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Discussion Starter #1
I would like to get larger wheels for my 1981 300TD to lower highway RPM and that will make it look nice. I'm looking to get educated on this issue and receive advice as well as rims that will fit the car.
 

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Discussion Starter #3
Thanks, I remember that thread. So that answers the style and availability question however its not clear what the size limit is before I run into major clearance issues. Will this adequately lower the engine's RPMs? I don't know what the best RPM would be but I imagine right at 2700RPM (engine's peak torque rpm) would be best at 70mph.
 

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If you want to lower engine RPM your best bet would be to get the differential from an '85 (2.88 gearing).

Your '81 300TD (turbo I assume if it's a US model) will have a 3.07 ratio, by comparison.
 

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Discussion Starter #5
Good info, it is a turbo diesel

Will it be a plug-and-play swap or will I need to modify?

What affects will it have on acceleration, MPG, and RPM?

Should I buy new or used?
 

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A quick trip to the spreadsheet yielded this:

195 / 70R 14 tire @ 60mph with 3.07 final drive ratio gives an engine speed of 2501.9 RPM.

195 / 60R 16 tire @ 60mph with 3.07 final drive ratio gives an engine speed of 2455.8 RPM.

So switching to 16 inch rims would drop ~46 RPM at 60mph. Not a whole lot.

The same tires with the 2.88 final would get you 2347 and 2303 RPM, respectively.
 

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Good info, it is a turbo diesel

Will it be a plug-and-play swap or will I need to modify?

What affects will it have on acceleration, MPG, and RPM?

Should I buy new or used?
Re: 2.88 differential

1. Plug & play (get corresponding speedo to ensure accurate speed reading)

2. Slightly slower acceleration (not much), slightly better MPG (if mostly performed on the highway) and lower RPM. MPG and acceleration are relative, depending on vehicle condition and manner of driving.

3. Used
 

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Discussion Starter #9
Haha, yeah something like the above. LOL JK It seems to me that these vehicles are not going to get significantly better MPG however, how would it affect engine life and keep carbon in the engine, turbo and exhaust to a minimum?

Also, I've been searching and its been difficult to find any 2.88 differentials. How much is a fair price?
 
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