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Old 07-14-06, 10:44 AM   #1
Allez3
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Suspension Corrected Fork Advice... With Technical

Converting two Mountain Bikes to touring bikes as previously noted.

Here are the specs:

Trek 4300's - 2002 model
Frames Size: 21" (both bikes)
Head Angle: 71
Head Tube: 145mm
Offset/Rake: 38.1mm
Existing Fork: 435.5mm (axle to crown)
Existing Fork Travel: 63mm
Steerer: 245
Headset: 1 1/8" - Threadless

Proposed Fork:

Tange Suspension Corrected
Steerer: 260mm
New Fork: 413mm (axle to crown)
Rake: 45
Headset: 1 1/8" - Threadless

I think I'm good to go, just want to check.
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Old 07-14-06, 11:35 AM   #2
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I don't know whether it is any help, but I am basically doing the same thing on my Sedona DX, and also switching from threaded to threadless at the same time.

I have always adjusted my preload as tight as it would go, so I don't really think the Tange fork will get me to exactly the same as I was, but I expect it to be close enough to not be detrimental to handling or ride.
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Old 07-14-06, 01:15 PM   #3
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I just recently put a rigid fork on my old MTB with far less thought and calculations then you have put into this with no ill effects. However based on your calculations all looks right. Your existing fork with 63mm travel calculated with a 25% sag would make the axle to crown of your 435.5mm axle to crown fork 419.75mm. The 7mm diffrence in the rigid fork should not significantly change anything. Now the difference between the Offset/rake. In my opinion the 7 mm should not change things significantly. We need to remember all these figures will change with a suspension fork as it goes through it travel.

What you will notice is a much superior feel to your power application and handling, both on and offroad.
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Old 07-14-06, 01:23 PM   #4
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Shortening the fork will steepen the head tube angle, decreasing the trail
Reducing the rake will also decrease the trail.
It seems to me that these changes will make the bike steer much quicker, don't know if that's what you want. If it was me I'd go with fork with less rake, like a 38.

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Old 07-14-06, 03:20 PM   #5
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Here is my 03 Trek 4300 with a Surly fork. Has same axle to crown as your fork. Unkown rake. It did drop the front end a bit but i notice no major side effects.


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Old 07-14-06, 04:48 PM   #6
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You might want to go with a bit longer fork, ca 425 mm, the 413 mm length replaces forks with ~ 50 mm travel . See below from the Vicious cycles Website:

How to select a mountain fork to fit a particular frame:
The best way is to measure! Using a tape measure, find the distance between the top of the front portion of the race ring (where the headset mounts) and the center line of the front axle, now to choose the necessary model compare your measurement with dimension "B" on the above chart. No tape measure? These are some general, but not foolproof guidelines to help achieve the correct fit. If your bike is a 1996 model or older use the 413mm model. If your bike is a 1997 model or newer use the 425 mm model. If your bike is a 1990 or earlier you will probably be needing a Vicious Cycles short length mountain fork which is available by special order. Please be aware that some manufacturers pay no attention to industry standards in which case only a direct measurement will be accurate.
Mountain


438 mm oversize steer *available in disc version
a 1.125" steer
b 438mm (17.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

425 mm oversize steer *available in disc version
a 1.125" steer
b 425mm (16.75") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

413 mm oversize steer *available in disc version
a 1.125" steer
b 413mm (16.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

413 mm standard steer
a 1" steer
b 413mm (16.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork
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Old 07-14-06, 10:13 PM   #7
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Quote:
Originally Posted by tonyt
You might want to go with a bit longer fork, ca 425 mm, the 413 mm length replaces forks with ~ 50 mm travel . See below from the Vicious cycles Website:

How to select a mountain fork to fit a particular frame:
The best way is to measure! Using a tape measure, find the distance between the top of the front portion of the race ring (where the headset mounts) and the center line of the front axle, now to choose the necessary model compare your measurement with dimension "B" on the above chart. No tape measure? These are some general, but not foolproof guidelines to help achieve the correct fit. If your bike is a 1996 model or older use the 413mm model. If your bike is a 1997 model or newer use the 425 mm model. If your bike is a 1990 or earlier you will probably be needing a Vicious Cycles short length mountain fork which is available by special order. Please be aware that some manufacturers pay no attention to industry standards in which case only a direct measurement will be accurate.
Mountain


438 mm oversize steer *available in disc version
a 1.125" steer
b 438mm (17.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

425 mm oversize steer *available in disc version
a 1.125" steer
b 425mm (16.75") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

413 mm oversize steer *available in disc version
a 1.125" steer
b 413mm (16.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork

413 mm standard steer
a 1" steer
b 413mm (16.25") length
c 1.5" rake
true temper oversize uni-crown blades
straight blade fork
+1
Vicious Cycles recommends the 425mm forks for frames designed around 63mm of travel.
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Old 05-13-07, 07:32 PM   #8
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Sorry for bumping such old thread but i'm in the process of converting my crappy geared hardtail to a rigid SS, SS part it done, now to lighten the bike and get rid of that RST fork

About the same as the OP, 63mm travel, 38mm rake and 438.7mm Axe to crown

So any updates? How did it go?
The 425mm rigids are quite more expensive
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Old 05-13-07, 08:27 PM   #9
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Quote:
Originally Posted by Daijoubu
Sorry for bumping such old thread but i'm in the process of converting my crappy geared hardtail to a rigid SS, SS part it done, now to lighten the bike and get rid of that RST fork

About the same as the OP, 63mm travel, 38mm rake and 438.7mm Axe to crown

So any updates? How did it go?
The 425mm rigids are quite more expensive
I love the Tange fork on my Sedona DX.

No bouncing when I am out of the saddle, and the chrome moly fork absorbs buzz adequately. I love the more responsive handling as well... Over-all better stability, and nice ride.

If you want to go rigid, you should try the Tange fork. I also converted a Raleigh MT-500 for a friend with the Nashbar fork, and it works well also... although the last time I looked the Nashbar fork doesn't seem to be in stock.

For looks I prefer the Tamge's more traditional looking fork...
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Old 05-13-07, 09:37 PM   #10
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Quote:
Originally Posted by Allez3
Converting two Mountain Bikes to touring bikes as previously noted.

Here are the specs:

Trek 4300's - 2002 model
Frames Size: 21" (both bikes)
Head Angle: 71
Head Tube: 145mm
Offset/Rake: 38.1mm
Existing Fork: 435.5mm (axle to crown)
Existing Fork Travel: 63mm
Steerer: 245
Headset: 1 1/8" - Threadless

Proposed Fork:

Tange Suspension Corrected
Steerer: 260mm
New Fork: 413mm (axle to crown)
Rake: 45
Headset: 1 1/8" - Threadless

I think I'm good to go, just want to check.

yes it works

good to go
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Old 05-13-07, 10:17 PM   #11
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Quote:
Originally Posted by Little Darwin
I love the Tange fork on my Sedona DX.

No bouncing when I am out of the saddle, and the chrome moly fork absorbs buzz adequately. I love the more responsive handling as well... Over-all better stability, and nice ride.

If you want to go rigid, you should try the Tange fork. I also converted a Raleigh MT-500 for a friend with the Nashbar fork, and it works well also... although the last time I looked the Nashbar fork doesn't seem to be in stock.

For looks I prefer the Tamge's more traditional looking fork...
So it's safe to go with a cheap 413mm $45 tange, instead of shelling more money for a 425mm..
lower front/shorter means quicker steering huh?

nashbar's is mucho longer at 453mm and is in stock at $55..hmm
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Old 05-14-07, 06:40 AM   #12
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Quote:
Originally Posted by Daijoubu
So it's safe to go with a cheap 413mm $45 tange, instead of shelling more money for a 425mm..
lower front/shorter means quicker steering huh?

nashbar's is mucho longer at 453mm and is in stock at $55..hmm
Pull out your ruler and look at how small 12 mm (or even 40mm) is... The difference is probably in the same range as the handling change between the lightest and heaviest preload settings on shocks that have the option.

I actually attribute the more responsive handling to the lack of sponginess from a front shock rather than the difference in length.

There is probably a difference in handling between a 413 and 425 mm fork length, but probably a lot less than the change inherent in the elimination of the pogo stick effect of a cheap front shock...

Also, the quicker steering isn't enough to feel twitchy or unstable (at least in my case) it is more evident as a better feel for the road. It still doesn't feel like a tight geometry road bike, but more like a relaxed geometry road bike... Which makes sense with the geometry of my bike in general.

So I can say that the Tange fork has worked fine for me, and will probably work well for you too.

Whatever you decide, good luck!

EDIT: The reason I used the Nashbar on the Raleigh was because the rider wanted the handlebar as high as possible, so every little bit I could add was a good thing...
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Old 05-14-07, 11:36 PM   #13
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I found a Salsa 425mm in stock at a local bike shop (CAD$113 with tax), bought it and installed it tonight at my coop, didn't knew it was that easy to work with threadless forks, took me about a hour
Waiting for my new crankset and chainring to get rid of my derailleur..


Old 2.2Kg monster fork
Close up of the fork

Thanks for the help and nvm for the thread jack
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Old 06-03-15, 12:01 PM   #14
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I'm going to bump and resurrect this very, very old thread and I hope no one minds. There is a A LOT of very good information here.

I am completely blown away that this not discussed more frequently. I have a 2014 Trek 8.2 DS with an el cheapo Suntour suspension front fork that is completely worthless since it cannot be locked out.
I have searched, scoured and looked for concrete data on replacing my Suntour with an aftermarket rigid fork and for the life of me, I cannot find any solid data.
I cannot believe I'm the only individual with a 8.2 DS (or other lower end DS series) that has not wanted to complete this sort of upgrade.
Maybe it really isn't as common as I would think it would be?

The offset according to Trek's website is 38mm.

I am going to check out Vicious Cycles website, but as someone else mentioned above (several years ago), they are a bit pricier.
I am contemplating the Surly Ogre which works with my cantilever brakes + 700 / 29" wheels + 1-1/8" tube.
My only concern being is the offset on the Surly Ogre fork is 43mm which is ever so slightly longer which would make the steering a tad bit slower.

Any thoughts here or other recommendations to a suspension corrected aftermarket fork that would work with my bike?
It sounds like 38mm is fairly small for a 700 / 29" bike and may not be that common to find.
Has any one else done this that would NOT affect the geometry or handling of the bike?
If so, could you share what aftermarket fork you went with....?

Thanks!!
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