There is a cycle path beside some of it. You need local knowledge.
Local erm um ok, Eek...
My most recent traversal was on the 28th of Decmber as far as Dalwhinnie...
Except over Drummochter and Slochd the majority of the sensible cycle routes up the A9 corridor are on bits left over of the "old road" and the "old old road"; (soon to have an extra level of Old on them in places)
The biggest problem describing them is there are some sections with multiple options:
If you're touring it I'd suggest rather than going to Perth, head for Crieff via Glen Devon and then up the Sma Glen and Griffin roads to Aberfeldy, then ride the north side of the Tay to Logierait, where we will pick up the route later.
If you insist on visiting the not very fair city (Perth) you have two options, the NCN 7 route which goes along the Inches and then out to Almonfbank from where there's a niceish country road route via Bankfoot to Dunkeld.
Another option is a path beside the A9 to Luncarty, then STanley and cross the tay at Caputh, where you join my regular route to Dunkeld from Meikleour (big hedge not much else)
I've never ridden this, because I'm always approaching Dunkeld from Dundee.
From Dunkeld you have 2 options to Logierait/Balinluig (Either side of the A9, now joined by a bridge)
NCN7 goes off road (and the only time I've ridden it, it was loose but I've heard it's got better) to the Tay Crossing bridge which you ride back over and up the road to Dalguise and then over the Logierait viaduct which is a wooden decked railway bridge that is open to motorised traffic on the promise of paying a donation.
The Regional route on the other hand is in some ways more sensible, it takes the old road out the back of Dunkeld to Dowally (Dowlie) and then uses paths and old road to get you into Ballinluig; the path sections can be a bit unclean but I've never found it impassable.
At Logierait/Ballinluig you again have 2 options (in order of preference)
1) The Etapé caledonia route to Pitlochry by Dunfallandy which I'd recommend
2) Dalcapon, this involves more climbing and sharper and unless I'm dodging Pitlochry and heading straight up the Moulin I go the other way.
If you want to go a bit off standard routes, one suggestion would be to ride to Alyth from Dundee, through Glen Isla to the A93 and then over Moulin Muir into Pitlochry, this is of course the Dundee in me talking and it makes no sense at all geography wise.
Pitlochry to Dalnachardoch Lodge is on the old road via Killiecrankie, Blair Atholl, Bruar and Calvine. Be aware that while the last section looks like it's a dedicated cycle track it's not, this becomes obvious at Dalreoch where heavy traffic is diverted round the Anderson bridge via the A9's main line.
I've heard that this section will have some changes to usage following the upgrade of this section.
Dalnachardoch to Drumochter is a mess, the bits that were built to deal with the old road being under embankment are rough and the old road bits are even rougher, but it is rideable on 30,,tyres.
From the summit of Drumochter there's a fantastic new surface (pending it surviving the winter) however there are a lot of wooden bridges on it to cross the drainage channels, and they're at right angles to the path, and with the resurfacing has come stupid concreted in bollards that necessitate losing a load of speed and I had a carradice rather than panniers.
Once at Dalwhinnie it's the old road again, typical scottish road surface and probably hasn't been resurfaced since it was sealed in the 1940s.
The road from Newtonmore to Carrbridge can be a bit wank, Carrbridge to Slochd is decent, the path over Slochd is Decent and then from Tomatin the path section to Moy junction is rubbish, from Moy you're being massivley detoured but it's prefferable to the A9; you can cut a corner of the NCN7 by turning off for westhill rather than going down to Balloch; by the time you ride it there'll probably housing estates stretching up to Slochd anyway. (this is a dig at the expansion rate of Inverness and chances are it'll be bigger than Dundee by the 2031 census, partly due to Invernesians dying of Poverty and drug abuse at a lower rate than Dundonians)
After Inverness use the middle road up to Tongue, cracking hostel there, and TBH you might as well stop there Thurso, Wick and JoG are utter dives.