Re: DYNO RESULTS -- STOCK vs AFTERMARKET WHEELS

[Benjamin Harder <vwtype53@yahoo.com>]

Jay,
 This is some good info...thanks for the homework!

I just have to know...what were the actual results?
Is your 16v still *healthy* or did you see a decline in results 
since your last dyno runs?  

Ben H.


--- 16v Jason <jason@scirocco.org> wrote:
> (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  
> 
> --
> Email problems to: scirocco-l-probs@scirocco.org  To unsubscibe send
> "unsubscribe scirocco-l" in the message to majordomo@scirocco.org
> 
> 

__________________________________________________
Do You Yahoo!?
Send online invitations with Yahoo! Invites.
http://invites.yahoo.com

--
Email problems to: scirocco-l-probs@scirocco.org  To unsubscibe send
"unsubscribe scirocco-l" in the message to majordomo@scirocco.org