Regarding design of the E-start, having an outside idler is a favourable arrangement for increasing number of grooves in contact with the belt at the driving sprocket. In this application however, the outside idler is far too small for a power drive. Going by the Gates GT2 design manual (other vendors will have similar recommendations), the recommended idler size is 1.3 x the size of an inside idler, which should be of the same size to the driving sprocket and no larger than 40 grooves. Hence, an outside idler should have a diameter corresponding to 35 to 50 grooves, which the current design clearly doesn't have. On the positive side we note that arc angle between the tangent lines is small, so directional change is quite low.
The disadvantage of having an outside idler is that the cord is subjected to alternating stresses rather than pure swelling stresses, which will reduce life expectancy, even though the belt's tension is low. The smaller the idler, the larger the stresses will be, hence the requirement for a large diameter idler.
The designer/builder of this kit claims he has used the setup for 10 years. At the time he made the comment, he was on his 3rd belt, so we may assume a life span of approx. 3.5 years. He didn't tell the audience which mileage he covered though, and we may guess that total mileage isn't a huge figure. When using this kit, carrying a spare belt on long trips may be a good idea.
Edit: The above does not apply to the production kit offered by Norvil, which despensed of an idler.
- Knut
