1. just the general crowd likes to "upgrade" from stock (sometimes its not better)
2. if you like 225's then keep em! :P but you have to see my 255/45's
3. if you like the tire size, you could always get the same size with a stickier compound (AAA traction rating, highest speed rating, and lowest treadware) but those are like 250+ per tire.

 

...not according to most any tire makers...245/40/18s are on the wide side for an 8" rim. OK, it's a more comfy ride, but to the detriment to absolute handling from the more bulging sidewall vs. the 225.

here's what I'm saying from the Bridgestone specs for the RE040:

225/45ZR18
rim width range: 7-8.5"
measured rim: 7.5"

...so the 8" OEM rim is already wider than optimum, giving slightly better sidewall bracing and slightly degrading comfort. Not a bad compromise for a sports car application.

as there is no RE-040 245/40R18 here's a Dunlop Direzza to illustrate

245/40ZR18
rim width range: 8-9.5"
measured rim: 8.5"

...so for this tire the 8" OEM rim is at the lower limit of the recommended for the tire giving extra sidewall flex that's great for comfort, but will tend to 'fold over' and tend to squeal under max cornering and feel slower in initial steering response.

Bottom line...Mazda specs the 225/45/18 tire well to complement the 8" wheel width. It's a great compromise for handling, comfort, price, ease of mounting, weight compared to larger tire sizes.


=================


To the OP, you've got a great analytical mind, allowing you to question the consequences of change vs. OEM interactions, which is a great asset over just "throw more at it and it'll be better!" attitude.

JMO but I tend to pretty much agree with your argument that 225 or something close like 235 is best for the OEM wheels...Mazda has it correct here. I disagree that Mazda chose the 'best tire'. They choice a best-compromise tire that did what was needed (when new specifically), that was cost effective for them.

However, your root question "So, why have so many of you decided to alter the tires?" is typically only half the story and radically changes the result that is optimum and does produce quite different result from the OEM spec Mazda uses for wheel/tires.

Many, if not most, add new wheels into the equation when purchasing new tires to obtain a significant real world performance upgrade. Now the 'right' choice shifts as well. Certainly, and specifically in this case, morel aspects of the car need top be evaluated to optimize the results as you alluded to. Spring and shocks or coilovers, overall tire/wheel size (17-18-19) & weight, offset and overall diameter, adhesion characteristics (e.g. Ultimate Street or R-Comps) sway bar stiffness, chassis stiffness and bracing...specifically need consideration/adjustment to take advantage of the changed wheel/tire aspect.

Here many earn a fail and upgrade for looks and cred only, forgetting the rest. Those that track and see, hear, feel the results of their changes get a chance to prove/disprove their theories and continue the joyous evolving experiment that is personalizing a sports car There are many paths to explore and no perfectly right answers, but in the end, and along the way, you can answer for yourself the question you asked.

 

Car manufacturers do tune their suspensions for the specific tire that comes with the car. That includes sidewall flex, etc. It affects bushing, shock, spring, etc. choices. That said, I think most people would be hard pressed to noticed a significant difference between similar types of tires in terms of the overall affect on the suspension. At worst I'm sure the difference is something you could become accustomed to.

For this kind of car I think one is best off buying tires with the best performance falling under one of following categories:
1. The best tires they can afford.
2. Performacne with great bang for the buck.

I think Tire Rack testing is a good source of information.
A C&D review from a few years ago: http://www.caranddriver.com/reviews/...omparison_test

 

Stock RE040s suck. Tirerack.com is your friend although they don't carry Falken, which a lot of people like on here.

 

ahahaha ya they suck, that's why a car riding on them gets rave reviews for handling characteristics. considering the tires actually connect the car to the road, they must not suck, although they might not be the absolute best.

 

Perhaps you should do more searching on her before you post and "considering the tires actually connect the car to the road, they must not suck"? WTH

The RE040s are decent in the dry, but are pretty much useless for anything after that. And the other characteristics like ride and noise are not great either. You might actually find that out if you had searched.

There are many tires available that are far better than the RE040s that include great dry and wet handling and have good ride/noise facets.

 

so, by that logic. if i slap a set of re040s on a ford fiesta, its going to be absolutely ballin, right?

 

Absolutely!! If Ford had thought of that, they'd be on top of the world.

The RE040s are a good choice for Mazda. They handle well in the dry and when they're new. That covers when customers will test drive the car, and when automotive journalists get their test cars. If they don't last long, or if they get noisy when worn...well, that's downstream.

Mine are close to worn out. I'll be looking for some high performance all-seasons with a longer tread life...which is what I wish had come on the car in the first place.

Ken

 

hmm, ya I don't see how you make your connections. One of them major points I make on this thread is the importance of the tires for the chassis as a whole; they are integral to the handling of a car when they work with a specific chassis, suspension, weight distribution, motor, etc...

Slapping on the re40's to a car that wasn't set up for them as the 8 was..well that might not work out very well.


But ya keep on trying, you'll get it eventually.

Also notice how you got owned from the poster above about your claim that 225 is too narrow for 8 in rims even though it's what the manufacturers recommend...


I trust you completely.

 

Hey Guys, enjoyed reading through these comments on tires. I got my RX last summer, and it just spent most of the winter in the garage, I just turned 2000 miles on it. Wow, what a car!! Anyways, one thing I like very much being a guy who is well past his youthful friskiness, is that the Bridgestones will let you know through the squealing that you might want to mellow out a bit. I WANT to know when I'm breaking loose (I know my tires are very new, one guy said that he hears more of a "scruffing" sound rather than squealing, I've heard the same thing. I certainly plan on running the Bridgestones to the end, in the meantime I'll continue to research what I'm going to replace them with. I'm in Souteast Alaska, so it is cooler and roads are often wet, but I'm planning on sticking with summer tires instead of all seasons--unless someone convinces me otherwise. I want a tire that has great grip, lets me know when it is breaking loose instead of just breaking loose! and I guess tread life is last on the list. cheers.

 

I've never been to Alaska, but I cannot imagine all seasons being appropriate for there. I'm in Virginia, where all seasons make sense. I can also work from home if we get any real (real for here, anyway) snow.

Just look for a performance tire that has good wet road manners.

Ken

 

may be off topic but i just slapped on 4 general exclaim UHP on mine. can say definitely better than stocks in terms of comfort and noise. still have to see the handling department.