OK, I know there are many debates over effect of lighter wheels and measurement in the butt dyno but I just have to share my personal experience and post a question.

I have several mods (see sig), and a variety of wheels laying around.
What the car came with: S-lites w/ GY Eagle RSA 205/45R17 46.5lbs 24"
O.Z. Prodrive w/ PZero 205/45R17 35lbs. 24"
Kosei Racing Seneka's w/ Mich PilotSX 215/45R16 35lbs 23.5"

The wieghts are using bathroom scale and the inches are the total diameter.

Thanks to Alex at Tire Rack I got the hardware I needed to put the Koseis on the car two days ago.

The big thing I notice is how much easier it is to pull out. The car doesn't seem to bog off-idle NEARLY as badly! (which seemed to be common in every one I drove)

The real performance difference (on the mini) I cannot comment on because the wheels and tires have been sitting since '01 and are too hard to grip under hard accelleration. I can say that on my '97 Integra GSR, which they were on originally, my GTech testing and butt dyno (which is a highly tuned scientific measurement instrument certified by NIST) these wheels un-did the horse power gain that I got from the Intake and Exhaust upgrade. That car had very light (~25lbs.) 15" wheels from the factory that were about .5 inches shorter than the Koseis.

I really want to install the O.Z. Wheels (they're white, which I love) but 2-3 of the tires need to be replaced.

So now for a question for the math and automobile equation guru's: What is the net effect on of the .5" diameter on the gear ratio? And how much does this play a part in the driveability and performance change?

I would kick myself if I bought new tires for the O.Z's and the performance was closer to the S-lites than the Koseis.

Peace, no flames please, I'm in my bathrobe.
--Sean

 

Ya lost me there a bit. You liked the koseis, lightest wheel/tire combo, the best? And which combo made you feel like you lost power???

 

The circumfrence of a circle is proportional to radius (or diameter). So if you go from X to X+Y in diameter, the effective change in final drive ratio is X/(X+Y) for a half inch chang on a two foot wheel, this is about 2%. Our cars have ~150 ft-lb of torque (nice round number to work with) so that's like loosing 3 ft-lbs. What killed you the last time, was going from a 15" to a 17" wheel. If the tire height was the same, and you went from a 22" overall wheel hight to 24", that's a bit less than 10%. Now your talking some real differences in percieved torque, but you get to go faster in each gear....

Matt

 

Hang on.. trying to follow...

we should be taking about overall diameter of the wheel/tire combination. Just because you goto a smaller rim, you should (ideally) goto a taller sidewall tire to maintain a similar overall diamter.

example:

Stock 17 rim 205/45/17 tire Overall Diameter - 24.3"
16 rim 195/55/16 tire " '" - 24.4"

So to clarify for my foggy mind... The actual discussion here is goign to a shorter wheel and smaller diameter tire.. right?

Example 15" rim 205/50/15 tire Overall Diameter - 23.1"

Now i forgot the question...

 

Going from the S-lites (17" Wheel, 46.7 lbs. and Tire diameter of 24") to the Koseis (16" Wheel 35 lbs. and Tire diameter of 24") noticably improved driveability (percieved improvement in torgue when pulling out normally).

The wheels I really want to run are O.Z's (17" 36 lbs. and Tire diameter of 24") but to try them I need to purchase at least two tires. Before I spend the money I was trying to figure out if

a. they will be nearly as good as the Koseis (since there is only 1 lbs difference in weight). Or if the difference in rim or overall tire diameter has a significant impact.

b. they will be more like the S-lites because of the wheel and / or tire diameter

--Sean

 

In 1998 I noticed a loss in power when I originally installed the Kosies on my '97 Integra which had 15" stock wheels that weighed about 25lbs.

On the Mini the Koseis are an improvement over the stock S-Lites.

 

Anything and everything is an improvement over the boat anchor S-lites, even the ultra heavy JCW 18" R95s...

 

Why? because everyone else says so? Because your speedometer might be off by couple percent?

Personally, I feel differently. In a car that's overgeared, like the mini, any chance to lower the gear ratio is a good thing - especially if you can do it without resorting to a super low-profile tire.

 

Well sice you asked, I made the statement to discuss similar size tire/wheel packages to provide an apples-to-apples comparison between 15" and 17" rims or heavy vs light rims. Not to discuss the gearing difference that one provides.

I agree that track/auto-X is a great place for the lower gearing an smaller diameter provides, that's why my auto-x wheels are 15" BBS with 205/50-15 rubber... BUT if you've ever had the fun of dodging debris on Boston streets, you'll understand that 1/2" difference in clearance is a big thing.

 

What do you mean by overgeared? Do you mean geared too tall like most BMWs are? If you do, no way. The MINI S eats gas at triple digit speeds 'cause the motor is spinning too fast. The MINI S is a pig (on gas) because it's not geared tall enough. It might be geared well for double digit American highways (like I-40), but not for triple digit Autobahns here in Germany. I keep trying to put it in 7th, but there ain't one... :smile:

Cheers!

 

good point, mate.