[Shotimes] my 89 SHO Sr 72 update

[Ron Porter]

You basically need rubber on the road in the direction of travel. For the
dragstrip, his means a longer tread contact patch, which is done with a
bigger diameter tire, taller, more flexible sidewalls, etc. For handling,
you want rubber on the road perpendicular to the direction of travel, hence
a wider contact patch is good, plus a stiffer sidewall to keep the contact
patch consistent. A larger diameter can also help to make the contact patch
larger, but as you say the size & weight can then affect acceleration.

Good point about suspension geometry. If people put on larger diameter
wheels than were originally available on the car, they can slow themselves
down, plus accelerate wear on tires and other components.

Ron Porter 

-----Original Message-----
From: Leigh Smith [mailto:leighsm@comcast.net] 
Sent: Friday, September 12, 2003 9:11 PM
To: Ron Porter
Cc: 'Mark Nunnally'; shotimes@autox.team.net
Subject: Re: [Shotimes] my 89 SHO Sr 72 update


Ditto here;

Drag racers still prefer 15 in dia wheels for that reason, they 
accelerate faster than a 16 in dia wheel, all else equal.

Ultimate cornering power is just the opposite, the larger the diameter 
the wheel, and the wider it is, the more cornering power the car has. 
The wheel edge simply moves closer to the edge of the tire at the road 
surface. IFIRC I think diameter counts for almost as much of an 
advantage as width. All else being equal, ie: tire diameter. Shorter 
sidewalls resulting from a larger wheel are a tremendous advantage.

Ultimately the best road racing setup is a compromise between corner 
exit acceleration vs cornering power speed.  It wil vary from track to 
track, even with the same car. IFIRC  the Formula one cars change tire 
sizes from track to track.

Also there is a big catch:  wider wheels, lower profile tires, and race 
rubber (vs street), are all progressively more sensitive / demanding of 
correct suspension geometry and alignment.

I remember an article where the exact same mid 80s Corvette actually 
 went slower on pure race rubber, vs street tires, at Laguna Seca, 
because it wasn't tuned for them.

I have seen 12 in wide race slicks on an autocross car with 10 inches of 
it in the air due to lousy geometry! duh! And he could not understand 
why it was so slow and hard / demanding to drive.

So how fast do you want to go??? (Speed costs money!!!)

Lee