I am tired of square cube and the whole insects can't be scaled up thing. I want a 4 x 4 bug. By 4 x 4 I assume something like a Jeep. A jeep is roughly 2 x 2 x 3 meters I think. How to make a bug that big?
I was going to start with a mighty coconut crab, but instead we will start with
Arthropleura the largest land dwelling invertebrate ever.
Arthropleura species ranged in length from 0.3 to 2.3 metres (0.98 to
7.55 ft) and a width up to 50 centimetres (1.6 ft). Arthropleura was able to grow larger than modern arthropods, partly
because of the greater partial pressure of oxygen in Earth's
atmosphere at that time and because of the lack of large terrestrial
As is this big bug has got the length. Now the other dimensions which we will achieve without violating the square cube law. We will put it on stilts, Opiliones style. These are the harvestmen, or daddy longlegs. They have got a lot of leg.
By the ruler I think that long leg is 15 cm and the body 0.5, so a leg to body ratio of 30:1. We will give our Arthropleural legs like that. The millipede body plan is better for this because the legs will presumably be supporting some weight, and so more is better.
With 2 meter body that gives us legs of 60 meters. That seems a little extreme and so to keep things sane we will take the legs back down to just 10 meters. Of course they would be as thin as human fingers. You would have something like an extreme version of one of my favorite bugs, the house centipede.
The 4x4 would have longer legs and more of them, being a millipede. Air intakes (spiracle equivalents) for the legs would help with oxidative metabolism out in the periphery.
Scoffer square cube fans might protest - the Arthropleura needs more oxygen than the atmosphere can provide! So your riders provide extra oxygen, which they carry in tanks.
And the question: fuel. I used a calorie calculator https://www.omnicalculator.com/sports/calories-burned. and asked about a 10kg individual (the big bug); assume 200 miles at 10 mph = 20 hours running equivalent. It needed 1420 kcal which is about a Wendy's triple cheeseburger, fries, small Frosty and Diet Coke. Acknowledged - this calculator is for humans, which might be more metabolically wasteful than a millipede. Also this calculation is without a passenger. I think it might make more sense for the big bug to pull a chariot rather than have someone sit on its back; the legs provide lots of traction but people are heavy.