Upping fork travel from 140 to 160mm

Mawby1710

Hey guys,

Im looking to upgrade my 140mm Marzocchi to a 160mm Rockshox 318.
I have a felt compulsion 4 and the fork that came out on this bike is not really good.

My main concern is that I will damage my frame.Is this the case? is 20mm really a great change??if I put a 20mm plank under my front tire,would that then indicate how high the front would come up?

Im looking to buy this fork next month so really need some positive advice.

Thanks

The Northern Monkey

I'd be looking at a revelation not a heavy Domain (assume its the domain 318 you're looking at as you don't say).
Domain isn't the right fork for the bike imo.

The 150mm Rev has a similar stack height to the earlier year 140mm rev, so the difference is minimal.

nicklouse

it is not just the travel change.

you need to look at the axle to crown height change.

1" gives a change of one degree.

there are lots of RS 318s which Domain or..... you could also be adding a lot of weight.

have a look at a Revelation.

bennett_346

Mawby1710 wrote:

if I put a 20mm plank under my front tire,would that then indicate how high the front would come up?

nope, so many reasons why that would not be the case, namely trigonometry and the fact that 20mm more travel doesnt always make the forks 20mm longer, you have to factor in the overall change to length, the crown can be different etc.

kevolution

The main measurement to look at is the crown to axle height. Marzocchi typically come up tall on this measurement, so it may be possible to fit a 160mm fork.
You'll have to check with Felt to see if they'll warranty the frame with a 160mm fork fitted.
It's not as workable as going from 100 to 130mm where the difference in sag can put the bike into it's correct ride height and retain the original geometry, so it's best to check with the manufacturer.

cooldad

kevolution wrote:

The main measurement to look at is the crown to axle height. Marzocchi typically come up tall on this measurement, so it may be possible to fit a 160mm fork.
You'll have to check with Felt to see if they'll warranty the frame with a 160mm fork fitted.
It's not as workable as going from 100 to 130mm where the difference in sag can put the bike into it's correct ride height and retain the original geometry, so it's best to check with the manufacturer.

What on earth do you mean. Increasing the sag to maintain the same geometry would result in the same travel. And the sag would be around half the available travel.
Or am I just too tired to understand the science.

kevolution

With 100mm forks you run 25% sag. 130mm forks run 30% sag so the difference can be minimal depending on the crown to axle height of the 2 forks.
But 140 and 160mm forks both run recommended sag of 30% so it's not as easy to up the travel unless the frame is designed to handle the extra load.

Most frame manufacturers quote a maximum fork length, but it's a guide based on average crown to axle height. The suspension is designed to give the correct geometry at the correct sag or "static ride height".

Forks never ride at full height even when locked out as the lockout is a low speed compression setting that still alows the fork to take it's sag and set at the correct geometry.

Negative travel is usable travel too. it allows the front wheel to drop into bigger holes in the trail while maintaining the ride height and front wheel grip.

peter413

kevolution wrote:

Forks never ride at full height even when locked out as the lockout is a low speed compression setting that still alows the fork to take it's sag and set at the correct geometry.

Thats just plain wrong. My forks always ride at full height when locked out unless I hit a big bump but then they return to full length. Also when you're landing from a jump/drop etc. the fork will be at full length momentarily

nicklouse

the problem of trying to compensate for a too long a fork by running more sag is that you still have a gert big lever there. and every time you leave the ground the fork extends.
and what happens when you land again?
Just the same as running the fork at full length. Extra forces into the frame.

Mawby1710

Ok sweet thanks for all the advice..

Does anyone know where I can get correct measurements for domain 318is crown to axle length??