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Thread: BFGoodrich KDW NT Does size, Really Matter?

  1. #1
    John Keehart Guest

    Talking BFGoodrich KDW NT Does size, Really Matter?

    I'm working on getting a new set of tires, like most of us from time to time. I have read all the threads and heard everyone talking about the same size of tire, 255/55x18 for the rear. I have a 410 gear and don't want to go backwards in performance with tires. Is the difference in our stock tire and the 255/55 enough to affect the performance the gear gave. I wouldn't thinks so but.... I have looked at some other options based on BF Goodrich, Tire Rack and Discount Tire. What do you all think of this optional size?
    255/45x18 Rear - 245/40x18 Front, (About the same ratio and rake but a little shorter) But, saves the gear,maybe even makes it a little better? Think it would look OK?

    At 255/55x18 sizes I found several different options, but BFG KDW NT for the price and reputation is pretty good!

    Just a thought, don't want to beat a dead horse!

  2. #2
    It may make a small difference in the spedometer reading,... If you get an Xcalibrator2 you can adjust tire size in the computer. Problem fixed.

  3. #3
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    John, I got your e-mail, but considering the impact of your suggestion, it's better to reply here in a post. Others need to hear this too.

    Use this on-line calculator to see the difference in what you suggest?

    www.discounttire.com/dtcs/infoTireMath.dos

    I'm presently using 245/45 on the front, and 255/45 on the rear, but in the Pirelli "P-Zero". P-Zero Directionale tread pattern/compound on the front, and P-Zero Assymetrico tread pattern/compound on the rear.

    I'm very pleased with the overall balance in lateral adhesion, side wall integerity, and wear. My on-line calculator says that my tire diameter difference is .36", therefore relatively flat. I like that, my MM is only 4.5" off the ground at the A pillar. Many of y'all may not like this "slammed" look, but it serves to provide the best possible weight transfer on a hard launch too. If you prefer to retain the OEM rake, you can play with the air suspension setting in the rear to "buff it up" a bit.

    John, your suggestion of 245/40 front and 255/45 rear seems very close, size-wise, but it's a yardstick away. Your size combination will result in a 1.32" difference between front and rear, and this difference suggests that the on-board ABS/TC systems will detect slip (or, skid) and react to that.

    The difference should be 1.10" or less, for a compatable tire size.

    Hope I have helped, keep us posted on what you discover?
    Last edited by SergntMac; 08-19-2005 at 02:24 AM.

  4. #4
    John Keehart Guest
    Thanks for the feed back. When I did my calculations, I was looking at the side wall height and not the overall diameter. Makes a big difference. Duh!

    I did the comparison with the KDW NT, using your suggested system and comparing the 255/45 rear and the 245/45 up front....Looks like I may have a good match with these. How do you like the look of the smaller diameter tire? Can we lower the rear air system down enough to not make the tire look too small in the wheel well? I like a lower flat look, if the car functions correctly.

    I appreciate the help and suggestions. I enjoy my MM and its a real Hoot changing and adding things to it.


  5. #5
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    Quote Originally Posted by John Keehart
    How do you like the look of the smaller diameter tire? Can we lower the rear air system down enough to not make the tire look too small in the wheel well? I like a lower flat look, if the car functions correctly.
    Not my best pic, but it is the most recent. I may take some more this weekend.

    http://www.mercurymarauder.net/galle...cat=500&page=1

    I love the look, and have no complaints on function. The rear air suspension is set to it's lowest possible setting, and highway driving is "slot car" like. I find this profile ideal when drag racing, low and firm reduces body roll and plants the car firmly on the track. Good luck with your selection.

  6. #6
    Hugh Brooks Guest
    Though I have monitored this site, this is the first time to respond - so forgive the lack of pictures etc.

    Considering the issues with BFG (availability of the 245/55 rear tires) and the rake of the car (I prefer flat), I was investigating the possibility of using 255/50-18 all around. I assume this will cause problems with the traction control requiring me to remember to disable it everytime I start.

    Does anyone have experience with this size tire on the Marauder? Will it clear front end components? Will there be additional issues if I install Eibach springs in combination with this size tire?

    Quote Originally Posted by SergntMac
    John, I got your e-mail, but considering the impact of your suggestion, it's better to reply here in a post. Others need to hear this too.

    Use this on-line calculator to see the difference in what you suggest?

    www.discounttire.com/dtcs/infoTireMath.dos

    I'm presently using 245/45 on the front, and 255/45 on the rear, but in the Pirelli "P-Zero". P-Zero Directionale tread pattern/compound on the front, and P-Zero Assymetrico tread pattern/compound on the rear.

    I'm very pleased with the overall balance in lateral adhesion, side wall integerity, and wear. My on-line calculator says that my tire diameter difference is .36", therefore relatively flat. I like that, my MM is only 4.5" off the ground at the A pillar. Many of y'all may not like this "slammed" look, but it serves to provide the best possible weight transfer on a hard launch too. If you prefer to retain the OEM rake, you can play with the air suspension setting in the rear to "buff it up" a bit.

    John, your suggestion of 245/40 front and 255/45 rear seems very close, size-wise, but it's a yardstick away. Your size combination will result in a 1.32" difference between front and rear, and this difference suggests that the on-board ABS/TC systems will detect slip (or, skid) and react to that.

    The difference should be 1.10" or less, for a compatable tire size.

    Hope I have helped, keep us posted on what you discover?

  7. #7
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    I have used Pirelli 255/50 on all four corners. With shorter springs in place, you will get some light rub when turning into hard lock. Other than that, no problem.

  8. #8
    Hugh Brooks Guest
    GREAT!! Thanks for the quick response.

    I will probably avoid the Eibach springs for now if it would cause problems in combination with the 255/50's. Also, I may see about having the traction control recalibrated - if possible, bypassed if not.


    Quote Originally Posted by SergntMac
    I have used Pirelli 255/50 on all four corners. With shorter springs in place, you will get some light rub when turning into hard lock. Other than that, no problem.

  9. #9
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    Mac I'm confused, the stock difference is 1.36... so how come we need to stay within 1.10?


    Quote Originally Posted by SergntMac
    John, I got your e-mail, but considering the impact of your suggestion, it's better to reply here in a post. Others need to hear this too.

    Use this on-line calculator to see the difference in what you suggest?

    www.discounttire.com/dtcs/infoTireMath.dos

    I'm presently using 245/45 on the front, and 255/45 on the rear, but in the Pirelli "P-Zero". P-Zero Directionale tread pattern/compound on the front, and P-Zero Assymetrico tread pattern/compound on the rear.

    I'm very pleased with the overall balance in lateral adhesion, side wall integerity, and wear. My on-line calculator says that my tire diameter difference is .36", therefore relatively flat. I like that, my MM is only 4.5" off the ground at the A pillar. Many of y'all may not like this "slammed" look, but it serves to provide the best possible weight transfer on a hard launch too. If you prefer to retain the OEM rake, you can play with the air suspension setting in the rear to "buff it up" a bit.

    John, your suggestion of 245/40 front and 255/45 rear seems very close, size-wise, but it's a yardstick away. Your size combination will result in a 1.32" difference between front and rear, and this difference suggests that the on-board ABS/TC systems will detect slip (or, skid) and react to that.

    The difference should be 1.10" or less, for a compatable tire size.

    Hope I have helped, keep us posted on what you discover?


    11.90 @ 117.5mph on 93 octane
    324 shortblock, Novi 2000, Now with optional axle removing tires
    Igziabeher

  10. #10
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    Quote Originally Posted by RR|Suki
    Mac I'm confused, the stock difference is 1.36... so how come we need to stay within 1.10?
    It's a typo, should say 1.40. I did this in another thread too, thought I fixed them both.

    BTW...Always double check your numbers with a second, or, third tire calculator, the calculations seem to change.

  11. #11
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    yeah I noticed on the calculators... I thought it was a standard formula... and on one calculator I noticed that the difference between front and rear were greeater than rear to front... as in the % was different if I inserted one before the other in alternate order


    11.90 @ 117.5mph on 93 octane
    324 shortblock, Novi 2000, Now with optional axle removing tires
    Igziabeher

  12. #12
    Hugh Brooks Guest
    So if I understand it correctly, the differential between the front and rear tire diameters should be less than 1.40 (with 1.36 being the stock difference). If the difference is zero (both front and rear), will that cause problems with the traction control and ABS? Or is there a minimum differential requirement too?


    Quote Originally Posted by SergntMac
    It's a typo, should say 1.40. I did this in another thread too, thought I fixed them both.

    BTW...Always double check your numbers with a second, or, third tire calculator, the calculations seem to change.

  13. #13
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    Look at the revolutions per mile and you'll see what's really up.

    I'm getting a set of KDW2s' next week (the Nittos are for strip and show only) and while the stock rear 245/55 tire shows 724 rpms the KDW2 255/55 rears are 717, a negligible difference.

    Are the KDW NTs anything like Windows NT?

  14. #14
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    Talking

    Quote Originally Posted by David Morton
    Are the KDW NTs anything like Windows NT?
    Try to avoid frequent crashes and the dreaded "Blue Screen Of Death" wth those new tires, OK?
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    Quote Originally Posted by SergntMac
    John, I got your e-mail, but considering the impact of your suggestion, it's better to reply here in a post. Others need to hear this too.

    Use this on-line calculator to see the difference in what you suggest?

    www.discounttire.com/dtcs/infoTireMath.dos

    I'm presently using 245/45 on the front, and 255/45 on the rear, but in the Pirelli "P-Zero". P-Zero Directionale tread pattern/compound on the front, and P-Zero Assymetrico tread pattern/compound on the rear.

    I'm very pleased with the overall balance in lateral adhesion, side wall integerity, and wear. My on-line calculator says that my tire diameter difference is .36", therefore relatively flat. I like that, my MM is only 4.5" off the ground at the A pillar. Many of y'all may not like this "slammed" look, but it serves to provide the best possible weight transfer on a hard launch too. If you prefer to retain the OEM rake, you can play with the air suspension setting in the rear to "buff it up" a bit.

    John, your suggestion of 245/40 front and 255/45 rear seems very close, size-wise, but it's a yardstick away. Your size combination will result in a 1.32" difference between front and rear, and this difference suggests that the on-board ABS/TC systems will detect slip (or, skid) and react to that.

    The difference should be 1.10" or less, for a compatable tire size.

    Hope I have helped, keep us posted on what you discover?
    It looks like you lowered the body more than an inch (not counting the tire drop)
    So how did you lower the body? Just springs up front? Did you replace the shocks also? The difference in travel with lowered springs/bag would make short life of the stock ones.

    How far can you lower the MM body before you affect steering geometry in the front or the Watts link in the back? Even with the rear UCA's and LCA's being parellel to the body at some point they may be affected.
    Does anyone have any hard info on this other than SOTP stuff?
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