For anyone interested: I took some time today to empirically measure the difference in force required to turn a vBelt and a microV (serpentine) belt around a 2 ½ inch pulley. The rate of pull was 3.5 seconds per inch for a total pull of 8 inches. The dead weight was pulled straight up, each belt was pulled around the pulley at approximately 270 degrees – I never measured the angle but the same length of belt, pre-load (weight of actuator) and placement of the anchor weight remained the same. Both the serpentine belt and the traditional vBelt were old used belts. The result. Absolutely the same. The deadweight measured 48lbs, to pull the weight up with either belt type resulted in a 45lbs force @ 3.5seconds per inch. In short, there was no increase in drag, no observed benefit in efficiency between belts. Bulleted details: 3.5s/inch. 12 volt linear actuator. 2 ½ inch pulleys – Mounted on same alternator 48 lbs dead weight Swiss Luggage scale 0-80lbs 1lbs increments Pulled @ 45lbs multiple repeated runs. 6 each. Used belts (as in worn belts not new) standard vbelt 6 rib microV belt Belts pulled around pulley for approx 270 degrees. Result – no observable or measured difference between belts. Picture of setup:
I believe the serpentine belt was implemented for simplicity, and better traction over the pulleys ( especially big amp alts.) and space savings (no need to stagger accessories for belt alignment )
Mark I believe you are correct, and some make the assertion and/or suggestion about efficiency as shown on Wikipedia and some vendor sites. Personally, I like the simplicity having just converted over. I also believe it makes the engine more accessible to maintenance, detailing and inspection. Briz, I had found no actual measured results and in a rare instance had tools and opportunity to do these measurements. Took maybe an hour to set up and measure.
Heres a thought. You measured the drag on just one accessory. Would the drag be multiplied for each V belt but the same for the serp running all of them at the same time? If so there is the advantage of having the serpentine set up.
Ive thought that as well regarding number of accessories in addition to belt's age and tension. Furthermore, the rate of pull is also a factor that could impact drag disproportionately. But honestly though, the only thing I would do again is use new belts and use a higher precision scale. 1lbs increment may not be sufficient to detect a difference.
Contact while turning results in friction. Less surface contact thus results in less friction. One belt hitting a drive pulley and all accessories will thus have less friction than two belts each hitting the drive pulley and (in total) all accessories. Also, with serpentine belts the whole install is necessarily simpler -- fewer parts. It is also possible to use automatic tensioners, which on my GN suck due to poor design / quality / lifetime but generally are quite beneficial. I agree that speed and measurement accuracy could drastically alter results. There is probably an SAE tech paper on the subject out there somewhere.
Regarding surface contact, your statement is probably false there is likely equal or more surface contact with a serpentine versus a vBelt. The logic implied is similar false logic when comparing fine thread to course thread, some assume fine thread has less grip than course thread fasteners when in fact the fine thread fastener has more contact and therefore more grip. Correct. I believe the traction is more efficient based upon design and disbursement of load and allows more accessories per belt without adding to the compounding friction required of a standard vbelt under tension. So total friction between the two for N number of accessories is equal to a point (what the number and or drag induce by accessories I don't know). The needed tension to maintain friction to turn an accessory via vBelt can be problematic in high rpm situations based upon transient effects of leverage due to the larger singular contact point of the angle. Either-way, fun experiment. I've had some recent inquires of the Serpentine setup so I thought I would bump my threads.
