Re: DYNO RESULTS -- STOCK vs AFTERMARKET WHEELS

["scirokn81" <scirokn81@email.msn.com>]

Jason,
Great to see tests like this, wish more people would list this kind of
technical data. Thanks 8).
Only one problem. Since both wheels weigh relatively the same, 19-21 lb. (am
I right on this?) I wouldn't have expected any difference. A good test would
have been to run the teardrops (or TSW's) against a much lighter set of
wheels like the Panasports, Revolutions, or ??? that would weigh in at 10-15
lbs. A 5-10 lb difference might show up on a back to back dyno run, but I
highly doubt a 2 lb difference would.
Thanks again for the post, these are the ones I look most forward to
reading.

Randy B
81 Cosmos Scirocco S - future project
81 Mars Scirocco S - tt 1847cc 8V
87 gold Scirocco 16V - soon to be a 2.0



> (2nd attempt at posting this message)
>
>
> Hey all,
> There was a local dyno day sponsored by the RX-7 club in my area.. $65 for
> 4 runs-- so I talked to the organizers and asked if I could do 2 runs
> instead, but swap my 15" TSW Hockenheims for the 14" stock teardrops while
> I was on the dyno.  I figured it would finally put an end to the mystery
of
> how much power the wheels robbed.
>
> I haven't weighed either of the wheel & tire combos, but the consensus
> among guys there was that the Hocks are slightly heavier than the
> teardrops.  In addition, because of the larger wheel size, the weight is
> distributed further from the axle, and therefore, the hypothesis was that
> running larger wheels would (significantly) reduce effective power output
> of my engine.
>
> From a physics point of view, the effect of greater wheel weight would be
> present the faster the wheel was accelerating.  Obviously, in 4th gear
(the
> gear of choice for dyno runs because of traction), acceleration is not as
> brisk as it would be in, say, 1st gear.  Therefore, I was expecting the
> power loss to be less than what it might be in lower gears.  I expected
> there to be little difference at, say, 1200rpm, when the wheels are barely
> being accelerated, and more of a difference at the torque peak, when the
> wheels are being accelerated the most quickly.
>
> I had the dyno operator start the test at 1000rpm in 4th gear (usually
> they start between 2000 and 2500), and continue until the rev limiter
> kicked in, no matter what the tach said.  So, the results for both runs
are
> from 1000rpm to 7300rpm.  I haven't yet scanned the results (my scanner's
> dead), but I will do so as soon as possible.
>
> THE RESULTS:
> There was *no* appreciable power loss anywhere in the rev range using the
> heavier wheels.  At lower rpms (and therefore, speeds), the two curves
were
> almost exactly the same.  As the revs increased, I expected the 15s to
> effectively lose power when compared to the 14s, but that wasn't the
> case.  The 15s actually put *more* power to the ground.  Why?
>
> Well, the dyno results show a vibration in the wheels caused by an
> unbalance in the tires.  Of course, those vibrations are speed-dependent,
> and lasted from 3000-4000rpm and then again from 5000-6000rpm.  Betwen
4000
> and 5000rpm, when the curve was smooth, the 14s put less power to the
> ground than did the 15s.  Why?  Again, most likely because of
> inbalance.  The difference, however, (between 1 and 2hp) is statistically
> insignificant, as back-to-back dyno runs can show differences of 2-3hp.
>
> Therefore, the conclusion is that for my tire & wheel combination, there
> should be no appreciable difference in power to the ground using either
the
> 14s or the 15s.  The biggest factor in this test was probably the
balancing
> of wheels.  So, rather than worrying about losing power by using larger
> wheels, you'll gain more by having your wheels balanced.
>
> Therefore, the handling benefits of using larger wheels is not compromised
> by their weight (at least at the 15" level).  Of course, common sense
> dictates that 17" wheels would be even heavier than 15s, and may show a
> significant power loss...
>
> Now, if I could find my Physics books and get the formula for the force
> required to turn different weights, we could do a theoretical analysis...
> but for the time being, I'm satisfied in knowing that I'm not losing any
> power by running 15" wheels.
>
> Jason
>
>
>
> ----------
> 1987 Scirocco 16v
> 1989 Mercedes 190E Sport Euro
>
>
> http://members.aol.com/rocco16v
>
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