Out of the factory, a bike’s geometry is wholly dictated by the shape of its frame, and the designers who put its angles together. That doesn’t mean that there aren’t a handful of things that can be done to adjust those angles to suit your particular needs. Here’s a list of what you can do to your bike’s frame to adjust its geometry.
What you need to know
With a lot of the methods of geometry adjustment you can add to your frame, there’s often a degree of give and take. Sometimes slackening your head angle can also slacken the seat tube angle and drop the bottom bracket. So the good things you might get from that newly slackened head angle could also put you into a slightly different position over the bike thanks to the now slacker seat tube angle, and you might find yourself with more frequent pedal strikes due to the now lower BB.
Also, because not every frame is built equally, not every geometry adjustment product will suit or even be compatible with your bike so be sure to spend some time researching your chosen method to make sure it’ll work with your frame. Often, it doesn’t take long to find forums where a certain bike’s users have given feedback on their newly modified frame.
We've also got tips on how to adjust your geometry through your bike's suspension and cockpit.
Offset bushings are a relatively cheap but effective way of adjusting the geometry of your full suspension mountain bike. By reducing the eye to eye distance, they allow your frame to sit in a slightly different position, therefore slackening your head and seat tube angle while dropping your bottom bracket.
They’re reasonably easy to fit too as the simply replace the DU bushing that’s already in your shock with a brass bushing with an offset hole for the mounting bolt to sit through. However, this is probably best done when your current DU bushings are on the way out if you’re looking to be super frugal but it’s something that can easily be done at home with the right tools.
They’ll work on any mountain bike with a shock that’s mounted with DU bushings with up to a 10mm bolt but the degree of adjustment will lessen with larger bolts. For example, a pair of bushings suitable for bikes with 6mm bolts will result in a 1.5° difference to your head and set tube angle. The thicker the bolt, the lesser the adjustment.
If your bike is kitted with a trunnion mount shock, you’ll only be able to mount an offset bushing at one end, limiting the amount of adjustment of offer.
Reach and angle adjust headsets
Reach and angle adjust headsets are probably the best way of fettling with either measurement without affecting the rest of your bike’s angles too much. Each is made up of offset headset cups that either you (if you’re handy enough) or a bike mechanic will press into your frame.
As its name suggests, an angle adjust headset offers adjustment to your head tube angle. They’re available in a range of adjustments but often, you’ll have to settle on a certain degree and unfortunately, they’re not something that’s easy to chop and change. That’s unless you go for Cane Creek’s famed Angleset, which offers adjustment from .5° up to 1.5° through replaceable cups.
A reach adjust headset follows the very same premise, it just shifts your steerer forwards, or back in the headtube. Adjustment on offer can range from 5mm to 7mm on certain models. Note, that reach adjustment isn’t the same as bunging a longer stem onto your bike as a reach adjust headset will shift the fork steerer, therefore your front wheel, fore and aft.
Again, these won’t work with all bikes, such as those with fully integrated headsets where the headset cups are moulded into the frame’s carbon.
The upsides are that they don't change the rest of your geometry too much, though with an angle-adjust headset, there will be a small change to the reach. They can offer quite a lot of adjustment too with Works Components offering a 2° angle adjust headset. However, they are a pricier option and as mentioned before, quite an invasive job to fit.
Angle adjust spacers
Angle adjust spacers aren’t near as common as the headsets but they’re an awful lot simpler and can very easily be installed at home. These spacers replace your fork’s crown race and lift the head tube from the fork’s crown; that’s where the geometry shift comes from.
The Angle Spacer from Reverse Components offers .5° of slackening adjustment, is suitable for headsets with 45° bearings and only works with tapered fork steerers.
The effects an Angle Spacer has on a bike’s frame are similar to those of a slightly longer travel fork. The stack and bottom bracket will rise, and the seat tube angle will also slacken by .5°. They are pretty cheap though, with the Reverse Components Angle Spacer being available for £12.
A big downside, in my opinion at least, is that they’re not invisible. However, there are the compatibility requirements mentioned before, and you’ll have to make sure that you fork’s steerer tube is long enough to work with the spacer.
Perhaps one of the more drastic methods of slackening your bike’s geometry is to convert it to a mullet wheel size. That means running a 29” wheel up front, and a 650b in the rear. It’s a wheel setup that’s quickly growing in popularity as it promises all of the best bits of each wheel size.
Not only do you get the best of both worlds but converting your bike to run odd wheels results in a bit of a geometry change. If you were to pop a little wheel into the back of your 29er, the head and seat tube angles will slacken, the bottom bracket would lower and the reach would shorten a touch. Putting a big wheel in the front of your 650b bike would achieve a very similar result but the stack will rise, as will the BB.
Both methods of mullety conversion come at quite a cost though, unless you already have bits sat in your shed. To convert a 29er, you’ll at least need a new 650b wheel and tyre. To convert a 650b bike, you’ll need a fork compatible with 29” wheels, then a 29” wheel and tyre.
As the conversion is quite a big one, it’ll effect your ride in more ways than just the geometry adjustment. We’ve got a pros and cons list of converting your 29er to a mullet bike here If this is a route you’re considering.
Flip your chip
Forgive me if I'm teaching you to suck eggs here but many modern bikes come kitted with a flip chip and they can be pretty easy to overlook. Most commonly known as 'flip-chip' but the 'Mino Link' on Trek bikes, they're a little spacer that often sits in a bike's seat stay that, like offset bushings, allow your bike to sit in a different way. However, as flip-chips aren't as permanent as offset bushings, they allow the rider to chop and change a bike's head and seat tube angles, and bottom bracket height with the flip of uh... A chip.
The benefit to these is that the geometry shift is dictated by the bike's designers, so you know that it's a safe adjustment and it won't destroy your bike after a mighty huck. However, like offset bushings, flipping that chip will affect a range of angles, so if you're simply looking to slacken, or steepen your head angle, you'll need to look towards angle adjust headsets.
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