I’ve had rather less time to ride on this than I planned. Conception and discussion is here:

Source for Closed Cell Foam – for Homemade Huck Norris

The potted version is that I put a 50mm polyethylene foam ‘packer rod’ insert into the rear tyre of my hardtail to try to replicate the commercial inserts at a fraction of the cost. Because, well, £40 for a bit of foam? Really?

I’m a curious type, but generally short of time. I’ve arsed about with DIY tubeless since before it was even a thing on mtb’s and mostly tubeless is such a good product these days, I’m happy with the way things are.

But I like big tyres on wide rims at low pressures, although current trends have eclipsed my once extreme preference of 2.3/2.4 tyres at 20psi, and my recent journey into carbon rims has seen me break 2 now.

It’s obviously because of the low pressures I like to run and it’s no coincidence that I’ve suffered snake bites at the same time.

Imagine my delight at the introduction of tubeless inserts, except, well, £40 for a bit of foam. Really? whats that? oh, yes, I do know its special MTB foam, but still, really?

So, here we are. I know a few folk were talking on that previous thread about options, so I thought I’d post up my initial thoughts for interested parties.

Fitting 50mm cylindrical inserts will have you cursing if you don’t stop and think. There is a video on youtube about cush core that shows how to push the tyre bead into the rim well and under the insert to give enough slack to get the tyre on. This is essential in my view.

The insert uses up quite a lot of air space, but does compress a little under normal inflation pressures. Uncompressed, my basic volume calcs show a reduction to 32% of the tyres previous air volume. This I think, has implications, which I’ll touch on later.

Now, the riding.

I have 4 hours of riding in my local, limestone based woods. Its short in significant elevation, but is rooty as hell, with plenty of rough surface rocks – think fixed baby heads, rather than loose. This is liberally coated in in clay, and right now it’s slippery as shiite thanks to Autumn leaf fall and rain. I do not take beginners here even if its the height of summer.

You can ride on the insert with no air in the tyre at all, but I don’t think it will last very long like that. Pumped up to my regular pressures the tyre feels firmer. I’ve settled for the moment at 5 psi less than normal, which is approx 15 psi.

Even at this pressure, bimbling riding feels a touch firmer and it’s definitely a bit less comfortable. It’s odd, since the grip is improved with the lower pressure and to date I associate lower pressure, grip and trail smoothing to go hand in hand. It’s most noticeable with one off hits like large single roots and rocks where the impact is not so bottomless as plain old air – that’ll be the insert doing its thing then.

Sidewall wall support is quite noticeable. The rear wheel kicks out a little more on those oblique – poke-into-the-side-of-the-tyre trail features. I’d expect in better conditions this would be less obvious because the tread would have better grip, but in current conditions nothing is hidden.

Add in a little more speed and things change though. The babyhead chatter is muted and the firmness disappears – presumably because enough force is entering the tyre/insert to deform sufficiently. Suddenly, in rougher, more chundery sections, the wheel has more composure and the most notable thing is much less rebound and ping from the tyre.

I’ve read about some of the commercial inserts providing this sense of composure and I think there’s something in it. I suspect this is to do with the reduction in tyre air volume and the concordant ramp up in pressures under trail impacts. Probably helpful to consider the tyre/insert systems like an air fork with tokens at this point. My current thoughts are to reduce the volume of the insert by cutting some foam off, thereby putting more air space back into the system, and adding some more linearity to the tyre, but I want some more time on the bike as it is before I start experimenting further.

Puncture protection – No idea. Conditions are poor and speeds are down. I’ll not have a feel for that until the dry weather arrives or i go somewhere with bigger rocks i expect. I’m certainly not going to start smashing rims just to do some empirical testing. I did ride deliberately heavy into some stuff and there was definitely a bit of kick back from the wheel, so making the system a bit more linear should in theory improve this. The foam is 4-5x less dense, but three times deeper. Clearly, the insert is going to need as much of its thickness as possible to compensate for its reduced density when it come to assisting with puncture prevention, but it has an assist by the ramp up of a smaller tyre volume.

I’m expecting as things move on to find a balance where tyre feel is acceptable and puncture protection is as good as it can be. More riding and more thoughts as I get more time on the bike.

Appropriate name 🙂

Well done sir. I’ll be interested in your experiments

(secretly high fives and awaits for part 2)

Fitted my packer rod version this morning to a 2.6″ Butcher Grid. Not had chance to try it out yet, but this looks promising!

Interesting stuff.

I was about to make a thread about doing this (it was my thread originally we were talking about it in I think).

I used 40mm in 2.35 maxxis tyres on 25id rims (perfect fit)

But what I don’t get is why you didn’t chop it in half!

Down the middle into two half cylinders, zip tie and place in. Then it mirrors cushcore and provides the sidewall support but the tyre still rolls on its own support in the top half.

But what I don’t get is why you didn’t chop it in half!

I thought I’d been clear about that – obviously not. Because it’s much less dense than Cush Core. It will therefore be softer and much less resistant per given thickness.

Anyway, I’ve posted up my most recent findings on the original thread.

Any chance of a link to the original thread?

I love to play about …

I quite fancy a play with this… Just how faffy is getting the tyre/insert on ???

One disadvantage (minor compared to the many advantages) of tubeless for me is I change tyres less than I would….  it’s not that much extra faff but it’s enough to make me not do it most of the time.

To an extent I probably also run tyres that are beyond their best because of this.

Hmmm, they do 100mm foam as well, wonder how that would fare in the fat bike.

Downside is it comes in 50m rolls so I’d need to find another 11 people to group buy it with!

Any chance of a link to the original thread?

The link is in my first post at the top of the thread.

Ta

I am intrigued as to what is actually going on inside the tyre.  Would pressure ramping up on impacts have much of an effect?  The % volume reduction in a tyre between unladen and compressed to pinching point is not going to be that great, though greater with the thing reducing pumpable air volume. The main forces transmitted to the wheel will still be changes in the direction of sidewall pull on the rim and in sidewall tension.  Which the stuff may affect.  Also, if it compresses, surely it will compress in all dimensions so become smaller overall and start to behave like a rim strip under tension around the rim.  Which might help hold the tyres on.  Them Huck Norrys are made loose so that wouldn’t happen, maybe for a reason?