Yes, the wheels I bought still haven't made it on the car yet...(been in guitar building mode) but I have a question as to why they are marked 30mm offset, "front" and "rear". What is the difference between the front and rear of an 18x8, 30mm offset wheel?

I think I'm gonna go with an 225/45/18 size tire, Avon front and rear. I know I'll hear "Thats too small"!!!, but I really don't want any rubbin issues if I deciede to lower the rear some.....I understand 245's will rub....if lowered.

Thanks.....

255/40-18 are fine on the rear with the proper wheel and offset. Front too, for that matter.

Are the rims staggered?

Mounting tires not meeting the 95 minimum OEM specified load index is not wise. If you get in an accident, any attorney worth his salt will own you and everything else.

What brings me to that size, is the original size of 215/65/15.

225/45/18 is smaller at 0.12% difference....from original, rim width range 7 to 8.5

235/40/18 is smaller at 2.31% difference....from original, rim width range 8 to 9.5

245/45/18 is larger at 2.55% difference.....from original, rim width range 7.5 to 9

255/40/18 is larger at 0.12% difference.....from original, but rim width range is 8.5 to 9.0 inches.

I don't want the tires to look flat all the time, (wallowing sidewall) or too big.

And so on.....I'm using this calculator....http://www.1010tires.com/TireSizeCalcul ... ion=submit

The 350z wheels 18/8 with 30mm offset.

I think you should go with the 255-40-18 personally.. it wont look bad..

245-45-18 will ONLY rub if you have a higher offset.. They rub on the suspension, not on fender.. Youll be fine..

Id personally go with 255-40-18...

Well I guess I should mount 1 front and and 1 rear wheel, and measure the dang thing....The outside to outside lip on the wheels is 9", which is a shade under 225mm.. :-(

The selection on 18" tires is limited...I really want those Avons 550's.......

You guys need to use my Excel spreadsheet that shows all the tire brands at various sizes and their weights, effective speedo errors, recommended rim ranges, etc. Compared to original tire sizes.

Separate worksheets for Q45 and M45 are included.

Search for it. Or if you want a copy of the latest version, please send me e-mail.

Z

Meaux wrote:Well I guess I should mount 1 front and and 1 rear wheel, and measure the dang thing....The outside to outside lip on the wheels is 9", which is a shade under 225mm..

Mesure center of beadset to center of opposite beadset.

Meaux wrote:The selection on 18" tires is limited...I really want those Avons 550's.......

May I suggest you read carefully at Tirerack on the Tech 500 vs. 550? Convinced me to get the 500 for my 1990 Legend.

In 255/40-18" tires, you may well be limited to Pirelli Rosso and Michelin PS2. Gotta pay if you want to play at that size, but anything else will be a step down.

Meaux wrote:Well I guess I should mount 1 front and and 1 rear wheel, and measure the dang thing....The outside to outside lip on the wheels is 9", which is a shade under 225mm.. :-(

The selection on 18" tires is limited...I really want those Avons 550's.......

I have 255/45/17 on Layla with an 8" rim. No wallowing there, due to the height of the tire. It really helps protect the rim, in those "kiss" situations in parking lots.

I have 245/40/18 on Lola, and Evie has scrubbed the wheel twice, where a 255/40 would have protected the rim (of course, this is the first time EVER she has gotten close to a curb in her life!). It is a good thing the wheels are a polished lip, so I could sand and polish the nicks.

The new 245/45/18's that I am putting on, have good ridges for rim protection. They are a Continental ContiSport. I was not happy as all with my last set of Continental's but I only paid $245 for this complete set of brand new tires! I can't afford to be too upset with mys results.

A good cheap tire with very good treadlife is the Sumitomo HTR+. They are much quieter than the directional treads. My only beef, is the lack of rim protection (hence the rim repairs).

Well, I reckon the 245/45's is the best bet. I'll have to read the 500 vs. 550 article...

Jeff, didn't you say awhile back that 245/40's were a little too harsh a ride for you?

Good point about wheel protection....didn't think of that, but then again, there ain't too many curbs in Foley Alabama...but I may have to take a dreaded trip to Houston....

Thanks........................

"A good cheap tire with very good treadlife is the Sumitomo HTR+. "

Not sure I would use the word good, in a Q45 application........somewhat suitable for a mild driver who doesn't expect much is a better term.

Must remember that most cars are lighter in weight [thus much less weight transfer]............when you chose lesser than Michelin [strength vs weight factor----amount of extra safety reserve corporately added for image] always bump up the load rating by 10%.

Lots of tires pass the few minute brand new test only Michelin can come close in a tire with 20,000 miles of service........even they note that after 20,000 miles the failure rate rises exponentially!!!!!!!!!!!!! AND THEIR TIRES SHOULD BE REPLACED IF YOU EXPECT NEAR NEW STRENGTH.

Really hard to find much in a V rating [minimum] above 95 [1521 pounds] as few 4300 pound cars can go over 149 mph........speed limiters to protect tires.

Not really safe to assume that a tire with a lower load index can be utilized just because you don't go even 100 mph.................85 mph in Summer [90F]on a 2-3 year old tire for 4 hours at a time........is more stressful [heat generation- buildup] than a few minutes at 149 mph on a brand new tire!

Meaux wrote:Well, I reckon the 245/45's is the best bet. I'll have to read the 500 vs. 550 article...

The M550 is available in 245/45-18, but the M500 is not, unfortunately.

Z

Wheels are also a concern as a 350Z can never extert the wheel stress at any possible G load that a simple HEAVY Q does in much less G load [cornering weight load]. Probably enough safety factor when 350Z wheels are new but how will they react after 3 years?

Why so many aftermarket fancy wheels bend eventually, they never factored in SUSTAINED USE on a HEAVY CAR..........why you don't get a warranty for road hazards.

JUST BECAUSE they fit, doesn't mean THEY ARE FIT!

Meaux wrote:What brings me to that size, is the original size of 215/65/15.

225/45/18 is smaller at 0.12% difference....from original, rim width range 7 to 8.5

235/40/18 is smaller at 2.31% difference....from original, rim width range 8 to 9.5

245/45/18 is larger at 2.55% difference.....from original, rim width range 7.5 to 9

255/40/18 is larger at 0.12% difference.....from original, but rim width range is 8.5 to 9.0 inches.

I don't want the tires to look flat all the time, (wallowing sidewall) or too big.

And so on.....I'm using this calculator....http://www.1010tires.com/TireSizeCalcul ... ion=submit

The 350z wheels 18/8 with 30mm offset.

When calculating speedo errors, something to keep in mind: "tire calculators" are way too simplistic! They assume certain generic conditions that are not always met. For example, sidewall stiffness can make a difference, etc. The same "size" tire from two different models can be quite different in actual results. Indeed, allowed rim width (for the same size tire) can be slightly different depending on the tire brand and model, because of these sidewall and bead seat design issues.

So, if you truly want to worry about these small speed errors, you need to use the revs/mile to do the comparison - these are published by the tire manufacturer and usually take all the actual real-world issues into account.

My Excel spreadsheet (older versions of which have been posted here in the past and newer versions are available to anyone who sends me e-mail ... I remain surprised that all the months/years I have offered it, only one person has ever asked for it!) can demonstrate the differences much more effectively.

Z

I recently purchased 225/40/18. I am going to put them on my 94 q45 tonight. If you want to wait to purchase, I will post some picks tonight or tomorrow. (off set + 40)

Mullet

Death by Mullet wrote:I recently purchased 225/40/18. I am going to put them on my 94 q45 tonight. If you want to wait to purchase, I will post some picks tonight or tomorrow. (off set + 40)

Mullet

225/40-18 on a Q45?

Most of these tires have a load index of 88 or 92. These are dangerously low for a Q45. Please reconsider your decision ...

Z

Z,

"Dangerously low"?Meaning the vehicle is too heavy for the tire? You think I will have a blow out or something?

Mullet

Death by Mullet wrote:"Dangerously low"?Meaning the vehicle is too heavy for the tire? You think I will have a blow out or something?

Static load max for a 88 load index rire is 1235 lbs, and that is at max psi - you have to derate for lower pressures. Multiply by four and you may not even cover the static weight of the Q45.

Dynamic load (road bumps, etc.) would be even more serious! Yes, you could have a blow out under certain conditions, and given probability, it will happen when you least want it!

The minimum load index for a Q45 is 95. Some folks here would like to see it higher!

Z

Death by Mullet wrote:Z,

"Dangerously low"?Meaning the vehicle is too heavy for the tire? You think I will have a blow out or something?

Mullet

You know, even if you don't read the previous posts here, nor your owner's manual, all you have to do is go to tirerack and read a couple of pages.

szhosain wrote:
The minimum load index for a Q45 is 95. Some folks here would like to see it higher!

Z

YES! Tech has said that when you exceed the 95 the tires just feel better do to the stiffer sidewalls..... Even with a lower speed rating, having a larger load rating is key! ESPECIALLY on the front...

I could **maybe** justify running a little lower than stock load rating on the rear, but NEVER on the front... I stilll am not a fan of the idea but if you had to do it, id do it on the rear...

This is why my staggered 17 and 18 combo makes more sense than it does look good (although it is growing on me)

Yes I jumped the gun there and didn't read the previous post.

Z, Thanks for recomending me to rethink using those tires. I was so concerned on the look, that I didn't do any more research on load ratings. Now I have to un mount and send these tires back. I still can't believe that the Q weighs 5,175lbs. That is the # I got off the door panel. Is that considering a full passenger load?

Mullet

Death by Mullet wrote:Z, Thanks for recomending me to rethink using those tires. I was so concerned on the look, that I didn't do any more research on load ratings. Now I have to un mount and send these tires back. I still can't believe that the Q weighs 5,175lbs. That is the # I got off the door panel. Is that considering a full passenger load?

I am not certain. As I recall, the normal, unloaded (without gas) weight of a 90-96 Q45 is about 4200 lbs. Combined with the derating of tires below the normal load measurement point of 36psi (some manufacturers bend this and use max psi of 44, 50 or 51 and this is not good!), this means that a load index of 95 (1521 lbs.) is a good minimum! More is better, of course. I am glad that you have decided to change - much better to be safer!

If you consider 245/45-18 as a good tire size for an 18" rim, there are some very good values in that size. With load indexes ranging from 95 to 100.

Regards,

Z