A minimum bend radius is the tightest curve a hose can be pulled into without deforming in a way it cannot recover from. It is not a handling convenience figure. It describes where the inner wall starts to fold, the outer wall starts to stretch, and the bore begins to lose its round section, which is the point where flow and sealing both suffer.
The published figure for a given hose is measured on a straight, unsupported length in a relaxed state. In a real engine bay the hose is usually supported, pulled, clamped and warmed, so the working radius is tighter than the nominal one. Route to a generous curve and treat the manufacturer figure as a limit, not as a target.
In any bend, the outer wall has further to travel than the inner wall. In a tight bend the inner wall corrugates and pinches while the outer wall thins under tension. The reinforcement is asked to handle both at once, and the wall thickness around the bend becomes uneven. Nothing about that is reversible once the part has been run hot.
The bend also changes the cross section. A circle becomes an ellipse, or in a severe case a crescent, which reduces the effective flow area and raises velocity through that section. On a charge system the effect is a local restriction; on a coolant system it can slow flow exactly where the fluid is hottest.
The failure people notice is a kink: a sharp fold where the hose has collapsed onto itself. Kinks usually appear where a hose is too long for the gap and has been forced into a curve tighter than it wants, or where it is pulled around a corner with no support. A kinked hose does not recover, and the fold becomes a permanent weak point.
Vacuum makes it worse. A hose that is only just stable at atmospheric pressure can flatten under vacuum, because the pressure difference is now acting inward on a wall already compromised by the bend. Small-bore lines and intake hoses are the usual victims, and the symptom is a soft, wandering signal or a whistle rather than a visible leak.
Wall construction sets the limit. A thicker wall and a helical reinforcement resist folding, which is why heavy-duty hoses can be routed into tighter spaces without collapsing. A thin-wall hose of the same bore will kink far sooner, and a reinforced hose can usually be taken closer to its limit without taking a permanent set.
Bore matters too, because a large bore needs a proportionally larger curve for the same amount of wall deformation. This is why swapping to a bigger diameter on a performance silicone hose run often forces a routing change as well as a new clamp size. Hoses built as heavy duty silicone tubes exist for exactly that situation, where the space is tight and the wall has to do more work.
Give every change of direction a generous curve and use a formed hose, a metal elbow or a moulded section where the geometry is genuinely tight. Keep the hose in its natural plane where possible rather than twisting it along its length, since a hose fitted under torsional load will try to rotate every time it is pressurised and warm.
Allow length. A hose that is stretched between two fittings has no slack for engine movement and pulls its own bend tighter as the mountings flex. A little extra length, routed in a gentle loop, protects the joints far better than a taut run that looks tidy on the bench but fights the engine in service.
Long runs need support between the ends. Without it, the hose sags, the bend at each fitting tightens under its own weight and vibration, and the joints work loose. A support should hold the hose without pinching it, ideally with a clip or saddle that matches the outside diameter rather than a cable tie pulled hard onto the wall.
Check clearances after fitting, not before. Warm the engine, let it move, and look for contact with the body, brackets, pulleys or the exhaust. A hose that touches a hot or moving part only under load will fail at that point, and the routing, not the hose, is what has to change.
