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Discussion Starter · #1 ·
Can you use a kinesium frame for (sometimes) hard riding? I am planning to put sun singletrack wheels on it and fox vanilla fork. The frame is actually designed for XC racing but I am not into that. Thanks.
 

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Former Bike Wrench
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Only if its designed for it

Kinesium is basically a fancy name that Kinesis Bicycle Manufacturer uses to name their aluminum tubing. It is not a brand, Kinesis does not sell bikes under its own name. Over the years they have made bikes for GT, Santa Cruz, Mountain Cycles (which they used to own), Jamis, etc. If your Kinesium frame was designed for a 80mm fork (ie XC), then putting a 140mm Fox Vanilla on it and using it to freeride is a REALLY bad idea...unless you like snapping a headtube and faceplanting.

:nono:
 

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Discussion Starter · #3 · (Edited)
mtnbiker72 said:
Kinesium is basically a fancy name that Kinesis Bicycle Manufacturer uses to name their aluminum tubing. It is not a brand, Kinesis does not sell bikes under its own name. Over the years they have made bikes for GT, Santa Cruz, Mountain Cycles (which they used to own), Jamis, etc. If your Kinesium frame was designed for a 80mm fork (ie XC), then putting a 140mm Fox Vanilla on it and using it to freeride is a REALLY bad idea...unless you like snapping a headtube and faceplanting.

:nono:
That is very serious then. The original frame had an 80mm manitou skareb. I put a 125mm Fox Vanilla. Should I take it off? Thanks.
 

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pronounced may-duh
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I don't think having a longer travel fork will destroy your frame. However the frame geometry was designed for a shorter fork so it will not handle the way it was designed to. What will break your frame is the way you ride. If the bike was designed for xc racing it probably wasn't designed for big jumps and freeride stuff. If your just doing regular trail riding then I don't think you will have a problem.

What exactly is "hard" riding for you?
 

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Discussion Starter · #5 ·
Maida7 said:
I don't think having a longer travel fork will destroy your frame. However the frame geometry was designed for a shorter fork so it will not handle the way it was designed to. What will break your frame is the way you ride. If the bike was designed for xc racing it probably wasn't designed for big jumps and freeride stuff. If your just doing regular trail riding then I don't think you will have a problem.

What exactly is "hard" riding for you?
No I don't think i ride hard anyway, just long trial riding and small jamps. just what mtnbiker72 worried me for a bit but after i searched i think my bike is fine, the fox fork adjusts anyway. Thanks.
 

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Longer travel, more leverage

A longer travel fork puts more leverage on your headtube (simple physics here, longer lever, more leverage). Over the eight years of being a bicycle mechanic, I saw at least half a dozen frames that had snapped headtubes from riders running long travel forks on XC frames. Since you have an older Vanilla 125, I recommend you run it at 100mm. At that travel, you should be much safer.

:thumbsup:

PS-if you snap the headtube from running a longer travel fork, most manufacturers WILL NOT warranty your frame...I know, I used to do warranty for several shops.
 

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mtnbiker72 said:
A longer travel fork puts more leverage on your headtube (simple physics here, longer lever, more leverage). Over the eight years of being a bicycle mechanic, I saw at least half a dozen frames that had snapped headtubes from riders running long travel forks on XC frames. Since you have an older Vanilla 125, I recommend you run it at 100mm. At that travel, you should be much safer.

:thumbsup:

PS-if you snap the headtube from running a longer travel fork, most manufacturers WILL NOT warranty your frame...I know, I used to do warranty for several shops.
All true especially the stuff about the warranty. BUT you must provide a serious impact to break your head tube such as a head on collision with a car or a huge jump with a hard landing. With any suspension fork on an XC frame, the frame will break before the fork. Long ago when people people rode on rigid forks, the forks often bent before the frame. Suspension forks are much stronger than the old style rigid forks and given a big enough impact will kill any frame.
 

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Not always true

Maida7 said:
All true especially the stuff about the warranty. BUT you must provide a serious impact to break your head tube such as a head on collision with a car or a huge jump with a hard landing. With any suspension fork on an XC frame, the frame will break before the fork. Long ago when people people rode on rigid forks, the forks often bent before the frame. Suspension forks are much stronger than the old style rigid forks and given a big enough impact will kill any frame.
I personally cracked a headtube on an Iron Horse Hollowpoint (fortunately saw it before the entire headtube snapped) from normal trail riding with a fork that was only 25mm longer than the stock fork. Everytime you hit a square edged bump, a fork will flex backwards before absorbing the bump. With todays stiffer forks (using 32mm+ stanchion tubes, like the Vanilla), that backwards flex is taken by the headtube. Again, the longer the travel fork, the longer the "lever" and the greater the force on the headtube. Bike manufacturers engineer this force into their bikes, so if the headtube strength is designed to absorb forces from a 80mm fork, then putting a 125mm fork on it will increase these forces and could lead to failure. It doesn't require any collisions, big impacts, or large jumps. Aluminum has a fatigue life, everytime you flex it, it fatigues. If you increase the amount of flexing...it will fail sooner.

I stand by my statements and back them up with 8 years of bicycle service experience. The only thing worse looking than a frame with a snapped headtube, is the sight of the frame owners face full of stitches and all black and blue.

But hey, its an extreme sport right?

PS-Long ago the frames were made from steel, which is WAY stronger and fatigue resistant than aluminum
 

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Sure all frames wear out over time. Aluminum is particularly prone to cracking and tearing from fatigue. A beefier, longer travel fork will transfer more stress on the frame. I get your point. Many people break frames. Many people don't. I still think he can still ride that frame with that fork and be OK. I personally would ride that set up without a second thought. But I'm a fairly conservative rider and don't break frames. We should all inspect our aluminum frames periodically for hairline cracks. I've seen an aluminum road bike torn in two from a hairline stress crack. I was also a mechanic for many years but that was a long time ago. Now I only fix my own bikes. I still ride a steel frame from time to time.
 
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