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Tires - planning way ahead


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My 73 Riv has radials. Scheduled to get them rotated next week. No idea if they ever were rotated before, but they have a good bit of tread and look fairly new. However, the amount I drive (6000+ a season so far) I'll be replacing them in a year or three or maybe 5. So my question:

 

1. Should I replace with the original bias ply style?

2. If I do, will I have to buy new wheels, too? No idea whether the wheels are original or not. I haven't checked the manual to see what the original wheels should be but I'm assuming they're original.

3. If I do get bias ply how will they handle?

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Check the date code on the tires. The date code is the last 4 digits of the DOT number printed on the sidewall. For example

if the last 4 digits are 1612 the tires were manufactured the 16th week of 2012. If your tires are 6 years old or older they need to be replaced as tires that old can explode and do massive damage to your fender, as one of our forum members recently found out.

I believe radial tires were original equipment on the 73 Riviera, so you want to get new radial tires. Bias ply tires ride rough and 

handling is far inferior to radials.

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1 minute ago, Seafoam65 said:

Check the date code on the tires. The date code is the last 4 digits of the DOT number printed on the sidewall. For example

if the last 4 digits are 1612 the tires were manufactured the 16th week of 2012. If your tires are 6 years old or older they need to be replaced as tires that old can explode and do massive damage to your fender, as one of our forum members recently found out.

I believe radial tires were original equipment on the 73 Riviera, so you want to get new radial tires. Bias ply tires ride rough and 

handling is far inferior to radials.

I didn't know there was a mfg. date. Thanks. All the google searches tell me the factory tire was a bias ply H78-15, IIRC. Not that I'm complaining about having the radials, tho.

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You are correct......I checked and the standard tires were Bias plies. In 1974 was when the radial tires became standard. I believe the radials were an option if you had a 73 GS Riviera......somebody who is a guru on 73's can chime in on that perhaps.   

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52 minutes ago, Seafoam65 said:

You are correct......I checked and the standard tires were Bias plies. In 1974 was when the radial tires became standard. I believe the radials were an option if you had a 73 GS Riviera......somebody who is a guru on 73's can chime in on that perhaps.   

 

Yes the Riviera GS handling package A9 included radial HR70/15 tires.  As Seafoam pointed out, if the tires are more than 10 years old, they need to replaced. 

 

Bob Bonto

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2 hours ago, Seafoam65 said:

Check the date code on the tires. The date code is the last 4 digits of the DOT number printed on the sidewall. For example

if the last 4 digits are 1612 the tires were manufactured the 16th week of 2012. If your tires are 6 years old or older they need to be replaced as tires that old can explode and do massive damage to your fender, as one of our forum members recently found out.

I believe radial tires were original equipment on the 73 Riviera, so you want to get new radial tires. Bias ply tires ride rough and 

handling is far inferior to radials.

👍👍👍

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Yes Bias were still standard in 73 but they were an option on the base model and as Bob said standard on the GS. 

 

Bottom line is you do not want bias tires if you plan on driving the car. The difference in ride and handling vs radial is significant in my opinion. Biggest mistake I ever made when it comes to tires was buying bias tires for a 67 just so I wouldn't get a deduction at BCA 400 point judging. They were horrible on long trips. Finally switched to radials and it was like driving a different car.

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I wanted an original look on my 63. I am very happy with radial bias look tires from American Classic. I got the Auburn 7.10 R 15 with one inch white wall. I was surprised to find the tires,my rebuilt suspension, and Rebuilt steering Box get along fine. I enjoy the ride. I got what I wanted and the tires are good,. You have many options  so do your best research and get what you want.

Turbinator

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AND if everyone is still using the original specs. for alignment your not getting the real true benefits from the radial tires.  Update tires or suspension need update on alignment specs. even with the old bias ply tires.  Time to step up to more modern technology.  The judges can't tell what your alignment is set up for.

 

Tom T.

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It is not rocket science.....all you have to do is increase the number of shims to dial in more positive caster.

The front end specs for an 87 Monte Carlo would work just fine. The limit to how much positive caster you can get

is determined by how long the bolts are where the shims slide in. When you run out of threads on the bolt you can't

put any more shims in. The main reason caster was neutral and not positive on the 60's cars is that a lot of them did not have power steering, and the more positive the caster, the harder it is to turn the steering wheel with manual steering. When power steering became standard on everything then positive caster came into fashion along with radial tires.

Edited by Seafoam65 (see edit history)
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4 hours ago, J3Studio said:

Do alignment specifications for radials exist for cars that never offered them?

 

Typically no, but a good alignment specialist will know what to do. The main issue is toe in.

 

Oversimplifying a bit, toe in is used to compensate for the drag/friction of the tires. If the tires are toed out, the car will be unstable, wanting to dart all over the place. As speed increases, so does drag and this loads up the suspension making the tires tend to toe out. The factory toe in spec will be such that when the suspension is loaded up at speed, the tires will be going straight, or still a tiny bit toed in. They should stay straight or toed in under braking too. There is rubber in the suspension...

 

Radials will work fine with original specs. the issue is that they drag less, and don't need as much toe in to never toe out. If you run factory specs, the tires will drag more than they need to at speed because they are toed in more than they need to be. Also they will wear faster than they need to. You can do better by changing the specs.

 

If you have to guess how much toe in, 1/2 of factory spec is a good place to start experimenting. Some cars are even fine with zero toe on radials.

 

I don't think the "more caster" thing is necessarily a radial thing. More caster causes the wheels to want to steer toward the center of the car. This makes the car feel really planted and stable. It also makes the steering return more positive (and harder to steer with manual steering). It makes the car feel more like a driver would expect today. There is such a thing as too much, especially on bumpy roads. If one wheel is knocked loose the other one will still try to steer toward the center of the car.

 

The more positive steering return of extra caster would likely be appreciated by the same people who would prefer the relaxed straight-ahead feel of radial tires. Maybe that's the connection.

 

For what it's worth, about 3 or 4 degrees positive caster can be very nice on a big American car with power steering. I am not sure what number would be ideal on a Riviera.

 

Edited by Bloo (see edit history)
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I’m all in with the experience you gents have. My tires are 7.10 R 15. I have a radial tire that looks like a bias tire. How should my front end man set up the alignment?

Now I can guess it is not rock science, but the subject can be perplexing if you’ve never aligned a front end. I will say aligning the front end of car is like playing guitar. Anyone can do either one, BUT first you’ve got to learn.

Turbinator

Edited by Turbinator (see edit history)
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Bob just tell him to change the caster specs to 3 degrees positive......the other specs would stay the same.

Generally on all rear wheel drive cars whether a 1963 or a 2013, the toe is going to be set  1/8 inch toed in plus or minus a 16th

of an inch. You don't ever want to be toed out at all as this causes wandering. On front wheel drive cars the toe on the front

is always set to zero(wheels straight ahead) and the rear wheels are toed in 1/8 of an inch if the car has adjustable settings in the rear. All modern cars since the mid 70's have positive caster listed in their specs.  On all cars caster varies from one side to the other in order to compensate for the crown on most roads (left side of lane higher than the right side) Incorrect caster that is way

off will cause a pull when you let go of the wheel, but does not cause tire wear except for the fact that you are constantly turning the steering wheel to go straight, so that if your car is pulling to the right and you are turning the wheel left to go straight, you will

wear the outside of the right tire and the inside of the left tire. Most tire wear is caused by incorrect toe .

The toe on your wheels is a critical setting that leaves only a very tiny margin of error before tire wear develops.Caster is  not a critical setting like the toe is, so if your car doesn't

pull, the caster is fine. Most pull problems are caused by bad radial tires with an internal tread separation. (pull is the tires 90 percent of the time, unless  the car has been wrecked and front end parts are bent) Modern front wheel drive Mcpherson strut

cars do not have adjustable caster, so if you have a pull, you either have a bad tire or bent parts, such as a bent lower control arm, strut  or spindle. To determine if the pull is your tires, swap sides with the front tires and drive the car again. If the tires were causing the pull, the car will either pull the opposite way after the swap, or if you are lucky it will go straight. If swapping the tires around makes the car go straight, you can just leave the tires like that....problem solved! This concludes my front end class for the day.

 

Edited by Seafoam65 (see edit history)
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Winston, when 3 or 4 things are going on at one time and changing one thing changes all the rest I’m in trouble. I’m not going to a front end school ( AC school was hard enough). 
Thank you for explaining the features in caster camber toe in and the rest.

im lucky. My car travels straight and feels good knowing my front tires are on the road. I had the car aligned with modern radials and Buick wheels. Now I have the 7.10 R 15 modern radial that looks like a bias. Just because everything SEEMS OK that doesn’t mean that it is.  I just wanted to make doubly sure I didn’t need to take the car in for alignment attention.

Thsnks again

Bob

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As stated above early cars had negitve caster for easier steering. With negitive caster the car is being lead by the rear wheels.

    I've stated this previously MANY times, especially for the Rivs. up until 1970 & beyond & '63 back full size cars.  Some cars from the factory today are running +12* to +15* of positive caster.  Now the car is being lead by the front wheels.   You ALWAYS do a 4 wheel alignment even if the rear is non adjustable.  This way the front is set by the rear centerline so you end up with a straight steering wheel driving down the road.

   My recommendation has ALWAYS been to get as much positive caster that you can get from our cars.  Normally you can get as much as +3* positive caster WITHOUT making any major changes.  When I install poly bushings for the strut rod/brake reaction rod bushings I usually remove 1/4" from the rear bushing.  What this does is pull the lower control arm forward approx. 1/4" & can add up to approx. 2* more positive caster.  By doing this it has nothing to do with ANY KIND of binding on the lower control arm inner bushings.  IF you watched while someone drove your car 1st. in reverse then forward & step on the brakes kinda hard, not so hard as to lock up the wheels, you would be surprised at how much the wheel moves back & forth. Mostly ZERO with the poly bushings. The lower inner bushings are designed to move to some degree so pulling it forward has zero affect on wear/binding of the bushings. As an example my '64 Riv. I bought new when I replaced the strut rod/brake reaction rod bushings (started out at 25K the 1st.time) when the car had approx. 100K miles on it I did the cutting on the inner bushing.  Today with over 300K the same original lower comtrol arm bushings are still in place, NEVER replaced them as I saw no need.   Granted they could possibly need to be replaced but why try fixing something that's not  brroken/showing any signs of detereration???? 

    So IF you could get 5* positive caster do it.  With positive caster the steering wheel will try to return faster to center, will be much more resistent to cross winds, will require less effort on the drivers part to keep the car going in a straight line WITHOUT as much  feedback from the driver to keep it going straight down the road, & other positive things I'm forgetting at the moment.

ALSO positive caster has nothing/zero to do with tire wear.  You wouldn't believe how much of a POSITIVE reaction to all this is & the way the car drives is more in tune with todays cars.

    Camber I like to set to 0* + or - 1/4*.   Now camber IF excessive + or - can cause tire wear.

Our cars take a lot of toe-in to keep the tires straight going down the road because of ALL the forces trying to toe out the wheels.   The specs are normally 3/16" (.1875") - 5/16"  (.3125") for total toe for both wheels. I try to set the toe at .06" each side to .010" each side for a total of .120" - .200" total toe.  As a beginning setting I start out at in the middle at  .160" total or .080" each side.

    With wider 17"-20" wheels there are even more forces trying to toe out the wheels so you may have to compensate more for the wider tires/wheels with more toe in.

 

Just my thoughts on the subject as I've, like MANY others on this forum, have the MANY YEARS OF EXPERIENCE working on these wonderful mechanical objects/wonders.

 

Tom T. 

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