Working in the tire industry for so long it surprises me to find out new things but I find that I constantly am. There is a world of DIY filling tires with polyurethane foam. This is primarily done to tractors and general agricultural vehicles. Generally these vehicles have small front wheels and these are almost always the wheels that are foam filled. The back wheels wouldn't be cost effective to fill with a suitable foam.
At first glance this seems a crazy proposition as increasing the weight of a tire means increasing the rotational weight of a vehicle significantly and thereby reduce the fuel economy and performance of the vehicle drastically. This ignores the use case of a agricultural vehicle though. To begin with a tractor has a very high center of gravity and this can lead to instability, in many cases heavier tires puts additional weight at the bottom of the vehicle and thereby can shift the center of gravity downwards.
The small front tires on a tractor are vulnerable to punctures as they are on uneven ground moving through areas with little driver visibility. The foam filled tire doesn't have to worry about going flat every time a thorn is driven over.
The downsides are pretty significant however. The largest being that when the tires need to be replaced the whole tire will need be sawn and levered of the wheel assembly. This will likely be a large undertaking and require scrubbing to fully clean the wheel. There are reports of flat spots developing in the foam and therefore the tire if the vehicle remains parked for too long. Pressure cannot be adjusted as needed and the ride will be extremely rough, so rough that it might even cause maintenance issues.
Foaming tires is an easy fix with a long list of pros and cons. It is one of those things where there is no obvious right or wrong answer to the practice. With all things involving a motor vehicle and the inherent safety concerns however it is advisable to engage the help of responsible experts than attempt DIY measures without sufficient knowledge.
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