Front forks

Madboy

Regular
Hi all

Once again I come to you guys for advice.

I have suntour front forks (image attached), these came with my Diamondback Decent 29er and I must say they are useless. I feel no damping whatsoever even if I turn the dial. The forks move up and down, but when I am on canal paths/roads I feel every bump etc. I am looking to upgrade but I am on a very tight budget of £100. I have seen forks called Rockshox and the like, however, I don't understand the tapered or non tapered and lengths etc. Could someone steer (pun intended) in the right direction on a good budget fork that I can fit.

Thanks in advance.
 

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Cubist

Still wavin'
Location
Ovver 'thill
Your fork is a Suntour XCT MLO 29 80. It has a coil spring, is made to fit 29er wheels, and has 80mm max travel. The MLO means "mechanical lockout" . The tech docs show it has no compression adjustment or damping and uses a coil spring.

Fork configuration is a bit of a minefield but here's a glossary style explanation:
Wheel standard: 29er, the fork will only fit 29er wheels, 27.5 will fit 27.5 and sometimes 26ers, 26" will fit 26 inch wheels and sometimes 27.5/650b. Your fork is for 29" wheels
Travel: The amount of suspension movement the fork will allow. Usually measured in millimetres the fork compresses by sliding the lower leg up the stanchion (that's the shiny leg) Your fork has 80mm of suspension travel max.
Spring type. Budget forks use a metal coil spring to allow compression movement. Yours is a coil spring. The rate at which a fork can compress depends on the spring strength. This can be adjusted either using a preload system, usually by winding an adjuster which twists and "preloads" the spring, making it stiffer or softer, or by changing the spring either for a stiffer or a more flexible one.
Some forks use an air spring, which is an air-filled airtight chamber with a piston assembly, and spring compression can be adjusted by adding or reducing air to the air chamber via a valve.
Compression rate. Adjustable compression rate is a way to tune a fork to react to different type of suspension movements and different riding situations/rider preference. You tend to find this sort of adjustability in higher budget forks. Your Suntour is not adjustable for compression rate as it stands, although the preload function might affect the way it compresses at the extreme ends of the suspension movement.
Suspension damping. When a fork spring compresses it wants to go back to where it started. At the budget end of forks you find little or no damping, so when you hit a bump the fork compresses then bounces back up at exactly the same speed as it compressed. This means that it absorbs bumps in the trail, but can bounce you back up again immediately afterwards. This means that the tyre doesn't remain in contact with the trail surface, and the danger is that the bike will have little grip, or may even spit you off on big bumps. Fine on a canal towpath, but difficult to live with on anything rocky or successive bumps. The most common type of damping is hydraulic damping- a system of valves in an oil filled chamber that allows the fork to compress quickly, but slows and smooths its return rate. Your Suntour does not have any damping system.
Lockout A big sales point for some folk, and a mixed bag in terms of usefulness. The MLO in your fork label means "mechanical lock out". A dial on the fork leg means you can stop the fork from responding to bumps, and make the fork rigid. Other lockout functions use the more sophisticated compression and damping systems to ramp up the compression rate so far that the fork barely reacts to little hits, thereby effectively "locking" the fork. Don't get hung up on lockout types, and in my personal opinion remote lockout levers on the bars are a bit "Emporor's New Clothes"..... It's easy enough to turn a fork top dial, and I find the remotes pretty unreliable.
So, that's how your current fork functions. The fit depends on the steerer, head tube of your bike, and the headset.
The steerer's the metal tube which fits inside the head tube of your bike. There are now two common standards, straight and tapered. Straight steerers are 1 1/8" in diameter, and tapered are 1 1/8" through the main length, but flare to 1 1/2" at the crown (bottom of the steerer tube). If you have a straight steerer you can swap for another fork with a straight steerer without changing anything else, as long as the steerer is long enough.
Head tube length varies from bike to bike and size to size. Basically the steerer needs to be long enough to pass through the headtube and the headset, then allow enough extra length to fit the stem clamp, a few spacers and to allow the top cap to load the headset bearings. This is a simple measurement on your current bike... basically run a tape measure from the top cap where it sits on top of the stem or topmost spacer, and measure to the top of the fork crown. If you aren't changing anything else, the steerer of a replacement fork needs to be at least this long. If it's longer it can be cut to fit, but any shorter and you'll need to calculate whether you can lose spacers and or stem stack height to fit it.
Finally, axle standards.
Three main types ox axle standards, and these are fixed on the fork. It will either fit a 9mm QR axle, or a 15mm maxle, or an older type 20mm QR or bolt-through. I suspect yours will be 9mm QR. You can't mix them without changing the fork lowers, or using wheel adapters on some hubs.
 
Last edited:
Location
Loch side.
For that type of money you can't upgrade, just sidegrade. You are riding canal tow-paths and don't really need a suspension fork for that. Just live with your current fork for now.

General question, why do people in the UK say forks when there is just one fork on the bike?
 
OP
M

Madboy

Regular
We say forks as there are 2 as in a pair. It might be a UK thing, but we always say forks for some reason. You are technically correct though, they are a fork!

Back to the question. These forks have no dampening effect at all. I have a rockrider 5.1 and the forks are lovely at dampening my ride and the bike only cost brand new £180. The new bike (Diamondback Descent) had disc brakes etc and the ride for going over bumps is awful. I would much rather "go sideways" and buy some forks that actually work! If that makes sense.

Thanks for the explanation on forks Cubist!
 
Location
Loch side.
I think you are confusing damping with compliance. Damping is a feature that resists either the compression, return or both actions. In other words, with damping off, the fork will compress/return quickly and with damping on, it will shoot back sloooooowly.
Spring rate on the other hand is how much it will sag when you get on the bike or... how much it will compress when you hit a bump. The term "rate" here has nothing to do with speed but rather mass/distance as in how much it will compress per kg of weight applied. A very stiff fork (high spring rate) will compress only a little bit and a soft one, a lot. This is the bit of a fork that provides the perceived comfort.

Now, the fork you have on the bike is a coil spring fork and cannot be adjusted according to your weight. Say the fork spring is too strong, then you will experience a harsh ride. If it is too soft, it will sag a lot when you get on the bike and bump through on a bump. The only way to alter it is to put in another spring.

The fork e-bay has the same problem. Coil spring forks have their place in the market but it seems like you are after comfort and comfort only. Therefore, either get a fork that you can test for your weight and riding style, or get an air fork that can be adjusted at your whim.

Air forks don't have steel coils inside but a column of air. If you want it harder, you pump it, if you want it softer, you let some air out. Look for a RockShock Reba or Fox F32 or Marzocchi Air instead. Alternatively see if you can get a weaker spring for your existing fork,
 
Location
Loch side.
How would I know if I straight or tapered steerer?
Show me a photo of the bike where I can see the head tube.
 
OP
M

Madboy

Regular
The thing is on my Rockrider they were coil sprung and when I turned the dial made the ride a lot better. The cushioning on them were streets ahead of the ones I have on my 29er. Honestly guys I feel like I am rattling along with these forks. And yes I want a little comfort as well. Sorry if I am being a pain.
 
Location
Loch side.
The thing is on my Rockrider they were coil sprung and when I turned the dial made the ride a lot better. The cushioning on them were streets ahead of the ones I have on my 29er. Honestly guys I feel like I am rattling along with these forks. And yes I want a little comfort as well. Sorry if I am being a pain.
Well, the reason your Rockrider was more comfortable is because it had a softer spring. The pre-load dial does not affect the ride at all, only the point at which sag starts.
 
Location
Loch side.
Many thanks. I have looked at these forks http://www.amazon.co.uk/Rock-Shox-T...&qid=1423404486&sr=8-1&keywords=rockshox+xc32 I know they are over my budget, but they are air and I think this is what I need? Can someone have a look please? I assume I have to cut the steerer down.

Thanks all
Yes, that will do the trick. Make sure your bike has a quick release in front, not a through axle. The fork is for QR.

Further, have a mechanic do the transfer for you. It isn't straight forward and someone with special tools have to remove the existing fork's crown race.

The fork you've chosen is an entry-level fork but it will be much better than the one you have. Buy a shock pump at the same time. It isn't a standard pump. Read up on damping and understand what the Rebound damping will do for you. It even has elementary compression damping by way of partial lock-lout.

For that fork to do for you what you want you need to:

1) Understand sag.
2) Understand damping
3) Understand spring rate (by way of air pressure).
4) Understand lockout and lockout over-ride.

Getting the fork tuned initially takes a bit of effort but it is well worth it.
 
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