Better ride with smaller tires?

Discussion in 'Tires and Wheels' started by davidjurss1, Jan 7, 2019.

  1. davidjurss1

    davidjurss1 Junior Member

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    So I got an 08 GT/CS back in July that came with 245/45R19 Goodyear Eagles in the front, and 275/40R19 Firestone Firehawks in the back. The ride was a little rough, but I took that as normal because the car was lowered.

    I replaced all 4 tires with 245/35R19 Nexens in front, with 275/30R19 Nexens in back so it's a matching set. Surprisingly, the ride got better. I wasn't expecting that. What would cause that? I'm not as keen on suspensions, so this got me wondering if a simple tire change could make a difference like that.
     
  2. Norm Peterson

    Norm Peterson corner barstool sitter

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    It can.

    Possible reasons include different inflation pressures (less with the new ones), different tire constructions (very likely), and your new tires being smaller possibly being less stiff vertically simply because they are smaller.

    Unfortunately, I can't find those sizes in any of the Nexen tires listed on Tirerack.com, but I'm more than a little concerned by how much smaller you chose to go with those front tires (it's a rated load @ inflation thing) based on looking up Load Index numbers by tire size.


    Norm
     
  3. Steve Waters

    Steve Waters Member

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    New tires always ride better. The old tires were probably OLD. Usually the larger the sidewall the better the ride but in your case it must of been old hard tires.
     
  4. davidjurss1

    davidjurss1 Junior Member

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    How do you mean? Front tires are a 93Y rating, and the rear are a 96Y. They're Nexen N'Fera SU1 tires front and back. Should I have gone wider up front? I went with the same width that came with the car, but didnt care much for the height so I went a little shorter.
     
    Last edited: Jan 27, 2019
  5. skwerl

    skwerl tree hugger

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    So different brand/style tires ride differently. Who'da thunk it? :headscratch:
     
  6. Norm Peterson

    Norm Peterson corner barstool sitter

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    You need bigger front tires, period. At least taller profile. 93Y is too small for an S197 Mustang if that's a Standard Load (SL) tire. Way, way too small if it's 93Y in eXtra Load (XL).

    Load index numbers by themselves don't tell the whole story; you also need to know whether it's an SL or an XL tire. SL and XL are different tables for rated load vs inflation pressure - an approximate correlation is that an XL tire needs to be four numbers higher in order to match an SL tire of some given number (i.e. 93 in XL corresponds to 89 in SL for inflation pressures below 37).

    Your 96Y rear tires are big enough if they're SL tires, but not if they're XL unless you want to run them at 4 or 5 psi more inflation than the door sticker calls for. I won't guarantee that 4 psi higher to meet rated load needs won't give you uneven tread wear (tread centers).



    I still can't find the information I'm looking for. Nexen's own site refuses to even let me enter it with the browser I use for everything, and I refuse to change things on my end just for them


    Norm
     
  7. davidjurss1

    davidjurss1 Junior Member

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    Here's the info I was able to download from their site on this specific tire. All are set at 50 psi currently.

    Starting to think I just made a very expensive mistake.

    Screenshot_20190127-095738_Adobe Acrobat.jpg
     
    Last edited: Jan 27, 2019
  8. Norm Peterson

    Norm Peterson corner barstool sitter

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    Thanks for the information.

    245/35-19 and 275/30-19 are both really small tires, and their small size actually does mean that they are "softer" in the vertical direction than proper-size tires are (OE sizes are typically 97 in SL or 101 in XL).

    275/35-19 rear with 245/40-19 would be much better from a load capacity standpoint, though even those should probably get slight inflation pressure adjustments above "door-sticker" (roughly +1 psi rear, +3 psi front)


    Norm
     
  9. davidjurss1

    davidjurss1 Junior Member

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    My main concern now is load capacity, and from I've been able to get is that, while they're small, they're still ok to drive. Eventually I guess I'll go back up to 45/40, but all the tires I had on when I bought the car were either balding or torn entirely so I needed new ones fast. Front and back, from my understanding, are above the front and rear GAWR as posted on the door jam. I'll start shopping for a new set in the next couple of months since I dont drive this car much, maybe one week out of a month at most.