Cons to changing tire size.

[Blue Mazda]

I am considering changing my tire size from the stock 215/50/17's to 225/45/17. The new tire size causes about a 2% difference in mileage and the speedo. This obviously throws off gas mileage calculations etc, which is no biggie. But are there any other real cons to this? My final two tires are the Toyo T-1S and the Bridgestone RE750's. The Toyos can be had in stock size, but are ligher in the changed size. The Bridgestones are not available in the stock size. Any feedback would be appreciated.

[stretch]

You will not notice a 2% difference. Besides, with a wider tire, your actual amount of sidewall "sag" will be a smidge less than with a skinnier tire- bet you didn't account for that :)

Below are two tires that have the unloaded diameter, but loaded- one has a much smaller radius, which would throw the speedo off:
http://www.mazda6tech.com/images/articles/contact_patches.jpg

See the difference?

I'm sure you can now guess that tire pressure would also make a huge difference!

My point is that calculating the true difference in speedometer calibration is difficult. And even if it weren't, 2% is virtually nothing!

[Blue Mazda]

Nope, didn't even think about sag. So it could be like 1% due to the extra sag, but no more than 2%. I know the overall diameter difference between the two sizes is only .5" without taking into account sag. The width difference between the 2 is 1/2 inch as well. Thanks!

[ashu]

Yeah - and the diameter and specs even vary on a per-brand and per-model basis.

The Toyo T1-S 225/45-17 have a larger rolling circumference than, say, the Kumho MX. But then again, the MX have a stiffer sidewall, possibly leading them to sag less. Both of these sag less than the stock 17" Michelins, though!

And as for speedo errors - the DOT or EPA or whoever controls these things, only requires a 5% accuracy. And some cars are typically around that much off. Try tracking the speed of a friend in a BMW sometime :)

I wouldn't sweat it ;) Your more aggressive driving with newer, grippier tires will influence your mileage MUCH more, as will the stickiness (increased friction). My mileage has dropped from 27-ish to 24.5 (and this is still 2.8% off from my 205/60-16 Michelins - so its EVEN lower than that - say 24, to be conservative) :)

[Blue Mazda]

Thanks guys. I am waiting to hear back from tirerack on the weight of the RE750's each and will make my decision on if I am going with the Bridgestones or the Toyos after that. I know the Toyo's are 20.9 each in the 225 size and I just want to see where the Bridgestones stack up. I have heard excellent things on the way the Bridgestones wear and people on the web seem to report excellent longevity with them.

[Blue Mazda]

I just spoke to tire rack and they advised me not to do the 225's becasue the computer says it is a tight fit and may require fender rolling. Is that true? I am going to be running them on stock rims......

[tireswap]

you wont require fender rolling on a stock wheel setup.

As far as speedo calculations go... the BMW is accurate.. but if you want to really test the accuracy.. find someone w/ a Corvette. The Digital HUD (Heads Up Display) is VERY accurate.

[Blue Mazda]

Well I was just looking, and the section width (cross section) on the stock Michelins is 8.7" mounted on a 7" wheel, while the cross section of the Bridgestones is 8.9" mounted on a 7.5" wheel, which means that mounted on my stock 7" wheel, the 225 size Bridgestone's won't be much wider than the stock Michelins. Maybe a little, but not much. Which to me would mean that they would be fine in terms of fitting and not requiring any fender rolling. Does this sound right?

[ashu]

Not only does it sound right ... it is! Tireswap said so. In any case, I prefer the Toyos to the 750s. The 750s are an OK performance tire, but you masy as well get the comfier and grippier (by all accounts) Toyos for around the same price.

IIRC - I considered the 750s early in my tire hunt - they're around 24.5 lbs or more in that size.

[Blue Mazda]

24 lbs flat is what I was quoted by Tirerack as the shipping weight. Dead on with the stock Michelins. From accounts that I have read, the RE's aren't going to be "quite" as good performance wise as the Toyos, but they will ride quieter and better and last a little longer. So to me what I would be giving up in performance, I would be getting back in a ever so slightly better and quieter ride and longevity. Haven't made my decision final yet, but I am leaning towards the RE's for sure.

[tireswap]

the ztoyo T1s weighs in at 21lbs

[crossbow]

I actually think the toyo's are quieter then the mich's...but I hate the mich's so I'm heavily biased.

I also don't see road noise as an issue...is there some large group of people who drive around with all the windows up and the radio off???

I always have my radio up at least on 8, and the windows down...the only time the toyo's make any sort of noise is when their communicating grip to you.

Also remember that Tire Weight is MORE IMPORTANT then wheel weight in regards to unsprung mass.

Since the tire is on the outside of the wheel...physics.

[Blue Mazda]

I am not sure. But I know there were more than a few folks over on 1010tires and epinions.com who described the Toyos as having "great grip but noisy". I also hate the stock Michelins and it is hard for me to immagine a worse more noisy tire. I am also aware that the weight of the 750's is 24lbs and the Toyos are 21lbs. The guy at tirerack scolded me for being so worried about tire weight until I told him that I want something that is at least similar in weight to the stock tires if not lighter. Both of these tires meet that criteria.

[crossbow]

Ha I am completely worried about the weight from now on. After seeing the utterly MASSIVE difference it made on my car, I will always try to shave weight off my tires. Hell I am even looking at the lightweight lug nuts :).

Think about...lets say dropping 4 lbs off the tires makes a 5% difference in steering feel. (These are all made up #'s).

5% isn't much right? How often is your hand touching the steering wheel? :wink:

[Blue Mazda]

I know what you are saying, but I am looking to upgrade performance without risking compromise to the noise and ride quality that this car has. My hands are always on the steering wheel, but my butt is also always in the seat, and my ears are also in the car listening to the noise or no noise. The stiffer side walls and stickier tread on either of these tires will make this car feel worlds better than it does with the Michelins on it. I spoke to Mitch on the other board who has the 750's on his car and he says that they are quiet and don't compromise the ride at all. He has done 9000 miles on them as well and shows no wear. Wear is my additional concern with the Toyos. I drive 20k+ per year. At $150+ per tire, I don't want to be buying them every year. I hear great things about the Bridgestones and the way they wear and age. Consumer reports did a test on the Bridgestone's with that 2nd tread and found they actually got BETTER in the wet with age because of this. Obvioulsy they like any tire will still hit a point where performance declines. I also have heard complaints that the Toyos wear out fast and get louder with age. I know, I know, not going for the best all out performance is blastphamy!

[ashu]

150+? Have you seen the current prices at TireSwap (http://www.tireswap.com)?

Also - here's the page with ALL positive and glowing reviews of the T1-S (http://www.carreview.com/Tires/Toyo/PRD_1008_1577crx.aspx). Its the highest rated performance tire, and I don't think any of the reviews is even mediocre - leave alone bad!

[crowan]

Stretch was raving on the club site about the virtues of smaller tires. Would Blue be getting any perceptible advantages of lowered gearing on his 17 stock wheels by going to 225-45 from 215-50 or do you have to get more radical?

[ashu]

215/50 is stock. The kind of benefit stretch was raving about may be observed with 215/45 or 215/40 or 205/45 - but the decreased tire width is a detriment.

225/40 would be a nice extreme mod too.

For the amount of eror that creeps in (and a handle on the % benefit in gearing) check
http://www.miata.net/garage/tirecalc.html

[tireswap]

any high performance summer tire is going to make more noise than you have now...

I really do not believe in those "reviews" on sites like TireRack or 1010tires... its all opinionated and most of it is not factual... for example... maybe the person saying they were noisy went from H-rated all-season Continental tires to the Toyos? Of course they are going to make a whole lot more noise...

but would the same comment be true if say the person went from Falken Azenis Sports to the T1S? I doubt it.

Same goes for ride quality etc,... lets say someone gets new wheels/tires that are 1" larger... is it reliable for the person to comment on harsher ride quality?

That's why I take those surveys lightly... too many variables to look at.

Think of it like this... your high performance air filter or exhaust makes more noise than stock right? :D

[crowan]

Ashu:
Neat calculator you pointed to. Tried it 215-50-17 vs 225-45-17. Told me my speedo wd. be 1.9% too fast--no big deal--but I'm too ignorant to translate that into possible effects on gearing.

Would the effect be:
1-Nonexistent, or so negligible as to be not perceptible?
2-Moderate and perceptible?
3-Great? (Surely not)
Wd. you or anyone else who's got a response to my question please PM me? I may be hijacking poor BlueMazda's thread...

[ashu]

Answer: 1.

The diameter will tell you what to expect. If diameter is reduced with your change in sizing, each spin of the driveshaft will lead to lesser distance covered on the ground (same number of spins of a 'smaller' whel-tire as before). If thi is substantially smaller, you would notice it, but I doubt anything under 6-7% is really noticeable.

Stretch is playing with 8 or more % (smaller) tires. He loves it.

[Blue Mazda]

Also as Stretch pointed out, the 1.9% difference does not take into account sag. The stock Michelins would have more sag than a 225/45 performance tire, so the real world difference is not actually 1.9%.