Conversion of XC hardtail into trail bike?

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Conversion of XC hardtail into trail bike?
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flag wallstbear
Posted: May 8, 2020 at 23:34 Quote
Inspired by Blake Samson's MegaAvalanche alloy hardtail, I am thinking of converting a carbon XC hardtail into a trail bike.

Here are some of the proposed changes:

100mm Fox SC becomes 150mm Rockshox Revelation
29 wheels w/2.25 Racing Ralphs become 27.5 wheels with 2.6 tires Nobby Nics (BB height will remain stable because of longer fork). Still playing with the idea of a Mullet Bike.
69 deg HTA becomes 67 deg due to long fork.
74 deg STA becomes 72 deg. Not great but pushing saddle all the way forward will help relieve the issue. Plus carbon seatpost w/ setback becomes a dropper post w/ NO setback.
Reach gets a bit shorter but manageable.
34T Chainring will become 30T. (XTR 11sp drivetrain so can't go too big)
60mm/720mm cockpit will be replaced with 50mm/760mm.
Front rotor may need to go up a size.

Bike is currently 10kg and should become 11.5kg ish. Frame is pretty sturdy and I will take my chances on the increased pounding.

Anything I missed?
flag ski-n-bike-da-east
Posted: May 9, 2020 at 4:09 Quote
The only thing I would be worried about is frame stress due to the much bigger fork but I am not an engineer so it might not be a problem
flag wallstbear
Posted: May 9, 2020 at 7:38 Quote
That's indeed a key issue here. I could also chicken out and put on a 130mm Fox 34 that I have lying around. 100 to 130 should be a lot more manageable, plus I need to use judgement in my line choice as well.

ski-n-bike-da-east wrote:
The only thing I would be worried about is frame stress due to the much bigger fork but I am not an engineer so it might not be a problem
flag ski-n-bike-da-east
Posted: May 9, 2020 at 7:40 Quote
I think that may be the better idea. If you wanted to make the bike more agressive you could add a slackening headset also
flag wallstbear
Posted: May 9, 2020 at 8:19 Quote
Do they make one for carbon frames though? According to Works or whatever that company is called, the angle set only fits head tubes that take cups. But most of the carbon frames have bearings directly dropped into the frame.

ski-n-bike-da-east wrote:
I think that may be the better idea. If you wanted to make the bike more agressive you could add a slackening headset also
flag justwan-naride
Posted: May 9, 2020 at 9:18 Quote
Don't bother, really, esp. with the overforking. It messes up the whole geo and then you have a bike that's not good at anything. Yes, head tube angle slackens, but so does seat tube angle climbing becomes harder. Front/rear balance is disturbed, so you may find the front washing out going round corners. Slamming your stem may compensate for this. But the most important for me: bottom bracket height increases, which means bike becomes more unstable.

If you insist on fitting a longer fork, don't use more than 20mm of extra travel.

An angleset alone is a better idea, as it will slacken the head tube angle, lengthen wheelbase (adds stability), slightly lower bb height (more stability) and ever so slightly steepen the seat tube angle. If your frame accepts an angleset I would go for that.

Short/wide cockpit is an easy and effective change, and so is moving to burly casing grippy tyres.

Best advice woud be: get a frame made for what you want to do with it.
flag ski-n-bike-da-east
Posted: May 9, 2020 at 11:34 Quote
If your bearings come in cups then it will work but if they drop straight into your frame it wont.

Like the person above said, you could probably find a good frame for not too much and transfer all the parts over and add the longer travel fork. That would be the best idea I think
flag Marininmaine
Posted: May 9, 2020 at 14:32 Quote
Don't put a fork that long on. Yes it will slacken everything, but it will 1) put you in a position like you're riding a harley 2) raise the BB way higher than is practical 3) shorten what's already probably a pretty short reach if it's a XC bike, which would counteract the trailizing effect. and 4) you won't be able to get much weight on the fork, so it will seem harsh, because suspension only works properly if their is weight on it. Over forking it by 30mm should be just fine. I did just that to my bike, but I also dropped my stem about 15mm in my headset, which I recommend, because like I said, it's hard to get your weight properly distributed when you over fork by too much. Don't expect your bike to feel like a different bike at the end of this. What makes bikes different is the frame, and if you overfork a XC frame, yes that slackens things, but it's gonna feel like a XC bike tilted slightly back, not some enduro hardtail.
flag wallstbear
Posted: May 9, 2020 at 18:03 Quote
justwan-naride wrote:
... But the most important for me: bottom bracket height increases, which means bike becomes more unstable.

That's why I was going to 27.5 wheels w/ 2.6s. BB height will be largely constant (maybe 2-3mm off but close enough).
flag wallstbear
Posted: May 9, 2020 at 18:06 Quote
That's why I am going to smaller wheels, plus the weight will definitely be fine because it has a shorter reach than most "trail hardtails" out there. Cockpit height should be OK because I will adopt a slightly more upright stance when riding trail rather than XC. Also my saddle will be pushed forward a bit.

Marininmaine wrote:
Don't put a fork that long on. Yes it will slacken everything, but it will 1) put you in a position like you're riding a harley 2) raise the BB way higher than is practical 3) shorten what's already probably a pretty short reach if it's a XC bike, which would counteract the trailizing effect. and 4) you won't be able to get much weight on the fork, so it will seem harsh, because suspension only works properly if their is weight on it. Over forking it by 30mm should be just fine. I did just that to my bike, but I also dropped my stem about 15mm in my headset, which I recommend, because like I said, it's hard to get your weight properly distributed when you over fork by too much. Don't expect your bike to feel like a different bike at the end of this. What makes bikes different is the frame, and if you overfork a XC frame, yes that slackens things, but it's gonna feel like a XC bike tilted slightly back, not some enduro hardtail.
flag TheSlayer99
FL
Posted: May 9, 2020 at 18:24 Quote
wallstbear wrote:
That's why I am going to smaller wheels, plus the weight will definitely be fine because it has a shorter reach than most "trail hardtails" out there. Cockpit height should be OK because I will adopt a slightly more upright stance when riding trail rather than XC. Also my saddle will be pushed forward a bit.

Marininmaine wrote:
Don't put a fork that long on. Yes it will slacken everything, but it will 1) put you in a position like you're riding a harley 2) raise the BB way higher than is practical 3) shorten what's already probably a pretty short reach if it's a XC bike, which would counteract the trailizing effect. and 4) you won't be able to get much weight on the fork, so it will seem harsh, because suspension only works properly if their is weight on it. Over forking it by 30mm should be just fine. I did just that to my bike, but I also dropped my stem about 15mm in my headset, which I recommend, because like I said, it's hard to get your weight properly distributed when you over fork by too much. Don't expect your bike to feel like a different bike at the end of this. What makes bikes different is the frame, and if you overfork a XC frame, yes that slackens things, but it's gonna feel like a XC bike tilted slightly back, not some enduro hardtail.

You have literally no responses saying this is something you should do. The geometry is going to be so short it won’t be worth it. You lose 20mm off the reach so it’ll be even more cramped with the shorter stem. The frame is highly unlikely to fit 2.6 in tires too. Pushing the seat forward will only do so much, even with switching from a setback post it most likely not compensate for the 2 degree slacker seat angle. With the 2 degree slacker head angle and the longer fork you are putting more force through the head tube, and voiding the warranty of your frame so when you snap your head tube off it’s coming completely out of your own pocket. With the changes you are suggesting and the goal you are trying to achieve, it isn’t worth it. Literally the only positive that comes from it is you don’t need a new frame, otherwise there are only negatives. You should look at instead to get a separate frame and put the parts you are suggesting on that frame. A proper trail of enduro hardtail would only set you back the frame, shifter, derailleur and cranks aside from what you already have. The overall end result would be better, you wouldn’t be at risk of breaking your frame, you would have a warranty and a bike designed for the task you want it to accomplish. Basically getting a dedicated trail hardtail is exponentially better than upgrading your current frame.
flag rahrider
O+
Posted: May 9, 2020 at 20:54 Quote
Agree with all the above warnings. There is much more than a longer fork to a hardcore hardtail. Your frame will likely flex too much and ultimately break. I realize you said you were ok if this happened but to be honest, the ride will probably suck. I've had frames that are too flexy and it's not really fun. Maybe I'm wrong though, what frame is it? What size?
flag OneTrustMan
Posted: May 10, 2020 at 11:04 Quote
wallstbear wrote:
Inspired by Blake Samson's MegaAvalanche alloy hardtail, I am thinking of converting a carbon XC hardtail into a trail bike.

Here are some of the proposed changes:

100mm Fox SC becomes 150mm Rockshox Revelation
29 wheels w/2.25 Racing Ralphs become 27.5 wheels with 2.6 tires Nobby Nics (BB height will remain stable because of longer fork). Still playing with the idea of a Mullet Bike.
69 deg HTA becomes 67 deg due to long fork.
74 deg STA becomes 72 deg. Not great but pushing saddle all the way forward will help relieve the issue. Plus carbon seatpost w/ setback becomes a dropper post w/ NO setback.
Reach gets a bit shorter but manageable.
34T Chainring will become 30T. (XTR 11sp drivetrain so can't go too big)
60mm/720mm cockpit will be replaced with 50mm/760mm.
Front rotor may need to go up a size.

Bike is currently 10kg and should become 11.5kg ish. Frame is pretty sturdy and I will take my chances on the increased pounding.

Anything I missed?
Lmao

That reminds me when I was converting my cheap daily beater 28er hardtail to a trailbike.

I did to test china parts, learn how to build up my own bike and also out of bordome.

The original fork had 60mm travel. HA was like 73° . The SA however was like 80°
Put on a 150 mm air fork.
Changed to 29er tires, 4 piston brakes, drivetrain.
Pretty much everything.
Bike became super light and actually fun to ride.
The BB was so high lol
The frame was super durable and didn't give a rats ass about the changed geometry.

Fun days.
flag lord-benjamin-coketon-of-baja
Posted: May 10, 2020 at 11:26 Quote
Don't do it. The ride will suck and the frame will break. Buy a frame built for what you want there are plenty of them out there.
flag penrice
Posted: May 16, 2020 at 16:20 Quote
Swap out the rear wheel for a 650b with as wide a tyre as you can fit, wider bars and a slightly shorter stem... job done.

Wont be perfect, but will lower bb, slacken head angle and cost a LOT less money (if you hate it then nothing much lost you can put it back to normal or buy a new better suited frame and swap parts on).

Also means you didnt mess with fork length.... if you like the build add 20mm travel to forks.

*disclaimer* I like monstercross bikes and spent tons of money building a 26" steel rockhopper as an xc bike... I also used to race a home made dh bike in about 1997/8 that was a broken kona mano mano with a steel head tube bonded on with slacker angles etc, so maybe dont listen to me unless that stuff sounds like a good idea
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