The goal of a BTA (Between The Arms) setup is to optimize aerodynamics while keeping your data in view. To avoid any interference with your face at full effort, here is the RocketTT method to calculate your ideal setup.
🚀 Don't feel like calculating? Use our riser calculator: enter your measurement and your options, and it gives you the height.
1️⃣ The measurement protocol
For maximum accuracy, do not measure on an empty setup.
Put your bike on a trainer.
Get into your aero position (hands on the extensions, flat back).
Ask someone to measure the vertical distance between the underside of your chin and the top of your arm pad plates.
2️⃣ Calculating the "stack" (cumulative height)
To find the spacer height you need, subtract the height of the elements that will stack up from your measurement:
Bottle + cage: 80 mm
RocketTT adapter plate: 10 mm (the plate is 15 mm tall, but 5 mm sit under the arm pads). Count nothing on bikes with a direct mount or a plate built into the bike (Giant).
V-FLOW double bottle mount option: + 20 mm
Garmin / Wahoo computer mount option: + 10 mm, in the low version as well as the high version
Comfort margin: 10 mm, so you can move your head without touching the bottle and allow for days when you sit less well on the bike
3️⃣ The magic formula 🧮
Spacer height = Measured distance − (80 mm + 10 mm plate + options + 10 mm margin)
Example: you have 160 mm between chin and arm pads, on a bike with a plate, with a single bottle and no computer mount: 160 − (80 + 10 + 10) = 60 mm. You need a 60 mm spacer.
Same bike with a double bottle and a computer mount: 160 − (80 + 10 + 20 + 10 + 10) = 30 mm, below our standard 40 mm range: contact us, we design ultra-low solutions.
4️⃣ The RocketTT tip: the Adjustment Pack
Unsure, or planning to change your position? Don't stay locked in.
You can choose a shorter main spacer and complete it with our Adjustment Pack.
Pack contents: 1 spacer of 10 mm + 1 spacer of 20 mm.
Modularity: these spacers stack. You can add + 10 mm, + 20 mm or + 30 mm of height with a few turns of a wrench, without buying a complete mount again.
⚠️ Safety reminder
All our spacers are made of PAHT-CF (carbon nylon) so your setup stays rigid, even with a large stack of spacers. Just make sure to use the matching stainless steel screw length (see our hardware guide).
0 comments