Forks spring or air? Why?


New Member
So in my research on e-bike. Fat tire. I found a review of the crusher nitro the reviewer was really down on the coil spring fork that came on the bike. It’s a triple clamp style ( think motorcycle style) with rebound and damping adjustment it has 165 mm of travel the next closest was a 150 mm air? Why all the air forks ?is it weight? 25 years ago I built a gt lts up from scratch white brothers cranks spin TRI spoke wheels. Magura “rim crusher hydraulic” brakes and every thing was about weight down to the gram. So a full suspension bike at 23lbs was pretty good. Now in the motorcycle world. Travel and rebound control is king. To my knowledge most dirt bike don’t have air suspension. Long travel 12 inches plus So on a fat tire e-bike that might weigh 80 lbs why are the vast majority of forks air sprung? What about down hill bikes that are routinely jumping 15-25 ft.? Are those air too?
Fat tire bikes are comfort bikes. Big oversized tires for suspension. You're not going to take one of those monsters on the technical. Springs forks are ok for the road.
Air sprung forks are mainly for the lightweight, not easily adjusted to suit a large range of damping or preload ranges.
Fine tuning for air sprung forks can be difficult without a suspension pump that has an accurate pressure gauge or no bleed valve.

Metal spring fork with oil damping offers the (easier) adjustability and wider range of adjustments, without plugging a high pressure air pump to the fork.
If you're jumping 15-25 ft. in the air on your rides, probably better off with a long travel metal spring fork with good oil damping.
You will know the reason for preferring air vs. coil just by riding one and then the other. Coil forks tend to be on the cheap end of the market. They feel cheap and behave poorly. When you get yourself an air fork, you immediately prefer it because it seems to work a) silently and b) noticeably better.

I suspect the difference between motorcycles using coils and bicycles using air is all about weight and lesser speeds/impacts. 60mph potholes require a higher level of fault tolerance, and a 400 lb motorcycle makes for a much more ponderous item to stabilize. Seems better suited to a coil.

You can confirm this bike/air quality assertion by looking at the high end forks out there and see what tech the expensive ones use. As always with the internet, you can't take for granted what you read from people who sound like they know wtf they are talking about.
In the mountainbike world (where they really care about suspension) things are mostly air these days. Air forks/shocks are more easily adjustable to accommodate a wider variety of riders, and the way they ramp up helps prevent bottom out on drops and big hits. Even the downhill/freeride world has mostly moved to air, though you'll still find people there who love the linear spring rate of coils. Generally air springs have a maximum pressure that limits total system weight, so very heavy riders often end up on coils. I'd guess thats why motorcycles tend to be coil as well. Coils are cheaper to build too; you don't need all the seals, chambers and precision manufacturing of an air spring, you can just dump a giant steel spring and a bottom-out bumper in there and call it a day.

You're kinda focusing on the wrong thing though, air versus coil is just the spring. The major factor in suspension performance is the damper circuit, which is what prevents suspension bits from being just bouncy springs. Thats generally where your money is going and what you'll really notice on higher end suspension bits. Smoother damping, better adjustment, generally separate high and low speed compression/rebound damping...

Also (for forks) the rigidity of the chassis plays a major factor. Double crown forks are generally more rigid front to back, but that rule has been upended over the last decade as fork mfgs increase the stanchion diameter and everyone has gone to through axles. I see a lot of cheap double crown forks on moped style bikes that have really spindly stanchions and I've wondered how rigid they really are.

I would caution you against getting too hung up shopping bikes based on spec sheets. Its possible for a double crown coil fork to be excellent and also possible for a double crown coil fork to be hot garbage.
the reviewer was really down on the coil spring fork that came on the bike. It’s a triple clamp style ( think motorcycle style) with rebound and damping adjustment it has 165 mm of travel the next closest was a 150 mm air?

Do you have a link? It seems odd to criticize forks based on air vs coil - most good quality forks have the choice, and really fussy riders fit coils. Was the comment " cheap coil forks " where the relevant information was "cheap" - as in poor dampening control / build quality ? Or perhaps they were complaining about how fitting a spring as standard equipment limits the range of rider weight / ability a stock bike is suitable for?

Air makes sense for a manufacturer interested in coping with a wide range of rider weight / ability - easy to adjust with an air pump +/- adding a few internal spacers as you get more fussy / want to adjust the rates of progression. At one stage, I was carrying an air pump on rides so I could swap bikes when my kids needed my emtb - a few minutes adjusting pressure and then a few clicks on dampening - easy.

BTW, in the motorbike world, higher quality suspension uses a combination of spring plus air chamber - but most are designed to run low static pressure in the forks - the air chamber only taking effect later in travel . We used to adjust oil volume in the forks to achieve similar effects to using volume spacers in mtb forks - fine tuning effective spring rate just before the forks bottom out. It gets a lot more complicated with really high en modern motorbike forks!