(taken from the GWRRA Tech board on 6-25-05)
The existence of the sweet spot for us bikers is a fact, but this speed cannot be arbitrarily set as it is constantly changing. However, if you can find it and adapt with it, you'll greatly reduce dangerous situations.
As all of you are well aware, virtually no one obeys the speed limits on high-speed, trans-continental interstates. Many of the states have the speed limit set at 70 mph. Typically, most vehicles (cars and trucks) will average around 80, or even higher, especially on the long downhill grades. If you are attempting to stay close to the speed limit, you had better hang in the right hand lane and only rarely venture out into the hammer lane when it becomes absolutely necessary to pass some really slow traffic. And when you "get left", do so ONLY by rapid acceleration, as the cars that seem to be pretty far back are actually only seconds away from climbing up your butt. FAILING TO DO THIS IS A COMMON MISTAKE WITH GROUP RIDERS. An opening appears and the group "looks left - moves left" and invariably maintains the same speed they were doing in the right hand lane, with maybe only a gradual increase. In short order, they have now become an irritating obstruction for the high-rollers coming up quickly from behind. To compound this mistake, the group will then hold fast until the drag bike has cleared the traffic being passed, and then go on to what I call a "parade show" with the group moving to the right in unison. It is not unusual for the vehicle directly behind the drag bike to become so impatient, that they will quickly dive to the right at the first opportunity and this could coincide at the same moment the drag bike makes his move --- not a good picture forming in your mind, right? The answer of course is quite obvious - once in the left-hand lane, you do NOT move the group back over to the right as a unified group - you do so individually as each bike passes the vehicle. This approach completely eliminates any confusion with the vehicles behind as to what your intentions are - -and that impatient guy will now wait for the last bike to clear.
Unless your group enjoys flirting with speeding tickets, you'll more than likely keep your average RIGHT HAND LANE speed to no more than 5 mph over the posted limit. (Again - we are talking interstates here, not towns, where I think you should stay AT the speed limit.) But, as I've already said, once you venture over Into the passing lane, you AND YOUR GROUP need to accelerate quickly to get around the slower vehicles. This may momentarily take you 10 or even 15 mph over the limit. But it'll be a much safer way to maneuver. Plus - if you are smart, you'll never hang next to, or slightly behind a tractor-trailer. For obvious reasons (all of them spelling DANGER) you should get around them PDQ -and if a group member In front of you is lingering, don't be timid about telling him/her to "get on it". And at the next rest stop, you all should discuss this strategy, the reasons for it, and hopefully make it second nature.
So, as you can see - the "sweet spot" is a speed ABOVE the posted limit - but not so high that it will get you a ticket. You can also see that it is constantly changing, all for one express purpose - to keep you and your group in the safest possible position.