I did a little test of my own comparing the contact patch of a 285/30-18 to a 225/50-16 and it came out pretty interesting. The 285 patch was close to an inch and a half wider and a 1/4 shorter. Measurement is a little tricky when both sizes are static and maybe a little more easy in a dynamic state. Unless I did something wrong in figuring this out, the 285 S0-3 has 18% more contact patch than the 225 A022. I was expecting to see both tires to have the same total area but with different shapes. Wider= wider but shorter. Narrower= narrower but longer. This is true but the total areas are different.
What I came up with:
- 225/50-16 has 30.9 square inches of contact patch, 7 inches wide by 5.25 inches long.
- 285/30-18 has 36.3 square inches of contact patch, 9.3 inches wide by 5

Criteria used:
- Tires: Yokohama A022 (24.9 inches in diamater) and Bridgestone S0-3 (24.7) at 35psi.
- Car measured on the rear driver's side wheel, 2 degrees neg camber.
- Wetted bottom of tire down with Formula2000 and put white construction paper underneath tire.
- Measured as an ellipse: length times width, divide by four, multiply by pi. Can also measure as a square though dynamically the footprint more resembles an ellipse.

The theory formula for measuring contact patch is weight of corner divided by lbs. per square inch, which would confirm that both tires have the same area though different shapes. Though in this experiment the the wider tire has more footprint. But I'm not sure if you could make a general inference out of this or if you could just say that a 285 S0-3 has more footprint than a 225 A022. Unless there's a factor I haven't considered yet.

<= was also going to compare a 205 vs. a 235 but couldn't fit the 205 over the Stoptechs.

EDIT: anyone want to send me a 225/50-16 S0-3?

 

Is your wife out of town or something?? lol

 

shut up.

 

Laugh Out Loud. Mean and Funny hand in hand.

 

I love this bar.

 

The technical experts at the Tire Rack did a similar measurement (two different tire sizes on the same car with the same tire pressure) and found that the difference in total area was less than the accuracy of their measurement (roughly 2 percent).

Of course, the area that is actually supporting the weight of the car must be equal, as a matter of simple physics - e.g. with tires inflated to 35 psi on a 3000 pound car, the area must by definition total 85.7 square inches, regardless of the size of the tire. Any differences are due to errors in measurement methodology.

Click here to get a better understanding and clear up myths about the contact patch.

P.S. You're still really obsessed about this, huh Ponyboy?



Modified by nsxtasy at 11:41 AM 12/30/2003

 

I understand the mathematics of it and the experiment did indicate a wider but shorter (by. 25 of inch) contact patch though the areas were different.

Still...

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ponyboy &raquo;</TD></TR><TR><TD CLASS="quote">But I'm not sure if you could make a general inference out of this or if you could just say that a 285 S0-3 has more footprint than a 225 A022.</TD></TR></TABLE>

Unless, I did something wrong in determining area.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">P.S. You're still really obsessed about this, huh Ponyboy? </TD></TR></TABLE>

Be careful, a psycho would misconstrue that statement (even with the tongue in check emoticon) as sarcastic and condescending.

 

As if anything posted by nsxtasy ISN'T condescending? lol

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knightsport &raquo;</TD></TR><TR><TD CLASS="quote">As if anything posted by nsxtasy ISN'T condescending? lol </TD></TR></TABLE>

C'mon, Knightie - he said "sarcastic and condescending". Get it right - I want full credit here!

 

I wonder how much more area, if any at all, the 285 will cover at it's ideal psi.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

C'mon, Knightie - he said "sarcastic and condescending". Get it right - I want full credit here!
</TD></TR></TABLE>

I can't.

I pick up the condescention all the time. The sarcasm? Not so much.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knightsport &raquo;</TD></TR><TR><TD CLASS="quote">I can't.

I pick up the condescention all the time. The sarcasm? Not so much. </TD></TR></TABLE>

Then I'm just not using the right smilies.