7 out of 10, and that's me being generous about the climb out of Mundaring. I rode this section twice last month, once solo on the gravel bike and once with the Sunday bunch dragging an old hybrid up the same hill, and the gap between those two experiences tells you most of what you need to know about doing the Munda Biddi Trail day ride through the Perth Hills properly.
The Munda Biddi is a long-distance off-road cycling trail that runs from the Perth Hills all the way down to Albany, and most people who've heard of it know the headline stat, not the texture. The Perth Hills sections get talked up as the scenic entry point, and they are good, but they're also where a lot of first-timers underestimate the gradient and overestimate what their tyres can handle.
The Perth Hills section explained
The section that most day riders use starts around Mundaring and threads through forest, old railway formation and a mix of gravel fire trails before linking back toward the hills proper. It's managed as part of the broader trail network by the Munda Biddi Trail Foundation, who maintain the route markers and publish the official track notes, which is worth checking before you head out because sections do close for prescribed burns or storm damage without much warning.
A good chunk of the day-ride crowd starts from or near the Perth Hills Discovery Centre and Campground, which has parking, water and a decent map board if you've forgotten to download the GPX file, which, lets be honest, happens more than people admit.
What the surface and climbs are really like
This is not a rail trail. There are stretches of smooth compacted gravel that'll lull you into dropping your tyre pressure right down, and then you hit a patch of loose granite scree on a descent that'll punish you for it. I run around 35-40 psi on the gravel bike for this section and still walked one short pinch climb with a fully loaded pannier, which I wasn't proud of but wasn't going to pretend otherwise either.
The gradients aren't brutal by hill-climbing standards, nothing you'd call alpine, but they're sustained. You'll get long drags at 6-8% through timber country, loose under wheel in places, firm in others depending on how recently it's rained. A hardtail mountain bike handles the rough sections more comfortably than a road-leaning gravel bike, but you pay for that comfort on the smoother fire trail stretches where a gravel bike rolls noticeably faster. There's no one correct answer, it's a trade-off, and anyone telling you otherwise hasn't ridden both back to back.
Before you go, it's worth a scan of Trails WA for current conditions, since they track closures and surface notes across the state's trail network and the information is more current than most forum posts you'll find.
A realistic day loop
Heres roughly what a sensible day actually looks like, rather than the ambitious version people plan the night before and abandon by lunch. Start at the Discovery Centre, ride the Munda Biddi north-east through forest for a few kilometres, then swing back via connecting tracks rather than committing to a full point-to-point, which needs a car shuffle most people cant be bothered organising.
On foot-crossing sections you'll pass near Cobb Road, an old heritage route that's worth a stop even if you're not walking it that day, just to read the interpretive signage and give your legs a break. Further along, the Mason Bird Heritage Trail intersects the bike route at a few points, and I'd genuinely recommend locking the bike up for twenty minutes and walking a short stretch of it. It's one of the better bits of local history signage in the hills and most cyclists blow straight past it chasing kilometres.
Total distance for a loop like this sits somewhere between 25 and 40 kilometres depending which connector tracks you use, which is a comfortable half-day for most riders with a reasonable gravel or mountain bike, three to five hours including the stop at Mason Bird and a lunch break.
If you don't want to ride it yourself
Not everyone wants to sort logistics, carry their own spares and figure out tyre pressure trial and error on the day. Fair enough. The Perth Hills Explorer Private Day Tour covers a lot of the same hills country with a guide doing the route-finding, which takes the guesswork out of it if you're visiting from interstate or just dont want to deal with a flat tyre forty kilometres from the car.
For families, skip the climb
Here's my one genuinely contrarian take on this: I reckon the Perth Hills section gets more credit as a family day out than it deserves. It's billed in a lot of travel content as an accessible, scenic ride for all abilities, and the scenery part is true, but the climbing and loose gravel sections aren't really suited to kids on hire bikes or anyone who hasn't ridden off-road before. If you've got young ones and want a genuinely easy, well-supervised day in the hills country further south, the Lane Poole Park Dwellingup - Junior Tree Ropes & Ziplining tour is a far better match for that brief. It's not on the Munda Biddi itself, it's down near Dwellingup where the trail eventually passes through, but it solves the actual problem families have, which is wanting an active day out without a six-kilometre uphill slog on loose rock.
Gear and timing notes
Water is the big one. There's shade through most of the forested sections but not much in the way of taps once you're past the Discovery Centre, so carry more than you think you need, especially October through to March when the hills get properly warm. A basic puncture kit is non-negotiable given the gravel content, and I'd carry a spare tube even if you're running tubeless, because the granite out there has opinions about sidewalls.
Morning starts beat afternoon ones, not just for heat but because the gravel sections firm up overnight and get a bit looser and dustier by mid-afternoon once a few dozen riders and walkers have churned through them. Weekday mornings are near-empty. Weekend mornings bring out a decent crowd of locals, which isn't a complaint, it's just worth knowing if you're after a quiet ride rather than a social one.
None of this is complicated once you've done it once. The surface asks a bit more of your bike and your legs than the marketing photos suggest, the climbs are real but manageable, and the pocket of forest around Mason Bird and Cobb Road is, flat out, the pick of the day if you only stop for one thing. Do the loop, check the trail notes before you leave, and dont trust a tyre pressure that worked fine on bitumen last weekend.