QotW: Can dog urine melt a car tyre?

We're looking into this wee-lly important question.....
18 May 2021

DOG

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Question

I just got back from walking my dog. Now about a block from my house there’s a trailer that’s been parked there for a year or two, and every time we walk by, the dog pees on the same tyre. It got me thinking: urine contains uric acid. Is that strong enough to eat through the rubber of the tyre? If so, how long would it take?

Answer

Urine for a treat, because Phil Sansom's been looking into this 'wee-lly' interesting question from listener Trent…

Phil - Hi Trent. While I don’t doubt your dog’s destructive power, its wee isn’t going to eat through that tyre - not in a lifetime of walkies.

To understand why, let’s look at what happens when the rubber meets… the flow. Starting with the flow - that is, urine.

Urine in mammals is about 95% water. The remaining 5% is various waste products of metabolism, like urea, mineral salts… and indeed, uric acid. That can mean that urine is slightly acidic.

But uric acid isn’t particularly strong. And compared to in birds, where all that white stuff in the droppings is uric acid, in mammals there isn’t that much of it.

The result is that dog urine normally ranges from only mildly acidic to even mildly alkaline. And the actual acidity will vary depending on the dog’s age, diet, and health.

What about the tyre then? Modern pneumatic tyres are usually made of cords of steel or fibre, covered in rubber. 

In fact, our tyres have been made out of rubber ever since Robert William Thomson invented them in 1846 - forty years before even the first car.

The reason being, rubber is firm enough to resist the road, but flexible enough to be comfortable on uneven ground - plus, the rubber is vulcanised, meaning that cross-links between the long molecular chains make it even harder.

All this is to say that rubber is a very resilient material, not known for its vulnerability to chemicals.

Unfortunately I don’t know if anyone’s done the specific experiment that would precisely answer your question. You should be the first! But - the rubber seal manufacturers Mykin do supply a chemical resistance chart to make sure you’re using the right type of rubber for your environment. SBR (the most common type of tyre rubber) has the highest possible rating against uric acid, meaning that they’re expecting it to be barely affected.

That’s why I’m confident in saying you’re not going to be done in for vandalism. I also asked David Williams, a vet from the Queen’s Veterinary School Hospital, who agreed that the wee would have no effect on car tyres! He says the more interesting question is how your dog is using it to communicate with other dogs, through what he calls ‘pee-mail’.

Thanks for your question Trent. Next time, listener Kelvin has a dieting trick he’s thinking of trying out...

Kelvin - We are told not to overcook our vegetables because this kills the nutrients. Now if that's the case, why don't we just overcook the food we enjoy and not run the risk of putting on weight?

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