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Unread 04-13-2010, 01:18 PM   #1
muttytruckster
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BFG KMs VS..... BFG KM2s

This is more of an informative post with some technical information
I wish I knew this before I bought my tires.
So let me explain
My 2007 jeep wrangler Unlimited JK Rubicon came with 255/75R17 BFG MT KMs.
We all known that the 255 is for width in millimeters and 75 is a protortion of the width to make up the profile of the side wall,
With this in mind all I wanted was a taller(Not wider) tire.
So I bought the new BFG MT KM2s in 255/80R17. So the same width however a higher proportion of the width to have a higher profile side wall.
Well I got them and they looked funny. So I measured and found the following in the picture below(See Link)
http://i213.photobucket.com/albums/c.../Wheels013.jpg
(KM2s is on the left and KM is on the right)

So for the BFG MT KM 255/75R17, the actual contact tread width is 8 inches
where as the BFG MT KM 255/80R17 actual width is 7 inches.

SO THE SAME WIDTH OF TIRES IS SKINNER BY 1 INCH in the KM2 version.

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Unread 04-13-2010, 01:26 PM   #2
USAntigoon
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This calculator might help you a lot..
I have the 255/75R17 BFG MT KM's and will switch to the KM2 as soon as these ones are worn..The KM2 are a generation further and have some sipes in them, which I prefer over NO sipes..But this a one man's opinion...
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Unread 04-13-2010, 01:30 PM   #3
muttytruckster
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I used your calculator and it says the section width is suppose to be the same(10.04) as my orginal BFG KMs however as you can see from my picture they are not.
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Unread 04-13-2010, 02:33 PM   #4
USAntigoon
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Thread width is different than tire width.. The tire spec's refer to tire width.. Also keep in mind that the KM2 and the KM have different load ratings and index..(KM2 load index is 121 over 111 for the KM)
Just my interpretation..
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Unread 04-13-2010, 05:14 PM   #5
fleck
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So what is the actual tread width on 305 width KM2's ??? Would it be 12" wide ?? or less than that ?? I want to buy KM2's but I also I want tires to have a wider look !
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Unread 04-13-2010, 07:05 PM   #6
muttytruckster
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Quote:
Originally Posted by fleck View Post
So what is the actual tread width on 305 width KM2's ??? Would it be 12" wide ?? or less than that ?? I want to buy KM2's but I also I want tires to have a wider look !
This is exactly why I posted this.
I wanted the same width look but ended up getting a skinnier tire in result as the change of the tire tread change in the KM2s
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Unread 04-13-2010, 07:15 PM   #7
yoda13
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wheel width affects tires differently as well, that might be making some difference...
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Unread 04-13-2010, 07:30 PM   #8
muttytruckster
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Yes I do agree wheel widths affect tires, however in my case I went to wheel that was 1/2 inchs wider which should allow the tire to spread out further and increase the contact tread pattern HOWEVER I lost an INCH of the contact tread width.
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Unread 04-13-2010, 07:35 PM   #9
rubizen
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I've always heard that tire companies don't always make the tires to an exact size. One companies' 255 tire may be 245mm and another companies' 255 may be 262mm's. I usually use the "spec" table on the Tire Rack website to get an idea of the actual tire size.
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Unread 04-13-2010, 09:17 PM   #10
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Quote:
Originally Posted by rubizen View Post
I've always heard that tire companies don't always make the tires to an exact size. One companies' 255 tire may be 245mm and another companies' 255 may be 262mm's. I usually use the "spec" table on the Tire Rack website to get an idea of the actual tire size.
Sadly, this is too true. Tire manufacturers frequently misreport tire specs. I'm not completely sure why, but sadly it's a proven fact that they do. Even when you mount the tire on an identical spec size rim that they measure on, the measurement is typically under what you'd expect. BFGoodrich is notorious for this but they aren't the only one. Everyone who is running 35-inch KM2s is actually running 34s. I suppose it's because it's guys that report this.

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Unread 04-14-2010, 09:18 AM   #11
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Yeah I hear you guys and while I do agree I am just saying I wish I knew they ran skinner otherwise I would of gotten a different size.
I just wanted to let people know who were considering these tires to know they run skinny, well at least for the 255s.
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Unread 04-14-2010, 09:34 AM   #12
fleck
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Anyone have the KM2's in a 305/60R18 and know what the tread width measures ??
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Unread 04-14-2010, 10:27 AM   #13
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IMO the (255) does not matter in this.The bigger the number taller the tire. It is the 80R17 instead of the 75R17. The lower the number the wider the tire. So a same height of 255 and a 75R would be wider than a 80R. Hope this helps.
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Unread 04-14-2010, 11:11 AM   #14
muttytruckster
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Quote:
Originally Posted by Dadstoys View Post
IMO the (255) does not matter in this.The bigger the number taller the tire. It is the 80R17 instead of the 75R17. The lower the number the wider the tire. So a same height of 255 and a 75R would be wider than a 80R. Hope this helps.
Can't say I Agree.
Its not like you give up height to get width or vice versa.
Also to go up to 80R17 from a 75R17 would thus indicate a lose of 1inch in tread width.....??? I just don't think so. Heck does that mean that to go to a 85R17 would indicate I loose another inch?? Heck my tread contact would only be 6 inches if thats the case.
I can understand they are running small, just like shoes or clothes or heck size varying from Company to Company, but like I said before ANd I will say it again, 255 --> 255 and I lost an Inch of width. HAD I KNOWN......... I would gotten a bit wider tire. I mean hell I went to a wider rim(By 1/2 inch) and end up finding out that I got a skinner(than the orginals) tires. I could understand this if I went from a 255 to 225. I don't think this is perception thing. I think its the new tread design change from the orginal Kms, and thus I am trying to make people aware that the KM2s are not to the same size scaling as the KMs, well at least in width.
I am not complaining I am just trying to help people out and make them aware when ordering say these size tires or Km2s in general.
I love my wheel/tire combination HOWEVER ..... I just wish I knew this tid bit of info, then I would of gotten a wider tire.
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Unread 04-15-2010, 02:02 AM   #15
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I have 255/80R17 KM2's mounted on stock Moab rims. Aired up at 30psi, not only are they a little on the skinny side (which, btw, is why I got them) they are a little short too! They are advertised as being 33.3 inches tall, but mine are exactly 32. I run them at 30psi because they are E rated and the ride is a bit on the rough side on the pavement. I love these tires, though. The perform very well in the dirt, mud and sand here in So Cal. I have not had them in loose sad or snow yet.
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