how much slower going from 16in rims to 17in rims

I was running the stock salad shooters with BF Goodwrich 255 drag radials on the back, Now I will be running 17 in ZR1's with Nitto 315 drag radials in the back, and yes they are the 11 inch wide ZR1's. Will I be slower at the track? Thanx for any helpful info!

yeah most likely a little slower. probably in the hundreths of a second. nothing big

Here's an article I found a while back that will probably blow your mind:


What is the effect of a change in wheel/tire mass? Several people have quoted factors of x6 or x8 to determine the equivalent non-rotating mass variation. That is, an increase of 10lbs/wheel could be as detrimental to performance as carrying Arnold Schwarzenegger and Scooby Doo as passengers.

I decided to refresh my Physics and came up with the following conclusion: from the point of view of acceleration, an increase of X in wheel or tire mass is no worse than an increase of 2X in passenger mass. Not 6x, not 8x, just 2x worst case. This is why.

At any given speed/gear combination there is maximum torque T available at the wheels. The torque does two things: (1) opposes the rolling resistance and the aerodynamic drag and (2) accelerates the car. The equation that describes the equilibrium is:

T = I*u + M*r*a + D*r

*: denotes multiplication
T: torque at the wheels
I: total moment of inertia of the rotating parts
u: angular acceleration of the rotating parts
M: total mass of the vehicle
r: external radius of the tires
a: linear acceleration
D: total drag and rolling resistance

The first term, I*u, is the torque used in making the wheels rotate faster. The second, M*r*a, is the torque used to accelerate everything (wheels included) in the direction of movement. The third is the torque used to cancel the drag and rolling resistance.

Another way of writing the equation above is:

T/r = I*u/r + M*a + D

Now the terms are forces. The left side is the force available at the contact patch.

If the tires are not slipping, the angular acceleration and the linear acceleration are related in the following way:

a = u*r

Replacing in the equation and moving things around, we get

T/r - D = (I/r^2 + M)*a

^: denotes exponentiation (r^2 means "r squared")

We can say that the left side is the force available for acceleration. Such force accelerates an "non-rotating equivalent mass" E,

E = I/r^2 + M

Now suppose that we increase the mass of the wheels and tires by an amount X. Both the total mass and the moment of inertia will increase; let's call the new mass M' and the new moment of inertia I'. Obviously,

M' = M + X

What about I'? Well, the moment of inertia of a "punctual mass" [m] (a mass concentrated in a point) at a distance [r] from the axis of rotation is [m*r^2]. That is,
the moment of inertia depends critically on the distance between the mass and the axis of rotation.

In a real wheel+tire combination the mass is distributed in different amounts at different
distances from the center. In order to compute the total moment of inertia we would need to know the mass distribution and use integral calculus. We can do a simpler thing though. We can make the pessimistic assumption that all of the mass increment is
located on the periphery of the tire, that is, at a distance [r] from the center. This assumption is pessimistic because in a real wheel some of the mass will be located closer that [r] and will contribute less to the total momentum (it is not too pessimistic though: most of the mass is located pretty far from the center, if not at the periphery). So now we can compute I',

I' = I + X*r^2

The new "equivalent mass" is,

E' = I'/r^2 + M' = I/r^2 + M + 2*X = E + 2*X

In other words, from the acceleration point of view, the equivalent non-rotating mass increment corresponding to an increment X in rotating mass is - at worst - 2X.

NOTE: After doing some approximations and assumptions about mass distribution in a typical wheel+tire combo, I believe that 1.7X is a better approximation. A 10lb/wheel mass increase would not hurt acceleration worse than carrying RinTinTin.

So in english, I wont run that much slower, I will run faster, I really didn't get anything in your reply. Sorry for stupidity I just like simple answers!

Nice article! :)

I went a tenth or two slower consistently after going from chrome 16's to powedercoated 17's (w/11 inch wide in the rear). This wasnt just one time out either, this was backed up with 10-15 runs on the 16's and 40-50 on the 17's.

BTW- I have still never beat my best time that I got on my 16's with my 17's and I have run alot more times with the 17's.

-James

When I go from my salad shooters with stock 245 tires to my 11" ZR1's with 315 Dunlop 's it sure feels like more than rin tin tin is riding with me. There is a 13 lb difference per wheel and tire combo.

so do you think I should hold on to the stock 16's for the track? I think I should, that scares me because I am going to the track tonight and I just got the Black ZR1s on my car. THanx for the heads up!

hmmm, maybe i'll stick to the salad shooters then :p

NO! Ditch those ugly fawkers. I allways cringe when I see them.

Actually, mine is not a good comparison. The Goodyear 245 is 24# and Dunlop 315 is 35#. A drag radial in 315 is probably a good deal lighter. Here are some wheel and tire weights

http://www.bfranker.badz28.com/fbody/weights.htm

NO! Ditch those ugly fawkers. I allways cringe when I see them.
I agree! they are not very attractive at all......if speed is the concern before the extra inch rim to fill the well, just hold off and buy a set of lightweight race rims...tons of em out there and plenty of them look awsome.

Aside from the extra weight.. those tires on 17" rims dont flex nearly as much as 16" so theres some traction benefits to consider.

I say it Depends on the tire...

17X11's are nice at the track... and deadly with a nice tire setup...

You can launch better on the smaller rim with a bigger tire because the wheel will have more flex.... but if you get a nice sticky compound to stretch that 17X11 wheel base you can seriously hall ass. Slower it...would just be a weight issue... But you'll have a wider wheel base for more grip.


Salad shooters = "vomit"

They were always ugly...

Well I ran my car last night with the ZR1's and my 315 Nitto Drags and lets just say I wanted to run home and put the salad shooters back on. I ran a very dissapointing 13.5 with a 2.02 60' and a trap speed of 99MPH That really sucks! Going from a 12.89 @ 103MPH with a 1.69 60' to the 13.5. I don't know what went wrong, I ran the Nittos @ 16PSI, I heated them up really good in the water box, I launched and killed an 03 Cobra off the line but he ended up pulling ahead. I just am going to run the stock salad shooters with either BFGoodwrich or Mickey Thompson Drag Radials, it makes more sense to stay with a tire made in the USA! I hope switching back will help, if not then there must be something wrong with the LT1. Either way it will be up and running strong soon continuing my goal of 12.5 with no heads, cam, headers, N20!

This may be of interest to some of you guys. This is a dyno graph of a guy that had his rims widened from 9 inches to 11 inches.

Link (http://ws6.com/wheels.htm)

It seems like you loose so little but I felt like I lost so much more, My wheels are tanks so I don't know if I should just keep working on the car with the new wheels on it or just swap the ZR1's with the salad shooters just for the track

Maybe you should try running both at the track and see what kind of differences you get. Could be an interesting experiment..

Dave