Factory rim spec

[TED]

WOW ! And to think GM has been lieing to us for all these years and no one else in the world has challenged them on this and their data but you !

 

[Phrede]

WOW ! And to think GM has been lieing to us for all these years and no one else in the world has challenged them on this and their data but you !

All I am asking for is your source of information. Where has GM stated this? Where is this documented? If it is so widely believed as fact then it should be easy to give a reputable source.

Additionally, my point is even IF it could respond in 1ms it would not be effective in smoothing out the single jolt. That is the law of physics.

 

[TED]

This is just ONE small article. If you do even a small search you will find many. This is such old news im surprised you havent read tons of them by now. I believe gm also post these FACTS and DATA On many of there sites Its been common knowledge at least this long www.theautochannel.com/news/2002/11/09/<WBR>150285.html

 

[TED]

Thats if you believe Popular Science to be a reputable source. If you need more im sure you could Easily find it with a search for GM Magnetic Ride Control

 

[Phrede]

Per this article you are correct that the response time is 1ms. I have no reason not to believe it. Every official GM document I find makes sure to mention the system "reads the road changes 1000 times a second". I wonder why they don't say it responds like that and are so careful to add the reads part.

Again, a 1ms response time can not help with the single jolt being felt. Changing the dampening after the bump is not effective no matter how quick. I think it would help on a rumble strip or similar repeating pattern.

I did find a Delphi document that proves there is no advantage in ride improvement for single event hits and only negligible improvement for slow frequency vibrations from a rough road.

http://www.vehicledynamics-expo.com/08vdx_conf/pdf/day_1/olivierraynauld.pdf

Compare the charts at .5Hz between the Reference Vehicle and the MR one.

 

[Phrede]

Just to put my opinion on things. I don't believe that the suspension might work fully hitting a random pothole at 60. It might sense the hole withe the front susp. and adjust the rear? What I do know is it drives like a cadillac and has good performance to follow!Sorry to interupt the current discussion but with the rim sizes i read that a 19/10 w 79mm offset will not fit hits inner fender alot, theirs no way. Now does changing the offset to 65 bring the rim away from the car or put it into the car? thanks for the great conversations.

I was trying to remember this thread and finally found it. Pictures of 10" wide wheels.
https://www.xlr-net.com/forums/cadi...by-got-new-shoes-today-thought-id-share-5359/

 

[Stella]

Thanks phrede on all the info on the rims and tires. Those rims in that thread stick out way to much. Looks like one of those grand Marquis with the spokes you see down here in the city. I'm trying to bring more SPORT out of the luxury. I also agree a 100 percent on your pothole theory. I think GM is okay in design but they will ride the coat tails of the myths of the magnetic suspension I personally have been in way smoother riding cars. Now to smash a lot of hp,performance,and luxury. You have to give to get. We should all know that! Good stuff guys!

 

[Phrede]

Thanks phrede on all the info on the rims and tires. Those rims in that thread stick out way to much. Looks like one of those grand Marquis with the spokes you see down here in the city. I'm trying to bring more SPORT out of the luxury. I also agree a 100 percent on your pothole theory. I think GM is okay in design but they will ride the coat tails of the myths of the magnetic suspension I personally have been in way smoother riding cars. Now to smash a lot of hp,performance,and luxury. You have to give to get. We should all know that! Good stuff guys!

Glad it helped. It is a personal preference on having rubber outside the fender. I prefer to have things inside the fender. Others like the way out look.

I did a quick look at the wheels in the pictures and it appears the largest offset is 35mm.

I went thru quite a bit last summer with wheels and tires and am glad to share. I was very glad to hear the the model tire I wanted came out in a size that would work on my stock rims. I personally would stick with the 8.5" width with a 255 tire with a 40 series profile. It gives the best balance of comfort and performance. I don't think the performance gain of 30mm additional width on the rear is worth having it stick out or the rest of the headaches on our cars unless there are additional mods needing more "stick". If I need more performance there is the option of going to a different model tire with the reduced mileage and harsher ride in the same size.

Maybe I will see you out and about next summer.

 

[TED]

Well at least were from cant be done to negligible improvment. Thank you. And if busa man figures are correct that at 60 mph it could correct 1 time every inch and the pothole is 6 to 8 inches long Well you do the math ! Some times this high tech is hard to get your arms around. I never thought i would hang a 70" TV on my wall either and yes i am one of those peolple that believe that we really did land on the moon.

 

[TED]

Also i look forward to meeting you someday and some of the other fine people on this forum. You guys look like you know how to have a good time ! Have a great day !

 

[Phrede]

Well at least were from cant be done to negligible improvment. Thank you. And if busa man figures are correct that at 60 mph it could correct 1 time every inch and the pothole is 6 to 8 inches long Well you do the math ! Some times this high tech is hard to get your arms around. I never thought i would hang a 70" TV on my wall either and yes i am one of those peolple that believe that we really did land on the moon.

You are again missing my point. I am saying the the system cannot respond to a single bump in the road. By the time the shock reacts the bump will be history. Not negligible, but zero response. This was my claim before and still is. Read the charts they clearly support my claim.

 

[TED]

Thats the begining of the bump By the time its over there is change Are you also saying that at 60 mph there is not a response for every inch traveled ?

 

[BusaMan]

Phrede, I think the best way to address this might be to do this: slow your vision of the vehicle hitting a vertical, 2" bump, as in very slow motion. The shock does NOT immediately go to the deflected position and stop there, for a couple of reasons: momentum of the tire/wheel, including the flywheel effect; the actual time it takes to make a deflection to absorb the bump, including the impact absorption of the tire. IF (!) the active suspension control system can, indeed, deal with real-time events in a millisecond frame time (more on that in a bit...), then the dynamics of the tire/wheel impacting the bump can be looked at as a series of "pictures" taken for each 1" of vehicle travel at 60 mph. At a more serene 30 mph, this would be a pic' for every ½". It would take a several frames to have the suspension deflect fully, between each of which the suspension would be variably damped by the control system. From the time of initial contact to steady state after the bump, there easily could be 1-2 DOZEN frames, particularly in the 30 mph case.

Now, over 40 years ago (!), we installed and implemented real-time systems at Edwards AFB. One such system was at the NASA facility, where we ran multiple, concurrent real-time applications with <50 ms frame times, with interrupts/interfaces addressed by the HRTM (Hardware Real-Time Monitor). The "frames" included all of the elements you alluded to earlier: reading of the inputs, scheduling, processing and output of the control signals (multiple). The laptop I am typing this on has two processors, each of which runs over 40 times faster than the CDC Cyber 74 we used for that real-time installation. I would be disappointed beyond belief if the computer technology were not readily available NOW to provide millisecond frame times for such a simple application. SIMPLE??? Yes, compared to all of the flight controls that had to be serviced in our real-time control applications. We "flew" model F-15's, dropped by high-altitude bombers, including flight data acquisition, stability coefficient determination, flight surface control, etc. I am not demeaning, in any way, the sophistication of active suspension control systems; rather, I am pointing out that a "position in, compute variance(s) from last position, damping control(s) out" application with millisecond response times seems to me to be eminently feasible, given the improvements in computing technology over the 4 decades since that particular installation.

FWIW

Tim

 

[Phrede]

Thats the begining of the bump By the time its over there is change Are you also saying that at 60 mph there is not a response for every inch traveled ?

I am not saying anything about the distance at any speed. It doesn't matter. A single bump is felt before the system can make any effective adjustment.

If an adjustment happens 1ms after the bump starts you will be 1.056 inches into the bump before any response at the update frequency of 1ms and velocity of 60mph. This is when the shock potentially changes. The question is change to what? Is the object you ran over compressing or expanding the shock or staying the same. There is no way to know. Since there is no way to know the actual road condition there is no way to know how to change the shock, if at all.

There are other things that happen during all of this including tire compression and suspension arm flexing. Also the rebound effect of these things as well. Keep in mind that suspension position sensor is positioned where it reads the motion of the suspension after any tire compression/expansion and close enough to the pivot point that most arm flexing is not measured.

The only way to be effective is to be able to accurately predict what is going to happen and prepare the shock for it. This is exactly the case when cornering, accelerating, decelerating or on a wavy road. This where the system is effective.

Imagine that you run over a 1" board laying in the road. At first (after compression and flexing) the sensor reads that there is a positive motion in the suspension. At this point all it knows is a magnitude and direction. By the time the next scan occurs the tire is almost on top of the board, and by the third scan there is probably some negative direction travel do to rebounding. By the 4th scan the tire is completely on top of the board and things are stabilizing. All 4 of these scans are providing different information but at no time can the system predict what is going to happen next so it cannot know if more or less dampening is needed.
The next thing to consider is when the tire comes off the board. Is the board 1" long? 6" long? There is no way to know so the system can not predict and therefore cannot compensate. Remember that the initial bump was felt by the driver before the 2nd scan.

Consider now those pesky expansion strips in the highway. They cause a thump in the suspension that causes little tire compression or flexing and lasts much less than 1ms. They happen at irregular intervals and cannot be predicted. I can sure feel them can't you? They are not as obnoxious with my new tires that have softer sidewalls.

The main intent of the system is to increase performance when needed and not having a super stiff ride. Adjusting every 1ms is plenty fast when going through a turn and the compression of the outside suspension is predictable. The concept also applies to acceleration and deceleration or a combination.

 

[Phrede]

Phrede, I think the best way to address this might be to do this: slow your vision of the vehicle hitting a vertical, 2" bump, as in very slow motion. The shock does NOT immediately go to the deflected position and stop there, for a couple of reasons: momentum of the tire/wheel, including the flywheel effect; the actual time it takes to make a deflection to absorb the bump, including the impact absorption of the tire. IF (!) the active suspension control system can, indeed, deal with real-time events in a millisecond frame time (more on that in a bit...), then the dynamics of the tire/wheel impacting the bump can be looked at as a series of "pictures" taken for each 1" of vehicle travel at 60 mph. At a more serene 30 mph, this would be a pic' for every ½". It would take a several frames to have the suspension deflect fully, between each of which the suspension would be variably damped by the control system. From the time of initial contact to steady state after the bump, there easily could be 1-2 DOZEN frames, particularly in the 30 mph case.

Now, over 40 years ago (!), we installed and implemented real-time systems at Edwards AFB. One such system was at the NASA facility, where we ran multiple, concurrent real-time applications with <50 ms frame times, with interrupts/interfaces addressed by the HRTM (Hardware Real-Time Monitor). The "frames" included all of the elements you alluded to earlier: reading of the inputs, scheduling, processing and output of the control signals (multiple). The laptop I am typing this on has two processors, each of which runs over 40 times faster than the CDC Cyber 74 we used for that real-time installation. I would be disappointed beyond belief if the computer technology were not readily available NOW to provide millisecond frame times for such a simple application. SIMPLE??? Yes, compared to all of the flight controls that had to be serviced in our real-time control applications. We "flew" model F-15's, dropped by high-altitude bombers, including flight data acquisition, stability coefficient determination, flight surface control, etc. I am not demeaning, in any way, the sophistication of active suspension control systems; rather, I am pointing out that a "position in, compute variance(s) from last position, damping control(s) out" application with millisecond response times seems to me to be eminently feasible, given the improvements in computing technology over the 4 decades since that particular installation.

FWIW

Tim

I see your points and appreciate your experience and input, Tim. A couple of comments.... While our cars are expensive, they have no where near the price tag or technology of an F-15.

Moore's law certain will support that computing power has come a long way.

The speed and response time of the control system is directly proportional with the budget allowed for the system. A dedicated purpose non-multitasking system will have greater speeds than a one that is having to share its resources with other systems. The question is not is it possible but how much did Cadillac spend on the system? Even with a 1 ms response time, the time needed to feel a single bump is much less.

I'm not sure I would accept that the suspension would oscillate and react for 2 feet (at 60MPH) after a single small, but significant, event on our cars. I don't have substantiating figures, but that sure seems under-damped to me.

There is an immense difference in masses between an F-15 and our cars, especially when comparing the unsprung weight.

Real-time is a marketing term and nothing ever happens in true real time. Everything takes some time. The single exception that MAY be true is what is happening at CERN with neutrinos.

There is never going to be an definitive answer to this discussion. Readers will need to create their own opinion and use there own experience with different tires to form that opinion.

I spend very little time in my XLR at sub 60MPH speeds.

BTW, I too have spent some time in the Mojave. Not at Edwards, but just a little south at Skunk Works.

 

[Stella]

Damm it I thought that's what the acc did scan the road I would think that yes their is that technology out their. I also think that GM doesn't and couldn't engineer it. Seeing all the stuff they overlook in design and engineering. Overall is the actual quality of the parts they put in their cars and at these prices come on

 

[BusaMan]

Phrede, I sure didn't want to give the impression we were dropping F-15's during the NASA/FRC (Flight Research Center) testing. They were scale models, but radio controlled from the ground, via the real-time system we implemented. We used the term "real time" to reflect that we were controlling real objects, subject to Newtonian and other forces, as it all happened. My departments also (later in life) did the flight verification ground testing for the cruise missiles produced by General Dynamics, where the TERCOM software aboard the missiles flew missions, while still in our lab. We also termed that "real time", since the controls "flew" as the missile executed the guidance program, and we captured the resulting control surface actions with analog/hybrid equipment to validate that they were doing what they were designed to do, when they were supposed to do it, and that the missile would go where it should be going.

I can't help but think that it would be really valuable to you, TED and to me (and, hopefully, others) to have someone from Cadillac Engineering contribute to this discussion. My guts tell me that a dedicated, "real-time" microprocessor could be packaged for this application, and manufactured cost/effectively nowadays for reasonable cost, given the scale of the number of vehicles using it. But then, maybe I'm in La La Land. Been out of the "game" for a while.

(^;

Great discussion. Made me dust off some old cobwebs. Lots of great stuff came from the "Skunk Works". Those were proud days for our country.

Tim

 

[Phrede]

Phrede, I sure didn't want to give the impression we were dropping F-15's during the NASA/FRC (Flight Research Center) testing. They were scale models, but radio controlled from the ground, via the real-time system we implemented. We used the term "real time" to reflect that we were controlling real objects, subject to Newtonian and other forces, as it all happened. My departments also (later in life) did the flight verification ground testing for the cruise missiles produced by General Dynamics, where the TERCOM software aboard the missiles flew missions, while still in our lab. We also termed that "real time", since the controls "flew" as the missile executed the guidance program, and we captured the resulting control surface actions with analog/hybrid equipment to validate that they were doing what they were designed to do, when they were supposed to do it, and that the missile would go where it should be going.

I can't help but think that it would be really valuable to you, TED and to me (and, hopefully, others) to have someone from Cadillac Engineering contribute to this discussion. My guts tell me that a dedicated, "real-time" microprocessor could be packaged for this application, and manufactured cost/effectively nowadays for reasonable cost, given the scale of the number of vehicles using it. But then, maybe I'm in La La Land. Been out of the "game" for a while.

(^;

Great discussion. Made me dust off some old cobwebs. Lots of great stuff came from the "Skunk Works". Those were proud days for our country.

Tim

Blowing the cobwebs off is right! It helps to keep the mind gears lubed and running. A dedicated system I also think would be doable if the different auto manufacturers could decide on some standards on some parameters so the cost/unit could be held down. That is the hard part since they never agree on anything much that the govt. doesn't mandate.

 

[johnpbaird]

I've been lookin' all over the place for advice and specs for "upgrading" the 2005 Cadillac XLR wheels.

(To me they're boreing)

I L-O-V-E the late model Corvette (C-6) Wheels,, but some say the Offset is too dramatic in the rear "19X9".

Will the front, (18X8) still work on all 4- corners???

 

[Stella]

Hey John I'm the one who originally posted this tread. I have heard that the 18/9.5 will fit all around but I have never gotten a answer ever on offset. Seems like people won't give other advice like that incase something doesn't go right? There's a guy that has the 18's up front and 19's in the rear. He just posted pictures of him at a event in Montana or something and it was a road course and the pictures show him driving hard. He says he had to sand the inner fender on the rear but that was it. I asked the inner fender is plastic how did he do so and haven't got a response yet. I'm tempted to find a set and try them on to see for myself but haven't yet. Big debate is my car has new run flats and will need tires on new rims. Do I spend the money on run flats for second set of rims or just get regular tires and take my chances. Hear a lot doing so along with a lot of vettes! Real chancy in my book.