How will heavier 225/16 tires affect Q45a computerized suspension performance?

[Busbin]

Here's a really esoteric question for the truely "technosavy" gurus out there.

My 1994 Q45a has original BBS "basketweave" style, 15 inch wheels. These wheels are hard to clean (get out the toothbrush), and I'll be needing tires soon also. So, I have a notion to install different wheels, maybe 16 inch, and slightly wider tires.

Michelin Pilot Exalto tires in 215/65/15 weigh 24 pounds. Michelin Primacy MXV4 tires in 225/60/16 weigh 26 pounds (these are on sale in V rating at Tirerack for $115; normally about a $170 tire). I'm not sure how much my BBS wheels weigh, or how much some alternative Infiniti 16 inch wheels would weigh.

However, Q45tech has mentioned that the computerized suspension in a Q45a can't handle the additional weight of upsized wheels/tires without compromising its performance.

How much additional weight can the "a" suspension handle? Would the benefits of a 225/16 tire offset the decreased performance of the suspension?

Jim PS: I live in the mountains of western North Carolina (constant ascents, descents, and curvy roads)

[maxnix]

The forged 15" BBS are about 16 lbs. each. The cast 20 hole 16x7 off the FGY33 are about 20 lbs. each.

Read 3QJay's posts about converting back to 16" from 18" on one of his actives.

Not available in 16", the PS2 is an exceptionally strong and light tire. And much better (like light years) than the MXV.

[Q45tech]

I would attack the question on a % basis: OEM unsprung weight vs new weight.Remember the brakes/rotors/calipers hubs bearings and half the suspension weight ~ 85+ pounds and the oem wheels tires weight ~ 44.

So +6 pounds is only <5%.

Changing from std wheels to oem forged dropped 5 pounds and an expert could feel the difference but the active provided much more isolation than the oem t suspension where the forged wheels were utilized. Just like a NASCAR driver can feel 1-2 psi change in tires. Most people cannot feel a 5 psi difference side to side and that is a 15% change in sidewall stiffness.

I'm sure for $10-50,000 we could rent test equipment and tracks and arrive at a better more scientific answer.

[Busbin]

Were I wealthier, the test equipment and track time would be interesting entertainment. However, I think I'd be better off to devote $10,000 to my "T3 fund" and hope it might cover all the deferred maintenance that is beginning to collectively accumulate in my three Q45's. Our 4th adopted child is now a toddler and requires less constant attention, so maybe I can work in an exodus to Atlanta in the spring.

It sounds like I would be better off the keep the 15 inch BBS wheels and mount some new Michelin Exalto tires.

Jim

[qship96]

You will love the Exaltos on factory wheels, based on my 61,000 mile experience with them. Excellent tire all around for Q in both nice weather and light snow.

[maxnix]

It sounds like I would be better off the keep the 15 inch BBS wheels and mount some new Michelin Exalto tires.

Jim

Yes, as used wheels are a crapshoot. Read 3QJay's relevant post. I think with forged wheels, one could go to 18" and get some real tires, but the sidewall spring rate may be what upset Jay's active. It comprises part of the expected spring rate the active computer expects to see, and the shorter sidewall definitely increases that component of it. But if you run at 38 psi on both tires, how much?
Modified by maxnix at 12:14 PM 2/7/2009

[texasoil]

I got a set of 16" 95 Q45a rims and put Kuhmo SPT ultra high performance summer225x50 tires on. Also put Porterfield 'racing' brake pads --kevlar/carbon--not REAL racing pads, Goodridge SS brake lines. Tightened up sway bar end links with 1/4" of washers on one end of front and rear, have FTSB. went to 'High Speed Driver Education' weekend in San Marcos --hosted by the Hill Country (Austin) Porsche Club.

I could not feel any deterioration in ride other than a little more NHV from the tires on 'Texas Gravel' blacktop. On concrete it was very smooth.

During the 'Track' sessions ( 5 -15 min sessions) I was not embarassed by the Porsches, Corvett ZO6 , Viper and a Ferrari. I was passed by 4 cars--only 4. I was held up by or passed the other 20 cars in the group. I was able to out brake the Porsches, gain distance on the straights except on the 2 tubro charged Porsches, and make up ground in the corners. My Instructor has like a kid in a candy store (He drives a Porsche GT3 and is THe Fastest' around the track) He was shocked and amazed at how well the Q45a (Qship) cornered, braked, and hauled *** and was so easy to hold right at peak performance through difficule, non steady turns (down-hill off camber, decreasing radius, chicanes,etc) The layout is one that pays nice dividends for holding the perfect line through the turns and the Qship did that very well and with great comfort at the same time!

The tires and brakes do NOT show any significant wear ,much less damage. Several Porsches overheated brakes! THe Porterfield brake pads are fantastic--work well at 50 ambient, like an aircraft carrier anchor when hot, and NEVER lost any of their teeth or controlability. I could bring the tires to ABS kick in at any time, any speed--with moderate pressure. The tires were very progressive with plenty of feedback as you reached their limit--both noise and feel) and I never lost grip with those tires, and was regularly 4 wheel drifting around the downhill hairpin where several cars spun-out into the grass.

Talk about embarrassing to the Porsches--there I was with an essentially stock 15 year old luxury street car, 158K miles, no suspention mods or repairs (all OEM original rubber except transmission mount), book value $3500 maybe--eating the lunch of their $65K new toys. And I AM NOT a really good driver--I am learning.

So, I conclude that small changes in unsprung weright will not significantly ride or handling performance.

[jjbuzzman]

Well, texasoil certainly fueled my imagination - there I am at Road Atlanta (my nearest track) attacking the track in my Q45a and humiliating smug Porshe owners by the dozens.

For added effect, I may even leave our two pink baby seats strapped in the back seat, along with a big, black, back-pack diaper bag. Then I'll pull into the pits alongside some of the Porshe teams that I just whipped, glance at all the baby-baggage in the back seat, and coolly quip, "Oh, wow, I forgot to unpack before the race! But then again, this gear might have come in handy as some of you guys might have peed in your pants when I passed you in my 4-door passenger sedan while carving that sweeping turn number 4."

Seems like good advice from all on the tires. Now to look for a good price - tires are getting cheaper!

Jim in the Mountains

[maxnix]

Now to look for a good price - tires are getting cheaper!

Very few of the good ones are.

The Goodyear F1 DS G3 is one, but not in smaller sizes. Anything in 16" of below is a just roller or for short lived track use on a lighter car.

[Q45tech]

Road ATL is for newbees: I used to live 3 miles away and had a free pass after selling them some land year ago.

http://www.motorcycleroads.com...shtml

318 curves in 11 miles - what more needs to be said?

[Busbin]

I live less than 15 miles from the south end of the "Tail of the Dragon" route that hugs the west end of the Smoky Mountain national park. As we use the Knoxville airport occasionally, this route is how we get there.

When I have the time, I hope to write up some of my adventures in driving this road - one day in particular was really sporty, and hilarious. Picture me in my '93 Q duking it out with a pack of sport bike riders, and not doing too bad, but losing in the end. There are also women invloved, and some too funny to believe comments made.

Jim in the mountains