SL/R129: 129 Tire Size
12-29-2014, 02:35 PM
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1999 MB SL500
129 Tire Size
I have a '99 SL500 with 18" wheels. I know I'm bucking the trend but I'd like to add 1-1.5 inches of sidewall height, perhaps with a touring tire. I'm not concerned about cornering characteristics. I'm hoping to improve the ride and also change the appearance by filling the wheel well a bit. Is there any way short of trial error to find out what, if any, taller sizes will work?
01-10-2015, 10:13 AM
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94 SL 600, 98 993, 89 XJS Conv., 85 Daimlier Princess 16 Hybrid Lincoln 16 Chevy crewcab
Because of brake caliper size you need to keep the 18" rim ( not back to 17 or 16" ) While you can change the sidewall profile, I think the trial and error system may be your only option ( I've been down that road, the other direction ) for the increase in the diameter of the entire wheel.
A sidewall profile ( ratio ) of 30 can be increased to 50, but the tire tread will be narrower in order to keep the tire size the same. The ride will be softer, as will the cornering. Because of the wheel sensor, cruise control connection all the wheels need to turn at the same rate. Tire rack charts will supply the math so it can become an issue of brand name. Rim width may be an issue with a large decrease in treadwidth.
Several of us "ego tire owners" have found the wheelwell, suspension support members and adjustable ride height issues that look and preform until we turn full or bounce into an intersection. Issues include fender destruction, damper boot tares and plastic liner friction.
good luck on your solution.
A sidewall profile ( ratio ) of 30 can be increased to 50, but the tire tread will be narrower in order to keep the tire size the same. The ride will be softer, as will the cornering. Because of the wheel sensor, cruise control connection all the wheels need to turn at the same rate. Tire rack charts will supply the math so it can become an issue of brand name. Rim width may be an issue with a large decrease in treadwidth.
Several of us "ego tire owners" have found the wheelwell, suspension support members and adjustable ride height issues that look and preform until we turn full or bounce into an intersection. Issues include fender destruction, damper boot tares and plastic liner friction.
good luck on your solution.
01-11-2015, 04:33 PM
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1998 SL500
You can calculate the tire outside diameter as follows:
(width * aspect * 2) / 25.4 + wheel size
so for a 275/30-18 tire this would be:
(275 * .30 * 2) / 25.4 + 18 = 24.4
Keep in mind that your speedometer and odometer readings will be off (read a slower than actual speed and record too few miles) if you make the tire diameter larger--you will also lose acceleration performance as the effect will be the same as installing "taller" final drive gears...
(width * aspect * 2) / 25.4 + wheel size
so for a 275/30-18 tire this would be:
(275 * .30 * 2) / 25.4 + 18 = 24.4
Keep in mind that your speedometer and odometer readings will be off (read a slower than actual speed and record too few miles) if you make the tire diameter larger--you will also lose acceleration performance as the effect will be the same as installing "taller" final drive gears...
