M45 with new wheels, tires, springs. Suspension upgrade. 4-Door Porsche 928

Forum for Infiniti M35 and M45, and Nissan Fuga owners.
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szh
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Re: 0-60 times and braking distances for the M45 (with new wheels and tires)

Postby szh » Wed May 26, 2004 6:08 pm

multisync1 wrote:Braking distances did improve considerably, however, most likely due to the far stickier Pirellis (and greater contact patches due to the wider wheels -- 1 extra inch in the front and 2 in the rear) and to a lesser extent due to the lesser weight of the tire/wheel combination.


Actually, contact patch area probably did not change much - the weight of the car is mostly the same and if the tire pressures are similar to before, then the square inches of rubber contacting the road is similar, no matter how wide the tire.

The stickiness of the tire had the most to do with the improved performance, I bet!

Good post and info, by the way! Thanks! :)

Z


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Postby HondaCRX » Wed May 26, 2004 6:08 pm

Nice M. I like the wheels, unsure about the colour on a silver car though. Black would have been a better option, if it was my vehicle...but, then it looks too "kiddy-like" and loses it's "majestic" (or grown-up) look.
multisync1 wrote:First, the transmission could be a little faster.
a higher stall TC will help a little. better fluid will too.

Quote »The second issue is the steering ratio. It's pretty slow for a car of this type. [/quote]Define "this type". You have a high-end luxury car. it seems like you're bothered by that. expect more "luxury" items over "sporty" items.

imagine a quicker steering ratio with grandfather time behind the wheel? scary.

Plus, it's not a sports car.

Quote »Changing out the steering wheel for a shorter diameter wheel is the easiest way to speed up steering. I wouldn't do that though as this would delete the air bag packed in the original wheel.[/quote]and could potentially be illegal in your state. another way is to dial in some toe-out in the front and toe-in in the rear. it'll help with making the car response quicker to steering inputs.

Quote »Does anyone know of anything else that could be done to speed up the steering ratio? One installer suggested changing out a pulley for a smaller pulley but recommended against that fearing it might burn out the power steering. Any thoughts? [/quote] or changing out the actual gear in the rack. But, now you're talking about major modifications. If you want a sporty car, why not buy it in the first place? I'm all for taking a car that's rarely modified and sprucing it up... but, there's a limit that you're bound to reach.

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Postby multisync1 » Wed May 26, 2004 6:08 pm

All the performance stats were done with the VDC off.

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Postby 1992Q45A » Wed May 26, 2004 6:08 pm

60-0 110 ft..

That's almost to good to believe.. That's 911 turbo with ceramic brakes numbers...

I guess the electronic brake force distribution must be good...

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Postby szh » Wed May 26, 2004 6:08 pm

HondaCRX wrote:a higher stall TC will help a little. better fluid will too.


Careful on this one. The M45 and new Q45 (and probably the G35 too) require Nissan J Transmission Fluid. This is a new formulation ... not using it will definitely void your warranty! The M45 Full Service Manual has dozens of warnings about this in bold letters.

Needless to say, this transmission fluid is a lot more expensive. :( I had the transmission flushed in my M at 7500 miles (I like to change out all factory fluids before 10k miles to allow the machining burrs to be taken out of the car early) and it cost an extra $75 over the normal cost of a flush.

Z

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Postby szh » Wed May 26, 2004 6:08 pm

multisync1 wrote:All the performance stats were done with the VDC off.


Good! :)

Z

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Postby multisync1 » Wed May 26, 2004 6:08 pm

Thanks for the info on the transmission fluid.

Did you also change out the radiator fluid and brake fluid at 7.5K?

I couldn't believe the numbers on the braking distances either. But those are the results indicated from two separate runs using the G-Tech Pro accelerometer. On the two tests, differences were within 1 foot of each other at 60-0 between the two runs (the second one was 111 feet). I will double check this against a stock Honda Accord LX to make sure the G-Tech Pro isn't giving unusually short distances. I'll post those results as a reference here once I do it.

Wouldn't wider wheels increase the contact patch? I've got 8.5 inch wide wheels on the front and 9.5 inches on the rear (compared to 7.5 inches all around from the OE wheels).

You do feel the EBD kick in because you can feel and hear all four tires scratching for grip during braking and they all seem to work equally hard throughout the entire range from 80 to 0.

I've actually heard that upgrading brakes to bigger sizes could actually hurt braking distances on many cars because the brake bias (front to rear) that was tuned by auto engineers could be compromised. Most factory brakes are already capable of locking up all four wheels at 80mph but are prevented from doing so by the ABS. The limiting factor then is whether or not all four contact patches are being utilized to their maximum at all times during the braking episode. Putting larger brakes in the front, for example, could cause you to use the front brakes more than the rear and then during braking you would be mostly utilizing the front contact patches at their maximum while the rear tires are hardly doing a thing. Brake upgrades are great for racing where you'd want to get more braking power from say 120mph and aftermarket brakes are usually better at dissipating heat thereby preventing brake fade. One interesting thing is that Brembo brakes does not do braking distance calculations and they state the reasons for this. Right on their site they say that a braking distance test from 80mph is more of a test of the tires gripping potential than of the brake's actual power since both OEM and aftermarket brakes can generate the force needed to lock up the wheel at that speed. I saw this on Car and Driver's Boost magazine which I found to be a pretty good source about aftermarket upgrades. It saved me quite a bit of money because I was actually considering upgrading the brakes to bigger rotors and calipers. Just changing the tires to stickier ones helped braking a great deal in addition to the handling improvements it made (and far less expensive than aftermarket brake kits).

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Postby jdmfreak » Wed May 26, 2004 6:08 pm

I guess Im late to this one, but that those wheels look sick on your car. For some reason I was expecting chrome rims. I saw a black Mwith 20in. chrome rims the other day and it was soooooooo nice.

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Postby szh » Wed May 26, 2004 6:08 pm

multisync1 wrote:Thanks for the info on the transmission fluid.
You are welcome!Quote »Did you also change out the radiator fluid and brake fluid at 7.5K?[/quote]I should have been clearer in my post. I mostly worry about the oils and fluids where there are machined metal surfaces that "rub" a lot. So, I have changed the differential gear oil (it is now Mobil 1), the engine oil (1500, 3750 and 7500 miles - last one was using Mobil 1 Synthetic 0W40), transmission fluid, cooling fan fluid, power steering fluid. Brake fluid and radiator fluid will be done at 15k and 20k miles (less real rubbing of machined parts in these systems of the car).

This may be gross overkill, but I am convinced that the left-over metal burrs that come off the machined parts in the first 5k to 10k miles are the true killers of long-term reliability for a car. So, I do this to any new car I get and they always last me well. In the one case where I bought a lease return, my 1995 Q45, I had the transmission go out, steering rack had to be replaced, etc., so my small statistical case says that I am right! :)

Z

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Postby HondaCRX » Wed May 26, 2004 6:08 pm

multisync1 wrote:I couldn't believe the numbers on the braking distances either. But those are the results indicated from two separate runs using the G-Tech Pro accelerometer. On the two tests, differences were within 1 foot of each other at 60-0 between the two runs (the second one was 111 feet). I will double check this against a stock Honda Accord LX to make sure the G-Tech Pro isn't giving unusually short distances. I'll post those results as a reference here once I do it.
Be very careful about quoting Ghetto-Tech results as fact. Yes, it's accurate within it's own measuring perimeters, however, measure it by actual tape, and it becomes inaccurate.

a few friends of mine did a testing with my vehicle back a couple of years. I was testing stock braking competents to wilwood 4 piston calipers. We used a g-tech as well as measured on the road.

the g-tech was posting 10-15' SHORTER distances, overall.

we did back-to-back stops, maybe with 5mins between each. Ran the same wheel/tyre combo. Stock, average from 60mph to nil was around 155', iirc. wilwood calipers, average was cut by 12'. This was mainly due to an old, worn out braking system getting replaced with new components.

Quote »Wouldn't wider wheels increase the contact patch? I've got 8.5 inch wide wheels on the front and 9.5 inches on the rear (compared to 7.5 inches all around from the OE wheels).[/quote]Only if the tyres attached to them are wider.

Quote »I've actually heard that upgrading brakes to bigger sizes could actually hurt braking distances on many cars because the brake bias (front to rear) that was tuned by auto engineers could be compromised.[/quote]Sorta. Most people who get bigger brakes, tend to get bigger wheels. Therefore, causing more rotational mass that has to be brought down to a halt.

Bigger brakes also carry more mass. This is GREAT for fade resistance, bullocks for cold stops. People can see shorter stopping distances with stickier tyres. People can get better fade resistance with better brake pads, larger rotors, thicker rotors, brake ducting, higher boiling point fluid, etc.

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Postby szh » Wed May 26, 2004 6:08 pm

multisync1 wrote:Wouldn't wider wheels increase the contact patch? I've got 8.5 inch wide wheels on the front and 9.5 inches on the rear (compared to 7.5 inches all around from the OE wheels).


A common misconception, unfortunately. Making the wheels/tires wider will make the contact patch width larger, but the contact patch area will stay the same, because the contact patch front-to-back length will decrease accordingly. (Of course, you have to make sure that the tire pressure ensures a reasonably "flat" patch; and of course, the tire sidewall stiffness has a tiny effect.)

This is because the total weight of the car is pretty much unchanged. So the amount of downward pressure on the tires is the same. Hence, the needed amount of contact patch area to the road to support the car remains the same.

Since the friction is related to the area of the contact (real-world issue, rather than what you learn in physics texts), the only effect you can really control to significantly improve braking is to increase the coefficient of friction of the tire - the "stickiness" of the tire. Everything else is a nominal effect on braking performance.

So, in general, wider tires, and "racing slicks", help some with better lateral acceleration, but not braking. The sidewalls are generally stiffer; there is less reduction in contact patch area as the tire changes camber during a hard corner; etc.

Finally, remember also that "sliding coefficient of friction" is always lower than "static coefficient of friction" between any two surfaces, which is why ABS is so dang useful (except on loose gravel surfaces, by the way, where sliding is better than not-sliding)!

Z

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Postby szh » Wed May 26, 2004 6:08 pm

Here is more info from the "Tire FAQ" sticky post by Exar-Kun in the "Tires, Wheels, Brakes and Suspension" forum (look to the menu on the left):

Quote »Why do people recommend wider tires? Don't wider tires mean more grip?

In a short version, no. Don't go e-mailing me about how wrong I am yet, either. Think about your tire as a balloon (more accurate than most people think) holding the weight of your car up. Now, if you place a balloon on the ground, it has a certain area that contacts the ground, this is the 'contact patch', now you can make the patch wider(wider balloon) but the total rear remains the same, because the pressure on the balloon is the same.

Now, what does this mean to YOU? It means that since the same amount of tread is in the contact patch area between either tire, 'grip' should be the same. Thusly, the only things affecting grip(since the area of potential contact is the same) are tread design and friction(tread compound).

Unfortunately it is not that simple. A wider tire does have some benefits over it narrower counterparts, with a wider contact patch comes a bit better lateral stability(to a point, lateral stress doesn’t vary THAT much between narrow and wide tires), but sacrifices some ride comfort, and less noise cancellation(in theory).

Something else to consider:

Think of a gap in the road surface, typically these run perpendicular to the tires contact patch. On a narrow tire, with a long contact patch, the gap in the road surface would take up more (percentage wise) of its contact patch than a wider tire. Make sense?

...so wider tires do provide some benefit, to a point. Wider tires usually come in stickier compounds, too. Yet, the compound and tread design has far more to do with tire grip than the size.

Now quit asking me how wide of a tire you can fit on something.[/quote]


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