Read This First.
CAUTION: Never mismatch types of tires either on the front or rear wheels. A bias ply tire should never be paired with a radial tire, and vice versa. Likewise, tread design, belt type and overall tread wear should be the same (or similar) side-to-side for proper handling, steering and braking. Intermixing different brands and styles of tires may cause similar problems in some instances.
As for the size of replacement tires, some people will try to use anything that fits. This may not be a good idea because a vehicle's handling, steering and braking characteristics can all be adversely affected by using tires that are too large or too small for the application.
Some people may want oversized tires on their rear drive wheels to improve the car performance but not necessary for Citroen. Switching to a larger diameter tire reduces the number of revolutions per kg. But it also affects the accuracy of your speedometer and odometer readings. Remember that wider or larger tires may improve traction for most car or to achieve a special kind of "look." , but wide tires, however, typically provide reduced traction on wet roads.
Clearance problems can arise, too, if the tires are too wide or too large. They may rub against the body when turning or when the vehicle hits a bump. This can not only damage the vehicle but also the tires, possibly causing a blowout.
Most importantly, using adaptor (or specer) is not suitable for your Citroen and all car, especially Citroen PCD alloy wheel is hard to find and if you can find them, it is no choice of design. If you really want one, you must make the adapter to fit in to your center hub of bareing in order to prevent your Citroen from shaking. Moreover, clearance problem can arise and bolts modification should be avoid.
On models that have antilock brakes (ABS) equipped cars, most vehicle manufacturers say replacement tires should be the same size as the originals. This is necessary because the diameter of the tire affects how the wheel speed sensors read, which in turn affect the operation of the ABS (and traction control) system. Changing to a larger or smaller diameter tire, or installing different sized tires front and rear can upset the operation of the ABS system. This may create braking problems and/or cause the ABS warning light to come on (which means the system is deactivated).
This recommendation is realistic where as Xantia model that equipped with 14 inch. wheels are using different set of wheel baring compared to that equipped with 15 inch wheel. (the different is that on the ABS wheel sensor)
This artical was modified from Yahoo!Autos