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CEG\'er
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Im getting ready to dyno my newly acquired csvt once I get a new computer/chip and the pro-flow 75mm MAF. It has 16" tires on it now with blizzaks, which im not too keen on keeping on the car much longer or dynoing with, and 17" rims with firehawk sz50s on them. Any thought on how much power is lost if I dyno on the 17s?
00 SVT Contour: SHM LT headers, LSD, Spec Stg 3...dyno:190.3whp sold 02/04
04 Subaru Baja Turbo 5-spd
00 Camaro SS 393cid: 510rwhp/469rwtq, 11.16 @ 124.95(hit 1-2 limiter)
www.erikz.org
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Hard-core CEG'er
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you don;t lose power (espescially if the after market rims are lighter then the ones you have) but it may feel like you chaged the gear ration a bit....putting bigger are or small rims has a non direct effect on your drive train, not your HP or TQ.
I think you might stay the same...If there heavier than your stock then I would say you might "lose" power because they are larger, and heavier so it would take more force to complete one revolution.
Roz
3.0 SVT hybrid...all the fixens...Track/Race ready very soon!!!!!! 20,000 + miles
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Back In Black
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Back In Black
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For every inch increase in diameter you increase unsprung weight by approx. 10lbs... per wheel. whp loss will happen because the parasitic drivetrain loss increases. As for specific WHP loss... I'm not really sure if there is a specific formula to figure it out.
-Mark
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I didn't think it made a difference how big you went, as long as the wheel/tire weighs the same, wont it put the same power to the ground? I can see that maybe with a bigger wheel the weight is concentrated more towards the outside of the wheel, requiring more torque to spin it. but I would think that would be negligable. Just curious with the physics of your statement. 
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Joined: May 2000
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I have no life
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I have no life
Joined: May 2000
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Kenny and I were also wondering about this as well. He went to 17" Kosei K-1's that weigh about 5 lbs. a piece less than a stck wheel. I guess we'll know in May.
-'96 SE MTX 3L
-'98 SVT 1,173 of 6,535
-'05 Mazda 6s, loaded, g/f's ride
-Need a 96-00 manual on CD? PM or email me
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CEG\'er
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My thinking, and from what I had seen previously, was that stepping up in size creates additional rotational loss on the drivetrain, but now I am wondering if that makes a difference if the overall wheel weight/height/width are roughly the same. Hmmm...
00 SVT Contour: SHM LT headers, LSD, Spec Stg 3...dyno:190.3whp sold 02/04
04 Subaru Baja Turbo 5-spd
00 Camaro SS 393cid: 510rwhp/469rwtq, 11.16 @ 124.95(hit 1-2 limiter)
www.erikz.org
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Veteran CEG\'er
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Veteran CEG\'er
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None, HP is a function of the engine not the wheels. The dyno might tell you otherwise, but your wheels cannot rob you of horsepower.
Sold 1998 Contour LX 13.868 sec 1/4 mile time.
Two years of rental cars, seriously.
Holding out for 07 Cobra Mustang.
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CEG\'er
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Originally posted by HoosierContour:
None, HP is a function of the engine not the wheels. The dyno might tell you otherwise, but your wheels cannot rob you of horsepower.
No no I understand that, but the dyno measures what your engine is putting down to the ground, through the drivetrain. It is a truer measure of useful power than simply what your engine alone is producing. I recognize the fact that flywheel hp is not affected. I am trying to get a handle on both, and understand how much loss at the wheels I might be looking at.
00 SVT Contour: SHM LT headers, LSD, Spec Stg 3...dyno:190.3whp sold 02/04
04 Subaru Baja Turbo 5-spd
00 Camaro SS 393cid: 510rwhp/469rwtq, 11.16 @ 124.95(hit 1-2 limiter)
www.erikz.org
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I say there is nothing better than trial and error....try it then report back to us...id likt to know too.
Roz
3.0 SVT hybrid...all the fixens...Track/Race ready very soon!!!!!! 20,000 + miles
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Hard-core CEG'er
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Hard-core CEG'er
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Originally posted by HoosierContour:
None, HP is a function of the engine not the wheels. The dyno might tell you otherwise, but your wheels cannot rob you of horsepower.
You are very much incorrect here.
Rim weight and diameter do very much affect the power put to the ground.
Larger diameter rims do so by making the weight you are trying to accelerate a larger diameter weight. This has a very pronounced effect on power production.
That 10lbs unsprung (which is ~40lbs! regular weight for real world driving & handling) per 1" is a good general rule of thumb.
Also more weight in general works the same way to reduce useable power. Then remember to factor in the weight increase on top of the larger diameter.
People may seem to like the bling bling looks of large heavy rims (or worse heavier chromed units) but the performance loss they incur is like shooting yourself in the foot twice. Ugly and performance robbing.
You can probably go with a set of ultra lightweight 17's over the stock 16" and come out fairly close in the power department, but otherwise you are going to take a major hit in performance. I mean a lot more then you can see on a static dyno too!
2000 SVT #674
13.47 @ 102 - All Motor!
It was not broke; Yet I fixed it anyway.
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