I've got a Diamondback Reactor Pro I'd like to use for some upcoming TT events. I've noticed that many pros race on small frames, so I figure I'll have an edge there too since smaller frames should be both stuffer and lighter. Plus, TT bikes often have smaller wheels, so I figure I'll have an advantage spinning up, particularly on hills.

I know I'll need skinnier tires and I've already picked up a set of Stelvios that should do nicely. But what parts of the bike do I need to upgrade? My budget is about $600. Thanks for any advice.

Learn from this guy...

https://www.youtube.com/watch?v=7JtZkNXfes4

You'll want to focus on getting your bars low enough to have a flat back. The aero-seatpost saves a few watts.

^ agreed, but the streamers may be a bit too much.

:facepalm:

aerotrike made my day. thank you bf.

Thanks for the info. Based on the video, it appears that gear selection is critical to top speed on bikes with smaller wheels. I wonder if there's some way to raise the cranks since it looks like pedal strike might be an issue in corners? But the good news is that the shorter wheelbase should result in significantly more responsive handling.

Well duh... $600 gets you basic aerobars. Invest in those, of course. I am thinking of putting those, along with a trispoke front/disc rear, on my Surly LHT for an upcoming tour myself.

did you get custom stelvio's to fit the 18" wheels? Can you just cut normal ones and duct tape them together to get the right circumference?

With those smaller wheels, you'll need a 75t chainring. Does Zipp make deep profile 20" wheels ?

Not all BMX frames are suited for TT riding. Need more info. What color is it?

Will you be keeping on the pegs? i think it would be pretty slick if you broke into some flat land tricks mid race, or even at the finish line.
https://www.youtube.com/watch?v=A2LTVhqHAdo

That's a great idea and I think it will work fine with the recommendations made so far, but don't forget that if it is not able to perform basic BMX tricks it won't be UCI legal. I suspect the aero position will work wonders on the half pipes especially being able to get air, you'll be a real missle.

Sadly, Schwalbe doesn't appear to be selling the Stelvios in 18" right now though they are still available in some shops. Happily, the Kojaks are available in that size and can be ordered online

I've decided to just ride 20's to improve tire and wheel selection. Although I don't have the budget for it right now, I'd like to get some aerospokes or some of these bad boys a little down the road:

An excellent question -- it is blue. Will I need to change this?

This is doable, but it will be tricky to make the bike conform to UCI specifications, which could cause you some issues down the road if you decide to go pro.

I doubt anyone makes a 75t chainring. You'll probably have to use a 50t and a25t instead.

It's also critical to have the right seatpost to put you into the aero position. I recommend one like this:

Don't forget the TT saddle

Happily, Greenspeed and Alligt models are available with enough teeth. Good tip on the seatpost though.