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

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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 

 

 

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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. ;)

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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. 

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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?  

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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

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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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