The McKenzie River Trail lies on the west side of the Cascades in a temperate rain forest and is a totally different experience than riding on the east side. There is huge old growth Douglas fir for much of the length of the trail along with moss, ferns and the crystal clear McKenzie River. The trail surface is generally softer with more forest litter than the exposed pumice soils on the east side. The downside is that with the increased vegetation there are more exposed roots in places, but not nearly as bad as some trails. There are enough rocky and rooty sections that a full-suspension bike will make the ride a lot more enjoyable.
The majority of people do the 25 mile ride from top to bottom with a shuttle. Do not think that just because it is mostly downhill that you will be fresh as a daisy at the end. It is definitely not too steep to ride up especially the lower half. If you can ride up and down, the whole length, you definitely will have earned your stud(ess) badge.
The level of technical riding varies tremendously and unfortunately for beginners the technical riding is not all concentrated in one spot that you can avoid. The three most technical stretches are in the upper third but there is also some super easy cruising to be had for the first few miles. The first real technical section is around the east side of Clear Lake although you can avoid this by riding the trail on the highway side of the lake which is about as easy as mountain biking gets. If you have a spouse that holds you personally accountable for the outcome of all outdoor activities or there is an inverse correlation between perceived risk and perceived love, you might want to avoid the ride through the lava field on the east side of Clear Lake. You would however be missing some incredible views into the depths of Clear Lake (come back and hike the east side to earn romantic bonus points). The next technical stretch is after you cross the highway and drop down past Sahalie and Koosah Falls. A beginner could ride the highway and pull in with the cars to look at the falls then rejoin the trail at Carmen Reservoir. The next and last really technical section is in a lava flow below Tamolitch Falls. This one is kind of hard to avoid without missing a major section of not so hard and beautiful trail. Plus, Tamolitch Falls is a must see place where the whole river comes up from a pool that looks like it should have a falls feeding it but is dry. This is a popular and logical lunch or snack spot for both hikers and bikers. The lava flow is short enough that the recommendation for beginners would be to not miss Tamolitch Falls and walk the difficult parts of the lava flow of about a quarter mile. Rumor has it that some riders from Eugene actually switch out pedals from platform to clip-in for certain sections of the trail, which sounds like a good idea if you are willing to take the time to do that. Below the blue pool of Tamolitch falls clip-in pedals would be preferable if you are used to those.
Speaking of hikers, this is one of those trails that is at least as popular with hikers as it is with bikers. It is a wonder with the number of shuttled bikers and occasional groups of bikers in full downhill regalia that they do not close it to bikes. Probably the only thing keeping it open is the length of time it has been used as a bike trail. Be extra courteous to hikers on this trail. Slow down and be ready to dismount. If they get off the trail for you, be sure to say thank you. The vast majority of hikers are coming up from Trail Bridge reservoir to look at Tamolitch Falls. It is also not uncommon to encounter hikers around Belknap and Paradise Campgrounds at the lower end.
The camping on the McKenzie is some of the best in the nation (for pay car camping). The trail is in National Forest and there are several pay campgrounds all in old growth forests. There is a commercial campground and hotel at Belknap Hot Springs near the lower end of the trail where the old highway 242 meets 126. If you camp at Belknap, the hot springs pools are part of the fee and well worth the price. However, it is becoming much more developed and the price is likely to increase. They seem to be catering more and more to the RV crowd. The National Forest campgrounds in the area are very popular so you may have to rough it in the surrounding National Forest accessed by logging roads if the pay ones are full. Many folks refuse to pay a dime for camping and always "primitive" camp. If you do be sure and pack out your trash. If you want to soak you can still pay to use the hot springs without camping. There are some free and natural (in more ways than one) hot springs in the area.
Getting to the lower end of the trailhead (very near the McKenzie Ranger Station) :____ In Google Maps copy and paste "OR-126 @44.17865, -122.12907" as a destination.
Getting to the upper trailhead:____ In Google Maps copy and paste "OR-126 @44.39468, -122.00269" as a destination. This one is a little hard to find. It is just south of Fish Lake, but on the other side of the road.