Do Inserts Actually Prevent Flats? An In-depth Look at Insert Testing with Rimpact

Do Inserts actually help? Should I run them? Are they worth the weight penalty?

This article is the first in a series in which we will share some of the testing we perform to show how different products stack up to the other offerings on the market. We have elected to show this competition testing, rather than the development process of new products as, frankly, it isn’t as exciting to see how different materials perform if you can’t go out and buy them in the form of an insert. For this first installment we will show you slow motion footage of 9 inserts being impacted by our test jig at a range of pressures.

Anyone who has ridden bikes for a while will have heard it. The speculation mill surrounding new technology and its usefulness. The rumours usually follow a peak in hype and calls in to question whether or not the industry direction is a positive one. High Pivot Enduro Bikes are a prime example of this. Everyone wanted one, they were clearly better in every way! Now the hype has died down a little it’s hard to talk about them without hearing “2-5% less efficiency” and “More likely to drop a chain”. Tyre inserts are no different, now they are no longer the newest technology giving racers the edge, questions are being raised throughout the Mountain Biking world as to their genuine benefits.

Top level athletes are still missing out on points due to flats in qualifying despite having access to systems that reduce the chances of being airless before the finish line. We’ve heard various hearsay out on the trail such as “My friend said his mate who races World Cups doesn’t run inserts because they increase punctures”, and “I’d rather run 2psi more and not have the extra weight in my tyre, it’s the same effect”. The rumour mill runs wild, does this phenomenon occur because humanity tends towards an aversion to that which is popular? Or is it more nuanced than that?

material is ‘3x stiffer’ is often taken at face value and the company selling said product does nothing in the way of presenting the evidence derived from testing. We aren’t claiming that product testing and comparison isn’t happening, but often it is hard for the customer to evaluate marketing claims for themselves as the proof is rarely shown. Here at Rimpact we realised we were equally culpable of this flaw. We have tested every one of our products in many rigorous ways to ensure the final result is the best version of itself that we could achieve. However, whilst we have carried out hours upon hours of documented testing, we have shared little evidence of this with the riders who trust our Inserts to keep them rolling.

What metrics make an insert worth running over regular tubeless? If we were to list them it would certainly include; puncture reduction, rim damage decrease, tire sidewall support improvement, vibration damping, rebound speed and rolling resistance improvements, to name a few. Today we are tackling the main selling point for many users – puncture resistance. Can Inserts provide a measurable improvement to reduce the chance of your tire failing? Is there any substance to a rumour we've heard surprisingly often - “Tire Inserts cause more punctures than they prevent”? Watch the slow-mo video below to find out.

Henry from Pinkbike completed similar testing last year and found very comparable results that can be seen here:

Testing Methodology

We used our impact testing jig to drop a 15kg weight onto a wheel that was fixed at the hub. The wheel is suspended in mid-air to simulate the hub mounting point on a fork and prevent the forces passing into the ground below. The weight was dropped at a height of 55cm (to the top of the tyre tread) and used a sharp, right angled, impact head to provide a ‘worst case scenario’ impact and mimic those instances where you land a drop into a shark tooth rock.

At 29psi, the force required to puncture a tubeless tyre without an insert installed was equivalent to dropping 15kg from 55cm on our Jig.

To determine these testing parameters, we selected a tyre pressure that was at the top end of what we believe riders should run, assuming they fall in a roughly average weight and speed range. At 29psi, the force required to puncture a tubeless tyre without an insert installed was equivalent to dropping 15kg from 55cm on our Jig. If riders find themselves wanting to run higher than 29 psi but fall within this average category and use case, we feel they would be better suited to a more substantial tyre carcass or..uh...better lines... From here we could be sure that any decrease in pressure without a puncture occurring could be attributed to a given insert’s improvement in impact mitigating performance. We kept as many variables’ constant as possible, using identical Maxxis Exo+ 2.5” DHF’s and Hunt Enduro Wide V2 Rims so ensure the only factor being measured was the insert’s performance. We felt this set up best represented the average use case for users without the tyre being too thin or too thick and masking the results.

For each insert we began at 29psi and dropped the weight onto the tyre. We then inspected the tyre and rim for damage, made a note and repeated the test at a lower pressure until the either the tyre or rim failed. A failure state was predetermined as a deflation of the tyre – meaning the tyre was punctured, or a major rim dent. We categorised rim dents into two separate states, minor or major. minor rim damage was defined by a misshapen rim that was small enough to be both unnoticeable to the eye at a one-meter distance and also not

the structural integrity of the rim or the tubeless seal of the system. A major rim dent was defined by a noticeable dent viewed at one meter distance or a failure of the tubeless system. We appreciate that this isn’t the most scientific approach to recording results as there is an element of opinion involved; however, for the purposes of this test we tried to remain as unbiased as possible. In any instances where there was a doubt as to whether a failure state had been met, we opted to continue to lower the pressure and give the product the benefit of the doubt. In all cases where this occurred, the tyre and rim failed at the next impact showing us that the fail state was definitely met. We ran each insert through this test, from 29psi to failure, three times to determine if any results were anomalies and found almost identical results each time, across all products. The results shown in the graphs are best performances to ensure fairness but not one product failed at an uncharacteristic pressure compared to it's other performances. We concluded each round of testing at failure or 17psi. Whilst we could have tested lower pressures than this, negative traits begin to creep in to the characteristics of the tyre and tyre performance can drop off rapidly so we typically suggest running differing tread patterns, softer compounds, thinner carcasses and adjusting suspension settings to gain more traction if you feel you need to run lower than this.

The Data Visualised

The graph below shows the pressure where each tyre failed plotted on the Y Axis and the insert used on the X axis. Essentially the higher the blue bar, the higher the impact performance of the insert. The Orange bars denote the point in which first signs of minor damage occurred. Once again these are not points where the tubeless setup failed but where damage occurred that you might not notice during your ride, but instead after a close inspection in the workshop. Ideally best-case scenario is to achieve as high an orange and blue bar as possible. In some instances, you’ll see that inserts were able to withstand the impact force at increasingly low pressures despite the rim or tyre sustaining damage at higher pressures. Both the Rimpact Pro, Cushcore Pro and Vittoria Airliner survived the 17psi drop and were able to continue past our cut off point, although the Airliner sustained minor damage at 24psi and then again at 21psi in their best performance test. Tannus fell short of the line at 18psi each time and Technomousse, the heaviest Insert on test by some margin only made it to 18psi whilst sustaining damage at 23psi as well.

The products on the left side of the graph represent a category of much lighter, less substantial and lower priced insert designs. Despite this lower price/ lower weight/ lower difficulty to install, all of these inserts would benefit users looking for minimal improvements by allowing them to drop their pressures between 5 and 9psi except for the DIY offering.

Our conclusion to the data gathered in this test is that inserts provide a significant uplift in puncture protection, reducing the need to pick smoother lines, run higher pressures, run thicker carcasses or replace your tyres as often. Thankfully we can happily dispel the myth that “tyre inserts cause more punctures than they prevent”. With the Rimpact Pro, Cushcore and Vittoria Airliner Inserts we were able to lower the air pressure by 41% and still not puncture the tyre or damage the rim. Could we could have lowered the pressure even more? Yes, we could have and did, the Rimpact Pro reached a surprisingly low 8psi. However we didn’t include it as part of the test as we don’t feel that these extremely low pressures are representative of what riders will be experiencing in the real world as tyre performance quickly drops off past this point. We also ran this group test prior to releasing the EDH which out performs the PRO insert in terms of impact protection. It appears that the question isn't "should I run inserts?" but rather, "Which Inserts should I run?"

Next time we will be looking either rolling resistance benefits, sidewall support, vibration damping effects or run flat capabilities. We'd like to thank Friction Cycles for their help in obtaining the number of tyres needed to complete this test. They are a fantastic and highly recommended bike shop based in Bedminster, Bristol, UK and are experts in tyre inserts and Mountain Biking in general.