245 vs 255 tires?

Discussion in 'SN95 4.6L Mustang Tech' started by sandiegostang, Aug 9, 2011.

  1. I convinced my friend to get nitto 555 tires. I didnt know what size would be best for him though. His wheels are 17x8 so i believe 245 45 17 are standard, but would 255 40 17 be a big upgrade. I am sure they would fit the rim, but is there a big difference in traction?
  2. I've got 275's on my stock 17x8 wheels with no problems. Go big or go home.
  3. Not a huge difference in traction w/ a wider tire on those 8" rims. Biggest difference is from the stickiness of the compound. If you are looking for "good bang for buck" (not changing out your rims) I would buy nitto 555's in size 245 45 17's for all the way around for the stock rims.
  4. I've never been impressed by wide tires. They certainly add rotating mass, and width has a very minor difference in traction. The end result is quite possibly slower down the quarter than a narrower (lighter) tire. I've gotten my 245-45-17 nitto 555Rs to low 1.7's in the 60'. I think they could go faster if I could put more power to the ground. They didn't spin or complain at all.
  5. I have 275's on the rear now on stock wheels. Had 255's too at one time.
  6. +1.

    275's FO SHO!!!! :rock::rock::rock:
  7. 255/40/17 on the front and 275/40/17 on the back.
  8. I have 255/45/17s on my stock Bullitts. I can tell they slowed me down slightly because they are heavier, and the fact they are slightly taller than stock makes my 373s a little less effective.
    They look great though, and fill up the wheel wells better than 245s.
  9. you want the long explanation or the short one.
    short one - wider is better.
    let me know if you want the long one.
  10. Let's hear the long one
  11. 275's are fine on an 8 inch wheel in the back. For standard radials, just know that you will sacrafice some life of the tires, and they will not perform as well since you are squeezing a bigger tire on to a smaller wheel(unless the brand runs narrow, like nitto drs). I've run tens of thousands of miles with 275/40's out back on 8 inch wheels in mustangs, with many different brands. They definetly look cool. I've got a sweet go pro video of a 600rwhp Vette dynoed today, with my go pro camera facing down on top of the tire from 70-140mph on the dyno. The tire litterly goes out of site on CCW wheels at the top of the pull.

    I have realized that tires are on the car for one reason. And that is to perform. For me, it is the lightest wheel/tire combo with the best grip in a strait line for the street, and switching out an extra set of stock rims for 600+mile road trips or if the weather forcast is bad, or it I get called out to a local road course. I still run the same size you are talking about on the street, 275/40-17, but in a drag radial and will be approaching 900-950hp at the crank very soon. Where you live, you and your friend have little to worry about for all season tires.

    Also note that the 255/40 will have a smaller sidewall than a 245/45. While you gain width, the sidewall is almost 3/4 of an inch smaller. A good front tire option, but a very poor rear tire option.
  12. That last part is very good to know. Here in San Diego i never have to worry about the weather. My friend wants a good softer tire that can still drive in the rain for the 5 days out of the year it does rain here. He does not want a radial because his car isnt making enough power to necessitate it. He wants the 555 extremes, and i think he is just going to stick to the 245 instead of the 255 or 275 because of cost. $127 for 245 VS $160 for 275. Not a huge difference in price, but again his car doesnt make enough power that he needs a lot more than the 245 Nittos will provide. Thanks for the info guys.
  13. The long one – you asked for it.
    A wider tire is better but the law of diminishing returns applies as in most things. Surface area greatly increases the traction – Take a large eraser and stand it up on the narrow end on a table and press down firmly as you slide it on the table – now lay it flat for maximum contact and apply the same down force as you slide it on the table. It is much harder to slide with greater contact. In cornering, an item with a wider base is harder to tip over than a narrower base. Point one.
    Point two. The tire you have on any one corner of the car does not have a fixed weight assigned to it. To illustrate this you would need to have a basic understanding of the “circle of traction”. If you plot the cars center of gravity at rest then you must take into consideration that the point moves under outside forces – accelerating, braking and steering. The total vehicle weight stays constant but the location of that weight shifts from wheel to wheel. For example, if you make a panic stop, a portion of the weight from the back of the car transfers to the front wheels and increases traction there while decreasing traction in the rear. This is good because the more traction you have in the front during braking, the faster you can stop – you want the nose to dive. This is true for turning as the weight transfers to the outside wheels to assist the turn and accelerating as the weight from up front transfers to the back and aids in traction for launching. This does not mean that the weight transfer is equal from one set to another – a panic maneuver of hard turning and braking at the same time puts a far greater load on the front outside tire than any other. That considered, you must then factor in the contact patch of your tire which is relatively small compared to the overall surface area of your tire when properly inflated. In a drag car like mine, one of the reasons you drop the air pressure in the rear tires is to increase contact area which increases traction for launch. The skinnys up front are okay for this application because they share the braking load (drag cars stop in a straight line, hopefully!) and are not required to make hard turns – this is far less than adequate for a panic maneuver as I mentioned previously because the small contact area will not be able to handle the additional traction required and a skid or tire failure will result . Dropping your air pressure may increase traction but it also increases rolling resistance and tire wear so it is not good for street or road course. The only other ways to increase the tire’s load capacity and traction is to change the tire size and/or compound it is constructed out of and the rigidity of the sidewall. The primary limiting factor of your tire width is what will fit without rubbing. While rotating mass is a concern, you can upgrade your brakes and in combination with your added surface contact patch you will significantly improve your stopping power – no change is needed to adjust your cornering weight increase and as for top speed and accelerating, you will usually notice relatively little decrease in acceleration because increased traction counters the increased weight and will net similar trap speeds (initial educated change) but this would require the variable of HP output to determine for your specific car. Note that in drag racing the front tires are skinnier because of the reduction in rotating mass, and friction – but these are not used for cornering! The higher the output the more the car is capable of using the larger tires and the faster the top end speed.
    I can continue with the explanation but if you understand the information so far you can determine that overall the widest tire for the application is usually the best for typical whoa, go and turn of your pony.
    Let me know if you do not understand any information or if you want additional information.
  14. I asked for the long one, not the really long one. :D

    great info though. Thanks
  15. You kidding? That is the abridged long version!