How many times have you seen someone admiring
the rear tyre of a motorcycle? Especially when it is super-wide. There is,
unfortunately, a difference between cool and functional.
Motorcycles are assisted in a turn by tyre
shape: as the bike leans off the centre of the tyres, the circumference becomes
smaller. This is demonstrated easily by taking a styro-foam cup, putting it on
its side on a table and pushing it. It goes in a circle, because the
bottom has a smaller circumference than the top. Motorcycle tyres work on
the same principle, unless you are still riding that classic motorcycle which has original tyres that are virtually square in profile. That's how it was back in the day...
A smaller section tyre (the big number at the
start of all modern tyre sizes) will allow the bike to roll into the turn faster,
because it takes less effort to get it from the big circumference in the centre
onto the smaller circumference on the side. Simple as that!
So, ignoring for a moment the effect of
aspect ratio (the height of the sidewall vs the width of the tread and the
second number shown on modern tyre sizes.) on overall handling feel, buying a
bigger tyre to replace the standard ..e.g. 200/60..over 180/60 WILL change the
ability of the tyre to move “quickly” in cornering situations and be
particularly noticeable when trying to change directions through an “S” bend. Also, a larger tyre with the same aspect ratio will have a greater circumference , which will dull acceleration, but will eventually lead to a higher top speed..if you can ever get there with Cameras and Traffic Officers waiting for you.
So now factor in the potential choice of aspect ratios; say 180/55 vs 180/60 and again the overall circumference changes affecting top speed, acceleration ( via an effective gearing change ) as well as handling feel...so....
Is a big tyre faster in a straight line or
does it offer better grip when leant over?? Nope, wrong again. The
amount of traction you have is a product of a bike’s geometry, weight and the co-efficient
of friction. In other words, the angles at which the tyres interface with
the road, the stickiness of the tyre, and the weight of the bike. If you
have a bigger contact patch, the weight is spread over a larger area, but the
amount of traction does not change. Motorcycle & Tyre manufacturers spend
large R&D sums on working out what size tyre will optimise the handling and
transferring acceleration and braking forces at maximum efficiency.
Unless you are drastically changing the power output of your machine, or adept at understanding the affects that size and aspect ratio changes have on handling feel, it is best to stay with recommended tyre sizes...
Oh, but wide tyres definitely look cool.
No doubt about that…just gawp at any over-tyred cruiser or superbike and
see the owner’s chest swell with pride..just don’t ask them how it feels now
through the twisties..
As always, stay upright and in control ..