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Cobtinental Dws Size Question

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  • 1 month later...

I have been trying to buy 4 DWS tires for awhile now, they are on National backorder, I can get a set of 235/55/18s the car calls for 235/50/18s!

Can I put the 235/55/18s on and nor create problems? Anyone know the differences in size between 50s & 55s??

As far as I understand tire size designations you have two considerations.

1. Will the larger tire fit?

2. Is the larger circumference an issue?

At the risk of stating what you may already be aware of I think the following calculations are what you need to perform to answer these questions.

The tire size designated for the car is 235/50/18.

- 235 is the maximum cross section of the tire at 235 mm or 9.25 inches

- 50 is the tire side wall height as a percentage of the cross section or 4.63 inches

- 18 is the diameter of the rim in inches

The replacement tire size you are considering differs by a side wall height that is 5% larger (55% - 50%) or 0.46 inches. The resulting total diameter of the wheel is twice the tire sidewall height plus the rim diameter. This works out to 27.25 inches for the designated tire and 28.18 inches for the replacement tire, a difference of 0.93 inches. This is the minimum amount of extra clearance needed.

If the larger tire does fit, I would imagine you would have to consider the adequacy of the reduced clearance when fully turning the wheel and suspension travel over bumps in the road. Also, are handling and control affected by this difference?

The circumference (Pi times the total wheel diameter) of the replacement tire will also be larger at 88.52 compared to 85.61inches. This is only a 3.3% difference. I imagine the odometer will therefore read too few miles travelled by this percentage and the speedometer slower by 3.3% than actual.

I guess this doesnt really answer your question but you might be interested in the considerations needed. Perhaps others more familiar with using larger rims and/or tires could offer a better informed opinion and comment on my calculations.


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