Modern Vespa

Why? Because I am now the owner of a GTS the discussion is no longer academic.

Did the search and read the threads. Verdict, no one has conclusively identified and solved the issue, band-aids only.

Coming from a S150 without a hint of wobble the question is, what is the difference between the two chassis that is causing this?

Obvious answer is the twin shock rear, less obvious is the engine swing arm.

Questions:
1) the Primavera/Sprint frame has an engine swing arm configuration similar to the GTS but single shock, does it experience wobble?

2) anyone who has replaced the silent block in the engine swing arm with the solid Malossi one, what effect if any did this have on the wobble?

3) anyone who has replaced the exhaust bracket/right shock mount with the billet Zelloni or the SIP Perdoi, any effect?

4) has any one tried tapered steering head bearings? Not necessarily a fix but these might tolerate added preload vs the ball bearings to act as a damper.

5) and finally long shot, who has a 2023- HPE2 with the revised front end? Wobble?

No wobble at all on my 23 HPE 2.

By chance I got to ride an older pre 2015 Gts last week. It wobbled.

Both my 2015 and 2018 models had this wobble if I took my hands off the grips. It rapidly became life-threatening. But if I just touched the grips lightly the scooters were dead steady. Could never find a cause.

My new 2023 model has no wobble.

Interesting. Maybe it was the front end all along.

I consider myself an authority on this subject. The verdict is that it is an intrinsic aspect of the GTS design. You will be much happier when you accept this fact.

Alternately, you can sell the GTS and walk away.

I've never experienced anything that I could call a wobble while riding my '20 GTS300 HPE, but other than momentarily fiddling with my helmet's face shield or adjusting a mirror, I've never taken my hands from the grips either. This is a new one to me, at least for this scooter.

The design of the bike isn't quite right, throw a bit of manufacturing tolerances in and a marginal design wobbles a bit in some instances. I've had two bikes that did this. The cure for my GTS was a 1psi increase in front tire pressure, never wobbles now.

The cure for my Kawasaki Ninja was being hit by a car. (No kidding, it had a slight wobble while decelerating before being hit and was steady as a rock afterward… bet the wheelbase was slightly shorter too.)

As Jess mentioned above, it's intrinsic in the design.

The steep angle steering rake combined with small wheels and short wheelbase are all contributing factors. Installing a rear rack and top case without adding heavier bar end weights will exacerbate the issue. Tire pressures will also make this more prevalent.

Simply keeping one hand on the bars at all times will eliminate your wobble. If it doesn't, then your front tire is likely far below recommended air pressure.

On my 09 and 07 GTSs, I did cure wobble with fresh CG2's inflated to 29 psi front and 32 psi rear, along with heavy bar end weights and a front rack installed. YMMV.

Every single GTS that I have owned had some degree of wobble. This new 2024 that I just got has none.

Like others have already mentioned, you can play with air pressure in the tires to see if it helps. I feel tires make a difference as well.

Tires absolutely make a difference. Some tread patterns will mask the wobble, like the infamous Savas that used to come on GTSs. Many people found that as soon as they put "good" tires on their bike, the wobble appeared.

On the other hand, Savas suck giant donkey balls.

I had a Sprint. Absolutely no wobble at all.

No mods, factory rear top case, tyre pressures as told in the manual.

nope

Thanks for the response. I'm actually considering removing the right side shock temporarily for troubleshooting purposes, though not sure what I would do next if it cured the problem, not like you can ride around with one shock.

I am going on record that this is a terrible idea. No, really.

The wobble is not caused by the rear shocks. It is caused by the steering geometry.

Of course you can ride with one shock. Fournales used to sell a single shock for many Piaggio/Vespa models that originally came with two. Very good they were as well, according to the folk I heard from who had fitted them. That may have been buyer's bias of course!

Meh. I think you're giving the donkey too much credit here.

Maybe, but why only the twin shock frame? My theory is the stamped steel engine swing arm is flexing.

Did a little parts catalog research. The obvious change to the 2023 HPE2 is the fork, but guess what else they changed? The engine swing arm. And it looks like it will retrofit.

OMG. I laughed out loud and scared the chihuahua.

Yes, the famous Dyna twin rear shock wobble. Scary stuff to go into a speed wobble on a 950 pound scoot.

By this logic, we could just as easily blame the retractable passenger pegs found on the GTS (but not the smaller models) for the wobble.

(Also, the swingarm is most definitely not stamped steel).

I am confident that the moment you disconnect one of the rear shocks on the GTS, you will instantly recognize why it is such a terrible idea. And if by some chance you actually make it to the end of your driveway like that, I hope you will at least consider updating your will before you depart.

[quote="skids"]
For some time now Harley touring models have been plagued with wobble issues as well.

I did not do a deep dive but I did read where it was also "intrinsic" to the design caused by frame geometry, specifically rake and trail.

Yo, skids! The Harley head shake happens to all the newer styled rubber mounted engines except the sportsters (different mounting system). I believe it started in the mid to late 90's. The problem is how the engine moves around. The engine can move forward and aft as well as side to side. The side to side is the deal breaker. Head shakes usually start upwards of 85 mph. My Dyna would do it at 90 especially in a turn. Fun stuff. Buell figured it out and solved the issue by keeping the engine moving fore and aft with his mounting system. Sputhe offers his positrac brackets for the Dynas which works really well and gives the bike a very solid feel especially in the corners. Of course you need to start with new rubber mounts and have the engine alignment trued to the frame. Most people suck at doing this critical step but totally necessary. The earlier rubber mount system like on the FXR was superior and only needed a bearing conversion in the swing arm instead of the rubber bushings. I've done it on a build and that bike handles awesome even for a Harley! I've never ridden a bagger (not my bag!) but all the extra weight on top of the front end probably makes the wobbles more pronounced.

nope

I have owned 5 Vespa GT200s, still have two of them, and a 2023 GTS 300, with more than 200,000 miles ridden on them.

They all have the front end wobble, some much more than others.

I do not know why they wobble, but I have found it to be harmless.

He only times it created a concern was when I would carry a camera on a lanyard, and take lots of riding photos while riding the worst wobbler.

Taking my left hand off of the grip at certain speeds caused a big wobble on that one.

On the others, especially the new GTS. The wobble is hardly noticeable.

While it felt a bit odd, it never was bad enough to cause stress.

Simply keep both hands on the grips at low speeds and you will be fine.

Bill

So out of curiosity this afternoon I took my 2020 Sprint S 150 up to 40mph and held my hands over the handlebars and sure enough, there was wobble. Got more pronounced as the bike started to decelerate. I've been riding around for months and never noticed this, probably because I've never taken both hands off the bar at once. Like everyone else says, as soon as any weight from my hands settled back on either grip, the wobble vanished. I have ridden with my left hand off the grip many times and it doesn't wobble then either. So it's a non-issue to me. I honestly wouldn't even have known had I not intentionally tried to find out.

The bike still has stock tires with 2k miles on them. The steering bearings were recently tightened by the dealer shop. Givi top case (empty at the time of the test) Last I checked, the tires were full but I suppose I should check again. If any of this is relevant.

So I guess it's not just a GTS occurrence?

This thread has been a success so far, you guys may have pointed me in the right direction.

While I do agree that it's not life threatening and is easily controllable with a light touch on the bars and I could live with it if my experimenting fails, I don't agree that it's intrinsic to the design and not fixable. Vespa fixed it in 2023. They were able to eliminate the bar end weights in 2023 because they engineered it out.

Obviously the front end was massively redesigned and a geometry change may well have been a part of that. This may have even been the "why" of the anti-dive. I'm not about to swap the fork, if this was the fix I will live with it.

But you guys got me digging in the parts books. All the way back to the GTs the engine swingarm has been fabricated out of sheet steel, die cut, bent, and welded into a box. The part number has changed over the years but the part is essentially the same. My theory is that the load path through the twin shocks is finding this weakest link and causing it to flex.

This also changed in 2023, in a possibly significant change the main element of the mount is now a flattened tube, no longer a welded box. Of course this could also just be a cheaper way to manufacture the part.

At $120 I'm going to buy one and swap it in. I was ready to source one of the older style and reinforce it anyway but Vespa may have done it for me. Will keep you posted with the results.

Good old percussive maintenance strikes again!

My wobble was night and day better after I replaced my older hard michelin city grips with a new pair and had the wheels balanced at the same time. Fresh rubber matters.

Glad we're discussing this. My resurrected '08 GTS250 does wobble, but it's only in certain circumstances: decelerating with the throttle closed at approximately 25 mph. It's a narrow range, maybe 23-27 mph where it wobbles. I removed those massive bar end weights and replaced them with bar end mirrors before I ever put the scooter on the road, so IDK if the weights fix it. I also tried adjusting the headset bearing tension (tighter), which had the effect of narrowing the range of speed that the wobble exists. It only wobbles with one or more hand off of the bars and while decelerating at a specific speed.

Putting my engineering hat on, I have developed a theory of what's happening. Weight shift during decel onto the front end causes a little bit of lateral flexing of the front axle/trailing arm that has a resonance at a certain speed depending on the tire, tire pressure, road surface, temperature, other factors. If the headset has any slack in it, then it will allow a greater deflection for the resonance.

The resonance is introduced both a side-to-side and an up-and-down motion, since the shock allows it to bounce. So the easiest way to alleviate it would be to increase the spring rate and rebound damping. You'd have to balance this with the same % increase in spring rate and damping in the rear. I would guess aftermarket shocks probably do this anyway. The tradeoff is going to be ride quality, especially over high-speed/small bumps.

I can feel a lot of looseness and lateral flexiness just riding my GTS, so I wonder if there's not some bushing or bearing change or adjustment that could be done on the swingarm that would reduce the wobble without requiring a shock change.

EDIT: I looked in the service manual, and there's a needle bearing on the leading end of the swingarm. I'm going to see if there's any way to adjust that bearing's tension or preloading, which could reduce lateral flex if there is any slack in it. Also, I didn't set the axle nut to any specific torque value when I mounted the hub, so this could be a point of adjustment as well. It occurs to me that people who report tire changes changing or fixing the wobble, it's probably the weight of the tire more than the tread design. I bet lighter tires wobble less, and a lighter wheel would wobble less. Perhaps the reason the GT/GTS/V wobble but the same era LX doesn't is due to the LX's 10" wheel, which is much lighter than the 12" GT*.

Yeah, that's what I'm chasing as well.

Actually 2 sets of needle bearings, preload set by length of internal shafts. I'm thinking the only thing that might need attention here is replacement of the plastic bushings with bronze.

I have the late style arm on order, will know in a couple weeks if it makes a difference. Next will try swapping the silent block for something harder. May end up with welded reinforcement which was original plan.

LX/S have a completely different style swing arm, 1 piece and rigid, after swapping out the rubber marshmallows for urethane zero flex or wobble.

I'll have to take a look at what bushings are there. I agree if there is any plastic bushing, it's gotta go. In my scooter, it's probably long gone already. I'm on pins and needles Or cotter pins and needle bearings? Something like that.

Update: 2023 swingarm installed. Didn't work, wobble still present. Points to the fix from Vespa for the 2023s was the revised fork.

It was worth a try. Answered that question. Obviously not going to replace the complete front end so what next?

Took a good look at the plastic bushings while I was in there. Initially thought replacing these with bronze was a must, but no longer of that opinion, needle bearings are doing all the work. May still replace them if easily sourced, but not a priority.

Also initially thought weld reinforcement of the swingarm to mitigate flex was in order, but the 2023 piece is plenty beefy, visibly more so than the piece it replaced. The arm is 2 pieces though, may still try adding metal to the other piece.

Tried so far:
1) 80A urethane shock top mounts all around, if anything made it worse.
2) no/different bar end weights, no discernible difference.
3) 2023 swingarm, no difference.

2 things left to try, steering head bearing torque and harder bushing at the swingarm.

Not optimistic that tightening steering head will make a difference, but may be able to strike a balance between too tight and tight enough to act as a damper.

I don't understand the why of the rubber bushing in the swingarm so for troubleshooting the initial approach will be to essentially eliminate it. Could go the Malossi route but am thinking custom 80A urethane.

Can anyone that has done a harder bushing comment on any effect?