99horsey

I finally need new tires and am torn between the stock size (for my 18x8.5 factory rims) or one size wider (same diameter). I know a lot of people make the jump to 255/45R18 from the stock size and I've read 1,000 threads where it's been discussed, but still can't make up my mind. Right now I'm leaning towards 235/50R18 because the tires I want (Cooper Zeon RS3-A)will cost me $90 more for the wider size and I'm worried about giving up traction and confidence in the rain. I run all season tires because I drive the car all year long in Ohio (not in the snow, but I still drive in the cold). My current tires (BFG KWDS 235/50R18) already suck in the rain and I don't want to take a step down due to wider tires. I know the wider tires will be better on dry, warm roads, but I'm already up to (or past) the speed limit before I know it on dry roads as it is and I don't really push it in the bends to be concerned with the stock tires. What I really hate is not being able to get around a soccer mom in her minivan on a wet road because I sit there spinning through the first 4 gears...

For that reason (more than to save $90), I'm leaning towards the narrower tires. Am I crazy?

UrS4

No, but I'm not following your logic about a narrower tire having more grip in the rain?!? If the tire is designed to handle wet weather, such as an all season or ultimate summer rather than a dry summer tire like a max performance or extreme performance summer tire (based on tire rack's categories), then a bigger contact patch allows for more grip and is better than a narrower tire. I would recommend a wider tire that has good rain characteristics.

99horsey

According to the experts, with all other factors remaining the same, a wider tire will be more susceptible to hydroplaning. The problem is that no one puts wider versions of the OE tires on, so they say that wet weather performance is greatly improved with new wider tires, but that's just because they're now using a better tire. I'm looking for opinions of anyone who's actually used the same tire in two different sizes and who can really compare. They say that wider tires are slightly worse in the rain, but is it even a noticeable amount, or only something that the Stig might notice on the track when near the absolute limit of grip?

Entaille

you're not looking at wide enough tires where you should be concerned with hydroplaning imo. you won't notice a difference in that regard.

Derf00

+1. Unless you are going with a 275, 295 or 315 it's a non issue. 235 vs 255, not gonna notice.

Personaly, I went with staggered sizing. OEM 235 50 18 up from and 255 45 18 in the rear for better traction. I live in AZ and went with a summer tire (Dunlop Dureza Z101) Had some great reviews on Tire Rack for DD, not so much for track but I never track it so I don't care.

The 255 looks better on the OEM wheels IMO. I have Factory polished Fanblades with the gray inlay. The 255 brings the tread more even with the wheel face and looks a little meaner than the 235.

Mighty impressed with the grip.

Derf00

What you are forgetting is that a wider tire spreads the weight of the car over a larger surface area (less pounds per inch squared) which means the car becomes more suseptible to hydroplaning (floating) versus a narrower tire where the weight is more focused into a smaller contact patch (more pounds per inch squared).

This is true in extreme cases but for 235 vs 255, not really a big issue.

99horsey

Thanks, guys. Your responses make sense. For such a small change in width, it doesn't seem like wet performance should be affected that negatively. The little bit of change in width will hopefully help more in the dry than hurt in the wet. And it will definitely look better. I know that the 235s are about as narrow a tire as one dare put on 8.5" rims. It seems like I stand more to gain than lose stepping up 20mm in width...

UrS4

Aquaplaning and wet traction are two different things and strictly speaking a wider tire may cause a slight increase in the tendency to aquaplane, however, there are many more factors that are more important and have a more significant impact on the tendency to aquaplane.

Aquaplaning occurs when there is a layer of water between the road and the contact patch (tire). The contact patch has both a length and width dimension. The contact patch that resists aquaplaning the best is a long and narrow contact patch meaning a narrow larger diameter tire. Narrower is a benefit as the mass of the car (force) is distributed over a smaller surface area which should result is the water being pushed away from the tire easier. However, there are many other factors that both affect the contact patch as well as how the water is evacuated from the tire in order to maintain the contact patch. Tire overinflation reduces the contact patch, decrease in tread depth decreases the tire's efficiency to evacuate water, tread design also affects water evacuation efficiency.

Traction either dry or wet is related to the size of the contact patch. A larger contact patch will have an increase in grip/traction as the power is distributed over a larger area. Spinning the rear tires in the wet is a result of overcoming the wet coefficient of friction, not from aquaplaning.

Lets assume that when the OP mentioned confidence in the wet, he was implying decreasing his tendency to aquaplane with his next set of tires. Additionally, his complaint of not being able to pass a soccer mom in the wet implied that he needs more wet traction with his next set of tires.

You are correct that if the tire has the same tread design and the only change is a wider contact patch, the tendency to aquaplane will be increased but the wet traction will also be increased.

Now, since the OP has the option of choosing a different tire. I would say that the increased tendency to aquaplane with a wider tire can be significantly decreased and potentially decreased below the tendency with the narrower stock tires if the tread design is optimized for wet driving, has deeper tread depth, and is properly inflated. This way going with a wider appropriate tire will give a benefit of better wet traction so he can get around the soccer mom and more confidence in the wet.

99horsey

Thanks, UrS4. Good explanation. To clarify, my concerns in the wet are both control and confidence in the bends (not that I push it in the wet at all, but my current tires make me clench a bit driving in the rain…) and getting traction for takeoff. Looking at the same tread pattern, does wider only potentially increase the chance of aquaplaning but not necessarily reduce traction for takeoff and cornering grip assuming puddles are not involved? I know we’re talking about what is probably an imperceptible difference in width here, but I’m just wondering in theory if aquaplaning is taken out of the equation if the exact same tire would grip differently on wet roads in different widths but the same diameter…

UrS4

Well there is a lot of complex math but to simplify, a 255 wide tire is 8% wider than the stock 235. The area of a circle is 3.14 x radius squared. The contact patch is not a perfect circle but in essence the area is increased by 314 mm. Remember that it is less than this as the contact patch is not a true circle as the increase in width does not change the length of the contact patch and since there are grooves in the tire, there is not 314 mm of more rubber on the road. I do not know how much this percentage wise increases your tendency to aquaplane. The increase in contact patch also increases wet traction but I don't know by what percentage. I would imagine these curves are not linear. Also remember, a wider tire ususally means the tread blocks are bigger and maybe the grooves are wider but likely not by the same proportion as the tread blocks.

I would only be speculating that the increase in wet traction is more significant than the increase in aquaplaning tendency when going from a 235 to 255.