Removing rear seats to increase payload capacity?

[rruff]

So if braking is determined by friction (tire to ground), the more tire that’s on the ground, the more friction you get. Bigger trucks typically have taller and wider tires. Failing that they are heavier and cause more deflection of the tire. The end result is the same - a bigger contact patch. And this translates to better braking performance.

So all other things being equal, a truck that is built for the weight will see a less variable contact patch front and rear because the suspension and load carrying is designed to properly carry the weight with minimal contact patch variability from shifting back and forth. And, the tires are typically taller and wider, with greater overall weight causing the tire to deform which further increases the contact patch.

Please not note that the "benefit" of greater weight giving better contact with the ground is more than cancelled by the increase in the amount of force required to stop.

Traction is friction coefficient * force (weight). So if the friction coefficient between the tire and road could be taken as a constant, traction wouldn't change with the size of the contact patch at all. In reality, bigger tires at lower pressures do improve traction. Bigger trucks actually have less rubber on the ground relative to their weight (tires are beefier and run at higher PSI), which is probably why they generally require a greater stopping distance.

I think in this discussion we are talking about a typical 1/2 ton vs a 1 ton. Stock tires on the 1 ton might be slightly bigger on average, but not much. If it has 80 psi tires there will be *less* rubber on the ground vs the 40 psi tires that come stock on 1/2 tons. If you go aftermarket you can get the same size tires for either. I have 35x13" 65 psi E rated tires on my Tundra which are larger and have more rubber on the ground than the great majority of 1 ton trucks.

The 1 ton truck is not going to stop better unless the pad-rotor friction is the limiting factor. I truly don't know which is typically the limiter, but I suspect that if you really need to stop in a hurry and slam on the brakes, the ABS will usually kick in... which means tire-road friction is the limiter.

Pretty much true except the part about "less impactful". The front does most of the work because weight shifts forward during braking and therefore manufacturers put better brakes up front. That does not mean that it is desirable to intentionally shift more of the load to the front. Ideally, the rear wheels and tires help out.

That's true. The ideal would probably be for equal weight and braking on all four wheels. Weight is shifted to the front when braking because the CG is higher than the plane of the tires/road where the braking force occurs. The higher the CG the greater the weight shift. It's a bug, not a feature.

 

[Porkchopexpress]

The 1 ton truck is not going to stop better unless the pad-rotor friction is the limiting factor. I truly don't know which is typically the limiter, but I suspect that if you really need to stop in a hurry and slam on the brakes, the ABS will usually kick in... which means tire-road friction is the limiter.

I would think that this is true, a 1 ton vs 1/2 ton does not have significantly larger tires, (if at all). However, they should have bigger brake rotors so over time a 1/2 ton would experience brake fade before a 1 ton under repeat breaking, (hilly terrain or traffic for example).

 

[tacollie]

We never experienced brake fade in 25000 miles with our overloaded Tundra. Coming down Pikes Peak we were the only vehicle out of six that wasn't required to stop for a brake cool down. Modern vehicles have huge brakes.

P rated tries and soft springs are the weak link followed by the rear axle. If you add oversized tires and use it on rough terrain you'll see accelerated component wear. Things like bushings, steering racks, and axle seals. Our overloaded Tundra had better on road handling than our F250 because it was IFS. I didn't have to modify the F250 to carry the camper. A half ton needs to be modified to carry the same weight. Oddly enough I spent the same amount of money making the F250 ride good on rough roads we I did making the Tundra handle good overloaded?

 

[ChasingOurTrunks]

Please not note that the "benefit" of greater weight giving better contact with the ground is more than cancelled by the increase in the amount of force required to stop.

Traction is friction coefficient * force (weight). So if the friction coefficient between the tire and road could be taken as a constant, traction wouldn't change with the size of the contact patch at all. In reality, bigger tires at lower pressures do improve traction. Bigger trucks actually have less rubber on the ground relative to their weight (tires are beefier and run at higher PSI), which is probably why they generally require a greater stopping distance.

I think in this discussion we are talking about a typical 1/2 ton vs a 1 ton. Stock tires on the 1 ton might be slightly bigger on average, but not much. If it has 80 psi tires there will be *less* rubber on the ground vs the 40 psi tires that come stock on 1/2 tons. If you go aftermarket you can get the same size tires for either. I have 35x13" 65 psi E rated tires on my Tundra which are larger and have more rubber on the ground than the great majority of 1 ton trucks.

The 1 ton truck is not going to stop better unless the pad-rotor friction is the limiting factor. I truly don't know which is typically the limiter, but I suspect that if you really need to stop in a hurry and slam on the brakes, the ABS will usually kick in... which means tire-road friction is the limiter.



That's true. The ideal would probably be for equal weight and braking on all four wheels. Weight is shifted to the front when braking because the CG is higher than the plane of the tires/road where the braking force occurs. The higher the CG the greater the weight shift. It's a bug, not a feature.

I would think that this is true, a 1 ton vs 1/2 ton does not have significantly larger tires, (if at all). However, they should have bigger brake rotors so over time a 1/2 ton would experience brake fade before a 1 ton under repeat breaking, (hilly terrain or traffic for example).

This is super interesting fellas - my understanding of the limitations of braking on bigger trucks isn't as robust as it should be based on this chat. I figured even a marginally bigger tire or even bigger weight would create a bigger contact patch, which I assumed would create a better functioning brake, but based on this there's more to it than that. Like I said, I've got experience driving overloaded pickups (A couple of times when I was younger and more invincible) so I know for sure a truck that's overloaded gets way worse at handling, braking, etc. than a similarly loaded truck designed for it, but the "why" is interesting to me.

So the question is how do HD trucks manage stopping the heavy loads so much better than the same load in lighter trucks. Maybe this isn't at all the case, but short of seeing a test, anecdotally this has been my experience. Maybe it's 100% the suspension and chassis rigidity that saves the day for the bigger truck.

Maybe it is a case of bigger rotors, but the rotor sizes are somewhat limited in size due to the wheel -- there's only so much rotor and caliper you can fit behind an 17 or 18 inch wheel, which most HD trucks come with I think. Perhaps thicker rotors dissipate heat better and thus the brakes are more effective? Or perhaps are the pads are larger? When I have a bit more time I'll dig into this.

Alternatively if anyone wants to loan me their Superduty and an F-150 and a few thousand pounds of gravel we can sort this one out on the weekend, just need to find an empty road!

 

[Sooper Camper]

Maybe it is a case of bigger rotors, but the rotor sizes are somewhat limited in size due to the wheel -- there's only so much rotor and caliper you can fit behind an 17 or 18 inch wheel, which most HD trucks come with I think. Perhaps thicker rotors dissipate heat better and thus the brakes are more effective? Or perhaps are the pads are larger? When I have a bit more time I'll dig into this.

It's the whole system, every component is bigger in every dimension that matters. You are correct, wheel size is the main constraint on overall rotor diameter. A quick search on Autozone brought up rotors for an F150 and a Ram 3500:
F150: 350mm x 34mm
Ram 3500: 360mm x 39mm

Most 'HD' trucks have a 'hydro boost' system which operates off hydraulic pressure and not vacuum, they are much more effective at amplifying foot pressure into brake pressure. Because you have a more effective foot power amplifier, you can use more/larger pistons (which have the net opposite effect, in relation to foot power) to apply more pressure over more surface area. It gets more complicated than that, because you have to start factoring in tire contact, pad friction coefficients and myriad other things that make this destined to always be

The original point of this thread, is quite comical though.

 

[bkg]

It's the whole system, every component is bigger in every dimension that matters. You are correct, wheel size is the main constraint on overall rotor diameter. A quick search on Autozone brought up rotors for an F150 and a Ram 3500:
F150: 350mm x 34mm
Ram 3500: 360mm x 39mm

Most 'HD' trucks have a 'hydro boost' system which operates off hydraulic pressure and not vacuum, they are much more effective at amplifying foot pressure into brake pressure. Because you have a more effective foot power amplifier, you can use more/larger pistons (which have the net opposite effect, in relation to foot power) to apply more pressure over more surface area. It gets more complicated than that, because you have to start factoring in tire contact, pad friction coefficients and myriad other things that make this destined to always be

The original point of this thread, is quite comical though.

Point of correction... My last 2 F350's have had vacuum boosters. The reason most Diesel trucks generally had hydroboost is because they don't create enough vacuum w/o a vacuum pump.

Many smaller vehicles have come with hydroboost as well - Chevy Astro van's are great sources for junk yard components.

 

[Sooper Camper]

Point of correction... My last 2 F350's have had vacuum boosters. The reason most Diesel trucks generally had hydroboost is because they don't create enough vacuum w/o a vacuum pump.

Many smaller vehicles have come with hydroboost as well - Chevy Astro van's are great sources for junk yard components.

Sure, and my dads gasoline GMC 2500HD has hydro boost. It's not a rule, but certainly more common in the HD applications, and you hit the nail on the head re: vacuum.

You could probably argue Fords aversion to hydro boost stems from their inability to source good power steering pumps...at least in the 90s and older platforms I'm most familiar with. They've always had junk Ford pumps in my experience...and Chevy Astro sag pumps are great for converting that as well!

 

[Buddha.]

My ‘01 mustang GT had hydro boost. I assume it’s because the mod motors are stupid wide and take up too much room.

 

[bkg]

Sure, and my dads gasoline GMC 2500HD has hydro boost. It's not a rule, but certainly more common in the HD applications, and you hit the nail on the head re: vacuum.

You could probably argue Fords aversion to hydro boost stems from their inability to source good power steering pumps...at least in the 90s and older platforms I'm most familiar with. They've always had junk Ford pumps in my experience...and Chevy Astro sag pumps are great for converting that as well!

Good call on the infamous ford steering pump whine...

At least it prevented a lot of truck/deer collisions.

 

[Sooper Camper]

My ‘01 mustang GT had hydro boost. I assume it’s because the mod motors are stupid wide and take up too much room.

Ya, same with the Lincolns and LTD's in the 70s, those often had hydro boost and a Saginaw pump...but my 10k GVWR 77 F350 came with the junk pump and junk vacuum booster. Best thing I ever did to the brakes in that truck was just put in a manual, Wilwood master cylinder...it takes a fair bit of effort but will lock up 35s.

 

[nickw]

Something else to consider is duty cycle....while a F150 w/HDPP may have same payload as a highly optioned 3/4T or an older 1T....the standard by which those trucks were built and the designed / expected duty cycle will vary immensely, there are very different design requirements that none of us are privy too and of course no metrics to compare rigs.

I can absolutely see a situation where certain HD work trucks are de-rated (larger factor of safety) since they will likely be loaded a larger % of the time while the lighter duty rigs are bumping up against the max (min factor of safety) for marketing purposes knowing it's a fractional use case.

I'm old enough to know, keep within design parameters....we have the luxury of debating this stuff to death, but reality is, we don't know why certain engineering decisions were made but we kinda have to trust why they were.

 

[nickw]

Personally, I'm following common sense by researching this topic before I buy anything. And I'm sharing what I'm learning here on this thread because the OP and myself are asking similar questions.

Common sense says that vehicle outfitters and camper manufacturers that have been installing campers on trucks for more than 20 years know a lot more than I do - and they seem to indicate a half ton truck can carry 10% over GWVR with E rated tires and air bags. They have skin in the game, by the way. They could be liable if they're outfitting vehicles and making recommendation that are unsafe.

Commons sense says that I should talk to others who are hauling pop up campers with half ton trucks to learn from their experience. Many of them are on this forum and have indicated that their trucks ride well with tire and suspension upgrades.

Common sense says that it's foolish to think your vehicle is safe if you're 100 pounds under GVWR but you're somehow negligent and breaking laws if you're 100 pounds over GVWR.

Common sense says that the engineers determine ratings with a large factor of safety built in. It would be great to hear from automotive engineers who have experience with GVWR and axle ratings. That's one of the reasons I'm asking about this topic.

Common sense says that, if some guy on the internet starts ranting about insurance and liability, you should follow up with someone who actually knows what they're talking about - the insurance company and the underwriting team. State Farm, by the way.

Common sense is a factor of perspective, common sense to an RV Camper manuf who wants to sell an RV to a market share using the most common truck out there (F150) is going to be different than common sense to an engineer who is designing the rig with certain engineering constraints in mind.

Engineering of this sort not black and white, it's why factors of safety exist, to account for unknowns and abnormal conditions.

 

[Todd n Natalie]

Common sense is a factor of perspective, common sense to an RV Camper manuf who wants to sell an RV to a market share using the most common truck out there (F150) is going to be different than common sense to an engineer who is designing the rig with certain engineering constraints in mind.

Engineering of this sort not black and white, it's why factors of safety exist, to account for unknowns and abnormal conditions.

Yep. I was shocked when we were RV shopping that I heard the salesperson and manager tell a guy his truck couldn't tow the trailer he was looking at.

 

[Porkchopexpress]

Yep. I was shocked when we were RV shopping that I heard the salesperson and manager tell a guy his truck couldn't tow the trailer he was looking at.

You were shocked because they were being honest?

 

[nickw]

You were shocked because they were being honest?

Crazy world we live in unfortunately