Belts, as with chains have a spring rate. Whether you need a damper
depends
on the system, not just the belt. A damper could make things worse if
not
needed.

Ken Bauman

Ken,
I am sure that Paul would mention this if no one else did.  Tooth belts
DO NOT ABSORB SHOCK LOADS! There is miniscule if any stretch. You can
figure this yourself if you think about how these belts are used.
Frequently they are used as TIMING BELTS. If these belts stretched at
all they wouldn't be suitable for that use. The rounded tooth, (HTD
profile) which is used for all the high power applications, has a
arimid fiber strength section. This simply won't stretch, it's srtonger
than steel of similar weight. If you use a toothed belt drive you must
plan on other damping. My rule of thumb is if you would use a damper on
a chain drive (steel chain) you will need a similar damper on a belt
drive.
Bill Jepson

Thanks Bill.

Not all HTD belts use aramid fiber. They still have a spring rate all
be it small. Shafts twist, props have MMOI, components have MMOI etc.
Unless the drive, engine and prop are analysed as a system you won't
know if you need a dampner or not. It can't be assumed. Run the
numbers and compute a Campbell plot and you will have a good idea.

Ken Bauman

Some new Harley belts use carbon fiber.