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Discussion Starter #1
hello everyone. I am thinking of changing my rear wheels and tires from 315x35x17 tire size to a 255 or 275 x45 x17 to improve the ride quality.I understand this will require narrower rims to accomadate the smaller tire.It will probably cost about $1000 to make the change. With everything else remaining the same on my car,will there be much of a difference in the ride. As always, thanks for your help.
 

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hello everyone. I am thinking of changing my rear wheels and tires from 315x35x17 tire size to a 255 or 275 x45 x17 to improve the ride quality.I understand this will require narrower rims to accomadate the smaller tire.It will probably cost about $1000 to make the change. With everything else remaining the same on my car,will there be much of a difference in the ride. As always, thanks for your help.
What rear shocks are you running? I'd seriously consider replacing shocks before investing $1,000 in new/reworked wheels and tires.
 

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What's been done to the car and suspension to accommodate the 315-35's?

What size wheel and back spacing are the 315's mounted on now?
 

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they are DSE/Koni in the rear and DSE/Koni Aluminum body coilover shock in the front
Adjustable in the rear? If so, have you dialed down compression damping?
 

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Bob - there must be more done, the 11" wide wheels with 5.25 bs just wouldn't fit in a stock '69 wheel well let alone one with a 2" drop. I was expecting to hear "mini-tub w/shortened rear axle or something like that or old school fender flairs...
 

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Discussion Starter #9
Sorry guys but i am fairly new at this. The rear shocks are non adjustable. the car has been tubbed and it has a 9 in ford rear but the fenders are stock. Does that help?
 

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What is it doing that you don't like?
 

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Discussion Starter #11
Mike,It seems like you could feel even the smallest bounce you go over and it is definetly coming from the rear of the car.I had the car on a lift and checked everything.Nothing is broken or loose,thats why I am wondering if its just the 35 series tires causing all the roughness. thanks.Bob
 

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Mike,It seems like you could feel even the smallest bounce you go over and it is definetly coming from the rear of the car.I had the car on a lift and checked everything.Nothing is broken or loose,thats why I am wondering if its just the 35 series tires causing all the roughness. thanks.Bob
What you're describing sounds like "stiction"; the initial resistance to movement. I'd look at leaf springs bushings and rear shocks.

If the car's mini-tubbed, the shock mount points have been relocated. Are the shocks the proper length and could they be binding?

Don't get me wrong 2" drop springs and 35 series tires in a first gen Camaro won't ride like a Camry, but you shouldn't be getting beaten up on small bumps.
 

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Can you come up with a part number for the Koni shocks? I bet they are adjustable and are set to the firmest setting. I have Koni Classic shocks and run them on the lightest setting in the rear because the firmest was way to stiff for street use.

Now as for wheel and tire fitment if you decide to change what you have you'll need to start with what you have and convert the backspacing to offset assuming everything fits properly. Once you have the offset then you just pick a wheel with the same offset in the size of choice. An 11" wheel with 5.25" bs has an offset of -19 (stock you would want about a +6 to center the wheel between inner and outer fenders). If you went down to a 9.5" wide wheel you would want a 4.5" backspacing in order to maintain the same center line as your existing wheels. Unfortunately the tire would probably look lost in the wheel well if you made that change.

I would work on shock adjustment and proper fit first, then if your rear springs are using solid bushings I would replace those with urethane and them possibly look into a tire with a bit more sidewall if they are available and not too tall overall!
 

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Discussion Starter #14
Dennis, the shocks I have are the Koni yellow and you are correct,,,they are adjustable. I am going to pull one off this weekend and check the setting and I will let you know. Thank you for your help also thank Mike for his thoughts.
 

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Going from a 35 to a 45 will not make enough diff to make it worth it

I would be looking at springs and shocks to take the harshness out of the ride.
 

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Going from a 35 to a 45 will not make enough diff to make it worth it

I would be looking at springs and shocks to take the harshness out of the ride.
I respectfully disagree, there is a 2" height difference in a 255/45/18 and a 255/35/18 so that's a 1" change in sidewall...
 

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I respectfully disagree, there is a 2" height difference in a 255/45/18 and a 255/35/18 so that's a 1" change in sidewall...
He has 315/35s now

Check your math a 315/35 has a 4.34" sidewall and a 255/45 has a 4.51" side wall

Pretty much the same.
 

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He has 315/35s now

Check your math a 315/35 has a 4.34" sidewall and a 255/45 has a 4.51" side wall

Pretty much the same.
You made a blanket statement initially about 35 - 45 series tires that I replied to! I gave a factual example of a 35 and 45 series tire having an inch difference in sidewall.

Kind of obvious one wouldn't pick different sizes that end up with the same sidewall height and expect better ride... :clonk: But you know what? In your size specific example the 255 is not near as wide as the 315 and that alone would provide a better ride! :yes:
 

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You made a blanket statement initially about 35 - 45 series tires that I replied to! I gave a factual example of a 35 and 45 series tire having an inch difference in sidewall.

Kind of obvious one wouldn't pick different sizes that end up with the same sidewall height and expect better ride... :clonk: But you know what? In your size specific example the 255 is not near as wide as the 315 and that alone would provide a better ride! :yes:
I was just responding to his query in that he has 315/35s and was considering 255/45s. My opinion is the the minor difference in sidewall height will not make a significant difference in ride.

IMO there are other factors causing his harsh ride. If the car is tubbed then the shocks were probably relocated. Perhaps from the OEM angle to more vertical. If this is the case maybe the shock is too long and bottoming on bumps. Sometimes the leafs are relocated inboard and maybe binding if not shackled correctly.

The first thing I would do is take the shocks out completely. If that eliminates the harshness on bumps (yes I know it's going to be lowrider bouncy) then you know its a shock issue. If it's still harsh with the shocks out you know it's spring related.

The reality is lots of us run tubbed cars with 315s - 335s and still have good ride quality.
 

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Discussion Starter #20
John, thanks for the info. My car is mini tubbed with 3 in drop springs from DSE.The shocks were specifically designed for that drop and were also from DSE.I checked a few things out today and I notided that I have about 1 1/4 inch of inward travel left on the shock with the car sitting normally. Does that seem to be right ? thank you.
 
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