I have KM3's on 2 vehicles (Raptor & CJ) and really like them, I would have put them on the defender but due to availability at the time I went with 30x10x14 maxxis liberty's, personally I prefer the 30" size, I haven't experienced any affects to performance, top speed, no low gear warnings coming up in the display, etc. Certainly Newtons second law of motion applies here but you're just not adding any considerable weight or rolling resistance, especially if your staying with the 27x11x14's