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post #131 of 304 (permalink) Old 09-07-2007, 11:05 AM
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I just got an email from my Mazda dealer. They are offering to install the 4 new tires I purchase and align the wheels for me per their "Goodwill" policy. I'll take what I can get. So I just have to buy the tires. I asked the Service Manager if he knew for sure if 225/45 R18 tires would not be a problem in replacing the 215/ 45 R18 OEM tires. He didn't really have a clue so I just want to verify one last time before I purchase these tires online.

I'm either buying the Continental ContiExtremeContact 225/45 R18's ($570 total includes road hazard insurance for each tire and shipping) or the Toyo Proxes 4 225/45 R18's ($676 total includes road hazard insurance for each timre plus shipping). Both seem like very good quality tires at a reasonable price.

Will these DEFINITELY fit my 18 x 7 OEM wheels? I'd hate to buy them and have the service guys tell me they will interfere with the traction control or ABS sensors (Firestone guy said he wasn't sure if this size would interfere with any sensors).

You guys seem real knowledgable about this stuff and I'm 99% convinced but a few more feedbacks on this would push me that extra 1%. Sorry if I'm being a Pain but I don't want to have to ship these back and incur more expenses than I'm already incurring.

Thanks,
Shades
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post #132 of 304 (permalink) Old 09-07-2007, 11:39 AM Thread Starter
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Will these DEFINITELY fit my 18 x 7 OEM wheels? I'd hate to buy them and have the service guys tell me they will interfere with the traction control or ABS sensors (Firestone guy said he wasn't sure if this size would interfere with any sensors).[/b]
Yes they will DEFINITELY fit. They will not interfere with any sensors because they are within 3% of the original tire's overall diameter.

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post #133 of 304 (permalink) Old 09-17-2007, 04:10 AM
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So I have a strange one for someone... I have some wheels that I took off my 1994 BMW 325i right before I sold it two cars ago. I have been storing them in the garage for a while now and would like to see if there is anyway I can put them on my 2007 Mazdaspeed6. The wheels are 18x8.5 with an offset of +45mm. The bolt pattern is standard BMW of 5x120mm. H&R makes wheel adapters that will allow me to physically bolt them to the car, but they are 20mm or 25mm thick. with the use of the spacer/adapter from my understanding it will bring the effective offset of the wheels down from 45mm to 25mm or 20mm.

Is it at all possible or am I just dreaming. When you refer to rubbing, where does it rub? I have a huge gap in my fender well and stiff enough suspension that it doesn&#39;t look like it would bottom out onto the fender if it was out too far. Would it rub in the front when I try to turn?

Right now the wheels have 225/4ZR18 88W on them, I suspect that if I was able to fit them that I would have to get new tires with a higher load rating? What is all in a load rating? On the side of the tire it states max load of 1235 LBS. 1235 X 4 = 4940. Car of 3600 lbs plus cargo doesn&#39;t weigh that much. Anyone have a good link to info on load rating so I can better understand this?

Sorry if I have asked any blatantly stupid questions, just saw that they made adapters and thought it would be cool to see the wheels used again.

Thanks,
Trever

[attachment=29381:BMW_325i...e_Wheels.jpg][attachment=29380:Foose_BM...5i_Wheel.
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post #134 of 304 (permalink) Old 09-17-2007, 09:36 AM Thread Starter
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^^^ Trever, this is a bad idea for several reasons:

1. Tire size is okay, but the load index is WAY too low. That tire won&#39;t carry enough load for the MS6.

2. With the spacers (already a bad idea), bringing the offset down to +20 or +25 is WAY too low. Your wheels will stick out of the fenderwells at least two inches (probably illegal in your state) and they will hit the rear fender upon compression.

With the offset so out of whack, even if you got this setup to work, your handling is going to totally suck.

Best thing to do is to get on ebay or some other website, sell your wheels, try to get some money back out of them and buy something that is MADE TO FIT the MS6.

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post #135 of 304 (permalink) Old 10-09-2007, 11:08 AM
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Hi all,

Surprisingly I&#39;ve seen few posts here regarding the widest tire size yet mounted. I guess that&#39;s because there is a lot of risk involved in not having the wheels fit and paid for. Regardless, I&#39;ve been researching this and want some tire/wheel experts feedback. As we all know these car are not light, therefore I&#39;d like get as much rubber down as possible. I&#39;m going to fit the 245/40/17 or the 245/45/17 to the car. At first I thought the way to go was 245/40/17 but many of the Bridgestone tires (my preference) don&#39;t have the appropriate load rating of 93 or better in the 40 size. So I thought about using the 245/45/17 on the car which has the appropriate load rating and putting it on an 8.5" rim with a 50+ offset. There are a few wheels offered in this size but they are available and they don&#39;t come cheap.

What are your thoughts on the 8.5" rim fitting with the 50+ offset. Should the offset be larger? Am I better going with the lower profile due to its smaller diameter for clearance reasons.

Before someone asks, yes I&#39;m more than willing to roll the fenders.
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post #136 of 304 (permalink) Old 10-09-2007, 10:19 PM
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Hi all,

Surprisingly I&#39;ve seen few posts here regarding the widest tire size yet mounted. I guess that&#39;s because there is a lot of risk involved in not having the wheels fit and paid for. Regardless, I&#39;ve been researching this and want some tire/wheel experts feedback. As we all know these car are not light, therefore I&#39;d like get as much rubber down as possible. I&#39;m going to fit the 245/40/17 or the 245/45/17 to the car. At first I thought the way to go was 245/40/17 but many of the Bridgestone tires (my preference) don&#39;t have the appropriate load rating of 93 or better in the 40 size. So I thought about using the 245/45/17 on the car which has the appropriate load rating and putting it on an 8.5" rim with a 50+ offset. There are a few wheels offered in this size but they are available and they don&#39;t come cheap.

What are your thoughts on the 8.5" rim fitting with the 50+ offset. Should the offset be larger? Am I better going with the lower profile due to its smaller diameter for clearance reasons.

Before someone asks, yes I&#39;m more than willing to roll the fenders.[/b]
Yeah there are very few trailblazers with the Mazda 6 crowd. I&#39;m more worried about not clearing suspension arms than rolling my fenders. Wish there were more people pushing the limits. I have heard of 265&#39;s being fitted under stock fenders with some rolling, however I have no specs.

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post #137 of 304 (permalink) Old 10-10-2007, 04:45 AM
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As we all know these car are not light, therefore I&#39;d like get as much rubber down as possible. I&#39;m going to fit the 245/40/17 or the 245/45/17 to the car. At first I thought the way to go was 245/40/17 but many of the Bridgestone tires (my preference) don&#39;t have the appropriate load rating of 93 or better in the 40 size.[/b]
You seem to have conflated several concepts.

A wider tire will not necessarily either help you "get as much rubber down as possible" nor address the issue that the car is not light.

For a given inflation pressure, the contact patch -- the area of the tread that actually is touching the pavement at any given instant -- will be the same size whether the tire is wide or narrow, low or tall. Going to a wider tire will just change the shape of the contact patch, not make the contact patch any larger. You can increase the size of the contact patch by running the tires at a increased inflation pressure, up to a point. (That point is an inflation pressure of about 35-36 psi with standard load tires, or about 41 psi with extra load or reinforced tires.) Decreasing tire pressure to get more rubber on the road, therefore, decreases the tire&#39;s load-carrying capacity.

However, if your main concern is to maximize the load capacity of your tires, there is a more straightforward way to accomplish it: get tires with a higher load index and inflate them to the proper pressure for the load you require. Appendix B of this document will assist you in that endeavor.
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post #138 of 304 (permalink) Old 10-12-2007, 07:06 AM
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You seem to have conflated several concepts.

A wider tire will not necessarily either help you "get as much rubber down as possible" nor address the issue that the car is not light.

For a given inflation pressure, the contact patch -- the area of the tread that actually is touching the pavement at any given instant -- will be the same size whether the tire is wide or narrow, low or tall. Going to a wider tire will just change the shape of the contact patch, not make the contact patch any larger. You can increase the size of the contact patch by running the tires at a increased inflation pressure, up to a point. (That point is an inflation pressure of about 35-36 psi with standard load tires, or about 41 psi with extra load or reinforced tires.) Decreasing tire pressure to get more rubber on the road, therefore, decreases the tire&#39;s load-carrying capacity.

However, if your main concern is to maximize the load capacity of your tires, there is a more straightforward way to accomplish it: get tires with a higher load index and inflate them to the proper pressure for the load you require. Appendix B of this document will assist you in that endeavor.[/b]
Interesting point. However, all things being equal the wider tire will have a larger contact patch. Just check the overall section width and tread width. You mention the patch shape changes. I&#39;d say yes it does. It become bigger or smaller. I realize we can play with preassures to achieve slight changes in character. My question was assuming we are starting with an optimal tire size for a given wheel. Otherwise we&#39;ll spend the next ten pages debating opinions. It&#39;s like economics. You have to hold some variables as given to talk about the bigger picture. Otherwise there becomes to many moving parts to have meaningful conversation.

I&#39;d agree too with gusto that the wheel needs to clear the arms. I just wish some people had tried something a little wider. Even just placed the rim on the car to see where it sits.

I think what my concern is that the load capacity must be enough to handle forces upon it during agressive driving such as an autocross. I think we all would agree this car would most likely make a better road car than track due to the limited tire size. Evo&#39;s and the like have a huge advantage on an autocross track where, in my experience, size of your contact patch matters. Again. Yes a skilled driver helps.

Anyones input regarding fitment is welcome.

Anyway, I hoped someone could give me a starting point to work with. Rims at $350/each aren&#39;t fun to test with.

Thanks for the reply&#39;s
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post #139 of 304 (permalink) Old 10-12-2007, 02:14 PM
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Interesting point. However, all things being equal the wider tire will have a larger contact patch. Just check the overall section width and tread width. You mention the patch shape changes. I&#39;d say yes it does. It become bigger or smaller.[/b]
Not true. The tire at rest, supporting the mass of the vehicle, is a closed system. The inflation pressure inside the tire must be in equilibrium with the pressure on the outside of the tire. The inflation pressure is measured (in the English system) in pounds per square inch (psi). On the outside of the tire, that same figure also is measured in pounds per square inch (psi). The inflation pressure inside the tire and the size of the contact patch on the outside of the tire are mutually dependent variables. While a wider tire has a wider contact patch than a narrower tire does at the same inflation pressure, the wider tire&#39;s contact patch is also shorter, front-to-rear; conversely, mounted on the same vehicle (and inflated to the same pressure), the narrower tire has a longer contact patch, front-to-rear, than the wider tire&#39;s contact patch. While the shapes of the two contact patches differ, the total area of each of the two tires&#39; contact patches is the same. All of this arcane stuff is explained in much greater detail - - here (clickable link).
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post #140 of 304 (permalink) Old 10-12-2007, 03:46 PM
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Not true. The tire at rest, supporting the mass of the vehicle, is a closed system. The inflation pressure inside the tire must be in equilibrium with the pressure on the outside of the tire. The inflation pressure is measured (in the English system) in pounds per square inch (psi). On the outside of the tire, that same figure also is measured in pounds per square inch (psi). The inflation pressure inside the tire and the size of the contact patch on the outside of the tire are mutually dependent variables. While a wider tire has a wider contact patch than a narrower tire does at the same inflation pressure, the wider tire&#39;s contact patch is also shorter, front-to-rear; conversely, mounted on the same vehicle (and inflated to the same pressure), the narrower tire has a longer contact patch, front-to-rear, than the wider tire&#39;s contact patch. While the shapes of the two contact patches differ, the total area of each of the two tires&#39; contact patches is the same. All of this arcane stuff is explained in much greater detail - - here (clickable link).[/b]

Thank you again. Looks like some light reading this weekend.

I checked out the Toyo site, along with many others, and noticed on the 245/40/07 Toto requires a 9.0" rim, others don&#39;t. While with no certainty my guess is that a 9" rim doesn&#39;t fit the car. Most other tire manufacturers recommend the 8.5" rim. This I&#39;m thinking of getting. What&#39;s your thoughts on this. Can the 8.5&#39; rim be adequate. I like the load rating on the tire.
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