This is for a film script I have written. I just want to get the details in the right ballpark.
What is the minimum HP a souped-up golf cart would need, to gain on and pass a 45HP dirt bike?
Let’s say the bike has a 10 second head start. What about a 5 second head start?
The surface is a grassy field.
Bonus question: what kind of modifications to the golf cart would be necessary?
Thanks.
It would be about power to weight really. A rough guide for a dirt bike and rider would give you probably 225 HP per ton if we take the 45HP figure for the dirt bike and assume an average weight rider.
A brief Google gave me the figures of 425Kg and 4HP for a golf buggy for weight and power. Not sure if that is average but that gives you a power to weight ratio of around 8 HP per ton again accounting for an average weight driver.
So to achieve the desired result all you need to do is increase the golf buggies power by about 30 times being as it has to outperform the dirt bike. That kind of result is obviously not going to happen with minor modifications. I doubt you could even do it with electrical power as the more powerful the motor the more battery power you need which means yet more weight. Of course money no object I would guess it could be done by someone. I would imagine you could stick a big V8 in there as a cheaper route but it’s tricky to see how it would then pass for a normal golf cart.
It seems like an awful lot of work for a very specific need. The idea someone would put that much effort into a fast golf cart just in case they ever need to chase a dirt bike in it seems somewhat unlikely.
Your typical electric powered golf-cart is going to have serious traction problems if you increase it’s power significantly, especially on a grass surface. Short of fitting it with a rocket, it’s not going to catch a dirt bike.
Here’s a video of a custom golf-cart that can allegedly do 80mph. The problem is, it looks nothing like a golf-cart, and no-one is going to look at it and say “that’s a golf cart”.
That is probably the way to go mechanically. A sports bike engine would get you to the sort of power levels you need. I would guess you could mask it’s looks a little better than that example as well though you could probably still need those sort of tires to give you any hope of having the traction levels required to put the power down on grass.
Masking the engine noise would be a problem. You could probably get it fairly quiet but I don’t see you ever getting it to the levels where it’s going to pass for an electric vehicle. Still maybe there are some non electric golf carts around. Maybe it does not have to be running before it start’s it’s chase.
Electric motors are only limited by the power you give them.
I was visiting a Secret Service buddy of mine in Maryland a while back. He showed me “Golf
Cart One”, and mentioned it was capable of “well over 60 mph”. The detail’s other carts were equally fast for obvious reasons.
They were all electric, but he declined to give me any more details!
For comparison, a Fisker uses a 400hp motor, a Volt uses about 225hp.
Gearing gets into the equation as well. By changing the number of teeth on the sprocket of my Harley, I can change the top speed easily. It may take me a little longer to get there but ----------
My numbers aren’t as pessimistic as glaeken’s. A 250cc dirt bike should weigh on the order of 250 lbs. Plus a 150lb rider and you’re looking at just under 9 lbs per hp.
A lightweight golf cart shouldn’t weigh much more than 500 lbs. Plus a 150hp driver and you’re only looking at about 75 horsepower to get to the same power to weight ratio.
As mentioned, the big problem is traction. Golf carts have wide wheels with very little tread so as not to ruin the grass. If the story permits, you may want to replace the golf cart with a UTV or side by side. It’s like a golf cart, but with better tires, suspension, and a much larger engine. They’re expensive, but the Ranger I linked to has 60hp. Still not dirt bike fast, but it wouldn’t take much in the way of modifications.
Bonus points if the “golf cart” driver is a bit of an unhinged redneck. Then you could explain his propensity for using a UTV instead of a more traditional golf cart, and you could have him install a nitrous system on it with a 35-shot. That’s entirely within the realm of reason and it would give the Ranger around 100hp. I don’t know if that would be entirely sufficient to catch a 250cc bike, but in most audiences’ minds, nitrous = rocketship.
The below is what I based the weight on.
http://www.golfbuggiesdirect.co.uk/style/2-seater-golf-buggies/e-z-go-rxv-electric-golf-car/
I know nothing about golf carts but that looks a fairly standard one to me. I would guess a lot of the weight is coming from batteries.
It does look from my calculations that something like a Hayabusa engine would probably give you enough power. It just would not pass for an electric vehicle when running. You could probably save a lot of weight going that route as well with dumping the batteries.
It sounds like from ducati’s post though it can be done with an electric motor. I would guess that was very much a money no object project though.
Ah, E-Z-Go’s website lists 635 lbs as the dry weight (no batteries), which is probably what I was seeing when looking at used carts. Curb weight with batteries is an extra 300 lbs. Gas-powered carts are probably closer to the dry weight.
EV motors and controllers turn up on ebay from time to time, like when fleets get rid of their electric Ford Rangers. But if a normal golf cart requires 300 lbs of batteries, I’d think a souped up one would be prohibitively heavy, or else it’d have to give up a lot of range. Sport bike power would be the way to go.
That could very easily be constructed to look more like a golf cart, except for that rear wheel extending thingy. I guess it’s necessary to stop it from flipping? If so, how fast could this thing realistically go without that device?
It’s a wheelie bar. Based on the height and the video description, I’d say it’s only there to prevent the thing from flipping when climbing sand dunes, and isn’t necessary when accelerating on flat ground.
You doubt you could do it? Are you not familiar with the car Tesla?
Just take a Tesla and put a golf cart body around it. Done.
or Killacycle?
Thanks!
A Tesla is a lot bigger than a Golf cart though. I know from a power point of view it’s no issue getting the required power out of an electric motor I just think the battery requirements might be a killer on the weight side.
From Ducati’s post though it certainly sounds like it’s been done.
Killacycle is not.
The Roadster is actually pretty small, wheel base is under 8 feet. There was one next to me on the freeway and I was surprised at how small it was.
Thanks so much for taking a stab at this!
steronz, the UTV suggestion sounds good.
It is supposed to be some campus security guards chasing the protagonists, who are riding the dirt bikes.
I know there are other alternate vehicles that security guards and police drive around, so I will do more research. The UTVs look like something the campus security guards might drive. Nitrous might be a bit much though. 
The movie does not have to be totally realistic, I just wanted to try to get close.
Replace golf cart with 4X4 Gator. Reduce size of dirtbike engine. Create surface traction issues - wet grass, sand, pine needles, water, etc. that would give a 4WD an advantage in a chase = Plausible.
Put the protagonist on a skateboard and the security guy on a Segway