Seizing up suspension forks (on purpose)

JBA

Just do a Google search for MTB Rigid Forks. Dozens of sites come up.

You don't need to spend anything near £200 pounds on rigid forks though. Buy something for £80-ish and use the rest of the money to pay a bike shop to swap the forks over, bleed your brakes, replace broken spokes and true your wheels.

By the way, if you can buckle wheels and snap spokes when riding with suspension forks you are going to do even more damage with rigid as there will be nothing to absorb the hits.

rubez

Yup, that's easy enough. How do I know if they are suitable?

Simply if it specifies "suspension-corrected"?

... cause most of them don't.

JBA

See Ouija's response(s).

Ouija

rubez wrote:

Good!

So, any of these would be acceptable. All prices are fair.

http://www.ribblecycles.co.uk/pp/road-track-bike/forks-forks-tt/fort

Non of those forks would work as they aren't suspension corrected. They are designed for road bike frames and when fitted to a mountain bike would drop the front of the frame by such a huge amount the forks themselves would be pointing straight down at the ground (or even backwards), which would ..

A) Cause you to flip over the front of the bike every time you touched the brake (especially the front one)

Cause the steering to be so twitchy you'd get speed wobbles at ridiculously slow speeds.

C) Drop the bottom bracket so that your pedals are scuffing the ground.

Suspension forks raise the front of a frame by a specific amount (100mm, for example). The frame builders then alter the frame to allow for this (upsloping top and bottom tubes with the steerer tube angled further back to keep the forks sticking out of the bike at the correct angle), meaning that a frame can only be used with a specific length of fork (fit a longer suspension/rigid fork and the bike will look like a Harley Davidson chopper with very sluggish and unresponsive steering, fit too short a fork and the bike becomes seriously twitchy, throws you over the front every time you try to brake and drops the bottom bracket so low your pedals are almost scraping the ground every time you turn the cranks).

For a frame designed with 100mm suspension forks you need a rigid fork with an axle to crown length of 44.5cm to around 46cm to prevent all of the problems mentioned above. The axle to crown (A2C) is the distance from the center of the wheel to the top of the fork where it touches the underside of the frame (typically where the crown race sits for your bearing to run around on). Compensating for a suspension or rigid fork with too short a A2C by simply having more steering tube stuck out of the top of the frame to keep the handle bars at similar height as before also causes problems (more chances of snapping the steerer tube, especially with carbon or aluminium ones) as well as looking dorky (been there, done that, which is why i recommend slightly longer 45/46cm A2C for 100mm suspension corrected frames).

And if your old fork is a 2011 Suntour XCM, chances are it has a straight steerer, rather than a tapered one. The on one forks will work so long as you get the right diameter and shaped steerer (1 1/8" straight steerer).

supersonic

This is as good as it gets:

http://www.carboncycles.cc/?s=0&t=2&c=43&p=959&

rubez

@ Ouija

OK thanks. They are Suntour XCM V3.0(!)

Can I tell by sight if they are definitely straight? (and not tapered)

The On-One fork is:
9mm / Raw With Matt Finish / 450mm


@supersonic

That fork is only 42.5cm. Seems too sort going on what Ouija is saying...

supersonic

There is a 44.5cm too - I thought I'd linked to it, must not have copied!

rockmonkeysc

Suspension forks are designed to absorb shocks. By running them seized you will be increasing the loads on the uppers by several times the normal forces. They won't be designed to take those sort of loadings and not take shock loads at all.
Forks are designed by engineers who have spent many, many hours modelling stresses through them and tested them in the state they are designed to run. They won't have allowed for some idiot deliberately making them rigid.
A worn, seized fork won't be absolutely rigid, it will still move on big hits.

njee20

SS's link is sound - as he says there are 44.5cm ones on there.

JBA

rubez wrote:

@supersonic

That fork is only 42.5cm. Seems too sort going on what Ouija is saying...

Scroll down the page...

Ouija

rubez wrote:

@ Ouija

OK thanks. They are Suntour XCM V3.0(!)

Can I tell by sight if they are definitely straight? (and not tapered)

The On-One fork is:
9mm / Raw With Matt Finish / 450mm


@supersonic

That fork is only 42.5cm. Seems too sort going on what Ouija is saying...

If you've removed them from the frame then it's easy to tell. Look at the two On One forks you listed earlier and you can see that the yellow and black one has a steerer that bulges out significantly at the bottom (tapered) whereas the plain black one doesn't (straight).

If you haven't removed the XCM's then you can usually tell just by looking at the frames head tube (the part the fork steerer actually passes through). If it's designed for straight steerers, the top and bottom will be the same diameter. Some head tubes are perfectly straight and take a straight steerer fork, others bulge/flange out a little at either end but if the bulge is the same at both ends it still takes a straight steerer fork.

If it's designed to take a tapered fork then the bottom diameter will be much bigger than the top.

Head tube for straight steerer...


Head tube for tapered steerer...


You can actually see how the bottom half of the steerer tapers out half way down...


The pic of the Cube by CubeCrazy looks like it's designed for straight steerer.

declan1

rubez wrote:

Pathetic... I can see due to a lack of knowledge, no-one knows anything other than 'be a good little consumer', so could I swap out the springs for some ULTRA stiff ones?

No, you're just bonkers.

SUPERSUTT

try and cellotape a piece of wood down the side of the forks that might work

rubez

@Ouija

Cheers, that clears up what tapered vs straight is for me. The Cube frame bit that holds the fork is totally flush, so in reality it has to be a straight...

Leaning towards the straight On-One fork. The axle to crown is 450mm (45cm) so that seems to be perfect.

The only thing I'm not clear on is how can I tell if the On-One fork is 1 1/8" for the steerer, as you said earlier I need?

SUPERSUTT

i still reckon cellotaping a long piece of wood down the side of the fork legs will work

brucie45

Have you got a link to the fork in question, we should be able to tell from that. If not just drop On-One a quick email and they will clear that up for you, the pics on thier page show 1 1/8 steerers.

rubez

brucie45 wrote:

Have you got a link to the fork in question, we should be able to tell from that. If not just drop On-One a quick email and they will clear that up for you, the pics on thier page show 1 1/8 steerers.

This one:

http://www.on-one.co.uk/i/q/FOOOSCF4709/on-one-monocoque-straight-steerer-carbon-fork

njee20

It is 1 1/8".

rubez

Nice, how can you tell? For my own referrence, not that I don't trust you

So... this On-One fork is totally suitable to replace my suspension?

cooldad

rubez wrote:

Nice, how can you tell? For my own referrence, not that I don't trust you

So... this On-One fork is totally suitable to replace my suspension?

Not sure if it's been mentioned before, try reading Parktools.

brucie45

rubez wrote:

Nice, how can you tell? For my own referrence, not that I don't trust you

So... this On-One fork is totally suitable to replace my suspension?

Rubez, you're really not one for listening to peoples advice are you?! Your threads don't half make me laugh

Its a 1 1/8 tube.

rubez

So you can tell just by eyeballing a jpeg? I wouldn't think that was the case is all...

If I read Parktools you wouldn't get the chance to referrence it every three seconds. I'm doing you the favour. Besides I've already bought a Parktools cassette nut thing. I've paid my dues.

So... This is my new fork then?

supersonic

It's an 1 1/8 th. It will fit your bike.

cooldad

rubez wrote:

If I read Parktools you wouldn't get the chance to referrence it every three seconds. I'm doing you the favour.

Could the clue be in the user name.

Rube - definition - "Idiot, mark, stupid, person who is easily fooled, target of con or scam"

I'm out.

brucie45

rubez wrote:

So you can tell just by eyeballing a jpeg? I wouldn't think that was the case is all...

If I read Parktools you wouldn't get the chance to referrence it every three seconds. I'm doing you the favour. Besides I've already bought a Parktools cassette nut thing. I've paid my dues.

So... This is my new fork then?

As above it's a 1 1/8 steerer and it will fit your bike.

"cassette nut thing"......... just gets funnier!

rubez

Where's ma z? Drop it for your own agenda?

Don't know what exact name of it, no need...it performed its job well.

Will be doing the brakes, then will be moving onto the forks... should be fun.

Chunkers1980

Angus Young wrote:

cooldad wrote:

And by nut you mean tool.

Clever...

Chunkers1980

Start a new thread about the brakes.

rubez

Shortening them should be the only obstacle, I think the video in the other thread should see me through though.

njee20

So you can tell just by eyeballing a jpeg? I wouldn't think that was the case is all...

Yes, the vast majority of straight forks are 1 1/8", the only other common 'standard' is 1.5" which are really the preserve of big burly bikes. A lightweight rigid fork like that will not be 1.5", plus, they look massive.