140/80-18 Rear Tire, that's crazy talk!

This question always comes up among the 950/990 crowd,

"Can you run a 140/80-18 size tire on the factory 4.5" rear wheel?"

Answer; yes, no, maybe...

There is no standard for measuring tires, it all depends on the manufacturer. Just because it says 150/70 that doesn't mean that it is the same size as an another manufactures 140/80-18. The only way to know if it can be run is to do some testing. For example, I have been running a Motoz Desert Tractionator H/T for well over 1000 miles with zero issues. However, after speaking with the Motoz "guy" while in Colorado he told me I should run the 150/70 instead because it was designed for a 4.5" wheel. 

My response, "why would I want to do that?"

A dirt oriented 150/70 is a tire that doesn't know what it wants to be when it grows up. Meaning, the 150/70 tire profile is oriented towards street performance, while the 18" wheel size is geared towards dirt. So a dirt oriented 150/70-18 sounds absolutely mediocre at best. Pick one side or the other; dirt or street. Anywhere in between is garbage...

 

Why would you want to run a 140/80-18 tire?

Answer; In general they're half the cost of 150/70-18, and more importantly the 140/80 has a taller sidewall that reduces your chance of pinch flat or rim damage when running reduced tire pressure. 

The 140/80-18 is only rated to 84mph, will it explode if I do 85mph?

Answer; No, that rating was designed as a reference with respect to steering, and braking input. 

Is a 140/80-18 the same as 120/100-18? 

Answer; yes, no, maybe...

Again, depends on the manufacturer. The tire data sheets show that 140/80 and 120/100 to be the same size tire. What I have found is that some companies sell one or the other. I was told that the 140/80-18 tire size was invented by Dunlop. 

 

Jerry 

 

 

Another factor with a narrower tire is simply traction.  You get more force per square inch to dig and bite in the dirt.  This is an advantage off road; not so much on pavement but won't kill you.

My rear is 3.5" Woody's so I can run either. I'm running a 140/80 in Baja Rally. ;)

Have you had the chance to experiment with tire pressures? 

Lowering tire pressure seems to be taboo on adv bikes for some reason. 

4 hours ago, Eric Hall said:

Another factor with a narrower tire is simply traction.  You get more force per square inch to dig and bite in the dirt.  This is an advantage off road; not so much on pavement but won't kill you.

My rear is 3.5" Woody's so I can run either. I'm running a 140/80 in Baja Rally. ;)

You can run a 140/80 on a 4.5" 

I'm curious why you went with a 3.5", a 2.5" would have let you run rim locks. 

Just at Woody's suggestion. He supplied the wheels.

For pressures on big bikes I guess it's just a matter of protecting the rim. I destroyed my original rims on the GSA doing LAB2V at 20 psi

5 hours ago, Eric Hall said:

Just at Woody's suggestion. He supplied the wheels.

For pressures on big bikes I guess it's just a matter of protecting the rim. I destroyed my original rims on the GSA doing LAB2V at 20 psi

20 psi on a 90/90 or 80/100 can beat the hell out the front wheel on a heavier bike. I know with a 90/100 I can 18 psi all day. 

With that being said, I know the stock KTM wheel sets are notoriously soft and can't handle rocks impacts. 

What are the BMW wheels like?  

They aren't that strong but the design with the externally laced spokes means any kind of dent on the edge of the rim immediately loosens spokes

To confuse the issue even further, my 990 Baja came stock with the Dunlop Rally Raid 140/80 18. So you wonder is the mfg saying this is the recommended size on this wide rim? Round and round we go....

RPM

2 hours ago, Allrpm said:

To confuse the issue even further, my 990 Baja came stock with the Dunlop Rally Raid 140/80 18. So you wonder is the mfg saying this is the recommended size on this wide rim? Round and round we go....

RPM

Case and point, you can run a  Dunlop 140/80 on a 4.5" rear wheel. It depends on the manufacturer though... 

 

 

Edited by 556baller

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