HICAS question on wheel/tire combo

[Highway Q45]

I am in the process of ordering new wheels and tires for my 91 Q w/ HICAS. I have settled on 17x7 +40mm offset wearing 225/45-WR17. From what I've gathered from this forum this combo should do fine. The suspension is in good shape with newer struts and ball joints. My concern is with the HICAS for the rear. Does anyone know of any rear clearance issues with this setup? The +2 sizing is fairly close in tire dia. but the tread is 1.6" wider than the stockers. I realize some ride quality loss and noise increase is expected but I want to get rid if the 15" Hicas rims. The choices in performance tires for 15-inch are very limited. Any comments always appreciated.

Steve

[maxnix]

The q requires at a minimum a 95 load rating.

To achieve the the proper load rating in a 17" wheel, you will probably have to mount it on at least an 8" wide rim.

I suggest you search on wheels and tires in this forum as there is a wealth of information. Afterwards, you might well decide that anything less than a forged wheel in 17" is either too heavy (unsprung weight is the surest way to degrade ride, suspension wear, and handling), too weak for the Q, or both.

Tirerack doesn't know caca about Q's, but they are a good resource on how to read tire sidewalls.

To look for wheels there, you might want to try to look under 1996 300ZX TT to see the availability.

[greg_atlanta]

I realize some ride quality loss and noise increase is expected but I want to get rid if the 15" Hicas rims. The choices in performance tires for 15-inch are very limited. Any comments always appreciated.

Don't give up 15" tires just yet... Yokohama AVS Intermediate are available from tirerack for $44 each in 225/60/15. They are summer tires ONLY, though. Where in NorCal are you?

As a rule there is plenty of room on back for tires up to 255 width. I doubt HICAS has much of an impact since the action is so subtle.

But before spending $1000+ on wheels and tires do consider the Yokohamas. Won't last long, but totally transform the driving experience!!!!!!!!!!!!!!

:rockon

[Highway Q45]

Maxnix: I saw those Yokies yesterday at TR and blinked maybe twice. The price is fantastic but I've run them before and they sounded like a meat grinder plus they wore out quick even on a light car. The problem is my wife swapped ends yesterday in a light rain while simply turning a corner from a stop. This is not the first time the Q has slipped out seriously while accelerating / turning at low speeds. She is no leadfoot trust me, that's my job. I blame the Michelin Pilot XGT H4's. They have less than 10K on them and stop great in the wet if pointed straight. For some reason the siping pattern does not agree with lateral movement. They have become absolutely scary! Does HICAS come with posi? I want a high performance all season tire. I've driven Kumho 712's in wet/dry conditions (no snow please!) on a Miata and 325i and have had great luck with them. They get slammed by those looking for ultimate performance but as far as bang for your buck I'm hoping they'll fit my immediate needs. I'm not familiar with what a "minimum load rating of 95" actually means; the tire I'm considering is rated at 1477# so I'm sure someone will enlighten me. I do know that the tire/wheel combo weight will increase to a substantial 46 lbs. I haven't weighed the stockers yet to compare. I'm not sure how senitive the heavier Q suspension is to additional unsprung weight; the Miata is very touchy about it. If any one has any suggestions as to max weight limits or experience with plus tire fitments, I'm all ears. I'd really rather have a good 16" combo but the wheels I like start at 17". I've planned on getting rid of the HICAS wheels since I bought the car in April; they don't provide adequate cooling to the front rotors. I swear you could light a cigarette on those HICAS wheels after above-average braking in hot weather. I've run a friends tuner style wheels for a comparison test and I could actually touch the hub they cooled so well. I know this subject has been beaten to death on this forum but the responses range from from 255-17's which handle like a slot car to stockers that squeal and squirm like a pig. I just hope I can land on a decent compromise between ride, handling, and looks before the El Nino rains hit. Thanks to all for the input.Steve

[maxnix]

I will vote with Greg for the Yokohamas in the wet. The 15x225/60 dB are much better in the rain than the XGTV I have on my other Q. I don't experience the feathering, but I don't autocross either. Cross mounting and rotation will help.

Many recommend the Firestone 50ep. I believe they are available in 15"-17" sizes, and prices at Tirerack have just been reduced. They are recommended neither for snow nor cold weather.

Check your inflation pressures; lower is not better in the rain. Check your tread depth; 5/32nds is pushing it in the rain.

A light rain after a dry spell brings all the oil to the top and is the most hazardous condition for poor traction. A summer thunderstorm in Texas can turn the streets slicker than snot on an ice rink.

A 95 minimum load rating translates to 1521 lbs. static load; not sufficient for loaded Q, nor a hard cornering Q.

If you don't plan on upgrading the brakes, the rear 300ZX TT stock wheels (16"x8.5") are forged and will carry a 255/50 tire with a load rating of 98.

[greg_atlanta]

Hmmmm.... not to confuse matters too much more, but if your primary concern is hot rotors you may want to use cross-drilled Powerstop rotors.

I'd agree that Yokohama AVS dB (which I use Nov - Apr) are good in rain, as are the Firestones mentioned (both in 225/60/15).The AVS Intermediate are great in rain WHEN IT'S WARM, but since you've been-there/done-that.......

Larger wheels are rarely the answer to a problem. In many ways they just introduce new problems (harder to balance, harsher ride, easier to damage wheel or tire, etc.).

I'm sure Dennis (Q45tech) will have something to say, so give him a chance!

[maxnix]

Quote »I swear you could light a cigarette on those HICAS wheels after above-average braking in hot weather. I've run a friends tuner style wheels for a comparison test and I could actually touch the hub they cooled so well.[/quote]I wonder which wheel conducted heat away from the hub better? The hot one or the cool one? Think about it.

The heavier Q will generate much more heat to be dissipated than a light import compact. A remote reading inferometer would be of great help to determine how hot each rotor is and how the heat is being dissipated.

[AZhitman]

*Simple-minded comment coming:*

The more I see Q's with tires sized 225mm or narrower, the weirder they look. Sometimes my 245/50's even look a tad skinny. Several members are running 245/45/17's and are VERY happy with the choice.

[Q45tech]

I'll take all [90-96Q] comers on with 215/65/15 Yok AVS Intermediates on oem 15" wheels assuming it is warmer than 50F ambient. Except maybe the Firestone non EP SZ50 [no longer available].I keep proving over and over [to myself] how much a stronger [load index] tire improves the ultimate G ability of any car [even 6.5%].

The Michelin [= or >300] are way to hard a compound to be called a rain tire.........this is a known trade off despite Michelin advetising to the contrary.......[compared to what, the common junk most passenger car owners buy!].

Tread depth only is valid before you reach that amount of water [5/32 tread = 5/32 standing water......etc.] Beyond that the molecular adhesion between the road and the compound, how soft and bendable around the asphalt with the water molecules squished out of the way by the weight on the tire.

Trucks with 60-80-100 psi squish water away better - that's why the don't hydroplane until 10-15 mph above passenger tires even with there harder compounds.......going straight!

[Highway Q45]

After Dennis' valued input you all have me looking harder into this whole tire/wheel decision. I really want to lose the HICAS wheels though, heat transfer or not. I guess I'll look for a better 16" combo with appropriate load rating, offset, and wet characteristics. As stated earlier I've felt the Michelins (@32psi) were the main cause of the lateral slip. Just for jollies I was able to duplicate this last night in an open parking lot while it was still very wet. The breakaway would occur about 3/4 of the way through a normal wide 90 degree turn (think left turn lane on three lane intersection) at about 22-25 mph under normal throttle. Let up on the throttle and the slide decreases but does not stop completely. This is quite fun in on an empty lot but a bit sobering in a busy intersection. I've wondered if the HICAS on my Q45t came equipped with posi which can get funny in the wet. If the load rating of a selected tire is increased beyond the 95 minimum would this improve or decrease these slide characteristics? I would think that if a wider tire tread width and larger contact patch was used to increase the load rating that it would increase hydroplaning; I think the slipout problem is a separate issue though based solely on the tread design of the Michelins. My Miata has +2 sizing with the Kumhos (215/45-16WR) used for winter. Even with a Torsen diff. it's hard to slide it unless I really goose it. You would think the lighter car would break away easier. The 16's degrade the ride, turn-in, and rebound but increase high speed stability. My16's get swapped out for forged 14's and stickies in the summer. The OEM sizing is much better for the Miata especially on track days. I'm glad to hear so many opinions on tire size; none of them are absolutes in every handling situation but it great to know the options. Thanks Again...Gotta Love this Forum!

[maxnix]

Positraction® it the GM trademark for their clutch-pack limited slip differential. The 1990-1996 Q45 has a viscous limited slip differential, upon its operation I will let someone else more qualified comment.

When either of my 1995 Q's step-out in the rain, it tends to be towards the left due to right turning, or, I imagine, engine/driveline rotation. I never step-out to the right on a straight ahead acceleration. I say step-out, because the LSD usually engages very quickly to distribute the power to the wheel with traction.

I can believe the Michelins are like ball bearing in the rain, but if you are not too enthusiastic about throttle transitions and application rates, it seems like you are having excess problems.

Anyway, buying rubber frequently in softer stock or near stock sizes is probably better than buying hard, oversized rubber on large and heavy weak wheels infrequently. It's all your dollars and physics (unsprung mass, coefficient of friction, load carrying capacity, carcass construction, tire compound properties, tread design).

[EWT]

Positraction® it the GM trademark for their clutch-pack limited slip differential. The 1990-1996 Q45 has a viscous limited slip differential, upon its operation I will let someone else more qualified comment.

When either of my 1995 Q's step-out in the rain, it tends to be towards the left due to right turning, or, I imagine, engine/driveline rotation. I never step-out to the right on a straight ahead acceleration. I say step-out, because the LSD usually engages very quickly to distribute the power to the wheel with traction.

I've never completely understood why Qs are so tail happy in the rain. I've driven RWD cars with LSDs and more power than a Q45 that aren't as easy to break loose going around a corner. I've gotten sideways more than once accelerating around a corner when I really wasn't going that fast. It may just be a function of the tires I've had on mine since I don't drive mine hard enough to justify buying really sticky tires that wear out fast (Qs wear tires fast enough as it is).

A viscous LSD consists of several plates with a silicone fluid between them that allows the plates to rotate at slightly different rates of speed (i.e. going around a corner). When a big mismatch in speed occurs, the fluid is heated up, it changes consistency, and it causes the plates to lockup (somewhat). They are better than no LSD, but they're not the greatest LSD since there is lag before they start to work, and they allow more slippage than some other types of LSDs. They are relatively cheap, simple and light compared to other types of LSDs, so they are becoming more and more popular. AWD Diamond Stars (Talons and Eclipses) have two of them in their driveline (center and rear differentials).

[911/Q45]

The Q has very nearly 60% of it's weight on the front end, making it quite tail happy in slippery conditions.

[AZhitman]

That, and the INCREDIBLY SKINNY TIRES most Q owners have!

I'm thinking of having my 99 rear rims lathe-turned and widened to 9"... Time for some steamrollers!

[maxnix]

I have a keen interest if a wheel this size with the correct offset (35mm-40mm?) will fit on a 1990-1996 Q. We know the 16"x8.5" will fit, so I bet the 17"x9" will clear the front suspension elements.

Have wanted to see if Tirerack would send one out for fitment, pending approval for the other three. Just not in the market for new wheels, yet. Make mine forged, please.