# tires and wheels



## LCS (Oct 13, 2020)

tHi does anyone know how wide of rim that will fit on a 66 GTO? And know what off set you can use on the front and back with out them rubbing? Thanks


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## pontrc (Mar 18, 2020)

I know on the rear you should be ok. The concern is the front, especially with 15 inch rims. RMTZ67 has a nice setup on his 67 he or Lemans guy could tell you. Minesa66 too


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## RMTZ67 (Mar 12, 2011)

I had a 9.5 wheel w/ a 4.5 offset and a 255/40/17 on the rear and always rubbed. Even with massaging the inner fender well and trimming. I now have 8"wheels all around....same offset and tires. Not as much of a rub on a lean but still there. 8" 4.5 Offset and 245 tires would be ideal. I thought I read a article that 14/15" tires of the same width were actually wider. What are you looking as far as height in your wheels?


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## 64since65 (Dec 11, 2019)

From an ex-wheel bearing engineer: Please put an offset on your front wheels - the bearing suppliers will thank you.

I think you'll actually get away with it longer on cars with tapered roller bearings for a couple reasons but it's murder on the newer cars with preloaded ball bearings. On the other hand, if you don't put a lot of miles on it (i.e., it's not a daily driver) or don't mind changing bearings more frequently, go for it.

Here are the details....

On a solid rear axle it may be less of an issue. I didn't work on solid axle bearings. On the other hand, when it's not a solid axle the bearings are designed so the load goes more or less through the center of the bearing assembly and splits the forces between the inner and outer bearings. In this case there is no torque applied to the individual bearings. However, once the center of force is outside the bearing itself, the bearings now need to resist a torque load as well as the plain upward force.

Here are some diagrams to show the basics of what happens to bearing loads (red) as the wheel load (black) moves out from the center of the two bearings - two bearings make up one "wheel bearing". (click to enlarge):


























And note that it has nothing to do with where the wheel mounts to the flange. It's all about the center of the tire patch on the road vs. the center of the bearings. And, of course, this ignores the issues with steering.

I'm not actually trying to discourage anyone from doing it as long as they understand the implications. You WILL have lower bearing life. How much lower depends on how much offset, how much you drive it, and how hard you drive/corner it.

And I hope everybody here knows - do NOT torque tapered wheel bearings! Finger tight is plenty. I was always taught "_finger tight while rotating the wheel then back off just enough to insert the the cotter pin_." A friend of mine torqued his to 25 ft. lb. and at about 3,000 miles I replaced all 4 bearings for him.


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## LCS (Oct 13, 2020)

RMTZ67 said:


> I had a 9.5 wheel w/ a 4.5 offset and a 255/40/17 on the rear and always rubbed. Even with massaging the inner fender well and trimming. I now have 8"wheels all around....same offset and tires. Not as much of a rub on a lean but still there. 8" 4.5 Offset and 245 tires would be ideal. I thought I read a article that 14/15" tires of the same width were actually wider. What are you looking as far as height in your wheels?





RMTZ67 said:


> I had a 9.5 wheel w/ a 4.5 offset and a 255/40/17 on the rear and always rubbed. Even with massaging the inner fender well and trimming. I now have 8"wheels all around....same offset and tires. Not as much of a rub on a lean but still there. 8" 4.5 Offset and 245 tires would be ideal. I thought I read a article that 14/15" tires of the same width were actually wider. What are you looking as far as height in your wheels?


Am looking to put 15X7 rims one the front, with a 235x60 15's and on the back am looking to put 15X8 rims on the back with a 255 60 15, know off set not good for the bearing but would like the rim to be a little deep dish. But do not want any rubbing.


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## RMTZ67 (Mar 12, 2011)

LCS said:


> Am looking to put 15X7 rims one the front, with a 235x60 15's and on the back am looking to put 15X8 rims on the back with a 255 60 15, know off set not good for the bearing but would like the rim to be a little deep dish. But do not want any rubbing.


o they sell 15


LCS said:


> Am looking to put 15X7 rims one the front, with a 235x60 15's and on the back am looking to put 15X8 rims on the back with a 255 60 15, know off set not good for the bearing but would like the rim to be a little deep dish. But do not want any rubbing.


255/60/15 might be a little tight. 245 would probably be ok. this is assuming your car is in the original stance. 17" are not all that tall with 40 tires,







and more choices.


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## LCS (Oct 13, 2020)

Well hay thanks a lot, will check this out! Again thanks a lot, And yes my 66 GTO is all stock here AND i can go with a 4.5 offset?


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## PontiacJim (Dec 29, 2012)

*64since65* "I'm not actually trying to discourage anyone from doing it as long as they understand the implications. You WILL have lower bearing life. How much lower depends on how much offset, how much you drive it, and how hard you drive/corner it."


*PJ *- Thanks for the info, but it needs to be explained more as what you have here is a generality.

First, the rear axle has a big spread between the outer and inner bearing, so my guess is that this changes the various amounts of weight applied to the bearings. Correct?

Acceleration from the torque applied through the rear axles and how well the tires grip have an effect on rear bearings as you can encounter axle deflection or even axle tube bending in some cases. So it does not necessarily have to be rim offset that adds the extra loads onto a bearing - and why Pontiac rear axles use a retainer vs C-clips like Chevy to hold the axle in place in event of failure of the bearing. I opted for heavier wall axle tubes on my aftermarket Ford 9" to eliminate any future issues with axle tube deflection or bending.

Bearing size also comes into play such as diameter/width of the bearing, the number of bearings within the race, and the individual taper bearing diameter size. So one bearing may easily carry a load at 4,000 lbs while another may only be rated at 2,000 lbs. So, if I know what the bearing rating is, I might be able to use a rim with a big offset that moves the tire outward and not have any issues. Those suppliers of aftermarket rear axle assemblies often offer or use a larger bearing as they know the intended use will be increased HP/TQ. I opted for the larger bearings on my Ford 9" assembly but the standard, and smaller bearing was what you got if you did not opt for larger bearings.

Weight of the vehicle can have an effect. That is why the bearings have ratings. But, if I have a 4,000 lb car and lighten it up to 3,500 lbs, I have changed the amount of weight distributed on both front and rear bearings.......and a big offset on the rim may have no effect on the original bearing. And, vice-versa, adding an extra heavy load, ie loading down the trunk with a complete Pontiac engine and driving cross country to deliver it, or adding a hitch to the back and over loading the tongue with too much weight, can cause bearing failure.

What also needs to be explained is that a 10" rim with a 5" back space means that the attachment point, the center hub, is in the middle of the rim - so "0" offset. 1/2 the width of any rim is the rim's centerline. The offset, if any, is where the hub center extends past the rim's centerline or is positioned before the rim's centerline as seen in the diagram.












A factory Pontiac rim having 6" and a 4 1/2" back space means the rim has 1 1/2" on the front of the center hub and 4 1/2" spacing on the backside of the center hub so it puts the weight more on the inner bearing of the front suspension and assume more on the inner bearing on the rear axle. The inner bearing on the front suspension is also larger for this reason as it carries a heavier load.

So the greater the positive offset from the centerline of the rim, ie "0" offset, the more weight the tire/rim combination applies to the bearings which are acting in the same manner a fulcrum/lever works. However, I see an awful lot of 4-wheelers with rims that are definitely all positive offset. 


*64since65* "And I hope everybody here knows - do NOT torque tapered wheel bearings! Finger tight is plenty. I was always taught "_finger tight while rotating the wheel then back off just enough to insert the the cotter pin_." A friend of mine torqued his to 25 ft. lb. and at about 3,000 miles I replaced all 4 bearings for him."

*PJ* - Your friend was following the Pontiac Shop Manual - But I think he was confused by the way it is written up: "Tighten adjusting nut 20-25 lb. in. torque." It should have been written 20-25 in. lb torque, so as not to confuse people that it is _20-25 *ft*. lb. _torque. And to further the confusion, the manual shows the steps in tightening the spindle nut and you "_rotate wheels and *tighten it FIRST to 10-16 ft. lb. torque *_(actually printed as _lb. ft._ torque in the manual)_, and then loosen_."

The Pontiac shop manual also provides an endplay measurement of .001"-.005"

So this is if you have replaced your bearings with new races/bearings, or had to pull the drums/hubs, or front disc brake rotors off. You can reuse the old bearings/races as long as they look good, no scouring,bluing, or a lot of excessive slop in the races. Clean them off, inspect, and re-grease if they look good. You cannot mix new bearings with old races - you are only asking for trouble as the bearing/races wear in together for their fit. So if you have to replace them, do so in a matched set. Don't forget to use a new grease seal on the inner bearing even if you don't replace the bearing.

I have never used the torque method. But, doing it by feel is how most install/adjust the wheel bearings. If you only do "finger tight" you may not completely seat the bearings or the seal, so _do not do just "finger tight._"

I tighten the spindle/bearing nut with a wrench or my old slip-joint pliers (which may be better for some as you can't get the torque out of them that you can hanging on a wrench - but I know what I'm doing). I like to install my rim/tire on the hub once I have the spindle nut installed and finger tight. Then while spinning the wheel, I tighten the nut down gently without a lot of force. Keep spinning the wheel as you slowly tighten and you can see/feel the wheel slow down its spin as the bearings begin to tighten. Too much and the wheel doesn't spin to freely - so the nut gets "snug", not cranked down on!

Why do it this way? It ensures the hub gets seated on the spindle. If the hub were to hang up on the inner seal or some kind of burr on the spindle, just "finger tight" may not seat the hub completely. The wrench will. I don't know if using the wrench might draw your bearing races into place should you have not completely seated them if you replaced these, but I doubt it - never had that issue because you can see that the races are seated by looking. It also forces any overloaded grease within the bearings out and seats them. - This is also why the Pontiac shop manual states to* initially tighten the spindle nut to 10-16 ft. lb. torque *and back off. I just never used the torque spec's.

Once I get the bearing snug, I back off the wrench while continueing to rotate the tire and you will feel/see the difference in how easy/fast the tire spins. I then tighten my spindle nut snug one more time while rotating the tire, again you can feel/see how it spins harder/slower. Then I loosen up the spindle nut again to where it is off the bearing, ie not applying any pressure. Next I do my final tightening by tightening up the spindle nut while spinning the tire and stop once I feel some resistance at the nut. The tire should spin freely and have very little drag stopping its rotation (this should be that factory 20-25 inch pounds of torque).

Then I look to see where the hole in the spindle is in relationship to the slot in the nut where I will be inserting the cotter pin. It is generally better to rotate the nut looser than tighter if you need to rotate it to align it up with the hole in the spindle. This is kind of an experience thing. If tightening up the nut a small amount gets me lined up, I do it. If it takes more than just a hair or two, I back it off. Again, the feel of the wheel and speed it spins is also how I judge this. If I go a bit tighter and spin the wheel and it seems to have added more drag on the spinning wheel, I went the wrong way and need to back off the nut 1 slot and insert the cotter pin there. If the wheel spins good and I don't see any real change in the rotation speed or effort to spin it, then I leave it. It is better to have the bearings loose than tight as tight will burn/wear them out faster.

Loose can be tolerated much more and I've had some that were noticeably loose and could rock the tire side-to-side. Bearings were just fine - repacked and re-installed. (as a side note - we service the ABS systems on the truck-trailers at work. If the wheel bearing gets a little sloppy, it has enough play to create too large of a clearance gap between the ABS sensor and the pick-up ring it works off of and the ABS on that axle side does not work - brakes of course still will work, just not the ABS feature. We simply tighten/snug up the nut on the wheel bearing and off it goes. Never seen the extra play cause a wheel bearing failure. Most all bearing failures are due to seal failure/poor maintenance and the gear oil leaking out causing the bearing to run dry.)

If everything seems right, then fold the cotter pin end over and install the dust cap. Adjust your brake shoes.


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## 64since65 (Dec 11, 2019)

PontiacJim, I agree with everything you said. As I said, I didn't work on solid axles so I didn't want to get into that. Also, you're right about adding more details regarding the offset. I said, "It's all about the center of the tire patch on the road vs. the center of the bearings" but didn't elaborate. I suppose I should have.

As to the "finger tight" issue, I guess I was being a bit simplistic just to emphasize the issue. As you pointed out, loose is better than tight. In actuality, I generally tighten a freshly greased bearing with a pair of pliers held at a comfortable angle while turning the wheel to seat the bearing through the grease then back off, tighten finger tight, then loosen just enough (if necessary) to install the cotter pin - sounds a lot like what you do. (The idea is to press through the grease so the steel parts just touch without preloading them. Of course, some preload is needed so you know you've seated them; just keep it minimal.)

For what it's worth, my friend's car actually came from the factory (dealer? it was a new car) like that. All four wheel bearings were torqued like that. It was a 4 wheel independent suspension but I don't remember the model of car other than it was a GM car. I know he didn't do it himself because he wasn't mechanically inclined at all - certainly not enough that he would mess with a new car. He had a enough issues with the dealer that he asked me to look at it first when he noticed all the noise. When I told him what I found, he told me to go ahead and replace them. It took about 25 ft lbs to loosen them but that's only an estimate. Anyway, I couldn't loosen them with a pair of pliers. My guess is that they either had a new person on the line or someone that didn't know what he was doing at the dealership - but I have no idea why the dealership would need to touch the wheel bearings on a new car.

Just as a matter of interest, I saw an example in the lab where they ran a chart of the outer raceway of a brand new tapered bearing to show the roundness of the outer raceway then assembled it to 25 ft lbs and re-ran the graph after disassembling it. You couldn't feel any difference in the bearing but you could see it in the chart. Note that we are talking about a chart that originally showed a roundness variation of probably somewhere in the 3 micron (as in micro-millimeters) range and probably not more than about 4 microns after tightening (best I can remember - it was probably 20 years ago) but you could definitely see where each roller had pressed into the race. The engineer's comment was that this would technically reduce the life slightly but not enough that most people wouldn't just assume it fell within the normal range or that maybe the driver was doing something like a lot of hard cornering or driving on a lot of bumpy roads.

I wish I'd kept a copy of even one runout chart when I left the company. It always amazed me that they could get so much detail at virtually the sub-micron level.


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