2WD or 4WD
I'm looking at the new cheverolet durmax to pull my fifth wheel. Do I really need the 4WD or should I go with the 2WD. If I go with the 4WD is the mpg a big difference and does the 4WD effective the...
Forum Discussion
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To the OP, the above discussion on "spinning vs slipping" may not mean much, but there is usually a difference in braking, and therefore handling between 4x4 and 2wd. The 2wd will likely handle better and safer in an emergency on dry roads.
The 2wd wins the highway "Tow Award" and here is why:
The center of gravity is normally higher on 4x4 than 2wd because the 4x4 is usually raised for more clearance. This not only makes a difference during cornering where a tall vehicle may tip easier, but also in stopping power. One need only imagine an exaggerated-tall truck might tip forward to stand on the front two wheels just it might lean up on two wheels side-to-side. A 2wd tends to better maintain even tire loading under acceleration stress.
In normal physics, greater weight per square area increases friction in a linear manner. So rotating a multifacet block of iron to slide on a smaller facet area doesn't change the overall coefficient of friction (cf). But rubber tires are different. With weight remaining the same, more rubber (as in a bigger facet) meeting a dry road is better for traction, which accounts for the wide tires on race cars. Wide rubber raises the cf, the traction adhesion.
Rubber tires also have another related peculiarity. As weight is added or removed from a tire, the cf decreases non-linearly. Therefore when a truck is stopping, the "lightened" rear wheels lose a certain amount of traction, and the fronts gain a lesser amount of traction than the rear loses. Some overall four wheel traction is lost because the weight shifted.
A tall 4x4 has a greater weight transfer forward and thereby loses a greater amount of total overall traction compared to it's lower-chassis'd 2wd. I deally the center of gravity would right at ground level, but this is not possible. Still, closer is better than taller.
There were some remarks about a 4x4 losing directional steering control because of the tractive effort of the front wheels pulling. It is true that each tire must share both steering and inline traction. But more of one means exactly less of the other. The commenter had the right idea that acceleration (and deceleration, ie braking) subtract from steering traction, except 4x4 inline forward traction is the same direction as steering traction. So 4x4 do steer better than non-powered front axles in every case "under power" because all traction is directed wherever the front tires are aimed. But, when it comes to braking straight ahead chassis and rig momentum, neither 4x4 nor 2wd have an advantage, and both front tires equally lose some steering traction during hard braking.
All our RV towing unbalances our tow vehicles overall traction to some extent because of uneven tire loading. Normally the rear tires get a greater load percentage-wise when hitched because the rear axle is designed to accomodate the extra weight. There arises a distinct advantage to dual rear tires because they increase the rear rubber to more closely approach the ideal matching weight on every tire that is the special rule in maximum rubber tire traction.
In conclusion, the 2wd is a better, safer vehicle on dry pavement. For a heavier rear axle load, the dually surpasses a heavily loaded single tire in the search for equal traction on all tires. Equal traction means maximum traction possible when it comes to rubber tires.
Wes
...
To the OP, the above discussion on "spinning vs slipping" may not mean much, but there is usually a difference in braking, and therefore handling between 4x4 and 2wd. The 2wd will likely handle better and safer in an emergency on dry roads.
The 2wd wins the highway "Tow Award" and here is why:
The center of gravity is normally higher on 4x4 than 2wd because the 4x4 is usually raised for more clearance. This not only makes a difference during cornering where a tall vehicle may tip easier, but also in stopping power. One need only imagine an exaggerated-tall truck might tip forward to stand on the front two wheels just it might lean up on two wheels side-to-side. A 2wd tends to better maintain even tire loading under acceleration stress.
In normal physics, greater weight per square area increases friction in a linear manner. So rotating a multifacet block of iron to slide on a smaller facet area doesn't change the overall coefficient of friction (cf). But rubber tires are different. With weight remaining the same, more rubber (as in a bigger facet) meeting a dry road is better for traction, which accounts for the wide tires on race cars. Wide rubber raises the cf, the traction adhesion.
Rubber tires also have another related peculiarity. As weight is added or removed from a tire, the cf decreases non-linearly. Therefore when a truck is stopping, the "lightened" rear wheels lose a certain amount of traction, and the fronts gain a lesser amount of traction than the rear loses. Some overall four wheel traction is lost because the weight shifted.
A tall 4x4 has a greater weight transfer forward and thereby loses a greater amount of total overall traction compared to it's lower-chassis'd 2wd. I deally the center of gravity would right at ground level, but this is not possible. Still, closer is better than taller.
There were some remarks about a 4x4 losing directional steering control because of the tractive effort of the front wheels pulling. It is true that each tire must share both steering and inline traction. But more of one means exactly less of the other. The commenter had the right idea that acceleration (and deceleration, ie braking) subtract from steering traction, except 4x4 inline forward traction is the same direction as steering traction. So 4x4 do steer better than non-powered front axles in every case "under power" because all traction is directed wherever the front tires are aimed. But, when it comes to braking straight ahead chassis and rig momentum, neither 4x4 nor 2wd have an advantage, and both front tires equally lose some steering traction during hard braking.
All our RV towing unbalances our tow vehicles overall traction to some extent because of uneven tire loading. Normally the rear tires get a greater load percentage-wise when hitched because the rear axle is designed to accomodate the extra weight. There arises a distinct advantage to dual rear tires because they increase the rear rubber to more closely approach the ideal matching weight on every tire that is the special rule in maximum rubber tire traction.
In conclusion, the 2wd is a better, safer vehicle on dry pavement. For a heavier rear axle load, the dually surpasses a heavily loaded single tire in the search for equal traction on all tires. Equal traction means maximum traction possible when it comes to rubber tires.
Wes
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