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Torrance00

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Hello All

Because of a laziness on my part I was forced to install a pair of 235\70 R 15
on the rear of my 74 Dart.
I have done a lot of reading on here and what size people are putting on there cars.
So with that in mind, here is what I found with the above setup on a stock
rear axle and no mods, there is no room between the Tire and body, I can not
even get a finger between the two. Also when looking at the backside of the
tire, I would say there is not 1" between the tire and the spring.
I've read where 245, have been installed.... ?????
I now notice that making a turn and or going up a driveway the tire rubs a little....
don't like that.
I don't know why the pic is on it's side, not my doing...sorry though.
Best
 

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I have a 67 Dart with no mods on rear. I have 245/50/17s on it. I could go with a 255 but would need a spacer. The rims are 7inch wide with a back space of 4inches. Unfortunately i have 215/50s on the frt and they are a tad to wide/tall. They hit the frt aspect of fender. Got to go narrower. What is the width of the rim you have?235 is 235mm wide and 70% of that is in height.......
 
using the tire size calculator your tires are 28 inches tall 9.3 inches wide.......mine 245/50/17 are 26.5 inches tall 9.7 inches wide so a bit wider but shorter, Not a expert by no means. I goofed on the frt because i forgot what i had on before. Not sure if this helps or not.The tires you have are quite tall is my thinking, good luck and i hope someone else with alot more knowledge will chime in soon
 
You can run as little as 3/32 inch to the springs, and they will not rub. On the body side I am running 1/2 inch, with no issues;but my car is lowered with de-arched nearly flat springs. The springs,with poly bushings,and HD shocks,help prevent thebody to tire contact in the turns. The wheel lips are sometimes excessive, and can de trimmed, bent up, or rolled.
So that means, with proper fitment, you could run 7/8 more tire to the inside and possibly 1/2 mote to the outside. That totals 1.375, which is 35mm; and 35 + 235 = 270mm. Since the nearest available size is 255s, you can see their popularity.
275s on 8 inch rims, can be made to fit, if you move the springs inboard to under the inner house, with the offset hanger kit. The perches will also have to be moved.The offset kit is definitely worth the trouble,cuz the 275s can be centered, with a custom backspace. And you will finally have some traction! And the back will finally stay in the back, during spirited cornering! And they look pretty cool in there!
275/60-15s are about 28 tall. 275/50s are about 25.8 tall
I see you have helper springs on there. With centered 275s it might be a good idea to ditch those in favor of new springs or freshened springs, depending on your intended usage. I have seen those helpers slip sideways some. IDK if they can get into the sidewalls, but it would be frightening and expensive if the could/did.
 
Simple fix: If you really have about 1" between the inside fenders and the tires, measure the backspacing of the wheels you now have and get a pair that have about 3/4" more backspacing.
 
even a 1/2" would work - so you need new wheels AND you really need new tires - tell me you're not actually running those - the dry rot is BAD. Just a side note - you could put a 1/4" spacer between the drum and the wheel.. not the best route but it'll add some clearance away from the leaf spring..

Oh - the pics are sideways because you are using your cell phone (from what I have read on other similar posts)
69_340_GTS said:
Simple fix: If you really have about 1" between the inside fenders and the tires, measure the backspacing of the wheels you now have and get a pair that have about 3/4" more backspacing.
Click to expand...
 
Scamp I know they tire is old, just had to throw something on the car at the moment..
interesting about the pic and cell phone
69, there is no 1" between the fender lip and tire, I was saying there is about 1" between
the tire and the spring..
I am not interested in moving the springs or anything else.
My reading indicates that a 245 is max on an 8" rim
Since my plan is to keep the wheels, I'll go one size narrower 225\70r 15 or even a 65
if I can get it...that should bring the speedometer back to calibration
from my reading a 245 is max width on an 8" rim...
thanks for the info guys.. always helps
 
Here is a formula for figuring the checking rim width that I think all tire manufacturers use. ............ Section width/25.4 x .7 = checking rim width.so with 245s it looks like this
245/25.4 x .7 =6.75. That means the section width was determined using probably a 7 inch rim. On an 8 inch rim, the section width will be wider(perhaps 255), cuz the beads are spread an additional inch.At the bottom of the catalog page is a note that indicates that you can usually mount any tire on a rim that is within 1 inch of it's checking width;so in this case the 245 can be mounted on a rim between 6 and 8 inches.The tire pressure may need to be adjusted to get the tread to sit flat to the ground, and thus provide optimum tire wear.

But you can work the formula backwards as well. Say you have an 8 inch rim and want to know what the optimum tire size would be to fit on there.
...............section width/25.4 x .7 = checking rim.........rearranging ,we get
..........section with = checking rim x 25.4/.7 = 290.
So, the tire manufacturer would build a tire, slam it on an 8 inch rim, and check the sidewall section and find it to measure 290mm, and he would then publish that in the catalog. And down on the bottom of the page it would allow a plus/minus of 1 inch.

Now most guys will tell you that an 7 inch rim is just way wrong for a 290, and I would agree. It will corner horribly.But at 9 inches it would be fine. I would not install it on an 8 inch either.But this is how the tire manufacturers determine the section widths.
Personally, I have had excellent results with 275s on 8inchers. Long tread life, with good manners at reasonable tire pressures.The checking rim for 275s is 7.6 inches.

The checking rim for 225s is 6.2 inches.So they would normally be mounted on rims between 5 and 7 inches, with 6 being the sweetspot. If you can actually get them mounted on 8 inchers,they will not do well. It will take a lot of tire pressure to get them flat to the road, and if one goes flat and pops off the bead, you will have to visit the tire shop to have it re-seated.If they are not inflated to run flat to the road, then the outside edges will be taking all the load. the carcass will overheat from flexing and kill tire life. And with any alignment error it will steer like chit.
I urge you to reconsider.

FWIW. It's a pretty safe bet that, whatever rim width you are using, you can mount a tire on it that has a similar tread width. So on an 8 inch rim, you can mount a tire that has a tread width of 8 inches. Unfortunately tire manufacturers do not normally supply tread widths on P-type tires. So bring a tape-measure,when you go shopping.
 
AJ/FormS said:
Here is a formula for figuring the checking rim width that I think all tire manufacturers use. ............ Section width/25.4 x .7 = checking rim width.so with 245s it looks like this
245/25.4 x .7 =6.75. That means the section width was determined using probably a 7 inch rim. On an 8 inch rim, the section width will be wider(perhaps 255), cuz the beads are spread an additional inch.At the bottom of the catalog page is a note that indicates that you can usually mount any tire on a rim that is within 1 inch of it's checking width;so in this case the 245 can be mounted on a rim between 6 and 8 inches.The tire pressure may need to be adjusted to get the tread to sit flat to the ground, and thus provide optimum tire wear.

But you can work the formula backwards as well. Say you have an 8 inch rim and want to know what the optimum tire size would be to fit on there.
...............section width/25.4 x .7 = checking rim.........rearranging ,we get
..........section with = checking rim x 25.4/.7 = 290.
So, the tire manufacturer would build a tire, slam it on an 8 inch rim, and check the sidewall section and find it to measure 290mm, and he would then publish that in the catalog. And down on the bottom of the page it would allow a plus/minus of 1 inch.

Now most guys will tell you that an 7 inch rim is just way wrong for a 290, and I would agree. It will corner horribly.But at 9 inches it would be fine. I would not install it on an 8 inch either.But this is how the tire manufacturers determine the section widths.
Personally, I have had excellent results with 275s on 8inchers. Long tread life, with good manners at reasonable tire pressures.The checking rim for 275s is 7.6 inches.

The checking rim for 225s is 6.2 inches.So they would normally be mounted on rims between 5 and 7 inches, with 6 being the sweetspot. If you can actually get them mounted on 8 inchers,they will not do well. It will take a lot of tire pressure to get them flat to the road, and if one goes flat and pops off the bead, you will have to visit the tire shop to have it re-seated.If they are not inflated to run flat to the road, then the outside edges will be taking all the load. the carcass will overheat from flexing and kill tire life. And with any alignment error it will steer like chit.
I urge you to reconsider.

FWIW. It's a pretty safe bet that, whatever rim width you are using, you can mount a tire on it that has a similar tread width. So on an 8 inch rim, you can mount a tire that has a tread width of 8 inches. Unfortunately tire manufacturers do not normally supply tread widths on P-type tires. So bring a tape-measure,when you go shopping.
Click to expand...

Thats some great info there........:glasses7:
 
Every tire company has a size chart for all their tires. It is one hell of a lot easier to just look at one of those charts! For example, click on the orange box here: http://us.coopertire.com/Tires/Passenger/COBRA-RADIAL-G-T.aspx You'll note that the tread width is sometimes on the chart too. Wheel size too. (Different manufacturers tires don't vary too much these days either.)
For a really complete analysis of tire sizes, go here: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46
 
OK all to end this conversation. there are many sites with all the tire, rim sizes
with and including best size, smallest size and largest size that will or should be used.
you don't put a 255 on an 8" wide rim....
After reading countless posting about tire size, and there are a few in this posting
I measured the physical opening, from wheel well lip to spring, from drum face to spings
from drum face to wheel well lip. and I thought I had more space then what I actually have.
Again the Tires are old, still hold air and have decent tread...but I never attended them to
be on this car, I had to use them just to have something for a few days,
I am going with a 225 tire instead of a 235 and If I can probably go with a 65 or 60
to keep the speedo close to factory, the 235\70r 15 are way to tall at 28" compared to the
factory tire E78 at 26"
I laugh at myself, after decades of laughing at others, who stick huge tires under there
rear fenders, and knowing they must rub, plus the ride difference...
Now I'm only talking about stock bodies, no flares, tubing, moving springs....
Best

225 = 8.85 width, 235 is 9.25.
Anyway like always there is healthy debate which I like.
 
Torrance00 said:
Hello All

Because of a laziness on my part I was forced to install a pair of 235\70 R 15
on the rear of my 74 Dart.
I have done a lot of reading on here and what size people are putting on there cars.
So with that in mind, here is what I found with the above setup on a stock
rear axle and no mods, there is no room between the Tire and body, I can not
even get a finger between the two. Also when looking at the backside of the
tire, I would say there is not 1" between the tire and the spring.
I've read where 245, have been installed.... ?????
I now notice that making a turn and or going up a driveway the tire rubs a little....
don't like that.
Click to expand...

How much room do you have to the leaf springs?

It's all about the backspacing. Also if you run a given tire on a wider rim the section width increases. A lot of guys here put big tires on small wheels. The result is a decreased section width and decreased footprint, thus sacrificed traction.

You can fit 9.65" section width under an unaltered 67-69 dart. That is a 235mm tire.

Some 245's will fit and others wont' you have to look VERY carefully at the section width and the rim that the tire was rated with.
 
Torrance00 said:
you don't put a 255 on an 8" wide rim....
Click to expand...

Why the hell not?

With a section width of 10"+ and a tread width of 8" + and 8" rim is pretty ideal.

Manufacturers minimum rim width on a 255 is 7" and the max in 9". (7+9=x)/2)
 
That^^
And 255/25.4 x .7 = 7.027 checking width. And at the bottom of the tire-page is the +/- 1 inch proviso; so the rim can be 6 to 8 inches. Thus 8 is a natural for 255s.

The section width will change when the tire is mounted on a rim size other than the checking rim. I have no spec for that , plus it's a moving target.
I would guess the change is small. Perhaps the 255 section width,on an 8incher might be closer to 265, or 10.43inches.
 
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