Pea gravel,,is what I've been using past several years,,comes in 50 lb bags at lowes,,got a long bed f150,,think I had about 400 lbs in end of bed last year,,have had 200 lbs all summer,,when plastic bags puncture,,I pour them in a picneck area ,,,got a toyato,about 100 lbs works on it,,but think I had 200 lbs in end of bed on it,,6 ft bed tacoma,,,the longer the bed,,the more weight you need,,the ford has an 8 ft bed,,,both four wd.,,300 or 400 hundred lbs,,really helps,,,you can always,for a short time,,reduce air in tires,,instead of maybe 35 psi,,reduce it to say,,30 psi,,,don't do a lot of interstate driving with low tires though,,,,or,,,just put it in 4wd,,,,thingy