Tyres for dummies

**Mom** · 12th October 2010, 17:37

Hello you clever lot. Can one of you please explain to us in plain english what those numbers on the side wall of tyres actually mean. I am going to assume here that everyone knows the last number relates to the rim size.

I have just changed the tyre on my bike. Old bike, never gave much thought to what if any difference (apart from improving handling) a new tyre would mean. I have dropped my bike once since the new tyre has been fitted, and did not enjoy having to get someone else to move her from where I stopped as I could not reach the ground safely

So, I checked today, the recommended rear tyre for my bike is 130/90/16.

A 180/90/16 has been fitted, and my feet dont reach the ground anymore

What is the difference between 130/90 and 180/90?

Thanks in advance.

**imdying** · 12th October 2010, 17:45

I don't want to sound like a Doubting Thomas, but are you sure about those numbers? That's a frightful difference!

Have a look on the rim, it'll have a number on it that's the width (it'll be in inches, so it's probably 4, 4.5, 5 etc). It's a good way to check as a certain width of tyre is designed for a certain rim width.

**slofox** · 12th October 2010, 17:50

"Let's start with the first series of numbers, 130/90 16, otherwise known as the metric designation. This is the most popular nomenclature today and it's practically a standard in the automotive world.

The 130 designates the tire's width in millimeters, measured in a straight line through the tire from one edge of the tire's tread to the other. The second number, 90, is a bit trickier to understand. This represents the aspect ratio between the tire's width and its height, or how tall a tire is in relationship to its width. Simply put, the higher this number is, the taller the tire will be. In this case, the tire is 90 percent as tall as its width, or 117mm.

The last number, 16, is the tire's rim diameter expressed in inches.

The width on some tires may be expressed in inches as well, but usually the aspect ratio is left off.

The other series of numbers and letters, MT90 16, represents the same tire size, but it's expressed in an alphabetical code. M means the tire is designated for motorcycle use, T is the tire width code, 90 is the aspect ratio and 16 is the rim diameter."

Does this help?

It means your new tyre is 180mm wide. 90% of this is 162mm which is the height
Your old tyre was 130mm wide. 90% of this is 117mm also the height.

So your new tyre is 45mm higher than the old one.

I think...

**Genie** · 12th October 2010, 17:51

Originally Posted by slofox

"Let's start with the first series of numbers, 130/90 16, otherwise known as the metric designation. This is the most popular nomenclature today and it's practically a standard in the automotive world.

The 130 designates the tire's width in millimeters, measured in a straight line through the tire from one edge of the tire's tread to the other. The second number, 90, is a bit trickier to understand. This represents the aspect ratio between the tire's width and its height, or how tall a tire is in relationship to its width. Simply put, the higher this number is, the taller the tire will be. In this case, the tire is 90 percent as tall as its width, or 117mm.

The last number, 16, is the tire's rim diameter expressed in inches.

The width on some tires may be expressed in inches as well, but usually the aspect ratio is left off.

The other series of numbers and letters, MT90 16, represents the same tire size, but it's expressed in an alphabetical code. M means the tire is designated for motorcycle use, T is the tire width code, 90 is the aspect ratio and 16 is the rim diameter."

Does this help?

Hey thanks...i'd always wondered myself, I only knew the diameter one.

**doc** · 12th October 2010, 17:55

Originally Posted by Mom

the recommended rear tyre for my bike is 130/90/16.

WTF

Thats the size of a Hardley tyre

**Phreak** · 12th October 2010, 17:56

Bloody hell! Who fitted the 180 wide tire? Something wrong there...

**Ntoxcated** · 12th October 2010, 17:57

Hi Mom!

Something doesn't sound right there. The first number is the tyre width in millimeters. The second number is the percentage of that giving sidewall height.

So, 130/90 has a sidewall height of 117mm while 180/90 give a sidewall height of 162mm. 4.5cm higher. And that is without the deformation of putting a wider tyre on a narrower rim. In fact I'm surprised a 180 will fit.

It will also take the circumference of the tyre from 201cm to 229cm which will make your speedo an additional 14% out.

Or have I got this completely wrong?

Edit: My maths must have been really slow. 4 posts while I was typing

**doc** · 12th October 2010, 18:01

You do realise if you take the 180 off and go back to the 130 your arse will look 50 mm smaller ?

**Mom** · 12th October 2010, 18:33

Originally Posted by Ntoxcated

Hi Mom!
Something doesn't sound right there. The first number is the tyre width in millimeters. The second number is the percentage of that giving sidewall height.
So, 130/90 has a sidewall height of 117mm while 180/90 give a sidewall height of 162mm. 4.5cm higher. And that is without the deformation of putting a wider tyre on a narrower rim. In fact I'm surprised a 180 will fit.
It will also take the circumference of the tyre from 201cm to 229cm which will make your speedo an additional 14% out.
Or have I got this completely wrong?
Edit: My maths must have been really slow. 4 posts while I was typing

See this is the feedback I need. My Blue Lovely has been rendered almost too hard for me to ride, from a position of loving riding because the ride height fit. More info please.

Originally Posted by doc

You do realise if you take the 180 off and go back to the 130 your arse will look 50 mm smaller ?

LOL...

I hate smart arses. I am actually trying to lose weight at the moment, excercising has been challenging and productive. I have lost a couple of Kgs, but my friggen bum measures bigger

Apparently blokes love big bums

Back on topic though. What is the the difference here? I know physically what the tyre change has meant to me. Much nicer handling, no fault corners. I am reduced to tippy toes.

What do these numbers on the side walls of your tyres mean?

**doc** · 12th October 2010, 19:16

Originally Posted by Mom

See this is the feedback I need.

What do these numbers on the side walls of your tyres mean?

I think ppl have answered your question. Maybe it's time to let Maha out of the kitchen, and ask him

**hayd3n** · 12th October 2010, 21:52

have a search and find out what the correct Tyre size should be for your bike

having a bigger Tyre wont give you any better handling or grip,
it can sometimes make it worse off
i remember a old bike i had that had the incorrect Tyre size fitted, they were to wide for the rim
when ever i did a nice tight corner i would always run out of Tyre and end up having a small slide, as soon as the sidewall touched the road
a wide Tyre on a narrow rim will change the Tyre shape and the ride as-well

**Jantar** · 12th October 2010, 21:56

That is dangerous. Take it back and demand the correct tyre as soon as possible. Your rims are designed for a 130 size, not a 180, that is 50 mm or 2 inches wider. Your handling will be affected, your ride height has changed, your steering geometry has changed. Overall, that is an accident waiting to happen.

**onearmedbandit** · 12th October 2010, 22:05

The first number is the speed your bike can do, in mph. So before your bike could only do 130mph, now it will do 180. You should be happy with this improvement. The second number is the number of laps it should be able to do of your local track, in this case 90 (don't think you're getting shortchanged here, just because this is the same as your previous tyre, remember your bike can now go 180mph!!). The last number, generally between 16-18 is the number of wholesalers/distributors/warehouses/retailers etc who have all added their little bit on to the cost of the tyre before it makes it onto your bike.

Don't know what the others are on about...