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Man this forum is dropping like mad lately... :(
Quick summary. Some 6 owners have done back to back comparisons on the track comparing 18x8 rx8 rims (with stock tires), vs 16x8 rx7 rims (14 lbs less a corner) with similar diameter tires...and have dropped as much as 0.5 off their 1/4 time. In almost all the situations, the rx7 wheels were usually in a condition which wasn't favorable for good results, but regardless, a significantly acceleration difference was noted. The performance benefits from reducing unsprung weight and rotational inertia are far greater then they seem on paper. This is of course completely ignoring the additional benefits to braking and handling which results from dropping unsprung weight. Articles Size Matters http://www.wam.umd.edu/~greghess/sizematters.pdf Finding Free Power http://www.nerocam.com/SCC_TAPnew.asp Bicycles and Unsprung Weight http://www.softride.com/bike/cornering.pdf Fixing the 350Z: Why Lawyers Want Everyone to Run Staggered Setups http://www.sportcompactcarweb.com/pr.../0404scc_350z/ Picking the Right Wheels For You http://grmotorsports.com/news/012005...ls-for-you.php Big Wheels, Big Trouble? http://money.cnn.com/2004/12/15/pf/a...ay_big_wheels/ Wheel Weights Can Effect Your Vehicles Show and Go http://www.tirerack.com/wheels/tech/...el_weights.jsp Automobile Ride, Handling, and Suspension Design http://www.rqriley.com/suspensn.htm Do Wheels Cost More than Money? http://www.turbomagazine.com/tech/0106tur_wheels/ Threads How much does wheel weight really matter? http://corner-carvers.com/forums/sho...ung+and+weight Are 18" wheels and tires bling bling or a performance advantage? http://corner-carvers.com/forums/sho...eel+and+weight How much will 17" wheels slow you down http://www.sccaforums.com/cgi-bin/ul...i/topic/7/303? Effect of Lighter Wheels? http://www.sccaforums.com/cgi-bin/ul...i/topic/7/301? Bigger Wheels and Tires? http://www.sccaforums.com/ubb/ultima...c/7/863#000004 Rotational Advice http://forum.miata.net/ubb/ultimateb...3;t=002795;p=1 If larger wheels are bad...why do sports cars have them?... http://forum.miata.net/cgi-bin/ultim...c;f=3;t=005169 Wheel Weight, Who Cares? http://forum.miata.net/cgi-bin/ultim...c;f=3;t=007412 1 Lb of unsprung weight =?? Static weight http://forum.miata.net/cgi-bin/ultim...=3;t=006390;p= Wheel Weights....Can They Make a Difference? http://forum.miata.net/ubb/ultimateb...=010655#000000 33.5 lbs/Corner Too Heavy?? http://forum.miata.net/ubb/ultimateb...=010570#000002 Don't Small Wheels Mean Heavier Tires? http://forum.miata.net/ubb/ultimateb...=010479#000009 Whats With Huge Wheels? http://forum.miata.net/ubb/ultimateb...=010436#000002 18" Wheels too big? Take a Look! http://forum.miata.net/ubb/ultimateb...=008412#000031 I'm Finally Completely Convinced About Lighter Wheels and Tires http://forum.miata.net/ubb/ultimateb...=010379#000000 Do Wider Tires REALLY Provide More Traction? http://forum.miata.net/ubb/ultimateb...=010206#000034 Unsprung Weight 101 http://forum.miata.net/ubb/ultimateb...=010206#000034 Unsprung Weight Effects Performance? http://forum.miata.net/cgi-bin/ultim...c;f=3;t=008986 WO! The Joy of Lightweight Wheels!!!! http://forum.miata.net/ubb/ultimateb...=010108#000033 0-60 simplified wheel physics and garfield's wheel test http://www.mini2.com/forum/showthrea...730#post279748 Spreadsheet blows lid off lightweight wheel debate!!! http://www.mini2.com/forum/showthrea...threadid=14738 Lightweight Wheels http://www.mini2.com/forum/showthrea...nsprung+weight In Defense of 17's http://www.mini2.com/forum/showthrea...nsprung+weight 16 or 17 Inch Wheels? http://www.mini2.com/forum/showthrea...t=wheel+weight 18 or 19 Inch Wheels? http://www.mini2.com/forum/showthrea...t=wheel+weight Effects of Wheel Size on Acceleration (TimeSlips) http://forum.mazda6tech.com/viewtopi...t=1762&start=0 6tech Article http://www.mazda6tech.com/index.php?...d=16&Itemid=32 Wheel Weight and Performance http://forum.mazda6tech.com/viewtopi...er=asc&start=0 Some Wheel Weight Sites http://www.wheelweights.net http://www.wheelspecs.com http://www.miata.net/garage/garagetires.html |
Right on crossbow...and WOW...that's one big list, lol
Also, not to question the weight...but I thought it was agreed that the rims on our 8's came in at 22.5lbs? What happened to that number? Lighter rims is something I was looking to do in the future, because as Crossbow said, the real world difference is more significant than it looks on paper. 17lbs is my goal to keep the rims affordable...I just can't see myself spending over $500 per rim...heck, $200-300 per rim is enough for me. |
Originally Posted by Sputnik
[/b] I've never heard of a ratio THAT high. The highest that I've ever heard is 4:1.
And you're calculations don't take tire weight into consideration (whether higher or lower). [/b] That's irrelevant. ---jps Anyone? Anyone? It's 2:1. And that applies only to the mass at the edge of the wheel. Nearer the hub the ratio is less. Center of hub is 1:1. |
The formula's don't work. Track results tend to report much better results then you get by calculating.
Check out one of the starter articles, by sports car compact magazine. http://www.nerocam.com/SCC_TAPnew.asp (This is also a hilarous article to read, and one of SCC's best) Step 1: Baseline Curb Weight: 2,762 lbs 1/4 Mile:16.3 @ 84.0 mph 60-foot:2.9 sec. 0-60 mph:8.6 sec. Step 2: 15-inch Wheels Curb Weight:2,707 lbs 1/4 Mile:16.0 @ 85.5 mph 60-foot:2.8 sec. 0-60 mph: 8.1 sec. By the formula calculations it would seem that they'd only have about 104 lb weight loss...but the results indicate closer to a 200 lb static weight loss. |
Originally Posted by MrWigggles
Alright I did the math anyway and it is about what mentioned earlier.
Assuming that all weight reduced from a using a lighter wheel is coming from the outer rim of the wheel (i.e. reduces moment of inertia the most); for an 18inch wheel with 26 inch tires it works out that each pound you lose from the wheel is equivalent to 1.5 pounds of car weight. So for a 3000 pound car, 4 wheels X 1.5 lbs eq./wheel = 6 lbs equivalent, and with HP/lb being the key to performance. 3000lb / 2994lb eq = X HP eq / 250HP Solving for X gives 250.5HP equivalent or 0.5HP increase equivalent by using a 1lb lighter wheel, best-case. The reason I say "best-case" is my analysis assumes that the weight is removed from the outer rim of the wheel and that the wheels are the only items in the car storing rotational energy. I neglected the flywheel, the crank shaft, etc, and even the weight of the original wheels. But any estimate over 0.5HP per 1lb is not accurate, 0.5HP per lb reduced is best-case. (at least for 18 inch wheels and a 3000lb car :)) -Mr. Wigggles So x4 wheels that's 14-26lbs rotating mass. Using the stated conservative .5hp/lb that's a 'gain' (please note I use 'gain' in this way - it is actually a 'quicker release' to accelerating the car - as you just cannot 'gain' HP this way) of 7HP to 13HP, best case. Not too shabby even that - And esp. for a measily ~$1800 wheel cost; or $257-$138 /HP 'gained'. Personally I might do it slightly differently, that is, Kosei K1 TS 17x8 ($239) at 15.4 lbs, saving ~5-8lbs/wheel - 20-32 rotating mass lbs/car for a calculated 10HP to 16HP 'gain' and a $100-$63 / HP 'gain'. Or do 17" wheels/smaller diam tires for more significant reductions. These are are argueably worth doing IMO, not simply trivial pursuits when considering potential numbers in this area. Althernatively, using the economies of scale a $4000 turbo gaining ~70 'real' RWH costs only $57/HP actually gained. |
3.7 lbs savings x 10 static rule of thumb x 4 wheels x 6 horsepower rule of thumb -------- about 24 horspower gain I set the alarm clock to 6am tomorrow morning, worth a run! (6hp, 6hp, 6hp... :)) Thanks ;) |
Originally Posted by crossbow
The formula's don't work. Track results tend to report much better results then you get by calculating.
Check out one of the starter articles, by sports car compact magazine. http://www.nerocam.com/SCC_TAPnew.asp (This is also a hilarous article to read, and one of SCC's best) Step 1: Baseline Curb Weight: 2,762 lbs 1/4 Mile:16.3 @ 84.0 mph 60-foot:2.9 sec. 0-60 mph:8.6 sec. Step 2: 15-inch Wheels Curb Weight:2,707 lbs 1/4 Mile:16.0 @ 85.5 mph 60-foot:2.8 sec. 0-60 mph: 8.1 sec. By the formula calculations it would seem that they'd only have about 104 lb weight loss...but the results indicate closer to a 200 lb static weight loss. Of course, it should be noted that the 15-inch wheels are 4% smaller than the 19-inch baseline wheels. That's going to give it 4% better acceleration (give or take a bit). Given the: 2% improvement in 1/4 mile time, 6% improvement in 0-60, 3.5% improvement in 60-foot times, and ?% Margin of error I'd say it was pretty much a wash for testing. Not that they were "serious" about the this, but, hey... --Massive |
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