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      11-12-2007, 02:52 PM   #1
footie
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What is the best weight balance for a car?

This is a question which has come from reading an article about the best M cars in EVO. I known that BMW in recent years have marketed in ads that the best is 50/50 but I noticed in the EVO magazine in which they preferred the E30 M3 that it actually has not the 50/50 split but 46/54 bias to the rear.

Does anyone know why BMW changed to this especially as a car that's almost 30 years wins out of almost every M car ever made, including the CSL, M1 and the new M3.
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      11-12-2007, 07:40 PM   #2
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The biggest advantage of the 50:50 weight distribution is inherently neutral handling. Of course, there are plenty of other factors to consider but this is the best starting point. A rear weight bias help with straight line acceleration (if car is RWD) and straight line braking at the cost a tendency to oversteer. Front weight bias will show a tendency to understeer. 50:50 weight distribution was also pursued by Alfa Romeo before it became part of Fiat.
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      11-12-2007, 10:43 PM   #3
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Weight distribution

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Originally Posted by footie View Post
Does anyone know why BMW changed to this especially as a car that's almost 30 years wins out of almost every M car ever made, including the CSL, M1 and the new M3.
vm summarizes the weight distribution issue nicely. One factor in the shift on weight distribution is the move to larger & heavier engines. BMW has done a remarkable job, considering, not letting the bias go front heavy. Moving the battery to the trunk, shifting the engine behind the front axle line and using lightweight fenders and hood have helped in that regard.

An E30 M3 with 50/50 distribution would be just as good, I suspect. The light weight of the overall car is a definite advantage that has been lost in newer iterations.
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      11-13-2007, 10:45 AM   #4
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The only reason apart from the article in EVO was the fact that other front engined rwd sportscars are now showing a tendency to move the weight balance to the rear, 599, 612 and ever the new Maserati are all going down this route.

I wonder are they under the belief that as more power is added (over 500hp) that acceleration and traction out of corners is more important than a neutral handling balance?
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      11-13-2007, 11:20 AM   #5
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OT: Weight distribution & performance

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The only reason apart from the article in EVO was the fact that other front engined rwd sportscars are now showing a tendency to move the weight balance to the rear, 599, 612 and ever the new Maserati are all going down this route.

I wonder are they under the belief that as more power is added (over 500hp) that acceleration and traction out of corners is more important than a neutral handling balance?
Here's some excellent analysis in that regard on the Ferrari 612 Scaglietti from [i]Motor Trend[/i. Maybe the M3 needs to go to a transaxle setup!

"The 612's ultra-long wheelbase makes it look a bit awkward from some angles, despite the "Ingrid scallop" used to disguise it, but Ferrari's engineers deemed it vital to approach the target front/rear weight distribution of 45/55. (The final distribution ended up 46/54.) That target was established after extensive testing on the effect of weight distribution on acceleration, handling, and braking, the graphic results of which are illustrated on this page.


Acceleration performance was found to improve markedly as the percentage of weight on the rear tires increases beyond the 40 to 50 percent most GT cars employ, before leveling off between 55 and 60.


The steering-wheel angle required to maintain a given lateral g load varies noticeably with weight distribution. At 0.90 g, the mule with the 55-percent rear bias required 28-percent-less steering input than the one with a similar front weight bias. Less steering input means less understeer, better handling, and improved tire wear.


Weight shifts forward under braking, which diminishes the amount of retardation the rear wheels can provide. At 0.90 g, the rear-biased mule's rear brakes were generating 64 percent as much retardation as its front brakes, whereas the front-biased mule's rear brakes could only manage 41 percent as much braking as its front brakes. The more evenly split the brake force, the less fade and the more confident the brakes feel."
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      11-13-2007, 12:20 PM   #6
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And I thought it was a case of when the power reached a certain power more weight was beneficial, clearly there was a lot more to it than that.

Thanks.

P.S.

So when will we see this happening do you think?
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      11-13-2007, 12:43 PM   #7
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Weight distribution

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And I thought it was a case of when the power reached a certain power more weight was beneficial, clearly there was a lot more to it than that.

P.S. So when will we see this happening do you think?
More weight is never beneficial for performance. You don't see Formula 1 cars adding weight, and they are plenty powerful and light.

BMW's design philosophy may well be different from Ferrari and others that strive for the rear bias. Hard with a front engine layout to get a rear bias. A longer wheelbase and a transaxle could help, but there are tradeoffs such as vehicle size and expense. I would guess BMW will stay with the 50/50 goal for the forseeable future.
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      11-13-2007, 01:52 PM   #8
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Big picture

I do not think you can say what distribution is "the best". Greg did find some nice data above though that speaks against the need for 50-50. The suspension, tires and brakes must work in harmony. Porsche is a perfect example. Take a design that really should not work very well (extreme rear weight bias). And in fact for many years the design did not work well, twitchy, unforgiving in corners to changes in throttle, and other nasty braking/handlign traits. Then absolutely tweak the suspension and brakes and other details to work with the exisiting weight bias. Net result is that today the cars work very well given this "handicap". They have also proven to everyone they have such a handicap with the Cayman.
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      11-13-2007, 02:09 PM   #9
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Quote:
Originally Posted by swamp2 View Post
I do not think you can say what distribution is "the best". Greg did find some nice data above though that speaks against the need for 50-50. The suspension, tires and brakes must work in harmony. Porsche is a perfect example. Take a design that really should not work very well (extreme rear weight bias). And in fact for many years the design did not work well, twitchy, unforgiving in corners to changes in throttle, and other nasty braking/handlign traits. Then absolutely tweak the suspension and brakes and other details to work with the exisiting weight bias. Net result is that today the cars work very well given this "handicap". They have also proven to everyone they have such a handicap with the Cayman.
I think I was misunderstood, I didn't mean add more weight, more a case of moving the existing weight more to a rear bias.

I know Porsche has done miracles with the 911 but though it's improved
beyond recognition it's still not a point where one would want to start, I think even Porsche would agree with that one.

By the way I wasn't wanting to start a debate on the subject, more understand why they chose this setup over the earlier E30 M3's setup when clearly it was so perfect that it could win a contest among such other amazing M equipment.

P.S.

I noticed in this review that the E30 M3 was the last M3 to have electronic adjustable suspension. Bodes well for the new E92 I say.
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      11-15-2007, 09:49 PM   #10
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Weight distribution dictates traction, quickness to rotate, and significantly impacts packaging. The Ferrari 599 is a LONG car for only a 2-seater. Much of this length probably came from their desire to achieve the rear-weight bias (must lengthen the hood and move the engine back and well behind the axle). The M3 starts as a 3-series, and thus by nature a more practical car that is not too long (180 inches) yet still can carry 4 folks and some luggage. Because they used a pretty small, light, and compact V8 they were able to position the engine pretty far back in the bay. Then they used additional light weight tech and weight tricks (battery in trunk, as mentioned) to nearly attain the 50/50 goal.

Keep in mind if someone orders some options (rear sun shade, ampified high end audio with amp in the trunk, etc) these options will add weight to the rear and may actually reach the 50/50 goal. Card and Driver weighed it as 51.9% front, 48.1% rear, which is pretty darn close to 50/50. If you want perfect 50-50 just throw a friend in the trunk.

For racing purposes I believe a slight rear bias is preferred (see Forumla 1 = mid engine, rear weight bias). But mid-engined cars are a lot less practical from a packaging perspective.
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      11-17-2007, 10:22 AM   #11
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I'm coming at this from a lowly 2.0 E36 point of view with an open diff, but I find that the inherent neutrality of the chassis helps when you go into lift-off oversteer and it still seems very collectable and not at all like you're about to lose all control, regardless of steering input. That's a huge benefit, because you can get your kicks without really endangering yourself.
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