We’re often asked about how bikes with a long wheelbase and wide tyre like Storm steer, and the answers can be somewhat surprising. Legendary chassis builder Jim “Puppet” DiTullio wrote the following piece a good while ago for the Stripbike.com website, but although the page no longer exists and Jim is no longer with us these words give a good description of what’s going on in a conventional Top Fuel / Funnybike design. I hope Gary of Stripbike doesn’t mind me reposting them. I’ll post our own thoughts on the matter later.
This may sound like a weird topic but it has been my experience that not many people even some pros understand how a big tire bike works. This also applies to smaller tires to a lesser degree.
We have all seen a new rider going down the track on a big tire bike and the bike starts heading to the centerline, the rider shuts it off and starts leaning the bike over till sparks are coming off the frame but it is still heading for the cones. If he’s lucky he will not hit any but usually they take a few out…You have no idea how many lower spoilers I have made do to cone damage…
In fig. 1…you will notice the tire is straight up and down and the contact patch is the full width of the tire. This is the way the tire works the best, as soon as you lean the bike ( fig-2)
you are asking for big trouble. When the bike is leaned over a thing called reverse steer happens, in other words, when you lean the bike to the right, it wants to go to the left.
In Fig-3.. I have drawn a top view of what happens when you lean a bike to the right. As you lean the bike over to the right, the contact patch moves out to the edge of the tire, driving the bike to the left…
I always tell the new riders to go and ride a one of those off road 3 wheelers because a big tire drag bike handles much the same way…You have to lean them to the right to make a left turn. When you make a left turn, What you are actually doing is pushing down with your right foot ( to load the right tire) and leaning your upper body to the left to control how high the left tire comes up. A big tire drag bike is like a three wheeler with narrow rear wheels…..
You actually steer a bike with your feet (If you use the footpegs)…When it is on the bar going down the track and you want it to go left, you apply pressure to the right footpeg which tips the chassis slightly to the right loading the right side of the tire which drives the bike to the left..A the same time you lean your upper body to the left so it doesn’t tip to far..
This brings up the subject of footpeg location. If you mount the pegs high as in fig. 4,
not much happens when you push on the footpeg. the best place to mount the pegs is to mount them as low as possible as in fig. 5 then when you push on them it is easier to tip the chassis and move the bike around…Whether you use the pegs or not ( Harley riders) this is basically how a chassis works..
In summary…It is best to ride a big tire bike under full power and on the bar, keep the chassis straight up and down and use the footpegs…If you want to experience how hard these bikes are to ride slow ask someone if you can ride it while being towed back to the pits…Sam Wills told me one time that these are not motorcycles, they are Uni cycles and he thought it would be easier to ride one if you had never ridden a bike before. That way you would have no bad habits (leaning the bike) to overcome…..