Tire size help..

[mopower440]

I recently bought a 1988 cr125 after being without a bike for 12 years. Now, this bike has a rather narrow tire on the back compared to the past 125's ive had, my old ones had pretty wide or 'fat' tires on the back. Ok, the tire on there is a dunlop sports K695 series, the size is 100/100/18

Now, to get a wider motocross tire, what size do i need? maybe a 100/80/18 or what? Not sure how to read dirt bike tire sizes, only car tires..
HELP!!

 

[rm_racer]

I am pretty sure it goes width/profile-rim size. I run a 110/90-19 right now, but I think im going to put a 100/90-19 on it next time. It seems like the tire is too heavy. So if you were wanting a wider tire, you could go 110/100-18 or 110/90-18, or so on. I think thats how it goes anyway, correct me if Im wrong.

 

[MX Junkie]

That's right

 

[mopower440]

hmm..car tires are the opposite, they go height/width/rim size.. so the second number you say is profile, that means the height of it, correct? you all know anywhere on the net to find out what came factory on my bike?

 

[MX Junkie]

80/100/21 front
100/90/18 rear

 

[TimberPig]

hmm..car tires are the opposite, they go height/width/rim size.. so the second number you say is profile, that means the height of it, correct? you all know anywhere on the net to find out what came factory on my bike?

In metric tire, sizing, like the bike is using, it goes width, aspect ratio (sidewall height as a % of section width), then the rim size. You are used to standard tire sizing.

Anything wider than a 100 wide tire on a 125, tends to be a bit harder for the motor to pull, and due to the rim width used, the profile is wrong. Stick with the recommended size, unless you also put on a wider rim, and are prepared to live with the extra load on the motor.