Geometry changes due to fork lengths :pros and cons ?

[doogie]

I am wondering what the effects on the ride will be if I put a longer suspension fork on my bike?
The merlin extra fat bike I recently bought came with a 100mm travel cannondale lefty.
I am pretty sure that these merlins originally came with a cannondale fork with only 50mm or was it 80mm of travel.
What effect on the frames geometry and ride does fitting a longer travel fork have :?
I have got a super plush set of Pace rc41 fighters that I would love to try on this bike as I am not 100% happy with the cannondale leftys lack of adjustable rebound.
These paces have 150mm of travel so there is obviously a big difference here in fork travel from the original spec of this merlin.

Can anyone help me out here please?

 

[orange71]

longer travel lifts the front of the bike up, increasing rake (I believe) making the steering less direct. I.e. if you took it to an extreme you'd have a chopper and imagine the steering on that! :shock:

 

[doogie]

Hello Ed,
Yes I realise the front end is lifted up more - but when I phoned Pace up a while back to ask them about fitting some forks to the rc200 they told me that I should only fit a fork with 50mm of travel and that I might get away with 80mm of travel but if I went any longer than that, then the rc200 would not ride very well. :?
Is the frame geometry that critical?

 

[orange71]

yes it can be if you're tuned into it. If you're used to twitchy responsive steering off 50mm forks, then you make a move to 80mm, you will probably notice the difference.

 

[cchris2lou]

I think the Merlin extra fat is designed for a lefty anyway , not sure you can fit a normal fork .

they were designed for 80mm lefty .

 

[xizang]

I think the Merlin extra fat is designed for a lefty anyway , not sure you can fit a normal fork .

they were designed for 80mm lefty .

Can't you get adaptors for a 'normal' fork?

As for the length, put them on (if you can) and try it. I put Super T's, 150mm travel, on a hardtail designed for 60-75mm travel forks. It felt a bit different, obviously, for an hour, then you just get used to the feel of it.
I wouldn't advise it for racing though but for general riding it should be ok, possibly???

 

[daj]

So what are we saying then, its not going to do any harm to put bigger forks than the bike was designed?

For an example a older ali frame that was designed for say 80mm fork could you get away with fitting a 100mm + fork without ruining the ride?

 

[doogie]

I would have thought it would only have an effect on the steering :?

 

[Andy B]

It's not the travel of the fork you need to measure, it's the axle to crown measurement, as most fork manufacturers vary in this measurement, even if they're the same travel.

Fitting a longer fork will affect the steering, IIRC the head angle gets 1 degree slacker for every 10mm increase in fork length.

You also risk snapping your frame if you fit too long a fork as you're putting extra stress on the frame, which was designed around a specific axle to crown measurement.

 

[daj]

Eeek now Im getting really confused!!

Ok then, Can I match a 19" 1998 orange O2 frame with 1998 Z1 bombers??