Modern Vespa

I've read several posts about the front end wobble on 2006-2010 GTS scooters (sorry, I realize there are other years and models prone to this as well). The ideas I've read include inflating the front tire to 42 psi, reducing weight load on the front and adjusting/tightening the headset bearings. I've inflated the front tire to 42 psi, which did help, but it got me thinking.

If inflating the tire to 42 psi increases the overall tire diameter slightly and helps with the wobble, what would happen if I simply went from a 120/70 front tire to a 130/70 front tire (the same size as the rear tire)? Has anyone done this before? If so,what were the results?

It can and has been done, as well as upping the rear tire size as well but there is no guarantee that it will stop the wobble.

My advice is keep both hands on the bars and don't worry about it.

I am sure going to a 130/70 in front can be done, but do you know if it actually helped?

Inflating your front tire to 42psi will diminish your grip and cause very rapid wear, squaring off your tire, leading to even worse handling problems.

How bad is your wobble exactly?

If you're talking about a mild weaving action on deceleration, pretty much every motorbike does it to some extent. It does no harm and extraordinary measures would be required to minimize (not eliminate) it. Hell, all of my BMWs did the same thing.

If it is more extreme, check to make sure your wheel is properly seated with correct (and even) torque on the bolts. Make sure all suspension components are straight and correctly torqued. Finally, check that your headset doesn't click from being loose, and that there is no brinelling (dents in bearing race).

Most likely everything is fine. You just need to relax. Keep your shoulders and elbows loose while riding.

The internet is often a cesspool. I see people with no technical training "improving" products that have been carefully engineered and tested.

42 seems way too high to me, I am able to fix by going up to 30 or 31.

42 seems way too high to me as well. I typically run my front at 30-31 and the rear at 32-34.

Have you changed out your bar end weights to a heavier set? That is one of the common ways of reducing front end wobble.

42?! Man you are in husky territory in the Sears catalogue. I have it on my 2017 GTV as well and it can be pretty bad. However it's nothing I can't handle and I live with it as it really isn't a risk to dropping the bike however just more of an annoyance when braking.

If someone really ever gets the answer to this age old question please let us all know

42psi in the front is plain daft. 29-30 max. If it's done more than 4-5000 miles, and a City Grip, look closely at the sides of the tyre. If there's any cupping, this could be the problem. Re-balancing (on a dynamic balancer, not a static one) can keep it going a bit longer - but replacement with a new one is the best bet.

I've cured the wobble on two GTSs by putting new tyres on. If you bike seems prone to it, it might be better to change to Power Pures for the fronts, as they are not dual compound, and don't wear in the same way with a completely different tread pattern. Not yet tested myself - but I will next time one of those GTSs gets the wobble again - sod the cost.

Fixed it for you.

Thank you - corrected.

On motorcycles front end wobble can offen be a sign on bad suspension out back. For what its worth.



Paul

A GTS250 that I service, apparently wobbles with the owner onboard, but it doesn't do it with me at the controls. Different rider weight, different sitting positions, and the fact I don't let go of the bars are all factors for it not wobbling with me on it. Maybe, change the rider!! But in all seriousness, heavier bar end weights often does the trick, but 42psi is just not sensible and is likely to cause an accident aside from anything else.

Read the thread that wherein I recently was investigating my own wobble and seemed to have solved such. There is a comprehensive dealer response there which includes all the items of consideration that matter.
And how the OP came to the conclusion this is limited to the year models they stated is not what I read for sure.
Getting weight off the front is certainly NOT! one of them nor have I ever read that from anyone on MV? if anything the opposite is true.
42PSI becomes even more PSI once your tire heats up. It is too much to retain proper traction, wobble or not. One comment about "properly seated" in this thread is meaning what? beyond wheel torque? Is that your way of stating the wheel is loose on the hub? If so, I assure you it would be worse than a wobble! Be more like a catastrophe.
As said a well worn tire could cause it out of balance or in my case new tires came into play in some fashion.
I do question why, Piaggio hasn't placed the heavier bar ends on every modern Vespa 300? Is it 50 cents or a dollar they need for lunch money?

kinda of funny that all the professional tire makers at the motorcycle race tracks only use static balance methods. These bikes can hit 180 mph or more at some tracks and balanced tires are pretty critical at those speeds.

There is no advantage of using dynamic balancing. Those machines are for the un experienced techs that think they are saving time. How often are they calibrated? and by whom? is the questions to ask the shops that use them.

A tire that hit pothole or other hard object can be damaged and cause all kinds of problems including wheel hop and wobble and apoear to have no damage.

The professional tyre makers tend to only supply known good tyres to race tracks.

If a tyre has extra weight on one side, and 180° around has some weight on the other side which matches, how will that be detected by a static balancer? However that scenario would introduce wobble straight away.

Why are you guys running such high pressures in the front?

Heavy agressive rider here on hilly twisty mountain roads.


36psi rear 27psi Front

Handles great, no issues at all. The higher you go up in the front the less grip.

Thanks all for the great input on this topic! I will def be checking out the headset bearings for flat spots and overall tightness as well as backing off the tire pressure. I've got a fair bit of weight already on the front with the crash bar setup so if there is a benefit from more weight, I've got it covered.

Or if that's not enough weight, you could always take a few friends along. I bet this guy doesn't worry about no stinkin' wobble!

Hmmmmm, could be aerodynamic instability caused by one or more of the canard wing???

Paul

This post was not quite
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This post was not quite
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Try again, perhaps?

You'd have to be pretty careful all those safety mirrors are well adjusted to balance out on each side or you could get a bit tipsy. No sneaking up from behind on a Mod when they are on their scooter... sucks for filtering through traffic though.

Jim your very knowledgable in a lot of stuff but tire balancing is not one of them.

first off when a new tire is mounted ALL weights are removed. then you find the lite spot on the static balance stand which will be at the 12 o'clock position, you mark that with a grease pencil so when you add or remove temporary weights you ALWAYS use that spot. once you get the optimum weight for zero tire rotation you install that amount of weight on the rim and double check it on the balance stand. Then if you want to be even more anal you cover the weights with a piece of duct tape, This helps to ensure the weights stay put and does not allow dirt and debris to breakdown the foam sticky tape that causes to weights to fly off. Remember to always clean the rim with alcohol to ensure there is no residue prior to installing weights.

Jim, you make a very good point re the dynamic balance of tyres. But my static balance machine will tell you where on the rim to put the weight and on what side of the rim. Indeed, it will tell you if you need weights on boths sides of the rim too. It detects all that stuff. Even gives a digital read out/picture on a screen showing where to put the weight/s. But, dynamic balancing can be very useful for cars or trucks, particularly on the drive wheels. It can help offset any balance problems with the driveshaft/s and running gear..

Understood - but that still doesn't address an imbalance between one side of the tyre and the other.

Thought experiment:

Get your static balanced wheel and tyre and now put a 20g weight on the inside of the rim right where it meets the rubber. Then 180° around the other side of the wheel put a 20g weight on the outside of the wheel right where it meets the rubber.

This combo will still appear balanced on the static machine. However it'll try to wobble like crazy when spun fast, as the neutral axis will no longer be perpendicular to the plane of the wheel although it'll still go through the centre. It's this side-to-side balancing that the dynamic balancer can do.

sooo.... you've got 50lbs of tat directly over your front wheel, crap ass shinko white walls that are wayyy over inflated and you're wondering why you've got a shimmy?

c'mon mannnn...

-g

Pretty much says it all. Hell I was a mod during the 80's revival but could just never get myself to do the mirrors.

Jim, I applaud your tolerance.
There are arguments for dynamic balancing that go beyond what any sane person would desire to replicate in this thread. Properly done it has merit, especially for the wide wheels used on modern cars/trucks. It measures forces not possible in static balancing, race cars aside.
having worked for years in a tire factory it is quite true that tires get variable builds and variable standards for balance and much more before they are shipped for use. OE tires alone, often have a different standard than replacement tires as manufactured. Race tires are in a special place and priced accordingly too.
FWIW ( once upon a time) I often performed repairs to the machine that dropped colored wax spots on passenger tires that indicated the balance category of that tire. As my old brain recalls there were 3 colors of melted wax used then.
The best argument for static balancing is it's simple and can be done on a cheap stand at home and it works OK. Many of us already know how to do it and don't require a tutorial.
I will throw in here that, like many others, I tape the weights on the wheel temporarily with masking tape until I achieve best balance. I never use duct tape as I have not found it necessary, even one time.
This thread began with the OP stating information that is known here on MV to be lacking in model year application and tire PSI logic.
It's hard to keep this ship, i.e., this thread from sinking given where it began?

Mirror story of the day:
In the late 1970's I was working in a Vo-Tech school, very rural, minimum security prison with open gates, etc.. The facility road that led from public road entry had these twin adult brothers who were always out picking up pop btls for deposit money and alu cans too. They pushed a wheelbarrow along that curvy public road and meandered down to visit us at times in the school area, as neither worked in a real job and lived with elderly parents down the road a piece.
Both brothers were mentally challenged. We had some old pick up truck mirrors lying around-the kind that clamped to the edge of the fly window on older vehicles and mounted them on their wheelbarrow, making them very proud of there barrow!
I still live here near where one of the brothers still living goes out from his independent living home to pick up cans-in a sack.

I didn't see how many miles are on your GTS, but it is a 2006. Perhaps replacement of the twelve year old shock would help. I also didn't see if you have a top box. I had no wobble on my 2010 until I put on a box. Bar ends and a performance shock eliminated the box induced wobble on my ride. I will add to the chorus of not riding with 42psi in the front.

Could be badly unevenly worn tyres and shock. The original shock that came with the bike is crap.

I just changed to racing bros air shock and my wobble disappeared. I can even ride at 80km/hr, let go both of my hands and it will be straight and smooth as hell. Even when there is slight wobble, it will correct by itself very quickly and it will be gone. This is the only shock i have ever use so i cant comment if the other shock will work, but i think a good properly tuned shock should work

Great input on this thread from all...thanks! I did the easiest suggestion first and dropped the tire pressure to 32 front, 34 rear. That alone seemed to remedy most of the wobble and make it much more tolerable. The scooter only has 1000 miles on it so I am guessing the front shock is still in good shape and likewise, the tires are brand new so I'm guessing they don't contribute much to remaining wobble. If I am into the handlebar are coming up, I may dig in and see what the headstock bearings look like for snugness.

Glad to hear its almost gone. Don't forget to maybe try heavier bar-end weights. That may take care of whatever slight wobble you still have.

I 2nd the bar weights. They do more than I would have ever guessed toward smoothing out this front suspension. I'll also share this tidbit on the Piaggio heavy bar ends: Scooterparts sells the chrome version as does SIP online from EU.
www.scooter-center.com in Germany sells both the chrome and black versions. For whatever reason the chrome ones weigh less than the black ones- 470 grams vs. 500 grams which is a tad over an ounce each weight. In the scheme of things the grips are black anyway and IMO, since weight matters, more weight is better!
I also feel that bar weight has a larger effect on the wobble than a front rack, not that both don't help.
A shock that's not worn from miles, especially hard miles on rough roads is not an automatic bad shock. I've seen MC shocks much older than that with function as good as when new-IF! not worn from use. Not what I'd throw money at is my point unless the shocks been tested and bad?
I see PSI (high PSI) as a factor but not a stand alone cause of wobbles.

My GT200 glovebox placard says front pressure should be 26 psi front and 30 psi rear.

Right?

Having said that, even with the heavier weights I still get le wobble, which is really only a pain when I'm riding with no hands, trying to do something I probably shouldn't be doing with two hands.

I hope you realise the maximunm pressure is 41PSI if they are
Shinko SR723 tires.

I have changed the two barn hands with 500g heavier ☝️ ones. I have a tall Waco windshield and a givi topcase on the back. The GTS rides up to 130km/h on highway without any wobble. When I take out the windshield and the top case (look and speed) my GTS 🛵 rides like naturally faster with less confort : all the mods (windshield & topcase) make quite a difference on the bike handling.

I wonder if changing the front shock for Malossi RS24 or BITUBO would be a 🤗 major improvement. Just put red shock bearing absorber on the back shock for stiffer handling (work good) on curves

Watch this :

I hope you realize that's not the vehicles recommended tire PSI. It is the tires "designed pressure limit" and includes the heat related pressure increase the tire will raise up to in service.
Every tire I have looked at has sidewall information with the designed limit of a tires PSI. That is not placed there because it means you should run that pressure. Shinko is little different in that respect.