Many of the tires for a stock 2002 C230K are load rated at less than 91. Their other ratings are good but the load rating is less than the MB recommended 91. Is it safe (or desirable) to use a tire with these ratings?
Thanks.

The Facts:

A P-Metric tires max load is achieved at 35 psi and a Euro metric tires max load is achieved at 36 psi adding more air pressure will not increase the tires load capacity but, lowering it will reduce the load carrying ablility. When increasing pressure all you are accomplishing is a lower rolling resistance, quicker steering response, stiffer ride and contact patch reduction.

Based on a c230:
the OE tire is a 205/55-16 89V
max load capacity is 1312 lbs.
load capacity at recommended pressure (which we will call PLC for placard load capacity at 28psi) = 1138 lbs.

so, the minimum load capacity for a c230 is 1138 lbs. according to the PLC

now lets consider the idea of running a capacity that is too low .... what happens:
the tire is put into a condition where it can support the car at a static rest point but, when driven aggressively the sidewalls are so over worked they can not properly control the contact patch of the tire allowing for excessive sidewall roll-over, irregular wear, tread block and contact patch flex which robs the tires performance ability and grip. also the added flexing of the tire will increase the heat it generates which can make a tire feel really slippery ....

A good way to understand this is: let's say I just put a 100lb. back pack on you .... you can stand there for quite a while (that's your car sitting in a parking lot) now go run up and down some stairs with that back pack .... that's normal driving and you can't do that very well, nearly as fast or for very long before your legs give out .... after you've recovered enough to walk (let the car rest once you arrive at the venue for your autoX), take a 500 meter sprint through deep sand, that's your autoX and you will most likely not make it to the finish without falling atleast once if you can finish at all.


so, with all that said you can run an 89 load index since the load capacity of that tire would be 1157 @ 29psi

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great explanation thanks