For about as long as there have been automobiles, people have had different tastes about the appearance of them and how they can be made to look better. One way many owners change the look of their car is by replacing the wheels. This is usually very easy to do and provides quick results without permanently altering the car. This may seem to be the ideal solution, but careful steps must be taken when choosing a new wheel so that the safety and reliability of your car will not be compromised. Most people who buy replacement wheels purchase them for the way they look and not necessarily for the dimensions that they are. Many of these proud motorists may be in for an expensive, if not dangerous, surprise for not doing their homework. First, you must know the type and dimensions of the wheels that your car was originally equipped with. Below are a few definitions to help you better understand the terms used to describe wheel dimensions along with some helpful information.

Steel Wheels: Most cars come equipped with wheels made from stamped steel because they can be easily mass produced and are relatively inexpensive. Steel wheels are usually quite strong, but are also very heavy making them a poor choice for good handling.

Alloy Wheels: Some cars (more all the time, in fact) are being equipped with wheels made from alloy metals such as aluminum. These wheels are usually cast making them very strong and more rigid than steel wheels. Alloy wheels also weight less thereby reducing the amount of unsprung weight of a car. Another advantage alloy wheels have over steel wheels is better heat dissipation enabling them to handle higher tire and brake temperatures.

Wheel Diameter: This is the diameter of the rim where the bead of the tire seats on the wheel. Wheel diameters are almost always measured in inches. If the diameter is not marked on the wheel it can be determined by the size tire mounted on it. Fitting larger diameter wheels with lower profile tires (to retain original tire diameter) will enhance handling and looks alike. Fitting smaller diameter wheels is not recommended and is usually not possible because of clearance over brake calipers.

Wheel Width: This is the distance between the vertical edges of the wheel where the tire bead seats. Wheel widths are almost always measured in inches, usually to the nearest half inch. If the width is not marked on the wheel it can be approximated by measuring the overall width of the wheel and subtracting a quarter inch for steel wheels and one inch for alloy wheels which have substantially thicker beads. The proper width wheel will be determined primarily by the size tire to be used. For best results the wheel should be approximately the same width as the tread of the tire. This produces vertical tire sidewalls for best tire support, grip, and long tread life. Although wide tires will fit onto narrow wheels it can be a wasted effort since a narrower tire will likely handle just as well, if not better. Narrow tires mounted on wide wheels serve about the same purpose and leave the edges of the wheels vulnerable to damage by curbs and potholes.

Offset: This dimension is the distance between the mounting surface of the wheel (to the car) and the exact center of the wheel. When the distance is toward the face of the wheel the offset is positive while away from the face is negative. Most wheels have some amount of positive offset with those designed for front wheel drive cars typically having more. Offset is usually measured in millimeters and is often not marked on the wheel. It can be determined by subtracting half the overall width of the wheel from the distance between the mounting surface and the outside (inner edge) of the wheel. Offset can sometimes be confusing when comparing wheels with different widths. Here is how it works:

Example #1:
13 x 5.5 inch wheel with 25mm offset and 13 x 7.5 inch wheel with 25mm offset. These two wheels would be positioned the same on a car with the wide wheel having one extra inch toward the inside and one extra inch toward the outside.
Example #2:
13 x 5.5 inch wheel with 25mm offset and 14 x 7 inch wheel with 36mm offset. In this case (because the offsets are different) the width of the wheel on either side of the mounting surface must be calculated and compared.
     13 x 5.5   Outside:  45mm  Inside:   95mm
     14 x 7     Outside:  53mm  Inside:  125mm
As you can see only 8mm (about 5/16 inch) of the extra width was added to the outside while 30mm (about 1 and 3/16 inch) was added to the inside. This could cause a serious clearance problem on many cars from only 11mm difference in offset.
Example #3:
13 x 4.5 inch wheel with 28mm offset and 14 x 6 wheel with 10mm offset. Again we compare widths:
     13 x 4.5   Outside:  29mm  Inside:  85mm
     14 x 6     Outside:  66mm  Inside:  86mm
In this case nearly all of the extra width is added to the outside of the wheel. This would give the car a wider track and better handling in corners.
Careful measurements must be taken before considering a wheel with different offset so that you know what range is acceptable for your application. Wheels with grossly inappropriate amounts of offset will greatly reduce the handling abilities of your car and put tremendous loads on bearings, ball joints, and steering components leading to eventual failure. You would be wise to give plenty of room to the modern low rider with so much negative offset that nearly ALL of the wheel/tire is OUTSIDE the fender so that you do not become part of the inevitable accident. The individuals that drive these cars are either ignorant of the mechanical torture they have put upon their cars or just irresponsible about their actions, both of which can be very dangerous. Another important note is that any change in offset will result in a change in steering geometry since the contact patches of the front tires will be a different distance from the pivot point of the front suspension. This will be especially evident at higher speeds or when turning sharply.

When considering the offset of a particular wheel be sure to keep in mind that most FIAT models have a 4mm spacer bolted to the outside of the brake rotor. This can of course be eliminated to accommodate a wheel with less offset. Likewise, multiple spacers can be used with a wheel having a large offset.

Wheels Bolts: Most FIAT models utilize wheels bolts rather than studs with nuts. These bolts have a 60 degree tapered seat which serves to center the wheels as they are mounted. This is the most positive method of wheel mounting and it is for that reason that FIAT chose to use it. Many aftermarket wheels re-quire using shouldered bolts with large cylindrical shanks. These are NOT recommended for ANY application because they result in centering and balancing problems that can seldom be overcome. Stock wheels bolts come in different lengths depending on the model and wheel option. If longer bolts are needed for your application, first try to obtain longer stock bolts, the chrome ones being the longest. If these are also too short, then studs and tapered nuts can be used provided that care is taken to prevent damage to the threads in the hubs. With any wheel bolt application be certain that 8-10 threads are in contact at every location. Also be sure to torque each bolt to specification using the appropriate tightening pattern. Remember that all four wheels are needed at all times, so keeping them attached to the car is of great importance.

Bolt Pattern: This is the number of bolts and the spacing diameter used to attach the wheels. FIAT uses a 4x98mm pattern. This is not at all common and so sourcing aftermarket wheels could prove to be difficult. Be very careful when measuring the bolt pattern of a particular wheel. Many cars use a 4x100mm pattern that appears very close to FIAT's, but do not attempt to mount them on the advice that "it's only 2mm." Doing so will put a severe strain on the bolts and will certainly damage the threads on both the bolt and in the hub. I personally have seen (and repaired) many unsuccessful 4x100mm attempts on FIATs. Broken wheel bolts, stripped threads, and abnormally worn tires are typical results from such adventurous undertakings. Remember, a poor application is bad judgment no matter how good it looks.

Hub Clearance: FIAT uses locating bolts with extended heads to secure brake rotors and drums to provide approximate wheel centering during installation. All stock FIAT wheels and factory option alloy wheels have clearance for these bolts. Aftermarket wheels may not have this and so their use should be questioned, as removal of these bolts is not recommended. If some clearance exists but is too shallow, simply replace with normal bolts. Any machining of the hub area on a wheel should only be considered as a last option, and then only after making certain that enough material will remain to ensure wheel integrity. This can also be applied to the hub diameter of the wheel as minor clearance problems may be overcome this way.

Wheels used by FIAT:

Designation                         Size     Offset  Models Used
Steel (round holes with hub cap)    4.5 x 13  --mm   Early 124, 128
Steel (8 short slots &  design)     4.5 x 13  --mm   128, X1/9
Steel (4 pairs of 2 short slots)    5 x 13    --mm   Later 128
Steel (4 long slots)                5 x 13    --mm   131
Steel (silver/black paint 4-spoke)  5 x 13    --mm   Later 124, Brava
Steel (silver/black center design)  5 x 13    --mm   F.I. 124, Brava
Alloy (Cromodora 6-spoke/6-slot)    5 x 13    27mm   Early 124
Alloy (Cromodora 4-spoke "Abarth")  5.5 x 13   7mm   124 Spider
Alloy (Cromodora 5-spoke "Daytona") 5.5 x 13  18mm   124, X1/9
Alloy (Cromodora 5-spoke "Daytona") 6 x 13    14mm   124, X1/9
Alloy (Cromodora 5-spoke "Daytona") 6 x 14    22mm   124, X1/9
Alloy (Cromodora "Iron Cross")      5.5 x 13  25mm   F.I. 124, Brava
Alloy (Speedline "Iron Cross")      5.5 x 13  25mm   F.I. 124, Brava
Alloy (Cromodora "Iron Cross")      5.5 x 14  25mm   F.I. 124, Brava
Alloy (Cromodora "Turbo")           5.5 x 14  25mm   Turbo 124 Spider
Alloy (Cromodora "Pinin")           6 x 14    25mm   Pininfarina 124 
Alloy (Cromodora 4-spoke)           5 x 13    --mm   Later X1/9
Alloy (Cromodora 4-spoke)           7 x 13    --mm   Later X1/9
Alloy (Cromodora large 3-spoke)     5 x 13    27mm   Later X1/9
Alloy (Cromodora "Bertone")         5.5 x 13  25mm   Bertone X1/9
Wheels used by Lancia/Maserati that fit FIAT:
Designation                         Size     Offset  Models Used
Steel (round holes with hub cap)    5.5 x 14  --mm   Beta Sedan
Steel (slots with small hub cap)    5.5 x 14  --mm   Beta Sedan
Alloy (F.P.S. webbed 8-spoke)       5.5 x 14  34mm   Coupe/HPE/Zagato
Alloy (F.P.S. slotted 2-spoke)      5.5 x 13  25mm   Scorpion
Alloy (disc style with slots)       6 x 14    15mm   Bi-Turbo

Back to Dave's Suspension Workshop

Back to The Fiat Page