Condensed Answer: Successfully equipping a 20″ BMX with a suspension fork is a difficult task because the geometry of a rigid BMX is not designed to operate with suspension.
Also, most front shocks for 20-inch wheels are either custom made and rare or designed for children’s mountain bikes and unable to sustain the stress of extreme BMX jumping.
If you want to ride a BMX-like bike with suspension, it’s wiser to look into 24″ and 26″ dirt jumpers.
The Problem With Suspension On BMX Bikes
Suspension on a BMX creates the following issues:
1. Negative Changes to The Geometry
The frame of an average 20″ BMX is designed for a rigid fork. If you install an after-market suspension fork on it, the conversion will create the following issues:
Raised front end. If the fork isn’t engineered for a BMX, it will be a lot longer than a standard rigid model. As a result, the front end of the bike will raise, and the headtube angle will become unpleasantly slack.
The maneuverability of the bike will suffer, and it will be very easy to “loop out” (the bike sliding in front of you).
For that reason, it’s not recommended to install a mountain bike fork on a classic BMX bike.
Steep Head Tube Angle. Even if the suspension fork is made specifically for a basic BMX bike, it can still create some issues because the frame itself won’t be built for a suspension fork.
When the fork compresses, the front end of the bike will naturally get closer to the ground. The head tube angle will become steeper, and the rider’s weight will shift forward.
On a frame engineered for suspension, this isn’t a problem because the headtube is “tall enough”. But in this case, the outcome could include an accident such as getting over the handlebars.
This aftermath could be prevented if the suspension fork and frame are engineered to operate in union. The frame needs to have a taller head tube than normal so that the HTA doesn’t get dangerously steep upon compression of the fork. At the same time, the fork shouldn’t be excessively long so that the HTA doesn’t become uncomfortably “slack”.
2. Low Availability
You will be hard-pressed to find a decent suspension fork for 20″ wheels. Most of the offers are either custom, rare, and expensive or taken from kid’s mountain bikes. A fork from a kid’s bike cannot cope with the stress that an adult rider would put on it.
3. Tricks Get Harder
A suspension fork complicates the execution of some tricks. For example, it’s a lot easier to perform a nose manual with a rigid fork because you have a stable base underneath you.
4. Lost Connection
A suspension fork absorbs the irregularities of the road. This is clearly beneficial for mounting biking, but when it comes to street and tricks the absorption has a negative side too – it reduces sensitivity and the “connection with the ground”.
5. Bad Habits
A rigid bike teaches you how to absorb landings without counting on suspension. Thus, in some regards, a suspension fork could be seen as a crutch, although that conclusion may a bit too opinionated.
Suspension forks are heavier than rigid ones due to the extra parts required for the proper operation of the shock’s mechanism.
7. Potential Point of Failure
Suspension forks aren’t nearly as robust as rigid models. For example, one has to be extra careful not to scratch the stanchions on a suspension fork because they can deteriorate. Also, a suspension fork needs frequent servicing which includes replacement of the suspension fluid, the lubricating oil, the foam rings, and the seals.
Interesting to Know: One of the most popular 20″ BMX suspension forks is Answer PRO FORX. The fork came out in the early 90s and was designed for BMX racing. Many of the professional racers advertising it were using a PVC elastomer which was essentially turning the fork into a rigid one. (source)
The Best Alternatives
If you want a street BMX-like bike with suspension, your best option are 24″ MTBs.
Those models offer the following benefits:
- Suspension-friendly Geometry
Unlike standard BMX bikes, 24″ inch MTBs have a frame designed for suspension. As a result, the head tube angle doesn’t experience dangerous changes when the fork compresses.
- More Choices
It’s notably easier to find a 24″ fork than a 20″inch one
- Small Tire Size
24″ tires are fairly small and preserve the “BMX feel” much better than 26″ models.
- Extra cushioning + Greater Roll-over-ability
24″ which tires are still notably bigger than 20″ and ride over obstacles with greater ease.
- Extra Speed
Larger wheels preserve their kinetic energy for longer once you get them up to speed. Hence why 24″ inch wheels require fewer crank revolutions in-between tricks.
Below is a list of 24-inch MTBs with suspension that are as close as possible to a BMX bike:
- Black Market Contraband
- Union Street Molly Maguire
- Specialized P.Street 24″
FAQ: Can I put a standard mountain bike fork on a BMX?
You could, but the final result will be non-satisfactory. The fork will be too long and will raise the front end of the bicycle tremendously. As a result, the handlebars will become too tall, and the headtube angle will get unpleasantly slack to the point where steering is a problem.
The only way to minimize this effect would be to get a fork with a shorter axle to crown length. For better or worse, such 20″ forks are hard to find since they aren’t mass-produced unless you count kids’ bikes.
FAQ: Can I put a suspension fork on a 24″ inch BMX cruiser?
You could, but the geometry will suffer unless the bike’s designed for suspension in the first place. If it isn’t then, the headtube angle will be all wrong in both states of the fork (compressed and decompressed).
The negative consequences will be minimized if the length of the suspension fork matches that of the rigid one. However, even in that case, the geometry will be compromised because the HTA will get dangerously steep upon compression of the fork.
If a bike isn’t built for suspension, it’s best not to put one on it.
Summary: What You Need To Know
1. Standard BMX bikes aren’t designed for suspension forks. Installing one creates unpleasant changes to the geometry harming the handling of the bike.
2. You shouldn’t install a mountain bike suspension fork on a BMX because it will raise the front end too much.
3. 20″ suspension forks are a rarity because there’s isn’t a market for them. The only available options are retro (made in the 90s), from children MTBs (too weak), or custom (expensive and hard to find.)
4. Freestyle BMX bikes will never adopt suspension because it’s heavy, vulnerable, and kills the sensitivity of the bicycle.
5. If you want to have a bicycle with suspension that feels as close as possible to a BMX, you should look into 24″ MTBs/dirt jumpers.