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Discussion Starter #1
I have an old school gfish genesis geometry, (not sure what year) that I'm project building for an entry level rig. To see if I dig this thing enough to spend car money on one. Fork now is 26r and only 80mm. Figure for better absorption and to catch a wee bit of air (read for some decent air you'll need at least 150mm, true or false?) and to be able to do some dh...was thinking of putting the 27.5 fork and wheel on it...cant for the back, no space. No understanding of the bikes geometry, but I'm hearing it'll be o.k. especially for a noob. Am I good or wreck waiting to happen. Any other advice would be dope as well. 🤘🤙✌
 

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Rabid Lana Fan
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If it's a really old bike, it may have a straight head tube (as apposed to a tapered head tube). Locating a straight tube 27.5 fork may be a challenge.
 

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Don't do it. That frame is not designed for that much fork travel. A shorter travel 27.5 XC fork may work, but I'd keep the travel low.
 

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Murica Man
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also, you don't need 150mm of travel to go big. the biggest jumps i've ridden (around 15ft gap) have been on a 130mm 27.5 ht.
 

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also, you don't need 150mm of travel to go big. the biggest jumps i've ridden (around 15ft gap) have been on a 130mm 27.5 ht.
That's true if you know what you're doing. Those old bikes though, they had 80 or 100 mm forks and steep geometry. They really weren't designed for jumping much at all. If you're a very skilled rider, you could do it.

Practically any modern bike would be far better for the purpose of catching air.
 

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It would be a really bad idea to try to put a 150mm fork on that bike ,you would have a front end that looked like a chopped Harley . The bike would not be rideable on any trail. As stated you couldn't find a fork that fit anyway. BMX riders jump without any suspension. What is reasonable ,is to ride that bike as is while saving for something new(er).
 

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If you need a 150mm fork for what you're intending to ride, that old frame probably isn't going to handle it for long. Save your bucks, enjoy riding the old bike for what it is, and upgrade to something more modern and robust if/when you can afford to and need to.
 

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Discussion Starter #8
Haha...uhhhhh my bad must be a misunderstanding some where. 80 - 150? oh indeed my fellow trekers...i know that would be extremely no bueno. I was just stating the 150 as you need that much for jumps, i was told. But someone here said 130 is groovy even for gaps. Me, i aint sendin nothing yet...the 27,5 fork i was pondering is only 20 up at 100mm. Anything more, i have researched will totally throw the geo out of whack. But the consensus is 100mm is ok. I was just trynna find out, pros and cons of a 27.5 front and 26r on back....and preciate the get backs....ride on
 

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A 27.5 wheel with a increased 100mm fork will also give a chopper type of ride. Your weight and the the weight of the bike will shift backwards. The less weight on the front will make it harder to keep That would mean a new front wheel, and depending on the front brake lever/ shifter you could need a lever or both. And you can't lace a 27.5 rim to to your hub, the sidewalls on disc rims aren't made to take brake pads rubbing on them. If you to get a mechanical disc , you might be able to use the lever you have. Some shifters and brake levers are one piece ,then you would need both. And then you still might have to change the cable to something longer ,because of the longer fork and bigger wheel.
 

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Out spokin'
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I bet you'll be fine with a 100mm suspension fork & 27.5" wheel on a bike designed for 26/26". Heck I put a 29er fork & 29" wheel on my old 2002 26" singlespeed and it handled better than before. But then my bike is rigid (no suspension). Anyway I'm betting you'll be okay. The swap you're talking about will rock your bike back since it lifts the front but not the back so you'll likely have to slide your saddle all the way forward and maybe lengthen & lower your stem a little. Maybe. Maybe not.

Life should be an adventure. Live it up.
=sParty
 

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Bicyclochondriac.
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I think this is mostly a waste of money, and it will likely just screw up the geo. Sure, you will slacken the HA, but you won’t be increasing the frame reach (might actually be shortening it) and you are raising the BB.

Best things you can do for this is leave the fork as is, stuff a large tire in the front, and look at getting a wider bar and shorter stem (if this was not already done)

Hard to give real specifics without knowing what you have.
 

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Amount of travel isn't the real operative dimension in question, either. Axle-crown measurement is what you should be looking at. Moving from a 26er 80mm fork to a 27.5 fork at 100mm of travel is going to increase a-c a couple of ways. One, from the increase in travel. Second, from the increase in wheel diameter capacity (which affects the fork lowers). And then, because there are variations from one comparable fork to another, you've got yourself set up for a much larger difference than just 20mm.

PLUS, you've got the difference in wheel sizes from front to back now that's exaggerating the choppered-out effect (and raising the bb). It'll also make the seat tube even more slack (those old bikes had slack seat tubes, anyway), reduce the reach, and generally make the bike ride like crap. There's also the chance that the whole suite of changes will get you well outside the designed parameters of the frame, and destroy your frame.

The bike isn't made for that kind of thing. It's not worth it, and is frankly a fairly dumb upgrade. Save your shekels for a new bike later on.
 

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I'm still stuck on "need 150mm for decent air". Looking back, we used to get the same "decent air" on 20" rigid BMX bikes as we now get on our fancy new geo long travel bikes today. Just sayin'. Well... bike park air.
 
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