[Redex]

Does your bike feel unstable at speed ?
The most common reason for this is too little pre load on the rear suspension. Under this condition the rear of the bike squats down on the suspension and weight is transferred to the rear wheel. Increasing spring pressure at the rear will raise the seat height and transfer weight to the front wheel increasing straight line stability.
If the instability increases carrying a pillion the most likely cause is rear spring adjustment. Try it !!!
A quick way to check the rear pre load is to sit further forward and move your body weight towards the front wheel. Instability reduced ? Yes !! Then increase rear spring pre load.
Sometimes you may need to reduce the front fork pre load if you can.
Adjusting the damping will have little to no effect.

Assuming everything mechanical is correct and changing pre load makes little difference, you probably need to change the tyres to a different pattern or brand.
However, first check the tyre manufacturers pressure for your bike, it probably differs from your owners manual. Especially on older bikes. The owners manual only gives the pressure for 1 or 2 patterns and brands that were fitted as OEM parts.

There is an endless list of faults that also cause instability of the front wheel. This adjustment is the easiest to try first.

After that, look at the tyres, pressure, balance, uneven wear, or wrong type !!!
Gets more complicated, worn head stock bearings, warped disc, binding brakes, low front fork oil, buckled wheel rim etc etc.

Regards Neil

[aargee]

In my humble opinion, when I feel my motorcycle shaky or unstable at speed, the very first thing I would do is fill in air in both the tires to 1 PSI more than manufacturer's recommendation.

This has not worked only once on my CBR when the front tire got punctured, otherwise this has worked nearly 100% of the time & not a very expensive affair.

[Redex]

Hi,
Whatever works for you. Personally I have never been able to feel any difference in pressures unless it is greater than 5psi. My experience is based on riding in the UK. Cruising at 120 to 130kph. High speed wobble is usually caused by incorrect balance front to rear. (Assuming there are no mechanical causes for the wobble). Tyre design, quality and age have a much greater effect on handling. Tyre pressures can increase up to about 5 psi when riding hard and fast. It only takes one ride sitting further forward on the seat to see if you need to increase the rear spring load.
I tried it on my Yamaha XT600e single 600 trail bike. Sitting forward made a noticeable difference so I increased the pre load. Still not perfect so I replaced front and rear tyres with Conti Trail Attack 2 tyres (designed for 90% on road use).
Now have the perfect combination in the wet and dry.
Bike is most comfortable at 120kph, it will max out at 160kph but the rpm is too high to sustain on a single cylinder 600cc bike. Not what the XT600e was designed for.
Ride safe, Neil
I fitted adjustable preload air suspension to my previous bike Honda Valkyrie 6 cylinder 1500cc cruiser. I find it perfect for providing a stable ride, with or without a pillion, and/or 3 hard luggage case attached, cruising at up 180kph, max out at 195kph.

[shabih]

I faced wobble on my interceptor front tyre. Got everything checked but the service centre could not identify the issue. Finally changed the tyres and it helped. Similarly, my street twin had the same issue and a tyre change helped there as well.