Sorry guys, i got a quick question about rims

[mhale71]

17" Japanese s15 s14 Silvia Skyline Wheels Rims & Tyres - eBay, Wheels and Tyres, Car Accessories Tuning, Cars, Bikes Boats. (end time 02-Oct-07 18:53:41 AEST)

NOW, i know that i need 5X114.3 , with 40 mm offset, and i dont really wanna lose a ton of performance by changing the shoes of the car, meaning im after a lightweight rim that doesnt change the total diameter, i have emailed the guy asking for the weight, wich he might not be able to give me because of the tires, i know that stock 6 wheels are 23lbs, or 40lbs with a tire according to someone on here (see, i can search).

What i am mainly curious about is that he says that the rims are 17X8 offset 38mm at the rear and 17X7.5 offset 30mm at the front, 255X40X17 on the rears and 235X45X17 on the rear.

Compare this with the stock 15X6, and my tires are 205/55R15 87V

i know 205 means thickness, 55 means % ofthickness as height, and 15 is the internal diameter, so i calculated

2(20.5 X .55)+38 should equal overal external diameter, i broke out a tape measure and it does, so sub in with these rims...

2(25.5 X.4) + 43.2 = 63, so a rough increase in diameter by 3-4cm, for the "rears"

2(23.5 X .45) + 43.2 = 64, so rough increase about 4-5cm for the "fronts"

with the 30mm offset, i will need a 10mm spacer right?, and with the 38mm offset ill need a 2mm spacer yes?

Also, will the somewhat 2" increase in width mean that these will rub on the inside of the wheel wells?

So basically im asking will these wheels fit my 6 , this is the info i have, All help is appreciated..

--mike

[I4MX6]

Yes they will fit, but it wont look right. The offset on the front indicates they will stick out 8mm more then the rear will. And with those tire sizes you might be close to rub. Look at the picture of mine with the 19's on in the Mazdaspeed thread and you'll see what 30mm offset's could look like. Take into consideration my suspension is different and so is my camber settings.

I wouldn't do it if I were you. I'd take the time to find something with the same offset on all wheels. A 35 offset will be perfect...well that or a 38...

[Evert]

Front will stick out more by 28mm and have 2mm less clearance inside wheelwell.
Rear will stick out more by 26mm and have 12mm less clearance inside wheelwell.
Basically the specs are so far off that you don't need to even bother about spacers etc.

[mhale71]

Ok thanks guys, i didnt get them.

My next question is : Its my understanding that a thicker rim will grip to the road better = better handling and perhaps acceleration (thanks to less wheelspin perhaps?[[shizzle] driver]), of course only with the right tire. So, with the same offset, will the extra inches of thickness poke out on the outer edge of the rim, or the inside edge, or will it be an even spread?, AND, what would be a good offset for a 17X7 or 17X8 rim? I4MX6 your car looks awesome but i would never get 19"rims, and 9" i imagine is wider then the average 17.
thanks,
--mike

[Blake]

Think of it this way...the more rubber you have on the ground the better grip you will get. The bigger the rim the worse the acceleration. To my understanding the wider tire will have an even spread but will stick out a little from the rim.
To me big wide bulky tires on such a small car is just dumb. I would just get an average size.

[neptune_51]

im now running a 235/45/17 on a 17x8 rims and it looks very aggressive with the current stance. The edge of the tires are almost flush with the fender and it looks mean

[I4MX6]

Originally Posted by mhale71

Ok thanks guys, i didnt get them.

My next question is : Its my understanding that a thicker rim will grip to the road better = better handling and perhaps acceleration (thanks to less wheelspin perhaps?[[shizzle] driver]), of course only with the right tire. So, with the same offset, will the extra inches of thickness poke out on the outer edge of the rim, or the inside edge, or will it be an even spread?, AND, what would be a good offset for a 17X7 or 17X8 rim? I4MX6 your car looks awesome but i would never get 19"rims, and 9" i imagine is wider then the average 17.
thanks,
--mike

Well the 19's weren't mine nor would I ever buy wheels that size...its overkill. But thank you for the comments none the less.

As far as width and size, well Blake is right, wider equals more grip and diameter equals less acceleration. But their is a lot to consider at this point too. Wider can also make turning harder since there is more rubber on the ground to pivot. But these cars have been proven well at track with 8" wide wheels, so don't worry too much about that. Diameter is rotational mass. No matter how light the wheel is, its still heavier on the ends then the stock 15's in reality. Try to get as light as possible without breaking the bank because it will not only keep stress off wear and tear components such as the transmission, but also improve mileage since the car isn't working as hard to move the weight of the wheels.

When buying tires, keep the diameter around stock. Although taller tires make the car look lower in relation to the wheel well, they do increase the overall diameter of the wheel and as discussed above, that reduces mileage and causes wear and tear to drivetrain. If you go with a 17x8, go with a tire like a 215/40R17. Its close to stock, wide enough, and easy to come by. Or you can go with something odd like a 245/35R17 but the cost is a little higher for just a bit in width. The 215/40 will have a bit of stretch too which will prevent a lot of tire sidewall play while cornering, so keep that in mind too. Wider may look cool, but match it to the wheel of appropriate size.

Now I get a lot of flack usually for the tire sizes, but its worth it to keep everything the same size. A 215/45R17 is very common amongst members here, but its too tall in compared to stock. So like I said, try to stay at a 24" tire diameter.

[michaelreich]

I just want to make a brief comment. For a given tire design (i.e. - radial), the actual sq. in. of footprint on the ground is the same for a given tire pressure and vehicle, no matter dimension the tire is. The only thing that changes is the shape of the footprint. A wide tire will give a short, wide footprint and a narrow tire will give a long, narrow footprint, but the actual area stays the same.Just my two cents...

[ragincanadian4]

Originally Posted by michaelreich

I just want to make a brief comment. For a given tire design (i.e. - radial), the actual sq. in. of footprint on the ground is the same for a given tire pressure and vehicle, no matter dimension the tire is. The only thing that changes is the shape of the footprint. A wide tire will give a short, wide footprint and a narrow tire will give a long, narrow footprint, but the actual area stays the same.Just my two cents...

You bumped this thread for that? Really?

[mhale71]

well, lets discuss it rather then flame him, what the hell did he say?

[Biffmeistro]

He basically said tire width doesn't increase contact patch.

A narrow tire with the same PSI will have the same size contact patch as a wide tire with the same PSI.

[ragincanadian4]

And I vote that he's wrong.

[Biffmeistro]

But he's not wrong. Contact patch doesn't increase when you widen the tire. The contact patch is only a matter of tire PSI and car weight. A wider tire just makes a wider patch from side to side, but shorter from front to back.

The reason a wider tire is good for drag racing is that you can lower the PSI and increase the contact patch without loss of tire stability.

The reason a wider tire is good for road racing is that it's more stable, and has more lateral grip. Very simply illustrated by the fact it's harder to push over a wide tire than a narrow one if they were just standing free. A fairly similar concept to the lateral grip aspect.

[ragincanadian4]

Rrrrrrrrriiiight.

[91turbo666]

a quote...

Originally Posted by Mr. MX6

A drag strip is not slipy like the road mate...


There are several issues that must be considered when choosing a dragster tire. Friction is surface-area independent in only a few ideal examples.
The real world is more complicated. Especially for tires that are made of rubber. You want to choose a width, height, and tire compound that gives the best friction for the duration of the race.
Top fuel dragsters have one-speed transmissions and slip the clutch during the run.
In engineering it is commonly thought that the friction force is proportional to the force pushing the two surfaces together.
This is only correct over a certain range of conditions and materials. The constant of
proportionality is called the "coefficient of friction." The coefficient of friction depends on the material and condition of BOTH of the surfaces beingrubbed together.
It is small for DuPont's Teflon (TM) rubbing on DuPont's Teflon (TM), larger for DuPont's Teflon (TM) rubbing on wood, much larger for wood rubbing on smooth concrete and very high for wood rubbing on rough concrete.

However, if the surface becomes actually sticky, then conventional 'friction' theory simply does not work. It is possible to have large friction forces in the absence of a force pushing the two surfaces together.
In fact, because the surfaces stick together when you try to pull them apart, a negative static friction coefficient is possible.
I made a phone call to a company that makes dragster tires and their racing expert (Les Garbicz) provided me with some information. For most dragsters, certainly top fuel, the tires and track are sticky like scotch
tape or flypaper. The tires may be inflated to only 7 psi and are fairly large. Thus, the contact area between tire and track can be a couple of square feet. (Each tire is 17 inches wide and the contact length is as much as 10 inches front-to-back). This enables acceleration to be up to five times that of gravity. The contact area decreases as the speed goes up.The flypaper analogy is a useful image to illustrate the stickiness mechanism.

However, the tire is not a flat surface sticking to a flat track surface. It is a rotating ellipsoid-shaped surface being compressed onto a flat unmovable surface.
These ‘flypaper’ bound aries are localized on the surface and are made and broken as the tire rotates through the footprint. The rubber compounds that are used have the property that
friction is low when cool. (Not really low, just lower than when hot).

The friction increases with increasing temperature, even including the temperature when the rubber starts to melt. During a burnout, there is some melting of the surface, but the tires do not actually get runny and
slippery. Prior to the race, the driver does a “burnout.” This short burnout liquifies a thin layer on the surface of the tire. This only makes the tire tacky and cleans the surface. This clean tacky surface grips the track very well.

A wing is attached to top fuel dragsters that produces a downward force. The downward force can be as much as 8000 pounds on a 2000 pound machine when traveling 300 mph. Thus tire slip is not a problem at high speeds. Centripetal force at high speeds keeps the tire from being squashed by the downward force of the wing. Increasing tire diameter and tire width increases the contact area. But there is a limit - a very
large tire would not be well matched to the engine or axle * the torque becomes impracticable.

When slip occurs between tire and track, the slip is not like a normal automobile tire where the tire slides on the road. Race tracks that are a quarter of a mile long are built of concrete and asphalt. The first 330 feet or so is concrete. The rest is asphalt. A new fresh track has a liquid rubber primer sprayed onto it which then dries. It is then mechanically abraded by a tractor pulling old tires across it.
Asecond coat of primer is sprayed on. The result is sticky. During the races, more sticky rubber is transferred to the track. This, as well as the sticky nature of the rubber, accounts for the tremendous friction.
Rubber is made into a useful tire by the process of curing at the factory. At a temperature much above 400F the rubber reverts to its uncured state, and becomes almost liquid. Obviously, the tire will fall
apart if the body of the tire becomes that hot. If a dragster tire is abused or under inflated, the internal temperature can get very hot during the race, and racers make sure not to do that. The internal
temperature is different from the surface temperature.
When the racer does a 'burnout' prior to the beginning of the race, this liquifies a thin layer on the surface of the tire for good traction.
The inside stays cool, and the clean, tacky surface is ready to race.

Aside from the friction issue is the “abrasion” factor. If the load is too high, the tire surface starts to form shavings instead of smoothly getting tacky. The shavings act like little bearings. Thus friction
plummets. The rate of this friction drop seems to be related to the “recipe” of the compound, also is related to its hardness (modulus). A a softer compound may become “greasy” on the track, leaving thick black lines on the surface while slightly harder compound may abrade into
shavings with tearing.
Fracture lines across the tread surface is called “graining” by engineers. These effects describe and explain the sliding coefficient of friction zone identified with high tire slip.

To make sticky surfaces adhere, you need to push them together. That is why you push down on sticky tape. Thus, there is a controversy about what happens when the leading edge of the dragster tire
slams down onto the strip as the tire rotates. It has been argued that this 'push' downwards causes the tire to grip much better than if it were gently rolling along.
Overall this is why tires need to be wide: a tire that is too narrow will abrade (which is bad) instead of getting tacky (which is good).