Team Bobs-Bicycles.com Mountain Bike Equipment Tips

Author: Fritz Stafford

Published: March 24, 2015

What kind of bike would be best, Full Suspension or Hard Tail or Fully Rigid, 26″ or 27.5″ or 29″?

For the case of XC MtB, the answer is 29″ Hard Tail for riders taller than ~5’8″. Shorter riders should also consider 27.5″ Some expert riders prefer fully rigid XC MtB due to simplicity and ultra light weight, but this provides harsh ride, and is not recommended as a first XC MtB.

For the case of Gravity MtB, the answer to the first part is Full Suspension, but there is variation of opinion on wheel size. I believe the Enduro enthusiasts argue between 27.5″ and 29″, and I know there are DH enthusiasts that prefer 26″ (i.e., wheels more bullet-proof, lower center of mass, more responsive turning).

For the case of Cyclocross, the answer is fully rigid with 700c wheels for riders 5’6″ and taller, and 650c wheels for riders ~5’2″ and smaller. Cyclocross frames are modified road bike frames with conventional road bike short cage rear derailleur and maximum rear cog size of 28 teeth (to provide the crispest shifting in muddy conditions), either cantilever or disc brakes (to provide stopping power in muddy conditions), 46/36 compact front chain rings and CX specific front derailleur (to minimize chain drops), inside of front triangle free of cables to facilitate bike carry over obstacles.

What kind of materials, Al alloy, Titanium, Carbon?

Carbon is the lightest and is adequately stiff for Hard Tail frame, hence the best choice for XC MtB and CX. However, carbon is expensive and fragile, especially the ultra light weight models.

Al alloy is cheap and very durable but heavy (although significantly lighter than steel), hence the best choice for DH frames. Al alloy is also a very good choice for Enduro, as weight compromises required for full suspension carbon frame reliability reduce the weight advantage. Al alloy is still a good choice for XC MtB and CX, as really deep discounts are available, especially from riders upgrading to carbon frames. Many modern carbon frame designs are available in cost reduced Al alloy models.

Titanium was the top of the line frame material until carbon came along, as it is slightly lighter than Al alloy, but significantly more forgiving (i.e., less punishingly stiff). There are not many benefits of Titanium over Al alloy for full suspension frames, and cost is higher. However, Titanium is still a very good choice for XC MtB and CX, as again, deep discounts are available, but frame design choices are becoming increasingly limited.

The Al alloy versus carbon material choice is also available for cranks, seat posts, stems, handlebars, and more. Be careful on these items, as some carbon implementations are significantly lighter and stiff enough but carry 2X-3X price premium (e.g., hollow carbon cranks), while other carbon implementations are not significantly lighter but still carry a 50% price premium (e.g., solid carbon cranks, “hybrid” seat posts and forks).

Titanium is also available as a light weight material choice to replace the remaining steel items on the bike, nuts, bolts, axles, bearings, cassette cogs, and more. These all carry a 2X-3X price premium, durability is often drastically reduced, and these Titanium components are generally not recommended unless you are fully sponsored pro with multiple bikes in the quiver.

How many gears, what gear range? Triple, double or single front chain rings?

Keep in mind that wheel size affects gearing. For example, a 36 tooth rear cog on a 29″ wheel provides the same gearing as a 32 tooth rear cog on a 26″ wheel, assuming the same number of front chain ring teeth.

Triple front chain rings were introduced on mountain bikes with 7-speed cassettes (originally with 28 teeth available on the largest cog), and remained the only choice with the migrations to 8-speed (originally with 30 teeth available on the largest cog) and 9-speed cassettes (originally with 32 teeth available on the largest cog). Over the last few years, 10-speed cassettes with 36 tooth cogs have made the double front chain ring more popular, especially for 26″ and 27.5″ wheel sizes.

However, many beginner and intermediate XC MtB racers still prefer triple front chain ring, as they like to have a very low gear option available to limp back home after bonking.

Today, there is single front chain ring option based on 11-speed cassette with 42 tooth cog, and this has the appeal of design simplification. However, the increased weight of the 11-speed cassette with 42 tooth cog more than offsets any weight reduction due to elimination of the inner front chain ring, front derailleur, cable and front gear shifter. The single front chain ring option suffers as a general purpose solution, as there will always be a lack of gearing on either the low or high end of the gear range. However, the single front chain ring option can be tuned for a particular race course by changing out the front chain ring, and this approach was utilized to set a new record at last year’s Leadville 100.

On the other end of the gearing options spectrum is the Single Speed option. This has the appeal of the ultimate design simplification and weight reduction, no shifters, no shift cables, no derailleurs, no cassette. However, this is another of those expert only options, and is not recommended as a first XC MtB.

What kind of wheels and tires?

Upgrading your stock wheels provides the biggest bang for the buck. The stock wheels that come with bikes with MSRP <$3000 are typically cheap, heavy junk. The rims are sleeved rather than welded and are otherwise not fit for tubeless conversion.

Tubeless Al alloy wheels are a great choice for XC MtB and CX. They have the benefit of tubed clinchers in that it is relatively easy to change tires for different race course conditions (i.e., versus tubular wheels with the tires glued onto the rims). Tubeless XC MtB wheels have many benefits: light weight; flat resistance due to sealant (i.e., goat head thorn resistant) and reduced susceptibility to pinch flats; lower rolling resistance due to elimination of the tube (constantly rubbing against the inside of the tire), reduced operating pressure improves traction and provides shock absorption. However, tubeless wheels carry a significant maintenance premium over tubed clinchers (see related Posts, …)

Carbon rim wheels that provide significant weight reduction benefits are also available for XC MtB and CX. For the case of CX, previous generation tubular time trial wheels have become popular (i.e., heavier and rims not as deep / aero as latest generation TT wheels, so deep discounts are available). For the case of XC MtB, the Carbon wheels with significant weight benefits are fairly new, and carry ~2X-3X price premium. For the case of Gravity MtB, the Carbon wheels that are currently available do not provide significant weight reduction.

In addition to rim weight, rim width is an important consideration, especially for tubeless wheels. Wider rims are heavier than narrower rims, but they provide several key benefits, better tire profile that provides wider contact / improved traction (especially when utilizing Stan’s wheels with BST technology), and improved strength. The wider tire profile may allow the usage of narrower tires in some circumstances (e.g., 2.1″ tires instead of 2.25″ tires in sandy conditions), and this can counteract the increased rim weight.

Some other wheel construction considerations are location of spoke nipples, spoke flange width, and type of spokes (straight pull versus J-bend). Spoke nipples that are accessible with the tire mounted on the wheel are highly desired in comparison to nipples than can only be accessed by removing the tire. Wider spoke flanges increase lateral wheel stiffness, assuming same spoke count and tension. Straight pull spoke designs can be more elegant, and can allow higher spoke tension (stronger wheel, or spoke count / weight reduction), but some implementations result in hidden nipples and / or narrower spoke flanges. Straight pull spoke hubs have less wheel design flexibility than conventional J-bend spoke hubs, and hence there is potential for increased cost, and / or utilization of non-optimal hub design.

The most common wheels at amateur XC MtB races are Stan’s Notube Al alloy wheels.

http://www.notubes.com/

Stan’s offers tubeless wheels for various MtB and CX disciplines and various rider weights. Pair these wheels with Schwalbe “Rocket Ron” or “Racing Ralph” “tubeless ready” tires with the reinforced sidewalls, and you will have as good a wheel set as anybody in your XC MtB race.

Bike Fit:

Frame size and geometry: Bike frames are typically available in a range of standard sizes that are suitable for most people with standard proportions and height range 5’0″ to 6’4″. In most cases frame size selection is based on the inseam measurement. Bicycle frames are designed for particular applications, and the bicycle frame geometry is a key aspect of the design. Be sure to select a frame design that best matches your application. For example, “gravity” bikes are not the best choice for “cross country” racing. Of course, there is an industry of custom frame builders who will build frames custom fit to your body geometry, application, skill level and technique, but it takes significant expertise to know what will work best for you, and this involves significant additional expense and lead time.

Crank length: There is much debate about whether the traditional crank length standards are optimum. However, the traditional road bike standard crank lengths are 165mm for height of 5’0″ to 5’6″, 170mm for height 5’7″ to 5’10. 172.5mm for 5’11” to 6’2″ and 175mm for 6’3″ to 6’6″. CX bikes utilize road bike crank lengths, and Mountain bike cranks are typically sized 2.5mm longer than road bike cranks. As most bike frames are sized based on the inseam, they also typically specify a corresponding crank length.

Cleat position: The starting point for cleat position is to center the ball of the rider’s foot over the pedal axle with the length of the shoe at right angle to the crank axle. I have found this is often the forward most cleat position.

The following bike fit adjustments are best done with the bike mounted on a “fixed” bicycle trainer on a flat level surface. Useful tools include a level, allen wrenches and torque wrench, plumb bob, tape measure.

Seat height: First, level the seat such that the low point in the center of the seat is level. Typically, the seat nose will be slightly lower than the back of the seat. The seat height is determined by sitting in the center of the seat with your cycling shoes on, placing the center of your heel over the center of the pedal axle, and adjusting the seat height until you find the point where your knee is fully extended but not locked. Next, do this with both feet and assure there is no rocking of the hips while pedaling with your heels. One approach is to determine the seat height where the onset of hip rocking occurs, and then reducing the seat height by 1/8″.

Seat fore – aft: The seat fore – aft position is determined by clipping-in and sitting in the center of the seat with cranks in the horizontal position, and then adjusting the fore – aft position until a plumb bob from the inside of the knee cap intersects the center of the pedal axle.

Note these two seat adjustments are inter-related, and will probably need to be repeated.

Handlebar height: The starting point for Mountain Bike handlebar height is ~1″ – 2″ below the nose of the seat. Riders with road bike background seem to prefer lower handlebar height, while riders from BMX or dirt bike backgrounds seem to prefer higher handlebar height. Handlebar height is adjusted by moving spacers from below the stem on the steering tube to above (or vice versa), and / or flipping the stem, and / or choosing handlebar with different rise. (See below paragraph regarding stem offset angle and handlebar rise and sweep.)

Handlebar reach: The more critical handlebar adjustment is the reach, which is primarily determined by the stem length. Stems are typically available in lengths ranging from 60mm to 120mm. As a starting point, adjust the brake levers to a slope of 45 degrees below horizontal. Clip-in, sit in the center of your seat and do your best relaxation meditation. The task is to find the zero stress upper body position, where you feel you are neither leaning forward nor backward. Now, lay your hands across the handlebar with outside fingers lightly wrapping the grips and forefinger(s) over the brake levers. Be sure your wrists, elbows and shoulders are flexed and relaxed. The handlebar reach is correct when you are in the zero stress upper body position with zero degree wrist bend while lightly gripping the handlebar.

Note that stems are available with offset angles that range between 0 degrees and 16 degrees. Hence flipping a stem from angling up to angling down will decrease the handlebar height. Handlebars are also available with a range of handlebar sweep and rise. For XC MtB racing, I have observed the popular choice is ~6 degrees sweep and zero rise.

Bike fit disclaimer: This bike fit discussion is intended as a starting point. It is strongly recommended to get bike fit done by a Bike Fit Professional. However, it is probably best to have done several rides with the bike fit starting point described herein before visiting a Bike Fit Professional, so you will not be starting from a point that is “way out of whack”.

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