Forks, rake and trail…?
Carlos Fandango –Forks, the rake and trail….what is right?
- This discussion has taken place amongst many buggy builders over the years as to what works and what doesn’t.
We all know if the forks are too steep or upright, your forks will end up with the shopping trolley effect, and if the make the
- forks too shallow like chopper forks, the buggy to run smooth on a run but in a turn, the front wheel will struggle to turn and cut in
- In recent years I have noticed on many new buggies and certainly a few of the race buggies that are used today, that the rake and trail is getting more and more shallow, which has surprised me, as to why they have been built like this, yes the will run straight, and take your feet off the pegs and it will still run straight, but the shallower rake and longer trail will not turn as efficiently.
- I have pretty much built most of my buggies with a 65/25 degree rake, and with a bigfoot wheel, this results in a trail of around 80-100mm. Adding off set yokes to the forks adds further trail if the rake has been kept the same….this rake and trails offers quite a neutral light steering.
KiteBuggy BagMan – good question, why does this work so well , when people see it they are skeptical, however once they have had a go the skepticism vanishes . i can never get my head round rake and trail LINK
Dimitri Melnik – ?45* and about 8cm seems to be a good compromise between high speed stability and turn radius.
- Wayne Carkeek – yes but your trail is just the same as a more conventional fork , with uber rake . motorbikes esp sports bikes all hover around the same trail and rake now , there seems to be only one right answer for them . and buggies arent much different in wheel base rake or trail .
Ken Shaw – I’m trackin’ on this because I’m trying to decide how I want to set up the front of my next four wheeler. For my purposes, there is much to consider with King Pin inclination, tire contact patch and scrub radius but my biggest question is why I can run as little as 3 degrees of caster and still maintain stability at speed ? Perhaps at 80mph+ that might be a different matter…
Wayne Carkeek – look at a gokart chassis , not so much a quad bike unless you are running off road clearances and big foots then look hard at that . if you start at the dims of a well sorted gokart you cant go wrong , trail will be altered by the wheel diameter and with 3 degrees you will likely have a major “flappy castor” tea trolley issue at a certain speed , say 30 kmph it will go nuts (tank slapper) and try to break your ankles . I love 4 wheeler concept post up some pics as you go Ken
- Steven Van Nguyen – I’ve seen alot of strange fork designs and my conclusion is that most builders out there don’t understand how rake and trail is related.
- This is how I like to remember the rules for rake or trail. First pick a rake for your turning requirements.
- Small rake angle , lets say 20 degrees, allows easy turning at LOW speed so will wobble at high speed. Stunt buggies = small rake angle.
- High speed buggies , less turning, large rake angle. Rake angle doesn’t make a buggy more stable. It just happens that the larger you make your rake, the larger the trail becomes if you keep your front axle in the same position relative to your steering line ( imaginary line to ground).
- The trail is what gives you leverage to auto correct, which means, longer trail, more stability.
- So when you increase your rake, your trail will automatically increase, therefore you have to offset your front axle forward to reduce trail to reduce the leverage which makes your buggy less stable and easier to steer from a straight line.
- So I always pick a rake around 26 to 28 degrees and then move the axle back or forward , depending on the tire size to maintain a trail of 3 inches or around 80mm.
Wayne Carkeek – ?… and different trail required for different diameter wheels , that is important to note
Steven Van Nguyen – wayne .. yes you are correct .. you have to adjust base on the amount of grip of the tire which is size and materal / design dependent!! oh.. one more thing .. I’ve design the trail to match the type of kite they are flying too.. whether it pulls more sideway or forward to edge of window. The tow point also affects your rake and trail too. That’s why blokarts have such huge rake angles.
- Chris Brown – I thought one of the key things, more than trail was the position of the axle (fore and aft) relative to the steering axis. With the axle in front of the steering axis the act of steering has to lift the front end of the buggy (assuming some angle of rake) therefore the weight of the buggy naturally keeps the sttering pointing forward. Or is this an overly simplified view?
- Steven Van Nguyen – Chris, you just explained “trail”. You adjust trail by moving your front axle relative to your steering axis.
- Chris Brown – isnt trail affected by the size of the wheel, the position of the contact patch relative to the stearing axis, not the axle relative to the stearing axis.