18 Inch Rear Tire Differences?

Hi all, so I've got a question about a rear tire choice. On my dirtbike it has a 21" front tire and 18" rear tire. On Motorcycle Superstore they have several different 18" rear tires in the specific tire that I want.

http://www.motorcycle-superstore.com/2/29/391/19525/ITEM/Dunlop-MX51-Geomax-Intermediate-Rear-Tire.aspx

100/100-18"

100/90-18"

110/100-18"

120/90-18"

What do the numbers mean? Obviously the 18 is for the tire size... but what does the 100/100, 100/90, 110/100, 120/90 mean? Is it something to do with like sidewall construction, I really don't know. Could someone clarify this with me please?

Thanks

The first number is tire width and the second is profile(how far it is from tread to rim)

I think anyway:excuseme:

The first number is tire width and the second is profile(how far it is from tread to rim)

I think anyway:excuseme:

Sort of what I was thinking, regardless of which number goes to height/width, ill take it as the bigger the number combo, the beefier the tire.

Yep first # is width & second # is the height of the tire. Tread to rim.

So a tire that is 100/100 will have the same width as a 100/90 tire, but will have a little taller height

Yep first # is width & second # is the height of the tire. Tread to rim.

So a tire that is 100/100 will have the same width as a 100/90 tire, but will have a little taller height

Ok, thank you very much for confirmation!

100/ 90 18

first # width measure in MM

SECOND # IS sidewall height measured in percentage of width

third # is size of rim in inches

100/100-18" 100 mm wide 100 mm tall

100/90-18" 100 mm wide 90 mm tall

110/100-18" 110 mm wide 110 mm tall

120/90-18" 120 mm wide 108 mm tall

wider will make the bike hook up better, but will affect the handling/ turning.

Height will also affect final gear ratio.

Another thing to be aware of is on some bikes a taller, wider tire may rub the inside of the swingarm or the fender flap thingy.

Sort of what I was thinking, regardless of which number goes to height/width, ill take it as the bigger the number combo, the beefier the tire.

You don't want a tire that is so 'beefy' that you can't spin the rear tire if you need to, like to accelerate, raise rpms quickly, or to turn with the rear wheel.

yea . Its hard to turn them big 120's in the tight twisties

Actual sizes vary a lot from manufacturers too.

Actual sizes vary a lot from manufacturers too.

Most are measured fairly equally, Michelin seems to have their own methods.

so on my 08 wr250 with the 100/100-18 combo will the s12 michelin in a 120/90-18 fit?

so on my 08 wr250 with the 100/100-18 combo will the s12 michelin in a 120/90-18 fit?

Yes

In theory, yes it would fit. There might be some swing arm or flap clearance issues but i'm not 100% sure. In my opinion though,  that's a lot of tire for a 250.

In theory, yes it would fit. There might be some swing arm or flap clearance issues but i'm not 100% sure. In my opinion though,  that's a lot of tire for a 250.

what makes you say that?

Since this thread came up, does anyone know why the 09 YZ450 came with. Different size than any other years?

Usually the 450's take something like 110/90r19, but the 2009 YZ450 states it takes a 120/80r19? Why the different sizes?

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