Spring or air??

Hi guys
I have a steel 26inch bike with mid mounted shock which is 16.5cm in height. I seen DNM spring shocks for sale as well as air shock types. The air shock looks a bit easier to clean and seem cheaper in price but which of the 2 would you rather have? Im sure both work fine. Just looking to replace the cheap no name brand one that came on mine?
Thanks!

ebike11 said:

Hi guys
I have a steel 26inch bike with mid mounted shock which is 16.5cm in height. I seen DNM spring shocks for sale as well as air shock types. The air shock looks a bit easier to clean and seem cheaper in price but which of the 2 would you rather have? Im sure both work fine. Just looking to replace the cheap no name brand one that came on mine?
Thanks!

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I always used air on my mountain bikes because of the weight. I initially used air on my ebike (fox talas), but switched to spring (fox vanilla) for the first time, and liked it a lot more. To me, the ride feels plusher than I could ever get with the air fork regardless of how much I messed with the rebound and compression damping. It's probably a matter of taste though.

I like air forks, but had bad experiences with air shocks. None of my bikes has an air shock, because they don’t last as long with the weight of the big hubs that I use, and I hate rebuilding them with the freaking bunch of O-rings that they have inside.

I use both spring or air forks almost indifferently. I prefer tuning a WC racing air fork, but a spring fork is slightly better after it’s fine tuned with patience.

coil is great if you got the correct spring rate. if not then you may have to experiment w/ different springs. with air you simply change your pressure w/ a shock pump

air has more stiction so less small bump sensitivity

coil more robust, maintenance free except for the damper part. air shocks need air can service as well as damper service

Well regardless of my opinion of what is better I would say the air shock is the better choice because it’s much easier to fine-tune the adjustments. There’s nothing wrong with coil springs but you may have to change the spring a few times until you get it right. Just go with the air shock

I hate having to pump up my air fork every 2 weeks. Maybe that's just because it's a DNM, but I wouldn't get an air fork in the future.

Addy said:

I hate having to pump up my air fork every 2 weeks. Maybe that's just because it's a DNM, but I wouldn't get an air fork in the future.

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Is your air fork located inside the mid frame?

Addy said:

Maybe that's just because it's a DNM...

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A complete DNM fork with shipping is half the price of a replacement air cartridge for a real DH racing fork. What did you expect?

Addy said:

I hate having to pump up my air fork every 2 weeks. Maybe that's just because it's a DNM, but I wouldn't get an air fork in the future.

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put some fox float fluid (the air chamber lube, not damper fluid)

or mix some SuperLube teflon grease w/ some fork oil. this solved my air leakage issue (not DNM)

Spring > Air.

1 million times over.

You wont catch me riding air. Maybe Nitrogen.. but no , no air. Air shocks wre tried on motorcycles and replaced with hydrolic dampers. Decades ago. Some say modern tech changed, with some of the newer off road forks for dirt bikes are air forks and they have won some races... ... but,

Every car you see with good handling has springs, any bike that goes over 100mph has springs, and springs last, where air leaks.

I promise you that if your "spring " is make out of metal, not air, it will not leak out.

Lol. yeah. Spring all day.

ebike11 said:

Is your air fork located inside the mid frame?

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It's a DNM USD-8.

Overclocker said:

put some fox float fluid (the air chamber lube, not damper fluid)

or mix some SuperLube teflon grease w/ some fork oil. this solved my air leakage issue (not DNM)

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Thanks for that suggestion, I'll give that a try :thumb:

Addy said:

ebike11 said:

Is your air fork located inside the mid frame?

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It's a DNM USD-8.

Overclocker said:

put some fox float fluid (the air chamber lube, not damper fluid)

or mix some SuperLube teflon grease w/ some fork oil. this solved my air leakage issue (not DNM)

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Thanks for that suggestion, I'll give that a try :thumb:

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Im jist talking about the downhill frames with the small rear shock...some are air and some are spring...not for the front

True. We enlarged the discussion to general air suspension. So, back on your exact topic: Air shocks can be good on light weight BB drives, but those suitable are MORE expansive and require more complicated servicing. Cheap air shocks are sh*t. DNM air shocks are absolute Sh*t. Even spring DNM are very low standard. With a hub motor, you need a very good spring shock ideally. With a big hub it is a must and even then, you might have to do some mods to the suspension design.

Shocks are a disposable wear item, and easily replaced. Get the Air shock if it interests you, but know you'll be replacing it eventually. it will probably "feel" better, but that comes at a bit of a trade off with higher maintenance, always needing to check and correct the air pressure.


Air spring shock: Easier to tune. lighter. Best ride "feel"
But also: Short life span. Easier to over load. Easy to overheat. High maintenance. Narrow use profile.
Failure mode is usually catastrophic.*


Coil Spring shock: Low to no maintenance. harder to overload or overheat. Long lifespan. Failure mode is usually non-catastrophic.**
But also: Harder to tune. Heavy. Will never feel as soft as an air spring.

An Air shock is something you put on a tuned ride, that you plan to use in a very specific way. A coil spring shock is better suited for bikes that are going to see all kinds of abuse in many different places. A Downhill or dedicated trail bike would be great with an Air spring. A cross country bike that you plan to take camping, loaded down with 100 pounds of gear one weekend, then go explore the river bed and mud the next, and ride around the city full of potholes in between would be better suited to a coil spring.

As for the failure modes, if you blow a seal on an airshock, they collapse. the bike may still be ridable, but you could damage the frame trying. If you blow a seal on a coil spring, it stops being a shock and acts like a Pogo stick. Annoying, but still functional enough to let you Finnish your ride, usually.

DogDipstick said:

Spring > Air.

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As long as weight is not an issue YES, spring will always be better (with the right spring which doesn't need preload) because it has better sensitivity at the beginning of the stroke, whereas an air system always needs to overcome the preload first before it starts moving so it cannot respond as quick to small bumps.

DogDipstick said:

Spring > Air.

1 million times over.

You wont catch me riding air. Maybe Nitrogen.. but no , no air. Air shocks wre tried on motorcycles and replaced with hydrolic dampers. Decades ago. Some say modern tech changed, with some of the newer off road forks for dirt bikes are air forks and they have won some races... ... but,

Every car you see with good handling has springs, any bike that goes over 100mph has springs, and springs last, where air leaks.

Lol. yeah. Spring all day.

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We’re not talking about cars that go over 100 mph dude we’re talking about bicycles. Obviously the most practical approach and simple approach is to use a air shock and throw the darn thing out once it goes bad and buy another one.

Since were off topic you do realize that 18 wheelers use air suspension right?

I have used both. Air shocks die but they work well up to that point. Springs are more robust but you need to make sure that the dampener is actually working. Cheap MTB springs have fake dampeners which will cause handling issues.

Eastwood said:

...Obviously the most practical approach and simple approach is to use a air shock and throw the darn thing out once it goes bad and buy another one.

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Practical but not optimal, unless you are willing to throw 700$ in the garbage can every riding season. A good air shock, I mean those that work and tune for a hub motor, with lo-hi compression presets and large range rebound control tuning, do start around 500$ and the best of them are closer to 1000$. They need rebuilding often if you are a serious rider, and rebuilding one is a puzzle for the long winter nights. I like them, but I quit using them on my ebikes because the equivalent spring shocks are cheaper and last so much longer without the busy maintenance schedule.

Racing Air forks are different. Very expansive but much more reliable than rear shocks. A quality air cartridge can last many years without any maintenance, and can be tuned with the tip of the thumb while riding. They replace faster than the oil change on a spring bath fork, and they are light weight. I have some WC air forks here that are 10 years old and still riding with their original air cartridges, but I never had an air shock lasting 18 months before a full rebuild.

Eastwood said:

DogDipstick said:

ings, any bike that goes over 100mph has springs,

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We’re not talking about cars that go over 100 mph dude we’re talking about bicycles.
Since were off topic you do realize that 18 wheelers use air suspension right?

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Yeah no, I said bikes.

When I build a 10mph bicycle up as a 50-60mph ebike... I look at the 100 mph roadgoing bikes .. and copy what they do there.. such as use springs, not air.. for guidance. Guidance in prudent, long lasting design. So I do not have to throw away a fork every season.

didnt say anything about 18 wheelsers or cars. ( well, didnt mean to say anything about cars.. but .. )

I dont care much about car and truck design when I build a bike.

However, I do study bike stuff. The bikes usually go really fast and last a really long time.

The reason air works well in forks (and basically all the best bicycle forks are air) is because the stanchions are sized for the required stiffness, and therefore already have an inherent level of sticktion, independent of the spring type. So air is generally better than coil in a fork because it is more tunable, and generally lighter.

The reason air doesn't work as well in a rear shock is because the shaft has to be enlarged for air, which carries a larger sticktion penalty than a thin shaft on a coil spring shock. Sticktion reduces small bump and low (shaft) speed tracking. So air shocks just aren't as smooth as coil shocks. Also due to the small size (relative to forks), heat can be an issue. They still carry the benefit of easier and better tunability of spring rate though.

serious_sam said:

The reason air doesn't work as well in a rear shock is because the shaft has to be enlarged for air, which carries a larger sticktion penalty than a thin shaft on a coil spring shock. Sticktion reduces small bump and low (shaft) speed tracking. So air shocks just aren't as smooth as coil shocks.

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Yes the larger shaft is also a reason but main disadvantage is preload.

Imagine what happens if you put a small weight (say 10kg) on a decompressed coil spring. The spring will compress a few mm, right?
If you do the same on an air spring, you will find out that it's doing nothing because there is a force inside from the air pressure and this preload must be overcome first (load > preload) before it will start to compress.

If someone would use a coil damper and preload the coil (to adjust sag..), it would also not respond anymore to small changes in load when fully decompressed.
Each time one is doing jumps where damper is fully decompressed, it needs to overcome that preload first when landing and the more preload the less smooth the landing will be.
The best suspension has a spring without preload.

madin88 said:

serious_sam said:

The reason air doesn't work as well in a rear shock is because the shaft has to be enlarged for air, which carries a larger sticktion penalty than a thin shaft on a coil spring shock. Sticktion reduces small bump and low (shaft) speed tracking. So air shocks just aren't as smooth as coil shocks.

Click to expand...

Yes the larger shaft is also a reason but main disadvantage is preload.

Imagine what happens if you put a small weight (say 10kg) on a decompressed coil spring. The spring will compress a few mm, right?
If you do the same on an air spring, you will find out that it's doing nothing because there is a force inside from the air pressure and this preload must be overcome first (load > preload) before it will start to compress.

If someone would use a coil damper and preload the coil (to adjust sag..), it would also not respond anymore to small changes in load when fully decompressed.
Each time one is doing jumps where damper is fully decompressed, it needs to overcome that preload first when landing and the more preload the less smooth the landing will be.
The best suspension has a spring without preload.

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some air shocks have a separate schrader valve for setting the "negative" air chamber. this helps w/ the issue you mentioned

serious_sam said:

The reason air works well in forks (and basically all the best bicycle forks are air) is because the stanchions are sized for the required stiffness, and therefore already have an inherent level of sticktion, independent of the spring type. So air is generally better than coil in a fork because it is more tunable, and generally lighter.

The reason air doesn't work as well in a rear shock is because the shaft has to be enlarged for air, which carries a larger sticktion penalty than a thin shaft on a coil spring shock. Sticktion reduces small bump and low (shaft) speed tracking. So air shocks just aren't as smooth as coil shocks. Also due to the small size (relative to forks), heat can be an issue. They still carry the benefit of easier and better tunability of spring rate though.

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the best forks are coil 8) air forks do have additional stiction compared to coil. there's a piston inside the stanchion w/ rubber seals to keep the air in

yes i believe it's spelled stiction :lol:






to answer's the OP's question. here's my X-Fusion E1 165mm. it's pretty good actually. i believe i paid about P5000 or USD100 for it. costs a bit more than DNM. i have tried some DNM's that "spike" (feel very harsh on fast hits).

The best air forks use a cartridge air spring, so the stanchions are not air containers. They have a small amount of oil and the same seals as a spring fork. The cartridge itself does have some additional stiction but the difference can hardly be felt. A coil spring has a better response, but the quick remote tuning of the air spring cartridge that can be adjusted while riding is a neat advantage on the terrain. We call them air, but most air spring cartridges are N₂ gas filled, with a small chamber that is air for fine tuning.

Overclocker said:

the best forks are coil

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Nope. Go look at any race results and what forks are being used. Go look at any website that reviews and ranks forks. Air > coil. Show evidence to the contrary.

Overclocker said:

yes i believe it's spelled stiction :lol:

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Ah yes, my spelling mistake completely invalidates my argument. Good job.

ebike11 said:

The air shock looks a bit easier to clean

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This is probably not a great reason to choose between air vs coil spring.

The correct approach:

DogDipstick said:

When I build a 10mph bicycle up as a 50-60mph ebike... I look at the 100 mph roadgoing bikes .. and copy what they do there.. such as use springs, not air.. for guidance. Guidance in prudent, long lasting design. So I do not have to throw away a fork every season.

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And you don't see air springs used on those roadgoing bikes -- for very good reasons, as described in this thread. In addition, air springs couple ride height with spring rate, and that spring rate is inherently non-linear and thus cannot be damped correctly. Air shocks are a compromise made in human-powered vehicles where the weight savings outweigh the penalty in suspension performance. There is no debate that coil shock performance is fundamentally superior.

However, as with anything else, a quality air shock will likely outlast and outperform a garbage coil shock.