Revised Review: 2010 trek 3900 disc

MSRP (new) $529.99

this bike is made for commuting I have it in size 18,and in orange

the geometry so, not good for Mtb, for me, but for people with short armed and short back, this is not a bad thing, but I am about 180 cm high and i am average sized  everywhere,so  I get a very upright position, But when I was a teen i was not as big as I am now so it was ok.

which is too small of mountain biking  but for commuting its OK, you will sit upright.

the bike is no real mountain bike, frame is way too short and the handlebar is too short too, this make the bike too responsive.

ignore the sticker that say trek mountain bikes, it just refers to the standard for mountain bike frames. it’s not a mountain bike,but it can be with some upgrades.

Seat post parts look like this:

2010 Bontrager seatpost  saddle clamp parts
2010 Bontrager seatpost  saddle clamp parts
2010 Trek 3900 disc 18'' chain drop damage
2010 Trek 3900 disc 18'' Right dropout
2010 Trek 3900 disc 18'' - dropouts- upside down

the frame can withstand mountain biking, but the geometry is horrible for mountain biking.

2010 Trek 3900 disc 18'' - BB shell -chainstays


  • max tyre size is 2.3
Chris King BB 30 & Race Face Turbine_0628
  • slack seat tube angle
  • steep head tube angle
  • horrible wheels, the rear wheel comes with a FH-M475 rear hub which has been troublesome, bending axle, possibly due to bad tolerances, this happen on all of the FH-M475 rear hubs I used.
  • The Shimano Acera M360rear dérailleur is horrible, too soft spring, no clutch. the use of a nut instead of a bolt was a bad choice.
2010 trek 3900 Shimano Acerarear derailleur
2010 trek 3900 rear a look from above
  • The handle bar bends in a crash, a simple side fall will bend it.
  • Steel stem with only two bolts which is also quite heavy & low quality:
my custom 2010 trek 3900
2010 Bontrager Approved 2 bolt stem

You can notice the low quality part I mentioned on the inside of the stem, weird wave pattern instead of a smooth hole, there were no wall there that has been rusted away, it is just made this badly, as you can see there is paint on it,so this means it clearly was like this when new.

2010 Bontrager Approved 2 bolt stem
2010 Bontrager Approved 2 bolt stem
2010 Bontrager Approved 2 bolt stem
  • The fork is a SR Suntour SF9 XCT V2, 100mm travel  does not have the promised 100mm travel, but more like 20mm, the fork had play and it got even more play so when i was braking hard i felt like the fork would snap or fall apart. it also lack of adjust ability.
  • Nylon Wellgo pedals, which were horrible, the plastic snapped on on side, I don’t remember how that happen, and they were very sketchy, foot coming off was a common issues for me. here is a review from Bikechanic for what seems to be the same or similar pedals:

  • The all in one unit Brake & Shifters/triggers: the stock are v brake lever and shifters, shifters are horrible you need to swing the lever way too far to change gear, so changing gear becomes unnecessarily difficult. if you want the shifter to be at a good angle the brake will be at a bad angle and wise versa.
  • Brakes: the bike comes with single piston mechanical brakes from Promax.. The mechanical brakes don’t work well you need to press very hard to brake. these brake are so bad that V-brakes actually are better for braking wise,not wear wise of course. so i upgraded  to hydraulic & shifters/triggers.
  • Saddle– saddle is way too big for me, it wears out fast because of flex in the saddle the plastic under  it that  have screws in it will flex too so the screws will pop out.
  • Overly beefy brake mount, it’s heavy, and wide.
2010 trek 3900 brake upgrade Shimano Acera M39
with upgraded brakes, but they failed.
2010 Trek 3900 disc 18'' - brake caliper mount & dropout
2010 trek 3900 downtube & bottom bracket shell
BB area 0508
  • horrible headset: VP-A68-TK, 1-1/8″ semi-cartridge, with horrible seal, making it a greasy rust water mess.
my custom 2010 trek 3900- Inside the headtube
my custom 2010 trek 3900- Inside the headtube
  • The Bontrager LT-3, 26×2.0 tyres got horrible grip in the wet they are a death trap. on wet asphalt they slip and you will crash, there is not enough space between the knobs and the rubber is too hard and not sticky enough to grab on to the asphalt check out the the review by Bikechanic :

  • 25221077486_cf268d17c3

winter ready & upgraded 2010 Trek 3900 Disc


  • replaceable derailleur hanger, which is a must.
  • decent welds.
  • stiff enough frame for a average rider for at least this size.
  • the brake rotors can handle metal pads.
Rusted Promax 160mm disc
Rusted Promax 160mm disc

Rusted Promax 160mm disc


seatpost swap Trek 3900_1900
Most recent state of the bike, assembled with parts from part I took from other bikes I have, and some parts I had used previously. this bike does not fit me, but I just did this to have a spare bike, I will eventually build a new bike with some of the parts I have on the fuel ex plus some new parts.

waste of money, unless you need a bike fast and it’s the only bike you can then at the point you are i the store.

I only used the 3900 as winter bike, plus the front dérailleur does not work in  below -2 degrees for some reason, maybe due to the wear it has.

the review was originally posted 26 june 2015, but I improved the text and added pictures.