I need tires, need some good options

Discussion in 'Tires and Wheels' started by Jean20057, Apr 29, 2018.

  1. Gabe

    Gabe Whippled Coyote

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    Lol, I know you weren't trying to come off as a wise ass Rocky ... I thought you might get a kick out of seeing the timeline of events for me though ;)
     
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  2. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    I'm always interested in seeing you're timeline of events, Gabe. Also thanks for understanding about not trying to come off as a wiseass as well, as that just isn't within my personality unless someone like the person who used to be on the other site forum thinks they're fucking "GOD" :laughlots:Anyway just to recap once again, would you still recommend going ahead with purchasing the Firehawk Indy 500's in 275/40/18 or would they end up getting bald from running a Saleen blower with 4:10 gear ratio?
     
  3. Gabe

    Gabe Whippled Coyote

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    Yeah that guy is nuts.

    How well are the current tires putting down the power?
    (the 20" Nittos)
     
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  4. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    That guy was definitely a real nut job to say the very least lol. Anyway, after 2 years with the current Nitto 275/35/20's, they handle the power just fine and appear to still be in like new condition, however, I don't track my car, to begin with anyhow. My Mustang is mostly a touring and show car, but do drive it under spirited conditions when on the interstate, around the twisties, and on some back roads. Just for info sake, Gabe, the Nitto 20's are 27.56" in overall diameter.
     
    Last edited: May 13, 2018
  5. Gabe

    Gabe Whippled Coyote

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    Well, if the 275 Nittos handle the power ok then the 275 Firestones should certainly be similar, if not better. If the tire compound was identical and both tires were mounted on same-width wheels, I would think the 275/40/18 tire should handle the same power better than the 275/35/20, if anything just because of the slightly taller sidewall that might allow a little more flex.

    Now. The 275/40/18 is shorter than the 275/35/20 which effectively makes the 4:10 rear axle ratio a 4.24:1 and that may make it seem like the 18's are not handling the power as well.
    That'd be about the only reason I'd say you should look into staying with a size that's closer to the same height as the 20's you have now.

    https://tiresize.com/gear-ratio-calculator/
     
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  6. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    So although the 275/40/18 has a slightly taller sidewall over the 275/35/20, the 275/40/18 also has a shorter overall diameter of 26.7" compared to the 275/35/20 of 27.6" diameter. Therefore if this would cause the 275/40/18's to not handle the power quite as well? Then it would seem as though I should consider going with the 285/40/18 at 27" in diameter just as I originally intended which would be closer to nearly the same height as the 20's that I'm currently still running over the 275/40/18 :shrug:
     
  7. Pentalab

    Pentalab forum member

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    The roush cars all came with 275-40-18's... on 18 x 10" rims ( 45 mm et). They also came with 275's on 20 x 10" rims. Square setup. Worked good, except when it came to high hp. The folks with the 2010 Roush 540 H cars typ dyno'ed 518-525 rwhp, right outa the box. No traction in 1st, 2nd, 3rd gears. Didn't get traction till 4th gear ( 1:1 ratio)...spinfest. That's starting from a greenlight, street use. Although they came with the roush UCA setup, and stiffer front / rear suspension, sway bars, monotube strut/shocks, it's still not enough. Forget what kind of rubber roush used.

    I measured my 275-40-18 Nitto NT-555's and the tread is exactly 9.75" wide (18 x 10 rim). My 285-40-18 Nitto NT-555's tread measures 10.0" wide. My MPSS in 305-35-19 measure 10.75" of tread width. (19 x 10 rim). So far, the wider tread = more traction. One spring, for whatever silly reason, I had 36 psi (early evening) in the rear 275-40-18's.... no traction.

    Dropped it down to 32 psi, all was well. I notice a big difference between cold pressures at 5:30 AM..and 4 PM. Also noticed a big difference if car was parked E-W,
    and pass side is facing south. Pass side (sitting in the sun) pressures were higher than driver's side. I think 28-30 psi cold, in summer time may be optimum, since it will rise a bunch during the day.
     
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  8. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    However, here's my concern, my car has 4:10 gear ratio whereas the Roush cars still have the stock 3:55 gears. With 4:10 gear ratio plus a blower, going down from a 275/35/20 which has 27.6" in overall diameter compared to 26.7" diameter for 275/40/18" the 275/40/18's may not have enough overall height to handle down the power from the blower and 4:10 gears. So I'm thinking that it may be in my best interests to go with 285/40/18" which are 27" in diameter and closer in height with my current 275/35/20's at 27.6" overall diameter or plan B, take out the 4:10 gears and reinstall my stock 3:55 gears and then go ahead with getting the 275/40/18's, as you don't really need a 4:10 gear ratio when running a forced induction application, to begin with anyhow:shrug:
     
  9. travelers

    travelers Senior Member

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    Option C you might want to consider a split in the gear ratio with 3.73s.
     
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  10. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    I've also considered 3:73s as a strong possibility and option as well :waytogo:
     
  11. Pentalab

    Pentalab forum member

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    IMO, a 3.73 (with a manual) would be optimum. The 4:10 would be ok for hardcore strip use... in some applications. A 4:10 would = 120 mph top speed if you had a 6 krpm rev limit..... and 140 mph with a 7 krpm rev limit. ( 27" tires).

    I use the oem 3.31 on my 2010. At 6 krpm that = 150 mph in 4th gear (1:1 ratio) + 27" tires. I have the rev limit set to 6250. But I have an automatic..and the lower gears are different than the 05-10 manual. My 2nd gear is 14% lower than 2nd in the manual. My 3rd gear is 16.5% lower than 3rd gear in the manual. You would require a 3.73 rear gear in the manual to equal my lower 3rd gear + 3.31 rear gear. You would require a 3.90 rear gear in the manual to equal my lower 3rd gear + 3.31 rear gear. That's why I left the oem 3.31 rear gear as is. Where I lose it is in 4th gear, where both the manual + automatic are both 1:1
    It's the best compromise I could come up with..at least for street use. For strip use, a 3.73 rear gear would be optimum.
     
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  12. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    For hardcore strip use, I totally agree with running 4:10 gears. However, as I mentioned earlier in the thread, my car is used only for the street and driven under spirited conditions when on the interstate, for around the twisties and on some back roads and local highways posted above 45-50 MPH. When on local town roads, I very rarely ever get on it hard. So for my particular application purposes, I'm thinking that either 3:73's or going back to my stock 3:55 gears would be considered as optimal for a 5 spd manual with a Saleen blower :shrug:
     
    Last edited: May 16, 2018

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