NICA Parent's First Mountain Bike Buying Guide

The National Interscholastic Cycling Association, or NICA, is exploding in popularity, and I've seen a lot of parents buying their kids their first mountain bike lately.  In almost every case I've seen those parents make the same mistake of not buying a bike that's going meet the needs of their young rider, even in the short term, and I wanted to lay out some guidance as a second-season NICA dad, a former bike shop mechanic, and as a newer mountain biker myself.  Before we get started on what you should be thinking about when picking out your first mountain bike, I want to lay out some basic truths:

1) Any bike is better than no bike, and I've seen some student athletes do very well in races on low-end bikes.  You can always buy a better bike later.  Your bicycle is not a tattoo; bikes are temporary.  I'm not here to shame anybody into buying more bike than they can afford, but I do think that too many parents are not buying what they should be buying out of fear that their kids won't be into it long term, or that the more expensive bikes and features aren't worth it, or that they won't be appreciated by a new rider.  The very opposite is true in each of those cases, to a point. A new rider will absolutely and instantly feel the difference between those bikes, and that difference will manifest itself as a desire to ride their bike more.  It's no fun to ride a no-fun bike.  

2) I think there is a perception that the difference between a $600 entry level bike and a $1500 bike is the difference between a Honda and a Ferrari, but in reality it's the difference between a 1984 Chrysler K-Car and a modern Honda Civic.  That K-Car will get you to work, and they sold millions of them, but you're not going to drive them for fun, and they're not going to inspire a love of driving.  They're not safe or reliable, and they were designed when the national speed limit was 55 mph.

3) The kind of riding that NICA is geared towards is most likely not the kind of riding your kid wants to do.  Cross country NICA riding is a wheels-on-the-ground affair, and any opportunities to catch air on the NICA race courses are typically roped off.  Let me tell you right now, your kid wants to jump. Luckily for your your kid, amazing flow trails with beautifully sculpted jumps are being built across the country at record pace. Unluckily for you though, the entry-level bikes that are made for those trails are somewhat more expensive than the entry-level cross country bikes.  Since all good bikes are expensive anyway, and since you're probably not going to buy a different bike for each of those disciplines, and since there's no cash prizes for winning a NICA race, and since your kid probably isn't going to win even with an expensive cross country bike anyway, I'm going to recommend that you buy a bike that's capable of doing what your kid wants most.  You'll get more use out of it, and it will inspire a love of riding that will last forever.  

With that being said, here's my list of must-have features on an entry-level mountain bike:

A dropper post.  Don't buy a bike without a dropper post.  The only situation I can think of in which you might not want to buy a dropper post is if your kid is coming in first place in track and cross country running events, and you think your kid might only be interested in pure speed.  Otherwise, that dropper post is going to make all other kinds of riding more fun, and by a significant amount.  A dropper post is like an office chair, which will lower when you're sitting and pull the handle, and raise when you pull the handle and take your weight off of it. This allows you to have your seat all the way up for uphills and fast flat riding, and instantly lower it for jumps and technical descents. Do not buy a low-end bike without a dropper post thinking you will add one later, even if the bike has internal cable routing for a dropper post already.  You won't, and if your bike came with a front derailleur then it's shifter is going to be in the way of the dropper lever, and the expense of converting a low-end bike to a 1x system so you can add a dropper post isn't usually worth it.

A 1x drivetrain.  All the cool kids are riding 1x these days, and for a good reason.  1x drivetrains (pronounced "one-by") don't have a front shifter or derailleur, but instead have 9, 10, 11, or even 12 gears in the back and a single (1x) chainring in the front.  They typically shift better, are lighter, allow you to put a dropper post lever where the front shifter would have been, but most importantly they're just easier and more fun to ride.  Thinking about when you should use your front shifter and when you should use your rear is just gone.  

A clutched rear derailleur.  Because of the increase in popularity of 1x drive trains, rear derailleurs must move from tiny rear gears to absolutely dinner-plate sized gears in the rear, so they have a lot of travel.  What the gear train manufacturers have done is to make that rear derailleur so that it doesn't flop around when you hit a bump.  You might remember that on your old bike you could take the jockey wheels of the derailleur and pull them up and forward, which makes the chain all floppy on the underside.  For reasons I don't fully understand, clutched derailleurs don't do that very easily and it keeps that long travel derailleur and chain from smacking against the bottom of your bike frame on jumps and bumps.  You won't realize how bad you need a clutched rear derailleur until you've ridden one.  I'm pretty sure almost all 1x drivetrains come with clutched rear derailleurs, but check to make sure.  

A quality air fork, with adjustable rebound dampening.  Do not buy a bike with a spring fork and no rebound dampening.  They are jarring, klunky, and loud. Your hands will go numb, they're heavy, and you will not have as much control over your bike in bumpy terrain.  You will not be happy after the first month of riding.  

Hydraulic disk brakes.  Even the worst hydraulic disk brakes of today are so much better than the rim brakes of old, and the cable actuated disk brakes of not-that-long-ago.  I'm not sure if you can even buy a new mountain bike without hydraulic disk brakes these days.

Those are my must-haves, even for a brand new mountain biker, and looking over Trek's website their cheapest new bike that meets those requirements is a Trek Roscoe 7, at $1,260.  I see so many parents buying their new mountain bikers a Trek Marlin 5 at $550, and that's a mistake.  The derailleurs are Shimano Tourney, and that's literally department store bike level stuff.  The fork is not made for off road use, but called by its manufacturer (Suntour) a "metropolitan" fork.  I made the same choice that so many other people make.  That was the first bike I bought my son, and a few years later that was the first bike I bought myself.  It was an OK choice for my son because he was still small and was not just his first mountain bike, but his first real bike at all.  It would not be appropriate for a high school student.  I was instantly disappointed in mine, and within a year I had spent significantly more on my next bike (a Remedy 8 at $4,000).  My son now rides a Trek Roscoe 8 at $1,790, which he absolutely loves (and spends about 6 hours a day on), but is not a particularly fast cross country bike for NICA races.  I know a lot of people who use their Trek Stache as a playful all-purpose fun bike, and also race them.  In fairness, I should say that I saw a student athlete place in the top 5 of the 9th grade race in Bentonville, AR on a Marlin 5, and he looked like he was having a great time, but I'll bet he upgrades soon.

I want to also list a few other considerations that I don't consider must-haves exactly, but I want you to be prepared to know about them when you're out shopping for a new bike.

Tire size: You used to ride a mountain bike that had 26" wheels.  ALL mountain bikes had 26" wheels for many, many years.  These days you can't buy a 26" wheeled mountain bike.  It's all either 27.5" (also called 650b) or 29".  Which one is best is hotly debated, but it is generally considered that 29" is faster, and 27.5" is more nimble, but even that is debated.  You will be blown away by the improvement these wheel sizes have over 26" wheels.

Tubeless tires: All better mountain bikes will have tires and wheels that are ready to run without tubes, but when you buy them in the store they will be sold with tubes in them.  It's easy to take the tubes out, and convert them to tubeless, and you will spend a lot less time on the side of the trail patching tubes, and you will get better traction as well.  It does make changing tires a bit more of a process, but it's not that big of a deal.  I would almost call this a must-have for NICA racing, since the rules do not allow anyone to help your rider change their tires on the course, and tubeless greatly reduces the chances of a flat.

Thru-axles: On your old mountain bike you used to have quick release skewers.  At first glance it will look like modern mountain bikes have quick release skewers, but they don't.  They have thru-axles.  A thru-axle is much thicker, stiffer, and screws into threads cut into the frame, which keeps everything perfectly aligned so disk breaks don't rub, and adds stiffness to the frame and fork.  This means if you have a roof-mounted bike rack that attaches to your forks, you will need an adapter or a different bike mount.

Head tube angle: Geometry of modern mountain bikes is nothing like the geometry of that old bike you used to ride back in the 2000s.  One of the most important differences is the head tube angle.  Modern mountain bikes have forks that stick out like old motorcycle "chopper" bikes (although not so obviously).  This angle is measured between the fork and horizontal (like the ground), so the lower the angle the farther the fork will stick out.  A fork with a low angle (like in the mid 60s) is called "slack" and a fork with a high angle (somewhere in the low 70s) is called "steep".  Steep bikes are considered more nimble (bordering on twitchy) and slack bikes are slower to turn, but are more stable.  Your kid will crash a slack bike less often when jumping.

Rear suspension: If price is any concern at all, I would avoid a bike with rear suspension as a first bike for a NICA racer.  Unless you spend significantly more money they will be heavier than a hardtail mountain bike.  Furthermore, a hardtail will develop better bike handling skills and will require less maintenance, and you can put that rear suspension money into better components.

Where does this leave you, considering your first real mountain bike purchase for your offspring?  Well, if you can, spend as much as possible on your bike. Buying used can be a great choice, and should be considered as an option before buying new.  You can get a lot more bike that way, but I still wouldn't buy anything more than 5 years old. Mountain bikes are experiencing a revolution in quality and innovation since about 2016 that is truly useful and valuable.  Also, check with your bike shop about NICA discounts, which can be as high as 25% off a new bike. 

One last thing: I would consider also buying a cheap "beater" bike for your kid to ride around the neighborhood and leave laying on its side in their friend's front yard while they play Minecraft in the basement during a rainstorm.  A $1,500 bike is too valuable for this kind of task.

Easier Way to Make Involute Bevel Gears in Autodesk Inventor

I have a long-winded way to make working bevel gears with involute tooth shapes for 3D printing here, but it's so long and such a pain in the butt that I thought an easier way is in order, so I streamlined the process.  I'm using Inventor 2019, by the way.  Here we go:

1) Make a new assembly and save it.
2) In that new assembly click the Design tab, then click Spur Gear.
3) Click the More Options >> button in the bottom right corner to expand the Spur Gears Component Generator window down.
4) Change Size Type to Module (if you're in my CAD 2 class, otherwise feel free to use Diametral Pitch).  Change the Input Type to Number of Teeth.
5) Change Design Guide to Center Distance.  Make sure the Internal checkbox is not checked.  Use a pressure angle of 20°, and a Helix angle of 0°.  Change your Module to 1mm, which is the smallest teeth I get a good result with on my 3D printer.
6) Type in the number of teeth you want on your smaller gear in the Gear1 area, then type in the number of teeth you want on your larger gear in the Gear2 area.
7) Hit Calculate.  If you hit the little >> bar on the right side of the window it will show you data about the gears it's going to make.
8) Click OK.  It will give you an error.  I've never had it not give me an error that says my gears won't work, but they always seem to anyway.
9) Inventor will put your gears in the assembly.  The teeth are not involute and overlap the teeth on the mating gear, so you can't use these parts in real life.
10) Right click on either of these gears and then choose Export Tooth Shape.
11) Choose the Pinion to export (which is Gear1).
12) If your 3D printer makes parts slightly too large (mine does) you will want to change your  Normal Backlash to .006, which is the largest Inventor will allow you to enter with a module of 1mm.
13) Hit ok.
14) Inventor will make an extrusion of a circle with a sketch on the end of it showing the space between the teeth.  Delete that extrusion, but leave the sketch.
15) Edit that sketch and delete the construction line circles (but not the solid outside circle).
16) In that sketch make a circular pattern of the space-between-the-teeth-shape, for however many teeth you have.
17) Trim the outside circle between each tooth so that it looks like a gear.
18)  Finish that sketch.
19) Click the Manage tab.
20) Click Parameters.
21) Click Add Numeric.
22) Type OtherGearTeeth as the new parameter name.  No spaces.  Capitalization is important.
23) Click the Unit/Type cell in that row, click the + next to Unitless, then choose Unitless (ul) and click OK.
24) In the Equation cell for that row, type in the number of teeth in the OTHER gear.  You will notice that there is already a parameter called NumberOfTeeth with the number of teeth in THIS gear, so make sure you enter the number of teeth in the gear that this gear is going to mate with.
25) Click Done.
26) Make a new sketch on the YZ Plane (which can be found under the Origin folder in the Model bar on the left side of the screen).
27) You should see the side of your gear sketch going through the origin, so it will look like a dotty line running up and down.
28) Now you are going to draw the following lines:

Make sure you don't accidentally make the two green lines perpendicular to each other.

29) Use the following picture to place the next 4 dimensions.  You can cut and paste these formulas into your dimension editing boxes.

29a) The angle between the left angled line and the centerline is:
90-(( 90 deg - atan(OtherGearTeeth / NumberOfTeeth) ) / 2 ul)

29b) The angle between the construction line and the centerline is:
90 deg - atan(OtherGearTeeth / NumberOfTeeth)

29c) The diameter between the centerline and the very bottom point of the two solid lines is:
HeadDiameter + .001

29d) The diameter between the centerline and the bottom of the construction line is:
PitchDiameter

30) Everything should be fully constrained now, so finish your sketch.
31) Revolve that triangle around the centerline.
32) Click Start 3D Sketch.
33) Click Project to Surface.
34) The "gear sketch end" of your cone is the Faces, and the sketch of the gear is the Curves.  You can just click on the end of the cone, but you have to use a bounding box to select the gear sketch. It seems to work best if you don't include the entirety of the near end of the cone in the bounding box along with the gear sketch.  Click OK.
35) Click Finish Sketch.
36) Click Axis and make an axis right through the middle of the cone.
37) Under Point, choose Intersection of a Plane/Surface and a Line, and make the surface the "non-gear-sketch-end" of the cone, and the line will be the axis you just made through the middle of the cone.
38) Click Loft, and as your first sketch choose the projected 3D sketch of the gear, and as your second sketch choose the point we just made at the other end of the cone.
39) Sometimes Cut works for the loft, and sometimes Intersect works, and I can't tell why it's not consistent, but one or the other will work.  You may have to try it both ways.  I try Intersect first usually.
40) Now you have a bevel gear.  You will need to trim it up to get it to fit into your model, but it should have the correct teeth.   Don't forget to save your work!
41) The process is exactly the same for the mating gear, but remember when you're adding the OtherGearTeeth parameter for the second gear, you won't type the same number of teeth into it as you did this time (unless both gears have the same number of teeth)