gravity racing, soapbox racers, gravity cars, gravity bikes, skate luge


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minimum tyre track width

Just wondering what everyone’s thoughts are on minimum track width for serious gravity racers.

Obviously everything is a compromise between aero frontal area/CoD and cornering stability/weight transfer.

My current racing roofbox’s track width is around 1100mm and is very stable but I reckon it’s excessive and therefore requires outboard wheels. However, to the other extreme, a 600mm track width would allow you to design a body with inboard wheels and the associated decrease in aero drag.

I suppose it depends on the course- twisty or flat out speed.

What’s the general consensus? What’s too narrow?


also depends on the event rules i know Worlaby states a minimum of 700mm. might be worth just checking as many event regulations as possible before doing anything drastic

Okay, what if there were no rules! Just the fastest straight line speed, kinda like Les Eboulements? Theoretically, what track width produces issues with stability?

i'd say its all down to the road your travelling.   Look at the atomic scalpel and grey ghost those machines are both built for Les Eboulements  (   both significantly narrower than there predecessors but with enough stability to negotiate that monster bottom turn  running small wide wheels with an extremely low centre of gravity

As an extreme case, even a trike can be stable. I would however move the center of gravity backwards and as low as possible, and the ratio of the rear track width to the wheelbase shouldn't be too small.

The grey ghost ( I hate that name) is running 26 in. on 53 in. wheelbase. The yellow car that broke the 100 mph barrier in 2016 was a road race car that was very stable and handled the most extreme twisty and high speed roads, the Eastern Sierras in California at 29 in. on 53 in. wheelbase. The Bodrodz cars are deceptive because the bodies make them look like they have a much longer wheelbase.

Donnie- how did the silver spectre (see, I fixed the name for you!) handle with the 26” track width?

Unstable/squirrelly at all?   The "silver spectre" sounds more badazz but I considered it the "primered pig" The car will be back to the trade mark yellow in 2019. As far as stability the car hunted a little at the bottom mostly I think from not having the weight bias correct (the car was about 45 lbs. light ) and I switched from steering wheel to handlebar steering which I had no seat time with prior to the event. I would be comfortable taking the car down any road with the narrow track.