Monday 6 February 2023

Sidecar steering, wobble, trail and leading links

 One of the most misunderstood areas surrounding sidecars is the steering.

The main issues that people are looking to solve are steering wobble and heavy steering. 

Before looking at how to solve these issues, it’s important to understand what is going on at the front wheel and how it steers. 

Your standard solo motorcycle has geometry that is set by the manufacturer to ensure that it steers in a stable fashion. This is known as trail. The trail figure is set to ensure that the bike steers in a straight line if it receives no inputs from the rider. This is required on a solo to provide stability at speed. We’ve all seen video or witnessed a riderless bike carrying on in a straight line, bolt upright, until it either slows down and falls over or hits another object.
Trail is what makes this happen.
You probably know that sports and racing bikes are built with less trail than other types of motorcycles, this is done to provide fast steering at high speeds. But it comes at a cost and that cost is a lack of stability. Often these are fitted with steering dampers to remove steering wobble. But we are not riding race bikes. Sidecars are different.

So in essence, trail keeps the steering in a straight line and makes it harder to turn the steering at an angle. You know that at higher speeds, more steering effort is required to turn the bike sharply. 

This is not helpful for a sidecar, since the only way to steer a sidecar outfit, is to turn the steering. 

Many people confuse the terms rake and trail and speak about raked forks and yokes, when they mean reduced trail. 

So if the trail figure is very high, it can be helpful to reduce it with some method, in order to provide a reduction in steering effort.

However, like everything with sidecars, there is a compromise to be reached. Because if we reduce the trail too much, we also reduce stability in a straight line. This is not helpful for a few reasons.
Firstly, it can make the sidecar difficult to control as there is very little feel in the steering and it is difficult to make accurate turns without over steering, which can also induce sidecar lift during turns towards the sidecar more easily. 

Secondly, the reduction in stability induces front wheel wobble.

A very common situation then occurs, whereby trail is reduced dramatically, giving very light steering but also a high degree of instability causing wheel wobble which is then hidden by fitting a steering damper.
A steering damper does not remove the steering wobble, it simply masks it. The wheel is still trying to wobble, but is prevented from doing so by the damper. 

It is better to provide a trail figure that reduces the steering effort to a reasonable level whilst retaining stability without the need for a damper. 

Many people suggest that fitting leading link forks will cure steering wobble. This is most certainly untrue. The primary reason that most people fit leading links is to lighten the steering, which is achieved through a lower trail figure. 

A lower trail figure will always promote the likelihood of more steering wobble.

However this is where things become less clear, since there are other factors which cause steering wobble. One of the main factors is tyre choice and pressure.
When leading links are fitted, most often the choice of a different tyre and pressure is made.
In many cases, the front tyre alone can solve steering wobble. 

So after fitting leading links and a new tyre, the steering wobble has gone and the leading links are claimed as being the solution. Whereas in fact, it may well have been the tyre that solved the problem. Or perhaps the steering head bearings are replaced at the same time as the new forks, also a prime factor in steering wobble. 

These are the reasons why people spread the idea that leading links solve steering wobble, it’s understandable, but inaccurate information. 

Let’s imagine that an outfit had minor steering wobble with standard forks, due to already having a relatively low trail figure. 
Leading links were made with the same trail figure as the standard front forks. The same wheel and tyre is used. The steering wobble might improve in this situation.
Leading link forks tend to be more structurally rigid than telescopic forks. This additional rigidity can remove some of the tendency towards steering wobble. The same effect could be achieved by fitting a sturdy fork brace to the telescopic forks.
A combination of a more suitable tyre, running at a different pressure, with a fork brace on standard telescopic forks with heavier oil and good, well adjusted steering head bearings can produce an outfit that is easy to steer with no wobble. All at considerably less cost than leading link forks. 

Many people suggest a trail figure of around 60mm is ideal for sidecar outfits. In almost all cases this is too low. The steering will be extremely light of course but with almost no straight line stability. A damper will almost certainly be required to prevent wobble, making the steering heavier again to a degree. 

If the trail was set to somewhere in the 80 to 100mm range, the steering would be light, but with enough feel to retain good control and also reduce the likelihood of steering wobble and not require a damper. 

Many standard solos have a trail figure around 90mm. Very often ADV style bikes are in this area. 

Low speed steering wobble, if it is not violent, and the trail is not set too low, can usually be controlled by driving technique.
Keeping both hands on the handlebars, without gripping tightly, can often be enough to prevent it happening. Moreover, a positive driving style will prevent wobble which occurs at around 15 to 20mph. This is the speed range when most wobble occurs.
Pull away positively on the throttle and drive through this range and it’s likely the wobble will not begin.
This assumes that there is no wobble at all at any higher speeds which will be caused by some serious irregularity with the outfit, including loose fittings, worn wheel bearings, any movement in suspension swingarms, worn or loose steering head bearings and the sidecar is accurately set up. 

The slightly heavier steering provided by a medium amount of trail rather than a super low setting can be perfectly acceptable if the outfit is ridden using the sidecar steering effect.
By this we mean the steering effect provided by the sidecar under acceleration or deceleration.

In turns towards the sidecar, accelerating or braking only the sidecar, will cause the sidecar to pull the outfit around the turn.
In turns away from the sidecar, decelerating either by simply rolling off the throttle, changing down through the gears or braking the bike only (not applying the sidecar brake), will make the sidecar pull the outfit around the turn. 

This sidecar effect means that you need to provide far less steering effort to make turns. 

You may have noticed that if you try to accelerate whilst turning away from the sidecar, the steering effort required is much greater. That’s the sidecar effect working against you. 

The heavier that your sidecar is compared to the bike weight, the more exaggerated the sidecar effect will be. So for example with a passenger, it becomes far greater. 

It’s worth pointing out that there are other methods for reducing trail, than just leading link forks.
There are reduced trail yokes (triple trees), leading legs and hub center steering. 

On some bikes like BMW’s that have a Telelever front suspension, trail can be reduced easily with a custom made bracket. 

Trail can also be slightly modified just by lowering the front end by dropping the yokes (triple trees) down the fork legs. For many outfits that start with a relatively low standard trail figure, this can be enough. 

Finally, what you choose as a trail figure is up to you. Some will still go for super low trail figures. I have seen outfits with as little as 40mm of trail. But at least make a choice with all the information in front of you.
The difficulty being that you cannot know in advance exactly how you will like the new trail figure before you make the changes, although with leading link forks, it is possible to provide adjustable trail, which might be the key to getting it right for some who don’t have experience of driving sidecars with different levels of trail. 

If you want to learn more about how accurate total setup of your sidecar and bike can eliminate steering wobble and provide a better sidecar driving experience, read The Sidecar Guide and The Sidecar Technical Guide books. Available in print from Amazon or in Ebook format directly from our website at


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