The advantages of small tires

Got some time to kill while my scallops dethaw. Drove all the way up to Cleveland to go the damn Whole Foods hoping they'd have dry scallops. Fresh out, did get a bag of frozen ones. They may turn out to be legit, we shall see.

Anyway. Seems these days that everyone and their brother is all about megawide tires.

Yea brah, think I'm gonna put some 325's on my Z28 Camaro. Gonna be wicked fast and everyone knows it. That'll get me some respect. That and the T-tops.

A lot of the time wider is better, but there's a limit.. particularly on light, low-power cars. At some point you can have too much tire and not enough load and speed to get it working right. There are definite advantages to using small tires in open wheel, since uncovered tires generate lift and drag. Yea, lift.

Tommy Sizzle... that's crazy, brah! So like, how significant are we talkin' bout with the lift and drag?

Glad you asked. I was thinking about that earlier today! I don't personally have test data, so I'll reference some values from Race Car Vehicle Dynamics, and we'll pick 120 mph as our test speed. Pretty sure these numbers only hold true for being in relatively clean air, but since I don't have any sort of reduction for the rears I got nothing better than to use the same assumption all around. It is what it is.

• 20.0 x 7.0F, 20.0 x 7.0R (FSAE): 26 lbf lift, 83 lbf drag (27 hp @ 120 mph)
• 21.5 x 8.0F, 22.5 x 11.0R (Star Mazda): 39 lbf lift, 124 lbf drag (40 hp @ 120 mph)
• 22.0 x 9.0F, 26.0 x 12.5R ('70 Ferrari 312 B): 48 lbf lift, 155 lbf drag (50 hp @ 120 mph)
• FSAE with flat wheel caps: 25 lbf lift, 70 lbf drag (22 hp @ 120 mph)

That's a significant quantity I'd say. Non-trivial at least. Essentially an extra 23 hp @ 120 mph by going from original spec wheels to FSAE size, and an additional 5 hp on top of that with caps.

There are a couple 13" radials I'll be looking at which might be good for this application. Light construction, and relatively soft compound that I can probably get away with. The thought is that with increased footprint efficiency I can get equivalent or better grip than a big bias slick, with a little better wear rate, and smaller profile. Win win win.