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Discussion Starter · #1 ·
Hi Everyone,

New owner of an '04 MCS and love this awesome resource. My question:

Has anyone measured the performance difference (drag strip, road course or G-Tech) between S-Lite wheels and a lightweight set of 17" wheels? I imagine the difference between the two sets of wheels is 50+ lbs. of unsprung weight - should be a measurable difference.

Thanks!
 

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I've heard one pound of rotational weight is as good as five pounds of chassis weight, when figuring the improvement in acceleration?
 

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RickB said:
I've heard one pound of rotational weight is as good as five pounds of chassis weight, when figuring the improvement in acceleration?

That is essentially true but it varies with the placement of the weight from the rotational axis. Weight taken off the rotating mass farthest from the axis has more impact than the same weight taken off closer to the axis. So it goes to reason that – pound for pound - lighter weight tires will have a better result than the same tires on lighter rims. But that is all academic crap. What matters are the butt dyno results!
 

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cristo
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I figure 1# off the wheels is about 2# off the chassis:

Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).

I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.

From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis

3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.

Some approximations were used (like the precise location of R).

Your results may vary.
 

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cristo
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Apparently, my results may vary as well.
It's been pointed out that I made a mistake in my calculations.

The actual result should be about 1.7# off the chassis should be
equivalent to taking 1# off the wheel/tire in terms of acceleration.
 

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MINI2 Master BLASTER!!!!!
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BLIMEY!!! Someone here is abit clever.

I'm lost if you haven't calculated that ;)


Nah good work Cristo
 
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