Just wondering if there is any rules of thumb to minimum rim sizes for a given tire width from a performance perspective at the track.

For example, is an 8" rim too narrow for a 245 tire?

 

Here's a table with min, max & ideal tire width vs rim width
https://www.tiresandco.ca/tire-equivalence-advice.html

 

The tire manufacturer specifies approved rim width ranges for the exact tire.

As for how rim width (within that approved range) affects performance, I cannot say. You could call the tire company and might be able to get an engineer on the phone to elaborate.

FWIW, A 245 in one model tire can be 20mm wider or narrower than a 245 from another model. Width dimensions on road tires are nominal, not actual.

 

There are a number of factors like...

- What tire compound? (not all are created equal)
- Are there any class rules? (drivers may pinch a wide tire on a narrow wheel if they don't have a choice)
- Is there enough inner and outer clearance on the front of this car to take a wider wheel?

Generally speaking we like running a wheel that is on the wider end of the spectrum for a given tire size to support the sidewalls. This typically improves handling/performance and wear.

A 245 tire can safely be mounted to an 8" wheel, but it is not ideal. 8.5" and 9" wheels are most commonly used with 245 tires with the 9" being my preference, but some track/race compounds that run real wide could even warrant 9.5" wheel in some circumstances.

- Ryan

 

If we strictly look at the rim and tire (ie no clearance, class rules, or other concerns), is there a rim to tread width ratio that is best adhered to? So a 8” rim and 245 tread width would make the ratio about 83% - is there some recommended minimum from a performance perspective?

Or is rim to section width more relevant in this case?

 

Every tire width has a recommended wheel width range. The narrower the tire on the wheel, the more "pre-tension" (support) that is provided to the tire, thus making it more responsive when turning because there is less sidewall deflection. However, the opposite ratio (the widest tire on the narrowest wheel) often provides more lateral grip, so if the driver can tolerate the sloppy steering response it can frequently result in better lap times. Autocross drivers typically go for the widest tire, both due to the rules and because steering response isn't as critical at autox speeds. Track drivers, however, will typically prefer a little better steering response.