So for the coming winter months I'm contemplating a fork change going from a suspension to a rigid, the bike is a Cannondale trail 7 (29er). For the type of riding I do, I'm fine with or without suspension but I really want to give it a try rigid.
My question is how to go about getting the right length for this particular bike whether I get carbon or steel. I've noticed most of the axle to crown lengths range from around 480mm to 490mm but then there's a description of "Suspension-corrected for 100mm".
Are measurements taken somewhere in the middle of the fork's range of travel? The fork on the bike measures around 480mm from axle to crown fully extended.

Any advice you can throw my way would be greatly appreciated!

If you like the way it handles while JRA on flat ground, I'd get on the bike, lean your shoulder against a wall, get into riding position and have a friend or family member measure the ATC with you on it.

I reckon corrected for 100mm means it's about the same as a fork with 100mm travel, dunno if they account for sag or not.

Suspension correction takes sag into account. Do you have an 80 mm travel fork now? Then a rigid equivalent might be 20 mm shorter to give the effect of typical sag.

The fork (XCT) calls for 100mm of travel.

Yep, stock fork on that has 100mm travel.

SR Suntour says the XCT 29 100mm has 515mm axle to crown. A rigid with 480-490mm axle to crown sounds about right.

Details*- SR SUNTOUR Cycling

Good lesson, got lots of ideas. I'll probably get this done in the winter, for now I just want to ride!
I'll post pictures when the time comes, thanks for all the tips!

Hi gilpi - did you have any luck on this front? I'm also looking to replace a Suntour XCT with a rigid fork. I'm open to carbon, aluminum, or steel. I'm having a hard time finding a combination of straight steerer tube, 490-ish axle to crown, and quick-release axle.

^^^^ Looked at Surly?

Well, I was lazy all winter and this summer I've been using my road bike a lot.
However, I still want to change the Suntour for a rigid on my Cannondale.

I have another question, are all disc brake mounts on forks universal?

Since posting, I replaced my 100mm Suntour suspension fork with a 490mm carbon fiber fork. The new fork is just a little shorter than the Suntour was when fully extended. It doesn't affect my riding position noticeably. I'm really happy with the setup.

When looking at brake mounts, I found this helpful for explaining the standards: https://www.bikeman.com/bicycle-repa...4mm-post-mount

And I found this most helpful for adapters: Art's Cyclery Blog » Rubber Side Down | Disc Brake Adapters

May I ask which fork you got?

Sure thing. I'm on a tight budget, so I needed to stay as affordable as possible, but I also wanted to steer clear of the no-name forks being sold on eBay, simply because I couldn't find any reviews for them. So I got a White Brothers "Rock Solid" carbon fiber fork. I found it on Niagara Cycle for $282.

Thank you for the info.
I am also on a budget mainly because I'd hate to spend $300 on a $500 bike.
I was just checking out a Niner carbon fork for under 200, post mount so it would be a seamless swap but, its 470mm crown to axle, that brings the front end down just over an inch.
Wonder how that would feel...

How much sag are you running with the current fork? A properly setup fork will run 20-25% of the travel as sag, which is likely why the Niner is spec'ed to be shorter.

Some 29ers have a floppy front wheel because of the slack geometry combined with the taller headtube. The tall front is also a liability for steep climbs in my opinion. If you use the bike on extended climbs consider a shorter fork to get the front of the bike lower. Some people have put rigid 26" forks on 29ers, also 27.5". Yes it steepens the frame geometry and lowers the bottom bracket one or two cm, but some people consider these benefits instead of liabilities. Alternatively, if you're considering a rigid because the front end seems far too high, you could install a freaky stem like the Satori Turn-Up or Cobra but keep your existing fork to get the handlebars lower then the headset. You can also install riser bars upside down, or road drop-bars.

So just as Im ready to purchase the Niner, the only ones available are the taper steerer.
Not too many budget choices with the straight 1 1/8 and brake post mount.

What are you interested in getting? I was frustrated too by the fact that non-tapered forks seem to be in short supply.

My advice regarding length would be to see if you can set your bike up to mimic the change in riding position and see how it feels before committing to a purchase. Flip the stem, maybe, to drop your bars a little? I made the mistake of buying a Cannondale years back that was a little uncomfortable, but I figured I could tweak things to make it work. 3 stems, one bar, one seatpost, and two forks later, the bike was still incredibly uncomfortable. In all, I spent more on the initially "cheaper" option than I would have if I'd bought the more expensive option from the beginning. And spent several years riding a bike I hated.

Appreciate the comment. This all makes so much sense and I always think about the $$ spent vs a totally different bike altogether.

So finally after much thinking about it got a Niner chromoly fork from the bay, fits like a glove.
Fork did drop the bike about an inch but at almost 490mm from axle to crown, it's a happy medium from the original 515mm pogo suspension. Bike went from just over 32 lbs to an even 29 lbs and feels like a totally different animal, very responsive and tight when compared to the Suntour fork.

Now, Why can't I upload a picture?

That's great news!

So here's a pic of the bike with the Niner fork. Got to admit, it beats me a little on rough trails but for most of the riding I do it's great, much lighter and responsive, dropping almost 4 pounds is a good thing too!