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Originally Posted by NeilBlanchard
The whole point of regenerative shocks *is* to regain some of the energy that would otherwise be waste heat. Don't forget that flexing in the pneumatic tire also produces waste heat in the tire itself.
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You are correct, but comparing the bump absorbing efficiency of a tire and the rest of the suspension, the tire will win every time.
The ideal tire/wheel/suspension system would be zero mass and ride on a frictionless air spring. The frictionless air spring would return darn close to 100% of the energy it absorbed when encountering a bump, and zero mass parts means no need to damp the suspension, the tire would just follow the road. The only reason a car requires dampers when encountering a bump is to control the inertia of the moving parts. The less mass, the less inertia, the less damping required.
A tire absorbing a bump is FAR closer to the ideal zero mass suspension system than the actual suspension is, as it does ride on an air spring and its moving mass is extremely small. Since the moving mass is so small it requires very little damping, and yes that little bit of damping generates a little bit of heat. The physics are unavoidable, and favor the tire strongly over the suspension.
Of course, since the tire has very limited "travel" and is relatively stiff, as the bump gets larger a higher percentage of the bump is absorbed by the suspension system.
And before someone else says it, yes dampers are required to control roll and pitch dynamics. This conversation is about absorbing bumps and the related energy, not handling related dynamics.
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Originally Posted by NeilBlanchard
My earlier suggestion does two things to increase the efficiency of a car - the rigid wheels would have the lowest rolling resistance possible, and with most of the motion caused by bumps and swells in the road surface being dampened by the regenerative shocks, they would produce a greater amount of reclaimed energy.
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I believe the #1 priority in gaining efficiency should be lowering the rolling resistance; on most roads under most conditions the greatest efficiency gains would be found there. Compared to rolling resistance, wasted suspension energy is a FAR lesser concern and this is more and more true when traveling on roads that are in good condition. If making the tire more rigid shows gains in rolling resistance then this would be a good direction to go.
Having said that, if making the tire more rigid was done purely to increase suspension activity and showed no real gains in rolling resistance, the overall vehicle efficiency will go down for the reason I mention above; a tire is more efficient at dealing with small road irregularities than the suspension system is. The higher the % of the bump absorbed by the tire, the less energy the car will lose.
I should have included that in my initial response.
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Originally Posted by NeilBlanchard
Other advantages of using airless tires: they never need to have their pressure checked, and they would never leak and lose efficiency. Also, you would not need to carry a spare, or a jack, and full wheel skirts don't have to be removed to change a flat. You would never have a blowout, either.
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All very good points.
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Originally Posted by NeilBlanchard
I'm pretty sure that the ride quality and handling could be tuned to provide normal characteristics.
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I'm not sure about this. Making the tire more rigid might mean adding more bushing compliance at the suspension mounting points to compensate, and then you are taking the energy "gained" at the tire and wasting it in the bushings, maybe? All else equal, stiffening the tires will reduce the ride quality...