The $6000 Question - Page 4

skunkd · 13th April 2010, 18:08

this guy obviously is not going to be racing much if he's not concerned about over 100mph... thats what you guys are missing. SO he should at least have some baller rims to make his car look super sexy while everyone else is cruising past him in the slow lane haha. come on seriously WHEELS are the BEST mod by far if racing is not a concern.

Find a nice set of used 20" 3 piece forged wheels used for 3k, then get a RPi pulley, RPi ram air scoops, and a RPi full exhaust, and there is your 6k

BMWPower06 · 13th April 2010, 20:13

Quote:

Originally Posted by Revo

You also need to consider the rate at which the pulley is accelerated.

In first gear the pulley goes from 1500RPM (clutch engagement point a casual start) to 8250RPM. The wheels go from 0RPM (still) to 580 RPM at 47mph. Now lets see, shift to second gear and the engine speed goes from 5000RPM back up to 8250RPM while the wheel speed goes from 580 RPM to 863 RPM. A small increase of 283RPM vs the again, 3250RPM span of the engine.

First gear:
Pulley: 8250-1500=6750rpm * .1lb saved = 675
Wheel: 580rpm * 10lb saved = 5800

Second Gear:
Pulley: 3250 rpm *.1lb saved = 325
Wheel: 283rpm * 10lb saved = 2830

Clearly the wheel is more advantageous all of the time by a LARGE margin.

Also, the weight savings by a pulley is far more than .1lbs, not to mention the reduced load of aftermarket pulleys under-driving.

The stock pulley itself weighs roughly half of a pound. There's little to no weight savings from the pulley, its function is mainly to underdrive components.

Secondly, prove to me you can save 80lbs by getting new wheels and tires. First off, when you go from 19 to 20" using the correct size tires (same outer diameter/width) - yes, the barrel of the rim only goes .5 inch further way from the axis of rotation, but it still goes out further. What you lose in this increased torque from this rotating mass totally outweighs the small gain you have by having slightly less sidewall rubber (your contact patch rubber barrel is still the same on both a 19" and 20" tire - the only difference is sidewall.

19" OEM wheel weights:
29-30lbs

18" Lightweight magnesium wheels:
14-15lbs

Weight savings from wheels alone here is ~15lbs add on top of that the lighter weight of the 18" tires and you have close to 20lbs saved per corner

This is not to mention that a pulley costs about $500 and high end, light weight wheels you seem to referring to cost about 8-10 grand per set.

he said 6k and he didn't say new.

But again, all that aside, I want PROOF you can save 20lbs per corner. Cause otherwise, I call BS on that one.

Answers are in bold above.

Quote:

Originally Posted by Myke951

Exactly... 18lbs a corner? what are you smoking? unless it is a wheel made of carbon fiber (yes i am aware of them)... Again revo I acknowledge that its not the same as shaving weight, BUT it does share similarities in acceleration through hp/weight ratio... (like a lotus versus an e46 m3 lotus= 2000lbs with 200hp, m3=3300lbs with 333hp)... I think you guys are taking what I said the wrong way... BMWPOWER06 I would LOVE to see your car with your wheels go against an rpi stage 2 car with stock wheels on... lol, itll almost be as good as you saying AFE actually made power...

Please quote me where I said MY car would take on an RPi stage 2 car. All I said was my 20" forged wheels are lighter than the 19" oem wheels.

BMWPower06 · 13th April 2010, 20:31

20 lbs/wheel
x 4 wheels
x10 (ratio of unsprung to sprung weight savings)
=800 lbs

4000lb/500hp = 8lb/hp on the M5

800lbs/(8lbs/hp)= a gain of 100hp simply from lighter wheels...

Or even a slightly lower savings of only 10lbs/wheel would still result in 400lbs saved or 50hp gained.

Danish-M · 13th April 2010, 20:35

Quote:

Originally Posted by BMWPower06

20 lbs/wheel
x 4 wheels
x10 (ratio of unsprung to sprung weight savings)
=800 lbs

4000lb/500hp = 8lb/hp on the M5

800lbs/(8lbs/hp)= a gain of 100hp simply from lighter wheels...

Or even a slightly lower savings of only 10lbs/wheel would still result in 400lbs saved or 50hp gained.

No bragging rights with that set up though.

Revo · 13th April 2010, 20:52

You still don't get it buddy.

Even with a set of used $10,000 wheels, you'll probably still lose in a straight line to an RPI Stage II car...

EDIT: Simply typing "these wheels weigh this much, these wheels weigh that much" isn't proof at all...

I could claim a pulley has negative mass and adds 1000hp, but it doesn't make it so.

Revo · 13th April 2010, 21:03

Don't know if you just realized it, but you claimed that you save weight by going from 19" to 20" because there is less tire, then you claimed you saved tire weight going 19" to 18" - don't know about you but that just doesn't make sense.

Also, $6000 set of wheels vs $500 pulley. Don't know about you, but even according to your numbers, the wheels aren't even close to being 12 times better...

BMWPower06 · 13th April 2010, 21:04

Wirelessly posted (BlackBerry Storm: BlackBerry9530/5.0.0.328 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)

Quote:

Originally Posted by Revo

You still don't get it buddy.

Even with a set of used $10,000 wheels, you'll probably still lose in a straight line to an RPI Stage II car...

EDIT: Simply typing "these wheels weigh this much, these wheels weigh that much" isn't proof at all...

I could claim a pulley has negative mass and adds 1000hp, but it doesn't make it so.

Lol that's the best response you got? That the numbers above are lying? Ill post links to some light weight magnesium wheels later as I'm on my phone now. But the fact is that the numbers above don't lie. You're telling me that an rpi stage 2 car can beat another M5 that has the equivalent of 600HP? That takes rpi nut hugging to a new level, no?

Revo · 13th April 2010, 21:15

Quote:

Originally Posted by BMWPower06

Wirelessly posted (BlackBerry Storm: BlackBerry9530/5.0.0.328 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)
Lol that's the best response you got? That the numbers above are lying? Ill post links to some light weight magnesium wheels later as I'm on my phone now. But the fact is that the numbers above don't lie. You're telling me that an rpi stage 2 car can beat another M5 that has the equivalent of 600HP? That takes rpi nut hugging to a new level, no?

Uhhh, I don't have a single power mod from RPI, so I'm not "nut hugging." Is starting with the insults/childish name calling the best response you have?

You posted saying a set of good wheels would provide more of a performance increase than an RPI Stage 2 setup (Pulley, Scoops, BMC Drop-Ins, full exhaust, ECU + SMG Tune). I simply disagree.

You somehow turned this into a wheel vs pulley debate and I'm simply pointing out wheels are not 12 times better than a pulley based on your own over-simplified numbers.

Lastly, can you please stop pulling numbers from thin air? Wheels giving an equivalent of 100hp? Right. Show me a stock M5 with wheels keeping up to a 599GTB.

You do realize that rotating weight has less and less of a difference as speed increases right? In first gear the load from the car vs the load of having heavy wheels (or pulley) might mean something. At 100mph+ when the wind resistance is huge compared to the small advantage of light wheels/pulley it beings to mean nothing.

Ever thought of why a 500hp M5 loses the "power to weight ratio" war from 0 to ~130mph but will destroy cars that weigh far less after that? It's HP.

Don't know about you, but an exhaust and scoops and what not provides HP no matter how much wind resistance there is. Not sure if your wheels do that.

But since this has gone from a fact based, mature discussion to some baseless name calling, I don't see myself continuing to respond.

Stormster · 13th April 2010, 21:19

WOW OP you started a heated debate here for sure

Go with what makes you happy is my advice, take your time modding the car the way YOU want it. You don't have to blow 6k all at once. Why not add bolt on by bolt on and cosmetic change as when you start to look at the car differently and enjoy what you have as you get it

NobleM400 · 14th April 2010, 07:08

Quote:

Originally Posted by Frankenspyne

Question: If you only had $6,000 to spend on performance mods for your 2006 M5 with SMG what would you get done? Let's assume you don't care about exceeding 100 mph.

For example, CPU chip, exhaust and air induction
or
headers and exhaust
or
throttle bodies and a rear

If you could be brand specific that would also be helpful.

Thanks, Scott

Scott:

I really think it depends on what you're looking for.Your preferences will play a huge role in what mods will work best for your situation.

Assuming you're looking for straight line performance, your best bet would probably be:

Intake.(the RPi solution is $349 for the scoops & filter, $22.50 for the blockoff plates, plus free shipping locally, or up to 30 minutes for install elsewhere.Solutions from other companies vary).20+ hp possible, depending on dyno.

Pulley ($400-500, plus about 1-2 hour install).HP depends on what dyno, but all of the ones on the market with the same diameter will give you roughly the same hp.The difference between brands comes down to coating (regular anodized or hard anodized), weight, color (OE color, or totally different), and price.It's a nice " border="0" alt="" />At this point, it's probably time to look at exhaust (if you're ok with a sound increase), or software (if you're not).

Exhaust sound is a very personal thing. You really should listen to some and see what you like. Some add HP, some do not, and some even lose power. While all of this is important, if you can't live with the sound, it's a moot point anyway. If you want only a smaller increase in sound, doing just section 1 or 2 may be the way to go.

You may want some handling mods too. Eibach springs may be a nice choice, and aren't too expensive. A set of spacers/bolts can be used to give you a slightly wider stance.

In terms of weight savings, going with lighter weight wheels pays off both on the straight line, and through the curves. However, it's not cheap.

Take for instance, the ultra-light BBS magnesium wheels (Dymag, the producer of the carbon fiber/magnesium wheels went Chapter 11 earlier this year). These lightweight, relatively delicate wheels weigh only 15.4 lbs in 18 x 8.5" and 17 lbs in 18 x 9.5". A set of 4 will probably run you $10k or more. The OE wheel is 26.5 lbs front, and 29.1 lbs rear, so these save you roughly 46 lbs total.

For the rear:

285/40R18 tires puts you close to the same diameter as the original 28 lb 285/35R19 tires. However, they're not available in many of the most desirable makes/models. However, there's the Goodyear Eagle F1 Supercar (32 lbs in this size), BF Goodrich g-Force T/A KDW2 (31 lbs in this size), and Pirelli P-Zero Rosso (32 lbs in this size). In other words, about 3-4 lbs heavier per tire than the stock 28 lb tire.

In the same way, the correct sized front tires (255/45R18) weigh an average of 29 lbs, about 3+ lbs more than the 26 lbs the OE tires weigh.

So, you save 46 lbs in wheel, and add 14 lbs with correctly sized tires, putting you at about a 32 lb weight savings.

Because of the many MANY variables, it's impossible to pinpoint an exact relationship of effectiveness of rotating, unsprung weight vs sprung weight. However, most reputable places put it at upwards of 3-4x the benefit. So, a 32 lb weight savings from the wheels/tires MAY give up upwards of roughly the same benefit of dropping 128 lbs from sprung weight (ie. lightweight battery, CF hood, etc).

A stock M5 has 500hp and weighs 4012 lbs.

Dropping the equivalent of 128 lbs puts the car at 3884 lbs.

At 3884 lbs and 500hp, we're at 7.768 lbs per hp.

To reach the same power to weight ratio at the stock weight:

4012 lbs / 7.768 = 516.5 hp

In other words, dropping 128 lbs of weight will give you the approximate performance (at least straight line) of increasing your power by 16.5 hp.