Esk8 racing - help me advance this new sport by fitting the right kart slicks

Other Motorsports Incl Sim Racing
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Hey! I’m new to the forum and while I love karting at a hobby level, there’s one thing I am even more passionate about - racing esk8s - electric skateboards - on kart tracks. Don’t let the word “skateboard” turn you off - on some tracks the fastest guys from our hobby can challenge kart lap times. If you are interested in the topic, bear with me until the end, if not, no worries. But I’d appreciate some input on gokart tire selection to advance this sport. TLDR: the post starts with introduction to racing esk8s, how I got to the realization of trying kart tires on my esk8, and then I am asking for help so I can select the right kart tires in the last paragraph.

Below is a picture of me turning at around 1.4G at Kartplanet Prague.

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This is a nice youtube series of one of the racing leagues over the 2024 season with some commentary for anyone interested in the sport: https://www.youtube.com/playlist?list=PLNcG9e7JvShOe43Kz1jOAy-r1m3orNaM3

Electric skateboard racing is still in it’s infancy, I’ll give you a short overview to catch up to what it really is. Most of the skateboards that are raced on at a competitive level are racer’s shed creations. Zero restrictions apply so long as we have 4 wheels, electric propulsion, and turn by leaning to the side. This along with the small form factor of electric motors has lead to crazy power to weight ratios even after accounted for rider weight - the best boards are not limited by power at lower speeds, but rather by traction.

My 4WD in the picture above can put down around 1200N of force theoretically after having accounted for efficiency while accelerating 110kg total - meaning about 1.1G theoreticaly acceleration - yikes. The highest I actually measured so far is about 0.9G acceleration, that was dancing on the limit of traction and not full torque. 4WD can deliver the same amount of deceleration while braking - we don’t have mechanical brakes, so therefore we need a motor on each wheel to have front brakes, which cuts lap times a fair amount, especially on shorter more technical tracks.

There’s a very interesting aspect to esk8 racing that doesn’t really apply to most other motorsports - the weight of the esk8 is around 20-30kg (44-66 lbs), whereas the weight of the rider is much more, usually 80kg (180lbs) or higher… Combine this with the fact that we are essentially standing on a wooden plank or a steel chassis, we can move the center of gravity around way move than it’s possible in most other motorsports. And we actually really need to move the weight around - without that we can’t turn - and if we give throttle input without moving our weight, well we won’t really be standing anymore.

However as our sport is so new, the optimal equipment is not yet figured out. This is especially true for tires, and some chassis development is still taking place - noone uses tires with an actual speed rating, we just hope they won’t blow up on us and balance them if needed. Some people are using RC dragster car tires and pull close to 2G cornering on them. Those tires however cost 1.5x per piece compared to a gokart tire, and due to their small size of 6" diameter, they limit how the chassis can be built.

There’s also race tires around the 6" size tubed and tubeless specifically built for esk8 racing, however I am not convinced those are the right choice either. They are just the easy choice.

Without going too complex into the chassis setup, the further the standing platform is above the axle, the more force it takes to steer in high G turns. If the standing platform is inline with the axle the steering feels great, however because the deck needs to be able to lean just like a skateboard deck would, it needs a good amount of clearance. You will end up either compromising the amount of lean you can have (therefore the steering will feel more twitchy) or need to increase the chassis height therefore you’ll have a hard time countering steering forces.

In the past year or so I’ve been experimenting with a few sets of lawnmower slicks - yep you heard that right :sweat_smile: that’s what I’ve been pulling about 1.4G on in the picture above. These are 9x3.5 slicks around 70A on the durometer scale. The compound is too hard, and they need every condition to be just right to heat up properly, but they allowed a nicer chassis setup for my board. This allowed me to have the axle inline with the standing platform so that the steering doesn’t tighten up on high G turns, while not having to take sacrifices on the amount of deck lean I wanted to have, and even resulted in a bit of excess ground clearance.

Not too long after the most prominent race team in esk8 (SRB) started experimenting with 8.5" ninebot kart tires with decent success as well, and just recently brought out a chassis where the standing platform is below the axle, resulting in a power steering effect for those high G turns.

However I have big plans for the 2025 race season. I’m increasing battery power to 23-24kW and I’m rebuilding my chassis from scratch from bent and welded sheet metal, that allows an adjustable ride height, taking the standing platform from about inline to well below axle - giving me plenty of power steering as I prefer an easy steering - and the ability (and, well, the need) to run gokart tires if I actually run the chassis that low. Going from the total amount of weight, and the fitment / size, I determined that the ideal tire size for me is a front gokart tire size. And my findings so far are that I prefer same size front to back on an esk8.

So I’ll need something 10" tall. I bought some 5"x5" rims, and I am getting some custom wheel hubs manufactured soon.

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There’s a couple things I am not sure on however, and that’s why I’m here. I don’t know much about gokart tires to be fair. I’ve been thinking that if I go for some harder duro, I definitely need to compensate by going less in width so that I can heat it up still. So there’s two ways I can see:

Either something around 10x3.60-5 in a medium-soft compound, or 10x4.6-5 in a soft compound. Honestly I think the larger width seems like a better choice if I can go super soft compound, because I when I fall I tend to mess up the rims of the rim extends past the tire - which would definitely be the case on the smaller width. But total weight is only around 110-120kg / 240-260 lbs, so I’m a little hesitant if I could heat up extra width.

Can you kart guys recommend me some good, really grippy, soft front tires? It doesn’t matter if it’s known to bog down engines because it’s so grippy - I’ve got plenty of power to spare. I’ve been thinking primarily MG yellow or maybe Vega White so far, but I really don’t have much knowledge about kart tires. Ideally the tire should heat up fast relative to kart tires, as I am more likely to struggle with low temps rather than high temps. I’m mostly going to be using it on asphalt. I wouldn’t mind if I could get over 100 km, maybe even over 200 km racing out of a set before they really fall off a cliff, but if I can’t - that’s one thing I can live with.

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This is very interesting!

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Maybe consider using tire treatments to soften the tires in whatever your preferred tire form factor is?

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I want to experiment with 10" height tires, so that I can have a chassis that’s a good amount lower than the axle for the power steering effect that brings. On the planned chassis I can stand about 5 cm lower than the axle, which would be a substantial power steering effect.

I am building the new chassis specifically to experiment with this power steering effect and I’m making it adjustable height, so I can still put on smaller wheels if I bring the chassis higher, or just fine tune how I want the steering to feel on larger wheels.

If I’m trying 10", I think the best tires are kart tires for my purpose in this size. Just need to stick to front wheel width due to lower total weight.

I want to get away from the current esk8 tire options, the grippiest ones are about 260$ for a set and their performance drops off like 1 sec over a 30 sec lap after one weekend. But because I live in the EU getting a set costs me about 400€, while I can get 4 high end race kart front tires for 200€. And I need to make compromises with the chassis to fit 6". It’s this type of wheel:

Noone experimented with softeners on these. It’s essentially a piece of foam glued onto a piece round plastic “rim” and a piece of rubber is glued onto the foam. If you use softeners you are probably risking the failure of the glue. To be fair, this type doesn’t really need softeners to begin with as it goes down to 45A, they grip seriously well. However, they just don’t have the ideal size and they cost so much. Also no speed rating.

I’ve experimented with one softener on a more traditional tire construction, however that tire offers worse performance to begin. It made some difference for sure but not enough to dethrone the airless ones. The tire still stinks a month and a half after applying that softener though.

I think I’d be best off with a race kart front tire around 40-45A hardness or maybe a bit below even. Not sure what to look for though.

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Not quite 40/45 but Hoosier do have a softer tire. You could also call them to see if that have something closer to 40 from their dirt range.

https://hoosierkartsport.com/products/

@Simone_Perego , is CIK “soft” homologation still a thing? I could only find what looked like medium on the latest list.

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Just found out MG SS green is 46A which is pretty close. Just slight issue with that one, I can’t find a shop where I can buy front only in Europe. Something I’ll look into more.

Might be worth looking into wet tires? They go down to 43-45A at Hoosier, probably similar range for other brands as well. Giving up some contact patch, but if duro is low enough might not be a bad thing necessarily. I want to try if I can get slicks up to temp first though.

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Wet tires on a dry track are going to give you worse grip and will shred themselves in a matter of laps. The loss of contact patch plus the tread blocks moving around makes the vehicle very floaty when on a dry track surface.

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The concept of “soft” or “medium” is something defined by each tire manufacturer and is related to an internal metric they each have to determine the compound hardness, but has no value from an homologation standpoint.

The only thing that matters is the “prime” (soft) or “option” (hard) that are linked to wether or not it fulfills the longevity tests (now done on the dedicated tire test bench).

This is why ultimate performance is not a metric taken into consideration for homologation purposes.

Also, as an overarching comment based on what I’ve seen recently re- shore hardness as given on homologation papers : please do not take those values as a way to determine if a tire is performant or not (ergo : the lower the shore, the faster the tire is). The value is outputted by cutting a small strip of compound and measuring it in a lab, at ambient temperature. You need to consider that different compounds and tires (from
Model to model and from manufacturer to manufacturer) will exhibit significant changes in shore hardness when at their operational temperature. For example , a measured 53 shore could drop to 37 when hot, while a measured 44 only drops to 40 when hot etc.

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Specifically to the OP’s question (Which is mega interesting btw, super cool project and a nice thing to nerd on about)

Above shore hardness, you need to understand what works best with the dynamics of the vehicle you are tuning for, and i am inclined to believe this will be directly correlated and dictated by carcass hardness and flex.

I honestly wouldn’t even know what educated guess to have in terms of what would work best, but consider the following:

  • Tires with soft carcases: MG, Vega
  • Tires with hard carcasses: LeCont, Mojo

Best case scenario would be to purchase the Prime compound of each of those and go testing. In terms of ultimate tire performance, the LeCont LPM Prime is the fastest kart tire that exists today, altough i do not know if it will “work” with the setup you are chasing. For instance, you may be faster with an MG just because the board works the tire better than a LeCont, indipendent of the compound’s delta performance.

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Really good advice, appreciate it!

I’ve grown to enjoy tires with a medium-hard sidewall. On a board they respond quicker once pushing the grip limit. A soft sidewall tire is easier to tame, but once you have the skill every time you go over the grip limit, and start correcting, you are forced to wait for the tire as it comes back slowly under you. With a harder sidewall, if it goes it’s much quicker, but once you are skilled enough you can also get it back under you quicker, meaning mistakes cost less time.

There’s a point where the sidewall becomes too hard though for my skill level and preferences, at that point if I go over the grip limit I can’t bring it back controllably. Might end with a spinout or at least way too much time lost. Or I might just end up getting used to them in a few sessions, that’s what happened last time I went up in sidewall stiffness. This is because countersteering is significantly harder on an esk8 - it basically means pulling back the 25-35kg board on the ground with my legs while drifting, and just like when you use your hands to steer, I need to give really fine, but also strong inputs with my leg… While pulling that heavy board.

The question though that only testing will answer is how well the esk8 tire sidewalls translate to the kart tire sidewalls. With most race oriented esk8 tires the sidewalls are a thinner profile compared to kart tires, especially on a 5" rim. The tall sidewall lawnmower slicks I’ve tried had super stiff sidewalls with weight ratings of 100-150kg for each tire, and at that tall profile they performed like a medium-hard sidewall of a slim profile, pretty good on the limit, maybe a tiny bit on the easier side rather than the performant side. Their weight at a 9x3.5 size was around 900 gram. Although no tire we ever raced on has had a speed rating over 20 km/h, so not sure how relevant that is. A 200 km/h speed rating like most fik-prime certified tires have surely brings improved tech to sidewalls, and I imagine it must mean that no kart tire with a similar speed rating would be equivalent to what I call a soft sidewall tire from esk8.

Sounds like I’ll start with trying the LeCont LPM and the MG yellows or maybe even MG greens if I can get my hands on only front ones, then decide what feels best! The only thing I am mostly sure of is that the softer treads are going to be the better ones, as there’s also going be a good amount of increase in total contact patch… So getting them up to temperature is a possible worry, especially on harder duros.

How much time does a tire swap take on a one piece kart rim? With esk8 we have 2 piece rims, five bolts and the tire just slides off easily… Super quick. But we mostly use tubed tires. I imagine the one piece rim is going to make things a good bit harder. Contemplating if I should just get a second set of rims :sweat_smile: Probably I should.

To be honest what the ideal sidewall stiffness is also depends on the track surface for us. Higher bite tracks work well on a quick reacting tire, but on low bite tracks I might need the slower response of the softer sidewall, for example on polished indoor tracks, although we usually only race on these once or twice an year so getting the feel right for this isn’t the main priority.

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Tire changes can be relatively quick and painless, but can be a bitch. It also depends on the rim you are using.

Magnesium rims will “ussualy” be harder to fit tires onto than alliminum, but will manage heat better when in opperation. Nonetheless, an OTK rim will be a very easy to mount onto for instance, while an AMV one is much more difficult.

Of course, all of this under the caveat that it will be harder vs a splid wheel design :sweat_smile:

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Gotcha! These are the rims I have:

Specifically chosen for the 55mm centering ring, as I’ll have custom made dual purpose wheel hubs. They will fit the airless 6/7" RC dragster tires as well as these kart rims, both with centering features and the perfect offset.

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Actually that opened a can of worms…… different rim material :open_mouth:

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Would aluminum have heat issues on his e-sk8? Magnesium better?

Have we found the one application MXJ is actually useful for? :joy:

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I would guess - but completely uneducated - that given the weight of board/rider is significantly lower than a kart, tire temp will be harder to generate… so probably looking to do anything possible to build and maintain temp.

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The right air pressure will be critical - not enough and you’ll never get the tire working. It would be interesting to hear @Simone_Perego recommended methodology, but a basic method to make sure that your air pressure is in the correct range is to confirm that it raises from cold by at least 2 psi when hot (taken immediately after session) but not more than 3 psi. If it hasn’t raised enough add some air until it does. If the pressure raised too much then take out some air.

As mentioned above regarding the lower weight the tire will bear compared to what they were designed for, it would probably make sense to start testing at the high range of whatever is recommended by the manufacturer, and don’t be afraid to go several psi above it if need be. (which is commonly done in the extenuating situations, like rain, extreme-cold)

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I’ve actually built some crappy tire warmers for my 6.5" indoor wheel setup for the last race. It was indoor but close to 0C temperature. Heating was quite uneven but even with spending about 3-5 minutes in the pit area waiting for the start without the warmers, when we actually started the race the tires were still 20-25C over ambient and they started working decently much quicker.

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I might invest into the same thing for kart wheels if it turns out necessary, just a more professional solution :smile:

I think I might be okay when our season starts late May with around 25-30C ambient. Late into the season as autumn is coming and the temps are dropping I’ll very likely need the warmers.

In our european race series we usually have about half a lap for tire warming, and most race heats are 3 laps time trial. So the tire needs to start working quickly. Then the best riders have a finals that’s usually 5 laps and here only position counts, but it’s not easy making it to the finals.

Depending on which track we are at the fastest riders have an expected lap time from 30-60 seconds, so it’s shorter and medium length tracks mostly. Comparable to kart times on a decent kart at the shorter tracks. Long track is much less accessible on an esk8 and only really exists in the US.

It’s not a lot of laps per heat, but trust me, on a skateboard it’s plenty tiring :sweat_smile: I can usually barely stand by the end of each heat.

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That’s quite a small window of ideal pressure to hit! With esk8 tires we usually just keep tweaking the pressure based off of feel how quickly the tire starts working. At the beginning of each race day we have about 2 hours of free track time where we can practice as much as we want. We use that time to tune in our turning characteristics for the track and pressures usually.

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I work in bar instead of PSI, but a baseline is ussualy 300 grams of increase from cold to hot.

Ergo, 0.550 bar cold, 0.850 hot. This equals to about 4psi of increase from conversion. If you want to be 100% accurate though, surface temperature is a better metric to determine if the compound is working in the correct manner (but that requires some sophisticated gear, as an infrared sensor is not really that accurate for this purpose).

Most race heats are 3 laps time trial.

This is very short to put karting tires in a working window. In this scenario, AL is deff the better material for the rims, and you probably need to start with what is considered to be “very high” tire pressures to get the tire working.

Keep in mind kart tires are designed to be progressively brought to temperature during a heat cycle (even agressive driving straight out of the gate is relatively progressive, under the assumption that you set off with low pressures). Starting with high pressures to chase correct opperating temps super fast will have degradation consequenses.

Only way to find out is to test, none the less :slight_smile:

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I defer to everything that @Simone_Perego says about the pressure. (thank Simone, very helpful/thoughtful!)

And while related, if you need your tires to come in that fast (it sounds like they essentially need be instantly warm for your purposes - in a kart race it would be expected to take a few laps to get fully warm), tire warmers are likely to be unmatchable.

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