Q: Significant vibrations after new rims and tires installation.

Unless you were previously able to operate at 90 MPH with no vibration, I would not necessarily expect such success now with the new tires and wheels. Once you get up to speeds like that, there are lots of possible causes of vehicle vibration and most vehicles will vibrate to "some" extent at those speeds. With regard to tires, brand new tires that are perfectly balanced can vibrate like crazy once in service due to radial force variation. The only way to minimize that possible source of vibration is to buy very high quality, and usually (not always) more expensive tires (e.g., Michelin). In your circumstance, part of the diagnostic would be to put each tire/wheel assembly on a radial force balance machine and measure the road force. Typically if it exceeds 25 pounds, that is the source of your vibration, especially at speeds of 90 MPH. You could also ask the balancing technician to balance each wheel/tire assembly and then remove the assembly from the balancer and re-position it on the balancer by say 90 degrees. Re-spin the wheel. If it doesn’t come up as "zero" out, the balancer is not calibrated, is not working properly, or the wheel is improperly mounted to the balancer. Another issue is your wheels may not be hub-centric but rather are lug centric which requires an adapter plate to balance them properly. There are a myriad of other possibilities. If you desire that this vibration issue be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a vehicle vibration diagnostic. If you have further questions or concerns, please do not hesitate to re-contact YourMechanic as we are always here to help you.