quick question tires

[joepua]

hey guys, quick question... what do the numbers mean when buying tires  (eg. 140-60-20)? my first guess was that the first number was circumference? diameter maybe?

Also, around what time do you guys think a tire change is needed? my bike has around 5500k.. was thinking about it but the treads still look good..

Ok, one last question, I hear ppl are putting bigger tires on the rear tires than the front... are there benefits to this? stock bikes, they are both the same right?

haha sorry, i guess these are 3 quick quesitons...

[Paulcet]

In your eg: 140=width in mm, 60=%of the width in height from rim to outside circumference, 20=diameter of the rim in inches

If the tread looks good, there may be life left in the tire.  But if the tires are old, they need to be replaced.

There may be benefits to a larger tire in the rear, but I'm not sure.  I think Honda and Kawasaki but smaller (diameter) front tires on the Hurricane and Ninja in the 80s to quicken the handling.

[beRto]

hey guys, quick question... what do the numbers mean when buying tires  (eg. 140-60-20)? my first guess was that the first number was circumference? diameter maybe?

The sidewall code gives you the tire size and load ratings. Wikipedia has a detailed explanation: http://en.wikipedia.org/wiki/Tire_code

Briefly, the first number is the tire width [mm], the second number is the sidewall height [% of width], and the third number is the wheel diameter the tire was designed for.

In your example (140/60-20), this works out as follows:

• width 140 mm
• sidewall height 60% of 140 mm = 84 mm
• wheel diameter 20"

Also, around what time do you guys think a tire change is needed? my bike has around 5500k.. was thinking about it but the treads still look good..

A tire change is needed when the treads wear out. It's not strictly dependant on mileage because it varies dramatically depending on your riding style. gsJack has posted a log of the tires he has used and the mileage they have lasted - I'm sure if you search for "tire log" by gsJack, it'll turn up.

You would also need to change tires if they are really old (say, more than 5 years) and especially if dry rot is setting in. Dry rot looks like little cracks in the tire sidewall.

Ok, one last question, I hear ppl are putting bigger tires on the rear tires than the front... are there benefits to this? stock bikes, they are both the same right?

haha sorry, i guess these are 3 quick quesitons...

Not sure. I bet gsJack will know!

[gsJack]

A 140/60-20 tire would be 140 mm wide, have a 60% aspect ratio, and fit a 20" rim diameter.  Don't know if there is such a size but a 140/60-17 would fit a GS500 rear wheel, we have 17" wheels.  GS500s all come with 110/70-17 front and 130/70-17 rear tires.  The aspect ratio is the height of the tire as a percentage of the width.

Most bikes have bigger rear tires than front ones since they carry most of the load, your sitting almost on top of the rear wheel.  A narrower front tire generally provides better handling.

Many people put larger (wider) rear tires on their bikes because they like the looks of them.  Most radial tires come in 140 or 150 mm and wider tires so it's usually necessary to use a wider than stock tire if you want a radial.

You need new tires when the tread wear markers show but it's safer to change them a bit before that if you ride much in the rain.