ROCKSTOP TIRE INSERT REVIEW

Review by Robert Johnston

Rockstop is a company founded in the Lake District, England, with expertise and specialist equipment for the manufacture of polymer moldings. Specializing in shock absorbing components used in automotive, aerospace, sports and a range of other industries, and exporting 60% of their output all around the world; it’s safe to say they have a good base from which to dive into the mountain bike market.

“Welcome to the toughest baddest coolest most radical tire insert on the planet…”

The Rockstop tire insert is the first product the company has produced for the mountain bike market. With such a bold statement used to advertise it, I was very intrigued to experience how the bright yellow complex moldings would perform when fitted to my ride. A couple of months being downright abused in the Autumnal English Midlands allowed me to find out exactly what they are capable of.

THE LAB
Rockstop® is made from a Polyurethane blown Elastomer- a tough, highly shock absorbing rubberised polymer. Used in shock absorbers in F1 cars and aerospace industries, it’s the “toughest flexible stuff out there”, and it’s high density means it can pack a punch without taking up a lot of space inside the tires. Tire manufacturers spend millions developing and testing tires to work under various conditions so adjusting the tire dynamics dramatically could adversely affect the tire performance, which is why the Rockstop is designed to sit closely hugging the rim as opposed to the more intrusive inserts out there. Because of its lower profile, it is designed to offer protection from the bigger hits where the tire has compressed close to rim-out, whilst also offering some bead-locking and sidewall support due to its edges pushing into the sidewalls of the tire.

Utilising a self-skinning polymer ensures the Rockstop will not absorb sealant, allowing the relatively high 250g weight to be offset by the lack of extra sealant needed to be used inside the tire. The standard version tested is designed for rim inner diameters from 24-34mm, with a wide version available for those plus and fat tire riders with rims up to 45mm.

Rockstop suggest their insert allows for pressures as low as 20psi in the rear with tires using a relatively sturdy carcass. As a 200lb rider who usually tends towards pressures upwards of 27psi, I was intrigued to see just how low I could go with one of these in the back of various test bikes.

Priced at £65 for a single insert (roughly 85 USD) plus some very reasonable international shipping, the Rockstops fall somewhere in the upper-middle of the insert price range. Certainly not a budget insert, but with promises of long lasting performance, it may save money spent on replacement rims in the long run.

THE DIRT
It may not come as a shock when I say that the September and October testing period was a wet one in the UK. With dirt that closer resembled soup than dust, and roots littering the trails with the grip levels of a Mario Kart banana, it was the prime time to drop tire pressures as low as they could go to help ease my riding back into the wetter conditions.

The Rockstop comes pre-assembled and ready to fit straight away. You can keep the same valves as your standard tubeless setup as there are regular cutouts that allow for the easy passage of air. They come with a basic fitting guide that goes some way to helping their insertion, but it’s certainly worth sitting down with a beer and a spare half an hour for your first try until you figure out the proper technique. “Tucking” the bead of the tire under the Rockstop and into the central cavity of the rim is a must-do unless you have Popeye thumbs for getting that final portion of the bead on. Once the tire is fully over the rim wall, tire inflation is a doddle thanks to the sides of the insert pushing up against the rim, so there’s likely no need to call in a compressor. One thing is for sure – you don’t want to be dealing with these on the trailside, so pack a set of bacon strips. Thankfully the sturdy construction of the Rockstop means if the worst happens, you can likely roll out and back to safety on a flat without too much trouble.

Initial testing saw a rear wheel with Schwalbes’ Super Trail casing Big Betty fitted with a Rockstop insert, inflated to 25psi – roughly 3psi lower than I’d normally run. In this setup, the insert went very much under the radar, reducing the snappiness of the acceleration without feeling any particular benefit to the ride. However, one thing did become apparent as I tried to push harder and harder through rock and root infested terrain – the rear wheel was remarkably silent through repeated impacts on squarer edges. At the time, it hadn’t necessarily registered that I was only running 25psi, as the grip levels were so low that the extra grip was almost imperceivable, and the tire felt as if it was maybe a psi or two higher when cornering.

Some laziness before the next ride led to the most telling test for the insert, as an uplift day on some particularly aggressive downhill trails with what turned out to be just 22psi in the Rockstop equipped rear tire didn’t end in any dented rims or torn tires. It’s hard to say if the insert was to thank for the intactness of the tire, since there’s no doubt that the moisture had taken a little of the bite out of the sharp edges, but there were certainly multiple heavy hits on that rear rim that I was expecting to see some sign of damage from. Again, it was the odd silence of the tire and rim that were most profound, with the usual “dung” replaced by a very muted noise of the rock or root itself moving instead of the painful sound of metal denting.

While the pressures do feel ever so slightly higher with Rockstop in place than without, it’s certainly not the best insert I’ve tested for offering support to the sidewalls of the tires in hard cornering efforts or off-camber g-outs, with most of the squirm still remaining for the given pressure. It does however seem to do a good job of preventing the tire from burping air, allowing for the squirmfest to last for a long time if desired.

Expecting a rather bruised banana, removing the Rockstop from the rim after 2 months of thrashing instead revealed a perfectly unscathed insert, with only some minor discoloration along the face where the rim bead sat. Rinsing off the sealant still remaining in the tire revealed an insert that appeared to be free from any sealant adhesion, performing as advertised. Contrary to the regular foam inserts that would usually show some signs of damage, the Rockstop provides another level of durability that goes some way to justifying its high weight and cost.

The Wolf’s Last Word

The Rockstop tire insert provides riders who frequently navigate rocky terrain with an impressively durable and effective barrier for their rim that will allow for the forgiveness of some janky line choice or optimistically low tire pressures. Trail feel is relatively unaffected, so it’s not the choice for those looking to optimize their tires’ vibration damping properties, but the reduction in tire pressures it allows may provide similar results. At £65 per end, it’s not a cheap option, but it’s likely to outlast most inserts many times over, whilst also saving rims and perhaps reducing tire damage too.

Price: £65 ($86)
Weight: 250g
Website: Rockstopmtb.co.uk