How is it supposed to feel at high speeds?

[zombie]

If the rear wheel is grabing at some point in its rotation... Something is bent/warped/out of alignment back there.

Fix that, and work from there.

[hypophthalmus]

I set up a primitive gauge to measure the runout with the wheel attached. I got consistent results of less than 1mm on both the the side of the wheel and the rotor. Is this telling of anything?

[BettinANDlosing]

Take a close up of your tires. Also what brand are they? Like zombie said tires can make s world of difference. How many kms on the scoot? Maybe the PO didn't tighten the shocks or motor mount all the way?

[hypophthalmus]

A close up as in picture? The rear is a Kenda Cruiser ST, the front is a Pirelli Diablo. I think replacing/balancing both tires is a good idea. The back one has a least one spot in the sidewall where there's cracks.

I believe checked the tightness of the rear shocks except for the one blocked by the exhaust the last time I had the plastic off. I can't remember if I checked the engine bolts or not, although I'm not sure why I wouldn't have.

There's nearly 7000km on the scooter.

[zombie]

Kendas are known to be out of round right from the start. They also are affected by oil or fuel so if it sat on a grease spot for just a few days it will have a soft/swollen spot.

If your tires are questionable I would start there. Being a cheep scooter I would suggest checking every nut/bolt you can find. Parts wear quickly, and once wear begins it snowballs.

[BettinANDlosing]

If that's the stock kenda rr tire, 7000km is high for those tires. I bet you anything a nice matched set of high end tires would cure your ailments.

[hypophthalmus]

Thanks for your help. I'll get to replacing the tires, probably with new Pirellis. While I'm at it I can check that everything's tight, and that the bearings aren't worn. Maybe even check the runout a bit more precisely.

[zombie]

Sounds like a plan...

Please keep us informed as to how it goes.

[Stig / Major Tom]

How is a scooter supposed to feel at h i g h speeds?
IMHO...pretty damn scary!
There's a reason for that.
Slow down. Get on a slower road.
I have several relatives who drive OTR for a living....they all tell me the same thing:
A scooter has no business being on the interstate highways!
Stig

[hypophthalmus]

Stig,

That seems like a strange sentiment to me. What's the point of even making or buying 250cc or larger scooters just to keep them on slower roads? Do you feel the same about similarly sized conventional motorcycles?

I actually haven't taken mine on an interstate highway though. The normal full access roads here frequently have speed limits as high as 70mph.

[Stig / Major Tom]

Stig,

What's the point of even making or buying 250cc or larger scooters just to keep them on slower roads? Do you feel the same about similarly sized conventional motorcycles?

Oh, not so strange a sentiment from my perspective.
You see, unless a scooter or a bike is going to be pulling a house trailer or fuel tanker....I've always thought 2 wheeled vehicles with engines bigger than say 250-350 cc's were something of a joke.
Even two-up you can travel comfortably at safe speeds with a bike this size on scenic country roads all over the world.
To propel oneself essentially naked of any real protection into constantly shifting traffic at 70MPH - with 80MPH cars and F-150's closing on you - while perched on a rail seat with your feet in the breeze on 3/4" footpegs.....hoping for the best - and for the good judgement of texters & those with anger issues ....is to display a complete lack of imagination. Like a kid doing 60 at night through a line of parked cars with his lights off. In itself it is not dangerous...but it surely shows a lack of imagination.
Can a big engined Vespa travel on I-275 around Tampa?
Sure.
Should it?
Heck no.
My point is that you do not need a big engined anything....you just want one. 
And I, for one, cannot figure out why.
Stig

[hypophthalmus]

That's understandable.  Everybody accepts different amounts of risk though. There are plenty of people who might say the same thing of driving a two-wheeled vehicle at all.

The roads I that I drive at these speeds on are quiet, although fast, country roads. One or two lanes, sparse and polite traffic. I've been on plenty of slower roads that are much more dangerous to drive on.

I suppose I thought you were saying that larger scooters are mechanically unsuitable for those speeds.

[zombie]

Dark Side meetings at the Ramada, Crawfordville. Tues/Thurs. at 9PM sharp.

I love ya Stig. You're the second person here w/ the balls to say it like it is. Anytime I am on a bike on the interstate/55 or above Hwy. I am the guy in the right lane w/ 4 mirrors. and doing 55 no matter what. The only reason I am there is because there is no other way to get where I am going.

A 250cc scooter has as much business on 55+ roads as a steel wheel skate board has in the X-Games. I say it all the time... a 500cc scooter is a 50cc scooter in bigger plastics. My top speed matches all of them.

No offense fellas/gal. It's just MY opinion.

[josephthediviner]

Probably time to involve a mechanic, I had my people downhill with the wind once and pegged the speedometer over 100 indicated it was smooth as silk, the only time there was any shaking was on a cupped tire at really slow parking lot turning speeds.   One of the great things about the People was it's smooth ride at speed it's resistance to induced shake or shudder from uneven pavement or passing tractor trailer's.   So please have the scooter checked out it should be smooth at any speed.   Jim.

[BettinANDlosing]

The older people have a horrible problem with induced shaking. You key go of the handlebars, instant speed wobble in EVERY one I've driven.