4 ms·
The last time this was posted I dug in to this and it appeared as though 2 vs 4 tires per axle was not tested, in the original or follow up paper usually refere
by reitzensteinm 6y ago
The last time this was posted I dug in to this and it appeared as though 2 vs 4 tires per axle was not tested, in the original or follow up paper usually referenced. They were testing trucks vs trucks with the same axle type, but different numbers of axles (hence axle weight instead of vehicle weight).
It could be that four tires on a truck axle are much more effective at spreading the weight than two car tires. Or it could be that it's not much better, as the forces are still placed on a relatively small area of asphalt.
How this makes cars and trucks compare is, as far as I could understand from the literature when I dug in to it, an untested open question.
There could be a 10,000 factor difference. Or if two tires at each end are spreading the weight over 2x the surface area and you assume that matters, then you have to divide that 10,000 by 2^4 and it's now only 625x as damaging.
I suspect the reason nobody cares enough to test this is that it would still be a gap large enough to make cars insignificant.
- dumbfounder 6y agoThe 4th power claim is alarming, yes. But are we focused too much on road wear and not enough on the money spent to increase the capacity of roads? My gut says that widening a road is at least an order of magnitude more expensive than maintaining one, so whatever we can do to reduce the number of cars is more worthy of focus than just getting all the trucks off the road.
- a1369209993 6y agoFWIW, if we assume it's based on tire weight, a 50-tonne 18-wheeler actually does (50/9)^4 ≈ 952.6 times as much damage, not 625. > I suspect the reason nobody cares enough to test this is that it would still be a gap large enough to make cars insignificant. That seems likely, yes.
- reitzensteinm 6y agoRight, because you don't double up the two front wheels which are used for steering. I suspect that more weight is put on the rear and trailer axles than the front as well, and that two tires in close proximity aren't as good as two tires separated by greater distance. So even 1000x is probably optimistic. My main point though is just that the study happened to use truck axles as a measurement and that can't blindly be substituted for car axles. The back of the napkin math is just there to show the difference it can potentially make.
- ballenf 6y agoAlso, truck tires are also much larger (than an average passenger car) and have a larger contact area. Passenger off-road vehicles with knobby tires might be harder on roads too in a different way than weight.
- reitzensteinm 6y agoI actually thought this was the case but a quick search indicated about twelve inches wide for both. Was I missing something? It would make a significant difference to the calculations, eg 50% wider tires would mean dividing truck severity by 5.