[CaveGiant]

It gets said often that you want air on the front, but coil on the back.

I've just been asked why, and to be fair it does not make sense to me.

I was wondering if anyone had any insights?


My thoughts:

Forks are larger, more seal contact area, and more flexible. They functionally have a leverage ratio of 1:1. All of these point to friction having a greater effect on the front.

Unless you are running a proper fork (triple crown) then the air spring is likely 2 chamber and will have a weird rate. This matters less on a shock as you can correct the rate with varying frame leverage.

Forks are generally seal facing up, so need tighter sealing to prevent mud ingress, sealing doesn't need to be as tight on a can (though higher air pressure).

Personally I can feel the difference between a dorado coil and a dorado air (with probably the best air spring on the market).

I can also tell the difference between a cane creek coil and air.

So is the opening statement correct?

Is it engineering or sales and marketing?

 

[spo0n]

weight and bottom out resistance? coil rear adds less weight and a progressive leverage ratio can help it resist bottom outs. Dunno, just some thoughts
progressive or 2 stage fork springs? anyone make them?

 

[CaveGiant]

2 stage or 3 chamber fork springs are great.

It's what I use I'm my Dorado, it's a huge upgrade.

Allegedly there isn't enough room in a single crown fork to fit a decent 3 chamber air, hence vorsprung smashpot and Secus.

The weight is a good point. Coiling a rear shock weighs less than coiling a fork and the coil shock weight is better placed.

 

[Cerberus75]

Coil on both ends are better a lot of times. But on the front it's added weight and more often your are between weight of a coil spring. You feel this in your hands or it dives. We notice less with our feet. We just notice the better traction and small bump control of the coil shock.

 

[LMN]

On a fork heat isn't transferred from dampening circuit to the air circuit. The air in the fork still increases in temperature but not nearly as much as in a rear shock.

Also, I think the weight penalty a much higher for a spring in a fork. Way back I had a set of Z2 Marazochi's that were 4lbs for an 80mm travel fork.

 

[tdc_worm]

Unless you are running a proper fork (triple crown) then the air spring is likely 2 chamber and will have a weird rate. This matters less on a shock as you can correct the rate with varying frame leverage.

Both Ohlins and Manitou offer triple chamber single crown forks and DSD has an insert that mimics the other two offerings. If a fork has room for tokens, it has room for a 3rd chamber.

Forks are generally seal facing up, so need tighter sealing to prevent mud ingress, sealing doesn't need to be as tight on a can (though higher air pressure).

Fork wiper seals are very loose compared to the air shaft seals. So much so that any friction introduced by those seals will be negligible compared to force need to break away the airshaft. The same is likely true with an air shock.

 

[RickBullottaPA]

It gets said often that you want air on the front, but coil on the back.

I've just been asked why, and to be fair it does not make sense to me.

I was wondering if anyone had any insights?


My thoughts:

Forks are larger, more seal contact area, and more flexible. They functionally have a leverage ratio of 1:1. All of these point to friction having a greater effect on the front.

Unless you are running a proper fork (triple crown) then the air spring is likely 2 chamber and will have a weird rate. This matters less on a shock as you can correct the rate with varying frame leverage.

Forks are generally seal facing up, so need tighter sealing to prevent mud ingress, sealing doesn't need to be as tight on a can (though higher air pressure).

Personally I can feel the difference between a dorado coil and a dorado air (with probably the best air spring on the market).

I can also tell the difference between a cane creek coil and air.

So is the opening statement correct?

Is it engineering or sales and marketing?

With a fork, the suspension motion is almost always linear (a few linkage forks such as the Trust Shout/Performance are exceptions), whereas a suspension/frame designer can be more creative with the linkage designs in the rear to provide a more progressive or regressive design. Of course, even with air these days, you can get quite tunable...

 

[AlienRFX]

On a shock a coil reduces dynamic sealing area by over 500% resulting in huge reduction in stiction. On a fork going coil only reduces dynamic sealing area by maybe 30% so you have a much smaller reduction in stiction and that small gain just doesn't seem to be worth the weight.

 

[RickBullottaPA]

On a shock a coil reduces dynamic sealing area by over 500% resulting in huge reduction in stiction. On a fork going coil only reduces dynamic sealing area by maybe 30% so you have a much smaller reduction in stiction and that small gain just doesn't seem to be worth the weight.

Interesting. Almost suggests that a different type of seals/sliders on coil forks could be a big improvement.

 

[mikesee]

Leverage.

 

[Chris2fur]

I completely disagree with what "often gets said." Installing a Smashpot coil in my Pike was the nail in the coffin of air forks for me. The key is having the right coil spring. Most manufacturers have too few choices (soft, medium, hard) which is far too broad to most to hit the sweet spot. Loss of stiction, use of travel, tracking of terrain... The performance is so much better that rear shock considerations are secondary. Just my experience.

 

[Mike Aswell]

As someone with very little technical know-how, this is a completely feel-based opinion: I converted one of my forks to coil and the difference is both noteworthy and significant. At times I actually get pis%y riding my bike with an air fork because the small bump compliance is so much worse.

However, there is a somewhat significant weight penalty and that has to be considered with regard to what bike you are building/riding and what is most important to you. If keeping the weight down is important I would go all air, or coil on the rear first.

 

[JohnnyC7]

I don’t agree at all, a good spring design makes all the difference at the front end

I think it’s mostly perpetuated by media that don’t know how to set up suspension (eg: Doddy from GMBN doing a coil vs air comparison but didn’t even try a different spring when the fork was clearly too soft) or simply the lack of decent off-the-shelf coil forks for the most part.

 

[Jayem]

It's hard to figure out, because back when coil sprung shocks were so prevalent, the damping sucked a$$. The damping systems were so damn crude and the decent coil sprung forks that DID have decent damping systems were only here for a season or two and then they disappeared, like the 55 RC3 Evo Ti V2 or whatever the hell it was called.

 

[CaveGiant]

Leverage.

Am I being daft here (not the first time if so)?

In the front wheel the friction will be felt on a 1:1.
The leverage on the back would reduce that friction by a ratio of e.g. 3.

Are you suggesting the opposite?

 

[Nurse Ben]

It gets said often that you want air on the front, but coil on the back.

I've just been asked why, and to be fair it does not make sense to me.

I was wondering if anyone had any insights?


My thoughts:

Forks are larger, more seal contact area, and more flexible. They functionally have a leverage ratio of 1:1. All of these point to friction having a greater effect on the front.

Unless you are running a proper fork (triple crown) then the air spring is likely 2 chamber and will have a weird rate. This matters less on a shock as you can correct the rate with varying frame leverage.

Forks are generally seal facing up, so need tighter sealing to prevent mud ingress, sealing doesn't need to be as tight on a can (though higher air pressure).

Personally I can feel the difference between a dorado coil and a dorado air (with probably the best air spring on the market).

I can also tell the difference between a cane creek coil and air.

So is the opening statement correct?

Is it engineering or sales and marketing?

I think it's the other way around. Coil fork provides far more benefit than a coil shock.

Shocks have less stiction to overcome due to the leverage action of the suspension, so no change in stiction unlike with a fork
Shocks have a shorter stroke than a fork, so coil benefit is limited on shocks compared to a fork, esp shorter stroke shocks
"Poppiness" is generally engaged from the rear of the bike, coils dampen the pop, so no real benefit to running a coil shock
Rear suspension can be changed by choosing a different suspension design, sometimes even using flip chips and linkage changes within an existing design, whereas forks are static outside of changing HTA and travel.

After numerous trials with coil shocks, I'm no longer running anything but air shocks, esp with the recent advances in air shocks; Mara Pro is my go to shock now.

Up front I am riding Cane Creek Helm MK2 Coil and see no loss of function over air, the ride is more damp so in theory I could benefit from some added poppiness if I went back to an air fork, but right now I like the improved ride quality and improved tire contact/stability/control.

Say no to rear coil unless you're riding big stuff, big drops, big hits, bikes with long travel.

Say yes to a coil fork if you appreciate a damp ride and don't mind the added weight.

 

[PHeller]

"Performance boost" is subjective.

An XC racer will look at a coil shock and hate the power sapping movement. They'll see a coil fork and shock as too much added weight when your competitor is counting every gram.

Even Pro DH and Enduro riders will sometimes experiment with different setups for different tracks. A really rough track might warrant a coil, a smoother, punchy event might get air. We even see the adapting of traditionally XC oriented features to coil shocks - like remote lockouts. One thing to keep in mind with these riders and the events they make their money on, is that they are doing them a few times a year. For a few hours. They spend tons of time training on road bikes, XC bikes, working out at the gym, etc. While coil forks or coil shocks might make a DH racer a little more comfortable, it might not make them any faster, and if their sponsors don't offer that product, they aren't going to rock the boat. Makes me wonder how many DH and Enduro racers are hiding coils in their forks with OEM top caps.

As others have eluded, coils can "deaden" the trail, sap energy and power from rider movements. If you watch EWS Pros, they are really manhandling the bikes. Coils could potentially impact how easily the rider moves and manipulates the bike as they get more tired at the end of events.

If I was rich, I'd ride both, or have two bikes for different types of riding (a coiled long travel bike, and an air short travel bike).

 

[Whiterabbitt]

I'm just observational, but I converted my 180/180 to a coil fork via vorsprung smashpot, and rented a 150/150 air bike before buying the 180.

I felt the rear of the 150/150 was so poppy. Not sure if I would have liked it for jumping, but for blasting down the trail it felt "bucky". I'm sure it was not set up well for me. But it had 30% sag, and still bucked lots.

on the other hand, I put the coil on the 180, and the bike is so so dead. It rides low. and it rides HEAVY! I really really struggle to get the front wheel up. Jumps are such an effort. That alone, I'm thinking of making a change. The smashpot added a pound of weight between the spring and the oil bath.

But I will tell you, coil on coil and high travel is ridiculously fast if you are pointing the bike down hill and just hanging on for dear life. The machine is compensating for so much of my bad technique, and just stays grippy and composed as I go flying down stuff I really shouldn't be. it's a huge confidence booster.

But the weight on the front end is soooo un fun and kills any playfulness on the bike. If your bike is already nose heavy, converting to coil won't help that at all.

my amateur observations.

 

[Dougal]

Because the rear shock carries the majority of the weight and can have a factor of 10 more damping than the fork.

This means small mis-matches in the rear can become big problems.

 

[cookieMonster]

Coil at both ends > any other setup

If you’re worried about the weight, your trails aren’t steep enough.

My ‘12 36 Van puts every air fork I’ve ever tried to shame, as did my old Marz 66 RC2X (‘06 I think). The 36 isn’t even that heavy.

I would run air in the rear if I had to, and have on previous bikes. It’s never as good. That said, I ride hardtails too so suspension in the back is less critical than the front.