Dealer options for tightening suspension?

I wouldn’t expect a dealer to be able to modify the suspension characteristics without installing aftermarket parts of some kind. Aside from product liability issues, Toyota’s Repair Manual doesn’t give them any information about how to do it, only how to restore the original performance by correcting the alignment or replacing worn or defective parts. The only substitute suspension parts in Toyota’s catalog are those for “Rough Road Area” specification vehicles, with 20 mm higher ground clearance.

Your extended warranty is unlikely to cover them, but Toyota does offer some functional suspension parts for the Prius in Japan under the TRD brand. The Suspension Set isn’t compatible with Toyota Safety Sense-P, but you might consider the Member Brace Set (part number MS300-47003, list price ¥60,000) which is supposed to “increase the rigidity of the vehicle.” I can’t find the installation instructions for the current version of this part, but the instructions for a discontinued version, MS300-47002 (PDF, in Japanese only) show how portions of the plastic covers underneath the car must be cut away.

 

The rear suspension seems to have some sorta cam washer, it changes position as it's rotated? Take a look under the rear bumper, it's visible on the rear suspension lower member. If you get a one day Repair Manual subscription on Toyota tech info you might find info on it.

Not sure if it would change ride quality, or just or just geometry.

 

You've got the wrong car.

 

Ask if there are TRD parts. I'm betting there are. They will honor the warranty if they install those.

Oh, and check the tire pressures. Put more in than on the door placard. I like 40 front 38 rear.

 

Is your 2017 a Touring model (Three Touring, Four Touring)? Those come with a tighter suspension and a 17-inch wheel package, which rides stiffer than the standard suspension with a 15-inch wheel package. Not that you can change now, but you would know that there were two flavors of handling packages available from the factory. If you already have a Touring model, then you have the best that comes in a Prius.

 

If you're looking at dealer fit, the only option really is 17" wheels with a lower profile tyre, which would improve it slightly.
I have the UK Excel trim (top trim available here) with 17" wheels and it's pretty flat round corners without being a harsh ride.

 

I'm just itching to go from our 17" to 15", have some sweet PIP rims ready, but the missus doesn't like the look. Every fall we do make the switch, from OEM 17" Michelin Pilots, to 15" Michelin X-Ice. The difference is really subtle, I wouldn't say it changes the "handling" at all, basically a plusher ride, especially going over pavement irregularities.

 

Having driven an Excel demonstrator with the 17" wheels and the Business Edition I eventually got with 15" rims, I have to say both handle similarly flat in the corners, though the ride is that little bit softer on the 15's. That said, I've only checked the tyre pressure once since last September and I'm still ge intting more than 63 UK mpg (measure from the pump). NB, I never hypermile, but I'm occasionally aggressive with acceleration.

PS, I got a speeding ticket in May.