i also found that the problem of the noise tends to happen 'more' when my air-conditioning is switched on, rather than just the cool air in the cabin. Thus, the elastic slip S can also be determined by the power loss ΔP with respect to the power P i at the input pulley: There is a wide variety of reasons V-belts and pulleys slip. Some important reasons are: Worn pulleys The relative motion on the pulleys, which is always present due to the elasticity of the belt, is called elastic slip (partial relative motion between belt and pulley)!

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The figure below shows schematically the distribution of the speed along the belt according to the animation above. Figure: Speed distribution along the belt Since the circumferential speeds can also be expressed by the rotational speeds n and pulley diameters d (v=π⋅d⋅n), the elastic slip can also be determined as follows:So if the driving pulley generally moves faster than the belt and the driven pulley is slower, then the circumferential speeds of the pulleys are obviously no longer identical (this would only be the case with a complete inelastic belt).This ultimately results in a loss of circumferential speed between the drive pulley (rotating faster than the belt) and the output pulley (rotating slower than the belt). The entire wrap area φ can therefore be divided into two zones. In the co-called sliding zoneφ’ a relative motion takes place between belt and pulley. With the acting sliding friction, this zone ensures the transmission of the circumferential force. In the remaining adhesion zone, the belt adheres to the pulley without a relative motion and without force transmission.

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In the animation below, additional marking lines are attached to the pulleys for better orientation. If one compares these pulley markings with the belt markings, the relative motion between belt and pulley can be seen very clearly. Animation: Stretching and shrinking of the belt around the pulleys Delta P = P_i – P_o = F_c \cdot v_i –F_c \cdot v_o = F_c \cdot \underbrace{(v_i-v_o)}_{=v_i \cdot S} = F_c \cdot v_i \cdot S = P_i \cdot S \\[5px] S =\frac{\Delta v}{v_i} = \frac{v_i-v_o}{v_i} = \frac{v_t-v_s}{v_t} = \frac{(1+\epsilon_t) – (1+\epsilon_s)}{1+\epsilon_t} = \frac{\epsilon_t-\epsilon_s}{1+\epsilon_t} \\[5px]i took it from london to manchester yesterday, around a 200mile drive, and found that when i got there, i started to get a squealing-screeching noise when i accelerate on first and second gear.

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S = \frac{\epsilon_t-\epsilon_s}{1+\epsilon_t} = \frac{\frac{F_t}{E \cdot A}-\frac{F_s}{E\cdot A}}{1+\frac{F_t}{E\cdot A}} = \frac{F_t-F_s}{E \cdot A+F_t}\\[5px]Note that in this case it is not, as previously always assumed, the static limit case in which the belt is not yet slipping. Rather, slipping is already present from the very beginning due to the elastic slip (µ s as coefficient of sliding friction!).

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The belt adapts to the different speeds by elastic slip on the pulleys! Circumferential speed of the pulleys If a belt section between two marking lines is now looked at more closely, this section is obviously stretched on the driven pulley during rotation. The stretching belt section is pulled over the pulley, so to speak, i.e. there is relative motion between belt and pulley and thus sliding!

In addition to elastic slip, which is due to the elasticity of the belt, the belt can also slip completely over the entire driven pulley in the event of overload. This is then referred to as sliding slip.Note that every belt has a certain elasticity and therefore always results in elastic slip, whereby sliding slip should always be avoided. i sprayed some wd40 on the drive and air con belt, i think it helped a bit, but the noise is still there. i know that there is a special spray for squeeky drive belts, do these work well? The strains ε can be determined as follows using the Young’s modulus E of the belt (not to be confused with the bending modulusE b!) and the acting belt stresses σ=F/A (with A as cross-sectional area of the belt):