Choosing alloys: load rating lower than max axle weights?

[RoVoFob]

Apologies for a tedious wheel question…

Is there any fundamental reason why you can’t use a wheel with a load rating that is lower than a car’s maximum axle weight rating - provided you don’t use the car’s entire possible payload?

I’m considering getting winter wheels for my newly bought Audi A6 Avant, and as a big estate it has a hefty maximum payload of 630kg and maximum front/rear axle weights of 1,265kg and 1,295kg respectively.

That means that if I filled the car to those maximum axle weights that’d be a maximum load per wheel of 638kg at the front and 648kg at the rear. The standard alloys have a rating of 690kg, however the ones I want to get have a rating of 625kg.

Is there any legal or safety reason why the rating of the tyre must exceed the maximum capability of the car? I can’t think of any occasion when I’d get close to the maximum payload, so I wouldn’t expect any likelihood of overloading the wheels…

[scorcher]

There will be loads of modified vans ( mainly VW’s) running on wheels and tyres that are under rated for them. I doubt many fail but it is a risk. It’s not check on MOT either. Could give your insurance co a reason not to pay out if you did have a failure though.

[RoVoFob]

scorcher said:

There will be loads of modified vans ( mainly VW’s) running on wheels and tyres that are under rated for them. I doubt many fail but it is a risk. It’s not check on MOT either. Could give your insurance co a reason not to pay out if you did have a failure though.

I’m sure there are many hugely overloaded van tyres and wheels.

It’s legal to use winter tyres that have a speed rating which is lower than the top speed of a car, so I don’t understand why it would be any different with this. Maybe if you crashed at 140mph with a tyre that was rated for 130mph there would be an issue, but simply having that tyre wouldn’t cause any legal/safety issues, I don’t think. That’s why I’m unsure about the load rating situation…

Surely an insurer would have to prove that you overloaded the wheel and that’s no different to them having to prove that you overloaded the car’s suspension and went beyond the maximum axle ratings.

Any idea whether manufacturers quote unladen axle weights…?

[stevieturbo]

RoVoFob said:

Apologies for a tedious wheel question…

Is there any fundamental reason why you can’t use a wheel with a load rating that is lower than a car’s maximum axle weight rating - provided you don’t use the car’s entire possible payload?

I’m considering getting winter wheels for my newly bought Audi A6 Avant, and as a big estate it has a hefty maximum payload of 630kg and maximum front/rear axle weights of 1,265kg and 1,295kg respectively.

That means that if I filled the car to those maximum axle weights that’d be a maximum load per wheel of 638kg at the front and 648kg at the rear. The standard alloys have a rating of 690kg, however the ones I want to get have a rating of 625kg.

Is there any legal or safety reason why the rating of the tyre must exceed the maximum capability of the car? I can’t think of any occasion when I’d get close to the maximum payload, so I wouldn’t expect any likelihood of overloading the wheels…

Why not just get a set of OEM wheels ? Bound to be plentiful out there ?

Although a friend has said OEM wheels cracking is quite common....

[GreenV8S]

The construction and use regs essentially say that parts, accessories, loads etc must be such that "no danger is likely to be caused".

As far as I can see what you're proposing is comipletely safe and within the letter of the law.

If I'm wrong and it's technically illegal for some reason, I doubt anyone would have any practical way to know that, or care if they did find out.

[RoVoFob]

stevieturbo said:

Why not just get a set of OEM wheels ? Bound to be plentiful out there ?

Although a friend has said OEM wheels cracking is quite common....

I am talking about OEM wheels. They’re just from an A4 of that generation rather than an A6, though they have exactly the same fitment and offset.

I just think these ones look much better, they’re 3kg lighter and have a slightly lower load rating…

[RoVoFob]

GreenV8S said:

The construction and use regs essentially say that parts, accessories, loads etc must be such that "no danger is likely to be caused".

As far as I can see what you're proposing is comipletely safe and within the letter of the law.

If I'm wrong and it's technically illegal for some reason, I doubt anyone would have any practical way to know that, or care if they did find out.

That’s my impression…

Legislation isn’t always rational, though! Are you looking at set regs? If so, where do these come from - DVLA/DVSA?

[GreenV8S]

RoVoFob said:

That’s my impression…

Legislation isn’t always rational, though! Are you looking at set regs? If so, where do these come from - DVLA/DVSA?

The phrase I quoted came from the Road Vehicles (Construction and Use) Regulations 1986.

[RoVoFob]

GreenV8S said:

The phrase I quoted came from the Road Vehicles (Construction and Use) Regulations 1986.

Thanks for that. Will see what other info I can find.

[E-bmw]

The issue for me would that YOU know that you won't exceed that, but does that mean that nobody else will & can you/anyone prove that. Then there is a whole potential insurance/liability issues further down the line.

Not worth the potential hassle, stick with the right ones.

[dhutch]

At 625kg rating the proposed units have 91% of the rating of the original 690kg rated units.
For that car they have 98% of the front axle loading, and 96% of the rear axle loading.

At which point, assuming there is a reasonable factor of safety, and you are not going to be loading the car to its max very often if ever, they risks in the real worked are going to be really very low, to the point my gut instinct is you will see no issues at all. If the law also recognises this, the that's also great if not my area of expertise.

However my gut instinct with this sort of thing is also to not mess with the system and to play it very safe especially if it is only 'for looks' as it where. That said, I assume the choices are limiting as the A6 is towards the top end? Not very many sporty Audi vans to choose wheels from!

Ask four people, get five opinions.


Daniel

[RoVoFob]

E-bmw said:

The issue for me would that YOU know that you won't exceed that, but does that mean that nobody else will & can you/anyone prove that. Then there is a whole potential insurance/liability issues further down the line.

Not worth the potential hassle, stick with the right ones.

I get what you’re saying, but that’s no different to you overloading the car’s suspension. There’s nothing to stop you loading the car with 800kg of concrete, which would be beyond the capacity of the tyres and the car, but if you don’t have a crash carrying 800kg of stuff, why would anyone accuse you of that?

Surely anyone raising any issues with those wheels would have to prove that the car was carrying more than 600kg of stuff…?

[RoVoFob]

dhutch said:

At 625kg rating the proposed units have 91% of the rating of the original 690kg rated units.
For that car they have 98% of the front axle loading, and 96% of the rear axle loading.

At which point, assuming there is a reasonable factor of safety, and you are not going to be loading the car to its max very often if ever, they risks in the real worked are going to be really very low, to the point my gut instinct is you will see no issues at all. If the law also recognises this, the that's also great if not my area of expertise.

However my gut instinct with this sort of thing is also to not mess with the system and to play it very safe especially if it is only 'for looks' as it where. That said, I assume the choices are limiting as the A6 is towards the top end? Not very many sporty Audi vans to choose wheels from!

Ask four people, get five opinions.

Daniel

Thanks Daniel. Actually, my main motivation was because the other wheels are substantially lighter, which should improve the ride and fuel economy - even with 17s and air suspension the ride is a bit unsettled. The looks are just a bonus.

Part of me would like the most fuddy duddy alloys to make this dark grey, small wheeled A6 Avant 4.2 V8 more of a Q car…

[GreenV8S]

Wheels aren't going to fail because you stacked too much concrete in the boot. They'll fail because of dynamic loads. In other words you're drifting round a roundabout paved with cobblestones and then hit the curb. The distinction between a wheel that will survive that indefinitely and a wheel which will fail is really hard to make and certainly not something ypou can infer from a weight sticker on the box.

[RoVoFob]

GreenV8S said:

Wheels aren't going to fail because you stacked too much concrete in the boot. They'll fail because of dynamic loads. In other words you're drifting round a roundabout paved with cobblestones and then hit the curb. The distinction between a wheel that will survive that indefinitely and a wheel which will fail is really hard to make and certainly not something ypou can infer from a weight sticker on the box.

Sure, impacts are no doubt what will make a wheel shatter dramatically, whereas excess weight over time is probably more likely to lead to cracks and subsequent issues.

The alternative is fitting some better tyres, with the expectation this will improve things compared with the current set of Avon ZV7s. They’re pretty new, but seem to be poorly reviewed…