[GarrettF]

On the way home froma a quasi, mini meet this evening in the philly area, Straz 330Ci and my slef found oursleves on our way home on the NJ Turnpike with almost no traffic... we did 2 runs from about 60 mph to roughly 100 mph..we both started side by side in 3rd gear and took off...needless to say i pulled on him every time through 3rd and 4th gear...

He is modded perfomance wise and i am not. He has Rogue pullies and gruppeM and SSK
all i got performance wise is an SSK

the reason i think i pulle don him is the fact that he had 19inch ACS wheels that were slowing him down as i was on my stock m68's..thast the only explanation i have for it..if any one else can thinkof something please chime in becasue right now thats all i got

 

[m3man]

not all production engines make the same hp or torque.

 

[ininfinitum]

I'm sure the 19s significantly slowed him down though. How much is the weight difference between M68s and 19'' Type IIIs?

 

[a s u r a 0 s 9]

m3man is correct....but

i'm sure the added weight on the 19's played a role too

 

[WarSong]

i go with your 19" wheel theory

 

[dboffa]

Just curious - what are the gear ratios for the 6-speeds?
And my guess is wheels made a big difference. Rotational mass can have a huge effect on performance. This is why I tell myself I don't need 19s (aside from the fact that my a$$ is broke! ).

 

[325seeeye]

That is likely the cause.........It is from larger overall tire size effectively making a lower gear ratio and inertia.

Check out the Chysler Crossfire and Mercedes Benz CLK. Exact same engine, exact same drivetrain, the Crossfire is 100 or so lbs lighter and the M-B is faster from stoplight to top speed. Some is aerodynamics sure, but the tire size and rotational mass overcome the 100 lb weight savings on the Crossfire, especially from 0-60 when air drag is not much a factor.

Something for all fanatics here (who mostly) worry about stoplight drag racing. Physics will kill you every time.

 

[dboffa]

Isn't there a formula for converting unsprung weight differences to actual weight differences? Like I know that according to my330i.com, each pound of weight saved in the flywheel is equal to about 10 pounds or so of car weight; so a ltw flywheel that saves 7 pounds is like taking 70 pounds off your car.
What's the ratio for wheel weights?

 

[sfzBimmer2]

The rule of thumb for unsprung weight (wheels/tires) is that one pound of unsprung weight equals 8 pounds of sprung weight. That's why forged wheels are the only way to roll!

 

[dboffa]

F*ck forged wheels...I'm going with some balsa wood and styrofoam!

 

[325seeeye]

BTW peeps, there is a big fat difference between unsprung weight and rolling inertia. Even if your 19's weight eactly the same as a 17", the 19's are going to have more inertia to overcome. If you are counting ounces, then bigger is not better, there is always a compromise between sidewall stiffness (brand dependant/tire size dependant) and wheel size. It is always your choice on the compromise, so there is no definate/eact answer on the best.

There is a reason why race cars dont have 26" wheels with 335/15 ZR26 tires, and wheel inertia affects their decision. Larger wheels (ie more rolling mass) also affect braking performance as well as acceleration. Always trying to educate!:thumbup:

 

[a s u r a 0 s 9]

325seeeye the edumacator!

 

[m3man]

BTW peeps, there is a big fat difference between unsprung weight and rolling inertia. Even if your 19's weight eactly the same as a 17", the 19's are going to have more inertia to overcome. If you are counting ounces, then bigger is not better, there is always a compromise between sidewall stiffness (brand dependant/tire size dependant) and wheel size. It is always your choice on the compromise, so there is no definate/eact answer on the best.

There is a reason why race cars dont have 26" wheels with 335/15 ZR26 tires, and wheel inertia affects their decision. Larger wheels (ie more rolling mass) also affect braking performance as well as acceleration. Always trying to educate!:thumbup:

If we want to get technical, it is called rotational inertia.

The moment of inertia (I) is equal to the sum of m r^2 (assuming a wheel is a cylindrical shell, which it's not), so two wheels of equal mass, one 17 inches and one 19 inches, differ by approximately 25% in their moment of inertia.

There is no one formula for unsprung weight. Different segments of your suspension are different percentages sprung and unsprung depending on their location relative to pivot points and the spring.

 

[e46shift]

dead hookers in Straz's trunk gave you the weight advantage:dunno:

 

[GarrettF]

dead hookers in Straz's trunk gave you the weight advantage:dunno:

Actually i had 50lbs of clean laundry and my new(used) 3.15 rear diff in the trunk..i think he dropped the hookers in brendans car..we both had almost no gas as well so if anything he had the weight advantage

 

[Straz M3]

How did I know you were gonna post this? I want a rematch. I couldnt believe that you pulled on me. The first time I shifted at 5k at 3rd which was a huge mistake. I dont know...Im getting my 19s off tomorrow but I didnt think they played that much of a difference. Now I am pissed at my car...

 

[GarrettF]

hey, at least i didnt post the wned: i am really curious to know how that happened that was the only reason for the post..oh and BTW... wned: :lmao:

 

[Straz M3]

Thats it...definately a rematch...I think it was a little driver error too...When we slowed down to like 55 I downshifted into 2nd and tried to go that way but that didnt work either....I want a rematch...hit me up on aim....straz330

 

[archspeed]

Wheel definitely played a role. I used to run 17 inchers on my Integra.

Now I run 16 inch rims (14.5 lbs) that are lighter than my stock 15 inchers (16.0 lbs)!

 

[Straz M3]

not all production engines make the same hp or torque.

If thats the case Im going to the dealer tomorrow and trading my "weak" 330 in for an M3...:ben: