Modern Vespa

As the title says, I wobble. And I need advice.

The story:
I picked up another 500 back in March. Rode it from Watsonville all the way up to Daly City, and it was...harrowing. Once out on the open highway (I took 1 up the coast), it was WOBBLY. I made it, but probably need some therapy after that. Turned out the tires weren't as good as they first appeared. The rubber was kinda crap, and the back tire had a worn patch that was very slightly sloped to one side, like it had worn to compensate for the crown of the road, so I figured I was fighting the edge of that flat patch. Fast forward a bit, and I had new rubber put on, expecting it to be like my first 500 when the new tires completely changed my world. Nope! It actually felt marginally worse. Now that the tires were nice and round like they should be, I didn't have the flattened patch to help provide that bit of lean resistance.

So here's the deal: When I take off, for the first 15 or so minutes, it's fine. Damn near perfect, even. I'm gliding down the road smooth as silk. But after a while, I become aware that I just can't track straight to save my life. Won't stay perfectly upright, it wants to lean one way or the other, and so rather than gliding straight, I'm undulating side to side like a snake. On the highway it just gets terrifying, as those wobbles at speed get exaggerated. Last night was a perfect illustration of the issue. I rode from Daly City down to Foster City for dinner on El Camino Real. Through Burlingame, it was great. Then a bunch of obnoxious and slow stop-and-go, and by the time that cleared out and I could cruise any length at all, I'm wobbling side to side. Got to Foster City, had dinner and chilled for a little bit, and by the time I got back on, it's dead smooth again. Fast forward another ten or fifteen minutes, and once again, it doesn't want to be perfectly upright and I'm swaying side to side. It's not MASSIVE sway, mind you, but the scoot just won't balance itself upright at that point.

Thoughts? The wheel balance checks out, alignment checks out, I don't *think* I feel any steering bearing notch, suspension seems to check out. I don't feel any play in any of the bearings when I check them at a standstill. Could it be defective tires and I am coincidentally having a similar problem with them? Anyone else have any experience with an issue like this? It doesn't bother me much riding around town, but not being able to get on the highway is really bumming me out.

Are you using quality name brand tires, and how old are they?

Always. Michelin City Grip 2, purchased in May. Manufacturing stamps say the rear was made August '25, fronts September '25.

and pressure?

I'm glad you asked. Everything was even and spot on (230 kPa front/280 kPa rear). According to my gauge, at least. Your question was tickling the back of my brain, so I borrowed gauges from two of my coworkers (I work in auto repair) to cross check against. Turns out my gauge reads 20 kPa lower than theirs. Both of theirs match, so I'm gonna chuck mine and get a new one, it's clearly out of calibration. Anyway, I've got my tires set to a confirmed 230/280 kPa now. I'll take it for a longer ride tonight and see if it's better now or not. The fronts were even to begin with, though, so I don't know how much of a chance this will make. Fingers crossed, I'll report back later on.

Sounds like a tire balance or internal defect.

Those new tires should have a small painted dot. Make sure that dot sits at the tire valve.

mine is wobbly too but i figure it out! The problems were tire lines or whatever you call them (chariots?) - small and long ''trenches'' in the asphalt that heavy vehicles make over time. From a distance looks legit, flat but it ain't. Driving over or in them WILL wobbly your motor!

Also check wheel bearings. Any play can also cause similar behavior

There are no painted marks. The tires were professionally mounted & balanced (I don't have a machine at work for that). I had to bring the scoot into the shop for unrelated work in June, and asked them to doublecheck everything after they finished up the work. That's when they checked and confirmed the alignment, confirmed the tire balance, checked the suspension, all the bearings, everything as far as they can tell checks out okay. Hence, the bald patch I'm developing from scratching my head over this. Rode it with the corrected tire pressures last night, no change. It still wants to lean this way or that after fifteen or so minutes of riding. Alas, it's not the wheel ruts in the road. It happens on old or freshly paved road, and over stretches that I had previously tracked smoothly. It's definitely an issue that develops over a period of time, presumably when everything has become fully warm.

Check the engine swing-arm bearings. The actual swing-arm, not the exhaust support bracket...

to add to Jimc post, also inspect the silent block and rear shocks and bushings.

What is this "silent block" thing people refer to on&off?


Is it a bushing, mount, or what?

My brain keeps thinking exhaust silencer

"silent block" are the rubber disks where you put the bolt thru just turn the nut tighter the the silentblock will expent more i use a airgun that goes up to 1600nm

But those aren't the problem!!

Most of the time the white plasic bushings are the problem behind it then the swing arm has room to swift side to side

I find that when i set off on a ride that i hold the bars tight when in traffic or just around the house's as still getting to grips with the top weight. I get the wobble when relaxing into the ride. I think because there are two wheels at the front that are steerable and these catch road surface conditions differently. Two wheels like on a traditional bike does not get effected. I am learning to just accept this and enjoy the ride.

This is the second MP3 I've had in ten years, so I'm pretty comfortable with the riding characteristics. My old one, that one was stable as a rock. I remember the first time I got on the freeway with it. I was a little nervous, I'd never straddled anything at those speeds before. Then a semi came barreling past me, and its wake felt like it wanted to shove me right off the saddle. The MP3, on the other hand, didn't even shrug. That's the very moment I developed my confidence in riding. That scoot tracked dead straight and solid, felt agile as hell, like an extension of my body.

What I'm experiencing with this one is a completely different. This wobble is not normal. I really don't feel at all safe on the freeway on this one. And when the problem begins to manifest in the ride, sweeping turns where I lean start feeling sketchy as hell, too. Wobble sucks when upright. It sucks worse when you're at a 60° angle to the ground. I'm still confused by the "silent blocks." They're the rubber discs at the bolts for what, exactly? The shock absorbers? And I will make a point to check those white bushings at the swing arm this weekend. The swing arm seems tight to me as near as I can tell at casual check, but I'll give it all a more thorough check, just to make sure.

Absolute classic sign of fucked swing-arm needle bearings. They come with bugger-all grease from the factory, and when worn the whole engine and transmission can move quite a bit side-to-side w.r.t. the frame - and thereby the front wheels. It's not a steering fault per se (but that could be an extra!). Cheapest and easiest is to replace the whole swing-arm. However, it can be rewarding battling with the beast and replacing the needle bearings. Plug the whole tubes full of grease when reinstalling.

Ugh...nothing is rewarding with wrestling this beast these days, I don't have garage access at home to tear it apart, and I don't have room at the shop to do anything I can't absolutely get done in a single evening unless I want to risk the idiot brigade kicking stuff around and half my scooter disappearing while they work. But what needs to be, needs to be.

I wasn't able to spend any time at the shop this weekend to go over things, so the best I could do was ride it until the issue became strongly prevalent (paying closer attention, it does feel like the source of the movement is coming from the rear so I think you're onto something here), then put it up on the kickstand and give everything at the rear arm a wiggle. I can't feel any play in the back whatsoever doing it that way, and visually I can't see anything that looks out of sorts. Is there a specific procedure I should be following to inspect these bearings and bushings and such? Also, if those swing-arm bearings were shot, wouldn't the issue be more consistent? Why would it only act loose and wandery after I've been going for a while? What am I missing?