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Swapping to suspension corrected rigid fork

Old 11-10-13, 03:51 PM
  #1  
Telly
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Swapping to suspension corrected rigid fork

I'm about to place an order for a (rather expensive) suspension corrected rigid fork and would like your advice/know-how so I don't make a mistake.

My bike currently has a RST Neon TnL (50mm travel) suspension fork which I wish to swap out with a rigid touring fork.

After a call to the bicycle manufacturer, I was informed that I should look for a suspension corrected fork where the crown to axle distance should be around 450-460mm (or something slightly smaller) with a 1-1/8 steerer tube.

Suspension corrected forks are hard to come by here in Europe, and the only thing I found which should work is the "Thorn Mt Tura MKII 1 1/8 Inch Ahead 80 / 100 mm Suspension Corrected Fork".

https://www.sjscycles.co.uk/thorn-mt-...ack-prod30197/


This fork seems to cover the specs with the exception of being 430mm from crown to axle. It's not a major difference (might even be null is I count the compression of the suspension with all the weight on it), but I would like your input so I don't order this expensive unit and end up having to send it back.

Also, I've notice that the Mt. Tura MKII has the v-brakes behind the fork. Does anyone have this type of v-brake setup, and what's the advantages/dis-advantages in it?
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Old 11-10-13, 04:18 PM
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I think the Thorn is meant for 26" wheels while your bike is a 29er.

The advantage of having brakes behind the fork is that braking doesn't pull the brakes away from the fork. In a normal fork there is the risk of the downtube getting in the way but there is ample space on a suspension corrected fork.
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Old 11-10-13, 04:37 PM
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Not sure why you need a 'suspension corrected' fork, suspension correction come into play for 80mm+ travel forks, yours have 50mm, which was the norm back in the early 90's, correction came in when travel increased in the mid-late 90s and people were putting longer (although short by todays standards) travel forks on frames not designed for them.
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Old 11-10-13, 06:05 PM
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Jimc101 makes a good point, albeit an antiquated one. We really shouldn't worry about the nominal travel offered by a fork, but rather it's ATC measurement, and then subtract a l'il bit for sag. there are other considerations, too, such as rake and offset, but I personally feel that the impacts these things have on handling tend to over-rated. Yes, you'll feel a difference if you change any fork parameters, but you'll also tend to find a way to compensate, if the new fork is anywhere in the neighborhood of the old fork's spec.

That being said, I couldn't find much info on your fork, but I saw some for the 60mm version. ATC is listed as 470, which is right near the ATC of most 80mm 29r forks. If you want a fork with similar ATC and all of the touring bells-n-whistles, check out the Surly Ogre fork:
(from surlybikes.com)
The Ogre fork replaces 80mm suspension forks designed for use on 29˝ wheeled bikes. Made of 4130 CroMoly, it’s got 51mm IS disc mounts, removable canti pivots, brake-line guides, low-blade threaded barrel bosses and mid-blade eyelets for a rack. This fork is designed to run disc brakes, fenders and a rack simultaneously. Two sets of water bottle cage mounts, one on each leg. Each cage may be run in a higher or lower position. Steertube is 1-1/8˝ threadless steerer. Black powdercoat finish.

Axle-to-crown: 468mm
Offset: 43mm
Steerer: 260mm
Tire Clearance: 29 x 2.5˝
Weight: 3.1 lb (1.4kg) uncut
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FK0029.jpg (7.8 KB, 173 views)
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Old 11-11-13, 12:32 AM
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Originally Posted by Bezalel View Post
I think the Thorn is meant for 26" wheels while your bike is a 29er.
I was informed that they also have a 700c compatible fork as well, which is the wheels the bike currently has (Mavic A719 rims with 622-38 tires).

Originally Posted by jimc101 View Post
Not sure why you need a 'suspension corrected' fork, suspension correction come into play for 80mm+ travel forks, yours have 50mm, which was the norm back in the early 90's, correction came in when travel increased in the mid-late 90s and people were putting longer (although short by todays standards) travel forks on frames not designed for them.
The frame itself is a 2008(9) build and I *may* be mistaken on the 50mm travel which may be 60mm, will check the documentation and see.


Originally Posted by surreal View Post
Jimc101 makes a good point, albeit an antiquated one. We really shouldn't worry about the nominal travel offered by a fork, but rather it's ATC measurement, and then subtract a l'il bit for sag. there are other considerations, too, such as rake and offset, but I personally feel that the impacts these things have on handling tend to over-rated. Yes, you'll feel a difference if you change any fork parameters, but you'll also tend to find a way to compensate, if the new fork is anywhere in the neighborhood of the old fork's spec.

That being said, I couldn't find much info on your fork, but I saw some for the 60mm version. ATC is listed as 470, which is right near the ATC of most 80mm 29r forks. If you want a fork with similar ATC and all of the touring bells-n-whistles, check out the Surly Ogre fork:
(from surlybikes.com)
You might be correct in stating the fork being 60mm (can't seem to find any info on this). i will take a look into the Surly Ogre fork, which hopefully will be available here in Europe.

Unfortunately I can't find a LBS which has experience with suspension corrected forks, and some found at a LBS had massive difference in axle-to-crown lengths and none of them were equipped for touring (no eyelets for racks or mudguards).


Thanks to everyone for your input and I'll have to check with Surly and see if their fork can cover my needs.
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Old 11-11-13, 04:53 AM
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From what I can tell, they made your fork in 50, 60, and 80mm versions. I just cannot find the specs for the 50mm version. Didn't look all too hard, though. =D
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Old 11-12-13, 02:18 PM
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I'm seriously thinking of going ahead and ordering the Surly Ogre 29" fork, which *probably* has a slightly longer Crown-to-Axle length; this taking into account the sag the suspension fork has when I'm riding the bike.

From your experience, would the longer Crown-to-Axle length cause any problems?
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Old 11-12-13, 02:44 PM
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To get a more actual axle to crown measurement, measure from the center of the rounded bit of the fork dropouts to the join where the fork meets the headtube on the bike.

Usual suspension fork sag meaurements are 25% or so, so you would subtract something like 12.5-15mm sag for your 50-60mm of travel fork to be a more real world ATC measurement.

Or if you really want to get tech, zip a cable tie around your fork, just above the dust seal. Carefully get on the bike without bouncing it or any sudden moves while supporting yourself against a wall or other object. The suspension will sag to where it should be at rest. Get off the bike carefully and when the fork extends, zip-tie will stay where sag settled out. That space between the tie and the top of the dust seal -- subtract that from the static ATC measurement to get real close to your stock geometry.

Then match that up against available rigid forks.

Longer crown-to-axle measurement will raise your headtube, lengthen trail, and relax the steering angle. It will lead to slower steering, larger turning radius, more straight-line stability.

Fork offset will also affect steering...
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Old 11-13-13, 05:26 PM
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Originally Posted by Telly View Post
I'm seriously thinking of going ahead and ordering the Surly Ogre 29" fork, which *probably* has a slightly longer Crown-to-Axle length; this taking into account the sag the suspension fork has when I'm riding the bike.

From your experience, would the longer Crown-to-Axle length cause any problems?
In theory, as mconlux mentions, you'd give up some of your steering response for greater straightline stability. The effect on trail will vary, depending in-part on offset/rake, as these factors also impact trail. IME, I tend to shoot to keep the ATC as close to stock as I can, but i've also found that I can quickly adjust to whatever unintended consequences occur. That being said, I've known ppl who switched forks and deeply regretted the change. As with most things, ymmv.

In the end, though, if you want a mass-produced 29er rigid fork with touring/expedition-style braze-ons, you're pretty much looking at the Ogre. The other stuff will likely have a markedly shorter atc length, or lack the braze-ons you're looking for. The only exception i know of is salsa's Fargo fork, which has an identical atc dimension. There may be other forks on the market, but I'm not aware of them.

Another option would be to go custom, to your exact specs, but this would be an expensive move. For me, i wouldn't go that to such extremes just to avoid @10mm of extra atc length....
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Old 11-14-13, 08:45 AM
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As a touring bike, I prefer greater straight-line stability anyway, so I've decided to go with the Ogre and have sent Surly an email asking about the closest dealer which can send me the fork itself (not worth buying it from the states since the customs will double the price of the unit).

Now one last question since I'm totally unfamiliar with the subject. With the new Ogre, I'm probably going to have to cut the steerer down to size, and if I'm not mistake (check photo below), will probably need a new headset, stem and shims/spacers, right? Can you recommend some of these components, and if possible, can the new stem be adjustable like my previous one?

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Old 11-14-13, 09:25 AM
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You will need a 1.125" threadless headset. There are many good options out there; look at a Cane Creek 40 as a starting point for a mid-priced, quality sealed headset but buy according to your tastes and budget. You'll need some 1.125" spacers, and probably a good many. You will also need a new stem, and threadless stems are available in adjustable models, although, personally, I'm not a fan. I'd suggest leaving the steer-tube uncut and use spacers to test-fit/mock-up various heights, til you get where you want. Then, cut the steerer to put the bars where you want 'em. This is probably a good idea whether you get the adjustable stem or not; just be prepared to use a lot of spacers....
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Old 11-14-13, 09:26 AM
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ps- Eyeballing it, your bike does look to be a 1.125" threaded set up, but please verify this before you buy anything. If it's 1" threaded, the fork'll be a no-go.
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Old 11-14-13, 09:36 AM
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Originally Posted by Telly View Post
As a touring bike, I prefer greater straight-line stability anyway, so I've decided to go with the Ogre and have sent Surly an email asking about the closest dealer which can send me the fork itself (not worth buying it from the states since the customs will double the price of the unit).

Now one last question since I'm totally unfamiliar with the subject. With the new Ogre, I'm probably going to have to cut the steerer down to size, and if I'm not mistake (check photo below), will probably need a new headset, stem and shims/spacers, right? Can you recommend some of these components, and if possible, can the new stem be adjustable like my previous one?
On my Extracycle, I changed out the suspension fork on my '03 Fuji Crosstown 700c. It had the exact same stem.

The New:








The old:







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Old 11-14-13, 09:42 AM
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Originally Posted by surreal View Post
ps- Eyeballing it, your bike does look to be a 1.125" threaded set up, but please verify this before you buy anything. If it's 1" threaded, the fork'll be a no-go.
I guess the 1.125" is the same with the 1 1/8th inch as my manufacturer informed me?

@Standalone, the stems are almost identical, with mine being manufactured by a company called ZZYZX which was bought out by Corractec and is surprisingly made in the US!
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Old 11-14-13, 10:01 AM
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yes. .125= 1/8. It's just, for me, a less clumsy way of typing it. Some folks type 9/8"; others go with the standard 1 1/8", which is how I say it aloud, of course.... Typing's different, though.
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Old 11-14-13, 10:32 AM
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yea Telly has a hybrid headset to use a quill stem, treadless fork, leave it tall ,

and use a threadless stem .. more level to the horizon,

I have 2 stems , lower one has the handlebar bag support mount.
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Old 11-14-13, 08:58 PM
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F-bob makes a good point.... many ppl who have enough "real estate" on a touring bike's steer tube will mount 2 stems, and use a narrow flat bar on the second stem to mount various accessories (eg, headlight, computer, various other electronics, bells, horns, a compass, a bag, etc. ) Basically, it gives you some room for your stuff, leaving your handlebar free to fit your hands and the bike's controls.

https://mgagnon.net/velo/potence-double.en.php

https://api.ning.com/files/GxNVrf8kg9...t_lights_3.jpg
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