|To be honest, there's not much between a lot of downhill bikes on the market, but the two that you're considering really are at opposite ends of the spectrum in terms of what they each excel at. Let's look at the Demo first: it's a nimble bike that is going to take less effort to ride and race on tracks that require a bit of pedalling or are less fall line in their layout, and it's a load of fun on smoother, jump filled trails that really allow its playful side to come out. Depending on the terrain, it's also one of the best cornering downhill bikes on the market, at least in my mind, thanks to its relatively short rear end and low bottom bracket height. If the Demo is the gazelle of downhill bikes, the Gambler has to be the lion. The Scott has a much larger presence on the trail, and while a solid rider is going to get it down any course in good time, it feels most at home on steep, chunky and fast terrain. It also sports adjustable geometry that allows you to tailor it to exactly those sorts of tracks, letting the rider slacken it out much more than what's possible with the Demo, and really feels at home on the gnarliest of trails. Where it doesn't excel, at least in my experience, is on tamer terrain that requires you to use some ponies to keep your momentum up. It's a serious bike that performs best on serious trails.|
I'd recommend that you make an honest evaluation of where and how you ride before laying out cash for either. I'd tell a downhiller who rides and races on more average terrain to go with the Demo, but the Gambler may be more up your alley if the only pedalling that's required on your trails is the twenty feet from the truck to the trailhead, which really isn't how it usually is. Sometimes the gazelle is fastest, and sometimes it's the lion. - Mike Levy
|Take the chain off the front sprocket and spin the crank. If it spins smoothly, you can eliminate the possibility that you blew up your bottom bracket bearings. Next, view the rear derailleur from the back of the bike to see if it is visibly bent inwards. If not, the most probable reason for your rumble is that the rear derailleur's B-tension screw is not turned in enough to keep the upper derailleur pulley from running into the cogs. The B-tension screw contacts the hooked tooth of the frame-mounted derailleur hanger. Turning it in (clockwise) rocks the derailleur body away from the cassette sprockets.|
Another problem that is specific to one-by transmissions is running the chain too short, which draws the lower cage pulley so far forward, that the angle the chain creates between the pulley and the chainring is greatly exaggerated when the transmission is shifted to the extreme ends of the cassette. This causes rumbling at the chainring as the links attempt to engage the sprocket teeth from an odd angle. The new chain and cassette may have tighter tolerances and thus would naturally make more noise. Check the B-tension screw first and then set your chain up as long as possible. Start by stringing it through the rear mech with the derailleur shifted into the smallest cog. Set the chain length so that the pulley cage just begins to angle downward - that's the longest that the chain should be.
Finally, you did not mention whether you were using a short, mid or long-cage rear mech. If you are using a mid or short-cage derailleur, it may not have enough chain takeup to cover your gear range, in addition to the amount of chain growth built into your rear suspension. A drivetrain with a perfectly tuned chain length on the bike stand may be pressed to the breaking point when the suspension is sagged or compressed while climbing. You may need to bump up to the next longer pulley cage if this is the case. - RC
The B-tension screw (left) keeps the upper derailleur pulley from running into the cassette cogs, which is the cause of most rumbling drivetrains. KEEPitSTUPID's narrow-wide Raceface chainring is probably not causing the noise.
|Bottom bracket 'standards' can be confusing, since the number of different options continues to grow. If your cranks are already removed, the easiest way to tell what you have is by measuring the spindle diameter. As the name suggests, a BB30 or PF30 crank will have a 30mm spindle diameter, while a GXP crank's spindle will measure 24mm with a 22mm splined portion on the end. If you look at your bike, the bearings for a BB30 setup are typically found inside the frame, while the bearings for a GXP would be housed externally in cups that thread into the frame. Another way to find out without doing any measuring or crank removal is to go to your bike manufacturer's website - there should be a section where all of the frame specs, including bottom bracket type are listed. - Mike Kazimer|
The bearing for a PF30 bottom bracket are housed inside the frame, as opposed to being housed in external cups that are threaded in.
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