Rear Wheels Inside Car Body More?

[Mr.Impreza]

Hey. I always had this on my mind and never understood it.

From what I can tell, most cars have the rear wheels inside the body of the car more that the front wheels. Or it just looks like that.

Even with our cars...I measured and noticed that the rear wheels sit inside the car by 5mm more than the fronts.

Is there a purpose for this?

[yelsew]

I have no idea If the engineers had this consideration when designing the dynamics of the car, but this is an excerpt from an SAE paper on racecar vehicle dynamics.

"When selecting the track width, the front and rear track widths do not necessarily have to be the same. For example, track width is typically wider in the front for a rear wheel drive race car. This design concept is used to increase rear traction during corner exit by reducing the amount of body roll resisted by the rear tires relative to the front tires [4]. Based on the corner speeds and horsepower to weight ratio of FSAE cars, this concept should be considered by the designer".

So perhaps this was part of cars design

EDIT: okay scratch everything I just said...I looked up the track width of our cars and the rear is actually wider than the front, and it is the fender that is wider on the rear... and I don't know what that purpose is, most of aero and body design are beyond me

[86Boyz]

Originally Posted by Mr.Impreza

Hey. I always had this on my mind and never understood it.

From what I can tell, most cars have the rear wheels inside the body of the car more that the front wheels. Or it just looks like that.

Even with our cars...I measured and noticed that the rear wheels sit inside the car by 5mm more than the fronts.

Is there a purpose for this?

I just thought the rear wheels sat inward because fat people are in the car.

[Tcoat]

Design choice for appearance.
Don't throw as much crap up at the cars behind you.
Larger trunk/hatch capacity.
100s of engineering reasons I don't have a clue about.

[Gunman]

I vote "styling", wider rear fenders give the car hips, and a slim 'coke bottle' shape. Sex sells, even with car styling.

As for why not make the rear track wider, to make it "more flush", too much widening of the rear track would probably throw the handling off too much. (speculation on my part)

[venturaII]

It's gotta be a styling thing, because increasing the taper to the rear will negatively impact aerodynamics. Maybe there's a functional benefit as will like rear passenger room or trunk space.

[Gunman]

Originally Posted by venturaII

It's gotta be a styling thing, because increasing the taper to the rear will negatively impact aerodynamics. Maybe there's a functional benefit as will like rear passenger room or trunk space.

Depends, tapered rear should lower drag, but reduce side force.

[venturaII]

Originally Posted by Gunman

Depends, tapered rear should lower drag, but reduce side force.

Isn't that a good thing? Maybe I wasn't clear with the increased taper thing...I meant narrower rear, like an Insight.

[Tcoat]

Originally Posted by Gunman

I vote "styling", wider rear fenders give the car hips, and a slim 'coke bottle' shape. Sex sells, even with car styling.

As for why not make the rear track wider, to make it "more flush", too much widening of the rear track would probably throw the handling off too much. (speculation on my part)

Originally Posted by venturaII

It's gotta be a styling thing, because increasing the taper to the rear will negatively impact aerodynamics. Maybe there's a functional benefit as will like rear passenger room or trunk space.

Originally Posted by Gunman

Depends, tapered rear should lower drag, but reduce side force.

Originally Posted by venturaII

Isn't that a good thing? Maybe I wasn't clear with the increased taper thing...I meant narrower rear, like an Insight.

I think when talking in general terms for normal production street cars the body designs are more for appeal with drag forces a distant second. Ya they want to make them efficient but they are not looking at F1 levels of drag and balance.

[Gunman]

Originally Posted by venturaII

Isn't that a good thing? Maybe I wasn't clear with the increased taper thing...I meant narrower rear, like an Insight.

Low drag is good if you want increased mpg, but then you get something that looks like an Insight.

More side force is good if you want handling

[jeepmor]

Originally Posted by Tcoat

I think when talking in general terms for normal production street cars the body designs are more for appeal with drag forces a distant second. Ya they want to make them efficient but they are not looking at F1 levels of drag and balance.

F1 deliberately adds drag to add downforce, like airplane wings upside down. The FRS/BRZ has an enviably low drag. The only two better production vehicle CODs at the time were Tesla and Prius, but 0.01-0.02 difference if IIRC. I wanna say 0.26-0.28 range, but might be 0.36-0.38. Regardless it was close. After watching some wind tunnel vids, the difference is largely windshield angle vs the hood and how smooth it rolls over the body. The winners always have the greatest angle between them. Look a Prius, it's pretty much a door stop with wheels.