Originally Posted by donv' date='Sep 18 2005, 07:18 PM

Hi All:

First, here is a question. How many miles would an average driver get on the 545i?s Dunlop run flats? The answer affects the economics of my/our individual weight-savings thoughts. Any thoughts? Anyone?

Originally Posted by donv' date='Sep 18 2005, 08:35 PM

[quote name='donv' date='Sep 18 2005, 07:18 PM']Hi All:

First, here is a question. How many miles would an average driver get on the 545i?s Dunlop run flats? The answer affects the economics of my/our individual weight-savings thoughts. Any thoughts? Anyone?

Originally Posted by UPENN545' date='Sep 18 2005, 08:39 PM

[quote name='donv' date='Sep 18 2005, 08:35 PM'][quote name='donv' date='Sep 18 2005, 07:18 PM']Hi All:

First, here is a question. How many miles would an average driver get on the 545i?s Dunlop run flats? The answer affects the economics of my/our individual weight-savings thoughts. Any thoughts? Anyone?

Originally Posted by UPENN545' date='Sep 18 2005, 08:35 PM

[quote name='donv' date='Sep 18 2005, 08:33 PM'][quote name='UPENN545' date='Sep 18 2005, 08:31 PM'][quote name='donv' date='Sep 18 2005, 08:17 PM'][quote name='UPENN545' date='Sep 18 2005, 07:48 PM']I now have a Headache.?

Originally Posted by donv' date='Sep 18 2005, 07:18 PM

Hi All:

First, here is a question. How many miles would an average driver get on the 545i?s Dunlop run flats? The answer affects the economics of my/our individual weight-savings thoughts. You?ll have to factor in your particular circumstances. Also, note that I am not working with package pricing below--just with per wheel/tire prices. Forgive me for any mistakes; please let me know if you see any or question anything in the calculations. I?ll adjust or clarify.

1. By buying, for example, Michelin Pilot Sport PS2's, one can save the following (all weights below in lbs.) over the Dunlop run flats.

2(32 - 25) + 2(29 - 24) = 24 lbs. Given that unsprung weight is being saved, the sprung-weight equivalent is about 2(24) = 48 lbs.

2. By buying, for example, BBS RGR's, one can save the following over the stock sports package wheels.

2(34(?) - 21.2) + 2(32(?) - 19.4) = (approx.) 51 lbs. Given again that unsprung weight is being saved, the sprung-weight equivalent is about 1.5(51) = (approx.) 77 lbs.

3. The donut tire and jack weight about 37 lbs., together, while an after-market exhaust is likely to be about 30 lbs. lighter than the stock behemoth.

So, in sprung-weight terms, one can save about 48 + 77 + 37 + 30 = 192 lbs. with ease and without hurting the esthetics any if at all.

4. Given use of the lbs./Flywheel HP ratio, 192 pounds translates into about 192 / 10 = about 19 flywheel HP--or (48 + 77) / 10 = 125 / 10 = about 13 flywheel HP from the wheels/tires alone.

So, the first question is how about the economics of obtaining, for example, the portion of the increase in flywheel ?HP? attributable to the wheels/tires alone? Suppose that one will need to replace his or her run flats before disposing of the 545i. If so, then the cost of the extra tires is pretty much nil and is ignored below for ease. And, given a US$ price of 2($702) + 2($731) = $2,866 for the RGR?s and that one could sell the wheels, plus what's left of the Michelins, when disposing of the 545i for half the cost of the wheels ($1,433), then the cost of the wheels is $1,433.

5. So, the extra 13 "HP" from the wheels/tires alone cost about $1,433 / 13 = about $110.23 per HP--which is somewhat economical given, for example, that a Dinan trottle body, when installed by a Dinan certified shop, will cost, with a 10% discount on the part, about $685--which yields a cost per flywheel HP of about $685 / (8 / .85) = $685 / 9.4 = about $72.78. And, the wheel/tire package also will result in more that just an increase in HP?specifically, it will improve handling and some might say the esthetics. Finally, the run flats and factory wheels would be available for use?say on trips. I am assuming that the throttle body will not be sold when the 545i is disposed of.

6. Similarly, consider the cost, for example, of a B&B exhaust. The cost if installed by a BMW dealer, after a 10% discount on the part, is about $1,063. The related flywheel HP gain is about (10 RWHP / .85) + (30 lb. weight savings / 10) = about 15 HP. The cost per HP is ($1,063 / 2 / 15 = about $35.44 assuming the exhaust can be sold net eventually for half of its cost (about $532).

7. Together, all the costly weight savings, plus actual HP gains from the related items, gives a net cost of ($1,433 + $685 + $532) = $2,650. The cost per HP is $2,650 / (13 + 9.4 +15) = $2,650 / 37.4 = $71?which is similar to the per HP cost of the throttle body, itself.

8. So, the 545i ends up with 325 + 37.4 = about 362.5 flywheel ?HP.? If one throws in the 37 / 10 lb. saving from removing the spare tire, then the 545i?s flywheel HP is about 366?which is not too shabby. Thus, either way, one ends up with performance in the 550i range and is much better off not buying a comparable 550i if he or she already owns a 545i (i.e., consider loss on 545i and probably non-discounted or higher discounted price of 550i, price increase on 550i, etc., etc., and etc.) (ignoring the other new features of the 550i--which mean nothing to me).

The final cost per flywheel HP is $2,650 / (37.4 + 3.7) = $2,650 / about 41 = about $65?but no spare in the car.

Phew. I?m tired; I?ll keep checking my calculations?later. Any thoughts?

Originally Posted by Bimmer32' date='Oct 2 2005, 11:41 PM

Assuming that your calculation is on target and the mods claims are closely accurate, my best economic advantage is to lose body weight (thereby retaining? the most of the existing HP), and get the throtttle body. I'm 155 lbs., so I can't trim anymore there.

I think BMW engineers have done their homework and priced the 550i appropriately . .? . you get what you pay for.? Thanks for the economic calculations.

Originally Posted by EBMCS03' date='Oct 4 2005, 09:39 PM

WOW! Thanks for the write up!

Originally Posted by allenman' date='Oct 4 2005, 09:52 PM

Thoughts? Yes.

1) You have entirely too much time on your hands.

I am very happy with the time I have on my hands and how I use it. Time time time is on my side. Oh, yes it is. Oh, yes it is. ~0{:^)

2) Once again, it is a two ton plus sedan. Okay, now it is a 3850 pound sedan (I know, you're going to tell me those are inaccurate numbers, this is just a relative indicator). But physics is still going to limit you from turning this into a Lotus Elise or even a 997. It's still a big box, designed with compromise in mind. If you want a different compromise, try a different flavor. It is a superb compromise, but a compromise it is.

I knew that. ~{:^) And, I have several flavors. Check my sig. Yes, I agree, the 545i is a great compromise. I love mine. I considered an Elise, but went with the 545i since it turned out to be the kind of compromise I currently am interested in. And, I felt the Elise and the Z06 would be too redundant.

Everyone that mods his/her car in anyway thinks he/she will be happier/enjoy it more given the mod--e.g., wheels, lowering, exhausts, etc. Is it your view that one should just leave the car as it came from the factory. That's a perfectly OK view. But, it's not always mine. The only change I've made on my Z06 is to put a shorty antenna on it. Modding a Z06 is no fun, but driving it is.

But, with respect to my 545i, I like the idea of having something a of stealth car and being an underdog. There is an interesting set of generally faster cars that a 545i can be competitive with given a few changes.

I am not sure what the weight of the car has to do with anything, except that I wouldn't mind if it weighed in about 3,500 lbs. Many very interesting cars are quite heavy. And, note that BMW has spent a great deal of money keeping the 545i, and its cars, in general, lighter than the competition. So, many apparently are interested, for example, in 3,850 lb. compromises that are lighter than the others in their class. Check out the weights of the 545i and its main competitors in the latest MT. The 545i is the lightest and, as I recall, has the least HP, but it still is the fastest and best handling. And, improvement still is possible.

OK, shutting up now.

No need to shut up. I value your opinion. It's as good as mine. I am happy to discuss your issue(s). Check my sig on the value of my opinions.