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#1
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16" to 19" Wheels Equal Loss of HP
Got a free dyno run at Verocious Motorsports this past weekend. Got to dyno 2nd from a raffle drawing and I had the SVX there.
I had a heavy 19" wheel/tire combo on. This was the same dyno but moved to a different location. At any rate, I got a paper hand out with the two dyno runs on it (that I can not find right now). Hp was around 165hp and torque was around 155lb-ft. So my hp was 10hp less and 20ft-lbs torque less than my previous run with the 16" RX7 wheel/tire combo. If you didn't know and you don't want to be slow, Lower rotational mass so you can be fast. Just a quick heads up for those that want to be blinging. The 19's will stay on but will come off only when dyno and track testing. Too lazy to look for the paper now but when I find it, I'll scan it and post up. L8Rs..
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Kevin Thomas 1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph 1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph 1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph ***R.I.P*** 2010 RAV4 AWD Sport (13.717 @ 99.19mph ) 2015 Honda Fit LX CVT (15.2 @ 90mph) |
#2
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size
I think it had more to do with the weight of the wheel/tire combo than the actual sizes. (even though they usually go hand in hand.)
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#3
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What is your weight ratio to your old 16" and newer 19"?
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-SSSVX 92 LS-L TEAL since Aug '01 92 LS-L YELLOW since Mar '05 |
#4
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The weight of the wheels has no affect on a reading in respect of HP at the wheels. Acceleration is the only factor which will change.
Any variation in rolling diameter will have a profound affect relative to HP measured/delivered at a given engine RPM, due to the change in overall gear ratio. All that said, wheel dyno measurements taken at different times/place, by different operators, etc, etc, can not be relied on.
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Trevor, New Zealand. As a child, on cold mornings I gladly stood in cowpats to warm my bare feet, but I detest bull$hit! |
#5
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Quote:
i disagree - i added lightweight 10" wheels and gained 50hp.
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Alan 1987 928 S4 (Black) SOLD! 1997 SVX LSi (Ebony) SOLD! 2005 Legacy GT (Silver) [Cobb Stg 2+] SOLD! 1987 928 S4 (Black) SOLD! 2005 Forester XT Premium (Crystal Gray Metallic) SOLD! 2008 Lancer Evolution X MR (Apex Silver) [Cobb Stg 1+] 2015 Outlander Sport 2.4GT AWD (Mercury Gray) 2013 G37xS (Obsidian Black) |
#6
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Quote:
I posted about it in this thread--> http://www.subaru-svx.net/forum/showthread.php?t=31601
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Kevin Thomas 1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph 1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph 1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph ***R.I.P*** 2010 RAV4 AWD Sport (13.717 @ 99.19mph ) 2015 Honda Fit LX CVT (15.2 @ 90mph) |
#7
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Quote:
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Trevor, New Zealand. As a child, on cold mornings I gladly stood in cowpats to warm my bare feet, but I detest bull$hit! |
#8
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Measured static, a lighter, larger diameter wheel can be harder to accelerate than a heavier, smaller diameter wheel. It's all about MOMENT OF INERTIA.
Torque is simply changed via leverage - in our case, gear ratios. In our case, if the tires are identical in diameter, the dyno should not notice the difference. Consider: at the crank, we get X torque. After the tranny, we get Y. Get to the axle, it's Z. Factor in the wheel diameter, and that's your result. Changes in gearing become cancelled by engine speed; this is why second gear and fourth gear (say) don't actually result in different torque readings. So, your torque is the same with any tires with the same diameter. This defies your claim, so let's prove it. If a car is sitting on a pair of 2700 lb. drums, and is responsible for accelerating (among other things) a set of tires weighing 50 lbs or 37 lbs, you can do a little bit of math to see how irrelevant the tires' weight is. INCORRECT MATH: (2700x2) + (50x4) = 5600 lbs (2700x2) + (37x4) = 5548 lbs Doing it wrong, you're looking at less than 1% difference in weight. But this situation isn't static - it's rotational! Moment of inertia must be considered. I have no idea where the moments of inertia are measured on either set of tires, and certainly not the pair of 2700 lb drums, but I can guarantee that the drums have a tremendous increase in their influence in our equations after the moments of inertia are factored in, making 54 lbs worth of wheels about as significant as a moth fart in a tsumani. Now, in a car's linear acceleration (i.e. quarter mile), there will be a notable change... but your torque is still the same.
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Disclaimer: The above post is on the internet. Last edited by LetItSnow; 07-14-2007 at 11:36 AM. |
#9
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<Mr. Obvious>
to keep it simple, power isn't the only thing to affect speed/acceleration. weight, aerodynamics, etc. come into play. my lightweight pulley adds no power, but it gets the turbo spooled up quicker, and that gets you moving faster, but it adds no additional power. same with adding or reducing weight. </Mr. O>
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Alan 1987 928 S4 (Black) SOLD! 1997 SVX LSi (Ebony) SOLD! 2005 Legacy GT (Silver) [Cobb Stg 2+] SOLD! 1987 928 S4 (Black) SOLD! 2005 Forester XT Premium (Crystal Gray Metallic) SOLD! 2008 Lancer Evolution X MR (Apex Silver) [Cobb Stg 1+] 2015 Outlander Sport 2.4GT AWD (Mercury Gray) 2013 G37xS (Obsidian Black) |
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