Landspeed Racing Question!

"BJL" (simplifyandaddlightness) 01/17/2018 at 17:26 • Filed to: Gofast

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Been pondering this one lately so I figured I’d ask!

Mainly just focusing on belly tankers in my mind. I am saying this because the tires are out in the open and therefore have the largest effect.

So, why are land speed car tires large and not small? I figure that smaller tires have less rolling resistance, and more aerodynamic (less un-aerodynamic?). I was then considering why. I came up with the only reason being that the contact patch between tire and earth must be larger due to circumference differences. Traction is important of course as you have to plow through the air more at high speeds. So- think go-kart tires.

Then, I must think the only reason why not is because of tire compounds at high rpm. However, racers like mikey Thompson went 450+ on their tires, so assuming similar compounds are available, going 300 is possible if using a tire smaller than the type those cars use.

Anyone know the actual reason for why larger tires were always/ are always used?

farscythe - makin da cawfee! > BJL 01/17/2018 at 17:42

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gonna pull an explanation out of me arse here (based largely on bicycles)

but they’re large and narrow because a bigger wheel can achieve more speed than a small one on the same gear

more distance covered per rotation... (and narrow for rolling resistance)

but as said.. just pulling that out of me arse... god knows if its right

benjrblant > BJL 01/17/2018 at 17:51

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Speculation: There are some speed record applications that use skinny tires such as pedal power. I think the skinny tire offers less resistance at these speeds but I’d guess that between friction and air resistance, the wider section tire might actually be needed for traction. 80mph wind doesn’t create near the resistance of 450mph of wind.

I’d also guess that the surface has a lot to do with it. Downforces created at 450mph could very well press tiny tires into the surface, adding more resistance.

Finally, I’d also guess that this has something with the tire’s ability to dissipate heat. Lots of heat in a small area = melting. Lots of heat over a larger area might fare better.

Mini Guy- Now has a 4Runner > BJL 01/17/2018 at 17:55

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Land speed record question. When’s the bloody bloodhound going to make its bloody land speed record run

Textured Soy Protein > BJL 01/17/2018 at 18:12

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I don’t know if there really is a performance-related reason for them or if they were more making use of the stuff that was available to them. More modern land speed cars are like this:

BJL > farscythe - makin da cawfee! 01/17/2018 at 18:26

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You’re correct, but rear end gears an transmission gears of properly chosen would make both ‘work’

lone_liberal > BJL 01/17/2018 at 19:13

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The ones pictured were just normal tires and wheels back in the day, but I’d guess that thin tires present less frontal area and rolling resistance. Kind of like pizza cutters on a drag car but to a lesser extent. I don’t think traction is a huge consideration since it’s not from a standing start and no corners are involved. All just a guess, though.

TheTurbochargedSquirrel > BJL 01/17/2018 at 19:47

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Smaller tires mean the tire has to do more rpm to reach the same speed which means you need stronger tires, bearings capable of more speed, etc.

gmporschenut also a fan of hondas > BJL 01/17/2018 at 20:06

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For the above image, as token liberal said they jsut used normal tires.

with little to no supsension hitting a bump at 150mph will really ruin your day.

Pending you don’t gear out, what will ultimatly prevent you from reaching a higher speed is the Force of the engine - rolling resistance = wind resistance.

https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/

In order to have a similar total speed, a smaller diameter tire would require, higher gearing in the transmission to make up for it. Your net force to the ground would be similar.

And along with turbocharged squirrel yo would be putting your drivetrain parts under much greater stress. Also the more gearing you put in the higher the drivetrain power losses would be.  

You can tell a Finn but you can't tell him much > Textured Soy Protein 01/18/2018 at 08:31

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The wheels and tires pictured there are runway wheels. The tires were originally used on the English Electric Lightning fighter. They only use those for “low speed” testing on a runway. 

For the Bloodhound record runs they are using solid aluminum alloy wheels. The rubber tires would come apart at the speeds they are aiming for.

http://www.bloodhoundssc.com/project/car/wheels/desert-wheels

You can tell a Finn but you can't tell him much > Mini Guy- Now has a 4Runner 01/18/2018 at 08:32

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They are planning a 500 mph test for 2018.

http://www.bloodhoundssc.com/project

You can tell a Finn but you can't tell him much > BJL 01/18/2018 at 09:24

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The belly tankers were pretty much running whatever wheels and tires were handy at the time. The reason LSR cars tend to run larger diameter skinny tires is that those match the application pretty well. The tall skinny tire gives a contact patch that is long in the direction of travel, which may allow for better acceleration and braking. Since they are travelling in a straight line they don’t need a wide tire to support cornering loads. As an added bonus, especially on fully bodied cars, the narrower tire ends up adding less frontal area, so a reduction in wind resistance. Since rolling resistance for a pneumatic tire is basically independent of tire diameter there isn’t any downside to running a tall, skinny tire on an LSR car.

Mini Guy- Now has a 4Runner > You can tell a Finn but you can't tell him much 01/18/2018 at 10:50

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Which means 2019, then 2020