Slacken Outdated MTB Fork Geo With an Angled Headset

Does your old frame geo need a refresh? An angle-adjust headset will lean your fork back by a full degree or two.

By Gerow
April 15, 2020 Last Updated: August 12, 2024

14 comments

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This 2016 Karate Monkey has some of the same angles as XC frames 20 years its senior. It was due for a shift.

Do you have a beloved older bike hanging around that you wish handled a little closer to modern whips? Maybe your bike isn’t so old, but you want to try a slacker front end to see how it alters the ride experience. Fortunately, there are a few options available to lean your fork back by a full degree or two — provided your frame uses a pressed-cup headset.

My size medium 2016 Surly Karate Monkey frame fell hard into the “old-school geo” camp, with its 71.5° headtube angle, 73° seat tube angle, and 415mm reach. I largely use the bike for dirt road training rides when the trails are soaked, but I plan to bring it along on some lighter bikepacking adventures this summer, so a little geometry shift seemed like a worthwhile upgrade.

This is the Slackerizer from Superstar Components.

There are a handful of brands that make angle-adjust headsets and I chose one machined in the UK by Superstar Components with 2° of added lean. The headset includes all the usual components: two cups, two bearings, a crown race, top cap and preload bolt, star nut, compression shim, and dust cap.

Diagram courtesy of Superstar Components.

The difference between this and a traditional symmetrical headset is that the holes where the bearings seat are offset and tilted to give the fork steerer a clean new angle while maintaining proper interaction with the bearings. The top bearing is seated a little toward the rider and angled accordingly, and the lower bearing seats away from the rider, creating the desired final angle. To make the headset angle steeper, simply install the angle-adjust set with the alignment markers on the opposite side.

The small guideline on the base of the cup needs to be accurately aligned.

Installing the angle set was as easy as any other, apart from the fact that you have to line it up precisely. There is a notch on the front side of both bearing cups that needs to align with the cross-section of the frame, and with the adjacent cup. I struggled to tighten my saddle in a straight-forward position the first time around, so this alignment task took a few tries. Once the cups were pressed into the head tube the whole thing went together without a hitch.

The photos below show the bike before and after installing the angle-adjust headset.

The geometry shift is hardly noticeable by looking at the bike, but it’s immediately noticeable while pedaling around. The steering is a little slower and feels slightly heavier in my hand, and the overall position is more upright given the shorter reach. These are exactly the changes I was aiming for. The slacker head tube angle will make the bike handle a little better on descents, and the shorter reach makes up for the Syncros Fraser integrated stem that was too long for this bike.

Before	After
Headtube angle 71.5°	69.5°
Reach 415.1mm	~395.1mm
Seattube angle 73°	~73.5°
BB Height 295mm	~292mm

I had hoped that the BB would drop more, readying the bike for a 120mm fork if I ever wanted to mount one up, but at only a few millimeters lower I definitely won’t be over-forking this bike. As the front axle extended forward the seat tube steepened slightly, which is always an appreciated change. I may slide the saddle back a touch to find the right fit once I get a chance to take the bike out for a proper long ride.

If you’re dreaming of inexpensive ways to refresh your bike, this option makes a significant difference for around fifty dollars/euros. Headset style is an element worth considering for some forks when buying a new frame, as drop-in-bearing or integrated headsets don’t leave space for angle adjustment.

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14 Comments

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m.krupp Kentucky // 2018
Apr 15, 2020

Thanks for article. This a mod I have considered on one of my bikes. I want to get a slightly slacker HA and had thought of lower bottom bracket and potential shorter reach but had not considered the seat tube angle. Would be a cheaper modification that could remove if I don't like it.

1 reply

orion86 Massachusetts // 2021
Sep 30, 2021

correction - slacking out the front with the same fork adds reach and reduces stack, making for a less upright riding position.

it's typically minor - the author clearly couldn't notice it, but the trend is the reverse of what's stated here.

Jeff Barber Georgia // 1998
Sep 30, 2021

I think I agree that stack is reduced with a more slack HTA. However, not sure about reach increasing since the head tube is dipping more toward the saddle as the HTA becomes more slack. I guess it really depends on what is being held constant, and what is allowed to change.

-1 reply

You're right, I'm wrong! According to this calculator, reach does get a smidge longer and stack decreases. At least, when using an angle adjusting headset. Tricky!

https://madscientistmtb.com/bike-geometry-calculator/

2 reply

tyriverag Wisconsin // 2020
Apr 15, 2020

Awesome, thanks for posting this. I have that same bike and am considering adding a fork, and would like to slacken it out a bit. The frame is rated for an 80mm suspension fork, but it is common to up that by 20mm. Is 40mm above the suspension correction worrisome at all?

0 reply

tyriverag Wisconsin // 2020
Apr 16, 2020

Right on, thanks Brian. My understanding is that too long of a fork could damage the headtube. I am likely going to add an angleset like the one mentioned here and roll with a 100mm fork. That should be great for the local trails here in NW Wisconsin. Considered a more modern trail bike, but the KM is just too much fun to ride.

AUTHOR

Gerow Washington // 2014
Apr 16, 2020

tyriverag, bumping up fork travel (overforking) by a full 40mm is something you might just have to test out to see how it fits with your style and trails. When I've overworked frames in the past the high BB made for poor handling that wasn't worth the added travel. Also, overworking can void your frame warranty, if that's a concern. Please let us know what you decide to do and how it works out for you.

Chainmail South Africa // 2016
Apr 19, 2021

I bought the angled headset, but at the same time picked up a 100mm travel 650b Sid fork and 650b front wheel which together have done the trick;- Kept the rear wheel at 26”, swapped from 3x 9 to 1 x 11, I haven’t measured the change, but the result is much improved handling and a revitalised old bike. Sold the unused headset on. Now I just need to find a way to steepen the seat tube!

c00lm0ss British Columbia // 2017
Apr 18, 2021

I had anticipated the less twitchy steering... and a more rider forward peddling position. I can imagine the stack and the standover dropping as you sweep the front tire further out in front of you. But how much further would a single degree add to any wheelbase? Say, a 650B?
I'm toying with the idea... not going to say the brand, of slackening the HT one degree. The bike in question, already has a tidy 337 BB, so any lower and I will hang up on everything. Luckily, I'm riding this bike in the 'low' position already... I can steepen things a degree by setting the bike in the high position...
Picking up what I'm laying down?
Slacken the HT... This steepens the STA and lowers the BB, standover, stack.
Set bike in high position... Returning HTA to original, Steepening STA (even further), bumping back up the BB, standover, stack (ever so slightly).
The benefit?
Longer WB and steeper ST. Rider forward geometry.
But again, how much longer would a bike be?

Gerow Washington // 2014
Apr 19, 2021

On my bike pictured above, a 1° slacker HTA would give a 20mm longer wheelbase.

Chainmail South Africa // 2016
Apr 16, 2020

I would like to do this too, but my fork has a straight steerer, is there an option for this or only tapered steerers?

Thanks, will give it a try and report back.

Chainmail, you can definitely use an angle adjust headset with a straight steerer. The steerer in this Surly is straight, and I used a reducer crown race to take up the extra space. The Supersstar Components headset offers the reducer as an addon for any order.

Eric J Owsley 2016
May 20, 2020

Thank you for this article. Exactly what I was looking to see. Considering adding a -2 degree headset to my Krampus. Your measurements on reach, seat tube angle and bottom bracket height are especially helpful. Two questions: how do you feel the stock fork offset on the Karate Monkey plays with the new slacker head angle? In an ideal world, would you increase the offset of the rigid fork to keep the handling more reminiscent of the original?

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