18 Inch Rear Tire Differences?

[motonack]

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

[jtiv19]

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

I think anyway:excuseme:

[motonack]

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.

[Desert450]

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

[motonack]

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!

[Jakeblues]

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.

[Swede73]

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.

[FORMA MOTO]

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.

[capt justin]

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

[J_Daniels]

Actual sizes vary a lot from manufacturers too.

[Jakeblues]

Actual sizes vary a lot from manufacturers too.

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

[srdupnock]

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

[Hans Schmid]

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

Yes

[massey1two8]

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.

[srdupnock]

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?

[MotoAce51]

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?