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I have a 2003 On One Tinbred frame which I've owned since new. Have run all sorts of forks on it over the years, Maz Marathons, Fox F80's, On One steel rigids and most recently a pair of 2008 Rockshox Revelation 426 100-130mm U-Turns wound down to 100mm (got a good deal on these second hand) Anyway I've had a quick go up and down the road with the forks dialled out to 130mm, didn't feel too different to be honest. Could running the forks at this length off road cause any any problems to the frame?
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Well, I think it is not recommended, but I have run a 115mm reba on a frame designed for 100 mm for about 5 years. Some people worry about a crack of the head tube, as the longer fork adds more stress.
I've got one of those Tinbreds - I currently run 100-130mm Bombers XCs on it. I wind them down for the ups and flat bits and out for the downs. I'm not a big air or drops merchant though - just old skool XC!...
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I've also run u-turn Revelations on it.
It will slacken the head angle by about 1.5 degrees, the seat angle by about 1 degree and raise the BB by about .7 of an inch. This is all very approximate.
Apart from the concern around the extra leverage on the head tube the geometry changes will likely be noticeable but maybe not to the extent that its distinctly positive or negative. Most people would welcome the reduction in head angle because it makes the steering less sensitive to rider input so the bike feels more stable at speed but that will be countered to some degree by the higher BB and you may find you lose some pedalling efficiency with the slacker seat angle.
I ran a 1995 Yeti built for 100mm forks with a 130mm fork for about 8 months and loved the effect. Long term I don't doubt I would have cracked something somewhere as a result but it would have been fun getting to that point.