I'm just making my hardtail Rock Lobster into a fully rigid bike.
The new forks are here, and, comparing the 2, the rigid are a hell of a lot lower than the sussys, at least 70mm difference.
If I put these on as they are, they'll be lowering the front end, and affecting the bikes geometry far more than I'd be happy with, so is the usual 'done thing' to put a long spacer between the bottom of the fork steerer and the bottom headset bearing?
get a for that is corrected for the length that you are replacing?
You would need the crown race at the top of the space, and I doubt it would fit. Have you taken off the amount of sag you would be running and considered the rigid forks as a replacement for the full range of travel, rather than remaining at full extension?
I'd return the forks and get ones with the correct a-c length
so is the usual 'done thing' to put a long spacer between the bottom of the fork steerer and the bottom headset bearing?
No...if it has been done, its unusual.
So what suspension forks did you have on? Standard 26" rigid forks are 440mm a2c, 29er 470mm a2c...more common to stick 470mm rigid forks on a 26er to lessen drop
As for the not fitting the bottom race, this is what got me thinking about it - the current race will no way fit onto the bottom flange, so much so that I thought I had bought the wrong size fork steerer, but close inspection shows it is flared out toward the bottom, so needs a spacer of around 20mm before the bottom race can be fitted and bottomed out.
Yes, you have a point about full length of travel, I just compared the 2 side by side, and, of course, the sussys will be lower once I have my bulk on the bike, so the spacer will be down to a more reasonable 20-30mm ish once pre-load is taken into account.
I've since measured the difference accurately, and my 75mm was OTT, the actual difference is 50mm, so a 20mm spacer, and 25mm or so of preload takes it down to an acceptable level, not affecting the geometry too much.
Thanks.
A quick measurement shows the sussys at 460mm, the rigid at 410mm.
A google shows the same problem has come up before:
http://gearinches.com/blog/reviews/mosso-aluminum-rigid-fork-review
but he has kept the crown height the same, but added spaecers above, which seems a little daft as it will affect the geometry of the frame.
I'll try it with a 25mm spacer under, and see how it works out.
close inspection shows it is flared out toward the bottom, so needs a spacer of around 20mm before the bottom race can be fitted and bottomed out.
Its normal for forks steerers to flare in the last 20mm or less...this is what the crown race should fit on to and it should need to be hammered into place (normally by using a bit of waste pipe on the crown race then hammering down).
Im dubious of what you have planned regarding fitting a 20mm spacer...this isn't adding up right at the moment 😕 460mm a2c suspension forks? Maybe older 60mmish travel forks? I think if this is the case 440mm rigid forks would have suited best rather than 410mm
I did it to make a cheap pub bike. Worked perfectly fine just pootling round town, not sure I'd trust it for any serious riding.
Putting a spacer under the headset sounds like a really bad idea to me, you're effectively extending the axle to crown length of the fork, which will put a lot more force on it than it is designed for. Plus, the crown race won't fit correctly as it's designed to be a press fit on the 30mm diameter section at the bottom of the steerer rather than the 28.6 bit where it will end up.
The usual 'done thing' is to buy a suspension corrected fork (440mm A-C for a 100m travel bike).