Trials Tech
your bike trials specific bike tech questions answered!

How do I keep my freewheel from blowing up? (tighten/loctite it!)

If you need tips on how to set up your bike (this includes proper chain tension, bar angle, brake lever angle...), click here!

Can't decide between getting a stock or mod trials bike? Click here!

Want to learn how to shave down a uni seat, apply tar, grind rims, etc? See the how-to articles

    Bashring (stock only)
    • protects front ring(s) from bashing
    • allows new ways through sections that previously would've been too extreme to get through

    Bashguard (mod only)
    • protects front ring/freewheel from bashing
    • protects bottom of frame
    • allows new ways through sections that previously would've been too extreme to get through

      Mod (personal preference)
        no seat
        • increases clearance
            You can bend as far down or back as you can without running into a seat. You can also trackstand in any position without your calves rubbing against a seat
        • decreases weight
        • increases safety
            The top tube is so low that you would be very hard pressed to crash and land on it. You have extra clearance.

        seated - every other mod bike on the planet
        • UNI seat - these itsy bitsy little seats from bmx days, I think.

      Stock (personal preference)
        no seat
        • same reasons as for mod

        seat - every other stock bike on the planet
        • usually flat (clearance)
        • usually narrow (clearance for inside of legs)
        • usually standard road or mountain bike seats

    Wide handlebar
    • makes it easier to balance
    • gives you more leverage for turning the wheel and moving the pulling the front wheel with you

    Thin grips (personal preference)
    • feel every little thing that your front tire is resting on

    Double-Caged Pedals (personal preference)
    • grip shoes well
    • grip obstacles better than anything else
    • are better than platforms with replacable pins, because the pins are punched out of the pedal in trials, ruining the threads in the pedal, making the pins in essence irreplaceable
      VP pedals

    Shorter cranks
    • for ground clearance (when spinning, pedals are less likely to hit something on the ground as you go over them)
    • make it easier to balance because your feet are closer together
    • make it easier to pedal-kick further (take into account how far you can move your body forward on longer cranks before you run into the handlebars or stem)
    • make a full 360 degree pedal rotation a lot smoother, which helps for ups and pedal-gaps.
      You lose some leverage with shorter cranks, howerver, making it harder for far pedal-kick gaps (according to Jeff Lenosky, says Chris Pascucci), making the happy medium for stock bikes 170 mm.
      Mod bike cranks are generally around 158 mm, while stock ranges from 158 mm to 170 mm

    Strong bottom bracket
    • to prevent serious ankle/calf injury (less durable bottom brackets will bend or snap without warning) Light-weight bottom brackets have no place in trials (titanium bottom brackets are for the most part out)
      A good quality, fairly light bottom bracket that should last you a while is the Shimano UN-72 (XT quality). The UN-52 is very strong, but also very heavy. You should be able to find either one for under $25.

    Front freewheel (mod bike primarily, although some stocks will have them)
    • Why a freewheel over a cassette hub?
        It's cheaper and more convenient to replace a freewheel ($11 brand new) than it is to rebuild a cassette hub

    • Why on the crank instead of the rear wheel?
      • Fixed rear wheels are cheaper than cassette hub rear wheels. You are more likely to be able to afford an extra rear wheel for emergencies.
      • Chain tension? - The chain is kept taught while rolling, although the benefit of this is unknown to me, as the BOTTOM of the chain is kept tight, not the TOP of the chain, which is what ought to be kept taught.
      • Smaller front ring (in this case freewheel, obviously) can be run than will fit on most cranks. 18t front freewheel will give you more clearance over the ground for your chain, which will decrease the chance of smacking it on stuff, which is always a good thing.
      • Smaller rear cog can be run than on most cassette hubs - I believe the front freewheel thing came about at a time where you could not get cassette bmx hubs, and certainly could not get freewheels as small as 12 teeth! With an 18 tooth front freewheel, you can run a 12 tooth fixed rear cog. This is a great ratio for mod trials, and has very good ground/bashguard clearance. Currently the only company I know of that makes a rear bmx hub that can take a 12 tooth cog on is Chris King. Profile Racing makes a rear bmx hub that you can run a 13 tooth cog on. I think front freewheel is a much more cost-effective way to go, though.

    Strong Chain
    • Oil them before each ride! This will keep your chains lasting longer by reducing friction inbetween the plates...
    • Always replace the whole chain when they break (replacing links with new ones with your chain tool make the chain weak where they are joined, the way the manufacturer joins links makes the chain MUCH stronger than the way your chain tool joins links)
    • Check often for split plates or missing rollers (this can occur from pedal-kicking and landing too far back on your bashguard)
      Note: It usually hurts a lot when your chain breaks, so learn to love it and change it often!

    Chain tensioner
      • keeps the chain tight (duh)
      • allows you to get the wheel angled straight
      • keeps the wheel from getting pushed further into the drop-out on huge rear-wheel drops

        How to get your chain tight with Monty snail style chain tensioners:
        Flip the bike over, loosen each bolt on the wheel one turn, pull out a pair of pliers or an adjustable wrench, then turn the chain side tensioner one slot tighter with the pliers or wrench and then do the non-chain side. Balance the bike on the rear wheel while tightening the bolts, just to make sure they're resting against the tensioners well.
      • keeps your chain from slapping around or falling off
        some riders take out links instead to tighten their chain

    Wide rims
    • keep tires running at low tire pressure from rolling off
    • provide extra stability

    Fat rear tire
    • absorbs impact of drop offs
    • grips better
      Mod rear tire is usually about 2.5" wide, while stock is usually around 2.3" wide
      Front tire doesn't have to be as fat because most of the impact is absorbed by the rear

    Low tire pressure (personal preference)
    • allows tire contact patch to be larger, gripping the surface better
    • allows bike to bounce more easily, which helps beginners (some pros like a little bounce)

    Strong wheels
    • for pedal-kicking
        Pedal-kicking puts a large amount of torque on the hub, which is transferred through your spokes and nipples to the rim, then your tire, and finally to the ground. If you are running anything weaker than 14 gauge straight spokes (what comes on an X-Lite rear wheel) and brass nipples on the drive side of your rear wheel, your wheel will break down considerably faster. If you seem to be breaking drive-side rear wheel spokes all the time, this is almost positively because of pedal-kicking. Some riders run 13 gauge spokes (about as strong and heavy as you can get).
    • for drop-offs and regular abuse
        Drop-offs put a good amount of stress on the spokes and the rim.
        Here are three ways to limit the damage caused by every drop-off:
        1. keep your spokes tight (ask your bike shop for help)
        2. run high enough tire pressure to prevent bottoming out and denting the sidewall of your rim
        3. learn to drop off very smoothly, distributing the force of landing out over a longer time period, using both wheels to absorb the landing (landing rear wheel first and foremost, however).

    Road cassettes (stock bike)
    • allow riders to pick from a tighter range of gears (12-21 compared to 12-32 for most mountain bike cassettes)


          Popularized by Shimano for cross country bikes. Forget cantis and u-brakes, this is the new leader in reliable, cheap, good performance braking.
          Good braking
          Decent modulation (varies widely, depending on your setup)
          Easy to set up
          Easy to work on
          Some v-brakes can't withstand the braking force in trials and develop play (you'll need a new brake if this happens)
          Don't feel as good as Maguras (personal preference)
          The best bang for your buck. If you aren't already sold on getting Maguras or disc brakes, just get a nice pair of Shimano XT V-brakes. Don't feel like you're going to grow out of them and "need" Maguras when you get better. Some pro riders run v-brakes, after all. Hey, Jeff Lenosky ran a Shimano DX V-brake on his bike for awhile (perhaps he still does?), and not only does he pull huge moves, but he's a huge guy!

      Magura Hydraulic Rim Brakes
          Have been around for years. Magura makes brakes for a lot of things other than bikes. The interesting thing about Maguras is that they use oil to push the pads onto the rim. Oil doesn't compress much at all, and I believe this is what gives the result of good modulation in Maguras. V-brakes use wire, which not only stretches over time, but stretches when you are braking. This is what can make V-brakes feel mushy. With Maguras, you will feel the pad hit the rim through the levers. Very positive feedback. I feel that I can always pull a v-brake lever more, even after it locks the wheel, while with Maguras, I pull, the wheel locks, and I can barely pull the lever anymore. It's all about feel, I think...

          The other interesting thing about Maguras is that there are two different mounts:
            Canti mount using the Evolution adapter - Your every-day, standard 2 bolt mount you see on almost all mountain bikes today

            Dedicated Magura mount - 4 bolt design allows you to set up your brakes easily and is stronger. This is the kind of mount you will see on almost all trials bike frames.

          The only difference between the two designs is the part that bolts the brake cylinders to the frame. The brakes themselves are exactly the same.
          Good modulation (varies widely, depending on your setup)
          Good braking
          Feel great
          Theoretically not as strong as V-brakes
          Can be a pain to set up (but once you get them set up, you're done forever)
          Some people kick the crossover line off with their feet (I've never had a problem)
          More expensive than v-brakes
          Best way to go for trials right now, at least until disc gets all it's bugs worked out.

      Disc Brakes
          The disc brake had it's birth in the motorcycle world, then trickled it's way down to downhill bikes, and then trials bikes. The true ultimate brake because it doesn't brake by squeezing the rim, instead it squeezes a small rotor attached to the hub. This avoids all of the imperfections of rims. It does not matter how true your wheel is when you have disc brakes. Disc brakes work well regardless of the amount of water, mud, dust, etc that accumulates on the rotor and pads. However, disc brakes put a lot more rotational force through the spokes than a traditional rim brake does, so you must build a very strong wheel to take the abuse. You cannot radially lace a wheel used with disc brakes. Currently, disc brakes do not appear to be a very good idea for the rear brake on a trials bike, because of the problem of ripping off the disc brake tabs or damaging the frame's stays. If you try it, be prepared to have problems (just in case). I'd recommend taking a Magura hydraulic rim brake (with tubes and lever attached, of course) with you to competitions in case you should brake the tabs off your frame. A certain pro that will remain nameless broke the tabs off his frame and ran a Magura rim brake until he could get it fixed.
          Great braking and lock-up power all the time
          Great modulation
          Can be nearly impossible to set up without having drag (this is the tendency for the pads to lightly touch the rotor when you aren't braking)
          Expensive - On top of the brakes themselves, you need to build up new wheels with the proper hub and rotor
          Some disc brake pads fall out when you brake while going backwards (depends on manufacturer, so be sure to check)
          Advanced and heavier riders cause severe wear on frame's chainstay (being addressed with better designed frames)
          Advanced and heavier riders brake the disc brake tabs off their frames (being addressed by better tab designs)
          Require you to build up new wheels with special manufacturer-specific hubs
          The spokes need to be strong enough to withstand all of the braking
          If you bend a rotor (supposedly pretty hard to do), you need a new one
          Great brake for the front if you have the money to spend. Rear brakes aren't ready for primetime yet. Hold out for a designed-for-disc-brake frame that holds up to months of abuse by the likes of Jeff Lenosky and JJ Gregorowicz.


          Roofing tar, to be exact. You can also find it on the beach. All you need is a small ball or chunk of tar. Old 35mm film containers work great to keep it from getting dirty or getting your pocket sticky. A small layer of tar is applied to the rims of the bike to increase the ability to immediately lock up the wheels. This technique works for all rim brakes (not recommended for disc brakes). It is not recommended for people who also ride their bike for mountain biking or as a get around town bike, as it makes the brakes VERY loud.
          Flip your bike over, spin the wheel, push the tar onto the spinning rim slightly on each side. Ride around and if you get that nice, grippy, squeaky sound when you pull the brakes, you're good to go. Just don't get too much on or your pads will stick to the rim even when you let go of the brakes. Try to put on just enough to get the braking power you need.
          Very grippy
          Locks up wheels easily
          Easy to apply
          Locks up wheels easily (not as much modulation)
          Turns slick when you get your rims wet (tar is oil based)
          Makes a horrible noise (although this is the official bike trials noise)

      Grinding your rim
        Grinding roughens the braking surface of a rim. This makes it sharper, which usually results in more friction between the pads and rim. The increased friction is usually both static (the brake will be less likely to slip when it is already locked) and dynamic (while the wheel is spinning, the brake will bring it to a stop more quickly). This is primarily done on the rear rim of a trials bike, to make it lock up more easily.
        Tools/Materials Needed:
          Hand disc grinder (I use a Makita 100 mm Disc Grinder with a Metal Professional 4" x 1/4" x 5/8" disc)
          Protective eyewear
        Directions: (if you are under 18, please have an adult watch and help you, or do it for you)
          Take the wheel you'd like to grind off your bike and remove the tire. If you're grinding the rear wheel, cover your gears with something to keep aluminum shavings out. Turn the grinder on, and rub it back and forth against the brake track on the rim. The grinding disc should be perpendicular to the rim, making cuts straight up and down. When you get the depth you want, rotate the wheel a little and keep going. You'll have to figure out how harsh of a grind you like. If you don't feel much of a bite with the newly ground rims, you might want to do it deeper next time.
        • Very good strength (medium to deep grind)
        • Good modulation
        • Works well in the wet (your grind will turn smooth fast, however!)
        • Nothing to apply to rims
        • Lasts longer than tar
        • Every time you grind your rims, your sidewalls get weaker (hasn't been a problem for me)
        • Possibly bad for your health (breathing in the fumes of aluminum probably isn't great - do it outside)
        • Your pads won't last as long (though you can make them last longer by only using the brake as on/off, and using your front brake to slow down)
        • Not all pads work well with a grind. Softer pads will just get ripped up by the grind, or will fill in the grind. In this case, the grind makes your braking worse. Most trials-specific brake pads work well with a grind.

      Plazmatic Coating
          You send your rims in to Plazmatic to get them coated. Check out Trialsin USA to find out more about it.
          The ultimate lock your wheels in any condition rim coating
          Expensive - About $200 to get a wheelset coated!
          Expensive - Go through brake pads fast (rough coating version. You can get medium caoting version.)
          Expensive - If you wreck your rim, your investment is gone
          Very little modulation
          Must send rims in to get coated

        Monty Pine Tar Spray - ?
        Coke/Pepsi (info thanks to Lester Bannister!) - I read it in MBUK and tried it and it does work - it makes your brakes very sharp. The only problem is that it can make the brakes squeak a bit. Another use for these fizzy drinks is to stick loose handlebar grips on. I personally haven't tried this but my mate had loose grips and put pepsi on the bars and inside of the grips. He then put the grips on and left them over night to dry and in the morning they were stuck tight. If you want to get your grips off again, Just get a thin screwdriver, dip it in a glass of water and slide it under the grip and turn it around the handlebar. This loosens all grips.