Nailing your cycling position is vital. Get it wrong and your performance will suffer. Get it right and PBs will be well within your sights. When considering ride position, stack and reach are two of the most important measurements. Nik Cook spoke to bike fitting guru Phil Burt to get his input.
What is stack and reach?
The first point to make is that there’s the stack and reach measurements that you’ll see on bike geometry charts and then there’s the stack and reach contact point measurements that apply to your position on the bike.
In terms of a frame’s geometry, stack is the vertical distance from bottom bracket to the centre of the top of the head tube. Reach is the horizontal distance from the bottom bracket to the centre of the top of the head tube.
For contact points, your reach will be from the middle of your saddle to either your elbow pads or where you’re holding your aero extensions. For contact point stack, you should measure from centre bottom bracket height, which is constant, to the top of your elbow pads.
Why is stack and reach important?
From a frame geometry perspective, the stack and reach effectively determine the position you will be able to achieve on that bike. There’s only so much adjustment you can make with stem length, headset spacers, saddle set-back etc. If you’re trying to shoe-horn a position onto a frame that’s not suitable for it, you’re onto a hiding to nothing, compromised handling and probably a bike sale!
Looking at how you sit on a bike and performance, if your stack is too high, you’ll be compromising aerodynamics. If it’s too low, your position may well be unsustainable and/or you’ll be losing power due to a closed hip angle. If your reach is too long, again, you’ll be closing your hip angle and you’ll struggle to get to a sweet-spot where your shoulders are directly above your elbow pads. If reach is too short, you’ll feel cramped and, because of this, your weight will be too far forwards and handling will be compromised.
Which is more important – stack or reach?
That’s a tricky call to make but I’d say stack is most important. Too low and you’re really going to struggle to get comfortable and hold that position. This particularly applies to newer riders or riders who are transitioning from a road set-up to a triathlon specific set-up. Adapting to an aggressive aero position takes time and work so don’t be tempted to try and go too low too quickly.
What is the stack to reach ratio?
In terms of frame geometry, it varies from brand to brand. For example Giant tends to be fairly generous with stack whereas Specialized is more aggressive.
I’m always wary of ‘rules of thumb’ and generalisations as the one thing I’ve learned from conducting thousands of bike fits is that all riders are different and you’ll always find exceptions to any rule.
This is why, if you’re in the market for a triathlon bike and don’t have a position, get a fit on a jig and then cross reference this with geometry charts to find a frame that’s compatible with the contact point position you’re trying to achieve.
How does stack affect reach?
In general, because of head tube angle, if you increase stack then you will effectively reduce reach. Conversely, if you decrease stack then reach will be increased.
How do clip-on aerobars affect stack and reach?
For triathletes, I think one of the biggest impacts of stack and reach is when you try to put clip-on aerobars on a road bike. I always use the analogy of putting lipstick on a pig and, because of the geometry of a road bike, it’s hardly ever optimal. The stack and reach of a road bike frame isn’t designed for you to be forward on your elbows and invariably you end up with an overly stretched and hip closed position.
Yes you can bodge a position with a stubby stem, angled seat-post and saddle slammed forwards but it’s never going to be optimal and handling will invariably be compromised. I’d always advise triathletes to optimise their position on a road bike, build fitness and experience on that and then, when ready, make the shift to a dedicated triathlon set-up.