RAKE & TRAIL EXPLAINED...

'To the point' advice on what fits what, parts interchangeability and simple solutions to common problems...
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Prof
Founder, Choppers Australia
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RAKE & TRAIL EXPLAINED...

Post by Prof » Fri Jul 04, 2014 10:01 pm

For diagrams explaining rake and trail, go to our website "Definitions" page. http://www.choppersaustralia.com/defini ... uipment...

Rake...

Standard rake on most bikes is around 30 degrees. A bike with stock rake is designed to be light handling and quick into corners around town. The downside if you like relaxed cruising is it needs to be continuously 'steered'. A large number of stock bikes including surprisingly, many current model cruisers will soon pick up a wobble in the front end if you take both hands off the bars (ooh sorry Mr Plod... we're not allowed to do that!) indicating they are not stable at speed. Stock bikes tend to be much more tiring to ride than choppers on the open road. They also do not do well with irregularities, potholes, bricks and other road debris in comparison to a chopper.

Raked front ends... 40 degree rake and 6' extended telescopics with a 19" front wheel should be just within the Ridikuluz550Rool. This will give you a very stable, safe and easy cruising bike. At walking pace the steering feels heavy (wheel wants to flop), but it is quite controllable. It is not noticeable at anything over jogging pace. On the highway it feels like it is 'on rails'. I like to say getting on my shovel with the above dimensions is like getting into a taxi. You tell it where you want to go and sit back and enjoy the ride!

An excellent compromise is 35 degree rake and 4" over front end. Bike will stay fairly level, be light handling at low speed and noticeably more stable on the open road. this set u will be well within the R550R.

45 degree rake will require 8"-10" extended forks. The steering will be heavy as you come to a stop, but beautifully stable on the open road. Over 40 degrees telescopic forks tend to get 'sticky' and don't respond to normal road roughness as well. Over 40 degrees rake, springer or girder forks are recommended. Their action is not affected by rake.

The more rake and therefore the greater angle of the forks, the better telescopics respond to pot holes, kerbing big bumps etc They compress rather than try to fold back or twist to the side as on a stock rake... a safety factor I think. Increased rake and trail improves steering in the dirt and sand.

Girders and springers move the axle forwards a couple of inches. To keep with in the R550R you can't go over 4" and about 33 degree rake. Most modern springers work well even at speed. Early ones (without extra set of springs to counter harmonic balance) could 'pogo' which usually meant a painful or terminal 'highside'.

Achieving rake... Dropping the rear end of a sports bike can add 3-5 degrees to your rake. Cutting the neck or lengthening down tubes (better way) can be used to increase rake. RTA requires engineering and inspection for frame mods. Raked cups provide a way of adding 3 degrees or rake without frame mods and inspections.

Raking by lengthening down tubes (see examples in The Chopper Shed forum) allows longer forks and more rake while observing R550R. It is also a safer and surer way of raking. If done according to instructions alignment can be achieved with only a ruler!

3 degree raked steering head bearing cups... These replace stock HD (and some other popular brands) bearing cups They can be used to increase rake by 3 degrees or reduce rake by 3 degrees depending which way you install them. Some enterprising chopper builders use them in reverse to get through RTA and then put them back in the way they are meant to go.

Raked triple trees... are a definite no/no on any front end that is legal in Australia. They drastically reduce trail ... the whole point of rake in the first place. They reduce trail and increase instability. Want to set yourself up for a highside? Go with these and don't let anyone tell you different. Raked triple trees (or extended rockers on a springer are only beneficial when rake trail is past 10". They are used to reduce wheel flop and heavy low speed steering on big rakes. Some bike owners with raked trees have told me they handle well, but are talking about lightness of steering rather than safe highway riding.

21" front wheel... Replacing a 19" front wheel with a 21 incher will increase wheel flop and effectively move axle forwards (Beware R550R). You will note that classic choppers (see CA website Galleries) often had 18" or even 17" front wheels. this was specifically to reduce low speed heaviness and wheel flop.

Steering lock... raking your steering head increases wheel base and means your wheel will tilt more as you turn it. Turning circle increases as a result. Look at classic choppers and you will see that their tanks are set further back form the steering head than a stock bike. This was done to allow extra steering lock to be built in by modifying fork stops. If you are going to extend forks and rake the neck, increase your lock as much as you can. This will be particularly helpful when manoeuvring your chopper between cars or around your workshop and yard.

Trail...

Trail (see Definitions page) is basically the distance of your axle ahead of the steering axis (think of shopping trolley wheels).

The more trail the more resistant your wheel is to a turning force. The obvious example being a stone or brick on the road. The wheel will both resist being turned also and return to its original direction quicker and more forcefully, so you will more likely stay on the bike. Excessive trail can cause the wheel to over correct, but this is past what any Aussies will ever be able to do.

Rake & approximate trail
28 degree trail (typical stock bike) and 19" wheel =2½" trail
35 degree rake (telescopics), 19" wheel = 6" trail
35 degree rake (springer), 19" wheel = 4" trail
40 degree rake (teles), 19" wheel = 8" trail
45 degree rake (teles), 19" wheel = 10" trail

Telescopic forks all have a forward offset. This varies bike to bike but usually between 50mm and 60mm. This affects the trail figures above but only by 10mm max Trail bikes usually have less offset which increases trail over a stock road bike for better handling in the sand and dirt. Springers do not have forwards offset, but axle is moved well forwards by the rocker length.


Image
40 degree rake, 19" wheel = 8" trail

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45 degree rake 19" wheel = 10" trail

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35 degree rake springer, 19" wheel = 4" trail
Chopit'nrideit... Prof

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