Hey everyone, need a second opinion. I have an '08 Gary Fisher Piranha that came with a RS Tora set at 100mm of travel. Currently, the fork is leaking oil out of the rebound adjustment knob which is common I've been told. So I'm going to replace it instead of fixing it. The fork I'm contemplating replacing it with is coil sprung at 140mm of travel but I think the head tube angle will be way jacked if I jump up the travel. I have a small frame, so it's a fairly short wheelbase. I've read that 20mm of travel = 1 degree of head tube angle change but that can vary with wheelbase and other factors. In all honesty, 140mm is more travel than I need but the fork is a good deal. I ride mainly XC/All mountain and I really like the way the bike handles currently, I'm worried that I will regret going this route if I slacken the head tube angle 2+ degrees. I know it will affect climbing as well as low speed handling, I'm just not sure if that change will be tolerable for me. I believe the bike's head tube angle with 100mm is 69.2 if the geo hasn't changed from '08 to '10 so I'm looking at a ballpark 67 degrees. Am I nuts to expect my XC rig to ride well with this setup? My DH days are over and I no longer lust for a super slack HT angle, I'm sure I'll be told to quit being a tightwad and buy what's right for the bike. Thanks!
Slackening head tube angle - a curse?
- Thread starter ChelanDHer
- Start date
You're not only going to slack out the HA by a couple degrees, you're also going to raise the BB a fair amount (maybe 3/4 to 1 inch), and raise the top tube/head tube junction by 40mm -- almost 2 inches.
It would be great if all you did was slack out the HA but the tipping upward at the head tube is going to mess with the geometry. The bike may ride okay in a straight line but I'll wager the cornering is going to suffer quite a bit. The steering also will probably feel really floppy when climbing and when not going down steep descents.
On top of that there's the usual issue of weakening the frame at the head tube - top tube - down tube junction, which may cause the frame to fail. A longer-travel fork puts more leverage on the head tube. Frames generally are designed for a specific travel fork. I doubt this GF Piranha is overbuilt with extra long forks (relative to 100mm) in mind.
Those are the potential problems I see. But it's your bike and if you want to experiment, it may be fun to see what happens -- provided the frame doesn't snap at the head tube and leave you injured!
I would suggest getting a fork that has adjustable travel like a Pike U-Turn and running it at around 110mm or 120mm travel. You should be able to find a used Pike for not much $$$. The problem with that idea, though, is that you'll need a new front hub to accept a 20mm axle. So maybe a regular-axle fork with adjustable travel? Like a RockShox Revelation?
It would be great if all you did was slack out the HA but the tipping upward at the head tube is going to mess with the geometry. The bike may ride okay in a straight line but I'll wager the cornering is going to suffer quite a bit. The steering also will probably feel really floppy when climbing and when not going down steep descents.
On top of that there's the usual issue of weakening the frame at the head tube - top tube - down tube junction, which may cause the frame to fail. A longer-travel fork puts more leverage on the head tube. Frames generally are designed for a specific travel fork. I doubt this GF Piranha is overbuilt with extra long forks (relative to 100mm) in mind.
Those are the potential problems I see. But it's your bike and if you want to experiment, it may be fun to see what happens -- provided the frame doesn't snap at the head tube and leave you injured!
I would suggest getting a fork that has adjustable travel like a Pike U-Turn and running it at around 110mm or 120mm travel. You should be able to find a used Pike for not much $$$. The problem with that idea, though, is that you'll need a new front hub to accept a 20mm axle. So maybe a regular-axle fork with adjustable travel? Like a RockShox Revelation?
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All valid points, the decreased strength in the head tube from the added leverage had crossed my mind. I'm bailing on this plan. Thinking about going for a Fox 32 F100, I've never liked RockShox and with this Tora blowing up on me, I guess I'm biased against RS.
Thanks for slapping sense into me, that was the response I needed to hear to get myself back into reality.
Thanks for slapping sense into me, that was the response I needed to hear to get myself back into reality.
I put a 130 on my cannondale jekyll which came with a 100mm fork (because I was a kid and MOAR IS BETTAR). Fortunately the jekyll has the adjustable rear shock so I was able to fix some of the rake but that only raised the BB more.
Honestly the thing still climbed, descended, and jumped awesomely. I could wind down the fork to 100mm but I almost never did, I actually felt much more confident on it than I ever have on my reign.. However I recently put a new headset on it and I could tell the frame had ovalised even the frame was designed to handle a lefty, but that could be a side effect of doing way too many stoppies.
Honestly the thing still climbed, descended, and jumped awesomely. I could wind down the fork to 100mm but I almost never did, I actually felt much more confident on it than I ever have on my reign.. However I recently put a new headset on it and I could tell the frame had ovalised even the frame was designed to handle a lefty, but that could be a side effect of doing way too many stoppies.
i say try it out and see if you like it and if not go another direction. not like its hard to swap forks. i have ridden an XC bike slightly raked out(fuel with a lyric) and it was good.
I've primarily experimented with a Giant STP, it's a DJ hardtail that I've used for XC type riding and I've ran everything from 80mm to 150mm travel. I don't think the geometry was a huge issue at 150 it's more the high feeling front end (yes with relatively low handlebars...like 1.5" rise).
If your Tora is an air fork it might be capable of going up to 130mm travel (just take out the spacer on the air cartridge thing). Maybe do a trial to see what you think?
If your Tora is an air fork it might be capable of going up to 130mm travel (just take out the spacer on the air cartridge thing). Maybe do a trial to see what you think?
Go for the long forks slap a short stem on it and have fun. I ride a HT with a 67deg HA on short XC runs with no problems, you just have to corner a bit quicker so you don't notice the slower steering.
Your rear suspension may end up a little bit off its intended angle/height however you will gain a slightly more rearward axle path which may help keep speed in the rough. It's all positives in my book, keep an eye out for cracks and hit the corners fast unlike the sissies on 70deg HA bikes.
Your rear suspension may end up a little bit off its intended angle/height however you will gain a slightly more rearward axle path which may help keep speed in the rough. It's all positives in my book, keep an eye out for cracks and hit the corners fast unlike the sissies on 70deg HA bikes.
What fork are you buying? Most can be lowered and there are guys around who will walk you through it.
Also, replacing seals in a rs fork is stupid easy. Find the RS service manual and do it up even if you just sell the fork.
Also, replacing seals in a rs fork is stupid easy. Find the RS service manual and do it up even if you just sell the fork.
Okay, I have a confession...I bought the 140mm fork already! I was having second thoughts about it, then came here to see if what I wanted to do was insane. I can trade it out for something else if need be, not worried about that. I just want the bike to be right. In retrospect, I got in a hurry and thought it would work. My Tora is shot and I wanna ride, figured I'd solve the problem ASAP and didn't do much homework before pulling the trigger. The DH mindset got the best of me assuming it would be okay, but in the back of my mind I know the consequences of jumping that much in travel. Bought a '10 Fox Vanilla RL, can it be lowered? I know the older Vanilla's can, but I was under the impression the newer Vanillas can't be lowered. The Vanilla is brand new and I don't believe my Tora is the air version so upping the travel to see how it feels isn't quite possible.
I will probably fix the Tora myself one way or another. I'm thinking in maybe a year or two I may want a different bike and would sell the Fisher complete but take whatever fork I end up with me. If the Vanilla can be lowered, that's my most versatile option. Set it at 100mm for now, up it to 140 if I get a frame with geometry that better accepts a 140mm fork.
I will probably fix the Tora myself one way or another. I'm thinking in maybe a year or two I may want a different bike and would sell the Fisher complete but take whatever fork I end up with me. If the Vanilla can be lowered, that's my most versatile option. Set it at 100mm for now, up it to 140 if I get a frame with geometry that better accepts a 140mm fork.
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just run it man. not like you are throwing a dh fork on it.
I fixed my problem. I measured axle to crown on the Vanilla, it was going to be a 2 degree change like I had thought. Sent the Vanilla back, found an '09 Fox Talas 32 100-140 that I picked up. This was the most versatile option, probably won't bump up to 120 and 140 very often, 100mm will see the most use. Additionally, if I end up with a frame in the future that can handle up to 140mm, I'm covered with the Talas. It wasn't the cheapest route but I think it was the best decision. Thanks for everyone's input, I appreciate it.
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