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Discussion Starter #1
I’m due for a new set of tires, excuse my noobness but a few questions. As of right now the tires are 255/40/19. I’m allowed to get something like 265’s right, even if those aren’t standard. Would it cause any complications? Another question I have is, more tire more grip right, no downsides? This means more grip in snow and wet weather also I assume? Last question is, for example, what is the “19x8.5” measurement I see when looking for rims? Thanks a lot, trying to get knowledge on these things slowly lol.
 

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Last question is, for example, what is the “19x8.5” measurement I see when looking for rims? Thanks a lot, trying to get knowledge on these things slowly lol.
The 19 is the diameter of the wheel, and the 8.5 is the width of the wheel in inches.

The main difference between a 255/40 and 265/40 is your overall diameter of the wheel and tyre combination will be greater.
Since you are keeping the aspect ratio the same.
i.e. 40% of 255 = 102mm tyre height versus 40% of 265 = 106mm tyre height.
So the diameter increases 2 x 4mm or 8mm overall.

As for handling performance, you would hardly notice a difference though.
 

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Tire sizing is a huge subject, and you've asked a few great questions regarding tire size that don't often get answered in one place.

Tires are measured using metric units combined with wheel diameter and width. As said above, 19" is the wheel diameter while 8.5" is the wheel width. Tire tread width is the primary number you're looking at, 265 vs. 255, and go up in 10mm increments. the second number 40 is a percentage of the tire's tread width, as @Go Further said above. If you go too wide and want to maintain the same overall diameter of the wheel/tire combination you may end up going down by 5% in the sidewall. I went from 245/40R19 to 285/35R19 on my car. If you hit the Tire Size Calculator that @johnnybee provided you'll find that those are the same overall diameter. You want to be careful about not oversizing too much because it does throw off the speedometer. Some tuning devices will allow you to change tire size to compensate.

Back in the day (or with off-road trucks today) when everyone had 14" or 15" wheels, you could pretty much go wider with your tires on a whim. The sidewalls were 60 or 70, so there was plenty there to allow for wide tires to go on skinnier wheels. The smaller your sidewalls are the more careful you have to be in making sure your wheel is wide enough to handle it. When I went up to 285 width, I also went from a 9" wide wheel to a 9.5" wide one. But! Not all tires with the same measurement are the same size! This is something I learned the hard way. There are a few manufacturers that kind of cheat a little and either make them thinner or wider in the sidewall area than just the tread width. On my car I have an Ohtsu tire in 285/35R19 on the front. It fits perfectly on the 9.5" wide wheels. On the back I have a 285/35R19 Nitto tire. It would be too wide for the front. It looks like I'm running staggered tires when in reality they're the same size, because Nitto decided to make their 285 tires just a little bit wider than the competition. It's more like a 295 tire. When choosing tires be mindful of this and lookat the data sheets for the tires themselves. The manufacturers will make a recommendation on what wheel width to use with each size they sell. No tire shop will mount a 285 tire on that 8.5 inch wheel, and it usually takes some talking to get them to put them on a 9" wheel.

You can go up (or down) by a size, in general without issue, but in general size alone won't aid in performance. There's a lot more to that. But...

If you live in a place where snow is an issue, you do NOT want to go with a wider all season tire. Stick with the stock size. In snow a tire needs to cut through the snow down to a layer that will get you some traction. A wider tire acts much like a snowshoe and tends to ride more on top of the snow than a narrower tire. This is why tirerack.com will recommend going with a narrower wheel and tire setup for dedicated snow tires than you would run in the summer. Wider tires also have a tendency to follow grooves in the road more than narrower tires. This really only comes into play with bridges and construction, but can be an issue.

Then there's summer traction...

As an autocrosser, I end up reading a LOT about tires. Tires are the main consumable item in any racing application and grip is the one thing everyone talks about. If you want the best grip, you go with a softer tire. The problems with that are that softer tires wear faster and are more expensive than "harder" tires. For this you have to look at the UTQG treadwear rating of a tire. a lot of people will recommend the Michelin Pilot Sport Cup 2 tires for Mustangs and with good reason. It's what comes on the GT350 and GT500. They're expensive and have a treadwear rating of 180. A more normal summer tire will have a treadwear in the range of 200-400. My autocross/track tires are rated at 200, and I go through a set every other year, or roughly 500-1000 miles. Yes, that little milage. Extreme cornering and track speeds wear tires out fast.

Of curse all of this is much more than I think you expected, and may bring up even more questions.
 

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Discussion Starter #5
Tire sizing is a huge subject, and you've asked a few great questions regarding tire size that don't often get answered in one place.

Tires are measured using metric units combined with wheel diameter and width. As said above, 19" is the wheel diameter while 8.5" is the wheel width. Tire tread width is the primary number you're looking at, 265 vs. 255, and go up in 10mm increments. the second number 40 is a percentage of the tire's tread width, as @Go Further said above. If you go too wide and want to maintain the same overall diameter of the wheel/tire combination you may end up going down by 5% in the sidewall. I went from 245/40R19 to 285/35R19 on my car. If you hit the Tire Size Calculator that @johnnybee provided you'll find that those are the same overall diameter. You want to be careful about not oversizing too much because it does throw off the speedometer. Some tuning devices will allow you to change tire size to compensate.

Back in the day (or with off-road trucks today) when everyone had 14" or 15" wheels, you could pretty much go wider with your tires on a whim. The sidewalls were 60 or 70, so there was plenty there to allow for wide tires to go on skinnier wheels. The smaller your sidewalls are the more careful you have to be in making sure your wheel is wide enough to handle it. When I went up to 285 width, I also went from a 9" wide wheel to a 9.5" wide one. But! Not all tires with the same measurement are the same size! This is something I learned the hard way. There are a few manufacturers that kind of cheat a little and either make them thinner or wider in the sidewall area than just the tread width. On my car I have an Ohtsu tire in 285/35R19 on the front. It fits perfectly on the 9.5" wide wheels. On the back I have a 285/35R19 Nitto tire. It would be too wide for the front. It looks like I'm running staggered tires when in reality they're the same size, because Nitto decided to make their 285 tires just a little bit wider than the competition. It's more like a 295 tire. When choosing tires be mindful of this and lookat the data sheets for the tires themselves. The manufacturers will make a recommendation on what wheel width to use with each size they sell. No tire shop will mount a 285 tire on that 8.5 inch wheel, and it usually takes some talking to get them to put them on a 9" wheel.

You can go up (or down) by a size, in general without issue, but in general size alone won't aid in performance. There's a lot more to that. But...

If you live in a place where snow is an issue, you do NOT want to go with a wider all season tire. Stick with the stock size. In snow a tire needs to cut through the snow down to a layer that will get you some traction. A wider tire acts much like a snowshoe and tends to ride more on top of the snow than a narrower tire. This is why tirerack.com will recommend going with a narrower wheel and tire setup for dedicated snow tires than you would run in the summer. Wider tires also have a tendency to follow grooves in the road more than narrower tires. This really only comes into play with bridges and construction, but can be an issue.

Then there's summer traction...

As an autocrosser, I end up reading a LOT about tires. Tires are the main consumable item in any racing application and grip is the one thing everyone talks about. If you want the best grip, you go with a softer tire. The problems with that are that softer tires wear faster and are more expensive than "harder" tires. For this you have to look at the UTQG treadwear rating of a tire. a lot of people will recommend the Michelin Pilot Sport Cup 2 tires for Mustangs and with good reason. It's what comes on the GT350 and GT500. They're expensive and have a treadwear rating of 180. A more normal summer tire will have a treadwear in the range of 200-400. My autocross/track tires are rated at 200, and I go through a set every other year, or roughly 500-1000 miles. Yes, that little milage. Extreme cornering and track speeds wear tires out fast.

Of curse all of this is much more than I think you expected, and may bring up even more questions.
This has been the single most useful post on tires I’ve ever read. Tons of great info. Thanks a lot. I’ll be sure to reply if any other questions come up, but as if right now, you got them all answered!
 

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Im running 265/35/19's in the front and 285/35/19's on the rear. Have the factory 19x9 PP wheels and have had no issues.
 

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Discussion Starter #8
This has been the single most useful post on tires I’ve ever read. Tons of great info. Thanks a lot. I’ll be sure to reply if any other questions come up, but as if right now, you got them all answered!
Now that I got a good understanding of regular tires. Another question I had is, are 2 winter tires better than all 4 all-season tires in the snow? I've had my car just for one winter but didn't take it out in fear of an accident. Luckily I had an older car that was FWD for the time being.
 

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Now that I got a good understanding of regular tires. Another question I had is, are 2 winter tires better than all 4 all-season tires in the snow? I've had my car just for one winter but didn't take it out in fear of an accident. Luckily I had an older car that was FWD for the time being.
No.

I no longer live somewhere that winter tires are needed, but I grew up in Indiana so I have a lot of experience diving on snow/ice. If you're going to get snow tires get 4 of them. This applies no matter what car you're driving.

Say you only get two snow tires for your mustang. Do you put them up front or in the back? Most folks would say in the back, so you can get traction to move. Fine, but now you can't stop or turn. So you put them up front, to be able to stop and turn, but now you just sit still with the back end spinning.

So, while I drive on summer tires all year round, because Texas y'all, if I lived somewhere with snow I'd have three sets of wheels: the summer set, the winter set, and the track set. Or park the mustang in the winter and get a 15 year old Honda to drive in teh snow. I just feel like life is too short to drive boring FWD cars.
 

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Discussion Starter #10
Lmfao amen. I know this may seem redundant so let me rephrase. With all seasons I wouldn't get any of the stoping turning or moving power right?, I would think if I had two winter tires it would be able to at least get some work done lol, compared to not being able to do anything. Now I have never seen anyone ask this upcoming question probably because it's dumb so hear me out 😅. But, what if, you do one in the back and one in the front.
Thanks a lot, been a big help.
 

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OK...

Go stand on a sheet of ice this winter. On your right foot wear a golf shoe with metal cleats. On the left wear a leather soled dress shoe. Now try to walk...

and hey, no question is really dumb if asked honestly. And I'm at work and bored all night so have nothing better to do...
 

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FWIW,
A few years ago Bridgestone had a commercial where they had adult size tricycles, one with all season tires the other with Blizzack winter tires.

They had people try riding them on a hockey rink. The ones with all seasons spun the tire with very little effort on the pedals and would spin out when turning. The ones with Blizzacks would accelerate from a stop and would even allow the rider to get up off the seat to put more force on the pedals. They would track through corners without spinning out.

Quite sure Bridgestone used an all season that would make the Blizzack look as good as possible but the difference between an all season tire and a winter tire in slippery conditions is truly amazing.

The TV show Every Day Driver took a Mazda Miata with winter tires and a Nissan Rogue AWD with all season tires. They put them through a bunch of winter driving conditions. The Nissan did better getting away from a stop but the Mazda did better in turning and stopping. There conclusions were; they were surprised how well the all seasons worked but there is no reason to park your fun to drive rear wheel drive car in the winter if you put winter tires on it.



Dave
 

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I do drive mine year round and can vouch for the winter tire route. Mine are mounted on the standard Ecoboost 17” rim, 235/55-17 Nokian R3. When it has snowed or is slick, I use the wet/snow driving mode and using even moderate throttle inputs she just picks up and goes, no drama. Bear in mind that at colder temps you get better dry traction out of a winter tire as well, they are not just for the sloppy stuff. If you are on a budget, I understand that the very late Crown Victoria 17” steel rim works on our cars. Just not very attractive. Note the 17” rim will not fit PP brakes.
 

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The same issue exists putting a low profile tire on to narrow a wheel as putting a low profile tire on to wide a wheel. There is not enough side wall that can flex and conform to the wheels bead and you run the danger of it coming loose resulting in a rapid loss of air. Most experts will say you get better traction with a narrower tire on a properly sized rim than a wider tire on to narrow a rim.

If you were to scan a web site like Tire Rack and look at tire specs you will find that the minimum rim width increases as the aspect ratio goes down.

My truck has 255/70-15 tires mounted on a 7" wide rim. The rim width range is 6.5 to 8.5" and has an overall diameter of 29.1".

My Barracuda has 255/60-15 tires on the rear mounted to an 8" wide rim. The rim width range is 7 to 9" and they have an overall diameter of 27.1".

My Ecoboost Mustang has 255/40-19 tires mounted to a 9" wide rim. The rim width range is 8.5 to 10" and has an overall diameter of 27.2".

FWIW, my son is the manager of an independent tire and service center he will not mount a tire to a rim if it is to wide or narrow for the rim width as recommended by the tire manufactuer.

Dave
 
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