F1Fan

Hi gnetster,

As usual my answer is "it depends." But to answer your question precisely sort of yes but basiclly no. The basic handling nature of a car is determined by thedistibution of mass vs. friction. The closer you can get to your ideal values the easier it is to keep the car handling the way you want it to under more dynamic conditions.

Knowing this, if you don't already knowlet me tell youthe S197GT is a front weight biased chassis. The S197GT's weight distribution is not nearly as bad as many other front engined cars likemost front and all-wheel drive carsbutnot nearly anideal weight distbution which in practiceon a road course ordrag stripfavors a slight rearward bias.

Anyway what thismeansthe S197GT's chassis already has a tendancy to understeer even if allfour corners of the chassis have equal grip. By moving the chassis' grip bias toward the rear of the chassis you are increasing the tendancy of the chassis to understeer. Sometimes the additional rear grip can be used to your advantage on the race track if the chassis is making big horse power but for most anyS197GT street application with less than around 400-450BHP equal grip front and rear is a superior configuration. This is assumming you are usingwider, lighter,high-performance wheels and tires already of course.

If you had a staggered wheel and tire setp with a moderate horsepower level say 400BHP or less the problem is that the extra wide tires out back are not really needed to put all the power to the ground. Oh sure, you say you can spin the tires easily whan launching I say get better wheels, tires and suspension and this will no longer bea problem once you learn to drive. Withthe grip balance biased toward the rear of the chassis when you make a turn you are going to have a stong tendancy to go straight or understeer when you need to turn. You can try to tuneout the understeer but all you are doingchanging the way weight is being transfered to the tires which will work at some speeds but not at others andmay have unintended consequencesunder differentconditions like slower or higher corner speed oversteer or understeer. But no matter you do to th chassisthe car's natural tendency will be to understeer given the opportunity. Like I said it's really about getting it as close to right as possible with your masses and friction and then tuning the balance for the most likely conditions the chassis will see. Altering the front and rear grip balance is just another way to sell tires and wheels, it does not improve your car's handling balance or cornering grip performance.

Of course thereare always going to bea fewcars, drivers and conditionsthe more balanced chassis is not right for. Say a dedicated drag racer or a roadracing car with higher horsepower. If you havea chassis withenough horsepower to take advantage of theadditional rear gripgains from installinglarger rear tires you may be able tooffset the less than ideal handling and cornering speed losses by the improved ability to put power to the ground around a road course. But there are very few drivers in the world who can really take advantage of this and I seriously doubt any of them are reading and posting on this board.

HTH!

F1Fan

Hi RedDot,

First let me tell you that there isno safety issue with a 255/45 on an 8.5" rim width wheel. Thar tires sizeon an 8.5" rim iswithin the recommended rim width range for that sectiontire and is the O.E. size as shipped from Ford.

As usual it depends on what you are doing with the car and the design intent of the tires you are working with. But generally speaking from a performance POV use the widest rimwidth you can for a given tire section width. This will give you the best possible steeringresponse out of a given tire and allows you to run slightly lower air pressures which can improve ride. From a ride POV use the minimum width rim that is allowed to give you the softest sidewalls and best ride with lowered impact transmission but depending on the tire design you may need to run slightly higher air pressures to keep the sidewalls from rolling over causing sidewall damage and increased punctures and higher air pressuresalso hurt ride. It is all a balancing act no?

HTH!

RedDot

Thanks F1Fan.

I'm going to switch to the Goodyear Eagle F1 All Season 255's when I need new tires then. I'm a daily driver type that prefers to be balanced right in the middle of performance and ride comfort. I've been running 33psi in my stock 235's. From your reply, I think I'll run about 35psi.with the 255's.The sticker in the door jam says 32 for the stock tires however.

Would you happen to know what the ideal pressure would be for good performance and good ride comfort? The middle road that is.

F1Fan

Hi RedDot,

Can I suggest that you look into the Yokohama Advan S4 and Michelin Pilot Sport A/S tires? These are the absolute best all season tires (really 3-season as none of the good performance tiresreally work in heavy snow or on ice), on the market in your size. The YokoS4'sare slightly better riding and much quieter but not quite as sharp steering as the Michelin Pilot Sport A/S tires. The Goodyear Eagle F1 A/S are too new and I have not driven on them yet but I hear they are very good. If it were up to meto decide on a tire for you I would buy the Yoko S4's and I think you would be really happy. They are going to cost you about $40 bucks more per set but I think they will be worth the slightly higher price. I think 35psi is a very good place to start with a 255/45 tire on 8.5" rims.

Cheers!

RedDot

Thanks for the info F1, I'll check 'em out

steelcomp

I have another suggestion for tires, the Nitto 555. They have a treadwear of 300, which, given the cost of the Michelins, is something to consider. I haven't had another tire give me better dry traction, and their recommended rim width is 8.5. I'm running them on the stock 18" Bullets, and it's really amazing how much cornering force these tires can generate. I've run them in the rain as well, but I don't push very hard when it's wet (unlike when it's dry) so I haven't found their limitations. They seem fine, though.
I have better than above average suspension under my car and love the Nittos FWIW. I may go to a 275 on the rear as traction seems limited on tighter corners, but I'm not sure yet. A rear swaybar upgrade may be in order at that point, but for now, I'm still on stock AR bars with excellent balance. When these tires wear out, I'm going to go with a whole different approach to tires and wheels, but for now, I can't get anyone to take a few specific 100+mph corners with me, including a few M's and Vette's that regurlarly run. (The only guy, funny enough, to even come close was a C55 AMG Benz...amazing car, indeed)

Sirsilent

I thought the stock 18" rims come with 255 tires, why do you have 235? I have stock 235 tires on my 17" stock rims.

Or am I wrong?

Aziraphale

Stock 18's come with 235 also.

Silos_and_Sirens

F1-Fan,

Would a 265/40 18 fit on the 8.5 rim? I am running the stock 235 in front and BFG 255/45 out back. I would like to run the 255 in front and 265 back. Is this safe, or am I asking for problems?

Thanks!

Norm Peterson

265/40's belong on wheels that are at least 9" wide. Although the difference isn't a whole lot, the "Go/No Go" line has to be drawn somewhere. FWIW, going outside the recommended width range has the potential for moving the sidewall "flex point" either above or below the region that it was designed to lie within, with a little more heat generation being a likely consequence. To which you add a little more sidewall flexing (a separate source of a bit more heat), since the narrower wheel offers somewhat less support. That's as good as I can remember a brief conversation some years ago with a tire engineer for one of the major brands regarding this topic anyway.

This is an enthusiast-oriented internet forum, and I have no idea who might view this topic, take something out of context, claim it to be an absolute truth, and either use it or pass it around elsewhere. So I can't in all good conscience override the recommendations of every tire mfr that provides this size through Tire Rack (typically my source for this sort of data). Perhaps somebody who always drives mildly, and never overloads their car or drives long distances in thesummer heatmight not have problems particularly worse than faster center tread wear. However, that description doesn't match up very well with the membership here in general or users of the specific tire size in particular, so I'm going to side with the tire mfrs and the Tire & Rim Association on this one.

Norm