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PostPosted: Tue Feb 26, 2013 5:06 pm 
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Joined: Mon Sep 03, 2012 2:26 am
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Location: Kuala Lumpur
Hi folks, i'm a bit confused, can you help please?
I bought a '99 Kona Hei Hei bare frame (19") and need to source forks. I believe older Konas had shorter Project2s (something like 390mm a-t-c?) and the later so-called "suspension corrected" frames from approx mid-90s onward had longer P2s (410mm or sometimes stated as 420mm). This would suggest i need to source the longer 420mm P2s for my '99 frame. OK so far so good.

However, Pace's website for their rigid forks states "440mm length forks are intended to fit directly onto bikes which were originally designed to take an 80 or 100mm travel suspension fork, whereas the 420mm length version is only intended for older design frames which were designed for rigid forks".

On-One's website for their rigid forks says something similar "Axle to crown 440mm. Roughly equivalent in length to 80mm of suspension travel".

Hmm... Pace seem to be saying that a bike with 420mm rigid forks would have a frame not suitable for suspension, but Konas with 420mm P2s were sold as interchangable with the suspension forks of the day, as stated in their 1995 catalogue. Kona's catalogue stated "2 inches" of travel on those 1995 forks which is only about 50mm. Kona's 1999 catalogue doesn't give a travel figure but they were using Marzocchi Z2 which elsewhere on the internet are described as having 70mm travel.

I am considering to get a set of rigid AND suspension forks so i can swap them and play around trying both. so...
RIGID: Should i get 420mm or 440mm forks (i guess i can't copy official/original Kona spec since i don't think the '99 Hei Hei was even available with rigid forks - or was it?)? Does it matter much - would the difference in handling between 420mm and 440mm be significantly noticable?
SUSPENSION: Should i get a suspension fork which duplicates the length of the rigid in the unweighted position, or minus the sag when sitting on the bike, or halfway between min and max travel? Or something else? I can't just buy old forks because i'm going down the route of (get ready to slap me) disc and 15mm axle, so i really need to understand the fork length topic.

Thanks!
PS: Note the irony of my avatar :oops:


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PostPosted: Tue Feb 26, 2013 6:37 pm 
retrobike rider / Gold Trader
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suspension fork should be around the height of your rigid when sagged.


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PostPosted: Tue Feb 26, 2013 7:41 pm 
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Joined: Fri Feb 22, 2013 8:07 am
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I have a 440 fork on my 1997 KHS and like it quite a bit. It does make for laid back angles but I can always jump on my Mongoose IBOC if I want something more snappy.

Wild guess is that 420 fork would be best for your ride.


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PostPosted: Wed Feb 27, 2013 12:18 pm 
retrobike rider
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Joined: Sun Sep 23, 2007 11:22 pm
Posts: 7305
Location: Hove
The P2 that Konas were designed for from 1994 onwards had a 410mm a-c (not 420, I've seen that suggested myself, but I don't know where it comes from). This means that if you want a 71 degree head angle, you need to fit a 41cm fork. If you fit a 42cm fork, you will get a roughly 70.4 degree head angle and if you fit a 44cm fork you will get a roughly 69.2 degree head angle. Some people like Lester may well prefer a 69 degree angle, but personally I don't and presumably neither does Joe Murray.

As to whether you would notice the difference, I think you would. The slacker the head angle becomes, the more the bike wants to go in a straight line and is reluctant to turn. This is sometimes referred to as dead or unresponsive steering. But as Lester says some people prefer the straight line stability and don't mind having to put in extra steering effort to make a slack head angle work.

The 41cm length was chosen for 'suspension-adjusted' frames when forks had around 50mm travel. The logic was that a 50mm fork has an unloaded a-c of around 420mm, so allowing for 10mm sag, a 41cm P2 would be equivalent. As designers thought about it a bit more though, they realised that although a 63mm fork with a 42cm sagged a-c might give a slightly slacker angle, this may actually be preferable, as the fork will compress more under hard riding and the head angle will then ramp up. So if it's 71 degrees at the basic sagged position, it will exceed 71 in most dynamic situations and maybe that's a bit steep for the average rider. So basically the Kona frame is best with a 63mm fork (and 99 frames had identical geometry to 94 incidentally). That gives a 70.4 angle, maybe varying in the range 70.5 to 71.5 in give and take, decently hard riding.

It's important to take account of the stem length as well however, as this has just as much effect on steering sharpness as the head angle. All the numbers above were predicated on 11-12cm stems, but a shorter stem will to a large degree compensate for a slacker head angle. So for example a Kona will handle pretty much as well with an 80mm fork combined with a 10cm stem as it will with a 63mm fork and a 12cm stem.

I haven't tried a 44cm rigid fork on a retro Kona myself, but I would guess that it shouldn't be too bad if combined with an 8cm stem. The downside of that though is that it might make the bike too short for you. You really need to decide what fork and stem you're going to use before you choose your frame size, but I think very few people actually do this even though they should.


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PostPosted: Wed Feb 27, 2013 6:54 pm 
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Joined: Thu Jun 23, 2011 11:25 pm
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Location: It's not easy being a dolphin.
Very good reply from Anthony.

I have always gone with the following:
- 410mm for 51mm - 63mm travel.
- 420mm for 63mm - 80mm travel.
- 440mm for 80mm - 100mm travel.

From around '99 I would guess a 420mm is the one most suitable.


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PostPosted: Sun Mar 03, 2013 7:44 am 
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Joined: Mon Sep 03, 2012 2:26 am
Posts: 710
Location: Kuala Lumpur
Thanks Anthony, i found your post very insightful and useful. That and WOZ's quick reference have given me the info i need to proceed with my build. Thanks to all who posted their tips. :)


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