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8.5" wheel help needed

This is a discussion on 8.5" wheel help needed within the Wheels and Tires forums, part of the General Help category; Ok folks, I've done a bunch of online searching and haven't been able to find an answer to my question. ...

  1. #1
    Member intheclouds1977's Avatar
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    2000 WS6 M6

    8.5" wheel help needed

    Ok folks, I've done a bunch of online searching and haven't been able to find an answer to my question.

    I recently bought a 2000 WS6 and it needs new tires. My front wheels are 18x8.5 with about 56mm offset. The 255/35r18 Kuhmo tires are wearing horribly on both outside edges even at max inflation (44psi). This is the pressure the previous owner ran the tires at. The alignment is spot on. Normally, wearing on the outside edges even at max psi would tell me that the tires are too narrow for the wheel. However, 255 is the max width generally recommended for 8.5 wide wheels. You can also imagine with such narrow wheels and such high offset, how very tucked the tires are.

    My question is...is the 255 max width on an 8.5 wheel simply a tire wear recommendation, or is it a safety concern? If it's simply for tire wear, I definitely want to go with a wider tire so I can get the edges to pull down more and get better tire wear over the full tread width. Better looks will be an added bonus.

    I appreciate any help you can give! I don't want to spend money on new tires and have them eaten up by improper tread wear!

    Thanks!

  2. #2
    Pontiac Addict 01RaptorTA's Avatar
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    Black on black
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    255 is the widest you can go safely, and even then i believe some tires would roll over due to not being exactly 255 wide. I would check out some nitto 255/40:18 NT555s for the front and NT555Rs for the rear. Ive always loved nittos, never had a complaint. And in your case, the 255s will act like 245s and conform for your rims better because nitto tires are known to be smaller than actually stated.

  3. #3
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    I know some people have put up to 275s on a 8.5 rim and thats what Im planning on.

  4. #4
    Pontiac Addict 01RaptorTA's Avatar
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    It is possible but it's not exactly safe to do and you're going to have uneven tread wear.

  5. #5
    Member intheclouds1977's Avatar
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    If you re-read my original post, I currently have uneven wear on the outside of the tread. Going wider would help give me better wear, not worse. The wider the tire, the more the tire wears in the center!

    However, if it truely is a safety issue, I don't want to risk it.

    I do not want to go narrower as you have recommended. If I already have poor treadwear on the outside edges, why would I wish to go narrower and make the tread wear even worse?

    Thanks for the response though.
    Last edited by intheclouds1977; 04-17-2007 at 05:55 PM.

  6. #6
    Senior Member JonB's Avatar
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    I'm still wondering why your running 44psi you should't run your tires at the max psi. There should be a proper psi listed on the tire, that is the psi you should run. Your problem is probably related to the 44psi tire pressure your running.

  7. #7
    Senior Member mrr23's Avatar
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    Quote Originally Posted by intheclouds1977 View Post
    I recently bought a 2000 WS6 and it needs new tires. My front wheels are 18x8.5 with about 56mm offset. The 255/35r18 Kuhmo tires are wearing horribly on both outside edges even at max inflation (44psi). This is the pressure the previous owner ran the tires at. The alignment is spot on.
    the problem is the factory specs are +0.40 for camber with a 4.80 caster. this puts a lot of pressure on the outside of the tire when cornering. bringing the camber to -0.50 will help in alleviating this all too common wear.

  8. #8
    Senior Member mrr23's Avatar
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    dark bowling green
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    Quote Originally Posted by JonB View Post
    I'm still wondering why your running 44psi you should't run your tires at the max psi. There should be a proper psi listed on the tire, that is the psi you should run. Your problem is probably related to the 44psi tire pressure your running.
    the tire pressure listed on the tire isn't always the correct pressure to run them at. the proper tire pressure is located on the driver's door placard. now, if you do not have the same tire size as listed on the door placard, you can call a local tire store and have them look it up on their conversion chart, if they have one.

    just because the tire has a MAXIMUM tire inflation, doesn't make it the correct pressure for the vehicle it's on. that tire can go on many different aplications.

    for his particular tire wear, it's not the inflation pressure. having too much pressure creates wear in the middle of the tire, not the outside edge.

  9. #9
    Member intheclouds1977's Avatar
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    I'm running max pressure for the tire to try to eliminate the wear on the outside edges. The more tire pressure you run, the more it shifts the wear to the center. Trust me, I'd prefer not to be running this much tire pressure...it's just intended as a fix for the tire wear.

    I'll have to try out the new camber measurement. Thanks for the tip! Positive camber is upper control arm toward the outside of the car...right?

    I like setting my own tire pressure...not rely on some chart or a door placard. I spread flour in front of the tire about 1/4" thick and drive through it. Looking at the tread pattern made, you can tell where there's more pressure on the tire. If you need more pressure in the middle, add more air. If you need more pressure on the outsides, take air out. The problem with this car is max inflation has been reached. I can see adjusting the camber to the above recommendation fixing this!!

  10. #10
    Senior Member mrr23's Avatar
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    Quote Originally Posted by intheclouds1977 View Post
    I'll have to try out the new camber measurement. Thanks for the tip! Positive camber is upper control arm toward the outside of the car...right?

    correct. but in our case, the adjustments are on the lower arms. so, positive camber is the inward movement of the lower control arm.

    the actual definition is the inward/outward position of the top of the tire when viewed from above. positive is outward from vertical. negative is inward from vertical.

    the back of an old hunter alignment printout i used to have:


  11. #11
    Senior Member mrr23's Avatar
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    Quote Originally Posted by intheclouds1977 View Post
    I like setting my own tire pressure...not rely on some chart or a door placard. I spread flour in front of the tire about 1/4" thick and drive through it. Looking at the tread pattern made, you can tell where there's more pressure on the tire. If you need more pressure in the middle, add more air. If you need more pressure on the outsides, take air out. The problem with this car is max inflation has been reached. I can see adjusting the camber to the above recommendation fixing this!!
    only problem with this is camber. this is really only accurate if the camber is at 0*.

    you ever wonder how manufacturers come up with alignment specs? they take tire temps across the tread after driving it around a road course. once the tire temp is even all the way acrross the tread, that's the settings they use.

  12. #12
    Member intheclouds1977's Avatar
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    Ah, good point!!

    The above camber setting then will help with cornering...but will it cause abnormal inside wear for daily cruising? Considering the manufacturer did all the "proper" tests via road course to come up with their recommendation.

    Thanks for all the help! FYI I am used to trucks with zero camber set in.

  13. #13
    Crazy Canuck ! Eugenio_SS's Avatar
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    Quote Originally Posted by intheclouds1977 View Post
    If you re-read my original post, I currently have uneven wear on the outside of the tread. Going wider would help give me better wear, not worse. The wider the tire, the more the tire wears in the center!

    However, if it truely is a safety issue, I don't want to risk it.

    I do not want to go narrower as you have recommended. If I already have poor treadwear on the outside edges, why would I wish to go narrower and make the tread wear even worse?

    Thanks for the response though.
    not true... the wear pattern will be worse.
    Actually, the wear on the outside is caused by the stock alignment... it has positive camber... meaning that on a straight line you wear more the outside than the inside... and when you turn, makes it worse. GM did this to force some understeer

    get a proper alignment with stock specs for toe/caster, but make sure to bring the camber in the negative side... -0.5' is great for street use and good wear.

    Now, to answer your question: i'd get some 245/40-18 in the front... would be great for overall diameter and size of wheel.
    Eugenio_SS
    almost stock triple-black 2000 SS convertible with 17x11s on all 4 w/ 315s at the track or on the street with 18x10.5s on all 4 w/ 315s: (1), (2)

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