So I was looking at doing a backyard kart track, but realized that the maintenance for such a thing would be pretty extreme compared for the time I am interested in doing such a task. Also, I realized what I really wanted was to be able to replicate the track I created with Honda Odyssey/FL350 (which I don’t have anymore, and was my first attempt at solving this itch).
That track was “created” simply by driving the FL350 across it enough times. But to do that you need a vehicle that has more than an inch of clearance and can go over at least some semi rough terrain (no jumps or anything like that, just basically a sprint track carved out of terra firma). This seems like it should be fairly easy to find, but believe me there’s a real gap in the consumer market in terms of 4 wheel dirt vehicles that don’t cost $40,000 and $5,000 ones that wouldn’t stand up to hard driving for longer than half a day. It’s not an underserved segment of the market, it’s not really served at all…
So, after a lot of dead ends and a lot of investigative looking, I finally came across evidence that some people have managed to make capable offroad sprint karts, which essentially are just sprint karts with 5" wide x 6" diameter rims and 145/70-6 tires (which after even more looking, as far as I can tell are literally the only ‘large-size’ choices there are using common front and rear hubs).
I haven’t put it together yet but I have a spare OTK frame and four PRD Fireballs ready and willing to go. The following is the stuff I currently planning to purchase.
The tires and wheels you show are just normal 5" diameter sprint kart wheel, what tires they are using i’m not sure. Another option if you want to use 6" diameter wheels is to get some that are intended for superkarts as they should be metric bolt pattern.
I’m actually pretty interested, within limits, to find some 6" metric-pattern wheels, but a quick search and apparently I don’t even know how to find superkart wheels really, and the few I saw were too spendy for this project. Even more pressing is that the number of offroad tire sizes for 6" rims only offers one tire size (145/70-6) that I have been able to find so far. (so even if I can source some affordable 6" metric wheels, unless the width is 5" I don’t currently know of an offroad tire that I can mount to them)
That said I won’t be upset if I just end up with the parts I listed since I know they can get me burning gas and getting sideways.
I know guys who have old beater karts with rain tires on and clone motors they rip around in their own dirt backyard track with and other than the usual shenanigans of crashing into each other on purpose, the karts tend to hold up okay for that level of abuse.
Nice. If my property was a little smoother I could get away with that, but there are variety of things randomly scattered about that are just enough of an obstacle to cause some major problems if you nail them.
So sitting on ideas sometimes pays off. After thinking about things and searching around I discovered that putting significantly taller tires/wheels on a kart will drastically affect it’s gear ratio (increase of theoretical top speed at the expense of loss of acceleration). For some idea of the effect, to keep the gear ratio of a kart that has an 11t front sprocket and 80t rear sprocket, when switching to a 14" inch tire, they would now need to run 102 tooth sprocket on the back (!). Going to a 10 tooth on the front would drop another 7-8 on the back, but a 94 sprocket isn’t anymore practical.
Not wanting to abandon the idea altogether, the choices are then:
figure out how to install and configure a jackshaft , which is getting a little more obscure-and-undocumented-DYI than I was hoping for with this.
figure out how to make something approaching normal kart tires/wheels work. Currently leaning in the direction.
max out the ride height of the kart frame using standard means (maybe worth 1/2")
install some treaded 12" circumference Burris tires on rear and 11" circumference tires on front (adding 1" of circumference to each end of the kart, which will result in a 1/2" increase in ride height - unfortunately these tires will still require 6" rims and adapters)
with the two changes above, should be an increase of an inch or total ground clearance all around
Still in the, ahem, kicking tires phases of things.
I just checked those out. Cool idea, kinda similar to a jackshaft in a way, but also the same issue for me - almost all the ones I can find are meant for clone type of 4 strokes. Because I have them just sitting around I’m trying to put my PRD Fireballs to work, so they pickings get really slim and kinda of spendy.
Parts ordered. After walking the property I think I can make the larger than normal treaded Burris Tires, plus ride height changes work just fine in terms of ground clearance. Also, I won’t need the American-to-metric wheel adapters, because I can just use normal kart rims on front, and I found some metric-pattern 6" rims for the rears. Next step, getting the kart assembled as it’s stripped down to the bare frame at the moment.
Ah, sorry I speed read the topic and saw a four stroke engine, figured you were doing an off road conversion with a four stroke.
It’s a bit late now, but Heidenau ice tires are 11.5” tall and fit on “regular” front kart racing rims that are 120/130mm wide. Essentially giving you an additional 1/2” of ground clearance.
They do blow the budget part of things out of the water though (big time), and the gear ratio/sprocket clearance issue would remain as you would probably use a larger sprocket on the axle to compensate.
Lastly, you’d be surprised how much you can clean up a dirt path with a simple drag made of angle iron.
+1 on the drag harrow - I totally forgot about those. When I had my FL350 didn’t even need to worry about it because that thing just brapped over anything in the way.
This is awesome! My kid and I were watching a Grind Hard Plumbing vid on the YouTubes the other day and they were off roading an old CRG they electric swapped. Looked like a ton of fun. They did mention that it was a pretty brutal ride and landings were hard on the back… You might come up with some shock seat struts or something?
You are right though, there is nothing out there for off roading/ yard karting that isn’t either absolute junk or like a mini trophy truck that’s priced accordingly. Would be neat to have something like this, with decent running gear that kinda does kart things.
Just sat down in the office and can’t stand the thought of work, so peeked into the tire option rabbit hole and these caught my eye… The title says lawn and garden, but the description says, “off-road sporting vehicles”. They would look mean and might fit the rims you got.
Edit: Somehow glossed over your gearing issue post with taller tires… You might be able to find a used jackshaft setup in the dirt oval kart world. The UAS/unlimited guys use all kinds of 2-strokes and jackshaft configs, I’ve seen them pop up for sale from time to time.
@C-Hogue070 - you bring up a good point to consider for anyone looking at a sprint kart chassis to get offroad. As anyone whose ever jumped a curb on a regular kart track could tell you, it’s not going to be a pleasant solution for getting ‘air’ or riding washboard whoops. But the extent that this is true could definitely vary based on the final tire selection.
The ones you list, or the 145/70-6 tires which are very low psi and flex a lot will definitely soften the ride considerably and open things up to riding more over rougher areas. (but as mentioned above, have a plan to be sure that you can end up with a gear ratio that is workable, because the taller tires can really make that a challenge)
On the other hand, the wheels that I’m going with are actual kart tires (just very oversized compared to normal spring kart tires, and treaded), and will not flex nearly as much as the much larger 13/14 inch offroad tires. I know this going into it though and plan on a) initially slightly groom the track (e.g., drag it with a harrow to take the edge off any substantial irregularities) and b) I’m planning on the kart being capable of going over ‘rough’ ground, but not jumps of any type or even whoops. The goal for my track will to be like an asphalt sprint track, just in dirt.
So, the kart is together and I’ve taken it for it first couple rides. Fairly immediately, a couple things became apparent.
Picking the wettest and coldest season of the year to do this isn’t exactly helpful. The soil here is itself wet and covered with wet leaves and grass.
Though the ground clearance itself is enough, the lack of suspension and thick top layer of wet slippery stuff dictates using a harrow, which thankfully just arrived, to smooth things out as well as to take the top layers of leaves and grass away. I just took my first passes with it today and haven’t gotten a chance to finish the job or ride the results yet. Unfortunately, there are several days of rain predicted, so it may be slim pickings for me in terms of opportunities in the near future.
Plan for judicious use of zip ties and tape to secure your coil and it wires. The rough riding beats the heck of it and it has shown itself quickly to be a weak link. This happens to coils on paved sprint tracks too, but the volume really gets turned up off pavement apparently.
The results of a couple test passes with the harrow in the foreground (with Lavender sniffing the harrow for good measure). You can see all the leaves and mulch the is being turned up (not a recipe for great traction!).
To start off I’m just making a little oval, but I have a lot of areas I can expand into once I’m satisfied with the initial grooming efforts and get any other kinks worked out.
