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Old 05-22-11, 04:10 PM   #1
igordoner
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Replacing a rigid fork with a suspension one - crown-race to crown compatibility

I'm replacing a rigid fork with a suspension one (both have threaded steerer).
I'm reusing the original headset (the suspension fork didn't come with one) and everything seems to match fine except for, potentially, the crown race which I'm slightly worried about.

The crown race is "coned" i.e. on the inner side it has a "step" between wider and a narrower "ring".
Code:
 
 / |   | \        - smaller ring/diameter 
/ |     | \       - wider ring/diameter
The bottom of the steerer of the original fork is cone-shaped (matching the coned crown race) whilst the crown of the suspension fork is flat in place where the crown race goes.

Effectively, the crown race I've got, once installed on the suspension fork, is "resting" only on the wider ring. As a result, the crown race is supporting the headset/headtube/frame/cyclist only via its wider ring and not the internal/smaller one.

I am worried that the crown race is going to break in no time (although I'm ok if it will just reduce it's life by say 50%).
I am also worried about any potential safety implications... .

I know mixing and matching crown races and headsets is not a good idea so replacing the crown race doesn't seem like an option.
Replacing the whole headset means additional cost and replacing head-tube races which I'd rather avoid. (not sure whether I can do it without special tools/damaging the frame)
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Old 05-22-11, 04:51 PM   #2
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I'm not sure I follow you. First of all why don't you transfer the crown race from the old (rigid) fork to the new one?.

if you are transferring it, you'll have to press it onto the seat (this might what you refer to the wide area) as it's an interference fit. You can do this with a piece of 1" pipe with a square end.

Normally you should check the sizes, but since there are only two common standards (26.4mm & 27.0mm) the race will either fit, or be too large (the chances of your having a 27.0 spec suspension fork are almost zero).

Removing and pressing the race does require special tools, and if you cannot do that bring both forks to the bike shop and pay them to do it for you. It shouldn't cost much at all.
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Old 05-23-11, 03:25 PM   #3
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I am transferring the crown race from a rigid fork onto a suspension one.
This is really down to the details of how the crown race is shaped and how the forks (steerers) are shaped so I've depicted the problem as shown below



I am worried about the empty spaces as the crown race is not getting as much support on the suspension fork as it did on the rigid one (you can see that the steerer of the rigid fork is shaped at the base to match the shape of the crown race).
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Old 05-23-11, 03:39 PM   #4
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you mixing steerer tube diameters too?
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Old 05-23-11, 08:21 PM   #5
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Nice graphic.

I just did the opposite (susp. to rigid) and found that the steerer tube on the rigid had the same lip. The crown race from my new headset did not fit on it well, and actually split when I put it on. Everything else seemed to go together ok, and since it's a cartridge headset, I figured it would last a decent amount of time. Since your option is to seek out a different headset or crown race, why not run it as is until it fails. It shouldn't be a catastrophic or dangerous failure when it goes.
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Old 05-24-11, 03:56 AM   #6
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Quote:
Originally Posted by Standalone View Post
Nice graphic.

I just did the opposite (susp. to rigid) and found that the steerer tube on the rigid had the same lip. The crown race from my new headset did not fit on it well, and actually split when I put it on. Everything else seemed to go together ok, and since it's a cartridge headset, I figured it would last a decent amount of time. Since your option is to seek out a different headset or crown race, why not run it as is until it fails. It shouldn't be a catastrophic or dangerous failure when it goes.
Are you sure it wasn't split before you started? Lots of cartridge style headsets use a split ring because it's not really a bearing race. The race is integrated with the cartridge.
Also, if it was 1", are you sure you had the ISO/ JIS thing right?
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Old 05-24-11, 04:17 AM   #7
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Quote:
Originally Posted by Dan Burkhart View Post
Are you sure it wasn't split before you started? Lots of cartridge style headsets use a split ring because it's not really a bearing race. The race is integrated with the cartridge.
Also, if it was 1", are you sure you had the ISO/ JIS thing right?
I took out a 1 1/8" threaded from an '03 or '04-ish Fuji Hybrid and put in a new dimension susp. corrected 700c hybrid fork. Every other measurement checked out with my vernier calipers. The crown, though, was like 30.3 or 30.2mm while the Cane Creek 10 headset (and it seems like all other similar headsets) was spec'd at 30.095mm. I think the fork was just cheap and machined/cast a little off. I thought I could tap it on and stretch it that extra 0.1mm but no dice. I decided it was only there to keep dirt out, so I took it apart and reinstalled with a bit of inner tube over the lower part of the headset. It's a little ugly and squeaky, but it works.

New:




Old:


The steering is a little quicker. There is no other fork being produced for the application, though, so I couldn't find one with more rake.
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Old 05-24-11, 11:42 AM   #8
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Originally Posted by fietsbob View Post
you mixing steerer tube diameters too?
I'm not mixing the steerer tube diameters. The diameters are the same except for the base as shown on the picture. The rigid fork is a bit wider at the base. The suspension fork has the same diameter all the way through.
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Old 05-24-11, 11:51 AM   #9
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Originally Posted by Standalone View Post
Nice graphic.

I just did the opposite (susp. to rigid) and found that the steerer tube on the rigid had the same lip. The crown race from my new headset did not fit on it well, and actually split when I put it on. Everything else seemed to go together ok, and since it's a cartridge headset, I figured it would last a decent amount of time. Since your option is to seek out a different headset or crown race, why not run it as is until it fails. It shouldn't be a catastrophic or dangerous failure when it goes.
Thanks. I guess if it fails the first thing I'm going to notice the steering will become rougher at which point I will need to replace the crown race (somehow finding one that will match the bearing which in turn may shorten the life of the bearing because of small build 'deviations') or replace the whole headset (a trip to LBS I guess owing to lack of tools).

I was hoping more people could share their experiences with replacing a rigid fork with a suspension one and any issues that arose around crown race compatibility. I've done a bit of a research on the forums/internet and couldn't find that much info. Thanks for your input Standalone.
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