Tongue Weight
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Elder User
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Tongue Weight
I have an excursion that I just bought.
I am going to take it to California later this year. I have a crate that I need tot ake that is about 48" wide, 54" tall, and 72" deep. It weighs about 800 lbs fully loaded. I was wondering if anyone had an opinion on mounting this on a hitch carrier (I can make one to handle the weight) and carrying this on the back of the SUV.
I have a small utility trailer that could easily carry it but parking when in San Diego will be an issue. Does anyone have an opinion on this? It seems like a lot of weight pretty far back on the thing.
I am going to take it to California later this year. I have a crate that I need tot ake that is about 48" wide, 54" tall, and 72" deep. It weighs about 800 lbs fully loaded. I was wondering if anyone had an opinion on mounting this on a hitch carrier (I can make one to handle the weight) and carrying this on the back of the SUV.
I have a small utility trailer that could easily carry it but parking when in San Diego will be an issue. Does anyone have an opinion on this? It seems like a lot of weight pretty far back on the thing.
Elder User
Joined: Aug 2007
Posts: 980
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From: Stuart, FL
The rear springs on the Ex re made for comfort not load carrying. My guess is that if you put that much weight hanging off the rear you will be sagging pretty good.
Plus, I don't know if you can extend the length of the Ex by 6'
and not be breaking any laws.
Plus, I don't know if you can extend the length of the Ex by 6'
and not be breaking any laws.
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Elder User
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I am not disagreeing with you - it seems like a lot and pretty far back on the chassis.
Posting Guru
Joined: Oct 2003
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From: Tulsa, OK
The worst thing caused by this is moving the CG (Center of Gravity) of the truck backwards AND increasing the polar moment of inertia (resistance to steering input). Plus, the 2" receiver hitch is "loose". The drawbar will rock around in the tube, exaggerating the rearward CG. Without beefing up the antisway bar on the rear axle, your Excursion may be more difficult to control in a quick maneuver.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
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From: Franktown, CO
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The worst thing caused by this is moving the CG (Center of Gravity) of the truck backwards AND increasing the polar moment of inertia (resistance to steering input). Plus, the 2" receiver hitch is "loose". The drawbar will rock around in the tube, exaggerating the rearward CG. Without beefing up the antisway bar on the rear axle, your Excursion may be more difficult to control in a quick maneuver.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
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Elder User
Joined: Oct 2004
Posts: 782
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From: Olympia, WA
The worst thing caused by this is moving the CG (Center of Gravity) of the truck backwards AND increasing the polar moment of inertia (resistance to steering input). Plus, the 2" receiver hitch is "loose". The drawbar will rock around in the tube, exaggerating the rearward CG. Without beefing up the antisway bar on the rear axle, your Excursion may be more difficult to control in a quick maneuver.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
Assuming your X weighs 8,000 lb (as mine does), you will be adding at least 10% of this mass about 2' behind the rear bumper, which is already about 4' behind the centerline of the rear axle. 800 lb, 6' behind the axle, is a pretty big shift.
Use a utility trailer. It is much safer.
OP - It's not a good idea. It's not the 800lbs, it's the fact that you want to hang it out on the end of a 4 foot stick. The hitch has to carry the downward 800lbs, but it also has to resist the moment or twist that your 800lbs on a 4 foot long lever is bringing.
More Turbo
Joined: Jan 2009
Posts: 530
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From: LI, NY
Polar moment of inertia? Please explain.
For a rectangular section with sides b and h:
In English... An Ex, which doesn't want to turn anyway, with that much weight that far back will be resistant to turning. And also want to keep turning once committed. Meaning it will be a real handful.
Posting Guru
Joined: Oct 2003
Posts: 1,198
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From: Tulsa, OK
[QUOTE=MagKarl;8484789]Polar moment of inertia? Please explain.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Posting Guru
Joined: Oct 2003
Posts: 1,198
Likes: 2
From: Tulsa, OK
[QUOTE=MagKarl;8484789]Polar moment of inertia? Please explain.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Elder User
Joined: Oct 2004
Posts: 782
Likes: 1
From: Olympia, WA
[quote=Forest;8487774]
I agree with your qualitative assessment of how change in CG and mass distribution can affect handling. But, this is not where polar moment of inertia comes into play, what you are describing is called rotational inertia.
Polar moment of inertia is a quantity calculated from the cross sectional dimensions and is used to calculate shear stress or torsional stiffness in a torsion element.
Polar moment of inertia? Please explain.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Think about an ice skater. If they are spinning, they can go much faster by pulling their arms into their body. They spin slower by letting their arms out. They are changing the polar moment of inertia (resistance to spinning about a vertical axis). It is conservation of rotational momentum, which is the same as linear momentum, except that polar moment of inertia relates to mass as rotational speed relates to velocity.
Cars and trucks interact with the road through their tires. Ideally, you want to balance the forces on all 4 tires. One of the best handling sports cars on the road is a Porsche Boxster (also Toyota MR2, several Ferraris, long-gone Fiat X19), with the engine in the center of the car (behind the seats) and a very low polar moment of inertia as a result. These cars can change direction very quickly with minimal stress on the tires.
The Excursion (esp. diesels) is reasonably nose heavy, and you can get away with some rear-ward shift. The downside is on original equipment suspensions. It is too soft on the rear axle, combined with the relatively high CG, and very soft anti-roll bars (if you have one at all).
If you move the high CG rearwards on an Excursion, with the already soft roll that these exhibit, it will be worse than trouble. Now you will have a very sluggish response to steering input and the truck will tend to roll around the longitudinal axis. Now, add in the "slop" that 2" receivers have and you have added a "big marble in a box" to slap you around. What load range tires? If they are "D", they will be too soft in side loading. Really bad combination.
Polar moment of inertia is a quantity calculated from the cross sectional dimensions and is used to calculate shear stress or torsional stiffness in a torsion element.
Posting Guru
Joined: Oct 2003
Posts: 1,198
Likes: 2
From: Tulsa, OK
[QUOTE=MagKarl;8489719]
I agree with your qualitative assessment of how change in CG and mass distribution can affect handling. But, this is not where polar moment of inertia comes into play, what you are describing is called rotational inertia.
Polar moment of inertia is a quantity calculated from the cross sectional dimensions and is used to calculate shear stress or torsional stiffness in a torsion element.
MarKarl--Oops. You are correct. It's been awhile. I meant to say "mass moment of inertia" (or rotational inertia). Thanks for jarring my brain back into Intermediate Dynamics. My background is primarily thermal/fluids engineering.
I agree with your qualitative assessment of how change in CG and mass distribution can affect handling. But, this is not where polar moment of inertia comes into play, what you are describing is called rotational inertia.
Polar moment of inertia is a quantity calculated from the cross sectional dimensions and is used to calculate shear stress or torsional stiffness in a torsion element.
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