There was quite a stir when Supercross BMX finally went into production with their first OS20 frame, a disc only version of the popular RS7 frame. It didn’t take long for the Supercross crew to be pressured into a cromo OS20 with the Supercross race winning geometry, the SX450, and it was lead by their own team riders.

OS20 isn’t new, it’s been around for some time, but acceptance has been a little slow. We have had two riders from the bmxultra.com team jump on OS20 early and speak highly of it, but personally I stuck with what I knew.

Our very own Paul Knox describes OS20 perfectly “OS20 is an oversized version of the pro sized 20″ rim and tyre combo. It’s close to the 22″ wheel size available to our freestyling counterparts. The OS20 standard was co-created by Tioga and Alienation for UCI World Cup time trial specialist and 2008 Olympic Silver medallist, Mike Day, specifically for BMX racing.”

It’s as simple as that really, a slightly oversized rim and tire combo. But because it raises the axle height you are already looking at a new frame and fork that’s OS20 specific.

Even though OS20 can be retro fitted to some standard 20″ frames and forks (where clearance allows). It’s not recommended, given it messes with the geometry of the frame.

Supercross took a slightly different approach with their OS20 set up. They started with a standard 20″ fork and built the geometry around that. It’s nice because you can use your existing 20″ fork if you are migrating across from a 20″ build, saving you a few bucks along the way.

First Impressions

Like I said earlier I was happy with a standard 20″ set up and I had my own cromo Supercross already. I love the feel of a cromo frame, a much smoother ride, and it’s important to me that I can ride the one bike for everything; the race track, dirt jumps, pump tracks, the road, literally everywhere.

I’ve heard the feedback of the os20 that it’s “fun”, “more comfortable”, “more stable”…only good things really, but I still wasn’t convinced that I needed a bike with bigger wheels. That was until Supercross’s Bill Ryan encouraged me to give it a try.

When the SX450 OS20 XXXL frame turned up, it is a beautiful frame, amazing clean welds, very classic looking in flawless show chrome, with an amazing decal kit that Supercross are known for. The notably thick dropouts and tapered seat and chain stays give it a modern look while adding to the stiffness and strength of the frame. I like the rear wishbone and front gusset that sits under the downtube/behind the head tube, both nods to some iconic frames of BMX past.

OK, so things were getting real, it was time for a new build. To complicate things a little for me I had to get a complete new brake and wheelset, the SX450 OS20 is a disc only frame. I always loved the simplicity of v-brakes, but it was finally time to dive in the deep end with disc brakes.

How did I build the SX450 OS20

I organised a Staystrong 120mm brake kit and some OS20 wheels built with Answer Pinnacle Pro rims and Profile AC-2 disc hubs. The rest of the parts I was able to transfer from another build.

The complete Supercross SX450 OS20 build looks like this

• Supercross 20″ SLT cromo forks with 20mm dropouts
• Speedline headset
• Profile Push stem
• Alienation NYC handlebars
• ODI Rogue V2.1 lock on grips
• Staystrong disc brake kit with a SRAM 140mm disc
• Profile Race cranks with outboard euro bb and spline drive spider
• Dane Design prototype chain ring
• Answer Pinnacle Pro OS20 rims
• Profile AC-2 20mm front/ 10mm rear hubs
• Tioga Powerblock OS20x1.60 tires
• Profile chain tensioners
• ACS Crossfire chain
• Supercross seat post
• Dia-Compe MX1500 seat clamp
• Profile logo pivotal seat
• Pedalling Innovations Catalyst pedals

It went together pretty well, I had some issues with the brakes initially. I found out later the best brake calliper to use with the 120mm set up is the Shimano XTR, but I had already committed to the Staystrong brakes. The problem was that the calliper didn’t sit as low as the Shimano, so it was only grabbing the end of the rotor, clearly it was time to bring in the professionals. Wes Colbran, good friend and a long time bike mechanic, with a whole lot of experience with disc brakes brought a few things to try and when we were finished we had to use a different disc brake mount adapter and went to a 140mm rotor. It was definitely worth it for the braking power, although I’m still not convince that disc is any better that v-brake for stopping power (but that’s another topic).

I had problems with the Tioga Powerblock OS20x1.85 front tire as well, it just wasn’t enough clearance for the 20″ fork for my liking, so I changed to a OS20x1.6 front tire. Despite my size it still provides plenty of grip no matter what the surface.  I’m told that the clearance was fine at time of the design but a casing change on the tire caused the latest tires to be slightly bigger and that Supercross SLT cromo forks in the future will be adjusted to allow for more clearance. My work around, running the smaller tire, was fine by me.

I was told I might want to switch my top load stem for a front loader to drop the handlebar height a little, but to be honest I was looking for a taller handlebar anyway, so I just stayed with what I had. Given the extra length in the frame I moved my bars back a touch. It immediately felt comfortable.

The ride

I raced the bike the day I finished the build. There’s nothing quite like putting it all on the line right off the get go.

My initial thoughts were “fun”, “more comfortable” … oh boy… they were right. Now let me set the record straight though, I am about 6’2″ I normally ride a Pro XXL frame, and this frame not only had OS20 wheels, but it was a XXXL giving me an extra 1/2″ in the top tube length on what I was used to. Being taller, it just made sense that it would feel nice to ride. Now the OS20 might not be for everyone, but the set up seemed to suit me nicely.

I was able to adjust to the bike very quickly and I didn’t touch my old race bike for about 5 months since that first day on the OS20, and the only reason I did that was to check it wasn’t just “new bike psych”.

The OS20 is quite responsive, it handles the corners well, manuals perfectly and feels very stable in the air when jumping. It just feels that little bit slower out of the gate (although my times are pretty much the same), but I can handle that, it gives me something to work on. Besides, given the amount of riding I do, the amount of time I spend on the gate is marginal at best.

Manufacturer’s Description

The OS20 SX450 features:

• Campy Integrated Headtube for 1 1/8″ straight steerer
• Side Mount Disk Brake Mount
• Threaded Euro BB
• 3/8″ Dropouts
• External Brake Routing

Available in 3 different sizes to fit all riders and 3 stock colours (Jet Black, Show Chrome and RAW ) and more to come.

If one of the stock colors isn’t what you want, we still do custom Powdercoat and Ceracoat to make the SX450 truly yours! Give us a call, and we will get you hooked up.

When we designed the geometry of the OS20 SX450 we based it on the regular 20″ Supercross BMX Fork. Our 20″ Carbon Race forks will work with the OS20 wheel, so no need to buy a OS20-specific fork. If you already have a 20″ Supercross and want to go to OS20 all you need to do is swap the frame and wheels, and you are set to go!

Comes with

The SX450 OS20 Frame comes with the Frame and a 120mm Side Mount Disc Brake Adapter.

What seat clamp is required

The SX450 OS20 Frame takes a 27.2 post and a 28.6 Clamp.

The brakes

The SX450 OS20 is a Disc Specific Frame. It does come with the 120mm Side Mount Disc Adapter.

Gallery

The Last Words

The Supercross SX450 OS20 is definitely one of my favourite frames of all time and I highly recommend it. It’s a head turner, that’s for sure, and rides so smoothly. Heck, it even makes me look good.

As I said earlier OS20 might not be for everyone, but make sure you take one for a spin if you are curious. It may not change your world, but it might be more comfortable, and more fun, than the bike you are already riding.

Rating 20/20

Value for money:	5/5
Weight:	5/5
Functionality:	5/5
Looks/Finish:	5/5

Comments

• One bike to do it all! It’s a lot more the price of a high end race bike, but worth every cent. My last Supercross cromo frame is still going strong and it’s almost 10 years old.
• OS20 isn’t a bigger frame, it’s quite low, it just has an adjusted geometry. It’s not heavy “because it’s cromo”, in fact it would compete well with some of the alloy frames on the market in the weight race.
• I have no complaints about the SX450 OS20, except maybe that it was available for v-brakes, but the disc brakes have their advantages, yes that’s right, now I don’t have brake wear on my sidewalls.
• I think you’ll be hard pressed to find a better looking cromo frame on the market.

Australia specific information

Supercross BMX is available through the Supercross dealer network check supercrossbmx.com.au for a list.

Reviewed by Shane Jenkins/bmxultra.com February 27, 2024