The PO of my 84' 300CD put 15" rims from a newer mercedes on the car.

What effects does this have on my gauges? odometer, speedometer?

There's no effect if the tire/rim diameter combo is kept at the same measurement as the OEM tire/rim diameter combo.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

I was told that moving to 15" rim is better as more and more cars came with 15" rim. Therefore R15 tires are cheaper so to speak.

There may be a slight difference in the speedo. It may be out by 1-2% when compared to actual. My 190D is stocked 14" and the PO changed it to 15". The ODO is out by 2mph at 70mph. I checked it with GPS. It could also be the tolerance of the speedo as it is an mechanical device.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I have 16's on a car that had 14's and the difference is negligable. About 3mph at highwy speeds. When I had 15's my gps would read 1-2 mph over my speedo

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1981 300SD 512k OM603

Like H said, if the tire OD is kept the same as the stock tire OD then the gauges will be spot on. The rim size does not matter. Thanks

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83 300D 227,xxx miles, sold
86 300 SDL 130,000 miles, sold

Yep, just a bigger hole in your same size doughnut.

The shorter sidewalls will provide a stiffer ride on corners - not as much sidewall deformation or sway.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)