My 1978 Jaguar XJ-S needed tires. The car came originally with 15 x 6 inch "Kent" wheels and 215x15x70 tires. Subsequently I upgraded to 15 x 6.5 inch "Starfish" wheels with 225x15x70 tires. I had two objectives in upgrading my wheel tire combination:
1) They must function better than the original.
2) They must look better than the original.
I also wanted to keep the odometer and speedometer fairly accurate; therefore I needed the overall wheel/tire combination's diameter to be in the 26.5 to 27 inch range.
I considered 16 through 18-inch wheels/tire combinations. I did not think the 16-inch rims visually "filled" the wheel wells adequately, while the 18-inch wheel seemed slightly out of scale. In addition, to maintain wheel/tire diameter within my parameters, the 18-inch rim would need an aspect ratio of 40 resulting in a sidewall of less than 4 inches. This low sidewall height seems not only out of proportion with the size of the rim, it affects ride quality and subjects the rims to potential abuse from normal road hazards.
I chose the 17-inch rim as the ideal rim height that visually looks best for the XJ-S wheel openings and car profile. Rim width would be 8 inches, tire 235x50x17.
The process of determining what tire / rim size combination would fit my 1978 XJ-S is covered in detail in the Rim / Tire Decision link in my website.
Finally, wheels and tires are a personal choice; this combination is my personal choice for my car. Others may or may not have different choices.
The 17x8 rims with 235x50x17 tires arrived from Ronal. Because of unidirectional tread patterns, the tires arrive labeled specifically front and rear.
The wheel offsets are achieved with unique spacers (red arrow photograph below). Ronal's "hub centric adaptor systems" allows the wheel to be pushed outboard from its mounting surface. These aluminum adaptors become a "back-pad extension" of the wheel and are an integral part of the wheel when it is mounted to the vehicle. The adaptor is hub centric to the wheel, and then is hub centric to the vehicle's mounting surface.
Longer lug nuts are also supplied and must be used. (red arrow photograph below) A set of the original lug nuts must be kept with the vehicle to be used with the spare if necessary. Be prepared. The cost of these wheels are augmented by higher that usual shipping and handling fees.
The old starfish wheels are removed.
The new wheel requires a thin wall socket to attach the unique lug nuts. Ronal recommends torque settings of 85 Ft. lbs. for these wheel lug nuts.
Note hub centric adapter, which is covered on another link of this website. (yellow arrow photograph below).
First wheel on and it looks good. Lower sidewall required higher tire pressure. Ronal recommends 37 psi.
These wheels and tires are significantly wider than the originals, creating a more attractive modern look.
The 28mm offset sticks the rear tire out pretty close to the fender. As discussed in the rim decision link of my website, the clearance is just barely adequate. (yellow arrow photograph below) The rear suspension is a swing arm design which allows the wheels to clear the fenders.
From any angle, these rims and tires vastly improves the appearance of the car.
There is no more important modification you can make to your car than upgrading its tires and rims. In addition, it looks good. This is the exact look I wanted when I started the project.
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