Switch from 16" Tires to 15" tires

[91StangLX]

Should I Switch from 16" Tires to 15" tires

I have a 1991 Mustang 5.0 with the 16" 5 star pony wheels with Cooper Cobra 245 55 16 tires. I was told if I switch to a 15" rim and tire I would run better in the quarter mile. Is this true. If so which rims and tires should I use. How much better will it run at the drag. I always thought bigger tires better traction and better times. I will list my mods.

91 Stock 108,000 mile 5.0 motor with forged pistons
GT40P Heads Ported and Polished with 1.90 x 1.60 Valves and a .550 lift Spring Kit
1.6 Proform Roller Rockers
Professional Products Typhoon Intake Manifold
Mac Cold Air Induction
TFS Stage 1 Camshaft
65mm TB
76mm MAS
24lb Injectors
Mac Shorty Headers, Mac Prochamber and Mac Cat back Exhaust
MSD 6AL Ignition with MSD Billet Distributer
MSD 9mm Racing Spark Plug Wires
Iridium Plugs
Mac Underdrive Pullies
Art Carr Street Terminator Transmission with a 2600 Stall convertor
FRPP 3:73 rear gears with 31 spline axles, an Eaton 8.8 Differential
Custom Burned Diablo computer chip
255LPH Fuel Pump
Adj Fuel regulater
Set the timing to 16 degrees advance and the fuel to 37 PSI
Eibach Drag 90/10 shocks, FRPP Progressive rate springs
Eibach upper and lower control arms
Sub Frame connectors
QA1 Tubular K Member
Fiberglass hood with 1.5in cowl
Race Weight with driver is 3120
Price to build about 10K

I average about 30 miles a day driving, I also get 18-20 MPG on the highway and 12-15 MPG in the city. I also have run a best 12.09 @ 114 MPH with this setup and I still have power everything including A/C.

 

[ECU5.0]

a smaller rim will give you a bigger sidewall....and if they are slicks or drag radials the side wall is softer so the surface of the tire on the ground is bigger. if youve ever watched funny cars and whatnot when they launch the rim almost does a quarter rotation before the rubber catches up....dont know what kind of gain you will see but it probably wont be much.

 

[MeenGreenGT]

It's not going to make a difference if you go to a 15" wheel. It all depends on the outer diameter (i.e. 26") of the tire itself. So you would have to a have a taller tire on a 15" wheel as compared to a 16" wheel to make up for the difference (1") of the wheels. You could do the same thing by just getting a taller tire for your ponies.

 

[sleeper89]

It's not going to make a difference if you go to a 15" wheel. It all depends on the outer diameter (i.e. 26") of the tire itself. So you would have to a have a taller tire on a 15" wheel as compared to a 16" wheel to make up for the difference (1") of the wheels. You could do the same thing by just getting a taller tire for your ponies.

that sounds great, and cheaper, in theory....but then you need to consider the car was designed around a 25.6" tire height and simply going to a taller tire will mess things up. it will increase braking distance, throw off your speedo/odo, and it will effectively increase your rear gear ratio. now, by going to the 15" rim and maintaining the stock tire height you get your extra 1" of sidewall AND everything else stays where it should be.

that having been said.... on a street tire i seriously doubt you'll notice any difference as they aren't designed with sidewall flex in mind. if you were doing this on slicks it might be worthwhile, maybe even dr's but not for everyday radials. JMHO.

-steve

 

[ninety15.0]

i honestly dont think you will see much of a difference at all. You are makin enough power that you could smoke a 15" tire just as much as a 16". if u really wanna get your ET down a little more i would invest in some real slicks that you only use at the track. Maybe some et streets that you can run on some 15" weld wheels. there isnt a cheap answer, and just making your tire taller on the rim you have right now is not the right answer. by doing that u mess up speedo and most importantly your gear ratio. You would def need some 4.10's of higher if you went with a 27 inch tire. get some slicks with rims and just put em on when u go to the track. good luck man