SUV vs. Sedan Decision

One of the most important decisions facing a large percentage of automobile prospects in United States is the decision to buy or lease a SUV or a 4-door sedan.  With the unprecedented proliferation of SUV models during the past 20 years and the advent of car-based CUVs (Crossover Utility Vehicles), the selection process between SUVs and 4-door sedans has become much more difficult and complex. The number of distinct models of SUVs available in the US market has grown from 15 in 1990 to approximately 80 models today.  More than 10 Million consumers, comprising more than 60% of new vehicle prospects in US,  face this decision annually.

While one of the main factors in deciding between SUV’s and 4-door sedans is styling and aesthetics, there are many other critial technical factors that have to be thoroughly studied and analyzed before the final decision between a SUV and 4-door sedan is made. 

THE most critical differentiating factor between SUVs and sedans that needs to be deeply analyzed is the issue of EMERGENCY HANDLING and an SUV’s stronger tendency to roll-over in sharp turns or during high speed emergency maneuvers. The tendency to roll over during emergency maneuvers is a consequence of both the higher weight and the higher center of gravity that SUVs generally command over 4-door sedans.

While due to laws of physics and their high center of gravity, SUVs have this inherent of weakness of tendency to rollover, automotive engineers have attacked this SUV weakness head on by incorporating sophisticated suspension designs combined with advanced electronic safety systems to mitigate the SUVs tendency to rollover.  Some of these advanced electronic systems include ESP (Electronic Stability Program), ARP (Active Rollover Protection) and Active Suspensions.   

Due to a significant variation betwen SUVs chassis/suspension systems and differences in offering advanced anti-rollover safety systems, there is a significant variation between different SUVs rollover tendencies and handling capabilities with certain SUVs incorporating such sophisticated suspension designs that enable them to handle better than many 4-door sedans.  For example, an Audi Q5 2.0T can measurably outhandle a Lexus ES350.  OC Auto Consultants strongly recommends interested clients to contact us and take advantage of our expertise and knowledge in choosing the safest SUVs with the best handling capabilities.

In simple physics, a factor called the Moment of Inertia has an inverse relationship with general handling ability of a vehicle with handling encompassing both stability/control during an emerency meneuver or tendency for roll-over.  Below you can review the formula for the Moment of Intertia of an automobile keeping in mind that the higher the moment of inertia, the worse the handling of the SUV.

I = Moment of Inertia of the SUV

M = Mass of the SUV

R = Squareroot (A**2 + B**2)

A = Distance between the center of gravity of the SUV and the geometrial center of SUV

B = Distance between the center of gravity of SUV and the ground

I = M * (R**2)

Note:  Higher vehicle mass linearly affects the moment of inertia of a vehicle and therefore has an inverse relationship with handling stability, thus SUVs which generally are significanly heavier than similarly sized 4-door sedans have their higher mass negatively affect their handling stability.  Improving the handling response and stability of a vehicle is a major reason automotive engineers work relentlessly to reduce the overall mass of the vehicle (i.e. aluminum engine blocks, aluminum suspension components, aluminum body structures in vehicles such as Jaguar XJ, Audi A8, Ferrari F430, etc.)

Note:  A in the above formula is raised to the power of 2, so in an ideal design, the engineers want the weight distribution of their vehicle to be such that the center of gravity of the vehicle is as close to he geometrical center of the vehicle as possible; thus you see a big effort by engineers to either move the engine (high concentration of mass) as far back and as close to the centerline of the vehicle as possible. The ideal weight distribution to optimize the handling of a vehicle is 50-50 for front and rear axles of the vehicle.  Thus, rear wheel drive or All wheel drive vehicles that have weight distributions closer to 50/50 (FWD vehicles carry most of their weight on their front axle, usually 60% or more on the front axle) often have better handling response than FWD cars and are more controllable.  Note that if the weight distribution is not an ideal 50/50, then A in the above formula is not zero and the higher A has an exponential inverse effect on the handling stability of the SUV (since it is raised to the power of 2)

Note:  B in the above formula is raised to the power of 2 meaning that a higher distance between the center of gravity of a vehicle and the ground has an inverse exponential effect on the handling stability of the vehicle.  Specifically, B has an exponential effect on the tendency of a SUV to roll-over. Because SUVs are inherently taller and higher off the ground than 4-door sedans, their higher centers of gravity negatively affect their handling stability and increase their tendencies to roll over in sharp turns.  Over the recent years, automotive engineers have been working relentlessly to reduce the SUVs’ center of gravity heights by reducing the overall height of SUVs, lowering the floor of SUVs (thus reducing overall ground clearance), repositioning concentrated masses such as engine and transmission closer to the ground and incorporating unibody constructions which are inherently lighter with lower centers of gravity compared to the traditional truck-based body-on-frame constructions

Caution to SUV Owners:  SUVs, even before being loaded with cargo and passengers, are more prone to roll-over due to their inherently higher centers of gravity.  SUVs heavily loaded with cargo and passengers are even more vulnerable to roll-over since their loaded centers of gravity are even higher than their unloaded centers of gravity.  Always avoid to put very heavy loads (anything more than 100 lbs.) on the roof of a SUV since that would have THE MOST NEGATIVE effect on the roll-over stability of a SUV.

 

OC Auto Consultants strongly recommends the prospective buyer to carefully study, analyze and incorporate the following important factors in their SUV vs. Sedan decision process:

SUV ADVANTAGES/POSITIVE POINTS vs. 4-DOOR SEDANS

  • SUVs’ driving position and the height of driver’s seat is on average 15 inches higher than that of a sedan, thus giving the driver better visibility and view of the road ahead                                    
  • SUVs have a much higher Space Efficiency than four door sedans
  • Space Efficiency = Interior Space / (Length * Width)
  • SUVs have substantially more cargo space than similarly sized 4-door sedans, on average two times the cargo capacity; thus for consumers who need cargo utility on a daily basis, SUVs always offer a better solution than 4-door sedans 
  • SUVs generally offer more space and seat-comfort for rear seat occupants due to the design and positioning of their rear seats being higher off the vehicle floor thus offering more leg room as well as more rear seat comfort
  • Many Crossover SUVs that are generally shorter (roof heights in the 63″ to 67″ range) offer seat heights close to many passengers hip heights requiring minimal bending maneuvers for vehicle entrance, thus significantly helping the entrance/exit of passengers with physical limitations such as those that have difficulty in bending their backs while entering or exiting a vehicle 
  • Many SUVs offer a 3rd row seat affording them a higher passenger capacity (7 or 8 passengers) vs. all 4-door sedans that offer 5-passenger capacity.  Out of the 80 models of SUVs currently available in the US market, about 30 of them offer 3-rd row seating as standard or an option
  • Due to their ruggedly engineered chassis systems, SUVs have significantly higher towing capacities than 4-door sedans.  While almost all 4-door sedans are not recommended for heavy towing, the majority of SUVs are engineered to tow boats, trailers, etc.  SUV’s towing capacities generally range from 3000 lbs to 8000 lbs with most car-based Cross-Over SUVs being capable of towing trailers up to 4000 lbs
  • Because SUVs generally weigh 500-1000 lbs more than a similarly sized 4-door sedan, they are generally safer in a front, side or rear collision. Specifically in the case of broadside collisions, the occupants of a 4-door sedan being hit by a SUV on the side are generally more vulnerable due to the SUV’s front bumper and crash structure overriding the sedans major crash protection structure
  • SUVs are always better than AWD sedans in OFFROADING due to higher ground clearance, higher approach and departure angles, more off-road oriented suspension/tires and more ruggedly engineered AWD/4WD systems (i.e. Lockable Differentials, Low-range Gearing, Hill-Decent Control, etc.)
  •  Although a percentage of 4-door sedans currently offer available AWD, 100% of SUVs offer available AWD with AWD being standard on many of them.  SUVs give consumers who need AWD systems for their adverse weather driving (snow, rain, ice) more choices.  Among 80 or so distinct models of 4-door sedans in US market, ONLY 30 offer avaible AWD.  Among 80 distinct models of SUVs available in US market, all 80 offer AWD or 4WD either as standard or optional
  • With their substantially higher ground clearance, SUVs reduce the risk of scraping and damaging the vehicle underbody on curbs, inclines and slanted drive-ways
  • With their ruggedly designed tires/suspension often engineered for durability, SUVs are more suitable for poorly conditioned roads such as bad asphalt or potholes. SUV’s have a substantially lower chance of tire/wheel damage from hitting the curbs or large potholes
  • A large percentage of SUVs have transformed from truck-based body-on-frame chassis systems to car-based unibody chassis systems affording them more car-like ride and handling characteristics.  This has transformed the majority of SUVs from vehicle specialized for off-road and/or adverse weather driving 20 years ago to everyday vehicles suitable for smooth highway driving, in other words direct competitors to 4-door sedans
  • In the past 20 years, the evolution of SUVs to more sophisticated suspension systems, lower weights, lower centers of gravity combined with advanced safety systems such as ESP (Electronic Stability Program) has significantly reduced the tendency of SUVs to roll over in sharp turns, thus mitigating one of the most critical safety issues SUVs have traditionally been associated with
  • Automotive Engineers have installed very advanced braking systems in SUVs.  These advanced braking systems combined with larger/high capacity brake systems have improved the SUVs braking performance significantly, reducing a major performance gap that has traditionally existed between SUVs and sedans.  Today, many high performance SUVs have equal or better braking performance to 4-door sedans
  • The combination of significant weight reduction, advanced engine/transmission systems and advanced aerodynamic engineering have resulted in significant fuel economy improvments for SUVs in recent years.  While at early as 15 years ago, an average 6-cylinder SUV might have used approximately 30% more fuel that an average 6 cylinder sedan ($400/month SUV gas bill vs. $300/month Sedan gas bill), many SUVs have reduced this 30% gap to almost 10% today ($330/month SUV gas bill vs. $300/month Sedan gas bill). For example, a BMW X3 3.5i on average uses only 10% more gas than its sedan counterpart, the BMW 335i.  However, many SUVs still use significantly more fuel (20% or more) than 4-door sedans. 

 

4-DOOR SEDAN ADVANTAGES/POSITIVE POINTS vs. SUVs

    •  4-door Sedans are significantly lighter than similarly sized SUVs (on average 800 lbs. lighter) and weight is the number enemy of handling (Scroll up to see the formula for the Moment of Inertia).  Therefore, in general 4-door sedans handle better than SUVs and are safer in Emergency Handling maneuvers.  However, in recent years SUVs have gone through intense weight reduction programs with increased use of High Strength Steel and aluminum in their body structure, suspension and powertrain components; thus reducing the weight gap with their 4-door sedan counterparts
    • 4-door Sedans have significantly lower centers of gravity than their SUV counterparts with their center of gravity on average 15 inches closer to the ground.  If you scroll up, you can see that a lower center of gravity has an exponentially positive effect on the handling stability of an automobile.   For example, a BMW 335i 4-door sedan will ALWAYS outhandle and is generally safer in high-speed emergency maneuvers than similarly sized BMW X3 SUV which uses comparable suspension components.  This handling superiority is primarily due to its 500-lbs lower mass combined with its 9″ lower center of gravity.   However, recent advances in engineering and technology have reduced the SUVs’ center of gravity heights significantly. That combined with sophisticated suspension designs and incorporation of advanced anti-rollover electronic technologies have improved SUVs emergency handling significantly to the point that a number of SUVs can outhandle some 4-door sedans. For example a BMW X3 SUV can outhandle a Mercedes E350 4-door Sedan eventhough it is both heavier and has a higher center of gravity.
    • 4-door sedans have lower floor heights than their SUV counterparts, thus improving the ease of entry and exit for passengers with certain physical limitations specially those that have limitations stepping over a higher floor
    • Since 4-door sedans are on average 10″ to 15″ shorter than SUVs, they are easier to park in parking garages with lower ceiling heights.
    • Due to their significantly lower weight and better aerodynamics, 4-door sedans have significantly better fuel economy than SUVs, on average 20% to 30% better than SUVs with similar sized engines, implying that your $300/month fuel bill for your 4-door sedan can potentially become $400/month for your SUV.  However, intense weight reduction activity combined with technological advances in engine/transmission and aerodynamics engineering has enabled a number fo SUVs to reduce this fuel economy disadvantage to as little as 10%.  For example, a BMW X3 uses ONLY 10% more fuel than a BMW 335i ($300/month fuel bill for BMW 335i vs. $330/month fuel bill for BMW X3 SUV).
    • Due to their significanly lower weights, 4-door sedans offer better acceleration and highway passing performance than their SUV counterparts.  In general, a 4-door sedans 1/4 mile acceleration performance is anywhere from 1 to 3 seconds better than a SUV using a simiarly sized engine.  However, in recent years, a number of SUVs have reduced this performance gap in acceleration to less than one second.  For example, a BMW X3 3.5i 1/4 mile acceleration is ONLY 1/2 second slower than that of a BMW 335Xi 4-door sedan
    • In recent years, the number of 4-door sedans offering AWD as optional has significantly increased; thus drivers that require AWD capability for their adverse driving conditions (Snow, Ice, Rain) have a lot more AWD 4-door sedan choices and DO NOT necessarily need to resort to buying a SUV in order to have AWD.  The number of AWD 4-door sedans avaible in US market has increased from less than 10 in 1990 to 30 today.


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