Fork upgrading with longer travel

Dyroon

Hi everyone, I need an expert's opinion!

I'm planning to swap my Rockshox XC30 (100mm) to a Reba or Revelation. The bike is a bTwin Rockrider 580 in size L (27,5")
The question is, what is the longest travel that my bike's frame could handle without any disadvantage?

I think 120mm should'nt be a problem, because I checked the 560 S which has a 120mm fork (ROCKSHOX XC 32 TK), and its "HT angle" is 69 degrees (mine 69,5), therefore it seems every 20mm has 0.5 degrees difference.
But can I go further, maybe around 130-140?

Specs of the 580 frame:
http://www.btwin.com/en/19045-98663/rockrider-580-mountain-bike-white-orange.jpg

Specs of the 560 S frame:
http://www.btwin.com/en/18892-98588/rockrider-560-s-mtb.jpg

The Rookie

Is yours the 580 hardtail or the 580s FS?

Either way I'd expect it to handle a 120mm OK, but wouldn't go any longer than that.

Dyroon

It's a hardtail.
However, I picked out a 130mm Rev for a great price. In theory, there would be around 1 degree difference (0.75° according to the specs), is that too much stress?
Maybe could I do some trick with spacers?

poah

should be able to get a 120mm air shaft for the rev. easy to change on a solo air fork.

swod1

Dyroon wrote:

It's a hardtail.
However, I picked out a 130mm Rev for a great price. In theory, there would be around 1 degree difference (0.75° according to the specs), is that too much stress?
Maybe could I do some trick with spacers?

you could swap the air spring inside it to a shorter one but that would be too much messing about, you could set more sag on the fork so it would be around 120mm.

I'd just look out for a decent condition 2nd hand or new depending on budget reba 120mm fork with 15mm through axle if your front wheel is compatible.

Dyroon

Thanks for your replies.
So you definitely don't recommend to go above 120mm, right?
Because I'm not gonna lie, the longer travel really attracts me, and I'm using the bike much more on downhill rather than uphill, I really want to go with the longest travel as possible without any harm on the frame.
So if the 130mm could fit (even just barely), I would be very happy and would go with that.

cooldad

You can't just measure angles and assume it will work. A frame will be designed around a certain use and size, and might or might not be strengthened in areas specifically.

So you can try it, it might work, or it might fail catastrophically and you will die.

Your choice. I wouldn't.

It sounds like you have the wrong sort of bike for what you want to ride.

rockmonkeysc

Going too long doesn't just risk frame failure you're also going to get in to poor handling. It will raise the bottom bracket height which causes the bike to fall in to corners rather than turn in smoothly, you'll also get a loss of stability due to the raised centre of gravity.
It's not really a suitable bike for downhill, it's a pretty decent xc bike.

larkim

We're into that downhill vs Downhill terminology thing again aren't we?

poah

swod1 wrote:

you could swap the air spring inside it to a shorter one but that would be too much messing about, you could set more sag on the fork so it would be around 120mm.

seriuously? takes 10 mins to change the air shaft at the most - run more sag and you get more brake dive and soggy handling.