Rear tire width requirements in relation to HP?

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1970dartcustom

1970dartcustom

of the Moore clan
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I was just wondering, I have seen several Mopars on here with HUGE motors and yet tiny rear tires...

How does that work??? Don't they just burn like crazy, and verge on dangerous in general around town?

In this light then, what is the balance? I have a pretty bad to the bone 383 my Dad built being put in my '70 Dart in the next couple weeks, and the rear 15x8 wheels have 255/60/r15's on them...

I felt like this was the minimum size when ordering them, (although, since it has the springs relocated some, with a bit more backspace I could go 275's looks like)...

So, am I way off base here??? With all the sweet parts going into these cars, like hardcore cams, head set ups, carbs, etc, how is it many of these have such tippy-toe tires???

(serious question, I have never built a Mo before, just drove stock 318's around)
 
Spinnin ain't winnin but less likely to break something.

Grippin is rippin more likely for stuff to break.

I run 275 bfg ta's on my 400 hp 340 and already have had to install a torque strap and bent a pinion snubber. I cant imagine drag radials or even slicks.

Thats when the u joints start to go lol
 
It's quite an thing to behold, or some of these guys are fibbers, or stuck in the past..


All kidding aside, your chassis setup, and local tarmac comes into play as well.


One of the reasons I went with 17x8 is the stickier tire compound, if you look at the UTSG grade for anything besides a drag slick in 14 and 15", you'll see nothing less than '400'. Which for the most part, translates to 'buy our hockey pucks designs from the 80's that we are beating to death...'

I'm still trying to figure out why my new tech '400' grade tires out stick my old '400' 2:1...

I guess tire tech has come a long way since the BFG T/A.
 
In addition to size, tire compound will matter as well as tread pattern. Also how the suspension "plants" the tires into the pavement before they cry out in agony!
 
Woods74 said:
One of the reasons I went with 17x8 is the stickier tire compound, if you look at the UTSG grade for anything besides a drag slick in 14 and 15", you'll see nothing less than '400'. Which for the most part, translates to 'buy our hockey pucks designs from the 80's that we are beating to death...'

I'm still trying to figure out why my new tech '400' grade tires out stick my old '400' 2:1...

I guess tire tech has come a long way since the BFG T/A.
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I assume you mean "UTQG"? Treadwear numbers indicate nothing regarding traction or rubber compound. And they only give some idea as to how long a tire will last. Per Tire Rack:

"Treadwear Grades

UTQG Treadwear Grades are based on actual road use in which the test tire is run in a vehicle convoy along with standardized Course Monitoring Tires. The vehicle repeatedly runs a prescribed 400-mile test loop in West Texas for a total of 7,200 miles. The vehicle can have its alignment set, air pressure checked and tires rotated every 800 miles. The test tire's and the Monitoring Tire's wear are measured during and at the conclusion of the test. The tire manufacturers then assign a Treadwear Grade based on the observed wear rates. The Course Monitoring Tire is assigned a grade and the test tire receives a grade indicating its relative treadwear. A grade of 100 would indicate that the tire tread would last as long as the test tire, 200 would indicate the tread would last twice as long, 300 would indicate three times as long, etc.

The problem with UTQG Treadwear Grades is that they are open to some interpretation on the part of the tire manufacturer because they are assigned after the tire has only experienced a little treadwear as it runs the 7,200 miles. This means that the tire manufacturers need to extrapolate their raw wear data when they are assigning Treadwear Grades, and that their grades can to some extent reflect how conservative or optimistic their marketing department is. Typically, comparing the Treadwear Grades of tire lines within a single brand is somewhat helpful, while attempting to compare the grades between different brands is not as helpful."


http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=48
 
71DodgeDemon340 said:
Spinnin ain't winnin but less likely to break something.

Grippin is rippin more likely for stuff to break.

I run 275 bfg ta's on my 400 hp 340 and already have had to install a torque strap and bent a pinion snubber. I cant imagine drag radials or even slicks.

Thats when the u joints start to go lol
Click to expand...

Well, my rear end is an 8 3/4 fully rebuilt with 742 posi carrier in it all rebuilt, with new bearings, seals, etc of course, n 323 gears in it, with small bolt set up, with steel wheels, with 255/60/r15's on them.
the tranny is a 727 newly rebuilt with a stage one shift kit in it,

The 383 up front is all brand new, with a healthy cam, 750 edelbrock carb, ported heads, comp springs, I am not sure about all the more specific compression and other numbers... :burnout:

SO, do you think 255/60/r15's are wide enough for this set up (just for street fun)??? I felt like they were barely enough when I ordered them.
I was gonna go 275's maybe with a little more backspace on the wheels, cuz I have enough room towards the offset springs...

Anyways, I surely can't imagine someone running the tiny tires they do with built 440's, super high horsepower strokers, or a Hemi up front... Isn't that just dangerous? Or inefficient?(This was my original question) :wack:
 
Also, does my setup seem to be one that would cause something to break especially?
What would help besides like a torque strap? (I just recently learned of their existence)
 
Do you like the way your car sits? Id say 255 are plenty especially if you are just street driving. If you can fit the 275 then that may be a better option for added grip. Id go through a trial period and only replace parts or upgrade as necessary.

Gotta remember all these cars came with what would be considered small or narrow tires.
 
71DodgeDemon340 said:
Do you like the way your car sits? Id say 255 are plenty especially if you are just street driving. If you can fit the 275 then that may be a better option for added grip. Id go through a trial period and only replace parts or upgrade as necessary.

Gotta remember all these cars came with what would be considered small or narrow tires.
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Hmmmm... Sounds like a plan to me.

Yes, the tires that came with these cars were ridiculously small...#-o
 
Any idea what that 383 is putting out?

Typical weak points are motor mounts and u joints. Also make sure you have a pinion snubber
 
Physics wise the friction doesn't change a bit because of the size of the contact patch. Real world, the wider and especially taller tire will help as it deals with imperfections in the road and heat better then the skinny tire. Most likely it's the compound on the skinny tire that isn't as good for drag racing as the taller wider tire. Plus the more tread the longer it will last in racing. There is also a point of diminishing returns. If your small block is making 300 hp you will go slower with full tubs and funny car tires because of their extra mass. If you are making 3000 hp then all that power has to be held with friction of the tires and you will make a ton of heat in those tires. Then there is the advantage of how those type of tires grow in diameter at speed giving you basically an change in gear ratio as you go down the track.

Anyway on a street car the difference in a 225 and a 265 tire will be almost 100% based on tread compound and nothing to do with size. Look at what size tire was the fastest 1/4 mile in this test
http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested
Granted we are talking a 16 sec lightweight car but still, I'd love to see a similar test done on a SRT8. I do know that Ram SRT10's were hurt straight line with their monster tires compared to the more resonable tires that came on the Ford Lignting.
 
I like my 295s cuz when Ima sliding sideways, I need all the slideways rubber I can get. With 275s that stupid pos car would want to swap ends on every stinking corner. Now with 295s,if I do get a little out of shape, I just put a little pedal on the clutch, and she snaps back and I got 'er under control again. I hate bustin' rims on curbs.(language added for effect)
255s were a joke! My S would regularly swap ends under spirited driving. I had to really be careful.275s were nearly as bad.
Somebody/everybody complains about the lack of sticky street 15s.And they are right.There are some sticky 15s but they are very pricey and sure don't last very long.I bought a front set of those back in about 2004. 245/50-15s. F1s I think were called.Man my S could corner with those. But they didn't last but 2 to 3 months of city driving, and started to lose grip at the halfway mark.
I tried some 325/50-15 BFG DRs in the stock rear tubs, but they are really tight with my lowered ride height, so I can't really blast around the turns. And on the street they don't seem to be much stickier than the crappy Coopers, so I don't run on them much. I save them for the track.
On the street,400 ftlbs will annihilate just about anything you can fit in a stock tub,all the way to 50mph,and beyond,so you might as well install the fattest, tallest thing you can fit in there. At least that's my opinion.
 
I'm running 205's on the back and they don't grip for nothing. Doesn't help they are old winter tires that were thrown on the car when I bought it. If I mat it, it'll just burn the tires through 1st, 2nd, and into 3rd before it really picks up. I can easily light them through the entire intersection if I want. Kinda makes it fun but also difficult to show up all the modern muscle. Burnouts for distance are easy, throw it in first and pin it and I've done block long burnouts. It's fun, but traction would be nice. It's getting new rims/rubber this spring. Going 245, maybe 255 if I use the offset shackles. Still haven't decided on tires. I like radial t/a but I'm still keeping my options open.
 
Lustle said:
I'm running 205's on the back and they don't grip for nothing. Doesn't help they are old winter tires that were thrown on the car when I bought it. If I mat it, it'll just burn the tires through 1st, 2nd, and into 3rd before it really picks up. I can easily light them through the entire intersection if I want. Kinda makes it fun but also difficult to show up all the modern muscle. Burnouts for distance are easy, throw it in first and pin it and I've done block long burnouts. It's fun, but traction would be nice. It's getting new rims/rubber this spring. Going 245, maybe 255 if I use the offset shackles. Still haven't decided on tires. I like radial t/a but I'm still keeping my options open.
Click to expand...


I got these cuz theyre sweeeeeet!
 

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1970dartcustom said:
I got these cuz theyre sweeeeeet!
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I like that tread. Looks good. I wonder how they compare to radial t/a's. I like the radial t/a's and have ran them lots before. I just want something that's a good street tire. Can curve corners, launch decent at the stop light and look good cruising.
 
SGBARRACUDA said:
Pinion snubber.

https://search.yahoo.com/yhs/search?p=Pinion+snubber&ei=UTF-8&hspart=mozilla&hsimp=yhs-001
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So, basically I learned from research is that pinion snubbers help reduce wheel hop and twisting of the rear. Some say good springs will make it no necessary to have a pinion snubber, but others say that it is important to have one because the higher hp you go the more it will come into play. So, it is a good idea to have? I am just using the ride for street cruising and some fun, with 235- 250 hp in a 70 dart, is it really necessary? I have extra stiff hemi springs I was told...
 
Lustle said:
I like that tread. Looks good. I wonder how they compare to radial t/a's. I like the radial t/a's and have ran them lots before. I just want something that's a good street tire. Can curve corners, launch decent at the stop light and look good cruising.
Click to expand...

My Dad runs Cooper Cobra Radial Gt's because they are 123 mph rated constant speed, have good hookup, u can still slide around a corner, and they are inexpensive (I paid 390 for all 4 from discount tire something or other on ebay)... and they look cool :)
 

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1970dartcustom said:
I got these cuz theyre sweeeeeet!
Click to expand...

I have'em on all 4 corners of my '79 Magnum. 245/60/15.

To address your tire size question, which has mostly been answered, there is no real direct formula for tire width/height vis HP &/or TQ output. As Larry Shepard once put it, on a drag car, the wide tire is only good and used for launch and to a lesser degree, the two shifts of the transmission during the race. Otherwise, it's just along for the ride. A wide tire just becomes resistance. Wind and rolling.

Cars with a narrow tire and big output engines are not putting the hammer down hard on launch but simply and gradually getting into the throttle. The things that aid a smaller tire besides a light pedal are the same for the drag racer. Weight transference on to the rear wheels and overall weight of the car.
 
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