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2WD 620 Tire Wear: Most Wear on Rear Axle?


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Have some different tread depth tires (6, 7, 7, and 11/32nds) to mount and trying to get it right the first time.

 

But I drive pretty hard in the corners on windy PA roads and since there is more weight on the front axle, I would expect more wear on the front.  In fact, I'd expect to see more wear on the heavier loaded axle.

 

I know the passenger size rear wears more than the driver's side.

 

People say rear because that is the drive axle.  While the L18 is not a lot of HP, 1st gear is pretty deep and does put some high load on the tires - so I'm sitting on the fence with this claim.

 

Thanks

Tom

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That is definitely true and what I've seen with the rear wheel drive cars I've owned, however I may be seeing the opposite in my pickup:

 

I've got some cheap 1-ply tires on the front and some nice snow tires on the rear that I want to replace with more of the cheap 1-plys.  The snow tires look like they're not wearing whereas the fronts definitely are.  Of course these are two different types of tires and so this proves nothing.

 

However, there are factors that contribute to front wear:

  • axle load:  nose heavy (about 55/45)
  • braking:  front brakes do most of the stopping
  • cornering:  more axle load, more wear:  nose heavy  (this is two-fold since turn-in really wears tires)

I think the lower the engine HP, the lower the traction wear - an L20B would wear the rears more than an L16?

 

 

Most passengers tense up when I go into a corner.

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The alignment is spot on - I do it all with temps and can nail pressures too using that method.  (After temp alignments, I'll never attempt to do a measured alignment unless for some autoX or track thing.)

 

But you know, I discounted the effect of the drive wheels.  Yes you use the brakes here and there, but when you drive down the road, to maintain your speed, you are continuously applying torque to the drive axle.  So it would make perfect sense that going down the highway, the rears should wear more.  And frankly, 55/45 weight distribution for a half ton is very good for a 2wd 1/2 ton pickup - those big block Ford CobraJet Mustangs were that bad and maybe worse.

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TW is 420 but the sidewall feels like an inner tube and I can press my thumb over an inch into the tread.  Not quite dirt track tires they fold up and stack on the car hauler.

 

They were 205/75r14 Douglas M&S on the WalMart closeout tire rack.  Noticed them, not even looking to buy tires, and they were $28 each.  So I got a set.  Then I have this other set of 3 older Douglas and figured might as well get one more to use up the other set.  So they still had 2 left.  Manager walked buy and having just asked if they wheel and deal the pair, they mentioned it to the manager and he said $20 each for the last 2.  So I bot them.

 

Crappy tires for a cheap price.

 

NOTE:  I would much rather use a lower aspect ratio tire for handling, but I have the 4-spd and man it is brutal at 70mph even though with the 205's the speedo is about 10% slow.  I should acquire a 5-spd for when I replace the clutch.

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The alignment is spot on - I do it all with temps and can nail pressures too using that method.  (After temp alignments, I'll never attempt to do a measured alignment unless for some autoX or track thing.)

 

How accurately does the temp gauge measure thrust angle? ;)

 

You might find that there are a lot of reasons why rear tire wear may be excessive on a 40+ year old truck. If your leaf spring bushings are stock, I bet they're shot. The axle U-bolts may not be tight. The leaf centering pin may be broken or gone allowing your axle to shift. The axle housing may be bent. The frame may be bent. 

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I use temps to set the toe and pressure.  I get nice perfectly even wear.  I'm surprised no one ever suggested temps when setting tire pressure for even wear.  It's so simple and effective. 

 

I'm going to put the new tire on the RR and just monitor wear.

 

I need to run down a 5-spd ...

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You might want to find someone local with wheel scales.

Could be that you have a spring that has lost just enough tension, that the tire in question tends to slip first.

Or possibly a front torsion bar just a tad out of adjustment.

If left to right weight bias isn't the same from front to back, then you maybe have too little force dialed into the drivers side torsion bar.

Wheel scales will show that.

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Tread Wear numbers are to compare tires within a single brand, not brand to brand.  

The numbers have no national scale, meaning from one brand to another a 300 is not the same.  In fact, it can be radically different.  

Some companies have raised their tread wear numbers to be higher than everyone else's in hopes that you'd make this mistake.  

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If there is no "wedge" in the suspension, the RR tire will wear more.

 

There are number of ways to explain this but the intuitive argument is that when an engine produces output torque, the block must be reacted by the motor mounts.  The engine block tries to rotate opposite to the crankshaft.

 

The same thing happens with the rear end.

 

As the rear end housing tries to rotate in a similar fashion, it lifts the RR wheel and plants the LR - which results in a type of "wedge" or diagonal tire loading.

 

Hopefully, I got that all right...

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I want to drive my 620 to FL which is 1100 miles.  And while I have 205/75r14's on it, I'd like lower profile tires. 

 

4-spd trucks with their 70 mph screaming engines are "screaming" for a clutch fan like in the L20B.  I wonder if the L20B fan would fit in the L18 shroud?  (Of course, I shoe-horned a new plastic L20B radiator and plastic shroud into my 1974 - and a new water pump too.  ONLY to then discover the L20B clutch fan setup AND the OE brass radiators on eBay (which I did buy one.)

 

Does anyone know if that L20B clutch fan has the bi-metal thermal control in it?  (I don't know if all clutch fans do/did.)

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There is more potential chance of front wheel tire wear because of braking, heavier load and steering direction changes... and more if the front end is out of alignment. The rears wear least and about equal side to side with the RR on an open differential more so, if you have a heavy foot. Properly looked after and not abused they all wear pretty much the same and if the fronts did wear more than the backs or one side more than the other, it would be common knowledge. I've never seen more wear on one or more tires that couldn't be explained by negligence or abuse. 

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