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I would like to know the same thing, even my 04 4runner had 6 lugs. Amazing how many guys have said nice truck to me only to comment about noticing the 5 lugs. I could care less if engineering calculations prove 5 is OK (I am an engineer by the way) I want 6 just to keep with the tough truck theme.
 

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Maybe money? That is 4 less holes to drill in the axles, 4 less holes to drill in the wheels, 4 less wheel studs to install and 4 less lug nuts to install per vehicle. That is a saving of 800,000 of each per year based on 200,000 Tundras being built each year.
 

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The reason for 5 lugs instead of 6? Simply put, it's because that's all that it needs. Why put another one in when you don't need it? That just adds cost to everything. I bet if you compare one of the 07's studs to the 06 or earlier studs, the 07's will be a bit larger. Plus they could be using a different steel alloy that has a higher tensile strength. About the only thing I can guarantee you is that this was more than likely tested fairly extensively. I doubt they're just going to all the sudden decide to switch the number of lugs just for the hell of it. ;)
 

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What's the big deal? Most performance cars and other vehicles use 5 lugs...
 

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The reason for 5 lugs instead of 6? Simply put, it's because that's all that it needs. Why put another one in when you don't need it? That just adds cost to everything. I bet if you compare one of the 07's studs to the 06 or earlier studs, the 07's will be a bit larger. Plus they could be using a different steel alloy that has a higher tensile strength. About the only thing I can guarantee you is that this was more than likely tested fairly extensively. I doubt they're just going to all the sudden decide to switch the number of lugs just for the hell of it. ;)
:tu: :tu:

Ford F-150 's use 5 lugs, 96-00 used 12mm studs, then 01-07 uses thicker 14mm studs.
 

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I haven't noticed a rash of 5 lug wheels falling off cars or trucks so I would say it's safe. Remember.... Quality over Quantity.

Jim
 

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Just think, that's four less lugs to remove too when you rotate tires and/or swap from your good summertime wheels/tires to the winter wheels/tires.
 

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That shouldn't be too hard to calculate. I'll try and run some numbers assuming similar materials for both (which is probably not the case)
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Do those calculations and let us know.
I would think 5 14mm studs would be as strong as 6 12mm studs. The older ones are 12mm not 12.5mm as someone else stated. 12mm-1.5 thread pitch. The real reason other than 5 will do just fine is the fact Toyota already uses this size stud on the Land Cruiser, as well as the bolt pattern.
 

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and really quick.. if the lugs are

14.5mm x 5 thats 72.5
12mm x 6 thats 72

I know i left length out.. but say that they are the same and they cancel out.
 

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Since circular area = pi * radius[squared], the five 14.5 mm lugs have 21.67% more area than six 12mm lugs.

:cool: [points index finger in the air and makes the sizzling sound]
 

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I'm just a simple farm boy but I think StatCoder is correct in pointing out the stress that each wheel lug depends directly on cross-sectional area, which, as he slyly pointed out, varies by the square of the radius (or diameter depending on your formula). Cross-sectional area is a direct reflection of stress loading within the wheel lug (stress is expressed as psi so area is in the denominator). This means the most powerful and efficient way for engineers to reduce stress in the wheel lugs would be to increase their diameter, all else being the same while maintaining appropriate edge margins in the alloy wheel and wheel hub. It is so powerful that more than likely the 6th lug nut becomes dead weight and cost.

Toyota has decades and decades of design experience and lessons learned.

When the lugs were designed the engineering stress analysis team took into account worst case loading, be it axial load (tension/compression like when mounting/unmounting wheel), shear load (standard rotational shear loads like extreme braking puts on the lugs), bending load (the lugs are cantileverd off the wheel hub, especially if things get loose) and pre-loads (nut clamp up force). The engineers used the "worst case" load of each category and applied them to the geometry of the wheel/lug/hub combination and made sure that the geometry and mechanical properties of the materials selected were strong enough to take the worst situation. On top of this were calculations verifying material fatigue life expectancy (should approach infinity for these parts) and damage tolerance (like when one or two lugs are sheared or the Gomer down at the corner gas station forgot to tighten a couple of lugs). They top it all off with considerations of corrosion protection and materials compatiblity (galvanic). All this comes on the shoulders of design parameters such as performance and physical size and interference considerations from both internal and vendor-supplied localized components. The wheel stress team probably kept kicking the design back to the design team until all conditions were satisfied.

Once the stress engineers were done both prototype and early production parts were pysically tested to verify the appropriateness of the design under the most extreme conditions (loading and environmental) and dynamically load cycled to well beyond life expectancy. The old "one good test is worth a thousand expert opinions" approach. It keeps the stress team from "torturing the numbers untill they confess".

I would be confident in what Toyota has done and not let the shade-tree experts get under your skin about "the durn lug-nut count".

But then again I'm not privy to how Toyota designs parts; but I did stay at the Holiday Inn Express last night....
 
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