Non-spec rims and tires ,do what???

[bpteacher3]

I have to say this forum's response time is as amazing , as it is helpful. thanks guys . On to the question , On my recently purchased 1999 911Carrera 4 cabri , it came with 19"rims with275/35R19 back and 235/35R19 front . These are non-spec ( of course ) However I've been given a wide range of conflicting responses as to compatibility . What's the straight word in terms of handling , performance, wear and tear ( on suspension, front end ,shocks.ext ) is there really any significant difference ? .....Mechanics seem to bend one way , tire people the other . Whats the word? Confused BRUCE

[Joe Bob]

If the tires and wheels overall height is the same as stock you will get a harsher ride. Wider wheels take more HP to move but 'can' give you a better grip in corners dependent on proper alignment and balance.

[KTL]

Yeah Joe Bob is right on. The original 17 or optional 18 in. 996 wheels had a tire size of:

205/50-17 front
255/40-17 rear

225/40-18 front
265/35-18 rear

Both of those tire combinations have an overall *theoretical* diameter of approximately 25 inches (the first three are ~25", and the 265/35-18 is around 25.3").

Your bling bling 19s have a diameter of 25.5 in the front and 26.5 in the rear. What that means is your tire sidewalls are going to be a little thicker/taller and the ride should typically be a little less harsh and slightly less cornering capabilty. But that's purely theoretical. Actual tire brand/construction is going to determine how good they ride and handle.

With the taller rear 275/35-19 your effective gearing is actually reduced. So your car accelerates more slowly that with original tire sizes. Your speedometer is also probably a little bit off because a taller tire has less revolutions per mile and therefore your speedo will read a bit low.

As far as wear and tear on the car, that's a bit of urban legend. As long as the wheels fit within the wheel wells, the suspension and wheel bearings can handle the wheels just fine. It's when you start sticking the wheels way out past the body line, thereby creating a lot more leverage with improper wheel offset, where loading on the suspension becomes an issue.

Lastly, the increase in diameter to 19 often comes with a weight penalty. As tires go up in diameter, so does the weight. Same weight increase typically occurs with the wheels too, unless your 19s are ultra expensive lightweight forged wheels. The increase in weight is an increase in unsprung weight and that hinders the peformance of the car as well.