Jag fick ett intressant svar från Bob Stuart på trikeslistan.

Sammanfattningsvis kan man säga att 559-hjul är bättre på löst underlag än 406-hjul och ett framhjul som styr och som har lätt belastning gör mindre motstånd än en tadpole med två framhjul som styr och som har större belastning och därmed gräver ner mer i det lösa underlaget.

Så ska man ha en trike som kan ta dåligt underlag bra ska det vara en LWB bakhjulsdriven delta med stora hjul. Fjädring gör också nytta genom att det inte går åt lika mycket energi till att ruska om hela fordonet.

Här är hans svar: ' Alex Moulton pointed out that with suspension, a tire could have a lighter casing because it was protected from bottoming out. Suspension pioneer Dan Henry ran the lightest track tires on the road. Going over bumps, suspension is clearly superior, because the energy that goes into throwing the whole trike up is seldom recovered on the return to earth, whereas a suspended wheel works like a roller cam follower, and conserves energy. (minus the shock absorber tax, and it's own weight, etc.) The classical literature is based on steel wheels, and shows an inverse relationship between diameter and rolling resistance. Double the diameter gives half the resistance, because there is less deformation. On the road, the effect of bridging small holes, and rising slower over bumps is also important. Narrow tires also have important aero benefits. However, with pneumatic tires, what really matters is how much the tread scrubs on the road as it is forced to conform to it, and the hysterisis within the casing as this happens, and a long contact patch is not always optimum. Unfortunately, much testing has been done on small rollers, which mask the effect of wheel diameter, so the data are inconclusive. On a non-tilting wheel, the radial-belted tire construction as pioneered by Michelin is clearly the biggest improvement available, but most of the valuable test results are proprietary, and radial options rare. I'm tempted to just get the lightest available tires, sand the tread off, and replace it with a multi-groove or timing belt, inside out. The casing would be good for more pressure that way, but the belt might not stand it. Suspension has no effect on breaking trail, at which a trike is always at a disadvantage compared to single or dual-track machines. Trikes also match the tire tracks of other vehicles poorly, so they break more trail and run on softer surfaces. Having the center wheel more lightly loaded can average out better where ruts are a factor, but then you want 2 or 3WD. On an electric hybrid, that's easy. Where snow turns to icy lumps, the usual suspension factors apply. Wheel position, front or rear, has no effect on rolling resistance, except insofar as the load on it shifts with acceleration or braking. If a more lightly loaded wheel "floats" while others dig in, you could make the others wider, but the pressure the tire exerts on a soft surface is pretty much the same as the air pressure inside, so unless you are starting off with different casing sections and pressures, there should be little difference. On soft surfaces, a large-diameter, narrow tire shows to advantage just as is the case with steel wheels, because once again, both the tire and the road are of more or less equal stiffness. You must compress the roadbed until it can sustain the pressure, but with a long contact patch, you ride on it longer, instead of compressing yet more roadbed to the sides.

Best, Bob Stuart

/Bruno

__________________________________________________________ Går det långsamt? Skaffa dig en snabbare bredbandsuppkoppling. Sök och jämför priser hos Kelkoo. http://www.kelkoo.se/c-100015813-bredband.html?partnerId=96914325