Want to use 305/40/18 rear, help me choose the front.

Discussion in 'Tires and Wheels' started by BlackGT450, Apr 8, 2021.

  1. BlackGT450

    BlackGT450 Junior Member

    11
    1
    Hello!

    I am about to add a Department of Boost GT450 supercharger on to my 2006 Mustang GT this year, just waiting for group buy to come in. That being said it is time for the stock rims and tires to go. This car is rarely driven it will be a weekend warrior, it will be street and track use, dry conditions only. I am considering AMR staggered 18x9 and 18x10 rims. I want to use Nitto NT555R drag radials in 305/40/18 in the rear for maximum straight line performance. I do not do much hard cornering. When I was talking with DOB about my setup they suggested a 255 or 275 in the front. I found a Nitto NT555 G2 in 255/45/18 but using a tire size calculator puts this tire at 27" tall and the rear at 27.6" tall and the OEM is 27.3". I know going off from the OEM will make the speedo a little off but what about the staggered difference in the front and rear? Is this a concern? Is there something closer I should look at?
     
  2. Pentalab

    Pentalab forum member

    3,981
    597
    I use a MPSS 305-35-19 for the rear...and a Nitto -555 in a 285-40-18 for the fronts. Standing back away, you can not tell the difference in the 19" diam vs 18" front rims.

    The..'staggered look' is a bit of a joke really. Unless I'm crouched way down low, or laying on my stomach, I can't even see the width of the front tires. I previously tried a 255-45-18 front on a 18 x 9 rim, and that worked pretty good ( stretched 1/2") . Then tried a 275-40-18 on the same 18 x 9 front rim...and that was a disaster ( 1/2" under the measuring width). Handling was unresponsive...and rubbery, fubar. Then tried the same 275-40-18 front, but on a 18 x 10 front rim..and this worked superb ( stretched by 1/2"). Currently I'm using a 285-40-18 on a 18 x 10 rim..and this works good.

    The 275 + 285 fronts ( on a 10" rim) work a lot better for handling vs the 255 fronts. The 'staggered look' is just a myth.

    The 305 rears really need to be on a 11" wide rim to be effective. My 305 rears are on 19 x 10 rims..and have no more rubber on the road vs the previous 285-40-18 rears ( on 18 x 10 rims).

    IF I had to do this again from scratch I would use 285-40-18's on 18 x 10 rims...on ALL 4 x corners. Then at least u can rotate front to back. My nitto's can't be rotated side to side.... but my MPSS rears can be rotated side to side.
     
    BlackGT450 likes this.
  3. stkjock

    stkjock ---- Madmin ---- Staff Member Administrator Super Moderator S197 Team Member

    39,273
    2,133
    the stagger is not an issue

    I run a 255/40/18 and a 325/40/18 F/R it's all good
     
    BlackGT450 likes this.
  4. BlackGT450

    BlackGT450 Junior Member

    11
    1
    The rims are both 18" I was speaking more of the difference in the complete diameter of the rim and tire together.

    Is there another good 11" wide rim in the price range of the AMRs?

    Nice.. what rims are you using for 325 tires?

    These are the rims I was looking at.

    https://www.americanmuscle.com/charcoal-amr-18in-stag-kit-0514.html
     
  5. stkjock

    stkjock ---- Madmin ---- Staff Member Administrator Super Moderator S197 Team Member

    39,273
    2,133
    BlackGT450 likes this.
  6. BlackGT450

    BlackGT450 Junior Member

    11
    1
    Nice GT500! Thanks for the response.

    How the heck does a 325mm tire even fit on a skinny 10" wide rim ?

    My issue with gross amounts of stagger is...(IE: 325 rear / 255 front) the car will want to under steer. And the only way to fix that effect is to use less rear sway bar diam ( or less rear bar on an adjustable rear sway bar). IE: u loosen the back end up a bit, to minimize the under steer. Then it's more like 4 wheel drift on corners. Loose up the back end too much, and it will oversteer. The real fix for under steer is to use wider front tires. I'm talking about street cars, or auto X or road course applications
     
    Last edited by a moderator: Apr 8, 2021
  7. Pentalab

    Pentalab forum member

    3,981
    597
    A 255-45-18 has a diameter as follows. EACH sidewall height is 255 X .45 = 114.75 mm. You have TWO sidewalls (top and bottom of tire). 114.75 X 2 = 229.5 mm. 229.5 mm / 25.4 = 9.0354" . (25.4 mm = 1" ).
    9.0354"( both sidewalls) + 18" diam rim = 27.0354" diameter.

    Same calcs, but for a 305-40-18 = 27.60" diameter.

    27.0354 / 27.60 = .9795 ( 2.05% difference in diameters). I THINK any difference < 3%, will NOT affect the ABS braking. IMO, I would not worry about the 2.05% difference in front/rear diameters.
     
    BlackGT450 likes this.
  8. stkjock

    stkjock ---- Madmin ---- Staff Member Administrator Super Moderator S197 Team Member

    39,273
    2,133
    The M&H runs a bit narrow and the higher aspect ratio allows a narrower rim
     
    BlackGT450 likes this.
  9. Norm Peterson

    Norm Peterson corner barstool sitter

    Age:
    73
    3,455
    245
    And your car's ABS tolerates about a 1.5" difference in diameter???

    Wouldn't that at least make the car apt to put the ABS activity on the front wheels rather than on the rears in a hard stop?


    Norm

    Even M&H recommends 12" wide wheels for that size. I can see going with 11" but I wouldn't even dream of running that much tire on 10" wide wheels anywhere but at the drag strip. Even there, I'd be a bit uneasy about lateral stability at the big end.


    Norm

    ABS will generally tolerate a 3% difference in tire revs/mile (about the same thing as 3% diameter difference). Some systems may permit more, but I've never personally run tires that were staggered enough to challenge that.

    305/xx is as wide of a tire as I'd ever suggest to anybody for putting on 10" wide wheels if there were any plans to drive it on the street.

    255/45 is the best answer for your front tire question. 275/40 is shorter and just barely acceptable for 9" wide wheels, and 285 is too wide for 9" wide wheels.


    Norm
     
    Last edited by a moderator: Apr 8, 2021
    BlackGT450 likes this.
  10. stkjock

    stkjock ---- Madmin ---- Staff Member Administrator Super Moderator S197 Team Member

    39,273
    2,133
    running them for 9 years or so and never had an issue.

    I know the website says 12" - however, that usually is a measuring size, not recommended or allowable by spec

    I spoke to M&H before I bought them and was told a 10" wheel was ok and many racers use that size on a 10"
     
    BlackGT450 likes this.
  11. BlackGT450

    BlackGT450 Junior Member

    11
    1
    Lots of great info here guys! Thanks for the input. I ended up ordering the AMR 18x9 18x10 staggered with 255-45-18 in the front and 305-40-18 in the rear. ~$1600 for everything seems like a good price and should meet my needs.

    I will be seeing all of you around here more I am sure now that I have finally started this project! This car has literally been sitting here doing almost nothing for the 7 years I've had it. It only has 52k miles and is in beautiful shape.
     
  12. Rugermack

    Rugermack Junior Member

    33
    6
    Same wheels I run 18x9/18x10 AMRs
     
    BlackGT450 likes this.
  13. 07 Boss

    07 Boss Senior Member

    2,987
    341
    I've been running 305/45/18's on a 10" rim forever. IMO the sidewall height plays a role in how wide or narrow of a rim you can use. With a taller sidewall tire the bulge is muchnless prevelant and the tire rides flat. With a shorter sidewall you will get the bulge pulling the tread off the road.

    With that said, My rear tire diameter is 1.8" taller than my front tires. She handles like a pig but no issues with ABS. Traction control is pretty much always off. I run no front bar and run the stiffest rear bar that I could find. If I drive her hard she will plow into the corner and when I really go hard the push turns into what I call snap oversteer situation. It does not make for the most comfortable of situations on the street but I built her to pretty much go in a staight line.
     
  14. 07 Boss

    07 Boss Senior Member

    2,987
    341

    Actually if you want to get rid of understeer you need to stiffen the rear sway bar or soften the front. If you decrease body roll you increase understeer. The best way to fight any understeer caused from different tires front and rear is through a combination of springs, alignment and sway bars.
     
    Last edited: Apr 24, 2021
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.