tyre sizes

[Emily]

hi,
i'm in a school team which design, manufacture and race miniture f1 cars using CAD/CAM programs in an international competetion. We are designing are car and wheels and I'm wondering whether anyone could give me some advise on which is better big or small diameter wheels and thick or thin tyres????

Emily

[West]

Well, Mini Baja may be different, but we used thin tires to offset our weak engine (10 hp lawnmower) and heavy weight.

[RH1300S]

I would take the view if you need grip to go fast, then wider tyres would be useful. Does the track have corners or does the car need to be able to accelerate or stop hard - (assuming that the engine drives the wheels and is not a jet/rocket motor)?

If none of the above, probably narrower tyres will reduce rolling resistance and give you more top speed.

As for diameter, truthfully - I don't know. But I would assume that a smaller diameter wheel will have less drag (if it's too small it has to turn faster and might create more friction which would also slow the car down).

[Emily]

thanks guys.

The car is made from balsa wood and is powered by a CO2 cartridge. The cars are very small approx. 200mm in length and the track is a staright drag stripe approx. 20m long.

Cheers

Em

[Venom]

thanks guys.

The car is made from balsa wood and is powered by a CO2 cartridge. The cars are very small approx. 200mm in length and the track is a staright drag stripe approx. 20m long.

Cheers

Em

I would prefer narrow tires with bigger diameter because it will reduce friction and bigger diamater will require less rpm of engine output to preduce more spin. However, I don't understand how CO2 catridges work, I assume the power is not transfered via tires so NOT too sure about that Despite that, I'd still go for bigger dimameter and very narrow tires becuse it will reduce friction.

Let us know who you get on

[DaveKillens]

The wider the tire, the more drag from aero and rolling resistance. And the larger the diameter, the more mass to the wheeel, which contributes to inertia. It takes more power to get them rolling. But if a wheel is too small in diameter, it has trouble when it encounters any surface irregularities.
If the track surface is very smooth and hard, my design would look like small, round razor blades.
I suggest you start with that concept, and add width to cope with road surface hardness (soft wood versus marble). And add diameter to deal with irregularities.
If the CO2 cartridge expends itself long before the end of the run, you may need wheel inertia working for you, to maintain speed. So wheel rotating mass depends on whether the cartridge is still producing forward thrust before or after the finish line. For example, if the cartidge expends itself after 0.2 seconds, yet it takes 1.2 seconds to do the run, then wheel inertia is important to have, and I would have larger diameter, heavy mass wheeels.

[mini696]

For C02 racers you want the thinnest tyres possible. The only problem you then need to overcome is their tendancy to wobble, and make the car veer offtrack.

[flynfrog]

The wider the tire, the more drag from aero and rolling resistance. And the larger the diameter, the more mass to the wheeel, which contributes to inertia. It takes more power to get them rolling. But if a wheel is too small in diameter, it has trouble when it encounters any surface irregularities.
If the track surface is very smooth and hard, my design would look like small, round razor blades.
I suggest you start with that concept, and add width to cope with road surface hardness (soft wood versus marble). And add diameter to deal with irregularities.
If the CO2 cartridge expends itself long before the end of the run, you may need wheel inertia working for you, to maintain speed. So wheel rotating mass depends on whether the cartridge is still producing forward thrust before or after the finish line. For example, if the cartidge expends itself after 0.2 seconds, yet it takes 1.2 seconds to do the run, then wheel inertia is important to have, and I would have larger diameter, heavy mass wheeels.

the heavier wheels take more energy to acclerate so it would not help at the end of the track

[mini696]

The wider the tire, the more drag from aero and rolling resistance. And the larger the diameter, the more mass to the wheeel, which contributes to inertia. It takes more power to get them rolling. But if a wheel is too small in diameter, it has trouble when it encounters any surface irregularities.
If the track surface is very smooth and hard, my design would look like small, round razor blades.
I suggest you start with that concept, and add width to cope with road surface hardness (soft wood versus marble). And add diameter to deal with irregularities.
If the CO2 cartridge expends itself long before the end of the run, you may need wheel inertia working for you, to maintain speed. So wheel rotating mass depends on whether the cartridge is still producing forward thrust before or after the finish line. For example, if the cartidge expends itself after 0.2 seconds, yet it takes 1.2 seconds to do the run, then wheel inertia is important to have, and I would have larger diameter, heavy mass wheeels.

the heavier wheels take more energy to acclerate so it would not help at the end of the track

The heavier wheels would only really help if it were a distance competition.

[Reca]

The first time I heard about this competition I made an approximate calculation of how much time the thrust lasts based on mass contained, initial pressure and nozzle geometry but then I simply forgot to post it... IIRC the result was less than 1 ms, something like 0.7 ms or thereabout. Anyway the exact figure is pointless, it’s an absolutely negligible quantity compared with the length of the run.