Useful newbie question of the day: Can I fit wider tyres to my motorcycle?

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New rider, you’ve asked one of the most common questions in motorcycling after ‘Will riding a motorcycle make me more or less attractive to members of the opposite sex?’ (a – depends on the bike.) But first go back a step and ask yourself honestly why you’re entertaining this idea. Is it from a performance perspective, or an aesthetic one?

The aesthetic one I get. We all have our preferences and if fat rubber is one of yours/you think it made your Citroen Saxo into a honey trap when you were 17, I have no problem with that. From a performance perspective though, it’s open and shut. If you really want to go wider, take the following into account before you take the plunge.

Unless you really know what you’re about and have a specific aim in mind, fitting wider tyres to your bike’s standard rims should be filed under plain bad practice. I’ve seen it many times and it stems from a lack of understanding of the motorcycle tyre itself – a highly precise piece of manufacturing brilliance that is technologically far in advance of the comparably humble car tyre.

Unlike cars, motorcycle tyres are bestowed with an expensively produced and nicely graduated rounded profile for you to exploit predictably and enjoyably in corners. This along with graduated rubber compounds are some of the reasons bike tyres are so cocking expensive compared to those of cars.

To maintain this profile and progressive handling characteristic, the motorcycle tyre is designed to fit perfectly on a rim of a specific width. If you suddenly decide to put on a wider tyre than your rim is designed for, the problem you face is that the wider tyre will itself have been designed for a wider rim. Squeezing it onto your smaller rim will unquestionably alter its profile – you will in effect be making it (high level tech term alert) ‘pointier’ than it should be (OK if you must, you’ll be altering the tyre’s carefully considered aspect ratio). If you persist with your ideas, the results of this will be severalfold.

That predictable profile your new wide tyre was designed with is trashed – on your smaller rim you’ve got something with a steeper and less predictable profile. And because you made that wide tyre pointier by squeezing it onto your rim, you’ve effectively reduced its contact patch with the road too, meaning less grip as a result– the opposite of what you might have thought. Your squeezing has also made that tyre taller than it was before which among other things could potentially alter your bike’s overall gearing and make it feel slower on acceleration as the actual diameter of your rear wheel in contact with the road effectively increases. Whaaaat? It’s true.

Now couple this lot with the fact that a wider rear tyre (the most common mistake) screws with the tyre and bike manufacturer’s research and development budget for your bike’s known relationship with its front tyre (bikes have two remember) and that wider tyres mean the contact patch moves away from the centreline of the bike as you corner leading to slower feeling steering, instability and more effort required from the rider in the curves then you should realise by now that for anyone interested in handling – which should be all bikers but in Instagram world sadly isn’t – fitting wider tyres to standard rims is a simple enough no-no.

If you don’t care for my words and absolutely must have wider tyres, first fit wider rims – probably not you were wanting to hear, but wheel swaps to gain better rubber are a common enough practice with specials builders who know what’s what. Note that they change both front and rear wheels as specials builders fit into the category of ‘bikers who generally know what they are doing’. They’re normally also obliged to fit brake and suspension upgrades too at this point – oh, the rabbit hole goes deep in motorcycle modification world.

So in the end the answer to what is a good biking question is a simple Yes. But no. Until you hit the spanners in earnest stick with standard sizing and enjoy your ride as the manufacturer intended.

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