No Such Thing As A Dumb Question

[ksagis]

Going back to why I *think* this topic originated (at least why it felt important to me). For locker diffs, you want the rotation rate of the axles to be the same. The test data conclusively (at least to me) shows if a tire on one side is under inflated, you are going to make the locker eat a difference in rotation rate.

Granted thats a sample of one, of a low profile automotive type tire (fairly sure it was a radial), maybe not reflective of all tires, but I’ll wager a beer that the general trend holds true for bigger truck type tires.

FWIW, Subie manuals allow up to 0.25” of circumference difference on tires, so the BMW 10 psi example would violate that (if my math was correct)

Again, thanks @EPB72 for the data

 

[jamesroney]

Going back to why I *think* this topic originated (at least why it felt important to me). For non locker diffs, you want the rotation rate of the axles to be the same. The test data conclusively (at least to me) shows if a tire on one side is under inflated, you are going to make the locker eat a difference in rotation rate.

Granted thats a sample of one, of a low profile automotive type tire (fairly sure it was a radial), maybe not reflective of all tires, but I’ll wager a beer that the general trend holds true for bigger truck type tires.

FWIW, Subie manuals allow up to 0.25” of circumference difference on tires, so the BMW 10 psi example would violate that (if my math was correct)

Again, thanks @EPB72 for the dats

Nope. You are stuck on pressure as a proxy for rotation. The original figure of merit was hub height. And the original hyperbole by me was that pressure had no impact on rotation rate. But I was really poor in my choice of words, because it became an exercise to prove that inflation pressure had SOME relationship to rotation rate. And that was a mistake by me. My point was that differential pressure does not account for rotation rate change in the way that it was being presented.

What I should have said was that rotation rate is primarily governed by belt circumference and design, and that inflation pressure can only account for marginal changes to stretch the belt.

I hope that it changes the model for everyone on the dynamics of the rotation of the hub to tread...and it's clear that everyone is on board with that.

Now that we are talking about the 2nd order nuance of differential pressure vs tread circumference...I am super happy. Also happy to take the hit for the exaggeration. If I had started this with: "air pressure from 0 to 35psi can only achieve a 5% change in speedometer reading, it probably would have been better for the technical analysis. I really do appreciate your scrutiny. And I think that your math is good, but I am not sure that the number of pulses per revolution is important. Does the change in period depend on the number of teeth on the tone ring? I hope not.

 

[ksagis]

Nope. You are stuck on pressure as a proxy for rotation. The original figure of merit was hub height. And the original hyperbole by me was that pressure had no impact on rotation rate. But I was really poor in my choice of words, because it became an exercise to prove that inflation pressure had SOME relationship to rotation rate. And that was a mistake by me. My point was that differential pressure does not account for rotation rate change in the way that it was being presented.

What I should have said was that rotation rate is primarily governed by belt circumference and design, and that inflation pressure can only account for marginal changes to stretch the belt.

I hope that it changes the model for everyone on the dynamics of the rotation of the hub to tread...and it's clear that everyone is on board with that.

Now that we are talking about the 2nd order nuance of differential pressure vs tread circumference...I am super happy. Also happy to take the hit for the exaggeration. If I had started this with: "air pressure from 0 to 35psi can only achieve a 5% change in speedometer reading, it probably would have been better for the technical analysis. I really do appreciate your scrutiny. And I think that your math is good, but I am not sure that the number of pulses per revolution is important. Does the change in period depend on the number of teeth on the tone ring? I hope not.

It’s been a fun and enlightening topic for me, thanks!

 

[Bitch'nBronco]

While we're asking dumb questions, how do I ascertain the correct coolant level on a modified cooling system? Mine isn't that wild, but I've wondered if I have the right amount of coolant. I have a 95 mustang water pump, hoses that are different length than stock Bronco, and a 95 F150 expansion tank. Right now my radiator is plumb full of coolant (to the base of the coolant cap) and the expansion tank is filled to the cold fill line.

 

[Wild horse 75]

While we're asking dumb questions, how do I ascertain the correct coolant level on a modified cooling system? Mine isn't that wild, but I've wondered if I have the right amount of coolant. I have a 95 mustang water pump, hoses that are different length than stock Bronco, and a 95 F150 expansion tank. Right now my radiator is plumb full of coolant (to the base of the coolant cap) and the expansion tank is filled to the cold fill line.

Sounds full to me. If you haven’t run it yet there could still be some air trapped in the system so it could go down.

 

[Yeller]

While we're asking dumb questions, how do I ascertain the correct coolant level on a modified cooling system? Mine isn't that wild, but I've wondered if I have the right amount of coolant. I have a 95 mustang water pump, hoses that are different length than stock Bronco, and a 95 F150 expansion tank. Right now my radiator is plumb full of coolant (to the base of the coolant cap) and the expansion tank is filled to the cold fill line.

This would be the correct amount. Adding the purge tank completely fills the radiator with coolant as the engine heat cycles. This is exactly what you want, no air in the radiator, it optimizes the ability to cool your engine.

 

[ssray]

That would vary by tire, and by the weight of the vehicle it’s lifting.
But you’re right in a typical scenario, that first 10 pounds makes a big difference.
In a light duty tire, going from a flat sidewall to probably half its height or more, from when inflated. The rest takes longer, but that first few pounds makes a big difference.
A big, heavy duty rated tire on a light vehicle however, probably would never even go flat at zero psi. I’ve run into that before.

Thanks Paul! And a good point about light vs. heavy duty tires. Truck tires that run at 110 psi can be tricky to eyeball. They can be 85 to 90 psi and be tricky to detect by sidewall bulge depending on surface conditions. Sometimes thumping on them might get a bit different sound but that can be sketchy as well.

 

[ssray]

Maybe this will help somebody figure something out. I might as well try to read Chinese hieroglyphics. At one point it says “puff up”. I understood that part.

http://wanderlodgegurus.com/database/Theory/TireGeometry.pdf

Not sure I’ve seen anything with the number of equations that publication has in it. If you could digest it all you could get a job designing tires. Skimming through it did find some of the concepts that have been discussed in this thread. Some of the pics help with some concepts along with reading between the equations. I know what you mean by hieroglyphics. I bought a used math textbook years back trying to figure out an equation I found online. It used integrals or differential calculus that I had trouble digesting. Thanks for the link!

 

[Bitch'nBronco]

Sounds full to me. If you haven’t run it yet there could still be some air trapped in the system so it could go down.

I've been running it completely full for 2ish years now. Seems like half the older car videos I see on YouTube or TV when they pop the cap off, the radiator is down 2-3" from the fill neck. Made me wonder if I had been doing something wrong all these years.

 

[Wild horse 75]

I've been running it completely full for 2ish years now. Seems like half the older car videos I see on YouTube or TV when they pop the cap off, the radiator is down 2-3" from the fill neck. Made me wonder if I had been doing something wrong all these years.

If you don’t have an overflow bottle you want to keep the coolant level down a couple inches when cold so it doesn’t puke all over the ground when it warms up.

 

[DirtDonk]

Exactly. Without a recovery tank/overflow bottle, the radiator goes to its natural full level.
Any expansion at full operating temperature pukes out the tube, leaving the radiator at a neutral height.
Sometimes it’ll just keep puking, no matter what you do, but in most cases, it reaches an equilibrium, and you can live with that.

Some modern radiator systems actually have a lower level than we would have in ours. Either an extra long fill neck, or some obstruction in the tank structure that keeps the fluid level lower than we are used to seeing.
Some cars are just a little different than others.

 

[ba123]

Wait until I finish mounting my seats and I’ll tell you how far back they go, but I think they’ll go so far back that they’ll get stopped by the wheel well or at least close.

@NickC24 & @Wild horse 75 the seat back, in the furthest back position if mounted in the stock location, is 53” to the firewall and seat almost straight upright. Lmk if you want anything else measured.

 

[CowboyGrin]

I could fill this thread up quickly. My first one: Why did Ford move the frame shock mounts from in the front of the rear axle in ‘66 to behind in ‘67-‘76?

 

[ba123]

I could fill this thread up quickly. My first one: Why did Ford move the frame shock mounts from in the front of the rear axle in ‘66 to behind in ‘67-‘76?

To keep you guessing.

No really. I don’t know why they moved them but I’m sure someone on here knows. I added duals so have both sides and ended up just using the fronts since it worked better for my brakes.

 

[CowboyGrin]

To keep you guessing.

No really. I don’t know why they moved them but I’m sure someone on here knows. I added duals so have both sides and ended up just using the fronts since it worked better for my brakes.

Similar deal, I put new shock mounts on ‘73 frame in front of the rear axle because of the frame repairs I had to do under the factory mounts toward the rear. Thought front would work based on what my research turned up. Now I’m not so sure since my rear sway bar wants to mount at the frame very close to the new shock mounts. That’s a lot of forces in one area for these thin frames.

 

[ared77]

What's a "cold duck"


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A Mallard in the Artic?

 

[Sendero]

Similar deal, I put new shock mounts on ‘73 frame in front of the rear axle because of the frame repairs I had to do under the factory mounts toward the rear. Thought front would work based on what my research turned up. Now I’m not so sure since my rear sway bar wants to mount at the frame very close to the new shock mounts. That’s a lot of forces in one area for these thin frames.

I ran into the same situation on my '66. I will say the factory '66 mounts are stud mounts while they transitioned to eye mounts when they went to the rear. Seems that the eye mounts allow for better movement at least but not sure why they moved them. I removed my stud mounts and replaced them with eye mounts, spoke to James Duff and they said it is best to install them in the front where they were instead of moving them to the rear where they might interfere with disc brakes unless you move the mounts on the axle. They said it should not affect drivability whether they are in the front or the rear.

I will say, the Hellwig Sway bar kit has interior sleeves which seems like it gives it some structural integrity and my hope is that it would help reinforce that area. Also, the shock mounts I welded on from TBP also seemed to add some structural integrity to that area and realistically, how much stress are the shocks really putting on the frame? Would love to hear a success story on this setup as now you have me second guessing my install.

Another questions here is why do many modern trucks have one shock in the rear and one shock in the front on the rear axle?

Cheers.

 

[Wild horse 75]

Staggered shocks were installed to help control axle wrap. It’s nothing new. Manufacturers have been doing it since the 60’s that I know and possibly earlier.

 

[Yeller]

What's a "cold duck"


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A Mallard in the Artic?

it is an auxilary low range built from a Dana 20 transfer case that goes between the transmission and transfer case creating a "doubler". I don't remember where the name Cold Duck came from. Someone here probably has one and remembers where the name came from.

 

[ared77]

Thanks! I'd never heard of it till I saw the wanted ad on here.