Quote:
Originally Posted by NeilBlanchard
Normal tires absorb most of the small bumps, so having a rigid tire (similar to the Energy Return Wheel) that had lower rolling resistance, and it would pass more motion through to the shocks. So, the ride would be similar, but the dampening work would be mostly done by the shocks, so you could regain more energy, as well.
This is the second stage of efficiency improvement that I hope to be able to try on my CarBEN EV5 project: rigid airless tires combined with regenerative shock absorbers.
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Using rigid tires would definitely transfer more energy to the suspension for recovery, but doing so would increase NVH (Noise, Vibration, Harshness) to dramatically unacceptable levels for a passenger car.
A car's suspension system has areas of compliance (assuming rigid road surface, hard parts and body mounting locations), listed in order of greatest to least:
1. Spring/Shock assembly
2. Tire Sidewall/Tread
3. Bushings/Isolators
Reducing/eliminating the compliance of any of these without compensating somewhere else will increase NVH.
Also WRT rigid tires, contact at the road surface will be drastically reduced as the tire gets more and more rigid. This is evident even when over-inflating a standard car tire. The stiffer the tire the more it will rebound off of road imperfections, increasing your energy recovery potential but reducing contact with the road and traction.
The tire is the car's most critical "suspension system" and is far more efficient at absorbing small high frequency road imperfections than the rest of the suspension system, since it's unsprung "mass" is extremely low (measured in grams instead of kilograms). For a car that travels on anything other than perectly smooth testing surfaces (any real road) I think your efforts would be better spent using a traditional tire and experimenting with inflation pressures to find an acceptable balance between all of the inevitable compromises.
I'm sure you and many others on the forum are well aware of everything I have posted above. I posted this specifically for those who may not be aware that all of these compromises exist and must be dealt with.
Having said all that...
The very act of compressing a car's suspension system requires energy, because dampers generate heat (resist motion). The more we reduce suspension movement the less energy we waste.
Remember that a large part of LRR tire design is efficient sidewall flexing, or compliance without generating heat. Compared to a suspension damper, tires generate very little heat as they compress.
The moral of this story is, the more suspension "work" you can do with the tires, the less you need to do with the dampers/springs, and the more efficient the suspension "system" will be at travelling over a given road imperfection.
Making the tires more rigid would be creating inefficiency for the sake of recapturing some % of the energy wasted with an EM shock absorber.