Friction modifiers in Gasoline engines neccesary?

[FCD]

I have been reading on friction modifiers recently and i'm a bit confused.
Some people claim they are beneficial in passanger car gasoline engines, and that they reduce wear at high revs and improve fuel economy.
However lots of people run HDEOs with little or no FM's , and also motorcycle oils in cars without issues.
Are they necessary, or beneficial or not?

 

[MolaKule]

Recently, FM's have been used in HDEO's as well.

In any engine oil, FM's are used to reduce friction which in turn increases fuel economy by a smidgeon.

We would prefer that friction be reduced as much as possible so that most of the mechanical energy produced is delivered to the wheels and not converted to engine heat.

Here is some technical info on the difference between FM's and AW's:

FMs and AWs

 

[SonofJoe]

FMs are very much a US PCMO thing because the ILSAC specs contain a pretty difficult fuel economy test that must be passed. Do FMs work? Personally I was never that convinced. The fuel economy performance of any oil is far more likely to be determined by the 99+% of stuff that ISN'T FM than the few tenths of a percent that is. Also if FMs did indeed work, there would be no reason to make GF-5 oils with absurdly low CCS's (to get the KV40 down). And they are absurdly low; all of them! However regardless of this, the prevailing mindset is that a smidge of GMO (the most widely used FM) is cheap and it's better to keep in and hope it does something than take the risk of failing expensive engine tests by taking it out.

 

[Michael_P]

Okay. I'm no FM guru, but shooting from the cuff and totally guessing; Here's a question. It seems the benefit from a friction modifier is more pronounced when the two materials in contact have a higher friction coefficient such as clutch material on steel, as opposed to two harder metals in contact such as steel on steel or steel on babbitt metal. Is this true?