Question about Torque and HP gain: Wheel Weight versus Sprung Weight
Mar 12, 2010, 06:48 PM
#46
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**Back From Dead**
Not to beat on a dead horse but I have some additional information that may pertain to this thread indirectly. I took my RAV4 to the track last Friday to test what it runs now vs previously when I had the runflats installed.
Previously I ran a best of 14.4 in the 1/4 mile on my 63lbs Runflat/stock wheel/tire combo.
With the lighter wheel/tire combo I have on now (36lbs), I ran a best of 14.1 in the 1/4 mile with no other changes to the vehicle. I couldn't wait until the track opened up to see real world results because the car felt quicker even though the dyno did not show any additional hp/torque freed up (not created) to the wheels.
So in a nutshell, the car is quicker and a tad faster (trap speed is in the 96mph range vs 94-95 before). Yeah...it's a RAV4 but I get around on many forums and read up. Anything to support or add as information though. That's all for now.
BTW: Mods I have on the SUV is only a custom cold-air intake and changing out of the muffler (still has stock piping). The wheels are lighter if some want to consider this a 'mod'.
Timeslip -->
BTW: It doesn't look like I followed up with the results I had on the dyno with the wheel/tire combination. Here it is --> http://rav4world.com/forums/viewtopi...514&highlight=
It didn't appear that the lighter wheel/tire allowed any freed up hp/torque to the ground. So no difference in before/after dyno results.
Not to beat on a dead horse but I have some additional information that may pertain to this thread indirectly. I took my RAV4 to the track last Friday to test what it runs now vs previously when I had the runflats installed.
Previously I ran a best of 14.4 in the 1/4 mile on my 63lbs Runflat/stock wheel/tire combo.
With the lighter wheel/tire combo I have on now (36lbs), I ran a best of 14.1 in the 1/4 mile with no other changes to the vehicle. I couldn't wait until the track opened up to see real world results because the car felt quicker even though the dyno did not show any additional hp/torque freed up (not created) to the wheels.
So in a nutshell, the car is quicker and a tad faster (trap speed is in the 96mph range vs 94-95 before). Yeah...it's a RAV4 but I get around on many forums and read up. Anything to support or add as information though. That's all for now.
BTW: Mods I have on the SUV is only a custom cold-air intake and changing out of the muffler (still has stock piping). The wheels are lighter if some want to consider this a 'mod'.
Timeslip -->
BTW: It doesn't look like I followed up with the results I had on the dyno with the wheel/tire combination. Here it is --> http://rav4world.com/forums/viewtopi...514&highlight=
It didn't appear that the lighter wheel/tire allowed any freed up hp/torque to the ground. So no difference in before/after dyno results.
Last edited by Myxalplyx; Mar 12, 2010 at 06:57 PM.
Mar 13, 2010, 01:09 AM
#48
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Atco sucks! It was the only track open this early though so..... Maybe I ran a perfect '0' but I doubt it.
Mar 18, 2010, 12:47 PM
#49
Bringing this back up for a reference for people. To quote an Audi Forum:
http://audiforums.com/forum/showpost...57&postcount=4
There is a nice little spreadsheet in that link http://audiforums.com/forum/showpost...57&postcount=4
http://audiforums.com/forum/showpost...57&postcount=4
I found some more information on wheel weights, rotational mass and weight reduction. This website has a spreadsheet with calculations that take EBAINES' formula (thanks again) for rotational mass and acceleration with tires using 3 calculations: one for uniform density (wheel and tire weight is uniform from center to edge of tire,) one for the wheel and tire weights separately, and one assuming more weight at the edge of the tire.
http://www.the-welters.com/racing/rotational.html
Long story short: Using the least advantageous calculation (Wheel and Tire calculated separately,) going from a 23lb. wheel to an 18lb. tire saves you an equivalent 50lbs. of chassis weight.
1 lb. (Wheel) = 2.5 lb. (Chassis)
So at the very least, going from a stock B5 Avus wheel (27lbs.) to a 17lb. wheel would be equivalent to shaving 100 lbs. from the chassis, or 0.1 sec from your 1/4 ET.
http://www.the-welters.com/racing/rotational.html
Long story short: Using the least advantageous calculation (Wheel and Tire calculated separately,) going from a 23lb. wheel to an 18lb. tire saves you an equivalent 50lbs. of chassis weight.
1 lb. (Wheel) = 2.5 lb. (Chassis)
So at the very least, going from a stock B5 Avus wheel (27lbs.) to a 17lb. wheel would be equivalent to shaving 100 lbs. from the chassis, or 0.1 sec from your 1/4 ET.
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