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Frame for suspension front forks.

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Frame for suspension front forks.

Old 10-07-15, 09:13 AM
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cncwhiz
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Frame for suspension front forks.

How can I tell if the frame for an older mountain bike works with suspension forks or not? I have a frame with a suspension fork on it but I think it is going to be to small.
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Old 10-07-15, 09:44 AM
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We need some clarification on this. Is the fork currently installed in your frame? If so and everything fits and adjusts correctly, it should "work," but the frame may not have geometry that would be optimal for use with the fork.

If the fork is not yet installed there are several things to be determined; steerer tube length and diameter will have to fit the frame in question, a proper headset to fit both frame and fork will need to be obtained and installed, a stem to fit into (quill-type stem) or onto (threadless type) the fork needs to be obtained and installed. You might want to take both frame and fork to your local bike shop for an assessment. Good luck!

Or are you talking about an existing frame and suspension fork combo fitting you? See what I mean about clarification?
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Old 10-07-15, 09:49 AM
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Most suspension forks are threadless for starters. Although some or 1", many are 1 1/8" steerer dimensions.

Another way is to look at the model line up for the year the frame was offered. Often the same frame was used on multiple models with the difference in price based on rigid fork or suspension along with components. Such was the case with the 1997 Specialized Rockhopper.

There are several considerations when replacing a rigid with a suspension fork. One is the off-set of the fork. Another is the adjustability of the travel which impact the overall length. You would like the distance between the axle and the crown to be close to the same between the two forks with you sitting on the bike. Most importantly, if you are buying a used suspension fork, make sure the steerer tube is long enough for the head tube. Measure the length of the existing rigid fork as a guide. Take into consideration if you are going to use the existing head set or replace it. Stack height will play a part in the required length. It is easier to cut than to add. It took me years to find a suspension fork that would actually work on my 20.5 frame. Most people cut the steerer to fit their bike which can eliminate some nice forks for purchase.

Sorry, but I have this habit of using pictures as an example.

Stock configuration:
[IMG]PA160495w by superissimo_83, on Flickr[/IMG]

Now with the suspension fork. Note that once I sit on it, the fork compresses to the correct height. This fork is air suspension allowing for such an adjustment. Handling was weird until the correct pressure was determined.
[IMG]RockHopper_ Sprung_2012_018 by superissimo_83, on Flickr[/IMG]

Now that I have looked at the pics, there is one more indication. The distance from the crown race to the axle. Here is a pic of a huge gap due to the length of the fork legs to compensate for using a suspension fork on the same frame.
[IMG]P1000035 by superissimo_83, on Flickr[/IMG]

What I did was buy a new head set with an extra crown race. This way I can easily change between the two forks in 20min or less depending on what my ride plans are. If I am commuting, on goes the rigid fork with fenders. Trail riding will cause me to swap to the suspension fork/wheel assembly. My small swiss army knife bike!
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Old 10-07-15, 11:19 AM
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I have a bike that has a suspension fork that it came with. It is a rock shock Judy. I am afraid that the frame is to small for me. I want to find another used frame that will work with this fork. I am not worried to much about the stack height and steer tube as much as I want a frame that is designed for a suspension fork
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Old 10-07-15, 11:23 AM
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Originally Posted by cncwhiz View Post
I have a bike that has a suspension fork that it came with. It is a rock shock Judy. I am afraid that the frame is to small for me. I want to find another used frame that will work with this fork. I am not worried to much about the stack height and steer tube as much as I want a frame that is designed for a suspension fork
If the frame is to short, would question if the steerer would also be too short if moved to another frame.

For the Judy, great fork back in 1996, not so great in 2015.
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Old 10-07-15, 07:34 PM
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What is your bike model, make, year, and size? From that we might be able to figure out how long the head tube is and whether a larger size frame would work with your current fork. A few good photos of your bike would be worth a thousand words. Also, we like to look at bikes.
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Old 10-07-15, 10:13 PM
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It's an amp research b3. It does not have the oem fork. The bike has a rock shock judy. I am 6 foot and it is a 19 inch frame.
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Old 10-08-15, 03:06 PM
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That's a tough one. Honestly, I think your best bet is to take it into a bike shop where they can measure the fork and determine the length and diameter of the steerer tube. Get those numbers and you can start shopping for a new frame.
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Old 10-09-15, 12:52 AM
  #9  
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Why are you trying to reuse the Judy? It is an old fork, even a used 10 year old fork would be far better.
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Old 10-09-15, 10:39 AM
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The Judy Is fine and will work with the geometry of the Amp. Anything with more travel is going to throw off the geometry on that frame. A clean rebuilt Judy is a fine fork.
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Old 10-09-15, 11:20 AM
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Originally Posted by redcaymatt View Post
The Judy Is fine and will work with the geometry of the Amp. Anything with more travel is going to throw off the geometry on that frame. A clean rebuilt Judy is a fine fork.
If you can get spares, and even then, a Judy just wont work as well as a current fork, if you were looking at period correct forks, only Bombers have stood the test of time (like those on #SJX426 Rockhopper)

Also, the AMP is an ancient bike design, unless you are riding it specifically as a retro bike, would be looking for a more up-to-date bike if going off road (which it was designed for). Damage any part of it, and spares will be hard to get, as AMP got out of the bike business back in 2000.
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Old 10-09-15, 12:24 PM
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Oh, it's about MTBs. I was kinda hoping for a discussion on this setup:

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Old 10-09-15, 12:56 PM
  #13  
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The Duclos Lasalle bike? Nice! Ruby SL, Mavic Starfish group....Exotique!
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Old 10-09-15, 01:16 PM
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Originally Posted by jimc101 View Post
If you can get spares, and even then, a Judy just wont work as well as a current fork, if you were looking at period correct forks, only Bombers have stood the test of time (like those on #SJX426 Rockhopper)

Also, the AMP is an ancient bike design, unless you are riding it specifically as a retro bike, would be looking for a more up-to-date bike if going off road (which it was designed for). Damage any part of it, and spares will be hard to get, as AMP got out of the bike business back in 2000.
I like the older bikes. I can get them for almost nothing and go to the bike project and get any parts I want. I also have never been on a newer bike nor can I afford one. You can tell me about how the new stuff works better than the old stuff but anything I build and ride is better than the one before it. I ride over 60 miles a week on a 91 trek mountain bike and it works fine for me. I am cool with the suggestion but this forum is for "vintage and classic" bicycles which is what I have and what I ride. I have thousands of miles of blm less than a block from my house and I ride out there all the time. The suspension fork will work great for me as that I am riding full rigid classic bikes it loose dirt and rock with no issues for me other than my hands getting beat. I posted her to ask for help not to be told that I need to go out and buy a four thousand dollar bike and that all my stuff is out of date.
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Old 10-09-15, 01:34 PM
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@cncwhiz - I hear ya. I over invested in my set up. The Bomber was a CL find for $100 (included the pump) after an overhaul. The front wheel with XTR hub was $50 (wanted disk brake capability). The Avid 7 was a NOS CL find for $35 complete in box. The head set was another IDK $35. So my font end is a very expensive configuration. Every purchase was a good deal and considering the front end is only 1 lb heavier than stock and the fork has three dampening positions + lockout and rebound adjustment (air suspension) and and and the stock bike weighed in at 27 lbs with the DB steel frame, I am happy with a stripped down trail rider under 30 lbs.

BTW: I am still using the original knobby.
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Old 10-09-15, 04:45 PM
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Originally Posted by AngryFrankie View Post
The Duclos Lasalle bike? Nice! Ruby SL, Mavic Starfish group....Exotique!
Exactly! I have been sitting on a NOS Rockshox Ruby for ages, waiting for a good idea for a build ...
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Old 10-10-15, 02:41 AM
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Originally Posted by AngryFrankie View Post
The Duclos Lasalle bike? Nice! Ruby SL, Mavic Starfish group....Exotique!
That's not a Ruby in the picture, it's a Paris-Roubaix SL, the Ruby was a different fork, with a single piece lower casting, unlike the SL which was very similar to the Mag series with a 3 piece lower leg. Never saw one on a bike, but remember seeing a pair in the window of the old Condor Cycles shop.
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Old 10-10-15, 03:11 PM
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Originally Posted by jimc101 View Post
If you can get spares, and even then, a Judy just wont work as well as a current fork, if you were looking at period correct forks, only Bombers have stood the test of time (like those on #SJX426 Rockhopper)

Also, the AMP is an ancient bike design, unless you are riding it specifically as a retro bike, would be looking for a more up-to-date bike if going off road (which it was designed for). Damage any part of it, and spares will be hard to get, as AMP got out of the bike business back in 2000.
I disagree, I ride an Amp weekly, along with a bunch of other obsolete mountain bikes like Merlin, Trimble, Slingshot, Fat Chance, etc. . And I can tell you for a fact that a Judy will work fine on an Amp frame. Anything with more travel is going to screw up the geometry like it did to that Rockhopper mentioned.Handling was weird because that bike wasn't designed for a fork that long and all the air pressure changes in the world aren't going to help that. This is a classic and vintage forum so I'm going to guess the OP is into that. New mountain bikes are overbuilt to the point that they are pretty dull to ride, especially if you're used to riding a rigid bike. So, yeah. OP use the Judy, plenty of spares on ebay and they are easy to pull apart and rebuild. Retrobike UK has the rock shox manuals online free to download.

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Old 10-10-15, 03:33 PM
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Originally Posted by redcaymatt View Post
The Judy Is fine and will work with the geometry of the Amp. Anything with more travel is going to throw off the geometry on that frame. A clean rebuilt Judy is a fine fork.
I don't know... My Mongoose came with a Judy XC that didn't work. I replaced it with a new 100mm travel fork and it works great. Everything feels right. Why rebuild a Judy when you can get a brand new 100mm travel RockShox for $100 now anyway?



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Old 10-10-15, 03:38 PM
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Because the Judy was a good fork that had 63-80 mm of travel and $100 rock shox fork like the one you show is going to change the geometry of the frame. If you like it thats great thats really all that matters . But when Rock Shox made the Judy it was they're best fork, $100 rock Shox are probably they're worst.
Originally Posted by CannedPakes View Post
I don't know... My Mongoose came with a Judy XC that didn't work. I replaced it with a new 100mm travel fork and it works great. Everything feels right. Why rebuild a Judy when you can get a brand new 100mm travel RockShox for $100 now anyway?



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Old 10-10-15, 03:55 PM
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Originally Posted by redcaymatt View Post
Because the Judy was a good fork that had 63-80 mm of travel and $100 rock shox fork like the one you show is going to change the geometry of the frame. If you like it thats great thats really all that matters . But when Rock Shox made the Judy it was they're best fork, $100 rock Shox are probably they're worst.
Yes, it's a low end NEW fork but it's still a major upgrade over nearly 20 year old short travel elastomer shocks.
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Old 10-10-15, 06:33 PM
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Originally Posted by CannedPakes View Post
Yes, it's a low end NEW fork but it's still a major upgrade over nearly 20 year old short travel elastomer shocks.
In your opinion that is. The OP could easily go with a spring or an air cartridge in the Judy, both are not very hard to find. Neither are elastomers if he wants to keep it original. He's got an Amp Research B3. It's a well made American bike from the 90's that will last just like the Judy will last. You guys telling him to buy a new fork are riding lower end Asian made bikes that were brought here by the ton, So if you want to put newer forks it's not a big deal. But on a vintage American bike there is something to be said about keeping it correct. BTW I guess you're also buying new brakes? Is that canti even hooked up? I don't know of any recent forks cheap or expensive that have a canti hanger.
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Old 10-10-15, 07:31 PM
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Originally Posted by redcaymatt View Post
In your opinion that is. The OP could easily go with a spring or an air cartridge in the Judy, both are not very hard to find. Neither are elastomers if he wants to keep it original. He's got an Amp Research B3. It's a well made American bike from the 90's that will last just like the Judy will last. You guys telling him to buy a new fork are riding lower end Asian made bikes that were brought here by the ton, So if you want to put newer forks it's not a big deal. But on a vintage American bike there is something to be said about keeping it correct. BTW I guess you're also buying new brakes? Is that canti even hooked up? I don't know of any recent forks cheap or expensive that have a canti hanger.
There's nothing special about American bikes. Plenty of Walmart Huffies were American made...
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Old 10-11-15, 01:51 AM
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Originally Posted by redcaymatt View Post
I disagree, I ride an Amp weekly, along with a bunch of other obsolete mountain bikes like Merlin, Trimble, Slingshot, Fat Chance, etc. . And I can tell you for a fact that a Judy will work fine on an Amp frame. Anything with more travel is going to screw up the geometry like it did to that Rockhopper mentioned.Handling was weird because that bike wasn't designed for a fork that long and all the air pressure changes in the world aren't going to help that. This is a classic and vintage forum so I'm going to guess the OP is into that. New mountain bikes are overbuilt to the point that they are pretty dull to ride, especially if you're used to riding a rigid bike. So, yeah. OP use the Judy, plenty of spares on ebay and they are easy to pull apart and rebuild. Retrobike UK has the rock shox manuals online free to download.

Guess it depends what you want out of riding, I've been riding MTB's since '93, when what's retro today was current, and still have a few HT bikes from '95, which are still ridable & ridden, but are also heavily updated with recent suspension forks, bars, stems etc which makes then still ridable (also due to many of the original parts having worn out or broken with use).

Would disagree with modern bikes being overbuilt and feeling dull to ride, try riding an old bike with say a MAG21 then a current SID, and your'll be able to tell the difference (I did this a few years back, and sold my MAG21's as they just couldn't compare with modern forks)
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