tires and "staggered fitment" ARGH!

[Kingcreek]

Geez. I have never had so much trouble buying a set of tires. 2008 Cadillac SRX with 255/65/17 on front and 255/60/17 on the rear. I like to do business local and tried 2 tireshops that offered none and one crappy option (hankook?). The GM dealer found a set for $1200(!) before taxes, mounting, balancing, disposal, etc.
So...as much as I hated doing it, I ordered a set of Michelin Latitude Tours online shipped for $815. after the mfg rebate and I'm taking them to the local tireshop to be mounted/balanced.
If anybody knows the GM guy responsible for the stupid "staggered fitment" thing and tire sizes, I would like his phone number or email so I could have a few words with him. and the Goodyear RSAs that came OEM were absolute crap junk tires with problems since 16,000 miles and my wife only drives like an old lady.

[CSM Kersh]

I think I'd be tempted to go 255/65R/17 Front and rear.  I doubt you'd notice the slight difference in sidewall height. 

[bedlamite]

I think I'd be tempted to go 255/65R/17 Front and rear.  I doubt you'd notice the slight difference in sidewall height. 

This. Then you could rotate them properly too.

[cassandra and sara's daddy]

they did that with some years of convertible vettes  staggered sizes

[Brad Johnson]

Geez. I have never had so much trouble buying a set of tires. 2008 Cadillac SRX with 255/65/17 on front and 255/60/17 on the rear. I like to do business local and tried 2 tireshops that offered none and one crappy option (hankook?).

Hope you haven't ordered yet as your fronts are actually supposed to be 235/65-17, not 255.  The 255/60-17 rear size you listed shows to be correct.

Discount Tire is showing prices ranging from $110 to $250 on the fronts with over a dozen choices, $150-$250 on the rears with ten choices.  The brands are the common choices (Bridgestone, Micheline, BFG, etc).  Your tire shops can easily get them, they just won't carry them in their everyday stock.

Patience, dear boy.  Patience.

Brad

[dogmush]

Brad beat me to it, your front tires are supposed to be 235's.

Those actually make sense for handling and traction.

[zxcvbob]

Are you sure it has 17" wheels and not 18's?

[Kingcreek]

my typo. yep 235s front 255s rear. I asked everybody about going same size and was told by dealer and 3 tireshops that because its AWD I can't/shouldn't vary size. and yes 17" wheels

[zxcvbob]

I looked up the tire specs on Tirerack.com, and (oddly enough) both those tires are the same diameter (29.1").  So there shouldn't be any problem changing tire sizes to put the same size all around.  Maybe 245/65-17's? 

[PTK]

...boy, that's some dumb engineering. I don't think I've heard of many modern cars doing that to the owners. Sorry to hear about that. :(

[Brad Johnson]

.

my typo. yep 235s front 255s rear. I asked everybody about going same size and was told by dealer and 3 tireshops that because its AWD I can't/shouldn't vary size. and yes 17" wheels

Correct.  The AWD system is brutally unforgiving in regards to tire diameter mismatches.  Screw it up and you begin breaking Very Expensive Things.  Also, the stability control system is programmed to compensate for the traction coefficient differentials of the staggered fitment.  Get it wrong and the system could rebel is some pretty strange ways, actually creating traction and stability problems rather than solving them.  In other words, stick with the stock sizes and fitment.  Monkey with them in an attemp to save a couple bucks might well end up biting you in the behind on several levels.

Again, don't panic just because no one in town carries them in stock or want to charge a mint for ones they do have.  They're not an unusual size, but they also aren't something the tire shops will sell many of on a daily basis.  Most tire shops stick to the 80/20 rule... carry the top 20% of common sizes and you can service 80% of vehicles.  For everyone else, special order. Welcome to the club. 

Your tire shops can get them through their distributors and it only takes a couple days in most cases.  Prices I'm seing are comparable to other touring-style tires.

PTK, it's not dumb engineering.  It's actually very good engineering.  It's just a PITA part of owning a modern sports car.

Brad

[PTK]

What benefit is there to daily driving, or is it just for the performance aspect, like a scaled-down funny car?

[Kingcreek]

nobody local had any of the tires in stock. the dealer and one tire shop said they could order but the cost was 1050-1200 for 4 tires PLUS all the mount/balance/tax/valve stem/disposal fees/road hazzard, etc.
as far as performance, it ain't a racy car. s'posed to be a "luxury crossover" whatever that is but I haven't been too impressed with the vehicle in general. I'm going to put another 20k on it with new tires and trade back to a jeep grand cherokee or something. We had 3 gr cherokees and loved em all. Our daughter still drives one of them with 240k miles and no problems, still runs and drives great (and all 4 tires are the SAME SIZE).

[zxcvbob]

nobody local had any of the tires in stock. the dealer and one tire shop said they could order but the cost was 1050-1200 for 4 tires PLUS all the mount/balance/tax/valve stem/disposal fees/road hazzard, etc. [snip]

Check with Tirerack.com and see if they have an installer in your area.  You can get a matched set of O.E. tires for half that (plus shipping @ about $20 per tire, and mounting, balancing, etc.)

[Kingcreek]

I used tirerackdotcom for the matched set of Michelins shipped for 814.97 after rebate.

[Tallpine]

You're supposed to put the bigger tires on the back. so that you get better gas mileage because you are always going downhill 

[brimic]

You're supposed to put the bigger tires on the back. so that you get better gas mileage because you are always going downhill

Ahhh. I thought that made cars faster for the same reason

[Brad Johnson]

I used tirerackdotcom for the matched set of Michelins shipped for 814.97 after rebate.

By "matched set" I hope you mean a matched staggered set.

Brad

[Kingcreek]

matched set= same brand and model, 2 different sizes in OEM specs.

[CNYCacher]

my typo. yep 235s front 255s rear. I asked everybody about going same size and was told by dealer and 3 tireshops that because its AWD I can't/shouldn't vary size. and yes 17" wheels

235/65/17 and 255/60/17?

Yeah well, those tires are the same diameter already so there's no problem.  Just different widths.

Tire sizing is very confusing and counterintuitive.  The first number is the width of the tread in millimeters.  The second number is the sidewall height, expressed as a percentage of tread width, and the last number is rim size.

65% of 235  is almost exactly the same as 60% of 255, which is why the tires are the same size, and by size I mean diameter.

[Hawkmoon]

my typo. yep 235s front 255s rear. I asked everybody about going same size and was told by dealer and 3 tireshops that because its AWD I can't/shouldn't vary size. and yes 17" wheels

As zxcvbob has already pointed out, the two different sizes ARE the same diameter, so putting the same tires on all four corners would not generate any problems for the AWD. Especially if the primary driver isn't into "sporty" driving, I'd settle for 235/65s on all four corners and be done with it.

One more example of why nobody should be allowed to work as an automotive engineer until they have worked in a garage as a mechanic for at least two years. I used to say one year, but now I think it needs at least two years to fully appreciate just how idiotic the engineers can be.

[rcnixon]

In my humble opinion, I'd stick like glue to the recommended sizes.  Insurance companies have investigators who get paid for finding ways not to pay claims.  Most states have provisions in their motor vehicle codes that require the inspection of modifications by a state authorized engineer.  Most auto policies have clauses that will allow them to deny claims for modified vehicles.  In fact. the big-box store tire departments won't install anything but the book stock tires to preclude liability claims.

Is the few hundred bucks and some time really worth the lives of you family and friends and the liability exposure you are incurring?

I buy nothing but Michelin tires from authorized dealers and I haven't had a problem yet.  My wife's T-bird uses about a thousand dollars of tires every sixty or so thousand miles.  It's worth it to me.

Russ

[dogmush]

As zxcvbob has already pointed out, the two different sizes ARE the same diameter, so putting the same tires on all four corners would not generate any problems for the AWD. Especially if the primary driver isn't into "sporty" driving, I'd settle for 235/65s on all four corners and be done with it.

One more example of why nobody should be allowed to work as an automotive engineer until they have worked in a garage as a mechanic for at least two years. I used to say one year, but now I think it needs at least two years to fully appreciate just how idiotic the engineers can be.

Yeah, Rear wheel drive car with front weight bias already, and sporty gearing, then you reduce the traction in the rear.....what could possibly go wrong?

More reason why folks shouldn't modify stuff they don't understand.

[sanglant]

even going to the wider tires in the front will make the car whats the word, oh yeah. squirrely.


this is one of those things you should check going in, right up there with tire size availability. cost of brake pads/shoes, headlight bulb type and prices, etc. and no, i'm not fun to take car shopping.


good luck with the road you choose.

[Brad Johnson]

matched set= same brand and model, 2 different sizes in OEM specs.

Then you're good.  Case closed.

Brad