are 160mm forks too much?

mickus

Hi all,

I have a 150mm frame (felt compulsion) which currently have 140mm(nackered) bombers on it. So I'm looking to replace the forks and have seen some 160mm Fox Vans at a reasonable price.

My questions is - will the 160mm travel be too much for the frame? I feel I can use a little more travel than currently offered but was looking to go to 150mm to match the rear. I plan on using it as an enduro/intermediate-DH bike so would welcome the little extra travel from a riders perspective.

Cheers.

386ka

Linky for the bike? PS, is it warranted for a 160mm fork?

delcol

what is the frames recomended travel,, ie will it invalidate your warranty,

i had 160mm travel forks on my pace rc 305 hardtail it was supposed to have max of 150mm i never had any issues with the frame... you could always run them with a little more sag..

mickus

http://www.evanscycles.com/products/felt/compulsion-4-2009-mountain-bike-ec017076?utm_source=78888&utm_medium=Awin&utm_campaign=Affiliate#features

That's the bike. I'll have to have a dig to see what they say about the warrenty.

DodgeT

Silly thought time here.. Lots of threads pop up and have people saying you can't fit longer forks cause of warranty issues, cracking your frame, you will die etc..
Lets assume that 10mm difference in fork length will invalidate the warranty. Why is this? Because the front of the bike is now 10mm higher, changing the angles, putting more stress on certain parts???
Assuming that is the reason, what is the difference with somebody fitting a bigger/taller tyre to the front, which could quite easily be 10mm bigger (radially) than an oem skinny tyre, making the front end 10mm higher, the same as fitting longer forks.
Will the warranty still be invalidated, frame crack, rider die etc?

Or should I go back to doing some work

1mancity2

Check the axle to crown length the vans could be the same, my reign should have 150mm but I have 160mm on, Giant said this was within the limits (usually +20mm)

jairaj

An extra 10mm is usually OK but double check if you still have warranty left on the frame.

Many forks also allow you to reduce the travel by adding a spacer inside the fork.

386ka

DodgeT wrote:

Silly thought time here.. Lots of threads pop up and have people saying you can't fit longer forks cause of warranty issues, cracking your frame, you will die etc..
Lets assume that 10mm difference in fork length will invalidate the warranty. Why is this? Because the front of the bike is now 10mm higher, changing the angles, putting more stress on certain parts???
Assuming that is the reason, what is the difference with somebody fitting a bigger/taller tyre to the front, which could quite easily be 10mm bigger (radially) than an oem skinny tyre, making the front end 10mm higher, the same as fitting longer forks.
Will the warranty still be invalidated, frame crack, rider die etc?

Or should I go back to doing some work

Actually, I have a friend who has fitted 180mm Domains to a XC 100mm KTM hardtail frame. Does it work? Yes. Did it broke? Not yet.

Would I recommend it? No.

leaflite

You need to check the a2c length of the foxes compared to a 150mm fork such as a revelation or fox 32. Whilst only having 10mm extra travel, burlier forks can have much longer a2c lengths.

bennett_346

DodgeT wrote:

Silly thought time here.. Lots of threads pop up and have people saying you can't fit longer forks cause of warranty issues, cracking your frame, you will die etc..
Lets assume that 10mm difference in fork length will invalidate the warranty. Why is this? Because the front of the bike is now 10mm higher, changing the angles, putting more stress on certain parts???
Assuming that is the reason, what is the difference with somebody fitting a bigger/taller tyre to the front, which could quite easily be 10mm bigger (radially) than an oem skinny tyre, making the front end 10mm higher, the same as fitting longer forks.
Will the warranty still be invalidated, frame crack, rider die etc?

Or should I go back to doing some work

Because it's to do with the force created due to the length of the forks axle to crown. The forces are actuated from the axle, so fitting a bigger tyre won't be increasing the size of force set up. Basically read up on moments, the greater the length the force acts from the pivot (the head tube/crown) the greater the bending force.

mickus

There's roughly a 30mm a2c difference between my current fork - Bomber 44, and the 34 Van's. That's for a 20mm increase of travel.

That sounds a lot to me. Looking at other models of Compulsion released in '09 the longest a2c released as standard compared to the 34 Van's is still a 20mm gap.

I've not found what the warranty says yet but I'm pretty sure I'm not under warranty anymore anyway... I just need to figure out whether my frame will last long enough to enjoy it... I reckon it will...

rockmonkeysc

While the warranty may be an issue there is also the effects on handling. It will take around a degree and a half off the head angle which may be good but it will also raise the bottom bracket which is not so good as it will make the bike less stable. It might also effect how well the bike climbs by making it difficult to keep the front wheel on the ground.
Cheap Fox Vans can be pretty horrible & heavy forks. There are some really good deals on 150mm Sektors which would probably be better.

pilch

RockmonkeySC wrote:

While the warranty may be an issue there is also the effects on handling.

This... built up a 575 with 160mm Lyriks, my reasoning was that I wanted as much travel as possible to soak up 'all the hits'.

What I found was that it made the front end very heavy and the bike felt out of balance to me, i'm not a big downhiller though, the majority of my riding is natural/techy/trail centre stuff, on the plus side however the front end was solid and tracked very well.

Whilst it was in spec for the frame the fork was overkill for my riding and the bike IMO so I changed it for a set of the recommended 150mm Fox forks, rode so much better, lighter, more nimble and easier climbing, better 'small bump' sensitivity too....

rockmonkeysc

small bump sensitivity is down to the quality of the damper, not the travel.
My BoXXer R2C2 has got incredible small bump sensitivity, so has my Lyrik RC2DH. My old Fox F120R had virtually no small bump sensitivity.

bennett_346

But you've never ridden a Lyrik R? And i would disagree that it's entirely down to the compression damping. Having no compression damper is effectively like running it fully open, so therefore at its most sensitive to small bumps. From my experience of rockshox forks all turning the compression damping up did was make the fork less active on small bumps, not more.

rockmonkeysc

But you've never ridden a Lyrik R? And i would disagree that it's entirely down to the compression damping. Having no compression damper is effectively like running it fully open, so therefore at its most sensitive to small bumps. From my experience of rockshox forks all turning the compression damping up did was make the fork less active on small bumps, not more.

My Lyrik RC2DH started out as a Lyrik R. I didn't like it at all so I sent it to TF Tuned and had the MiCo DH compression damper fitted and then fitted a dual flow rebound damper myself just because I found one dirt cheap.
The Lyrik R tends to dive through the travel far too easily not sure how it effects the small bump sensitivity but it really makes a difference, probably because the compression is controlled by dampers and allowing the spring to get on with it's business.

bennett_346

RockmonkeySC wrote:

But you've never ridden a Lyrik R? And i would disagree that it's entirely down to the compression damping. Having no compression damper is effectively like running it fully open, so therefore at its most sensitive to small bumps. From my experience of rockshox forks all turning the compression damping up did was make the fork less active on small bumps, not more.

My Lyrik RC2DH started out as a Lyrik R. I didn't like it at all so I sent it to TF Tuned and had the MiCo DH compression damper fitted and then fitted a dual flow rebound damper myself just because I found one dirt cheap.
The Lyrik R tends to dive through the travel far too easily not sure how it effects the small bump sensitivity but it really makes a difference, probably because the compression is controlled by dampers and allowing the spring to get on with it's business.

I don't think you really know what you're talking about. Yes, it's a huge improvement over the R, but that's no reason not to buy the R then upgrade later down the line like you did. Not everyone has all the money to blow all at once.

pilch

@ Ridemonkey

This may be of interest http://www.pinkbike.com/forum/listcomments/?threadid=99244

I drew the line at taking the fork apart and removing bits as it was new, but it seems the above is a well documented mod for the damping issues on small bumps...

I sold it and got a 150 talas 2nd hand and it did everything I wanted, it was lighter and the bike rode better - job done.

rockmonkeysc

That is a well known mod but the DH damper comes without a floodgate anyway and the R just has no compression damper. It's not a cheap upgrade. £230 for TF Tuned to fit the MiCo DH damper. I got a dual flow rebound damper for £80 but to be honest I would stick with just the standard rebound damper if I did it again.

YeehaaMcgee

I thgouht they all had compression damping - it just wasn't adjustable.

b45her

why do people get so concerned about warrenties and fork length??

if the frame cracks take off the 160's and put the 140's back on before you start the warrenty process ,it's not rocket science.

with the intended use of a compultion i can't see 160 forks being an issue .

bennett_346

YeehaaMcgee wrote:

I thgouht they all had compression damping - it just wasn't adjustable.

I don't think they even have fixed compression damping. As far as i know they're just riding the spring on compression stroke then relying on the rebound damped to stop pogo effects. They seem to do an alright job of it from what i hear from a mate who has it.

RockShox lists them as only having a rebound damper:

Damping Rebound Only

That would suggest the damping is rebound only, otherwise i'd imagine it would say damping adjustment - rebound only.

The Lyrik my mate has is the R and taking the damper side top cap off where the compression would be just reveals an empty space where the moco unit would go. So i can't see where the fixed damping would be.

rockmonkeysc

There is no compression damper in the Lyrik R

jairaj

YeehaaMcgee wrote:I thgouht they all had compression damping - it just wasn't adjustable.

yep thats my understanding too. well not externally adjustable anyway. TF told me they can open up and fiddle with the internals to change the compression on most forks that do not have a external adjuster.

Most people tend to adjust a fork to their liking and leaving it there negating the need for external adjusters. but off course will get expensive send back and forth to TF each time you want to change the compression.

bennett_346

jairaj wrote:

TF told me they can open up and fiddle with the internals to change the compression

Don't see how they could, there isn't anything in there to adjust from what i can gather.

jairaj

I'll take your word for it. TF did say "most forks" and not "all forks" also didn't give specific model names.

YeehaaMcgee

Hmm. I'm pretty sure Fox all have damping, but, not externally adjustablele. Even the lowly Fox Float R has factory-set compression and propedal damping, but you need to dismantle it to change settings.
I'd guessed that Rockshox were the same.

b45her wrote:

if the frame cracks take off the 160's and put the 140's back on before you start the warrenty process ,it's not rocket science.

Trouble is, if you do rip the headtube off - you may not be in a position to stick 140s back ont he bike. It generally results in a horrendous smash.

rockmonkeysc

The extra leverage from adding an extra 30mm to the A-C is very small. If you manage to snap off the head tube I'm pretty sure you would have done a good amount of damage even with the original fork. My 456SS is running a 160mm fork, I'm sure that won't be as strong as the Felt but even after a season of hardtail downhill racing, freeride & uplift days it's still solid. I know of people who have fitted Boxxers to a Reign X & a Specialized SX trail, both rode like crap but neither snapped despite repeated crashes and constant hucking off cliffs at the local quarry.
Fitting 140mm forks to Giant Trances is a common mod even though Giant won't warranty the frame with more than a 130mm fork, never heard of one breaking.
How many head tubes have you seen ripped off? To be honest I would be more worried about the negative affect on the handling, though I don't know what a Compulsion rides like to start with, a longer fork could improve it.

b45her

YeehaaMcgee wrote:

Hmm. I'm pretty sure Fox all have damping, but, not externally adjustablele. Even the lowly Fox Float R has factory-set compression and propedal damping, but you need to dismantle it to change settings.
I'd guessed that Rockshox were the same.

b45her wrote:

if the frame cracks take off the 160's and put the 140's back on before you start the warrenty process ,it's not rocket science.

Trouble is, if you do rip the headtube off - you may not be in a position to stick 140s back ont he bike. It generally results in a horrendous smash.

unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .

YeehaaMcgee

b45her wrote:

unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .

Well, here's an SX trail...
http://ap1.pinkbike.org/p4pb5428691/p4pb5428691.jpg

It does happen on occasion. The longer fork doesn't just increase leverage, it also slackens the head angle, meaning that the force of landing a jump is going to apply more twisting force.
There's been plenty of crash videos on youtube where you can see the headtube coming off the frame.
It doesn't happen to everyone, but you'd have to be foolish to just suggest that everyone will be fine with far longer forks than intended.

b45her

YeehaaMcgee wrote:

b45her wrote:

unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .

Well, here's an SX trail...
http://ap1.pinkbike.org/p4pb5428691/p4pb5428691.jpg

It does happen on occasion. The longer fork doesn't just increase leverage, it also slackens the head angle, meaning that the force of landing a jump is going to apply more twisting force.
There's been plenty of crash videos on youtube where you can see the headtube coming off the frame.
It doesn't happen to everyone, but you'd have to be foolish to just suggest that everyone will be fine with far longer forks than intended.

your clever picture is irrelevant , the sx trail comes from the factory with 66's and the guy has put 888's on there , the a2c difference is just 3mm i.e that accident would have happened longer forks or not , its the a2c length thats immportant not the travel figure .
the OP only wanted to know if his frame will handle 160 forks and the answer is yes it will .