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10-02-2011, 07:30 PM | #45 |
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A certain amount of sidewall flex is necessary to generate maximum grip. This is called "Slip Angle". The fact that there is less sidewall flex on a tire does not necessarily equate to better cornering grip and as a matter of fact there is a point where if the sidewall is too stiff cornering grip will suffer.
I would not characterize " there is very good evidence that the 18s outperform the 19s." as a blanket statement, but for what it is worth at least some (if not all) of the racing versions of the M3 use 18" rims. It would seem to me that if 19s were faster they would use them. Here are the specs of the Rahal Letteman racing version of the M3. Note that it has 18" Rims. Technical Specifications of the M3 Race Version. Weight 2,745 lbs./1245 kg Tank capacity: 23.7 gallons/90 Liters Chassis/body: Unitary construction steel body with welded safety cell made of extremely rigid precision steel tubing; safety fuel tank in CRP sandwich tray; pneumatic four-stamp jack system Aerodynamics: Front fenders, rear apron, hood, roof, trunk lid, rear wing, front wings, and flared rear wheel arches in CRP Transmission: Carbon fiber clutch with hydraulic central slave cylinder; 6-speed sequential racing transmission with straight-cut, unsynchronized gears; additional oil/air cooler; quick shift system with ignition cut-out controlled by shifting force; mechanical limited slip differential with additional oil/air cooler Front axle: Based on production version, with increased wheel caster angle, enlarged track width and enhanced wheel camber; five-way adjustable shock absorbers; tubular stabilizer bar Rear axle: Based on production version, with enlarged track width and enhanced wheel camber; five-way adjustable shock absorbers, tubular stabilizer bar Front brake system: Six-piston aluminum brake calipers, inner-vented grey-cast iron brake disks 15.0 in./380mm in diameter Rear brake system: Four-piston aluminum brake calipers, grey-cast iron brake disk, 13.1 in./332mm in diameter Steering: Rack and pinion steering with electro-hydraulic power Wheels: Aluminum wheels, 18 inches
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10-02-2011, 07:43 PM | #47 | |
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I have first-hand clinical results - running 18's versus 19's back to the back on the same car, same day with same alignment and same rubber I was able to shave off almost 4 seconds at road atlanta - thats what I have to report from experience from MY car - I don't speak for all. |
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10-02-2011, 07:55 PM | #48 | |
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The general rule of thumb is that for racing and high performance tires between 6 an 10 degrees of slip angle will generate maximum grip. If you are cornering and the slip angle is below its optimum range the tire is considered to be under-used. If it’s above this range the tire is being over-used. The trick is to stay within this optimum range so you use the tires to their fullest potential. As you pointed out "Between 6 and 10 degrees" does leave some leeway as to what is the optimum amount and obviously there are other factors to be considered. My point is that the ideas that "the stiffer the sidewall the better the performance" and "the stiffer the suspension the better the handling" are only true to a point. I do claim to speak for all either and I do not dispute your findings. I will stand by my statement that "There is evidence that 18s will outperform 19s." CA
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10-02-2011, 07:57 PM | #49 | |
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I've got first hand evidence that 19's did better than 18's at a race track with as many variables constant as possible. |
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10-02-2011, 08:10 PM | #50 |
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OK, who cares. The OP is worried about ride quality, not lap times. Geeze...
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10-02-2011, 08:29 PM | #51 | |
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As I stated I do not dispute your claim but a sample of one is not exactly conclusive. As you stated "I don't speak for all". Well neither do I so apparently in some cases 18s may outperform 19s and in some cases they may not. This however is not what I was originally claiming which was that a stiffer ride does not necessrily equate to increased performance and may in fact equate to decreased performance, CA
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10-02-2011, 08:31 PM | #52 |
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During cornering, there's a difference between the direction that the wheel's centerline is pointing and the direction that the tire is traveling. The difference, measured in degrees, is referred to as slip angle. Different tires have different slip angles at which they generate maximum cornering traction.
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10-02-2011, 08:34 PM | #53 | |
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Ca
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10-03-2011, 12:17 AM | #55 |
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10-03-2011, 05:03 AM | #56 |
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Thanks again for all the suggestions. I drove today for the first time since Friday, it takes an hour to get home from where I spend the weekend. When starting out I thought I may have been overreacting.
But after a while the ride got very annoying, not because of the bumps, it is the vibration that irritates me. The house keys jangling on the seat. The coke zero rattling in the cup holder. My head wobbling against the headrest. I drove on an empty stomach and felt a bit nauseous by the end. Surely that's not how an M3 is supposed to feel? Am going to the dealer tomorrow to check for shipping blocks and discuss options. Kmarei thanks for the idea, and I like your pic |
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10-03-2011, 05:13 AM | #57 | |
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Wow, are you driving down a gravel road, or are the roads really bad there? That sounds like a way rougher ride than it should be. If it turns out to be the shipping blocks then maybe you can get your boxers back
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10-03-2011, 05:19 AM | #58 | |
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For example, F1 cars are restricted to 15" wheels, does that mean we should all get smaller brakes and run 15" wheels too?
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10-03-2011, 05:27 AM | #59 |
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10-03-2011, 05:35 AM | #60 | |
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Also, is it actually a jarring ride, or heavy vibrations? If it's vibrations it may be indicative of a wheel/alignment/suspension problem instead. Anyways, I would definitely check for shipping blocks first, then if that isn't the cause, have them check your wheel balance.
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10-03-2011, 05:44 AM | #61 |
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Rshane,
It's the vibrations that are noticably different from the 320. It comes straight through the steering wheel and by the journey's end it feels like I've just driven the Singapore GP. |
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10-03-2011, 07:20 AM | #62 |
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Well, vibrations are a different matter which leads me to believe you may have a wheel out of balance. No matter what, take it to the dealer and have them take a look. We could speculate all day long on what it could be, but the experts should be able to figure it out quickly.
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10-03-2011, 10:20 AM | #63 | |
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CA
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10-03-2011, 12:10 PM | #64 |
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Yeah...I was scratching my head at that too. I never run "comfort" as it feels too bouncy. Depending on what I'm doing, I run a mix of normal and sport.
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10-03-2011, 12:13 PM | #65 | |
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10-03-2011, 12:16 PM | #66 | |
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