Has anyone out there had experience going tubeless with Maxxis Hookworm tires?  I am attempting to do just that and I think I have cracked the formula to make it work, but I am curious to know what issues others have come across and how they solved them.

So far I have concluded that the perimeter bead area of the tire sidewall is porous and will leak air fairly rapidly.  I tried using Stan's tire sealant, but it did not seal sufficiently on it's own.  I then tried painting the entire inside of the tire with a flexible rubber sealant and this seemed to work well.  I am also experimenting with double-sided tapes to seal the bead to the rim.  I have found two tapes that seem to work - one even seems to be reusable while the other is gummy and really sticks, but makes replacing the tire a major chore.  The rims we are using are one-piece custom machined units, so there are no spoke holes to deal with.  So far I am at the stage of keeping air in the tire and have not road tested this setup yet.  That will happen in the coming weeks as we get our new car out for testing.

Any thoughts or advice?

Nick Gilbert

Advisor, George Fox University Engineering

Newberg, oregon

I am running 16" Hookworms 'tubeless'. I started running tubeless a few years back after a series of blown inner tubes. The only inner tubes that lasted for me were the very thick "thorn-proof" with 'slime' sealant inside.

Tubeless worked flawlessly with the carbon fiber plastic wheels. I used the DIY method of cutting a 14" inner tube for my 16" wheels and using that as the liner. I used Stan's sealant. There is no need to paint the inside of the tire with anything. I do scrub the inside of the cut 14" inner tube with Simple Green to remove the talc. Some types of rims will seal easily with a bicycle pump. Some require getting the pressure up faster with a air tank or higher powered pump.

Unfortunately the carbon fiber plastic wheels keep breaking and I had to move to spoked wheels. These were cheaply made and had a folded metal rim. This did not work well with DIY tubeless. I think it was because the folded metal edge meant there was less surface area for the cut inner tube and tire to seal.

I have move to aluminum wheels that have nice flat sides and am running tubeless again. I ran the last race at 100 psi and had zero problems.

In theory, tubeless should offer less rolling resistance since the thickness of the tire rubber contributes to rolling resistance so the extra layer of inner tube on the flexing part of the tire increases rolling resistance. I have read arguments that the liquid sealant sloshing around inside the tire might change this calculation but I have not done any back to back testing. I keep tring less and less sealant.

BTW Ryan, worn tires should have less rolling resistance than new tires, so keep running those bald tires!

Here are a few pictures of our wheel setup.  We are using 16" rims and we made the rim wider than a stock bike rim to hopefully get better cornering performance out of the tire.  One picture shows tape being applied in the bead area.  This seems to be necessary since the tires have 8 raised ridges across each bead caused by the molding process.  These ridges were preventing the bead from sealing properly in those areas, so the tape provides some conformability to help with sealing.

Two pictures show the wheels attached to the front upright assembly.  This design of wheel allows us to get the steering pivot points inside the wheel, which allows much better camber control throughout the steering range.  You can also were where we forgot to allow clearance for the valve stem and had to mount a short one off to the side.  Tubeless was always a goal in this design, but a lack of space for a conventional tube valve stem has now made it essential.

I haven't posted pics of the full chassis yet, but basically this car is designed for short track performance, hence the more elaborate suspension design.  We chose to sacrifice overall lightness for an increase in cornering performance.  That's the idea - still to be tested.

Nick.

Wow.

Those are pretty cool wheels. 

Expensive to make?

Now I want to see the rest of the car...

The cost for these wheels was not outrageous, but I am not sure how they rate vs other options. Material cost was about $125 per wheel, and that was buying through a machine shop that buys in quantity, so the price per pound was good. The machining was done partially by a student on a Haas VF1 and partially by a local machine shop - the mill was used for the inside geometry and a lathe for the outside geometry.  In the end, the machine shop that we bought the material through decided not to bill for the material, and the CNC lathe work was donated too, so we actually got the wheels for no cost. I was not expecting that.

When I picked up the wheels from the CNC lathe shop, I asked what he would charge to machine the whole wheel in a quantity of 10 - 20 pieces. He gave a rough estimate of about $150 per wheel. So combining that with material cost, an approximate cost would be about $275 per wheel. I am guessing that is quite a bit more than other options, but there are some advantages and savings in this design. They should be much stronger than bicycle-style wheels, so there is a saving there in not having to replace wheels often.  They also allow space for much better steering geometry and possibly a more aerodynamic package if you tuck all the bearings and brakes inside the rim and add a fairing to the inside.  These are a bit wider than stock BMX rims (2.5"), so there will hopefully be improved cornering performance included as well.

So whether all these benefits prove out to be real and whether they are worth the expense, only testing and racing will tell.

Very impressive build quality. I hope you post more as you run the car.

From your posting, it sounds like the bead not sealing to the rim is where you have identified the leaking. I am not clear why coating the inside of the tire with rubber sealant would help with this.

From my experience, I agree that the leakage is at the bead. I have never found any sign of leakage from the carcass. I assume the Stans spinning inside would fix this. 

We use the rubber of the cut inner tube to provide the conformability with the tire bead. Before I blow up the tire, I hold it horizontally and slosh around the Stans already inside. I then flip the wheel and repeat. Still horizontal, I inflate the tire. The Stans sealant leaks out the side some as the tire seals. 

When we disassemble a wheel, the inner tube rubber is compressed and 'glued' to the tire bead.

When we are cutting the inner tube, we split it down the outside circumference but you could bias the split to one side to allow the tire valve to go through your existing hole.

We are still experimenting, but here is what we have discovered so far:

The Maxxix Hookworm tire carcass is not air-tight. They will leak air through the sidewalls, so some sort of sealant is needed. I placed one tire with no sealant into a water bath and I could see multiple lines of tiny bubbles permeating through the sidewall. These lines of bubbles corresponded to the threads in the sidewall.

Using Stans sealant on this tire reduce leakage enough that racing for an hour would be possible. We did get quite a bit of sealant coming out of the tire onto the outside, though.

Next we tried painting the inside of the tire with one coat of Flex Seal rubber coating.  This sealed the tire well enough that racing for an hour is possible.  I think the ideal solution is Flex Seal and a liquid sealant added for extra sealing.

We haven't tried the inner tube modification idea, but we plan to in the future.  Unfortunately our hub geometry won't allow space for a standard length valve stem, so we would have to deal with that issue.

We have tried mounting tires with and without tape for a bead seal and the conclusion is that bead tape is not really needed.  However, we are choosing to use it because it makes reinflating a tire much easier as it keeps the beads in contact with the rim even with no air pressure.  Our rims are wider than stock, so the tire does not want to stay in contact with the rim on it's own.  We have trouble inflating the tire for the first time because of this.  We solved that problem by using a nylon band clamp from the wood shop.  We wrap it around the perimeter of the tire and tighten it up.  As it compresses the perimeter of the tire, the beads expand out and touch the rim.  The tire will then seal and hold air.  We are careful to only inflate to a low pressure while the band clamp is on, so as not to explode the clamp.  Once the clamp is removed, we can inflate to full pressure.

Our tires do not hold air for long.  After a day or two, they are flat.  Pressure loss over an hour is small though, so completing a race with correct pressure shouldn't be a problem.  Adding a liquid sealant should improve this further.

Hi Nick,

I looked at the Hookworms we are running and do not see any line of threads. I am running 16 inch. Are you running 20 inch? That might explain the difference. We used to run 20 inch Maxxix Hookworm tubeless using a 16 inch tube (split down the center) and Stans and did not have any problems. I guess the combination of the tube rubber and Stans kept us from seeing this leakage.

I noticed that in my earlier replies, I did not say why we were having so much problems with tubes but we run aggressive regen through the rear wheel. Between the torque of acceleration and regen, the tire was rotating some on the wheel. The tube would either abbrade from the inside of the tire or fail at the stem when the whole inner tube tried to rotate.

The only thing I can think of on the valve stem length is a spacer inside the wheel such as washers to let only a small amount of valve stem peek out.

I found some data on tubeless, worn tires, pressure etc for rolling resistance. Here is the website with a description of their testing method: https://www.bicyclerollingresistance.com/the-test

They are using about 94 lbs as their weight which is not too far off for a three wheel Electrathon. I like that the results are in Watts, so triple for three wheels and that is Watt hours due to tire rolling resistance per race.

The test are all for much larger diameter tires. Do they have less rolling resistance?

They do some MTB tires which might be closer than road tires.

https://www.bicyclerollingresistance.com/specials/tubeless-latex-butyl-tubes

At 55 psi, 15.5 vs. 18, so 7.5 Whrs advantage during a race.

They also look at worn tires where they conclude might have an advantage if not too old. And how much sealant to use(for their size tires).

Some broad strokes here. Using 20 Watts per wheel gives us around 60 Watts hours lost to rolling resistance during a race. What uses up the rest?

Motor inefficiencies, wire losses, bearing drag, drive train drag (chain and gears), alignment drag (from toe, camber, castor), mis-alignment drag, aero drag. Have I missed any?

I have attached a picture that shows the construction details of the 16" Maxxis tire (20" appears to be the same construction).  You can see the carcass threads are quite visible on the inside surface, and in places they are somewhat visible in the sidewall.  As-is, air will permeate into the threads from the inside and find it's way out in the areas that have the least external rubber, which is the sidewall area.  Under pressure, the thin coating of rubber on the outer sidewall will rupture and create numerous tiny leaks.  In one experiment, I could actually hear tiny popping sounds as air broke through.  The rubber sealant that we painted on inside seems to seal up well enough to prevent this, and adding liquid sealant helps even more.

You can also see the molding mark that was occasionally causing leaks in the bead area.  That is one reason we are using tape between the bead and rim, to conform around this bump.

Definitely some good info on rolling resistance on that website.  Looks like tubeless could have some significant advantages to Electrathon.  I do wish the Hookworms came tubeless ready.

One area of drag that you didn't list is cornering drag.  Cornering forces and tire slip can result in a huge amount of lost energy.  We are hoping to try to quantify this in a future test session.

I see the texture of the material that makes up the tire contains threads. I was confused and was looking for some kind of separate thread rows running along the sidewall.

Since rolling resistance is increased by the thickness of rubber, the rubber sealant might have a tiny negative impact. With Stans, we only see minor leakage (100 psi to 80 psi in a week). We always set the tire pressure right before the race, so, in my experience, I do not see a need for rubber sealant.

Unfortunately, this seems to be a moot problem. Maxxis Support replied to my query that the 16" version of the Hookworm has been discontinued.  

I ordered a set of the Kenda Kwest high pressure. They are rated for 100 psi. They are skinny at 1.5 width and look a little cheap and plasticy. I will test them and see how they go.

Anybody have any suggestions for a high pressure wider 16"?

I was not aware they had been discontinued - that's aggravating.  I knew it was a risk to go with 16" because of the sparce selection of tires, but the advantages seemed worth it for us. 

Looks like we will be researching alternatives too.