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Discussion Starter · #1 ·
Hi Folks,

I'm new here, living in Portland, Oregon. I just got into mountain biking last year, I bought a Kona Unit X 2020 sort of on impulse. A friend out in Ashville NC has a Unit and loves it, I test rode one here, and got it. I've enjoyed riding it around some of the trails outside of town, but I realize maybe I should have gotten something with suspension. There are places where roots and rocks are pretty gnarly, or maybe its just my lack of riding skill. Some of the places I have gone include Hagg Lake, Stubb Stewart, Post Canyon, and some of the Wilson River Trail. I would like to go try the Lewis River next year. I enjoy mellow flow trails and single track with some downhill, but I doubt I will ever be doing any crazy big jumps or drops.

My thought is to either get a whole other bike, a hardtail or maybe FS, put a suspension fork on my Unit, or just keep it as fully rigid. Kona recommended a 100mm fork, but I see folks on Instagram putting longer travel forks on their Units. How does that work, I assume it changes the geo, especially the head tube angle. Is it bad for the frame? For example, this example is a 140mm fork.

I really like the Unit so i lean towards keep it as is, and using it for bikepacking and maybe commuting with a second set of tires. Though thought of adding a sus fork and not buying a whole other bike is appealing, but i also hate to mess up a good thing.


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ForaBot's answer is created from summarizing the responses in this thread.

Based on the information provided by members of the community, it is recommended to stick to a 100mm fork for the Kona Unit X. This is because a longer travel fork may change the geometry of the frame, which could be bad for the frame.
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Discussion Starter · #2 ·
I've thought about it some more and I'd like to add a suspension fork to my Unit X eventually. I was wondering if folks can help me sort out some of the technical details.

I'm thinking a 120mm fork, and someone pointed me towards this article. https://meatengines.com/f/my-dream-unit-a-recipe-for-min-maxing-rigid-shore-single-speeds

It sounds like a -2 angle set with a 120mm fork will keep the front end the same height and make it two degrees slacker. The part I am confused about is the headtube bit.

The Kona has a 44mm headtube. It will work with straight or tapered steerers by switching out the lower headset cup. I'm a bit unsure what kind of lower headset cup I should be looking for.

Would a different fork allow me to raise the stack height, or is that pretty much fixed based on the frame geometry? I am currently using all the spacers, and on longer rides I end of feeling more bent over than I would like. Looking at the numbers its stack height in a large is 606mm.

If anyone has any good resources to learn more about this stuff I'm definitely interested.
 

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Yeah, Kona recommends a max of 100mm on the Unit. If you're not a heavier guy or not a super aggressive rider you'll probably be OK at 120mm, and the Angleset can be used to adjust/control BB height, STA, or wheelbase. (HTA is not always the primary reason to use an Angleset) I'd plug these numbers into a geometry calculator so you can see what changes result from both a longer fork and angled headset. It will help you make an informed decision about what combo will work best for you.

The headset is easy... IS44 upper, EC44 lower.

If you want more Stack, you'll get more height from the front end when you add a suspension fork. Using a geo calculator will help you determine how much height you'll gain from that alone. Your new fork should also come with a full length steer tube so you can add a few extra headset spacers to raise it up a little before you cut the steer tube. Alternately you can buy riser handlebars if you buy a used fork with a cut steertube.

Theres lots of information available online, you'll have to do some searching on each topic and do some reading to learn. I don't know of a 'resource' other than stuff like MTBR. If you have a question about headset compatibility or something, go to the manufacturers website and look for Tech Documents or PDF's or whatever information they provide.

Here's a comparison I did on my Honzo ST with a 140mm fork and -1 headset. My primary goal was to raise the BB a hair without making the STA too slack. Love the results! (also note that a longer fork and -1 headset resulted in a change in HTA of 2 degrees. Your proposed 120mm fork and -2 headset could result in >3 degree change in HTA. Do you want to go that far?)

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The Kona has a 44mm headtube. It will work with straight or tapered steerers by switching out the lower headset cup. I'm a bit unsure what kind of lower headset cup I should be looking for.
That would depend on which fork you buy. A fork with a straight steerer tube can use an internal lower cup, a fork with a tapered tube requires an external cup. The external cup will add about 10mm to the head tube height.


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Discussion Starter · #6 ·
Thanks for the info folks, on what upper/lower headset to buy, the geo calculator, and thoughts in general. Yea if a 120mm fork could possibly slacken the HT angle by 3 degrees or more I don't know if I want to go that far.

Maybe sticking with a 100mm fork will just be simpler, as mentioned. I wouldn't mind raising the stack somewhat, maybe I can get one with a tapered steering tube and use external cup.
 
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