Active Q45’s wheel size affect on system function

[bruce.weiland]

Active Q45’s wheel size affect on system function.

As you know the active cars (‘91 – ‘95), and all cars of that ventage, came with 215x65x15 95V 35 psi tires mounted on 15x6.5 wheels.

I have the BBS OEM West German made wheels on my ’94 Q45a.

Many on this board have recommended that Q owners go to larger than OEM diameter wheels. And rightly so. Perfromance tires are getting very hard to come by in 15” diameter.

On my two previous active Q’s I ran Yokohama AVS Intermediates (many sets, extremely happy with them until they were discontinued) 255x50x16 on 16x8.

There are very few performance tires available in 16” that are the right size and load rating for our cars.

That leaves 17” or 18”. I had 17’s and did not like the combination.

Keith Bowers (active specialist ) has stated that, in his opinion, 18’s do not belong on an active car. He mentioned that the system is “tuned” for the frequency of the OEM wheel tire combination. Keith also has a Mercedes with ABC (automatic body control – a system that in many ways is very similar to the Infiniti active – but about 10 more years of computer development and the hydraulics modulate the spring perches rather than a shock/acctuator). His experience with his Mecedes with a wheel and tire combination that is 10 lbs lighter than OEM, but with ½” less sidewall, is that it comprimissed the system to some extent.

I need some new tires on the Q. It has lots of tread left on some very, very old Michelin Symmetry 215x65x15 95S 500 AA.

I decided to try some 18’s on my active just to see what they would do. I have recently replaced all 9 accumulators and the system is working flawlessly. I have an I30 with new 215x55x16 Goodyear F1 GS-D3. I have not tried this on the Q yet. I have a G35 sedan with OEM sport wheels and tires with about 9k miles on them. 235x45x18 94W 180 A A, Bridgestone Turanza E33 . I realize that these are 26.5” unloaded diameter as opposed to the 26” OEM. Additionally they are 51psi tires, so I had to really pump them up before I did my test.

The OEM 15” BBS tire/wheel combination weigh approximately 35 lbs ea. The wheels/tires from the G35 weigh approximately 45 lbs. each.

Here is my experience.

First, Keith IS RIGHT! 18” wheels screw with the dynamics of the active suspension. The first thing I noticed in the first 100 feet of driving was a lot more road noise making it into the cabin. Secondly, acceleration seemed, seat of the pants, to be noticably affected in a negative way. It could be the slightly larger diameter, or more likely the additional 10 lbs of rotating mass on each corner, or both. It certainly did not accelerate as quickly.

At speed (60 to 80) the system seems to over compensate for sweeping dips and rises. I belive the two 16 bit processors and active software are being confused by the short sidewall (1.5” less than OEM), in that the data from the wheel position sensor, and the vertical accelerometers are initially changing more quickly than would be the case if the 5.5” sidewall was taking up the initial portion of the road uneveness.

The only benefit to the 18’s was less body lean on turns. That can be made up for to some extent by poly bushings on the bars, so that is coming.

OK, so other than price and the 26.5” unloaded diameter, tell me why I don’t want Pirelli P4000E’s.

Specs: 225/65 ZR15 99W (1709 lbs.) SL, 180 A A, 44 psi, 25 lbs, 6-8” rims, 9” section measured on a 6.5 rim.

OK, flame away. I can take it.

BruceOnce a Marine, always a Marine


Modified by bruce.weiland at 10:10 PM 2/25/2007

[maxnix]

Pirelli 4000E are, at best, pedestrian tires.

While the active software is tuned for a different tire spring rating, that tire no longer exists.

You will have to choose some good comprmises, but I doubt you will find any in mid-pack tires models.

By the way, I think your experiment with less than OEM minimum load rated tires is reflective of that parameter in particular. While slower acceleration is probable, much can be achieved by working from the top and not going too far down. It is a much longer road from the bottom up, and more expensive in the long run.
Modified by maxnix at 9:49 AM 2/26/2007

[bruce.weiland]

OK Brian, I know the Michelin XVGT (or what ever they were) are long gone.

By the way I edited above the G tires are 94W and 51 psi for max load.

I am confused by your response. These particular Pirelli's are not cheap. $164 ea., have a 99 load index, a W (169) speed rating, a bit stiffer sidewall (44 psi max load), and a soft compound, 180 wear index.

They are used OEM on heavy Jags, the "sportier" two door-XJS and on the XJ6 and XJ8.

I thought these might be one of the few, from the top down tires.

What else is there that has this soft of a compound, with a high load index and isn't a 51 psi tire?

Bruce
Modified by bruce.weiland at 10:20 PM 2/25/2007

[3Q Jay]

Bruce- interesting. my experience in going 15 to 18 on the active is nearly identical. I've not given up on the 18's yet, although my system is also only semi-active at the moment as a work around until i change out the MV (again).

If i stayed (went back to) 15's, I was gonna go exalto in 225/60 (instead of the 215/65).

btw, i think the BBS germany rims are class. too damn hard to keep clean though!

[maxnix]

XJs and XJ6? Haven't been made for years. The various Pirelli Corsa Rosso or similar are current top of the line Pirelli's.

The Goodyear F1 might be similar enough to a 15" wheel as they seem to have a litle more give in the sidewall. All curent top of the line tires are now around 51 psi for maximum load. I think a run flat would not be a good choice either in a larger tire.

I guess the only way to tell is to pump them up to 35-40 psi and compare bounce first harmonic to current best 15" tire to try to match spring properties.
Modified by maxnix at 7:58 AM 8/3/2007

[Q45tech]

Load index is not really a useful parameter but it is all we have available.

It only specifies at what weight/load a tire with zero camber will fail/survive for a minimal number of minutes BRAND NEW..........the problem is different manufacturers have different levels of safety reserve.

If I was ever going to under tire a car I would use MICHELIN as they have the highest INTERNAL STANDARDS.

A MICHELIN tire might last hours were as a lesser tire might be 30 minutes.

The problem is internal stress is cumlative. Even MICHELIN warned the US government that tires beyond 3 years or 20,000 miles had failure rates that rose exponentially.

Back to wheel size: Members forget that the tires and wheel stiffness are in series with springs thus reduce the springs effective stiffness. Afterall what counts is the unsprung weight and the tire road stiffness.

The active software was tuned for a specific tire size and wheel tire weight this MUST BE MAINTAINED if you expect normal performance.

I would just use Exaltos in 215/225/15" and accept the slightly reduced performance because going LARGER will just add addition problems.

Problem first showed up when using the lighter forged oem T wheels on Active Q.

[bruce.weiland]

Yes Jay, I think that Keith knows something.

Back when I had my '91 I had gone through a couple of sets of OEM tires, not realizing how special and good they were. I didn't have a problem with the low mileage per set. I thought it was just my agressive driving.

When my chromed pie pans began to leak I went to 16x8 with 255x50x16 AVS Int. and was very pleased with the improvement in handling. I did not notice the system being perturbed by the sidewall decrease.

I find that interesting because the AVS Int. was a 35 psi tire with a very stiff sidewall and of course 1/2" less sidewall.

One of the benefits of staying with 15" is no expense for rims.

Question, I realize comparing Michelin to some other brand is apples to oranges but...

The Exalto A/S is 95V compared to 99W, 400 wear index compared to 180. OK and $123 compared to $164. There is that. Four for the price of three.

Given Q45tech's bend for higher load rating and higher speed rating and soft compound tires, wouldn't the Pirelli be a better choice for we Southern Californians, or is Pirelli that poorly made compaired to Michelin?

Bruce

PS Now that I have the active working, we need to get together to compare notes. I also have a noise I need an opinion on. Percy that applies to you too.

[maxnix]

Members forget that the tires and wheel stiffness are in series with springs thus reduce the springs effective stiffness. Afterall what counts is the unsprung weight and the tire road stiffness.

Problem first showed up when using the lighter forged oem T wheels on Active Q.

What I was trying to get at. The spring rate of the tire. Weight (mass) will affect the active's program also. Note that Keith has Superlegerra III (forged, strong, and light) on his SL600. Not cheap, but beautiful. Titanium bolts.

Thought all actives had the forged wheels from the factory? In any case, another argument with perhaps more relvance for active owners, when you go larger, go with the lightest strongest wheel and tire you can find. Don't think cheapest.
Modified by maxnix at 9:50 AM 2/26/2007

[bruce.weiland]

Problem first showed up when using the lighter forged oem T wheels on Active Q.

Q45tech,

To which problem are you referring. Are you indicating that "a" owners noticed the system not working properly when they put on a lighter, lower wheel/tire weight 15"?

I just saw some OEM pie pans advertized on ebay. They listed them as 15x7.7. Is that correct?

The BBS OEM are 15x6.5. Do you think they made any software change in the '94, for the OEM supplied BBS?

ThanksBruce

[elwesso]

I would say that all of this qualitative analysis would probably only equate to a 15-20% difference at worst. Remember, that most of what you're experencing is not related to the active suspsension, it happens on every car.....

IF you do not have a tire with the EXACT SAME sidewall stiffness at whatever tire pressure then the active will not behave. Study the sidewall stiffness of the OEM tires and then decide on a tire that would be suitable. Remember that the OEM tires pressure spec was pretty low (im thinking it was like 30psi or lower, look on the door jam). If you can find something pretty close, you could probably play with tire pressures to get it within 5% of factory with a 17 or 18in wheel. Its going to be easier to do with a 17.

REMEMBER ALSO THAT you cannot compare treadwear ratings absolutely, they can only be compared within a brand.... So a 400 TW will wear 1/2 as fast as a 200 TW in some brand.... but a 300 in some brand might be similar to 150 in another brand... Likewise, a 95 in a michelin tire might be like a 98 in a cheaper brand..... Food for thought!

If this were my vehicle, I would probably go with areally nice and semi lightweight (around or under 20lbs) 17 or 18in wheel and a good high performance summer tire, and live with the small side effects.

[AZhitman]

Wes, any chance we could compile the good parts of this thread into a useful article?

[Q45tech]

Remember it is the loaded radius that counts...................a 15" tire may compress down an inch in road contact whereas a 17" may compress 0.6" and an 18" ~~ 0.5"..........................measure this compression precisely to derive the sidewall stiffness:

1200 pounds on the tire /1.0" = 1200 lb/inch on 0.6" ~~2000 lb/inch

[elwesso]

After reading this thread again, I dont really think that its the wheel size per se but it is the tire.

I dont think that the active really knows (or cares) if the the OD of the tires is off by a little bit. I dont know enough about the active to make this definite but what I do know, I dont think it matters.

I tihnk what does matter is the sidewall stiffness. I recently got done experiencing an active Q and with the 18s i thought it was great. The only thing that I didnt like is that it seemed over some things to overcompensate... Like you would feel the car move for a bump that you just hit. VERY VERY minor, and it didnt do it all the time...

The only thing that was really an issue was when you would go over a fairly steep hill at speed, it would be very abrupt. You would be at the crest of the hill and it would try and keep the car level as long as it could, and then it would jump down instead of following the hill. It really didnt bother me either way, just different, was not harsh or anything negative, just not what one would expect.

on this Q, it had 245-45-18 Nexen tires. They seemed pretty stiff.

For anyone who wants to ride 18in wheels and tires on their Q, here is my opinion. Its FAR better in terms of ride quality and such going from 15in to 18in on an active Q than a standard Q. If you didnt mind going from 15s to 18s on a standard Q, you wont mind it on an active Q.