Wheel Weight - Speed - Feel - PeachParts Mercedes-Benz Forum

dtanesq · #1 05-02-2002, 05:33 PM

Hi Folks:

I thought I'd post this question here on the best enthusiasts'
forums I'm aware of. The Bimmerhead forums aren't as impressive by far. Some of you may remember that I once owned a W124 and hung out on this forum for awhile.

I'm not an engineer and never really studied this stuff, but would like a layman's explanation of the following phenomenon.

I now own a relatively pristine 1993 BMW 525i. When I received the car, it was shod with the stock 15" wheels with the 20-something holes. Pretty boring wheels in terms of looks, etc. Recently, I ran across a very nice set of 16x8 BBS alloys (OEM from a 1996 740il), which I purchased. I had Michelin Pilot Sports mounted and then mounted the wheels and tires on my car. The BBS wheels are MUCH lighter than the stock wheels. Also, on 3 of the 4 wheels, no balancing weights were necessary as they zeroed out on the balancer. The fourth wheel required a quarter of an ounce.

From the moment I first drove down my street, I was surprised at the massive difference in feel and would like some assistance in explaining this to myself. The car feels as though it accelerates quicker. The M50 engine in these cars is notorious for being a dog at around 2000 rpm (I haven't dropped in a performance chip yet - coming soon), and while that is still there, it is relative to the overall change in feel and now much less annoying. I can't verify that the car is actually quicker, I'm just saying it FEELS quicker. The rest of the handling characteristics are also greatly enhanced. More precise turn-in, quicker steering, flatter and more stable cornering behaviour, blah, blah, blah. Kind of feels a little like a go-kart, actually. I love it.

I can guess what a set of 50-series Pilot Sports are contributing to handling feel. But, what role does weight at the end of the axle play in all of this?

Thanks.

bobbyv · #2 05-02-2002, 06:11 PM

if your new wheel/tire setup has a smaller rolling diameter than stock, then your acceleration will indeed improve, as this is equivalent to improving your gearing.

the michelin pilots are largely responsible for the cornering feel, in terms of steering response and grip.

road feel is also affected by the tires. In general, a plus-1 setup will feel harsher than stock, but the tire itself could also compensate for this - Michelins are known for a smooth ride.

but what you have not really described in your note was road feel over bumps at speed:

- the lower unsprung mass would make the ride less harsh, as there is less mass (and therefore kinetic energy) on the jounce portion of suspension movement, that would be transmitted to the body (net of what is absorbed by the shocks)

- the lower unsprung mass would also tend to aid roadholding (i.e., on bumpy high-speed corners), as the lower unsprung mass of the wheel/tire combination will make them remain in contact better with the road surface.

how's your car in terms of reliability? you should post some stuff about this.

JCE · #3 05-02-2002, 06:14 PM

Hi David:

I was going to write up an explanation on the physics, (less momentum / inertia to have to control, easier to keep the tires on the road, etc.) but being lazy I checked to see if someone else had already done a better job - and indeed they had.

http://integra.vtec.net/wheels/lightwheels.html

Ashman · #4 05-02-2002, 07:01 PM

My friend has a 1991 525 I Auto, and has 17" Very light Alloy BMW wheels I thinkt hey are 6 spoke, I think they are great looking.

Anyway, his car is no dog, it actually is quite quick, at most any speed.

I had looked at the same cars, only I was going for a 540 because the car is fast, but decided I didn't like the way the BMW interiors seem to fall apart and how the leather seems like plastic at times.

I'm not sayign they are all like this, but I have noticed it with man.

My benz interior is still near perfect, with 10 years on it and 100,000 miles.

Congrats on the car. My friends has been very reliable, he takes it in for repairs maybe once a year. The only issues he has had that were major was a collapse of the suspension. So My suggestion would be to make sure the front suspension is all ok, because his was fine and one day while driving, it just collapsed.

Other than that, He has had minor issues, apart from replacing the tranny, and one of the computers. He has done nothing more than regular maintenace items.

The engine has been extremely reliable though.

Alon

dtanesq · #5 05-02-2002, 08:24 PM

Hi guys:

Ashman - What happened to your car? Ouch!!! In terms of the front suspension on the 5, I had some minor issues with the entire suspension when I received the car, so I had all of the strut cartridges replaced with Bilstein HDs. The springs are fine, the suspension pieces themselves (links, bushings, etc.) are all fine. A few months ago on a Saturday night an idiot in a Toyota Corolla missed his freeway exit (or was drunk) and cut across four lanes of freeway traffic. I was in lane 3 - counting the inside lane as 1 - and the 5th car in the pack. All of the cars in front of me did a panic squeeze to the right shoulder as Corolla-man dived for the shoulder himself. I had nowhere to go but over a curb, into the air (still in excess of 50mph by that time) and up a dirt embankment onto another freeway's on ramp. The new wheels were in part a reaction to two collapsed front rims. I had the suspension pieces checked out and they're all fine. Just needed alignment. So all of the pieces in the suspension should last awhile longer.

John - Thanks. I will pursue your link when I have a longer moment. I hope all is well and things worked out with the C-class tranny issue.

Bobbyv - The overall circumference with the new tires is only marginally smaller than stock, since I was careful to keep that variable within a small difference to keep the speedo and wonderful on-board computer reasonably accurate. The feel over road bumps and such, while different from stock, is not at all harsh. The car stays glued much better than previously. I now have more road feel, but my kidneys are not impacted. Steering self-centering is slightly reduced. I love the feel overall. I'm guessing, though, and this is NOT meant to be a gender-based comment, that my girlfriend will not like driving my car (which she will be doing on Highway 1 north of San Francisco this weekend), since it requires attention - steering is VERY quick compared to the 300E (and the stock 525i) and, likewise, her Toyota 4Runner, and the reduced self-centering makes inattention a no-no at speed. The movements made to the wheel are much more subtle than in those other cars.

Reliability. Hmmmm. I hope this is responsive.

The questions are build quality and systems design. I prefer the build quality of the Mercedes. My 300E is still "in the family" as it's now owned by a close friend of mine. I still monitor the maintenance (he's an automotive...uh...neophyte...) and still occasionally drive the car. I recently took the car in for service and some repair as his proxy because I am more conversant in those matters than he is and the car's longtime mechanic is a friend of mine. The E is 9 years and 50,000 miles older yet about 2 times tighter than my 5 Series. I've had to reglue some trim pieces in the BMW's interior, tighten some connectors (some of the wood trim actually fell off) and there are ongoing issues with the rear door seals and the window moldings on the front and rear windows. My 7-year old daughter is pissed because I can't isolate and turn on the rear seat lights so she can play with her dolls at night as one could with the 300E. She also misses the rear headrest switch which drops the headrests in the rear.

Mechanically, there is a glitch in the central locking system, but that's simply an adjustment problem that I haven't had the time to correct - easy fix, just need to adjust the trunk lock mechanism. Otherwise, the major mechanical system, the engine and drive train, is exemplary. I've already talked about the suspension system. Interestingly enough, oil changes have been kinda weird in a good way. There is almost no color or clarity change in the oil at the end of the 3000 miles (must be pretty damned clean in there). I use synthetic oil exclusively in the car. So I have no complaints with the drivetrain other than the minor weakness in horsepower at the bottom of the curve (see below re: chip). The brake system works great and service is easy DIY. Easier than my 300E was. There is an upgrade that the BMW community talks about involving installing M5 brakes. Huge stoppers those. Probably whiplashers. I'm intrigued by that and will look into it.

Electrically, it's there the design seems weird to me. The Bavarians have this little thing called a "fusible link" which is simply a heavy fuse in the positive cable from the battery (which is under the rear seat...). If the fusible link fails, supposedly the windows, door locks and windshield wipers will fail to operate. From my experience, nothing operates, since in my car the link seperates the positive terminal from the electrical system. I keep three extra in my ashtray. There is also a separate fusebox under the left side of the rear seat in addition to the fusebox in the engine compartment. Consequently, there are 3 places to check for a fuse failure. Strange to me. On the other hand, unlike the W124, there is not the possibility of being stranded due to a relay failure (OVP or fuel pump relays come to mind - and having been stranded in the 300E one Halloween night with a carful of princesses and goblins because the latter failed). Also, unlike the W124, there is no intermittent stall issue, no rough idle thing and most interestingly of all, for $250, one can drop in an engine management chip in the black box which will give the engine another 20 horsepower and 20 foot-pounds of torque. My understanding is that only an idiot can screw up that upgrade (watch me...) and the difference is dramatic. One is stuck running 91 octane after a chip replacement, but...so what? BMW sort of acknowledges it detuned the engine for the American market so as to have the "appropriate" performance gaps between the 525i, 535i and M5. Most tuners make an attempt to bring the engine management system in line with the engine's true potential. I like the sound (and feel) of 210 horses more than 190. 20 footpounds at the bottom end is also mucho appealing. Think of this, too. I have the same engine in my 3600 pound car that the much lighter 325i and 325is had in the same model year. Those engines are detuned even MORE, which is, I would guess, why they are so popular with the club racing set. I've read that one can even tune the low-revving eta engine into a little growler....

To me, the difference between the cars lies in their purpose in life. I know, I know, John is going to remind me about his W124 with Sportline suspension. In my view, in terms of the driving experience, there is a very definite difference in the cars. Again, I still drive the 300E from time to time. It now feels stiff and unsupple to me. Too much body lean in hard cornering (it has Bilstein HDs, too). The limit feels like it comes sooner. That steering wheel is just too damned big too! My 525i is a freaking road rocket at speed, smooth as silk, and very, very light and nimble on its feet, especially now with the BBS alloys all around. I love it, while my passengers tend to be holding on for dear life. I also think my 5-Series is as sexy a car as I've ever owned (I still haven't owned a CLK, though). It's black as night, the BBS basketweaves are gorgeous and it just screams speed. The taller 300E doesn't, to me. It's in the driving experience that I prefer what I now drive to what I used to drive. Someday, the door panels are going to fall off the 5-Series, the fenders are going to rust away and the exhaust system will fall off. Meanwhile, my old 300E will still be steaming along like a solid little tank (at 300000 miles). I'll have rubbed through 9 sets of Pilots while my friend will still be *****ing about the $600 it costs for a set of MXV Plus 4s. I'll have speeding tickets and maybe another wild evasive action notched on my gunstock.

For my personal vehicle, when this 5 is done, I'll go out looking for a balls to the wall M5. I simply love the driving experience of my BMW. My wife (by that time) will drive the Mercedes with our kids in it.

I continue to, and will always, pester my investment banker friend to let me have his 500E. Now THAT car.....

Ashman · #6 05-02-2002, 09:22 PM

Thats how my friend is. He wants to upgrade to an M5 sooo badly. He had hsi car clothed in an M5 bodykit just to wet his appetite.

I know what you mean. they do drive nice, and I like the way my friends car drive, on city streets, twisties and highway its a very solid car. In fact that bodystyle is one of my favorites out of all of BMW's lineup in the last 15 years.

I dont know exactly what happened in his suspension that caused it collapse that one time, but I assume it ws some kind of mount, link or something that broke or came off.

These cars are very modifyable, and in turn, there are some great looking nodykits, and accessories for them.

Sometimes I wish I had gotten one because of allt he readily available mods for the car, but I love my benz.

Congrats on the car, I know you are enjoying it, I would too.

Alon