305s VS 315s

[redthies]

I am running 315 Procomp Xterrains now and love the size, but have a chance to swap for KM2s in 305. Both are 75-80%. The main reasons to consider this is a) noise level, b) I have always wanted to try the KM2s. I do go off pavement as often as possible, but like most of us, I am 80% or more on roads.

The questions are a) Will I lose much offroadability for the 3/4" - 1" less clearance?
b) Will I gain anything in fuel economy from size / tread difference?

I am running stock gears and do pull a 3500 lb trailer fairly often. I must admit if the KM2s were the same size (315) I wouldn't think twice. Is it just the meathead in me that wants the 35s?:safari-rig:

 

[redthies]

If anyone has pics of their 80 with OME medium and 305s that could post or link, that would be appreciated!

 

[Klierslc]

305s are the same OD as the 285s just wider. You should see a bit better economy and the truck should feel a little faster. As far as off road goes, unless you are doing hard core stuff, it won't matter, but if you are, 3/4" is the difference between driving over a rock and sticking your diff on it.....

 

[redthies]

Those are pretty much my thoughts. There might be the odd cross ditch that I scrape with 33s but there is no rock crawling in my area, or my near future plans. The guy is going to come tommorow so we shall see if a swap happens. I have heard the KM2s are fairly quiet, and on the 6-8 hr trips I take regularly the Xterrains are really loud and tiring.

 

[fjfar80]

Here is the break down -

BFG KM2:

285/75/16 = 11.3" width, 33.1" outer diameter, and 59lbs
305/70/16 = 12.2" width, 33.1" outer diameter, and 59lbs
315/75/16 = 12.3" width, 34.8" outer diameter, and 64lbs
345/75/16 = 13.6" width, 36.4" outer diameter, and 74lbs

The difference between the 285's and 305's is going to be minimal, you will have a wider tire on the 305's which means you are going to have a bit more rolling resistance. However, you will not notice a big difference until you go to the 315's or 345's. With those two sizes you are adding more un-sprung weight and the diameter is significantly larger. You are gaining 1.7" in outer diameter by going from 285's to 315's which equates to .85" additional clearance. Is .85" a game changer...it can be depending upon the trails you are doing. When I went from 285's to 315's I had a significantly easier time rock crawling; however, I noticed no other "trail" improvements on anything other than rocks. Also, if you are not running modified gears (4.88's) you will be much closer to stock with either 285's or 305's.

Hope that helps.

- Mark

 

[redthies]

I have 315s now. No issues with gearing. Buddy the guy is bringing the 305s up tomorrow so if they are in good shape we will likely swap. I just want something quieter for the long highway days.

 

[redthies]

Swap is complete! I am happy with the deal. His KM2s were a little better in the tread depth dept. but my Xterrains are more evenly worn. I think the life expectancy will be about the same as the rubber on the BFGs is quite a bit softer.

The 305s are an inch or so narrower so they tuck in better on my recently de-flared 80. They are also night and day different in the noise they make. As people have said, then KM2s are much more like an AT in that regard.

End result...:elkgrin:

 

[thecriscokid]

Good to hear. Any regained pep up the hills?

 

[redthies]

Seems to be a bit more pep. I had 285s before the 315s so it is back to "normal"... I want a 34-10.50-R16 for my "ultimate tire".

 

[Prich1973]

From what I've seen and heard, you probably won't notice much of a difference in offroadability between the two tires. As for fuel economy, it really depends on a lot of factors (driving habits, terrain, etc.), so it's hard to say definitively. However, smaller tires generally tend to improve fuel economy, so you might see a slight increase there. Hope that helps!