The Good: I-drive suspension works well. Formula RX brakes and levers are excellent.
The Bad: Stand-over clearance will have you singing soprano. Crazy long wheelbase. Rock Shox Recon Gold mates choppy travel with lots of lateral play. Alex XD-Lite rims are weak. Maxxis Aspen tires not ideal (regional consideration).
[Note: This review is of the 2012 model which appears to be identical to the '13.]
Without burying the lead, I will start by saying that I consider GT to be an iconic bicycle brand and I have ridden many GT's in the past including my first mountain bike, a 1993 GT Tequesta. I wanted to love the Sensor 9r so badly but after about three weeks and 15 rides I ended up returning it. Here's why:
On paper the Sensor 9r Expert seems like a good value with Fox's Float CTD shock, RockShoz Recon Gold fork and Formula RX brakes.
One thing I noted from the moment I climbed on the bike is that at 5'10" with a 30" inseam, the size Medium frame (which is the smallest size available) lacks adequate stand-over clearance. But once in the saddle, the geometry of the bike feels ok. I was assured that the lack of stand-over clearance would be a non-issue (turns out that was very wrong).
First ride impressions was that the bike climbs surprisingly well for a 30 lbs. trail bike, even on techy climbs with lots of roots and large step-ups. The hydro-formed tubing seems to provide a reasonably stiff frame and the i-drive system works as advertised with very minimal bobbing, though on longer sustained climbs I locked out the CTD shock. All this comes with one major caveat: this bike likes to track straight. The 29" wheels provide excellent roll-over capability but the very long wheelbase (more about this later) makes quick turns to avoid obstacles or improve your line very difficult. Net result is that I would end up straight lining many tech sections that I would normally weave through on my 26er and the results were mixed. if the 29" wheels were able to roll over an obstacle then great. If not, I was usually unable to flick the bike up and over like I would my 26" wheeled bike.
When the climb ended and the trail turned to downhill the slack head tube angle and active (though not plush) suspension of the Sensor 9r is confidence inspiring. Unfortunately, that confidence is very short lived due to the RockShox Recon Gold's stanchions having an uncomfortable amount of lateral play and very choppy travel. At first blush, I thought the play might be coming from the head-set, but upon closer inspection all the play was, in fact, coming from the fork arms, not the head.
As during the climb, if the downhill section is straight and does not require any serious maneuvering, the Sensor 9r is fine. It also feels balanced launching small bumps. However, on more technical sections or through tight twisty turns where there is a premium on acceleration, the length of the bike coupled with the loose and shaky front end leaves one wanting.
On a high note, the Formula RX brakes with 180mm rotors provide excellent and quiet stopping power.
On a low note, the stock Alex XD-Lite rims couldn't go two rides without having to be trued and the Maxis Aspen tires with their thin sidewalls are the wrong choice for rocky east coast trails. I ended up having to run 40 p.s.i. to avoid constant pinch flats.
As a result of long chain stays (possibly to make room for 29" wheels on a bike originally designed as a 26er) and slackish head angle, the wheelbase of the Sensor 9r is crazy long for a trail bike. Test riding the bike in the parking lot of the LBS did little to prepare me for what to expect from the length of the bike in real world trail riding scenarios.
The underlying mistake I made with choosing the GT Sensor 9r was to give GT too much credit based on past successes. There are several factors that lead me to suspect that GT's engineers did not give this frame enough careful consideration in retrofitting it as a 29er. The wheelbase makes the bike difficult to manage. The stand-over height is so tall that I would have to stand on the tips of my toes to avoid a sudden change in singing voice and in one particular emergency ejection situation this contributed to a rolled ankle -- that's when the honeymoon was officially over.
One final gripe is that the cable routing on the frame appears to have been an afterthought. At several different locations along the cables' paths, the cables rubbed the finish down to bare metal. I realize this is mostly a cosmetic matter, but it tends to shed some light on how much or how little attention was given to the design details. Between that and the cheap finish on the Deore cranks being burnished off by the inside of my bike shoes, after merely three weeks of use the bike looked like it was three years old.
Despite my mostly negative thoughts on this bike, I still believe GT is an excellent bike company. And they must have been listening to their consumers because the Sensor underwent a total revamp for 2014 and will come back as a 27.5" wheeled bike. Unfortunately, for the 2012/2013 Sensor 9r, I believe this bike is lacking.
This review, however, would be woefully incomplete if I failed to mention that I purchased the bike from Performance bike shop who impressed me with the way they stood behind their product. I explained to the shop manager that, although the bike was not dismal, I was certainly less than satisfied with it. After a short discussion of my options the manager was happy to refund my purchase price in full, without further question. That is impressive customer service!
All-in-all I think the GT Sensor 9r is a small dark spot in GT's otherwise sterling catalog. Even the 26" wheeled version seems much more in its element. The 9r sort of feels like you're wearing shoes that are three sizes too big. However, the 2014 model looks like a very serious improvement and given my feelings about the 9r not really feeling right, I think its interesting that GT is reincarnating the Sensor line as a 27.5" only model.