High speed highway Vibration - RESOLVED

My 2018 SV had a high speed vibration in the steering wheel and seat that started at about 68 MPH up to 75 MPH. I never really drove it past 75 mph.

The car has 3,000 miles on it. Brought it to the dealer and they called to say my right front tire was defective. It had a “flat spot” when they tried to road force balance it. They originally thought it wouldn’t balance because of a bent rim.

They ordered a new Michelin, installed it under warranty today and the car. I took it on tithe interstate and it is now Smooooth as silk up to 85 mph.

My '86 Civic Si developed the same kind of vibration - but at a very inconvenient 55-60MPH. I left it at the dealership for a day, and they replaced both front axles under an extended warranty I'd bought. ($500 got me $1500 in new axles at 55k miles.) I picked the car up, and, you guessed it, the vibration was still there. I left it again and they finally diagnosed it: damaged belts in the tires. All of them, actually. I think I know how that happened...

There is a connecting highway between two interstates in Latham NY. It connects I-787 along the Hudson river with I-87 up above the valley, with a long, and in one spot very steep, 2 mile hill. It's a short highway and the police didn't often set up speed traps there - at least not at night. So once in a while, in the wee hours mainly, I'd redline my car in 4th, shift to O/D, and hold it floored going downhill. I got my 110MPH Civic Si up to 125MPH on several occasions. The OEM tires were S rated, meaning 110 MPH. I got H rated tires after that...

Congrats. Always a good feeling to get rid of a shake or noise.