Since the tyres have flexible sidewalls, a single tyre size suits a range of rim widths. The tyre width range defines the narrowest to the widest rim widths on which the tyre is intended to be installed over its tens of thousands of miles and years of operation.
The thickness of the rim can affect the thickness of the tyre. A tyre mounted on a narrow rim would be “narrower” than if the same size tyre were mounted on a wide rim.
Note: Due to the fact that the overall diameter of the steel belt radial is essentially determined by the steel belts, there is little, if any, change in the overall diameter of the tyre due to differences in the width of the rim.
The industry rule of thumb is that for every 1/2 “change in the width of the rim, the width of the section of the tyre will change accordingly by approximately 2/10.”
“The rim width range of the tyre defines the narrowest to the widest rim widths on which the tyre is built to be installed during its tens of thousands of miles and years of service.”
For example, the tyre size P205/60R15 is measured on a 6.0 “wide wheel and this size tyre has an acceptable rim width range of 5.5” to 7.5 “width. The tyre has a section width of 8.23” (209 mm) when mounted on a 6.0 “wide wheel. If that tyre was mounted on all rims within its length, the average section width of the tyre will change as follows:
Difference from Rim Tire Section
Measuring Rim Width Width
0.5″ narrower 5.5″ 8.03″
Measuring Rim 6.0″ 8.23″
0.5″ wider 6.5″ 8.43″
1.0″ wider 7.0″ 8.63″
1.5″ wider 7.5″ 8.83”
Due to the various widths of the wheel used in the example above, there is an estimated 8/10 “difference in the width of the segment of the tyre when comparing the tyre mounted on the narrowest rim to the widest rim within its radius. This can have an effect on fender well and frame clearance when choosing available aftermarket wheels and tyre packs.
Combined Size Tyre Rims
In addition, some vehicle manufacturers have developed Original Equipment applications in which the width of the rim does not fall within the original approved width range of the rim. For instance:
1995 BMW M3 combined 235/40R17 diameter tyres on 17×7.5 “rims (which are 0.5” narrower than the narrowest 8.0 “wide rim of the size).
Corvette C3 models combined P225/70R15 sized tyres on 15×8 “rims (which are 0.5” wider than the 7.5 “wide rim now indicated for the size).
Corvette C4 models combined P255/50R16 sized tyres with optional 16×9.5 “rims (which are 0.5” wider than the 9.0 “wide rim now specified for the size).
The rear tyre application for Porsche 911 GT3 cars during the 2010-2012 model year combined 305/30R19 rear tyres on 19×12 “rims (which are 0.5” wider than the 11.5 “wide rim indicated for the size).
While outside the normal recommended range of rim widths, these applications comply with the vehicle manufacturer’s specifications.
What is The Rim Width of A Space Saver?
Space savers often have smaller rim widths compared to the wheels that are fitted onto the car however Road Hero space savers are available for specific vehicles.
Road Hero packages usually include:
- Wheel and tyre
- Wheel brace
- Bags for storage and more.
Where required, nuts, bolts, and spigot rings are also given. Within the storage bags offered, anything supplied with the Road Hero Space Saver Wheel and Tyre Kit can be easily packed away.
Some new cars come only with puncture repair kits for tyres, instead of a full spare wheel/space saver and tyre. Many drivers would prefer a tyre and a spare wheel so they can get going again as quickly as possible, this is why Road Hero space savers and spare wheels are an essential in 2020.