Sus fork length longer than "Sus-compatible" fork?

[x]

This topic is an offshoot of my other post about how to communicate requirements to a frame builder.

One of my unsuccessful custom's little idiosyncracies is that it was built around a
"suspension-compatible" rigid fork.

I took that to mean that the rigid fork could be swapped out for a sus fork without altering the
geometry of the frame too much.

But when I lay the Manitou Black 3" travel fork I'm using up against a (standard?) rigid fork, the
Maintou is an easy inch longer - maybe more.

I don't think that preload is enough to make them the same because the bike is really, really
twitchey with the Manitou fork on it. I don't have a rigid fork, so cannot compare.

SO - bottom line question: Is there any kind of standardization in the MTB fork world or am
I dreaming?
-----------------------
PeteCresswell

 

[A Muzi]

"(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...
> This topic is an offshoot of my other post about how to communicate
requirements
> to a frame builder.
>
> One of my unsuccessful custom's little idiosyncracies is that it was built around a
> "suspension-compatible" rigid fork.
>
> I took that to mean that the rigid fork could be swapped out for a sus
fork
> without altering the geometry of the frame too much.
>
> But when I lay the Manitou Black 3" travel fork I'm using up against a (standard?) rigid fork, the
> Maintou is an easy inch longer - maybe more.
>
> I don't think that preload is enough to make them the same because the
bike is
> really, really twitchey with the Manitou fork on it. I don't have a
rigid
> fork, so cannot compare.
>
> SO - bottom line question: Is there any kind of standardization in the
MTB fork
> world or am I dreaming?

Theoretically, a properly adjusted boinger fork should drop one inch when the rider is on the bike.
That is to say that if one were to measue the head angle of an unladen bicycle, it would appear too
slack. Getting on the bike would return it to the designer's intended dimension. And that is
theoretically standardized such that swapping a Psylo for a Bomber should not change the geometry. I
have specified that to Waterford and got back bicycles which could be ridden with the supplied steel
fork or a modern shock fork without noticeable change in handling ( until or unless the front wheel
was bounced of course).

I'm not at all a MTB expert but that is my understanding and it is effective for purposes of selling
bicycles and servicing them.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

[Kinkycowboy]

On Sat, 29 Mar 2003 01:29:50 GMT, "(Pete Cresswell)" <[email protected]> wrote:

>This topic is an offshoot of my other post about how to communicate requirements to a
>frame builder.
>
>One of my unsuccessful custom's little idiosyncracies is that it was built around a
>"suspension-compatible" rigid fork.
>
>I took that to mean that the rigid fork could be swapped out for a sus fork without altering the
>geometry of the frame too much.
>
>But when I lay the Manitou Black 3" travel fork I'm using up against a (standard?) rigid fork, the
>Maintou is an easy inch longer - maybe more.
>
>I don't think that preload is enough to make them the same because the bike is really, really
>twitchey with the Manitou fork on it. I don't have a rigid fork, so cannot compare.
>
>SO - bottom line question: Is there any kind of standardization in the MTB fork world or am I
>dreaming?
>-----------------------
>PeteCresswell

You're dreaming! Even single crown suspension forks come with anywhere from 60mm to 150mm of travel,
there's no way a frame builder could build one geometry which wou;d be right for any fork. MTB
frames should come with a recommendation of what length travel fork they've been designed for. Your
bike is designed for a 3" travel fork if it works OK with a rigid fork 1" shorter than an unloaded
3" suspension fork - 25% sag is a normal setting, which should make the head angle about 0.5 degree
slacker than the rigid.when you sit on the bike with the new fork, and it will get about 1.5 degree
steeper than that on full compression. Neither should have the effect of making the bike more
"twitchy" in the sense that the term is normally used, slackening the head angle should actually
make the bike steer slower and the steeper head angle at full compression is compensated by the
increased front tyre load (This is why motorcycle racers keep using telescopic forks despite the
obvious drawbacks - the steering still feels right even when you're standing the bike on it's nose
on the brakes ready to turn into a corner)

If your bike is really twitchy with a 3"(75mm) travel fork, go back to the frame builder and ask
what fork length it was designed for; 100mm is becoming the new standard for XC apart from real
hardnuts who are sticking with 80mm, and freeride/dirt jump hardtails are more likely to be built
for 125mm to 130mm travel forks. The corollary of all this is that if you want to put a rigid fork
in a frame designed for a 100mm suspension fork without completely cocking up the steering, you need
a special fork with looks like it was built for 36" wheels, not a pretty sight!

Kinky Cowboy

*Your milage may vary Batteries not included May contain traces of nuts.