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      10-02-2011, 07:30 PM   #45
captainaudio
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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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Last edited by captainaudio; 10-02-2011 at 07:42 PM.
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      10-02-2011, 07:38 PM   #46
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i wonder if maybe you'll just get used to the stiff ride after a while, and start to appreciate it.
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      10-02-2011, 07:43 PM   #47
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Quote:
Originally Posted by captainaudio View Post
A certain amount of sidewall flex is necessary to generate maximum grip. This is called "Slip Angle".
Of course a certain amount of sidewall flex is needed - but the question is HOW MUCH? There is an optimum slip angle for max grip which depends on ALOT of things. The type of tires you're running (slicks, r-comps, streets have VERY different optimum slip angles). Also your alignment, weight, suspension, geometry will all matter. Just because you threw out a race car example doesn't make much of a point.

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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Quote:
Originally Posted by 4sevens.com View Post
Of course a certain amount of sidewall flex is needed - but the question is HOW MUCH? There is an optimum slip angle for max grip which depends on ALOT of things. The type of tires you're running (slicks, r-comps, streets have VERY different optimum slip angles). Also your alignment, weight, suspension, geometry will all matter. Just because you threw out a race car example doesn't make much of a point.

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.

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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Last edited by captainaudio; 10-02-2011 at 08:04 PM.
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      10-02-2011, 07:57 PM   #49
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Quote:
Originally Posted by captainaudio View Post
I will stand by my statement that "There is evicedence that 18s will outperform 19s."

CA
There's evidence that you need to check your spelling.

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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Thickness feels good to me and my hands aren't that big.
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      10-02-2011, 08:29 PM   #51
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Quote:
Originally Posted by 4sevens.com View Post
There's evidence that you need to check your spelling.

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.
And I have evidence from several professional drivers to the contrary.

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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Last edited by captainaudio; 10-02-2011 at 08:41 PM.
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      10-02-2011, 08:31 PM   #52
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Quote:
Originally Posted by captainaudio View Post
A certain amount of sidewall flex is necessary to generate maximum grip. This is called "Slip Angle".
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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Quote:
Originally Posted by Doc V. View Post
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.
That was my point. Reducing tire flex and consequently slip angle will not neceesarily increase grip and at some point it will decrease grip.

Ca
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      10-02-2011, 08:35 PM   #54
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Quit being a pussy.
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      10-03-2011, 12:17 AM   #55
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Quote:
Originally Posted by captainaudio View Post
so apparently in some cases 18s may outperform 19s and in some cases they may not.
That's a more intelligent statement .
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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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Quote:
Originally Posted by ASENNA View Post
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

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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Quote:
Originally Posted by captainaudio View Post
Here are the specs of the Rahal Letteman racing version of the M3.

Note that it has 18" Rims.
Wheels: Aluminum wheels, 18 inches
Although I do agree that 18" wheels may provide a SLIGHT performance advantage, I've got to point out that what goes on a race car can mean absolutely nothing for the equivalent road car. First, those 18" wheels on the ALMS GT car are 12" F and 13" R. Second, I don't know off the top of my head, but all of this may be dictated or engineered to meet some form or regulation or requirement by ALMS for this particular car.

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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Quote:
Originally Posted by Rshane View Post
If it turns out to be the shipping blocks then maybe you can get your boxers back


The roads aren't the best, but I didn't get the vibration in the 320.
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      10-03-2011, 05:35 AM   #60
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Quote:
Originally Posted by ASENNA View Post


The roads aren't the best, but I didn't get the vibration in the 320.
Yea, in that case I'm beginning to agree with the other folks here, it is most likely the shipping blocks. It's happened a few times to folks in the US.

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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Quote:
Originally Posted by ASENNA View Post
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.
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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Quote:
Originally Posted by e1000 View Post
Although I do agree that 18" wheels may provide a SLIGHT performance advantage, I've got to point out that what goes on a race car can mean absolutely nothing for the equivalent road car. First, those 18" wheels on the ALMS GT car are 12" F and 13" R. Second, I don't know off the top of my head, but all of this may be dictated or engineered to meet some form or regulation or requirement by ALMS for this particular car.

For example, F1 cars are restricted to 15" wheels, does that mean we should all get smaller brakes and run 15" wheels too?
Actually I believe you are very likely correct and ALMS cars may be limited to 18". Also the ALMS M3 is very different from the production car.

CA
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      10-03-2011, 12:10 PM   #64
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Quote:
Originally Posted by radiantm3 View Post
And here I was feeling like the M3 is too soft even on the sportiest setting.
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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Quote:
Originally Posted by ASENNA View Post
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
Yeah...that doesn't sound like the way mine rides at all. Sounds like something isn't right.
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      10-03-2011, 12:16 PM   #66
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Quote:
Originally Posted by Nelrock View Post
Yeah...that doesn't sound like the way mine rides at all. Sounds like something isn't right.
Does not sound like a suspension stiffness issue to me either. Sounds more like an alignment or balance problem.

CA
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