2021 Tahoe Braking performance?

[Hrocks]

Or the PPV retrofit which is the same thing but only a couple hundred.

Unfortunately, neither of these will upgrade the brakes where they are needed the most which would be the rear axle.

Sorry Polo, that info is totally bass acwards...at least 70% of your braking effort is concentrated on the front. The front Brembo brake package (or any other 6 piston fixed caliper system) with 16" rotors and 6 pot calipers are not cheap but would totally transform the braking capability on a GMT T1XX truck. There is no debate on that.

 

[Polo08816]

Sorry Polo, that info is totally bass acwards...at least 70% of your braking effort is concentrated on the front. The front Brembo brake package (or any other 6 piston fixed caliper system) with 16" rotors and 6 pot calipers are not cheap but would totally transform the braking capability on a GMT T1XX truck. There is no debate on that.

That would be true if you don't have a trailer and significant tongue weight or payload. But if that's not the case, then why would you need a 1/2 ton based full size SUV.

It would be similar to why performance cars that have more weight over the rear axle like a mid or rear engine car have impressive rear axle brake systems.

Now your point does hold for front engine sports cars and you can see the disparity between the front and rear axle brake systems like the G80 M3 and F90 M5 which have enormous 6 piston front calipers and relatively smaller floating rear calipers. But those cars have a weight balance closer to 50/50 than a fully loaded long wheel base SUV, pickup, or mid/rear engine sports car.

It depends on how much weight you can transfer over to the front axle while threshold braking. If you can't transfer 50% or more of your GVWR to the front axle under threshold braking, then the front and rear axle brakes should be more equally balanced.

Now is a front brake system upgrade better than no upgrade. Probably. The stability control systems these days can generally keep your rear end from coming around even under threshold braking. But the real reason why GM doesn't have a rear axle brake upgrade is because electronic parking brake systems are expensive. That's part of the reason why the new G80 M3 and F90 M5 have puny floating rear calipers. I'm not aware of any electronic rear parking brake setups that have four piston monoblock calipers unless the parking brake was its own separate caliper. I believe the C8 Corvette uses this setup.

 

[Hrocks]

That would be true if you don't have a trailer and significant tongue weight or payload. But if that's not the case, then why would you need a 1/2 ton based full size SUV.

It would be similar to why performance cars that have more weight over the rear axle like a mid or rear engine car have impressive rear axle brake systems.

Now your point does hold for front engine sports cars and you can see the disparity between the front and rear axle brake systems like the G80 M3 and F90 M5 which have enormous 6 piston front calipers and relatively smaller floating rear calipers. But those cars have a weight balance closer to 50/50 than a fully loaded long wheel base SUV, pickup, or mid/rear engine sports car.

It depends on how much weight you can transfer over to the front axle while threshold braking. If you can't transfer 50% or more of your GVWR to the front axle under threshold braking, then the front and rear axle brakes should be more equally balanced.

Now is a front brake system upgrade better than no upgrade. Probably. The stability control systems these days can generally keep your rear end from coming around even under threshold braking. But the real reason why GM doesn't have a rear axle brake upgrade is because electronic parking brake systems are expensive. That's part of the reason why the new G80 M3 and F90 M5 have puny floating rear calipers. I'm not aware of any electronic rear parking brake setups that have four piston monoblock calipers unless the parking brake was its own separate caliper. I believe the C8 Corvette uses this setup.

The real reason is because it's not a widely needed system in the rear. The F/R brake balance is controlled by a proportioning valve. If you have too much rear brake, your vehicle will swap ends. If you're hauling a trailer (and I admittedly have limited experience, only from hauling my race car around quite a few years ago) the tongue weight is critical so that the total rig is balanced. I don't know what the formulas are, but you definitely can't have the preponderance of trailer weight concentrated on the real axel of your hauling vehicle. For example, fifth wheelers are designed to balance the load throughout the suspension of the truck hauling the trailer. Regardless, proportionally the front axle will always be required to handle the overwhelming majority of braking effort.

 

[Polo08816]

The real reason is because it's not a widely needed system in the rear. The F/R brake balance is controlled by a proportioning valve. If you have too much rear brake, your vehicle will swap ends. If you're hauling a trailer (and I admittedly have limited experience, only from hauling my race car around quite a few years ago) the tongue weight is critical so that the total rig is balanced. I don't know what the formulas are, but you definitely can't have the preponderance of trailer weight concentrated on the real axel of your hauling vehicle. For example, fifth wheelers are designed to balance the load throughout the suspension of the truck hauling the trailer. Regardless, proportionally the front axle will always be required to handle the overwhelming majority of braking effort.

F/R brake balance can also be modified by the brake pad compound (difference between the front and rear axles).

Almost all of your trailer weight will be concentrated on the rear axle of your tow vehicle for both bumper pull and 5th wheel/goose neck configurations. The load that is shared on the front axle is quite minimal - that's why the 1 ton HD pickups come in a dually configuration. If the load was spread equally (or near equally) between the front and rear axles, then you'd also need a dually configuration for your front axle.

Also, I haven't seen many 5th wheel or goose neck configurations that place the pin weight forward of the rear axle. I've seen some configurations where the weight is placed slightly behind the rear axle.

Also, I don't think the front axle will always be required to handle the overwhelming majority of braking effort in all vehicles. I admit this is probably true in a front engine sedan, but the case doesn't necessarily hold with a vehicle with a greater rear weight bias.

2020 C8 Corvette Stingray Brembo Performance Brake Specs

The new Brembo brakes offered in the Z51 Performance Package are just what’s needed when driving a 2020 C8 Mid-Engine Corvette from 0–60 mph in 2.9 seconds.

www.motortrend.com

If you look at the specifications, you'll see that the rear rotors are actually larger than the front rotors in the C8 and I'm sure the engineers accounted for weight transfer under braking as well.

The difference in weight distribution for a towing application would be even greater between the front and rear axles.

 

[Hrocks]

We can debate this all night...

The C8 rear wheels are an inch larger than the fronts. The rear rotors on the Z51 C8 are indeed .440" larger in diameter, but are about .125" (or an 1/8") thinner than the fronts. That gives them a better mechanical advantage than the "smaller" diameter rotors, albeit without the extra needed weight of the thicker rotors. The forthcoming ZO6 has front 6 pot calipers with 15.7" rotors with 4 pot 15.4" rotors (both are carbon). Using your mid engine/towing logic, why then does the 670 HP ZO6 not have marginally larger rear rotors? Because the overwhelming majority of the braking effort is applied in the fronts. Even though the suspension on that vehicle is very firm with limited dive under braking, the physics of weight transfer cannot be overcome. Regardless of the differences between the various systems, they all have to be in sync and balance under adverse conditions. I promise you, under any circumstance the front brake system makes the most energy (heat) and takes the majority of the load regardless of the vehicle.

 

[NIevo]

Or the PPV retrofit which is the same thing but only a couple hundred.

Unfortunately, neither of these will upgrade the brakes where they are needed the most which would be the rear axle.

I don't think I've read such a wrong statement in a long time on a car forum

 

[Polo08816]

We can debate this all night...

The C8 rear wheels are an inch larger than the fronts. The rear rotors on the Z51 C8 are indeed .440" larger in diameter, but are about .125" (or an 1/8") thinner than the fronts. That gives them a better mechanical advantage than the "smaller" diameter rotors, albeit without the extra needed weight of the thicker rotors. The forthcoming ZO6 has front 6 pot calipers with 15.7" rotors with 4 pot 15.4" rotors (both are carbon). Using your mid engine/towing logic, why then does the 670 HP ZO6 not have marginally larger rear rotors? Because the overwhelming majority of the braking effort is applied in the fronts. Even though the suspension on that vehicle is very firm with limited dive under braking, the physics of weight transfer cannot be overcome. Regardless of the differences between the various systems, they all have to be in sync and balance under adverse conditions. I promise you, under any circumstance the front brake system makes the most energy (heat) and takes the majority of the load regardless of the vehicle.

I believe the Z06 comes with stickier tires from the factory and would, thus, be able to transfer a bit more weight to the front under braking.

The static weight distribution of the C8 platform is about 40:60. I wouldn't be surprised if it's dynamic weight distribution could be 60:40 under threshold braking.

A front engine rear wheel drive vehicle might be closer to a static weight distribution of 50:50 and experience a weight distribution of 70:30 under threshold braking.

If you look at the brake specifications for 1 ton SRW HD pickups, you'll see that the Ram 3500, Silverado/Sierra 3500, and Ford F350 all have very similar brake rotor diameters. The variance is at most .2 inches. In fact, in the gas motor (non diesel) 1 ton HD pickup configurations, you could see a static weight distribution of 30:70 when loaded.

In a dually diesel configuration, that weight distribution would be even more extreme when loaded and it would make sense that the exhaust braking is applied to the rear axle. You wouldn't want that braking force to be applied to the front axle instead of the rear axle.

 

[Polo08816]

I don't think I've read such a wrong statement in a long time on a car forum

When loaded from either payload and/or trailering, what do you think the weight distribution of the SUV would be between the front and rear axles?

 

[Polo08816]

I don't think I've read such a wrong statement in a long time on a car forum

Actually, let's take some numbers and figure out this weight distribution when loaded.

I believe the Z06 comes with stickier tires from the factory and would, thus, be able to transfer a bit more weight to the front under braking.

The static weight distribution of the C8 platform is about 40:60. I wouldn't be surprised if it's dynamic weight distribution could be 60:40 under threshold braking.

A front engine rear wheel drive vehicle might be closer to a static weight distribution of 50:50 and experience a weight distribution of 70:30 under threshold braking.

If you look at the brake specifications for 1 ton SRW HD pickups, you'll see that the Ram 3500, Silverado/Sierra 3500, and Ford F350 all have very similar brake rotor diameters. The variance is at most .2 inches. In fact, in the gas motor (non diesel) 1 ton HD pickup configurations, you could see a static weight distribution of 35:65 when loaded.

In a dually diesel configuration, that weight distribution would be even more extreme when loaded and it would make sense that the exhaust braking is applied to the rear axle. You wouldn't want that braking force to be applied to the front axle instead of the rear axle.

When loaded from either payload and/or trailering, what do you think the weight distribution of the SUV would be between the front and rear axles?

I've used a trailering sticker for a 2022 Yukon XL Denali from this site:

GCVW of a Newer Yukon XL Denali - Forest River Forums

I have been searching and just can't find the GCVW rating of a newer GMC Yukon XL Denali. Anyone here have that information? Even GMC's tow guide doesn't list it--only the towing capacity. I know the

www.forestriverforums.com

GVWR = 7500 lbs
Curb weight = 6035lbs
Payload = 1465lbs
RGAWR = 4300lbs

GVWR - RGAWR = Front Gross Axle Weight Rating
7500 lbs - 4300 lbs = 3200 lbs

Front Gross Axle Weight Rating = 3200lbs
Rear Gross Axle Weight Rating = 4300lbs

Static weight distribution = (FGAWR / GVWR) : (RGAWR / GVWR)
(3200lbs/7500lbs) : (4300lbs/7500lbs)

With a fully loaded 2022 GMC Yukon XL Denali:
Static weight distribution = 43:57

Now I looked up the factory brake specifications for the vehicle and this website says the following:

2021 GMC Yukon Specs - iSeeCars.com

See complete 2021 GMC Yukon Specs at iSeeCars.com

www.iseecars.com

Brake​

Front brake diameter	13.5
Front brake type	ventilated disc
Front brake width	1.18
Rear brake diameter	13.6
Rear brake type	ventilated disc
Rear brake width	0.79

 

[R32driver]

In a dually diesel configuration, that weight distribution would be even more extreme when loaded and it would make sense that the exhaust braking is applied to the rear axle. You wouldn't want that braking force to be applied to the front axle instead of the rear axle.

Not to start a different argument than the entertaining one y'all have going on here, but you do understand how an exhaust brake works right?