tire size confusion

[tripleup05]

yes, i know it isnt THAT complicated. so feel free to me on the head for not knowing all of these aspect ratios and blah blah. damn metric crap. anways I am about to purchase a set of Kenda 270's from Americanmototire.com but don't know what size to get. According to an online tire size calculator, the stock front tire is 27.3 tall x 3.9 inches wide. The stock rear is 26.5 tall x 4.7 inches wide. What is available online...

3.50 x 18 (i guess this is in inches. if so, too narrow right?)

4.00 x 18 (still narrow)

4.10 x 18 (closer...)

4.50 x 18 (maybe, but still would prefer close to stock as possible)

5.10 x 18 (wider is better...maybe this one?)

100/90 x 18 (ok now i'm thrown for a loop. what size is this?)

120/80 x 18 (again, confused. close enough to stock 80/100?)

and the front...

3.00 x 21 (too skinny)

3.25 x 21 (still to skinny right?)

By the way, I am really short and can

barely tip-toe the bike as is.I wouldnt mind a slightly shorter tire, but there is no way i can handle one that will raise the bike even slightly. A little wider than stock would be ok though, but that doesnt seem possible. So...are these sizes dead on, or is there a little variance and i could get by with 4.50 x 18 and 3.25 x 21??? sorry for the stupid questions

[DRZ400SK4]

A 120/100 rear and a 90/90 front is the combination I prefer on my DRZ400.

[motoinmoab]

Don't know if you have an S or an E? A Dunlop D739 100/100 rear knobbie will drop your seat 1/2" lower than the stock E's D756 110/100. It's a little narrower but still hooks up well enough in the desert. Dunlop's site http://www.dunlopmotorcycle.com/tirecatalog_category.asp?id=4 gives the dimensions of their tires.

The 2 numbers (110/100) are the aspect ratio of the tire, not really simple numbers in the same way as the old "4.50 x 18" or "3.25 x 21" that us old timers are used to. But it's what companies are switching to, same as car tires. And the new numbers are kind of confusing, this is from Dunlop's FAQ's: Aspect ratio - The relationship between the section height and section width of a tire expressed as a percentage of section width. If the section height is one half the section width, the aspect ratio is 50%.

[Noble]

You can find most of this info in a tire fitment chart.

3.50 x 18 (I guess this is in inches.) ----Right. When no aspect ratio is given it is assumed to be 100, (Side wall height is same as width, more or less). About a 100/100 size

4.00 x 18----Old sizing, close to 110/100

4.10 x 18 ----Actually no. Before aspect ratios were given in % this method was used. 4.10, 4.60, 5.10 were smaller than 4.00. 4.50. and 5.00. This size is about a 100/80.

4.50 x 18 ----Close to 130/100

5.10 x 18 ----lower spec ratio again. Maybe 130/80

100/90 x 18 ----- current sizing 100mm wide, sidewalls 90% of width.

120/80 x 18 (again, confused. close enough to stock 80/100?)----No no. 120mm wide, 80% aspect ratio. Sidewalls are 80% of width. This is a good choice for a rear tire.

and the front...

3.00 x 21 (too skinny)---no, it is fine. About a 80/100

3.25 x 21 (still too skinny right?) ----no, about a 90/100 This is a good size for a front. A 90/90 is also a good choice.

All sizes do not perfectly cross reference and there is a lot of variance in true size from one manufacturer to another. Any less confused now?

[tripleup05]

thanks everybody, especially Noble for goin question by question! and yea, i am a little less confused. now to just be able to actually install them when they get here