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Going from a suspension to rigid fork...help with bearings?

Old 03-29-20, 07:17 PM
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batpot
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Going from a suspension to rigid fork...help with bearings?

It's been a while since I've put a head tube together, but know I need a cup to be pressed into the replacement fork. Going to be a surly fork (probably ogre, but maybe 27.5 ecr) - straight, so it's going to be significantly narrower than the current fork and bottom of the head tube.
So the bottom line: Will I need to replace the bottom of the head tube also, or just add a cup to the new fork, and get the right size bearing?
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Old 03-30-20, 05:42 PM
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It's the other way around, cup on the lower head tube and a headset race on the fork steerer. Just look at a headset diagram on the web like cane Creek.
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Old 03-31-20, 12:27 AM
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Thanks, yeah, same difference.
i haven't taken the old fork off, but it's a very good possibility it's a straight fork anyway, so even better.

​​​​​​On a related subject, Surly recommended getting a fork length ~10% shorter than the fully unsprung length of the suspension fork. That would put me at a bridge club fork vs an ogre/ecr.
But I'm still heading towards Ogre at 5% less.

Any thoughts on length?
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Old 03-31-20, 12:40 AM
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dabac
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Originally Posted by batpot View Post

​​​​​​On a related subject, Surly recommended getting a fork length ~10% shorter than the fully unsprung length of the suspension fork.

Any thoughts on length?
That surprises me. The general recommendation when going from sus to rigid - assuming you want least amount of change to handling - is to look for a fork that matches the ”sagged” height of the sus fork. ”Sag” meaning how much the fork compresses with rider on the bike, rolling along casually.
And sag is usually recommended to be considerably more than 10%.
The sus-to-rigid swaps I’ve made, I’ve always aimed for the sagged height, or shorter.
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Old 03-31-20, 05:50 AM
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Originally Posted by batpot View Post
Thanks, yeah, same difference.
i haven't taken the old fork off, but it's a very good possibility it's a straight fork anyway, so even better.

​​​​​​On a related subject, Surly recommended getting a fork length ~10% shorter than the fully unsprung length of the suspension fork. That would put me at a bridge club fork vs an ogre/ecr.
But I'm still heading towards Ogre at 5% less.

Any thoughts on length?
Which frame is this going on?, sag is one of the biggest contributors. Along with offset/rake and your riding expectations.
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Old 04-01-20, 08:56 AM
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The rule of thumb I have always heard is 25% sagged.

You are going to need a conversion headset, it sounds like
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Old 04-02-20, 12:44 AM
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25% of the travel is like 1.25 in or 30mm for most hard tails today. 10% of the fork length is like 50mm or two inches. So there’s a disconnect somewhere.

while this does change the geometry, it’s not going to explode and kill you if you get it wrong.

Last edited by Darth Lefty; 04-02-20 at 12:50 AM.
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Old 04-05-20, 08:10 PM
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The ogre and ecr are identical, except some versions of the ogre have canti mounts.

And I ended up getting ~40 cm shorter, which is only about 5% of the overall axlebto crown length, but 25% 5if there total fork range of travel, so it's right in the where it should be based on above.

Surly rep meant 10-20% of sag; believe I misunderstood what he was saying, and paraphrased incorrectly.

I also pinged Cannondale find out what headset bearings they use, but haven't heard back yet.
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