Vorsprung Smashpot Coil Spring Fork Conversion Kit
Test Location: Washington & Oregon
Test Duration: 6 months
Compatibility: Many modern single-crown forks with 35 mm or larger stanchions; see here for details
Blister’s Measured Weight (added weight, RockShox ZEB version, w/ 45lb spring): 565 grams
MSRP: $460–470 CAD ($354.20–$361.90 USD at the time of publication)
Bolted to: RockShox ZEB Ultimate, on Nicolai G1 and Kavenz VHP 16
Reviewer: 6’, 170 lb (183 cm, 77.1 kg)
Intro
Few manufacturers still offer coil-sprung mountain bike forks these days, arguing that air springs are lighter, more tunable, and better suited to fork designs — and if you’re interested in more detail on their reasoning, Fox’s Jordi Cortes goes deeper on the subject in Ep. 92 of Bikes & Big Ideas. But proponents of coil springs argue that they’re lower friction, offer better small-bump sensitivity and midstroke support, and require less maintenance than air springs. Enter Vorsprung Suspension and their Smashpot coil spring conversion kit for many of the most popular single-crown forks currently on the market. So why offer a coil kit, when the major players have eschewed coil forks in recent years? Here’s Vorsprung’s take:
“Why coil? Air springs have improved substantially over the years — and we’ve been at the forefront of air spring development for years, so we’ve got no bridges to sell you. Yeah, coils are heavier than air, and for some riders that alone is a dealbreaker — fair enough. The advantages of coil springs, however, are clear:
- Zero stiction or friction in a coil spring. And no moving seals in the spring system to wear out, cause friction, or leak.
- Zero spring rate variation allowing more mid-stroke support and consistency.
- More oil in the fork — lubrication and service life are improved.
In short, improvements in sensitivity, grip, compliance, mid-stroke support, and consistency, with reductions in harshness and hand pain.”
I’ve now spent six months testing the Smashpot, and Vorsprung is right about a lot of the benefits. But who is going to find all that worth the (hefty) weight penalty? And are there any other downsides?
The Design
The idea behind the Smashpot is straightforward — you take the stock air spring out of your fork and replace it with a steel coil spring.
Now, air springs are inherently progressive, getting stiffer as they get deeper in their travel for increased bottom-out resistance. Coil springs (generally) are not. Bike designers can get around this on rear shocks by designing progression into the rear suspension linkage, but the telescoping forks typically used on mountain bikes don’t have that luxury. So the Smashpot also incorporates a hydraulic bottom-out circuit, which adds compression damping deep in the travel to firm up the fork when you’re nearing the end of travel. Both the HBO feature in the Smashpot (and some other forks and shocks that also use them) and the progression of an air spring increase the amount of force required to compress the fork as it nears the end of its travel, but there are some differences in their behavior. For one, a damper (such as the HBO in the Smashpot) converts the energy it absorbs into heat; a spring returns it to the rider during rebound. The Smashpot’s HBO is also speed-sensitive, so if you’re nearing bottom out but the fork is not compressing quickly (i.e., it’s nearing the maximum amount of travel you’re going to use on a given impact, and bottoming out isn’t likely) it doesn’t firm things up as aggressively. In theory, that all makes for smoother, better-controlled behavior near the end of travel, with less aggressive rebounding from deep compressions. The HBO on the Smashpot is externally adjustable, via a knob at the bottom of the fork leg, and Vorsprung also provides instructions for making larger-scale adjustments via the internal shim stack in the installation instructions for the Smashpot.
Of course, changing the spring rate in a coil-sprung fork requires changing the coil spring itself. And to that end, Vorsprung offers 11 different spring rates for the Smashpot, from 30 to 80 lb/in, in 5 lb/in increments. That’s a whole lot more options than most coil-sprung forks have available (the Marzocchi Z1 Coil, for example, has only four) and should both accommodate a larger range of rider weights and allow for more fine-tuning than most coil-sprung forks, though it obviously can’t match the infinite tunability of an air spring. Vorsprung says that their range of springs covers riders from 100 to 275 lb (~45 to 125 kg); the Smashpot comes with your choice of spring rate, and additional springs are available for $80 CAD ($61.20 USD at the time of publishing).
Vorsprung says that the Smashpot adds between 250 and 500g to a fork, depending on the air spring that’s being removed, and the rate of the coil spring being installed (stiffer springs weigh more than softer ones). That sounds about right for just the parts that are being swapped, but once you also account for the increased oil volume in the spring side, our RockShox ZEB test fork gained 565 g over the course of the conversion, with a 50 lb spring installed. That’s… quite a bit. We’ve often argued (and stand by) the point that bike weight matters less for most types of riding than many folks tend to think, but adding more than a pound to their fork rightly won’t be for everyone. Coil rear shocks are often not much heavier than comparable air ones — for example, the EXT Storia that came on our Kavenz VHP 16 review bike weighs a whole 14 g more than our measured weight for a Fox Float X2 in the same size, including the spring on the Storia — but coil forks are a bit of a different story and the added hydraulic bottom-out circuit in the Smashpot and the extra oil that it requires don’t help the cause. But the Smashpot was never supposed to be for the gram counters; it’s all about maximizing suspension performance and, spoiler alert, it’s excellent on that front.
Compatibility
The Smashpot is compatible with a lot of modern single-crown forks from Fox, RockShox, Öhlins, Marzocchi, and DVO, with stanchion diameters of 35 mm or greater; check out Vorsprung’s website for the complete list. It’s also important to note that, while the Smashpot can be set up for anywhere from 130 to 180 mm of travel, certain fork variants have lower maximum allowable travel, and adding a Smashpot doesn’t change that. Check with your fork manufacturer to verify that your fork can handle it if you’re hoping to use a Smashpot to run longer than stock travel. And while the RockShox ZEB offers a 190 mm travel version with the stock spring, the Smashpot still tops out at 180 mm.
The base Smashpot unit is the same for all the compatible fork models, with only the top cap and/or foot stud changing to convert between models. Vorsprung sells those parts separately, so if you’d like to convert your Smashpot from one fork version to another, it’s relatively inexpensive to do so. The Fox 38 and RockShox ZEB versions also add an extra spring isolator sleeve between the spring and the inside of the stanchion, to further mitigate any potential rattling (the larger 38 mm stanchions mean there’s enough room to squeeze one in around the spring).
Installation & Service
Installing a Smashpot will be fairly straightforward for anyone who’s comfortable doing a lower-leg service on a fork (which is to say, not very hard) though it does require a heat gun to install some shrink wrap and a few other basic hand tools. The Smashpot ships partially disassembled to allow the user to set the travel to whatever setting they’d like. We won’t run through the full instructions here — Vorsprung’s website has very good ones — but take a gander at them and see if it all sounds within your mechanical abilities; if not, Vorsprung has service centers around the world that can handle it for you.
Swapping between spring rates can be done fairly quickly and easily with the fork still installed on a bike, but changing between travel configurations requires a more complete teardown of the unit, including installing new heat shrink tubing. Vorsprung sells replacements, but it’s standard off-the-shelf heat shrink if you want to source it elsewhere. The Smashpot outer tube (the part you’ll disassemble to change travel) uses 2:1 single-wall polyolefin non-adhesive heat shrink, with an initial (non-shrunk) diameter of 3/4″; the spring uses the same but in 1.25’’ or 1.5’’ diameter. Replacing the tubing on the spring isn’t needed when changing springs or travel configuration, but it may wear and need eventual replacement after significant use.
Having a Smashpot installed doesn’t significantly change the lower leg service procedure for whatever fork you might have it installed in, other than possibly changing the spring side oil spec to 20wt, and almost certainly using more of it (110 cc) than your fork does stock. The Smashpot itself requires no additional service, besides checking the location and condition of the heat shrink on the outside of the spring and replacing it as needed to prevent rattling. Vorsprung also notes that the Smashpot’s performance doesn’t degrade with time, unlike air springs which develop more friction over the course of their service intervals.
It is worth bearing in mind that converting your fork back to air after installing a Smashpot may not be possible, since the spring can scratch the inside of the stanchion, preventing the air spring from sealing properly. This isn’t an issue in the Öhlins RXF 36, since its air spring is a self-contained cartridge that doesn’t seal against the inside of the stanchion, and Vorsprung says that the additional isolator in the Fox 38 and RockShox ZEB (see the “Compatibility” section, above, for more on that) typically prevents such issues in those forks, but other models are likely to have issues converting back to the stock air spring.
Setup & Performance
It had been a long time since I’d ridden a coil-sprung fork before I dropped the Smashpot into a RockShox ZEB Ultimate (the original model, not the brand-new 2023 version — review of that coming soon). So I was pretty curious to see how the Smashpot would perform, especially after my extremely positive experience with Vorsprung’s flagship air-spring upgrade, the Secus, on that same fork.
When I began testing, Vorsprung published a suggested spring rate chart based on rider weight and fork travel (shorter-travel forks need stiffer springs), with options for a softer, medium, or stiffer setup, with the “stiffer” portion recommended for more aggressive riders and/or those in steeper terrain, and the “softer” one for folks looking to maximize compliance and grip. I typically run my air-sprung forks a bit firmer than most manufacturers’ recommendations for my weight, and on the basis of the recommendations in the “firmer” portion of the chart, Vorsprung sent the Smashpot for testing with 45 and 50 lb/in springs — the former being the recommended option in the “firmer” range, and the latter being a notch firmer than that, as an experiment.
Vorsprung now has a more involved spring-rate calculator on their site, which factors in a bunch more information including bike weight, the specific fork model, rider aggression, preferred feel, “strength to weight factor,” and a bunch more. An honest assessment of my parameters suggests the same 45 lb/in spring; the calculator only suggests the 50 lb/in option if I bump myself up to two out of three of “World Cup/EWS Pro” level aggression, “high” strength-to-weight factor, and “high-speed/wide-open” terrain, all of which are… generous.
And when I started testing the Smashpot during the winter, the 45 lb spring did indeed feel like the better option. I tried the 50 lb one for a bit and the extra support and stiffness felt good when I was really charging but felt a bit much a lot of the time. And so I settled into running the 45 lb spring through the wetter months. Initial small-bump sensitivity was outstanding, but unlike trying to set up an air-sprung fork super soft to get that sensitivity and traction, midstroke support didn’t feel like it was suffering badly to get there. I did a little re-adjusting of the damper settings to pair with the new spring (mostly adding a significant amount more low-speed compression than I ran with the stock fork), and the ZEB + Smashpot combination felt excellent.
But then summer finally showed up in western Washington, the trails dried out, and I started wanting a bit more support in some instances, particularly on moderately steep, rougher trails where I was able to carry a lot of speed but things were steep enough that I was putting a lot of weight on the front wheel, too. With the drier, faster-rolling, harder dirt, a lot of my home trails were running faster than they had in a while, some new holes started to develop, and a lot of the little edges and bumps started to feel sharper. And with those changing conditions, the fork started to feel like it wasn’t always staying up in its travel quite as well as I wanted it to. I experimented with adding extra compression damping, which helped to some extent, but I gave the 50 lb spring another try, and the results were exactly what I was hoping for.
The 45 lb spring is definitely still more plush and sensitive, and appreciably less fatiguing for my hands and wrists on really long days, but for pushing hard and trying to go fast on drier, quicker-running trails, the 50 lb one feels very confidence-inspiring and stable. The fork rides higher in its travel and it’s easier for me to stay centered and balanced on the bike when pushing hard, without feeling like I need to fight to hold myself up as the front end of the bike falls away underneath me, and the bike stays more composed and level when things get really rough. My home trails aren’t particularly wide open for the most part, and I don’t think I’m all that wildly strong (if we’re being real, Vorsprung’s lowest “strength to weight factor” tier of “beer > gym” is literally true of me, for sure), and I’m definitely no EWS or World Cup pro, but the stiffer 50 lb spring is really working for me. Maybe I’m secretly Amaury Pierron now. I’ve grown a mustache just in case.
Particularly with the 50 lb spring installed, I found myself mostly running the bottom-out adjuster a bit on the softer side of its range. The stiffer spring does a lot to help keep the fork up in its travel and the bike’s chassis composed, and I’m definitely opting to go that route for midstroke support and stability over huge bottom-out resistance. (Similarly, my preferred setup for air-sprung forks usually winds up with more pressure but often a volume spacer removed from stock / recommended settings.) And though I’ve mostly run the HBO adjuster on the lighter end of the range, it’s definitely not to the point that I was ever tempted to try re-valving the shim stack or anything like that. I also haven’t found myself changing the HBO settings all that much with a given spring rate, but it is easy to do and the adjuster makes a very real difference — so if, for example, you’re often inclined to go for a softer, more plush setup but occasionally need some extra bottom-out resistance for a bigger jump line or the like, it’s a nice option.
Coil-sprung forks can definitely be noisy, since having a very long, thin spring bouncing around inside the stanchion is an easy recipe for rattling and the like. But the Smashpot has been impressively quiet in my time on it. The extra spring isolator that the larger 38 mm stanchions in the RockShox ZEB test fork undoubtedly helps, but Vorsprung has also done a nice job with their spring perches (the Smashpot comes with a bunch of different size ones, so you can dial in the fit and spring retention on assembly) as well as the placement and arrangement of the various heat-shrink tubing to keep things quiet, and the results are very good.
Smashpot vs. Stock ZEB
The first-generation ZEB Ultimate has a lot going for it, but its lack of midstroke support was essentially a deal breaker for me; as I’ve hopefully made clear in the “Setup” section, above, fork support is a real priority of mine, and the original ZEB left a lot to be desired there. (The new 2023 ZEB is a big step up in that regard — full review of the new fork coming soon.)
When set up to my preferences — which, again, centered around a very stiff spring for support — small-bump sensitivity is improved by a bit with the Smashpot, and midstroke support is on a completely different planet. But if you opt for a softer spring rate and more balanced setup, the Smashpot has the potential to make a very substantial difference in terms of sensitivity and traction, while still improving midstroke support, too. The Smashpot is undeniably heavier (by a lot) and does give up some fine-tunability as compared to an air-sprung fork, where you can make adjustments by whatever infinitesimal increment you want with a shock pump, for free, but the suspension performance of the Smashpot is so clearly superior to that of the stock fork that I think the overwhelming majority of people will be able to find a setup that works better for them, even if it’s not strictly 100% optimized (I’d love… about a 48.5 lb spring, I think), at least if they can overlook the weight penalty. And the flip side of losing the micro-adjustability of an air spring is that a coil stays consistent and doesn’t require periodic pressure adjustments to maintain a given spring rate, and doesn’t accumulate friction nearly as significantly as an air spring as service intervals wear on.
Smashpot vs. Secus
As impressed as I was with the Smashpot, in a roundabout way, trying it only made me appreciate the Secus even more. The Smashpot does clearly have less friction and therefore better small-bump sensitivity and traction, but the Secus does a remarkable job of emulating the overall spring curve of the Smashpot and therefore getting me the improved midstroke support that I sought out of the original ZEB, all with a much more modest weight penalty (about 130 g), and while preserving the adjustability of an air spring. And as someone who’s generally more focused on getting the support I want out of a fork than finding maximum sensitivity and traction, that’s a tradeoff I’m pretty happy to make.
But there are definitely folks who would be better off with a Smashpot, too. In very general terms, I think they break down into a few groups:
(1) People whose top priority is sensitivity and traction. The Secus can make a real improvement over the stock ZEB on that front without completely sacrificing midstroke support too badly if you chose to set it up with sensitivity in mind (check out our Secus review for a whole lot more on that) but it can’t match the low friction and initial smoothness of the Smashpot, no matter what you do with the setup.
(2) Set-and-forget types who don’t want to deal with maintaining air pressure or servicing their fork as often to maintain performance. The caveat here is that the Smashpot doesn’t actually change the manufacturer’s recommended service interval for whatever fork you might have, and you still need to take care of the lower leg oil, wiper seals, and damper as per usual. But due to the extra oil volume in the spring leg, and the elimination of a bunch of dynamic seals in the air spring, a Smashpot-equipped fork’s performance definitely does not degrade as quickly as an air-sprung one does as the last service fades into the rearview mirror. And the spring rate won’t change due to gradual air pressure loss, changes in temperature, and so on.
And conversely, the Secus is likely a better option for some folks:
(1) Riders who want some combination of improved midstroke support and/or small bump sensitivity, but can’t stomach the weight of the Smashpot, especially if improved support is the higher priority.
(2) Folks who really care about dialing in exactly the right spring rate and want to preserve the ability to do so quickly and easily with a shock pump.
(3) Bike flippers who want to be able to sell their bike in the stock configuration, and move the upgrade over to a new bike. A Secus installation is easily reversible; a Smashpot one likely isn’t, somewhat depending on the specific fork in question.
Who’s It For?
The Smashpot isn’t light (our Smashpot-equipped ZEB weights more than a stock Fox 40 downhill fork) but it makes a huge difference in terms of small-bump sensitivity and plushness, which you can either choose to take on its own, or go firmer in spring rate and get an exceptionally supportive setup without the same compromises in terms of harshness that you get with an air spring. And it’s been consistent, reliable, and quiet in my time with it, without the need to check and maintain air pressure. The weight penalty will be a deal breaker for some folks, but if you’re willing to look past it there are some real advantages, both in terms of suspension performance and in consistency and reduced need for maintenance.
Bottom Line
Coil-sprung forks are a rarity these days, especially among high-end offerings, but the Vorsprung Smashpot makes a compelling case for why some riders should consider one. The suspension performance it offers is excellent, and consistency and reliability are improved over an air spring. The additional weight — nearly 600 g in the case of our RockShox ZEB test fork — is substantial, and some folks will miss the ability to fine-tune their spring rate with a shock pump, but Vorsprung offers far more spring rates than most other coil-sprung options to mitigate that limitation. Especially for folks who are after an ultra-sensitive, plush setup that still maintains good performance elsewhere, there’s still a lot to be said for coil springs, and the Smashpot is a well-sorted conversion kit for many of the most popular single-crown forks out there.
I have run a smashpot converted Lyrik on and off for around 1.5 years now on 2 bikes, one at 170mm travel the other (current) at 160mm travel. Biggest takeaways for me are the small bump sensitivity and mid stroke support mentioned above. The weight gain is very noticeable and the bike seems more planted/less poppy compared to an air fork. I ended up settling on using the coil fork at my frame’s max travel for bike park/shuttle days and have an air fork with less travel for more pedal days. FWIW I’ve also switched between coil and air rear shocks with both forks and found the air fork works fine with air or coil shock but the coil fork definitely feels unbalanced with an air shock. Going forward I will continue to use the coil fork intermittently though I don’t switch to it as often as I switch between air and coil rear shocks.
I have a first generation Zeb and never been totally satisfied with its performance. I have a luftkappe now but I’ve been thinking hard between the Secus and Smashpot coil for it. Or just buying an entirely different fork. That Smashpot sounds excellent but the weight might sway me in favor of the Secus. Its hard for me to justify dual crown weight in a singlecrown fork especially with the new bike park opening soon.
Timely review, I have been thinking of this to add more support to my Lyrik on my Geometron G1. The rear suspension on this bike is so good that it really highlights the support issues in the midstroke on the fork. Any idea what the weight delta might be for a Lyrik – comparable to the Zeb kit?
Yeah, the weight difference in most modern forks is going to be fairly similar, give or take a bit of spring weight depending on the rate needed.
I gained 525g on my Lyrik with the Smashpot. I think I’m running a 600 lb spring, I’m 200lbs and more high speed riding.
Hey David I really enjoy the suspension reviews. I’m curious if you guys have gotten your hands on a DSD Runt. We can speculate it would improve the midstroke support without as much improvement in the small bump as a Secus but a direct comparison on a Fox or RS would be cool. It’s a cheaper/lighter upgrade and doesn’t risk being damaged.
Thanks, JD! I’d love to get on a Runt too, but we haven’t been able to make it happen yet. I’ll try again to get in touch with DSD.
Great review. Thanks!
“People whose top priority is sensitivity and traction.” That’s me, and I love my Z1 coil on my OG Slash for rugged chunk riding. The improvement in sharp-edged absorption has been great.
Great in depth review…as always with Blister. Best review resource on the web in my opinion. I’ll be replacing my air spring with in Z1 with a Smashpot…
Hey David
Might you try the coil in the 23 Zeb please? I’m getting fat too much ramp up
What id really love is a Secus v Smashpot fur 23 Zeb comparison.
Thanks
As usual a great informative review.
Just a comment about converting back to air if it’s not to your liking. On Rockshox 35mm forks at least you can run the damper in the stock spring side and the Smashpot in the damper side. That way you can swap back to air without worries about damage to the inner surface of the air spring stanchion.
Replying to my own comment, I had it on good authority you could do this. Unfortunately you can’t because the air and damper side lower leg castings have different internal lengths. I know because I tried. Maybe moderator can take these two comments down.
What fork did you try it in? I’ve seen the swap done successfully in a Zeb.
Should these be fitted as standard on e mtbs?
Hi David, did you ever try Smashpot / Secus in the newer Zeb (the one with buttercups from 2022?) – I’d love to know what you thought of each.