rigid fork - geometry changes

Pepi said:

I'm converting my old MTB to city/road bike.
Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

If it helps, the bike is a '01 Trek 810.

--
Pepi

You could try here -

http://www.bikemannetwork.com/biking/c/COMPFKMTNR

Maybe not, your IP looks to be in Croatia....

--

Let the bridges I burn light my way...

ask at flea markets
i swapped a male fork for a female fork lookin like 1/8" more trail and
had a 50% reduction in twitch on sand skim over pavement

yeah further-adaptor kits are available to place threaded into
unthreaded and ...
speak with harris yellow jersey -or biketoolsect if that becomes your
next problem.
even 27" seem to be around-trek may have a one piece fork that goes
into a 27" after filing off the 700cc fork's top bottom.

further duh-the idea is that an entire bike-with the correct
fork-needing a headset-see biketoolsect.com
can be bought for $25 with fork plus off course

Quoted message said:

even 27" seem to be around-trek may have a one piece fork that goes
into a 27" after filing off the 700cc fork's top bottom.

The "top bottom"... ? My head hurts.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

Pepi said:

Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Consider installing spacers between crown and crown race
to "suspension correct" your rigid fork. The ones normally
used above the headset are cheap and should do fine.

The steerer will see slightly more bending than it would
have so I'd want to stick with steel.

I'd undercorrect a bit so that its a little more lively
than your MTB geometry. Also remember that your weight
normally compresses the suspension a bit (don't just
measure with no load on the suspension-fork).

Ed

Pepi said:

Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Consider installing spacers between crown and crown race
to "suspension correct" your rigid fork. The ones normally
used above the headset are cheap and should do fine.

The steerer will see slightly more bending than it would
have so I'd want to stick with steel.

I'd undercorrect a bit so that its a little more lively
than your MTB geometry. Also remember that your weight
normally compresses the suspension a bit (don't just
measure with no load on the suspension-fork).

Ed

Ed Cory said:

Pepi said:

Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Consider installing spacers between crown and crown race
to "suspension correct" your rigid fork. The ones normally
used above the headset are cheap and should do fine.

The steerer will see slightly more bending than it would
have so I'd want to stick with steel.

I'd undercorrect a bit so that its a little more lively
than your MTB geometry. Also remember that your weight
normally compresses the suspension a bit (don't just
measure with no load on the suspension-fork).

Ed

Have you ever tried this? How does the crown race seat?

I have not yet tried it. I intend to try it to go
the other way: fit a 26" mtb susp. fork onto my 700c
hybrid. I haven't even measured anything yet.

The loads are conveyed through a much larger
contact area than the bearing to race interface,
for example, so this doesn't worry me.

There will be a slightly longer moment arm
turning off-axis forces into moment at the
bearing than there would have been (about 31
inches instead of 30 from the tire contact patch).
a three percent increase isn't much.

There have been a couple reports recently of
frames buckling (at the down tube) before the
steerer so I don't think we need to worry as
long as we avoid steerers which might have
less margin (carbon or aluminum steerers
may have less since their design is trying to
minimize weight).

The crown race is an interference fit (it is
pressed on). see
http://www.parktool.com/repair_help/howfix_headthreadless.shtml
http://www.ehow.com/how_14185_install-new-bike.html
http://www.ehow.com/how_14186_install-bike-headset.html

The thermal install trick would be nice if it works.

Ed

Ed Cory said:

Pepi said:

Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Consider installing spacers between crown and crown race
to "suspension correct" your rigid fork. The ones normally
used above the headset are cheap and should do fine.

The steerer will see slightly more bending than it would
have so I'd want to stick with steel.

I'd undercorrect a bit so that its a little more lively
than your MTB geometry. Also remember that your weight
normally compresses the suspension a bit (don't just
measure with no load on the suspension-fork).

That sounds like a Bad Idea [tm], if for no other reason than the
larger OD portion of the steer tube that the crown race is driven on
to will now be below the crown race (how you gonna install it?).

Also, you'd be changing the forces acting on the steer tube in a
significant way - maybe not enough worry about, but having a section
of the steer tube exposed as an unsupported shaft just seems "wrong".

Plus, it'd be ugly as sin.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

Ed Cory said:

I have not yet tried it. I intend to try it to go
the other way: fit a 26" mtb susp. fork onto my 700c
hybrid. I haven't even measured anything yet.

Quoted message said:

The crown race is an interference fit (it is
pressed on). see
http://www.parktool.com/repair_help/howfix_headthreadless.shtml
http://www.ehow.com/how_14185_install-new-bike.html
http://www.ehow.com/how_14186_install-bike-headset.html

The thermal install trick would be nice if it works.

Sounds like you've never done one. My point was/is, the interference fit
only happens at the bottom of the steerer. If you put spacers there,
you won't get an interference fit higher up the tube. Besides, as Mark
said, even if it did work, and was safe (both unlikely) it would be
fatally ugly.

You might reconsider passing advice that you haven't actually tried...

"Peter Cole" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Ed Cory said:

Pepi said:

Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Consider installing spacers between crown and crown race
to "suspension correct" your rigid fork. The ones normally
used above the headset are cheap and should do fine.

The steerer will see slightly more bending than it would
have so I'd want to stick with steel.

I'd undercorrect a bit so that its a little more lively
than your MTB geometry. Also remember that your weight
normally compresses the suspension a bit (don't just
measure with no load on the suspension-fork).

Ed

Have you ever tried this? How does the crown race seat?

It doesn't. That's the problem. I've never seen how this would ever work,
except if it was a 1mm spacers, which wouldn't produce a tangible
difference.

--
Phil, Squid-in-Training

"Pepi" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I'm converting my old MTB to city/road bike.
Since I don't realy need a suspension fork, I was thinking
of puting a rigid fork on the bike, but I'm concerned with how
it would affect the geometry, ie bike handling.
The original sus fork has 63mm of travel, and i cannot find
any "suspension corrected" rigid forks around here, so
i'm stuck with normal ("non-sus-corrected"😉 ones.
I know this would steepen the angles a bit and make the bike
steer faster, but will it be too twitchy?

Hey Pepi,

I have a frame designed for 100mm suspension forks, and I put a 125mm fork
on and rode it just fine. Recently, I put on an uncorrected fork (400mm
axle to crown) and I noticed almost no handling difference, but a much lower
front end. Since I was riding the rigid while on the MTB trail, this was
actually good. I didn't have any problems with twitchy steering at all.
Around town, it steerered a tiny bit faster, but it's an effect you'd get
used to quick.

Go ahead with the uncorrected fork... you'll get a bit more of an aero
position and your steering won't suffer.

--
Phil, Squid-in-Training

Quoted message said:

Ed Cory said:

I have not yet tried it.

Peter Cole critiqued:

Quoted message said:

Sounds like you've never done one.

What part of "I have not yet tried it." don't you
understand?

I provided links to basic info when I guessed
that someone was asking for that. Try to be
clear next time.

Quoted message said:

My point was/is, the interference fit
only happens at the bottom of the steerer. If you put
spacers there,
you won't get an interference fit higher up the tube.

....and you must have experience that the interference
fit is essential to function, and have therefore reported
(where?) on the methods you have personally tried to
attach the race and spacer to the steerer.

Or are you blowing smoke as in "passing advice that
you haven't actually tried"?

Quoted message said:

Besides, as Mark said

Take your lips off your navel (or whatever) and
try to post your own thoughts.

Ed Cory said:

Quoted message said:

Ed Cory said:

I have not yet tried it.

Peter Cole critiqued:

Quoted message said:

Sounds like you've never done one.

What part of "I have not yet tried it." don't you
understand?

I meant never had installed *any* HS.

Quoted message said:

Quoted message said:

My point was/is, the interference fit
only happens at the bottom of the steerer. If you put
spacers there,
you won't get an interference fit higher up the tube.

...and you must have experience that the interference
fit is essential to function, and have therefore reported
(where?) on the methods you have personally tried to
attach the race and spacer to the steerer.

Well, the Park site seems to think so. My guess is that a sloppy fit on
a crown race would be a bad thing. A moving crown race might wear on the
steerer. Off hand, I'd think a worn area on the bottom of the steerer
might be a bad thing.

Quoted message said:

Take your lips off your navel (or whatever) and
try to post your own thoughts.

Sweet. You're just tweaked because you're so busted. Get over yourself.

Mark Hickey said:

That sounds like a Bad Idea [tm], if for no other reason than the
larger OD portion of the steer tube that the crown race is driven on
to will now be below the crown race (how you gonna install it?).

Yes, until you attach the race to the steerer it won't be
attached. I wondered if there might be some other reason.

Quoted message said:

Also, you'd be changing the forces acting on the steer tube in a
significant way - maybe not enough worry about,

Please define what you mean by "significant" then.

Quoted message said:

but having a section
of the steer tube exposed as an unsupported shaft just seems "wrong".

Yeah, I would think that that you or some other dealer
could offer the OP something less ugly since he can't
find one.

The intention would be to have the spacers taking the
off-steerer axis load so that the would see little of it,
the 3 percent increase would be if these took none of it.

Quoted message said:

Plus, it'd be ugly as sin.

The price you pay to experiment on the cheap.

I also can't imagine how anybody could be seen in public
with ugly black spacers visible, ugh. Especially since
they're so obvious below the the head tube instead of
above it where they are beautiful.

Ed

Peter Cole said:

I meant never had installed *any* HS.

No, I have only paid for this.
I will not need to have personally experienced
the press fit that I will *not* encounter.

Quoted message said:

Quoted message said:

Quoted message said:

My point was/is, the interference fit
only happens at the bottom of the steerer. If you put
spacers there,
you won't get an interference fit higher up the tube.

...and you must have experience that the interference
fit is essential to function, and have therefore reported
(where?) on the methods you have personally tried to
attach the race and spacer to the steerer.

Well, the Park site seems to think so. My guess is that a sloppy fit

on

Quoted message said:

a crown race would be a bad thing. A moving crown race might wear on

the

Quoted message said:

steerer. Off hand, I'd think a worn area on the bottom of the steerer

Quoted message said:

might be a bad thing.

good advice. The race integrity might also be a concern.
After brief testing I planned to try to use a soft metal
shim lubed with threadlocker. I don't want to deform
the race.

Its interesting that Park suggests locktite when there's
marginal interference. I'd have thought that very little
would be needed.

Ed Cory said:

Mark Hickey said:

That sounds like a Bad Idea [tm], if for no other reason than the
larger OD portion of the steer tube that the crown race is driven on
to will now be below the crown race (how you gonna install it?).

Yes, until you attach the race to the steerer it won't be
attached. I wondered if there might be some other reason.

I wouldn't need a reason beyond a loose crown race, personally but
YMMV.

Quoted message said:

Quoted message said:

Also, you'd be changing the forces acting on the steer tube in a
significant way - maybe not enough worry about,

Please define what you mean by "significant" then.

Bigger than "insignificant". Any time you take a part and subject it
to stresses it wasn't designed for, in a way it wasn't intenced to be
used, you should understand what you're asking of the part.
Considering that normally the steer tube is entirely enclosed by the
head tube, and there's no portion of it cantilevered at all, the
change is "significant". What is the magnitude of those stresses? I
dunno, and won't lose sleep over it since I'd never attempt it (I'd
just buy the right fork).

Quoted message said:

Quoted message said:

but having a section
of the steer tube exposed as an unsupported shaft just seems "wrong".

Yeah, I would think that that you or some other dealer
could offer the OP something less ugly since he can't
find one.

There are plenty of "suspension corrected" forks out there... they can
be purchased for as little as $30-50.

Quoted message said:

The intention would be to have the spacers taking the
off-steerer axis load so that the would see little of it,
the 3 percent increase would be if these took none of it.

The spacers won't "take the load" in any way, shape or form. Yes,
they'll support weight, but have no effect on the lateral load. The
steer tube will deflect as much with or without 'em (if you could keep
the fork in the same position either way, that is).

Quoted message said:

Quoted message said:

Plus, it'd be ugly as sin.

The price you pay to experiment on the cheap.

I also can't imagine how anybody could be seen in public
with ugly black spacers visible, ugh. Especially since
they're so obvious below the the head tube instead of
above it where they are beautiful.

Yep.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame