Quote:
expeditionswest previously said:
I believe the paper is not overly simplistic. It is appropriate to the intended audience and is meant as a primer, a position based on my time testing tires for the manufacturers and consulting on tire construction with tire engineers.
To go into greater detail would require additional testing and detailed review of the physics behind the process, including environmental variables, carcass variables, compounds, soil and geo-science, etc.
If you can ever corner a real tire engineer and ask what they think of overly wide "off-road" tires, it will be an enlightening discussion. They mostly just roll their eyes and say "that is what marketing wants"
The article is specific to expedition vehicle use, which I state clearly in the assumptions section:
I don't acknowledge that?
Here is a quote, directly from the Typical Questions section:
I also include a chart with recommended section widths. I do not recommend narrower than 8.5", even for the lightest of vehicles.
There absolutely is a point of diminishing return, at both sides of the width equation. Performance values drop off precipitously for a 33" tire when they become narrower than 8" or wider than 13". There is a clear bell curve that defines itself in testing for 90% of trail conditions. For a vehicle in the GWV range of the FJ Cruiser, the sweet spot is right at 10".
I clearly state the paper is not about air pressure, which would require volumes on its own. The paper is about tire selection for expedition vehicles, not rock crawlers. Rock crawling has a very clearly defined medium, which varies in its adhesion properties and surface properties, but the goal is essentially maximum deformation and adhesion, combined with sufficient track width for stability in cambered obstacles. Many rock trails are highly tactile, or highly irregular and air pressures are 10-15 psi lower (or more) than would typically be run on a heavy expedition vehicle. A completely different scenario and criteria. Competition rock crawling on man-made courses takes the criteria even further from natural terrain variables and present the driver and vehicle designer with a highly tactile terrain and consistent surface (essentially irregular concrete poured over dirt or foam or other medium). This favors adhesion over macro and micro deformation, which favors very low tire pressures and maximum rubber contact to the surface, in addition to very soft compounds, bead-locks, etc.
As you no doubt know, the specification for a vehicle and tires from rock crawling in Florence Junction to driving around the world is completely different.
Carcass construction and rubber composition is out of the scope of this paper. The paper is specific to "The impact of tire width on traction" and does not go into detail on carcass construction, rubber composition, tread design, air pressure, etc. My SAE library has thousands of pages dedicated to tire theory. I specifically reviewed tire width.
In summary, running a 12.5"+ wide tire on an FJ Cruiser that is intended for exploration and general trail/DD duties will clearly create a negative performance, reliability and efficiency outcome. If you want to turn an FJ Cruiser into a dedicated trail machine and run a solid axle and the largest tires possible, then that would be an entirely different discussion.
Hope this helps.
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Of course you don't think it overly simplistic....you wrote it.
The fact is and you admit: it's a very narrow use article. It was intended for expeditionary vehicles.....this is not an expedition only site and my comments were directed to those who are going to use their vehicle for more than just expeditions that might read this thread.
I've talked with Gary Enterline at BFG....the guy responsible for the best adhesion rockcrawling competition tire ever produced and he chose 12.5 for the section width. I don't think he considered that "overly wide", nor was it what "marketing" dictated. He picked what worked. I do
completely understand your point that
rockcrawling man made or natural courses or trails is completely different than expedition use....to an extent. However, traction is traction. You either make it up an obstacle or you don't. You'd be niave to believe that the two areas of 4wheeling don't ever encounter the same type of terrain or traction requirements regardless of it being Florence Junction or elsewhere.
As I said in my first post.....I agree with much of your theory. I find you to be correct that narrower tires (10.5-12.5) are the best fit for most vehicles for
MOST applications (not necessarily expedition use).
Yes, you did acknowledge the diminished returns....I overlooked it. My apologies. I do have to wonder though: how did you determine that the sweet spot for the GVW of the FJC is 10"? Why should we believe your numbers over anyone else's? What constitutes your "90% of trail conditions"? I'm pretty sure that 90% of my trail conditions would be different than your's. Where'd you get the number?
Again, you say it's not overly simplistic, yet you leave out the number one factor (air pressure) that a vehicle owner can manipulate to make a difference in how his tires perform. That doesn't make sense to me. Do your theories about 10" on an FJC being optimum for 90% of trail uses hold up if we
do change the air pressure varaible? What if we add beadlocks and really start dropping down into the single digits?
You leave out construction and compound, when HUGE strides are being made in these areas to come up with the ultimate tires for traction? Again, overly simplistic, IMO. I realize you tried to narrow the scope.....but the fact is: the topic of tires is too dynamic to leave out other vital areas to a tire's performance to solely focus on one area alone. These areas are all inter-related and cannot be seperated if one is hoping to get a full, accurate picture. Yes, the major components can be examined individually, but not without a context.
Sean
