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  #1  
Old 07-10-2000, 12:20 AM
Subman's Avatar
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Join Date: Apr 2000
Location: South Florida
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In the new August European Car their is an article about the trends in tire and wheel sizes (pg. 42-44). I just scaned over it but it says that skinny tires make the car handle better and that low profile tires redeuce the contact patch of the tires. And that the true bennifiets of big wheels and low tires can only be seen on the track. The article then talks about how adding big wheels to a 300E made it handle worse on the street and wonder a high speeds.
Is this true?
Has anyone expierenced wanderind after adding bigger tires on to their 300E?
Or lost handleing around town?

Their is more to this article, read it and see what you think.

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  #2  
Old 07-10-2000, 04:55 AM
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There is so much physics wrapped up in tire selection that you need a Ph.D to get it even nearly right. Those of us without doctorates rely on trial and error instead. Here is what I've learned the hard way:

Lower profile tires allow quicker transient response to steering inputs. The trade-off is less sidewall flex and a harsher ride.

A larger contact patch allows for greater adhesion...to a point. When the optimum size of contact patch is exceeded, which is dependent on vehicle weight and the coefficent of friction for the road surface, you actually decrease traction by reducing the tire-to-ground loading per square inch.

Wide tires do tend to follow road surface irregularities more than narrow tires. This seems to be more pronounced on some vehicles than others, due to suspension angles. Again, there is an optimal width for each vehicle.

Of course, the manufacturer's tire size reccommendations are the safest bet and you vary from that at your own risk. Forums like this one let us share our experience with what works and what doesn't. Also, individual drivers will tolerate some trade-offs in ride harshness or tracking more than others.

And some just go for a certain look and don't really care what their beast drives like!



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Dean Albrecht
94 E500
99 ML320

www.need2speed.web.com
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  #3  
Old 07-10-2000, 12:27 PM
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JCE JCE is offline
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when it comes to tyres, a PhD in physics may be of limited help - there is often a huge gap between theory and practice. Also, the tyre compound and road/climate conditions will often have at least as great an impact as the dimensions. A "sticky" compound in a skinny tyre may outperform a wider but harder "mileage" tyre under dry conditions, but may not do as well under wet conditions. There is are way to many variables here for a blanket, rule of thumb to always hold true

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JCE
87 300E, 65k miles
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  #4  
Old 07-10-2000, 01:00 PM
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Location: ajax, ontario, canada
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i've been following the series of articles of the European Car magazine on suspension basics up to a few months back, and handling is only part of the story, and tires do play a role in this. The current issue of European Car contains the 6th in the suspension series, if i remember.

following are other points on the use of low-profile tires on road and track:

- lower profile tires (again, all other factors being equal) tend to have a more sudden breakaway when cornering. Higher-profile tires give you lots of warning. Race drivers have the reflexes to deal with the sudden breakaway.

- given a tire's rolling diameter or the car's wheel well size, a racing car would tend to use the largest wheel possible, simply to accommodate the biggest brakes possible. This means having the lowest profile possible. Ride quality is way down on their list of priorities.

- wide and low-profile tires tend to be more sensitive to camber change as the suspension moves, as it significantly affects the shape of the contact patch.

Passenger cars have a lot of wheel travel for comfort and ground clearance, and allow for some amount of body roll. Compared with a race car, the changes in tire camber of a passenger car (due to suspension geometry and body roll) are significant. Mercedes cars, in particular, traditionally have lots of body roll, although its suspensions generate some negative camber as they compress to counteract this. As a result, passenger tires are of the higher-profile variety, which can accommodate a wide range of camber change.

Race car suspension on the other hand is very stiff and roll is minimal, and wheel travel and camber are tightly controlled, allowing for precise suspension tuning. Another reason for the stiff suspension is to accommodate the significant downforce generated by the aero aids.

- a minor tradeoff is frontal area of the tire - wider tires generate more drag, but this can be reduced by fairings (which reduce the drag coefficient) or lowering the car (which reduces the exposed frontal area of the tire).

For curb appeal, a low-profile tire definitely looks better, but pizza-sized brake rotors are definitely sexier.
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  #5  
Old 07-10-2000, 09:32 PM
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Location: Toronto, Ontario, Canada
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Very good comments. Like most motorheads, I just assumed that the lower profile and more grip tire the better. The closest that I come to a track is the highway commute. I have a 99 C230 Kompressor and upgraded to 16 inch rims with a wider track at the rear. They run on Pirelli P7000. These tires are excellent in the rain. However, on the highway they wander a lot. In fact, it can tiring on a long trip as it requires a lot of concentration to keep the car in a straight-line. In fact, this is so bad that I am going to have MB check the alighment and tire balance even though the car is relatively new.

Given what I have learned from these comments, I will seriously reconsider upgrading to a lower profile tire on my next MB. I think the comments about MB's steering and suspension on lower profile tires are correct. I did not experience this wansdering problem on other automobiles. I had a 98 Volvo S70 with lower profile tire and did not experience such steering problems.
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  #6  
Old 07-11-2000, 12:11 AM
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In my experience, you can usually go significantly wider than MB OEM on many models without too many problems. The 300E does very well on OEM's but can be sharpened significantly by just sportline sizes. A 400E overwhelms the OEMs and does okay on Sportline sizes but really shines in the plus 1 fittment. 500E's can really overwhelm the stock fare but do great on plus 1's. The newer cars came with a more aggressive fittment from the factory so you see a less dramatic improvment than the older cars in my opinion. Unless you've done significant suspension work more than a plus 2 wheel/tire combo will not help handling. If your going for cosmetic appeal its great, if its more performance then it can vary some. Then again, beauty is in the eye of the beholder... Know your priorities going into an upgrade, get all the info you can, then do what (by all your info) seems to be the best option. Of course, talking to the folks in this forum and Luke ALWAYS helps.

Lee
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  #7  
Old 07-15-2000, 12:28 PM
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I disagree on the 400E. I think it shines best in its TRUE plus 0 fittment. 215/60/15. Best feeling one I've ever driven had that WITH 7" rims. That is a necessity. This combo sucks on 6.5" rims.

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