Staying upright Motorcycle Tyres 101
Dunlops. Metzeler. Pirelli.
Bridgestone. Michelin.

Just to name a few manufacturers of the black round things which prevent your paint and chrome bits from scraping the road.

Motorcycle tyres are very different from motorcar tyres in that they have to operate in an unstable environment from the outset. Unstable? Try letting go of your bike at a standstill without the stand(s) down. Result? Major expense. Conversely, the faster you go, the more stable the motor cycle becomes — hence the amazing ‘90’s World Super- bike video from Phillip Island of Stephan Mertens’ rider less, flaming Ducati running down the long pit straight still upright. On the other hand, a car just sits in perfect stability on its four tyres and only becomes unstable when the tyres are going faster than their designer intended. What I’m getting at is that the motorcycle’s tyres have to work from a cold, stationary start, often in the wet, and keep you upright. They do this extremely well in a straight line but become increasingly prone to distress when cornered. So they’re probably THE most important single component on your bike. Having made that bold statement, the obvious question is which tyre is best for my bike? In general the best tyre set (front and rear) is the OEM (Original Equipment Manufacturer) tyre that the bike came with inflated to the recommended pressures (checked cold). This tyre set has been tested thoroughly by Kawasaki and the various other factories and OEM replacement sales stand at around 40%.

So if your 2001 ZX-6R came with Dunlop 207s in 120/65- ZR17 (front) and 180/55-ZR17 (rear) then you can be sure you’ll get a proven and reliable tyre if you fit them again. But you can’t, because Dunlop don’t make them anymore, so what to do? Read on.

Compounds, sizes and pressures.
What may have been best for the bike originally may no longer be available (as above) or even applicable. If your bike was originally a sports tourer and is now a track day bike (many early ZZ-R600s come to mind) the OEM tyre was the Michelin Macadam. The mighty Macadam was a great tyre for the road, but its ultimate level of grip isn’t up to modern standards for track work and I wouldn’t recommend them for this use unless you enjoy sliding the bike around. So replacement for a dedicated track ZZ R600 should be in the original sizes but in much softer compounds i.e Michelin Pilots Sports or even Pilot Race if you’re a gun, which are available in the original 120/60- ZR17 (front) and 160/60-ZR17 (rear) sizes. Alternatively Dunlop, Pirelli and Bridgestone etc make great track tyres for a huge range of bikes in the appropriate sizes too. Now, we’re talking sizes, let’s make another bold statement.

DO NOT FIT BIGGER THAN STANDARD TYRES. Tyres are arguably the most important single item on your bike....

Many people fit a wider rear tyre in the hope it’ll make the bike grip like a GP bike. It won’t. In fact it’ll much more likely change the whole dynamic of the bike’s handling and grip levels for the worse for two reasons:

1. The chassis of the bike is designed to turn evenly at all lean angles. If, as you lean, you make the back end rise more than it was originally intended (remember the wider tyre the more it raises the bike’s rear end as it is leaned over), the steering head angle also changes more than intended making the steering increasingly light (the bike self steers into the turn) the further you lean. This makes the bike “flop” into the turn and can severely upset the level of grip from the front tyre, plus you apex the corner earlier causing you to stand the bike up and run wide on the exit. Not good.

2. The original wheel width is designed to accept a narrow range of tyre widths. If you fit a 20mm wider rear, the bead of the tyre (the bit that fits into the rim) is also 20mm wider and will be pulled in if fitted to a narrower than designed for rim. Thus the shoulder of the tyre will deform into a steeper shape making the tyre taller and the shoulders much more rounded. So your tyre’s contact patch will be reduced and even at full lean you’ll never get to the edge of the tyre. Result? Poor handling, less grip and uneven tyre wear. Again not good.

Another measurement is the aspect ratio of the tyre. This is the /55 in 180/55-ZR17. The tyres height from bead to crown is a ratio of the width, thus a 180/55 tyre has a crown height of 99mm or 55% of 180mm, or put another way the outside diameter is 198mm bigger than the bead diameter which is 17 inches in a 1 80/55-ZR1 7. So the overall diameter of this particular tyre is 630mm. With me? Good.
But what about the front?
Unlike rear tyres which generally only come in one aspect ratio (i.e height) per size, front tyres are often available in many aspect ratios. For instance the standard sports bike wears a 3.5 inch x 17 inch front wheel which more often than not carries a 120/70-ZR17 tyre. However, most manufacturers make 120/60-ZR17, 120/65-ZR17 and 120/70- ZR17 tyres. What does this mean, and more importantly, what does it do? Effectively, the lower the aspect ratio, the stiffer the tyre and the less overall circumference. So fitting a 120/60-ZR17 to a bike designed for a 120/70- ZR1 7 will lower the front by around 12mm. The sidewalls of the lower aspect ratio tyres are almost always stiffer so the front suspension will feel harsher while the bike will turn in more quickly and have less ground clearance. Again, some things about this are good, but generally it is better to stick with OEM sizes and vary your bike’s steering by other means, such as pulling the forks up through the triple clamps.
Finally, fit the correct tyre in regard to load and speed rating (your tyre supplier will help here) and don’t stray too far from the recommended pressures. Underinflating tyres for the track can lead to a miserable time as the tyres squirm excessively and overheat rapidly. Poor handling and a sudden lack of grip are the indications. Conversely riding with rock hard pressures will not allow the tyre to deform as designed and will decrease the size of the contact patch resulting in less grip and less give in the sidewalls giving a harsh, uncomfortable ride.

Matched sets
The manufacturers design motorcycle tyres to be a matched pair. The front tyre compliments the back and vice versa. Putting tyres from different manufacturers in each end of the bike can (and almost always will) upset the delicate balance of grip versus wear, and stability versus sharp steering. Overall the handling of the bike will suffer especially when approaching the limits of adhesion when you need everything on your side.
So, ladies and gentlefolk, that’s it for now, there’s a lot more to be said, but my fingers are numb.

This document was written by a motorcyclist who is not a representative of any tyre manufacturer. This document is for information only and the author in no way accepts responsibility if you crash as a result of utilising the information contained herein. That’s your fault and while you continue to be the one holding the throttle it will always be. The author rides a 2003 Kawasaki Z1000 currently fitted with Pirelli Diablo Corsas in the standard sizes. These give more grip than he can use as do most modern, soft compound, track-oriented tyres. Tyres have been subject to huge improvements in the last 15 years and anyone returning to motorcycling will be amazed at the tenacious levels of grip available.

Reproduced from Kawasaki Riders Club December newsletter “Legend”