Why is our BMW Compact's space saver wheel a different diameter to its 16-inch wheels?

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Why is our BMW Compact's space saver wheel a different diameter to its 16-inch wheels?

In Honest John in August a reader mentioned that his Astra space saver spare wheel was two inches smaller in diameter than the road wheels. My BMW Compact has 16-inch wheels, while the space saver has a 17-inch wheel but the former has a deeper section tyre than the latter, so that, overall, the space saver is about 1-inch smaller in diameter. How can this discrepancy not be a threat to ride and safety?

Asked on 4 September 2011 by PS, via email

Answered by Honest John

It is a threat to safety. It alters the roadholding and handling characteristics of the car, and, more seriously, it increases the braking distances in the wet. That’s why speeds on space savers are limited to 50mph. I cannot tell you how the law was allowed to be altered to permit the use of space savers. Presumably EC law.

Tags: space saver spare wheel safety

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