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| XR6T citric |
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Does the size and weight of your wheels make a difference on the dyno?
I was told by a very reputable tuner that my 20 inch wheels, size and weight of them cost me upto 20rwkw on the dyno? He said hes seen it time and time again, people with big wheels get lower Dyno numbers with the same car. He said if i popped on a set of 17s there is 20rwkw there? Is this a porky or does it have some merit?? Maybe it will effect the gearing? Maybe the weight of the wheels but 20 rwkw??
_________________ XR6 Turbo, 20 inch wheels, citric acid, 300rwkw |
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| XH XR6 |
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20rwkw is a big difference.
if you went to a lighter wheel then it would make more power as their is less resistance on the axles ,but that much gain? I was also reading in some jap crap magazine that grippy tyres will rob you of horsepower as it relates back to rolling resistance. ben |
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| Casper |
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I think 20rwkw may be a bit over the top but yes, bigger, heavier rims most certainly rob you of "dyno" power.
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| efmarek |
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thats s**t!. wheel size has nothing to do with power.....but with torque.
_________________ LUMPY-6 |
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| FordFairmont |
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Posts: 6113 Joined: 8th May 2007 |
larger diameter wheels slow the car slightly when taking off at low speeds because of the extra intertia, but when the car gets up to speed its fine
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| 4dlvr |
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according to my physics teacher, max kw will be increased, but the torque will be reduced...
_________________ 96 EF FAIRMONT |
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| stockstandard |
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The dyno will cancel out the larger rolling diameter. Extra weight and friction of wider tires will change the reading somewhat, but 20rwkw is a bit of a joke. Off the top of my head I would say no more than a couple of HP. I googled the question and found quite a few dyno tests and I noticed a max difference of 4hp between extremes of wheel size.
In one of the first hits on google they go from a 13" rim/tire that weighed 13kg and went to a 17" rim/tire weighing 17.5kg and they lost 3.8hp. The results I found also suggest that the more powerful your car is the smaller the % change.
_________________ Stoke me a clipper, I'll be back for Christmas |
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| smiley235 |
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Larger diameter is effectively changing your final drive ratio. Slower acceleration yet higher top speed.
_________________ 178.3 rwkw
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| FairmontXR6 |
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i heard that tyre pressures make a (large) difference... most dynos run tyres at or over 40psi
_________________ 1993 Ford Fairmont EB II 5.0L V8 Wagon |
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| smithy_1 |
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The relationship between power & torque is
Power = Torque x RPM So anything that robs your torque at a given RPM, like bigger rolling diameters, robs power. And extra weight adds to rotational inertia - harder to spin up. So bigger heavier wheels will rob power - but how much is the question isn't it. But they do look good.
_________________ 95 EF Wagon, Dedicated Gas |
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| stockstandard |
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smithy_1 wrote: Power = Torque x RPM
So anything that robs your torque at a given RPM, like bigger rolling diameters, robs power. Not quite. The (incomplete) power:torque:rpm relationship you have posted applies to power at the flywheel - before the wheels. Dynos measure power at the drive wheels and and use the same basic principle but there is a twist. Bigger wheels do lower torque, but they increase speed proportionally. So for the same engine speed changing to a larger tire means you have lowered the torque but increased the dyno roller speed and the end result is the same power.
_________________ Stoke me a clipper, I'll be back for Christmas |
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| smithy_1 |
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thanks stockstandard
The plot thickens! Sounds like someone needs to go to a dyno and do some tests with 20 inchers and 15inchers and report. I just love fordmods.
_________________ 95 EF Wagon, Dedicated Gas |
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