wadadlig: i wasnt responding to you directly. there was about a full page of talk blaming the tires. yes, it play a part, but 1" doesnt play the part of 30hp. if the wheels are lighter, as he claims, then the distance vs weight combination works TO his benifit, not against it. in your example, the brake rotors are also spinning....and they were added as well. im sure that was the focus, as lame aftermarket rotors can be made to weight a ton =)

i was assuming the rim was a light weight rim. IE: my 14lb wheels do move the majority of the weight out 1/2", but also drop the weight by about 35-40%. his rims, according to him, are 2lbs ligher. not much. but at this weight, the rim material is probably lighter than the rubber, which is an additional savings. we will ignore this and just look at the rim.

math time

F=ma, this works for angular acceleration, too. but a=rt in angular acceleration, so:
a=rt (t = tangental acceleration, r = distance from axis)
and, we can then say the following about force:
F=mrt

lets shoot for a tangental acceleration of 30ft/sec (IE: 2.0 60' time. pretty good). we will then find the amount of force needed to spin the wheel 30f/sec at differents weights/lengths. i know, the units arent uniform, but it really doesnt matter that much. its just multiplication

stock wheels: my guesses
m = 24lbs
r = 8inch

F = 30ft/s * 24lbs * 8in
F = 5760
so we need 5760 'forces' to move this wheel 30ft/s

my new wheels:
m = 14lbs
r = 8.5
F = 30ft/s * 14lbs * 8.5in
F = 3570

even though the mass is further away (for the most part, i know, i would have to integrate over the entire lenght of the wheel and tire at each sectional weight all the way though...i dont have the data do to this, but it gets the idea across) it shows tha the distance is so small and the diff in weight so great that the distance barely plays a factor in performance.

he said his tires are lighter than stock by 2lbs, so lets try:
m = 22lbs
r = 8.5in
F = 30ft/s * 22lbs * 8.5in
F = 5610
Should still take a bit less force (2%) for him (with this rough estimate). As I said, a bit more goes into it than this, but the point is that the difference is so small that it doesnt matter. wheels did not make the difference on the dyno run.

 

good physics there

 

Check out some OZracing Supperleggara's .... like 15.1 lbs. for 17 inches

 

blk-majik, they're only a pound lighter. so if i use your equation:
m = 23lbs
r = 8.5in
F = 30ft/s * 23lbs * 8.5in
F = 5864

so i guess it still takes more force to move the wheels even if they're somewhat lighter, just because the weight is further out.

 

Well my numbers were horrible i expected much higher. i ran 138.53 hp and 146.54 tq that was without the piggy, and now with it i run 149.32 hp and 156.54 tq. now i don't understand why my numbers are the way they are. it was at 59.90 F and humidity was 22% plus i got threw traveling about 70miles to get a dyno run but he gave it about a 2 min each run than the last one he gave about 5 mins to cool with fan and thats the highest i have gotten. I used dyno jet by the way. he ran mine starting from 3 gear so if i did a 1/4 i think ill prob. run about mid 15s

 

i was talking to a guy at work that does anything and everything with cars (and has his whole life) and he basically confirmed what you guys have been saying. the larger wheel (even if it's a little lighter) will have a negative effect on performance because the weight is further out from the center. so, it takes more effort to turn the wheels. after the local car show this weekend, i guess it's back to the stock wheels for a while until i get it dyno'd again. so if you're wanting performance instead of looks, just stick with 16's. i guess i'll just get some better tires for the stock wheels now.

 

just get rrm turbo to offset the power loss. lol

 

yeah really. if i had the money, i'd already have it. maybe one day, hopefully.

 

I didn't read everything, but...

Metal weighs more than rubber. There is more metal from the center of the wheel. Centrifical force is multiplied exponetially.

Example.

16" rim 22 lbs

18" rim 17 lbs

I give you my full assurance that the 16" will have less drivetrain loss because the metal is all closer to the hub.

 

yeah, that's basically what everyone else has said. i guess i'll just use the 18's for show and the 16's for go (well, once i get better tires on the stock wheels anyway).

 

Do you have an auto?

 

the "exotic" explantion makes my head hurt

KISS (keep it simple stupid):

a longer pry bar works better because more force is being levered into one point

the converse is true.. to lever metal that is further away from the middle of the wheel takes more power.. there is no freaking way to cheat physics

a pound moved an inch away might seem small to you.. but it probably takes power still

-joe

 

With all of this said, Does anyone know if there are 15 inch lightweight wheels that will fit around our calipers? On our stock set up it looks like there isn't room to go smaller but I don't know how thick the outer part of the rim is on the inside.

 

naw i have a manual

 

15" wheels fit, I'm using steelies in that diameter now for winter.