Topic: Occasional vibration while riding at 1 second increments

[Archaeodude]

Hey all, this is my first time posting on here and I'm so glad this forum exists because I have an issue I can't seem to figure out. I was hoping some of you may have an idea.

The bike is a 1972 CB500, I just got new tires on it and the shop balanced the rear but didn't balance the front. The issue I'm having is that, while I'm riding, it'll occasionally vibrate like the tire is deformed but only for 1 second intervals. It vibrates for 1 second (approximated by 1 Mississippi), then is smooth for 1 second, then vibrates again for 1 second, and so on for the entirety of the ride. It happens at all speeds from about 30mph to about 60mph, and I'm afraid to take it much past that at this point. I haven't really felt it below 30mph but I also may just not be looking for it.

Do you all have any idea what it could be?

Thanks in advanced!

[scunny]

I would get the front balanced.

[jaytee-nz]

Scunny, I sent you a PM about some shocks on Trademe - did you get it? (sorry for the thread hijack).

[madmtnmotors]

Variable vibration can sometimes be related to the fact that the front and rear tires are different diameters (by design). I had a new set of tires that would cause a slight vibration, seemingly beginning in the front then traveling down the centerline of the bike and finishing in the rear. Things would smooth out at that point and then it would begin again, continuing to repeat the process. I raised the air pressure in the front tire by 2lbs and lowered the air pressure in the rear by 2lbs. This "broke up" the harmonics between the front and rear tire enough that the vibration is gone.

Maybe adjust your tire pressures a little and see what happens?

[HondaMan]

Keep in mind: the tires you now have are NOT bias-ply tires, but metric round profile type. This means yo need more air PSI than is shown in old manuals and the labels on the bike. Modern tires must have at least 32 PSI, and 35-38 is much better. Low tire pressures can make a lot of strange things happen on these bikes.

[madmtnmotors]

Keep in mind: the tires you now have are NOT bias-ply tires, but metric round profile type. This means yo need more air PSI than is shown in old manuals and the labels on the bike. Modern tires must have at least 32 PSI, and 35-38 is much better. Low tire pressures can make a lot of strange things happen on these bikes.

+1

I was running equal pressures, around 36psi IIRC, so upping the front to 37-38psi and dropping the rear to 34-35psi resolved the issue I was having.

[PeWe]

My CB750's feels very good on Honda's "Sustained high speed" labeled pressures. 
Front: 2.2 BAR (32PSI)
Rear: 2.4 BAR (34PSI)

Now Heidenau tires
3.25-19, 4.0-18

Before
Dunlop StreetSmart
Metzeler LaserTec
100/90-19, 120/90-18, 4.0-18
Same feeling.

I have tried higher pressure in the Metzelers 5 years ago but not comfy, bike felt jumpy on the road.
My K6 runs stable in 160-170kmh, sometimes 190-200kmh when checking the main jets
Ikon shocks, progressive fork springs on both my bikes.

[Archaeodude]

Thanks all. Super helpful suggestions. Just as an update, I tried running slightly different pressures and the issue remained. So I decided to take the front wheel to get balanced, they did, and the guy at the shop said the wheel was slightly out of true. So maybe that's been my issue. I haven't put the front wheel back on yet since i decided to take this opportunity to replace the fork seals and boots with new oil. Once I put it all back together and test-ride, I'll come back with an update. Seems like I may have to true the wheel if it persists.

[PeWe]

I have had issues with tire not correctly set on rim. Entire bike jumped as a crazy cartoon bike.

Lubed the tire where meeting the rim, deflated it and rode the bike slowly around the block so tire could let go of the rim. Inflated tire to double pressure, direct followed deflation and another try to inflate to running pressure.

The root cause was not enough tire lube when mounting it.

Bearings feels OK when rotating the wheel?
This have I (or the tire shop) noticed when changing tire, wheel on axle and it feels like sand in bearings when rotating the wheel.

[HondaMan]

I have had issues with tire not correctly set on rim. Entire bike jumped as a crazy cartoon bike.

Lubed the tire where meeting the rim, deflated it and rode the bike slowly around the block so tire could let go of the rim. Inflated tire to double pressure, direct followed deflation and another try to inflate to running pressure.

The root cause was not enough tire lube when mounting it.

Bearings feels OK when rotating the wheel?
This have I (or the tire shop) noticed when changing tire, wheel on axle and it feels like sand in bearings when rotating the wheel.

This also happened to me when I had a tire with real stiff beads. It was hard to get it to seat right!