Quote:
Originally Posted by X5-User
I wish BMW introduced the 8 speed ZF transmission as they did in the E70 35i. It would have differently improved fuel economy at HWY
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This is the ultimate wish for me too, but alas, need to upgrade to the n57 to get the 8 speed. That's out of the question for me at the moment, but one day maybe I can start thinking about it...
Truthfully, even if the swap only cost me $1500- would I ever see the savings in fuel back on that?
Lets see- fuel by me is right around $3.00, but national diesel average is around3.50, so lets be generous and say 3.50. 1500/3.50=428.6 gallons of fuel. so, how long would it take me to sip 428.6 less gallons of fuel? Lets say my highway is around 30mpg, which is usually is close to. Lets say the diff sway to lower the rpm by 300 nets me a 3mpg increase, which I'm not positive it would. Maybe it would be more though?
3mpg is 10% Savings, so I would have to spend 1500/.10 = $15,000in fuel to make up the difference. 15,000/ 3.50= 4286 gallons, 4286 gallons*33mpg= 141,428 miles. So, I would break even after 140k miles, if my quick "I just got to work and don't want to do my work" math checks out. No guarantee that it does, but I'm 60% confident in my thought process.
So, I think I'm better off using that 1500 on new headlights bulbs , maybe new halo bulbs, and a set of Michelin defender tires that will last 70-100k miles, than swapping out the diffs for $1500.
Or... replacing every component of my front suspension, which would cost right around $1300 how I've priced it out. I can't see this reasonably being worth it, but it would be a cool novelty to get better mpg's, and have a lower RPM running while cruising. I suspect it would be a bit quieter too, which would be the main draw for me to swap the diffs.
Now, If I found a wrecked 50i on craigslist being parted, and was able to snag the diffs for $100 each, would I do it? Probably. That would mean in the ballpark of 30k miles to make it up, and 30k miles is a year of driving for me.