Have a 3.5" James Duff lift and a 2" body lift Lubr....looking at 17" smoothie wheels, what size tire?

[chuddy]

Hi all, I'm so lost in choosing the right rim/tire combination. I'm looking at these Boyd Coddington wheels: https://www.summitracing.com/parts/rwa-61w-77093?rrec=true and have a few questions:

1. The 17x7 have a backspacing of 4" and the 17x8 have a backspacing of 4.5"....any recommendations on one or the other?
2. I *think* a 35" tire would look best, I was looking at 315/70/17....any input if that makes sense?

 

[toddz69]

Hi all, I'm so lost in choosing the right rim/tire combination. I'm looking at these Boyd Coddington wheels: https://www.summitracing.com/parts/rwa-61w-77093?rrec=true and have a few questions:

1. The 17x7 have a backspacing of 4" and the 17x8 have a backspacing of 4.5"....any recommendations on one or the other?
2. I *think* a 35" tire would look best, I was looking at 315/70/17....any input if that makes sense?

That would probably look pretty good with that combo.

Todd Z.

 

[chuddy]

So I mocked the rim/tire up, and it's clear that the tire is too large. I'm going to try a 235/80-r17 next and see if that works better.

 

[duffymahoney]

Did you move your axle back?

 

[chuddy]

Did you move your axle back?

I don't believe so, I purchased this as an unfinished project from a guy, so I can't confirm what was done to it.

 

[duffymahoney]

I don't believe so, I purchased this as an unfinished project from a guy, so I can't confirm what was done to it.

Axle back 1" helps a ton. I running 265/70-17 or something now.

 

[DirtDonk]

Which wheel was that you mocked up with? The 7, or the 8? The 8 would be sticking out slightly more to the outside, but you have two clearance issues it looks like.
One is the width, which hits the body opening at the top. But it also makes hitting the leading edge there even more of a problem. Which is the second issue, and that's that a tire with a larger diameter is going to hit that leading edge.
Hence the mention of moving the axle back an inch or so. Common issues with larger tires and uncut rears.

Paul

 

[chuddy]

Which wheel was that you mocked up with? The 7, or the 8? The 8 would be sticking out slightly more to the outside, but you have two clearance issues it looks like.
One is the width, which hits the body opening at the top. But it also makes hitting the leading edge there even more of a problem. Which is the second issue, and that's that a tire with a larger diameter is going to hit that leading edge.
Hence the mention of moving the axle back an inch or so. Common issues with larger tires and uncut rears.

Paul

Agreed, I'm in the process of moving the axle back 1" to center it in the wheel well. These wheels are the 8" wide version with 4.5" of backspace. The 7" wide version has a 4" backspace, would that fit better?

 

[DirtDonk]

Not accounting for slight variations in what's what and where, the wider 8" wheel will have 1/2" of it's bead sticking further out than the narrower 7" wheel will.
That half-inch might not be much (it isn't!) but it's still in the wrong direction from what you want. In other words, the 8" wheel pulls things outward slightly, where they are more likely to interfere with the body.
Will going to the 7" wheel cure the issue by itself? Not likely, but it can only help.

Paul

 

[chuddy]

Not accounting for slight variations in what's what and where, the wider 8" wheel will have 1/2" of it's bead sticking further out than the narrower 7" wheel will.
That half-inch might not be much (it isn't!) but it's still in the wrong direction from what you want. In other words, the 8" wheel pulls things outward slightly, where they are more likely to interfere with the body.
Will going to the 7" wheel cure the issue by itself? Not likely, but it can only help.

Paul

After doing some reading, it looks like the lower the backspace, the further out the wheel sits. So while the 7" rim is narrower, it also has a smaller backspace which would seem to cancel out the "narrowness", if that makes sense. Correct me if I'm wrong, I'm still trying to figure this stuff out.

 

[DirtDonk]

You're correct in what backspacing is, but not the cancelling out part. Hopefully someone will correct me if I'm wrong, but here's how I see it.
Backspacing is the measurement from the wheel mounting surface (where it touches the axle/drum/rotor) to the inside edge of either the bead, or lip. I think it's the bead, but don't quote me on that. I always get them mixed up and "offset" uses the other surface.

So, you have one wheel with a width of 8 inches and a backspacing of 4.5 inches. Leaving 3.5" of wheel outside of the mounting surface.
You have a wheel with a width of 7 inches and a backspacing of 4 inches. Leaving just 3" of wheel outside the mounting surface.
The difference of the two is that half-inch that I mentioned. That 1/2" is OUTSIDE of the mounting surface, pushing the wheel and at least part of the tire outward by half an inch.
It's not much, but seems to me that right now you're counting fractions of an inch and even millimeters to get that tire tucked in.
Wheel width differences of an inch do not make a notable difference in the width of the tire at the tread. Or even much of the sidewall in fact. Usually it's wider ONLY at the bead itself. So it's more that half inch backspacing difference than it is the width of the wheel acting on the tire.

So, narrower wheel for me, along with probably a narrower tire. Maybe...

Paul

 

[chuddy]

You're correct in what backspacing is, but not the cancelling out part. Hopefully someone will correct me if I'm wrong, but here's how I see it.
Backspacing is the measurement from the wheel mounting surface (where it touches the axle/drum/rotor) to the inside edge of either the bead, or lip. I think it's the bead, but don't quote me on that. I always get them mixed up and "offset" uses the other surface.

So, you have one wheel with a width of 8 inches and a backspacing of 4.5 inches. Leaving 3.5" of wheel outside of the mounting surface.
You have a wheel with a width of 7 inches and a backspacing of 4 inches. Leaving just 3" of wheel outside the mounting surface.
The difference of the two is that half-inch that I mentioned. That 1/2" is OUTSIDE of the mounting surface, pushing the wheel and at least part of the tire outward by half an inch.
It's not much, but seems to me that right now you're counting fractions of an inch and even millimeters to get that tire tucked in.
Wheel width differences of an inch do not make a notable difference in the width of the tire at the tread. Or even much of the sidewall in fact. Usually it's wider ONLY at the bead itself. So it's more that half inch backspacing difference than it is the width of the wheel acting on the tire.

So, narrower wheel for me, along with probably a narrower tire. Maybe...

Paul

Assuming you're right, then using the same tire still won't help, it would be narrower around the rim, but likely be the same width up around the tread?

 

[DirtDonk]

Well, yes and no.
It's narrower only at the bead, but it's ALSO tucked inward by that half-inch difference in where the outside of the wheel sits.
That half of an inch is a key factor here. Whether it's the key for this discussion, but whether or not it turns out to be the key to fitting without hitting, I'm just not sure.
Hence the hedging of bets by bringing narrower tires into the discussion as well.

It's nice that you can test fit these things. Is everything in the shop you're working at? Or do you have to order the other wheels?

Paul

 

[DirtDonk]

Also, you're there, but we're out here. Happen to have another picture more from the tail end, to see just how wide the tire is? It sure looks close, but maybe not close enough for that half an inch to do the trick.
Can't really tell from here.

Paul

 

[chuddy]

Well, yes and no.
It's narrower only at the bead, but it's ALSO tucked inward by that half-inch difference in where the outside of the wheel sits.
That half of an inch is a key factor here. Whether it's the key for this discussion, but whether or not it turns out to be the key to fitting without hitting, I'm just not sure.
Hence the hedging of bets by bringing narrower tires into the discussion as well.

It's nice that you can test fit these things. Is everything in the shop you're working at? Or do you have to order the other wheels?

Paul

Thanks, I'm going to order a 17x7 and see how it goes, I will definitely document in this thread so others can see.

 

[DirtDonk]

Thanks! That'll be good information for sure.
And while you're at it... (naturally there's always more) maybe take your own on-site measurements of the backspacing to see just where the manufacturer is taking the readings.
And measure the tires overall dimensions even though the weight of the vehicle is not on them at this point. That way you can see just where the tire changes, or does not change, for the wheel width change.

Paul