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  #1  
Old 10-09-2007, 11:59 AM
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Costco Tire Buying Strategy

Costco website for buying tires forces you to buy tires in the exact
size the manufacturer lists for that specific vehicle.

I assume this is for liability reasons.

For years I have used a different size, mostly to get the largest diameter
because I think I'll get better mileage on the highway.

So, on my 300D or 300SD which came with 195/70/14 I like to use 205/75/14.


The trick for me was to take the wheels in loose and then ask to sign a waiver
that would allow them to install a non-vehicle specific tire.

After some research I found a 1999 Plymouth Minivan model Voyager Base
on the Costco website that used the 205/75/14.

My plan is to buy on the web from now on using this model vehicle.
Take the wheels in loose. Then have them installed.

Anyone else have any thoughts on how to circumvent these systems
and does anyone have a chart that lists tire sizes and the vehicles they came on ?

NOTE: another 205/75/14 was 99 Dodge Minivan Caravan Base
and the 2000 Chrysler Minivan Voyager Base.

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  #2  
Old 10-09-2007, 12:06 PM
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There is another thread about this subject that reports people can sign a waiver to get non-OEM size tires. I think its over in the diesel forum.

So if they give you a hard time, ask for the waiver form.

Ken300D
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  #3  
Old 10-09-2007, 12:16 PM
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Are the tires at Costco really that much cheaper? I know a lot of things there are only cheaper if you buy them in huge quantities.
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  #4  
Old 10-09-2007, 05:34 PM
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Actually in "Signing a waiver", anywhere does not really rotect the retailer. In fact it completely puts them in liability for what they do for you, if taken to court.
For example.
You and Me = Consumer, whats whatever, not knowing all. ( In legal issue)
Retailer = Professional, Knows what is correct for your car tire. ( in legal issues)
So if the retailer has you sign off on a "Waiver". They have actually admitted to thefact that they know this is not aorrect setup, but i will still let the conumer have it, wh ay or may not know this is the right safe setup for ther car. So, Now the consumer goes down the hwy and tire blows up, kills himself and 15 other people in Huge firey mess. Guess were the fingers will point to when the family ges to court over this. See where i am going, with this. Most aftermaket wheel/tire shops will not get involved in practices like this. Including our sponsors Tire Rack.
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  #5  
Old 10-09-2007, 08:32 PM
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For me the cheapest tires are at Tirerack.com (which not long ago opened a warehouse in Midway GA, about 15 miles from Ft. Stewart) or Edgeracing.com out of Miami. The advantage is I have family in GA, so if Edge Racing has the better price (before FL sales tax) I have them order the tires and I pick them up on my next trip up (monthly).
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  #6  
Old 10-10-2007, 10:43 AM
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Sometimes people have the misconception that specialty retailers have a higher markup on what they sell. I've found that often they can give you a better deal or at least get close to the prices charged by discounters. In spite of this, the specialty retailers have knowledgable people and are way more helpful.
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1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
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  #7  
Old 10-10-2007, 11:24 AM
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You're sorely mistaken if you think larger tires will increase your fuel economy.

Larger tires are heavier and have greater rolling resistance.

This means it requires more power to move them down the road which means burning more fuel.

You haven't seen laws of physics repealed.
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  #8  
Old 10-11-2007, 11:05 AM
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. . . and if lkchris' warning isn't enough, try these.
1) the bigger tires cause the speedo to be 5.5% slow, so when your speedo reads 60mph, you'll be doing almost 64mph.

2) In addition, any tire larger than 3% could cause brake failure. Maybe that's why Costco is concerned?? If they're not, you should be!

http://www.miata.net/garage/tirecalc.html
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  #9  
Old 10-11-2007, 05:49 PM
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Quote:
Originally Posted by JimF View Post
.
2) In addition, any tire larger than 3% could cause brake failure. Maybe that's why Costco is concerned?? If they're not, you should be!
you may want to double check the facts for that statement .... because it's not correct
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  #10  
Old 10-11-2007, 11:38 PM
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A number of tire/brake sources say . . . "When changing tire sizes, we recommend staying within 3% of the diameter of the original tire. Any more than this and you face the risk of brake failure". If you disagree, that's your right. However, it goes against the information presented below.

Tire Diameter:
A larger tire size increases stress on the differential and transmission.

In addition, larger tires heavier than smaller tires. This increases the rotating mass and thereby increases the leverage placed on the rest of the drive train. Larger tires will increase the torque loads placed directly on axles, u-joints & drive shafts.


Also larger tires are more difficult to stop and as a result most tire/brake shops recommend that you increase your braking power. Sometimes simply switching brake pad/shoe materials may be the solution. You may have to go to a larger master cylinder, larger disks, drums or calipers. These "pros" recommend this so I wouldn't underestimate the importance of proper stopping capabilities!

Increased weight caused by the larger tire and any axle or brake upgrades also increases unsprung weight. This is probably small for the tires in question. However when mounting the tire you will find that it is often much more difficult to balance the tire correctly. This is due to the extra weight of the tire, the increased rotating inertia of the tire and manufacturers tolerances on larger tires. It can take quite a bit of weight to balance a large tire. A dynamic balance would be the recommended thing to do here.

Tire Width:
The larger tire increases the rotating mass, a wider tire provides a larger contact patch with the ground. A larger contact patch provides more friction requiring more power to rotate putting even more stress on the drive train.

In addition, wider tires may require a different wheel offset and/or width for a proper fit. As a result, you should pay special attention to your turning radius; the increased width may now rub on the suspensions components when turning lock to lock. You may have to install wheel spacers.

So these are facts that various shops have advised when one goes to a larger tire. With those generalities as a backdrop, the 5.2% increase in tire size will cause increased stress on the drive train and tax the braking system by, most likely, an additional 5.2%. It is NOT recommended without making some mods to the car.

A better way would be to do a "Plus One" or "Plus Two"; this way you get the bigger tire you want but don't tax the brakes or drive train. The tire’s diameter is the same ‘before’ and ‘after’!

Should this information be ignored? Some might but I wouldn't.
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  #11  
Old 10-12-2007, 04:01 AM
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Quote:
Originally Posted by lkchris View Post
You're sorely mistaken if you think larger tires will increase your fuel economy.

Larger tires are heavier and have greater rolling resistance.

This means it requires more power to move them down the road which means burning more fuel.

You haven't seen laws of physics repealed.
Maybe it would help, since it would make the gearing taller, but it would probably be negligible.
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  #12  
Old 10-12-2007, 11:51 AM
Moderator and Tire God
 
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Quote:
Originally Posted by JimF View Post
A number of tire/brake sources say . . . "When changing tire sizes, we recommend staying within 3% of the diameter of the original tire. Any more than this and you face the risk of brake failure". If you disagree, that's your right. However, it goes against the information presented below.

Tire Diameter:
A larger tire size increases stress on the differential and transmission.

In addition, larger tires heavier than smaller tires. This increases the rotating mass and thereby increases the leverage placed on the rest of the drive train. Larger tires will increase the torque loads placed directly on axles, u-joints & drive shafts.


Also larger tires are more difficult to stop and as a result most tire/brake shops recommend that you increase your braking power. Sometimes simply switching brake pad/shoe materials may be the solution. You may have to go to a larger master cylinder, larger disks, drums or calipers. These "pros" recommend this so I wouldn't underestimate the importance of proper stopping capabilities!

Increased weight caused by the larger tire and any axle or brake upgrades also increases unsprung weight. This is probably small for the tires in question. However when mounting the tire you will find that it is often much more difficult to balance the tire correctly. This is due to the extra weight of the tire, the increased rotating inertia of the tire and manufacturers tolerances on larger tires. It can take quite a bit of weight to balance a large tire. A dynamic balance would be the recommended thing to do here.

Tire Width:
The larger tire increases the rotating mass, a wider tire provides a larger contact patch with the ground. A larger contact patch provides more friction requiring more power to rotate putting even more stress on the drive train.

In addition, wider tires may require a different wheel offset and/or width for a proper fit. As a result, you should pay special attention to your turning radius; the increased width may now rub on the suspensions components when turning lock to lock. You may have to install wheel spacers.

So these are facts that various shops have advised when one goes to a larger tire. With those generalities as a backdrop, the 5.2% increase in tire size will cause increased stress on the drive train and tax the braking system by, most likely, an additional 5.2%. It is NOT recommended without making some mods to the car.

A better way would be to do a "Plus One" or "Plus Two"; this way you get the bigger tire you want but don't tax the brakes or drive train. The tire’s diameter is the same ‘before’ and ‘after’!

Should this information be ignored? Some might but I wouldn't.
Your cut and paste is a nice, theoretical, look at the subject at hand but, doesn't really hold water in real world applications. While I do agreed with upgrading brake components when increasing unsprung weight to improve braking performance. The "brake failure" is a bit over the top, and basically, an alarmist type statement .... I guess you have never seen a lifted 4x4 truck with large tires or a drag car with large slicks .... remember weight is much more critical than diameter.

you keep referring to "these Pros", just so you know, I have been in the automotive industry for over 3 decades, hold many ASE certifications and have achieved the master technician level, have instructed hundreds of classes for other technician across the country for several automotive equipment and vehicle manufacturers .... I think I may have a little knowledge regarding this issue. I am also considered a "pro" in most circles

While for most cars a larger diameter isn't the best of ideas because the suspension geometry is adversely affected not because the brakes are going to fail. There is a huge safety margin built into braking systems. 5 - 8 percent diameter change in the tire will have little effect on the reliability of most braking systems if any at all.

the plus 1 or plus 2 you mentioned when done properly does not give you a larger tire. what you get is a shorter sidewall and larger wheel
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Last edited by Luke@tirerack; 10-12-2007 at 12:01 PM.
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  #13  
Old 01-16-2008, 04:00 PM
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They stopped selling my favorite, but I like these too

I had been buying a BF Goodrich for $65 that I really liked,
65,000 warranty.

It is no longer available so I went for the Michelin with 80,000 warranty
for $85.

I really like the ride. Even though they cost a little more.

Used the same technique to avoid waiver and general crap at the seller.
Told them it was a 99 dodge caravan base minivan and I want 205/75/14.

Then he says - what color ? Huh ??
Sure this does not matter, the wheels were loose.
But I told him it was white.

I liked the argument for not changing tire size based on mass/weight change
and the little effect on gas mileage.

Then I remembered that I like the larger tire filling in the wheel well.
Factory tires look undersized.
Second, I do believe the RPM is lower by just a smidge at 65mph.

Of course the speed rating is different, but I don't drive my diesels real fast.
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  #14  
Old 01-16-2008, 08:02 PM
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On the subject of big tires, I used to have an '88 Suzuki Samurai. The stock tire size on this vehicle was 205/70-15. I ran 235/75-15's. The stock tires were 26.3 inches tall, and the ones I used were 28.9 inches, an increase of almost 10 percent. The only other mods to the vehicle were a 2" shackle lift and a freer flowing exhaust. The brakes weren't exactly great, but they were good enough for something slower than a 240D. The extra power to turn the wheels (and overcome the extra wind resistance from the lift) limited the top speed to 62 mph, whereas I've heard stock Sammys will do upwards of 75.

So yes, a large increase in tire size will have a noticeable effect, but it won't make your car explode or anything like that.
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  #15  
Old 01-17-2008, 09:56 AM
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I'll chime in here... A DIFFERENCE of more than 3% in tire size from one wheel to another ON THE CAR can lead to ABS failure, not brake failure. Wanna try it out? Find a pair of really tall or short tires and bolt them on the front or rear axle of your car. Almost immediately your brake light or ABS light will come on...if your car is equipped with ABS. The computer is detecting different wheels speeds and will freak out.

As for taller tires...if you go wider, you're not doing yourself much good. If you're sticking to the same tread width or narrower, that's where you get into the economy area. Personally, I don't worry about it...because I like my traction and always go wider.

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