Why small bolt pattern?

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coffeedart67

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The discussion on the why of right and left hand threaded lug nuts, got me wondering if anybody has any info. on why Chrysler came out with the small bolt pattern on a-bodies, when they had been using the big bolt pattern for years(my 49 Dodge B1B pickup had large bolt pattern, and not sure how far back the large bolt pattern went). Any inside information or theories?
Aaron
 
I'll take a wild guess and say less material saved them some cash. Money is why they do anything. If no one wanted a muscle car, there wouldn't be any.
 
Who knows? Why do manufacturers do "anything," I'm sure "they thought" it was a good idea

Why did some cars (Not just Mopars) have left hand wheel studs? Why did/ do heavy highway trucks have LH wheel studs?

Now I'm 65, and "back then" I don't remember a whole crapload of cars with LH studs on the side of the road, LOL because the nuts came loose on one side. I ALSO don't remember seeing any GM cars with "all RH" studs on the side of the road either.

What I DO remember is having to watch tire store jocks like a hawk to be sure they didn't get out the 3/4" impact and strip my LH studs!!!!
 
Five lugs to maybe to "one up" the Ford & Chevy compacts that came with only 4 lugs?

Also perhaps for "aesthetic" reasons when using a 13" rim? Smaller wheel smaller bolt pattern, and smaller studs using smaller lug nuts?

Those would be my theories...and I am sticking with them.

Paul
 
The engineering on left hand lugs is sound. They normally shouldn't work themselves loose, same as the right hand lugs on the other side would tend to stay on as opposed to unscrewing completely. It is of course confusing as most drivers and tire people for that matter are not engineers. Some trucks may have left hand lugs for the same reason, but it doesn't keep the entire hub assembly from going flying.
 
magnumdart said:
The engineering on left hand lugs is sound. They normally shouldn't work themselves loose, same as the right hand lugs on the other side would tend to stay on as opposed to unscrewing completely. It is of course confusing as most drivers and tire people for that matter are not engineers. Some trucks may have left hand lugs for the same reason, but it doesn't keep the entire hub assembly from going flying.
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"Sound" according to who?


Like I said, there are not great smoking piles of wrecks on the sides of the road of all the cars and trucks who have either left, -- or right studs.

I say it's bullshit

Think about THIS. Which can generate more force in most cars, the forward acceleration of the engine or the brakes? In the vast majority of cars, it's brakes. You don't see more wheels or less wheels flying off in stop and go?? or some other situation where the brakes are used a lot.

How about engines using crank and or cam center bolts? LOTS of force increasing / decreasing there.
 
The rotation of the wheel will actually try to tighten the nuts. Not tight as in torqued, just in the direction of tight. So if you were to forget to tighten them there is a chance they would not come off. It isn't a matter of who, it is a law of physics.
 
Great question why make two different bolt patterns on the cars. It's cheaper to make one size bolt pattern and wheel selection is basically the same. Whatever?
 
magnumdart said:
The rotation of the wheel will actually try to tighten the nuts. Not tight as in torqued, just in the direction of tight. So if you were to forget to tighten them there is a chance they would not come off. It isn't a matter of who, it is a law of physics.
Click to expand...

Like I said, I think this is BS and you have not proved a thing except "saying so."

When you "blip" and engine what do you think the crank bolt is trying to do?
 
I bought my wife a TVR, a small british sport car with a 307 h/p Shelby 289.. 60 mph in 1st, 95 in 2nd, 130 in 3rd, - 160+ in 4th..

It had wire wheel knock offs.. In the first 2 weeks the LF wheel separated from the car at speed, thankfully it's only 3 inches off the ground, so driving on the disc was no prob,, lots of sparks..

Long story short,, the front knock-offs were on the wrong side, as I noted the engraved arrow on the "nut".. Changed them to the proper side ( L thread on driver's side), kept the wheels on forever after,, what a car... FFFFaaast.

0 - 60mph - 3.8, - 0 - 100mph - back to 0 - 13.8..

tvr%201967%20grantura%201800%20tyl.jpg
 
My 64 Imperial had a 5'' or 5 1/2'' bolt pattern.They were bigger than 4 1/2'' I do remember that much.
 
The Left hand threads on the left side goes way back to the chariots then carried forward to buggies , covered wagons, automobiles as a means of keeping the wheels on the rig.

We're talking about the axle nut on all these early vehicles. The logic was sound, It kept on to later vehicles when lug nuts and studs were used to hold the wheels onto the hub.

But as you know Chrysler was the last to use them all the way into the 70's.
Old habits die hard.

The fact worked on the axle nut until the cotter pin came along, and on knock off hubs.

But the theory falls apart on lug nuts.


As for the SBP on the early A bodies, remember they only had 9" brakes so the hub was smaller and the wheels were only 13". Not much room for a larger BP.

What I find as real odd in 73 they put single piston Disc brakes on the front of the A bodies with the LBP and if the car was a \6 it had the 7 1/4" rear axle with 9" brakes and a SBP.

And NO it wasn't just on one odd car. I saw it on a few dozen cars. But I've never seen a multi pattern wheel for the cars. Go figure.
 
magnumdart said:
The rotation of the wheel will actually try to tighten the nuts. Not tight as in torqued, just in the direction of tight. So if you were to forget to tighten them there is a chance they would not come off. It isn't a matter of who, it is a law of physics.
Click to expand...

This is the reason I always heard Chrysler installed right and left hand lugs.
I'm not a physicist,so I can't tell you if it's true,or not. But in theory,it makes sense.








.
 
The theory that lug nuts will loosen or tighten due to wheel rotation is incorrect as long as the nuts tighten into a bevel with the same angle as they have. It is this bevel that keeps the nuts tight. This is why with any other type nut that does not have a bevel, such as a mag wheel lug nut you are recommended to recheck the torque every so often.
 
Chrysler did extensive testing on the right hand left hand thread lug nuts and studs,
and conclusively proved that even if the lug nuts were not tightened properly, the wheel would stay on the vehicle,
when the same test is preformed on a vehicle with all right hand threads, the wheels will fall off in a short time
dont believe it? loosen up your lug nuts and go for a drive, see what happens
 
RustyRatRod said:
The theory that lug nuts will loosen or tighten due to wheel rotation is incorrect as long as the nuts tighten into a bevel with the same angle as they have. It is this bevel that keeps the nuts tight. This is why with any other type nut that does not have a bevel, such as a mag wheel lug nut you are recommended to recheck the torque every so often.
Click to expand...

The bevel is not what keeps the nut tight. It's true that a taper fit does offer a significant friction fit (Tip your hat to ball joints and tie-rod ends once in awhile), but lug nuts are held on by the same mechanics that govern all bolts and nuts.

It's the stretching of the fastener that provides the retention. As the nut is tightened, the bolt or stud stretches (pre-loads, in engineering mouth noise) and this preload pulls the nut and joining parts together. Think about a paper clip: the paperclip trying to return to its original shape is what holds the paper together. In order for it to fail, it has to be bent beyond its yield point. Up until then, it's holding tight but once over-bent, it's junk. Same deal on Lugs: If they're stretched enough to hold but not so much they can't pull back to normal, you're golden.

Friction is a function of the force applying the friction: more force equals more friction:
Ff=u x Fn
Where Ff is the friction force,
u is the coefficent of friction
Fn is the normal force

It's a combination of the preload and the friction that provides the clamp load that holds things together. The conical seat serves more to locate the wheel and distribute the load than it does to hold the nut in. (Look in your machinery handbook or engineering guide for taper fits and the taper versus load charts). The 45 degree conical seat on a lugnut is too wide for much of a taper-fit (most machine tapers are about 7 degrees), and the lugnuts aren't hard enough to use it well.

 Remember George's '68 Dart 4-door? He changed a tire and put the lugs on backward. He got 'em tight but the traction action eventually slotted the lug holes. The nuts never came loose, but the load wasn't distributed via the conical seat and so something hadda give.

Just like the nut doesn't hold much on the tie-rod end, the taper doesn't hold much on the lug nut.

Mag wheels required retightening because the Aluminum was not as hard as the steel, and because the wheel couldn't deform elastically when tightened as steel wheels do (Look at the back side of an OEM steel mo-rim sometime. The wheel deforms when tightened, and this also contributes to preload). The aluminum deforms plastically and can shift and squirm under load (without returning to its prior shape. It has a lower yield point), and this reduces the preload on the fasteners, thus requiring re-tightening. Modern alloys don't have this issue because the material is tougher and the conical seat allows higher preload but distributed over a greater area so deformation is not a factor.



Why the small pattern versus large?
Simple! Bean counters and engineers, working together, often at odds with each other.

Think: Smaller car, needs less wheel, less stud, and has less profit margin. Not only was the pattern smaller, but so too were the studs. That means cheaper studs, cheaper nuts, and you can pull it off because the car weighs less.
I'm inclined to believe that GGs66GT was partially correct: smaller brakes leaves less room for bigger patterns but the fact of the matter is, the larger the bolt pattern, the more the load is distributed. If you bolt a 15 inch rim at the outer edges, then the leverage you can apply to that rim is minimal; the force goes straight to the studs. If all the bolts were as close as they could be to the middle, the force has to travel through the rim on its way to the studs (which is what's holding supporting the load), first, and it gets a nice boost in leverage from the wheel in the process. The rim sees more load and the load is not applied favorable to the studs.

Think: Trucks. The old Jeep and truck rims still sought a 5-lug pattern but they spread the studs out even further. Why? Because trucks and jeeps see higher loads. Your GVWR isn't increasing dramatically, but you are side-loading the wheels more, and you're more likely to push the load rating of the wheels and tires to the max.
Whereas a passenger car usually doesn't get a bed full of 5/8 OSB and then go around a bunch of corners, or traverse a steep hill crossways whilst chasing cows, the truck or Jeep will. Wide pattern reduces the load against the wheel and studs.
Now, take it to the other end of the spectrum: Small car, small brakes, small wheels, and even less load to worry about. The competition has weak-dick 4-lug rollers. We could get away with it but 5 is oh-so-sexy and it makes nice for the saleman to point out that there's one extra nut on there, just in case (Extra care in engineering, anyone?), when he's selling Grandma a nice new Signet. So for a small price, we add an extra lug, but then we make it up by going to a smaller pattern (Ever seen a 5.5 on 5 on a 13" wheel? ugh.).

Sure, we'd save money by only stocking one set of wheels and all that, but the cost saving on smaller wheels (with thinner material, natch), smaller studs, etc. makes it a winner. There's a reason new cars don't come with monster-truck tires, and even if they worked great, they're $$.

As the cars got bigger and power increased (Compare the shock loads applied to the lugs on a Slant 6 '65 Dart to a Big-block '68 sometime) the need for smaller patterns went away and it became cost effective to share wheels and tires. I'm still amazed that the big block Darts didn't shear studs on a regular basis.

LH vs. RH
In theory, the spin would have little to do with it. The nuts aren't being spun about their own axis when the wheel turns, they're being rotated about an external axis. If the inertia of the nut was a factor, it seems it'd loosen being a LH nut on the driver's side. Lots of big trucks are still this way. I guess the parallel axis theorem might apply, but I don't really know.

I also wondered if it was something like "a little extra", back when materials weren't the best and tightening lugnuts wasn't the art form it is today.

Even still, the LH lug nuts is something I truly do not get.

I will say that I'm sure that it was long-outdated before the changeover, and that Chrysler was just waiting for the tooling to wear out before re-tooling.
 
67Dart273 said:
Like I said, I think this is BS and you have not proved a thing except "saying so."

When you "blip" and engine what do you think the crank bolt is trying to do?
Click to expand...

think about safety wiring... i learned how to safety wire from a Ex chopper crew chief and you always make sure the tension is to tighten, if bolt a were to try to loosen it would tighten bolt B. also never go more than three bolts per stand.

GGs66GT said:
The Left hand threads on the left side goes way back to the chariots then carried forward to buggies , covered wagons, automobiles as a means of keeping the wheels on the rig.

We're talking about the axle nut on all these early vehicles. The logic was sound, It kept on to later vehicles when lug nuts and studs were used to hold the wheels onto the hub.

But as you know Chrysler was the last to use them all the way into the 70's.
Old habits die hard.

The fact worked on the axle nut until the cotter pin came along, and on knock off hubs.

But the theory falls apart on lug nuts.


As for the SBP on the early A bodies, remember they only had 9" brakes so the hub was smaller and the wheels were only 13". Not much room for a larger BP.

What I find as real odd in 73 they put single piston Disc brakes on the front of the A bodies with the LBP and if the car was a \6 it had the 7 1/4" rear axle with 9" brakes and a SBP.

And NO it wasn't just on one odd car. I saw it on a few dozen cars. But I've never seen a multi pattern wheel for the cars. Go figure.
Click to expand...

my second owner 103K (bought it from the original grandma with 87K) is a 73 swinger with a slant, LBP, and a 8.25 with 3.21's...
 
67Dart273 said:
Like I said, I think this is BS and you have not proved a thing except "saying so."

When you "blip" and engine what do you think the crank bolt is trying to do?
Click to expand...
Who cares. It is on far too tight, and if it falls off, oh well it falls off. If I'm not mistaken I have had engines that didn't even use one.
 
now now lets not fight. lets all make up and watch some techno boobs shall we?

[ame="http://www.youtube.com/watch?v=zuQ--hEdq4U"]Techno Boobs! - YouTube[/ame]
 
OH my God. What the heck ever. lol
 
To discuss the original question of Why small bolt pattern?

I would guess it was done because of the 9" drums and the cost savings as an assembly using 9" componets.
 
For all you "experts". READ under DESIGN.

http://en.wikipedia.org/wiki/Lug_nut

And I quote:

"The lug's taper is normally 60 degrees (although 45 is common for wheels designed for racing applications), and is designed to center the wheel accurately on the axle, AND TO REDUCE THE TENDENCY FOR THE NUT TO LOOSEN, due to fretting induced precession, as the car is driven."


Lemmie tell you something, and then I am OUT of this ridiculous thread of complete and total misinformation. I changed my first tire in 1973. I was eight. By the time I was 19 I was an alignment man at a local tire store. I have been to so many different seminars through the years regarding tire/wheel/lugnut safety that it ran out of my ears. Some of yall come on here with so much BULLSHIT spewing out of your ignorant assed mouths and you have ZERO real world experience. You really oughtta stay on the couch with your bottle of lotion. You do no one any good with your argumentative attitude and know it all bullshit. Sorry, some of yall are good at makin yourselves sound smart, but you're just plain STUPID when you argue with FACTS.

Now, there's yall something to argue about for the next twelveteen pages......even though the FACTS have been presented. Morons.
 
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