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Discussion Starter · #1 ·
Hey everyone,

Just a quick question with regards to the front fork on my Giant Sedona CX. I'm quite new to this so I need a bit of help as I am trying to change the SR Suntour suspension fork out for a rigid steel fork. I am not sure what size the steerer is before I go an order a rigid fork (doing e-bike conversion and need a steel fork for hub motor power). Is it 1" or 1 1/18"?

Also, the store wants to sell me a Kona fork. I haven't been able to find what models of Kona fork is available until Monday when they open again, I am assuming this would be the P2 fork if suspension corrected? or do they stock other forks (Kona website shows no forks :( so doesn't help).

Thanks.
 

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Fat-tired Roadie
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I don't know, and it depends.

You can figure out steerer diameter petty easily. Can you post a pic of your stem/head tube area? The next step depends on what you have...

Kona makes a number of P2 forks. Some are suspension corrected and some are not. Some are for mountain bikes, I think they have some road models, and they probably have options for all three MTB wheel sizes.

If you're buying from your shop, bring your bike with you and let them sort out all of this.
 

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If that Suntour fork is a 80mm travel version, its probably got an axle/crown (AC) measurement of 460mm. If its a 100mm travel version, the AC is around 480mm. You will have to subtract 20-25% from the travel version to get the suspension corrected AC length you will need to know. Example, if its the 100mm travel version, you will subtract 20-25mm from the AC and get 455-460. If its the 80mm version, you want 440-444. You could also measure from the axle to the head tube and it will tell you the unsagged AC length if you're not sure what travel version you have.

I will assume, even though i hate to, that most mtb style bikes built within the past 5yrs is likely to have a 1 1/8" steerer. Unless of course, a lefty, tapered, or downhill rig. You can remove the top cap from the steerer and measure across if you don't trust it.

If the shop wants to sell you a Kona Project 2 fork... its probably got an AC length of 410 or 440. If its the 440 version, you will probably be fine if your fork is the 80mm version. If your Suntour fork is the 100mm travel version, i would look for a rigid fork with an AC of 450-465. I worry the 410 would steepen the head angle too much.
 

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Discussion Starter · #4 ·
Thanks everyone, I finally had time to get around to pictures/measuring. Seems like my crown to axle is 460mm. When I jump on the bike it sags by about 20mm on the hardest setting of the shocks.







... and also took off the cap and got a diameter of 28.53mm for the steerer tube, which I think is 1" 1/18???

Now back to the fork, I managed to find one on ebay for $70 shipped from the USA, compared to $179 for a Kona fork locally (pretty dear). No name but made of cro-mo so I am okay with that. It's 425mm from axle to crown so it might work with a stoop of 30mm on my bike... any other problems I should be aware of though?

EBAY LINK

PS: Recently converted to 200W electric as seen... hanging onto dear life everytime I get on lol.
 

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Fat-tired Roadie
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Pretty good calipers. You landed within .05 mm of nominal, assuming a 1-1/8" fork. So, yes.

Ideally, you'd want a 435-445 mm fork. I bet you're fine with 425. If you look at how compact a rigid fork for a 26" wheel can be if it's not corrected, that's what you really want to avoid. It can be less than 400 mm A-C.

I can develop over 200 W at threshold, but if I also had a power assist... looks kind of fun. Does the hub just have a reaction arm that attaches to the fork?
 

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Discussion Starter · #6 ·
Pretty good calipers. You landed within .05 mm of nominal, assuming a 1-1/8" fork. So, yes.

Ideally, you'd want a 435-445 mm fork. I bet you're fine with 425. If you look at how compact a rigid fork for a 26" wheel can be if it's not corrected, that's what you really want to avoid. It can be less than 400 mm A-C.

I can develop over 200 W at threshold, but if I also had a power assist... looks kind of fun. Does the hub just have a reaction arm that attaches to the fork?
Thanks for that. :)

Well, I'll take a look at the Kona fork tomorrow in more detail and see if they have any Surly forks at the store I am checking out, before comparing Kona again to the eBay fork. I have to take into account that I have an electric motor out the front and that's quite a bit of torque on the whole fork... no name vs. Kona. :-/

Anyway, as for the motor, yes it does have a reaction arm (called a torque arm on the left hand side in photo) installed. It was the first thing I installed before getting on.



Basically holds the motor from blowing the dropout... but I still want a steel fork.
 

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Fat-tired Roadie
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Huh - that reaction arm is tiny! I was expecting something bigger, like the ones on internal gear hubs. Though those can develop a pretty ridiculous amount of torque; depending on your motor's torque curve maybe not a big deal.
 

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Discussion Starter · #8 ·
Huh - that reaction arm is tiny! I was expecting something bigger, like the ones on internal gear hubs. Though those can develop a pretty ridiculous amount of torque; depending on your motor's torque curve maybe not a big deal.
Yeah, I just got a simple torque arm made by eZee for $18 since I only had 200W motor. It hooks up to the fender eyelet. Since I have only 200W, it wasn't even neccesary for a torque arm but this is a safe guard. 1000W or more is when we need strong arms etc.

Now back to the fork. I ended up buying a Surly 1x1 fork today during lunch time as I passed a Surly dealer. I was sucked in cause I saw a Surly big dummy bike... then ended up with the 1x1 453mm fork, closest I could get to 460mm. Now I need a star nut and a crown race cause I'm not bothered to take the one off my Suntour to save $6.
 
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