres!

I've had the same thing said when fitting All-Season tyres to a Subaru Outback - which is a 4wd SUV anyway!

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Thanks RT, when you say fitter has lack of knowledge, do you mean the one who fitted them, or the one that advised me against them?

And if the latter, would you recommend 4x4 SUV tyres for an Astra?

Genuine question, not trying to be rude.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - RT

Thanks RT, when you say fitter has lack of knowledge, do you mean the one who fitted them, or the one that advised me against them?

And if the latter, would you recommend 4x4 SUV tyres for an Astra?

Genuine question, not trying to be rude.

The one who advised you!

Michelin Latitude/Tour wouldn't be my first choice for an Astra GTC but they aren't "wrong".

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - John F

I bought car from dealer and called him to tell him what I'd just heard, and he told me they are perfectly safe and that the tyreshop are just trying to con me into buying new tyres.

Front is 2 x Michelin Latitude tour HP 235/50/18

Rear is 1 x Michelin Latitude tour HP, & 1 x Avon ZX7 235/50/18

What are your thoughts?

These are quality tyres, not bargain basement. No need for winter tyres! The tyreshop is exhibiting the sharp practice sadly widespread in the motor trade. I would take my custom elsewhere in future.

Am I worrying now about nothing?

Yes, assuming legal tread depth.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Engineer Andy

I bet that the Michelin tyres were fitted as a cheap replacement set - normally those tyres will be expensive, but I'd check what the manufacture date was on them, as they could've been a set of tyres that whoever sold them had unsold for a long time and wanted to shift them, thus they got them cheap.

With the Avons (unlike Michelins), they are generally known for faster wear rates than premium brands, so the overall effect may be that they all will need replacing roughly at the same time. I suspect that the Avons were fitted to 'match' the Michelins but at a vastly cheaper price than if they got a brand new (i.e. within 6 months of being manufactured) Michelin tyre.

I agree that as long as the tyres look in good condition / well above legal tread depth and are not over 6 years from their manufacture date, then they should be ok, but the OP cannot expect them to perform as well as a set of non-4x4 all season tyres and especially summer/winter tyres designed (and recommended) for cars of this type.

If I were the OP, I'd look into what tyres all four existing ones could be replaced with (probably a medium-high permformance set from a mid-range or premium brand) and check / keep an eye on the existing set to see how close they are to needing replacing (my guide is always at 3mm or if they handle poorly / unsafe [esp. braking/cornering], especially in bad weather) so that they can take advantage of any good deals at tyre fitters, because I suspect whatever they get, they won't come cheap.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Pinstripe

Michelin Latitude/Tour wouldn't be my first choice for an Astra GTC but they aren't "wrong".

It depends on what the previous owner did with the car.

One of our household's cars is a GTC. Some time soon its ageing and well-worn tyres will be replaced by a set of all season tyres.

Is it a waste of a sporty car? Not if you want a sporty drive in autumn and winter where summer tyres will slide about all over the place on the cold, damp, greasy roads.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - SLO76
While not the tyre I’d fit to an Astra either there’s absolutely nothing wrong with them at all. They’re a premium tyre that’ll last well. It’s likely the last owner got a deal on them. There’s no safety issue and the fast fit centre are doing you a disservice by suggesting there’s a problem. I’d go elsewhere in the future. They are a little firmer riding though but I doubt you’ll really notice much difference.
Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Ok thanks all, I'll stick with them.

When time comes to replace them, can I change 2 at a time (1 axle) to non 4*4/SUV, or will I need to have 4 matching,?

And are the mixed brands on rear axle OK, or should I ditch the Avon (good tread) and have 4 matching?

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - _ORB_

And are the mixed brands on rear axle OK, or should I ditch the Avon (good tread) and have 4 matching?

If the amount of tread is the same as the other and the tread pattern is similar, just leave it on.

When you change . it's up to you.

But as many here will say, that patch of rubber is your contact with the road, buy the best you can.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - FP

I believe best practice is to fit identical brand and specification on each axle.

Edited by FP on 25/09/2020 at 15:49

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - badbusdriver

What I’m curious about here is the 97 weight rating. This seems excessive for an Astra, even one with a heavy old 2.0 diesel lump in the nose.

I drive a VW Caddy van for my work and before that a Ford Transit Connect. These have ross vehicle weight’s of 2200 and 2300kg respectively. I use 95 rated tyres but could easily manage on 92 or 93 rated tyres. As far as I can ascertain, the Astra GTC 2.0 diesel has a gross weight of 2040kg. 97 rated tyres are good for 730kg per corner, or 2920kg in total. It could be this weight rating is the reason some members are suggesting the tyres are actually for an SUV (possibly also why your tyre fitter reckons they are wrong?). It also could result in a harsher ride than necessary.

As to the speed rating of ‘V’, my understanding of this (not 100% sure though), is that you must have a tyre in keeping with the car’s top speed, regardless of how fast you plan on driving. Now assuming your Astra is the 165bhp version (I believe there was a twin turbo version available), it has a top speed of around 130mph. So your ‘V’ rated tyres are absolutely fine, but if it had a top speed of 150mph or more, (legally) you’d have to get the next grade up, ‘W’ (I think), which is for up to 168mph.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - RT

As to the speed rating of ‘V’, my understanding of this (not 100% sure though), is that you must have a tyre in keeping with the car’s top speed, regardless of how fast you plan on driving. .

Although that's true in parts of Europe, I don't believe that's the law in the UK.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - badbusdriver

As to the speed rating of ‘V’, my understanding of this (not 100% sure though), is that you must have a tyre in keeping with the car’s top speed, regardless of how fast you plan on driving. .

Although that's true in parts of Europe, I don't believe that's the law in the UK.

Even if that is the case, I wouldn’t chance it. After all, your insurers will look for any excuse not to pay out on a claim, and a tyre not up to the capability of the car, or the specifications of the original equipment could be just the excuse they need.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mcb100
Unless they’ve been superseded, The Motor Vehicles (Approval) Regulations 2001 state that:

16. Tyres
6. Each wheel on each axle shall be equipped with a tyre which has a load capacity such that when the axle is loaded to its maximum permitted axle weight, the weight transmitted to the road surface by that tyre does not exceed that load capacity.

7. The speed capability of all tyres fitted shall be not less than the maximum design speed of the vehicle.
Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Manatee

*Don't* under-pressure them to 'compensate' for the stiffer sidewall. The tyre walls don't carry the load, the air in the tyre does.

What you have is akin to using extra load tyres which is very common in some sizes anyway. Just use recommended pressures.

They are good tyres. The Avon is of the same load and speed rating (good). They are both high performance tyres with an all-season style tread pattern, just looking at the appearance (extra sipes). They are made for high performance vehicles and I see no reason to expect any problems, other things being equal.

I wouldn't mix brands on a 4WD as they might be a slightly different diameter - that is not a problem for the Astra.

I'm not a tyre expert or claiming to be but I am very fussy about tyres, to the extent of moving them around to even out wear and replacing them as a full set.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Update, I've emailed my insurance company, and if they're happy then so will I be. If not, then I will be contacting the dealer with a request that tyres are changed. As was pointed out, if there were a claim. claims assesor will be looking for a reason not to pay.

If they are happy, I'll be buying a part worn Michelin to match the single one on the rear axle. Then later buying a part worn Avon and fit the pair on whichever axle comes first. But I'll be swapping axles when appropriate so I can change all 4 together when the time comes to non SUV/4*4 ones.

I'll let you know what the insurance Co. say,

Thanks all.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - badbusdriver

As was pointed out, if there were a claim. claims assesor will be looking for a reason not to pay.

I think you misunderstood what i was saying. The legal issues was regarding having tyres with a lower speed rating than your car is capable of doing. But that isn't the case here, a V rating (up to 149mph) is absolutely fine for a 130mph car.

I don't believe having that higher load rating would have any legal implications, they are not massively over specified after all.

Maybe different if you had tyres for a 3.5 tonne van on it!

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - John F

*Don't* under-pressure them to 'compensate' for the stiffer sidewall. The tyre walls don't carry the load, the air in the tyre does.

No it doesn't. The air just allows the tension in the sidewalls to carry the load.

www.millersville.edu/physics/experiments/059/index...p

Air inside the tyre doesn't carry any load.

On the road, the bottom sidewalls are compressed and bulge outwards. This stretches the sidewalls at the top and generates tension in them . Now these stretched sidewalls pull the beads upward and the beads of tyre attached to rim pull the rim upwards. So, wheels are not supported from bottom , they are hanged by top part. Easy to understand when you see a flat tyre pumped up.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Manatee

*Don't* under-pressure them to 'compensate' for the stiffer sidewall. The tyre walls don't carry the load, the air in the tyre does.

No it doesn't. The air just allows the tension in the sidewalls to carry the load.

www.millersville.edu/physics/experiments/059/index...p

Air inside the tyre doesn't carry any load.

On the road, the bottom sidewalls are compressed and bulge outwards. This stretches the sidewalls at the top and generates tension in them . Now these stretched sidewalls pull the beads upward and the beads of tyre attached to rim pull the rim upwards. So, wheels are not supported from bottom , they are hanged by top part. Easy to understand when you see a flat tyre pumped up.

Yes you need the tensile strength in the sidewall. The pressured tyre is a system under preload which depends both on the air pressure and the casing tension (including tension in the tread) which maintains that pressure and the tyre shape. You need both.

I wasn't giving a physics lesson, I'm neither a physicist or a teacher. It's a shame we can't quiz your source because I can't see how the bead can pull the wheel rim anywhere or how the rim can be "[hung] by the top part"- it isn't glued on and there's no mechanical purchase there, the vertical component he refers to is pulling against the tensile force in the bead wire not against the wheel rim - often there is actually lubricant between the two. Without that opposing force the tyre would pop off, not lift the wheel up.

I don't think the man on the Clapham omnibus would take issue with the idea that a car on pneumatic tyres rides on a cushion of air.

Try taking the air out of the tyre and see what happens to the ground clearance.

Even your man says "The tensile stress in the sidewall... is related to the pressure...in the tire". As indeed it would be because the sidewall has stretching forces in it from holding the air in the tyre!

He's made a simple job very complicated. Yes there are forces in the sidewall but we (unless we are tyre designers) don't need to know what they are. In any case any vertical force exerted by the bead on the top of the wheel would be cancelled by the opposing force on the bottom of the wheel.

Just consider the contact patch.

For a 2000lb car (we're using psi) the load on each wheel is 500lb (average). As the car is going neither up nor down, and the only part of the tyre in contact with the ground is the tread, the force the tread applies to the ground is 500lb. That is spread over the contact patch. If you know the weight on the wheel and the excess pressure as read by a tyre gauge (note not absolute pressure) in the tyre you can work out the approximate size of the contact patch.

This seems to work quite well.

Here's a link to a site that has a number for the contact patch of a Crown Victoria with tyres at 32psi

vehicledynamics.com/the-tire-contact-patch/

They don't give the weight of the car but google says it's 4129lbs.

Average load per tyre is therefore 1032.25lb. At 32psi that suggests a contact patch of 1032.25/32=32.26 sq in.

In fact the contact patch is 36.75 sq. in. per tyre, which therefore exerts about 28.1psi on the road.

(Yes there are no doubt different weights, pressures and tyre sizes but the result is not an order of magnitude different if you fiddle about with the assumptions)

Back to the higher load tyres on the Astra. It has often been suggested, counter intuitively, that extra load (XL) tyres need slightly more than standard pressure to achieve the right shape with lower load than they were designed for. There is a rule of thumb method of working out how much this is using the maximum allowed pressure for the tyre, but the adjustment needed is usually too small to worry about.

I'm not sure I've thought about this enough particularly the relationship between the tyre pressure and the ground pressure but I don't think your man's ideas are very helpful.

P.S.

I suppose the wheel might be said to 'hang' from the bead but not from the top - it sits on the lower bead.




Edited by Manatee on 27/09/2020 at 13:47

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - John F

I suppose the wheel might be said to 'hang' from the bead but not from the top - it sits on the lower bead.

Exactly. The pressure is needed so the sidewalls can take the strain. I always find it amazing that sixty tonsworth of airbus can be landed, sometime quite firmly, onto only six wheels. Their tyres need around 300 psi for this amazing sidewall feat.

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - Manatee

It's still the air wot does it:)

Vauxhall Astra GTC 2.0 cdti - Incorrect tyres on new car? - mikert

Update, Insurance company have replied to say they're OK, so end of problem for me.

Thanks for all help & advise

 

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