Spare not the same.

Can any one help. Just had my tyre blow on my disco 3. It's running on sport wheels with 270 40 20s but the spare is the original disco hse wheel. Will this be ok. Have been told it will wind up the diff and make it go bang. I only need to go about 5 miles max to get a new set fitted.

bertiemje said:

Can any one help. Just had my tyre blow on my disco 3. It's running on sport wheels with 270 40 20s but the spare is the original disco hse wheel. Will this be ok. Have been told it will wind up the diff and make it go bang. I only need to go about 5 miles max to get a new set fitted.

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The rolling radius or circumference is the key thing. You know the size of the tyres on the car but what about the size of the spare??

Once you have both sizes, go to this site and plug in the details, it will show any difference in circumference, there potential danger.

Tire size calculator

Thanks for that. The flat is 28.7inch diameter and the spare is 30 inch. Thinking that can't be good😒

bertiemje said:

Thanks for that. The flat is 28.7inch diameter and the spare is 30 inch. Thinking that can't be good😒

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Are you actually measuring the tyre????? Because you don't need to do that.

Just make a note of the tyre sizes off the tyre wall, put them into the tyre calculator and then note the circumference or rolling radius as it is sometimes called.

If the results show more than 10% difference, it might cause trouble, if it's less then you should be ok, ok?

Different sized tyres running on the same axle can be ok if the difference is not too large. Imagine for example a worn tyre on the LH side versus a brand new tyre on the right - they will have a different circumference but the differential can cope with that.

Hope I've explained things a bit more clearly????