110 or 100 rear tire?

i just purchased a set of 21/18's for my wrx, so i dont get stuck in mud...

i am going to buy the mitas c16/c17 combo. i am unsure whether i should go with the 110/100 or 100/100. all the small bore motorcross bikes run a 100, so i assume that size would be fine for offroad, but wouldn't i want a slightly wider tire for the road? the dualsport ktm's come with a 140.

Stock size is a 120 rear. I'm currently running that width (Dunlop 606) but would like to hear opinions from people running a 110 or 100. The 120 does seem like a pretty wide tire for the amount of power we have.

Thanks,
Scott P.

I've read some posts from people using 110's and really likeing them, don't recall anything about 100's. no personal experience though on the WR with anything but a 120.

Rodney, the stock tire size for the WR-250R is equivalent to a 100/100-18.
That's what I used when I had knobby tires on my WR-250R.

The confusing thing is that the 120/80-18 tire that is stock for the WR-250R is an older way of designating the size of the tire, and the 100/100-18 is the newer way.

YZEtc wrote:

Rodney, the stock tire size for the WR-250R is equivalent to a 100/100-18.
That's what I used when I had knobby tires on my WR-250R.

The confusing thing is that the 120/80-18 tire that is stock for the WR-250R is an older way of designating the size of the tire, and the 100/100-18 is the newer way.

I have not heard of this new way, what do the 100/100 numbers mean then in this new way?

I think it has to do with a different way of measuring the width and sidewall height of the tire.
As far as I know, the first number is the width in millimeters, and the second number means the tire is 100% as tall as it is wide.

That's what the numbers meant in the old way, too, but apparently, they've got a newer way of measuring the width. :)

well that makes perfect sense, why didn't they just do it that way in the first place

mattf wrote:

I have not heard of this new way, what do the 100/100 numbers mean then in this new way?

I'm not aware of a newer measurement system beyond the existing metric, inch, and Alpha measurement systems. Yamaha's datasheet for the 2011 WR250R still shows the rear as being 120/80-18, same as three years ago. There may indeed be a new metric system for sizing tires adopted, but there is no mention of it on the Internet, and it is unlikely that Yamaha would refuse to adopt a new standard in the industry.

However... I could be wrong. I would like to see a reference to a new system if it does exist.

Stock WR250R wheels/tires
Front
Rim size WR250R 21x1.60
Tire: 80/100-21M/C 51P

Rear
Rim size WR250R 18x2.15
120/80-18M/C 62P







Width
The first number in a tire size represents the nominal width. Width is measured in a straight line from the furthest point on one sidewall, across the tread, to the furthest point on the opposite sidewall.

Aspect Ratio
The second number represents the aspect ratio. Aspect Ratios indicate a tire's cross-sectional profile. The smaller the number, the lower the profile. It expresses the height to width ratio as a percent. A 90 aspect ratio means the tire's cross sectional height is 90% of it's width.

Permissible Rim Widths For Tire Width

1.60, 1.85	70
1.60, 1.85	80
1.85, 2.15	90
2.15, 2.50	100
2.15, 2.50, 2.75	110
2.15, 2.50, 2.75	120
2.50, 2.75, 3.00	130
2.75, 3.00, 3.50	140
3.50, 4.00	150
4.00, 4.50	160

there is no new system, its just the way manufacturers are measuring now. many measure sidewall to sidewall on a given rim width, others measure tire width, ie outside knob to outside knob. pirelli MT21's are a perfect example, a 120/80 MT21 looks more like a 130 or 140 because they measure sidewall width and the knobs stick out further.

To the OP, depends how you ride, if you like to flick it round the 100 will lay over a little easier, 110 may give a fraction more grip and a little extra tread life.

Quote :

To the OP, depends how you ride, if you like to flick it round the 100 will lay over a little easier, 110 may give a fraction more grip and a little extra tread life.

...that's what I was looking for....Good Thread!
Just ordered a 110 rear MT21. The D606 120 seems to have too much meat for these little tiddlers. I like to spin the rear more to stear.
120 Dunlop rear a9aand other 120's I've tried) seem to make the bike push the front more as well.
Also seems like it's too tall, making the bike iffy over 75mph, gets the weave thang going.

The stock tires handle street very well. I suspect many WR riders by more beef than is needed.
BTW, I hav plenty enough mojo, Athena kit installed....

I am running this tire

http://www.mx1canada.com/mitas-c20-offroad-rear-tire.html

No issue spinning it free. Tons of grip. This particular tire width is the carcass of the tire so the knobs stick out each side a little more. My bud runs a maxxis 110/100 and this one seems wider. However, rim width will make a tire "balloon" more which could affect its width.