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Sanctifier
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 Posted: Sat Sep 16, 2006 8:51 am Post subject: Evo Tech: ~Rims & Tyres~ |
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#2. Evo Tech: ~Rims & Tyres~
Taking Important Measurements.
Source: http://www.ccwheel.com/files/technical.php (scroll to last article.)
| Quote: | OFFSET is measured from the centerline of the barrel of the wheel to the hub mounting surface. If that hub mounting surface were in the exact center of the barrel of the wheel the offset would be �0". If the mounting surface is away from the center of the wheel the offset is measured in millimeters. There are 25.4 millimeters to an inch. So if the mounting surface is 12mm from the centerline of the wheel it has a 12mm offset. That would also mean that it is about � inch. If the mounting surface is moved away from the vehicle that is a positive offset.
The picture shows a wheel with the positive offset. A positive offset will cause the wheel to set in or tuck into the vehicle. Originally you found positive offsets on just front wheel vehicles. Due to that some people refer to positive offset wheels as front wheel drive offsets. Currently there are many rear wheel drive cars and trucks with positive offsets. The higher the positive offset the less it sticks out from the vehicle and it will have a higher Backspace.
If the mounting surface is moved in toward the vehicle past the centerline, that is a negative offset. A high negative offset will produce a lower Backspace. Once again the measurement in millimeters is how far away from the centerline the mounting surface is. A -24mm offset means that the mounting surface is located 24mm or 1 inch from the centerline toward the vehicle. The wheel will come out farther from the vehicle and will have that deep dish look.
WIDTH
The width of a wheel is measured inside the beads which are usually � inches. If you measure on the outside of the beads an 8 inch wheel will measure 9 inches.
BACKSPACE
Back spacing is measured from the inner edge of the wheel to the hub mounting surface. It is a convenient measurement in that, as long as the back spacing remains the same, the clearance to the suspension also remains the same. If you know the width of the wheel and the offset you can compute the backspacing. For example if you have an 8 inch wheel with a +24mm offset. An 8 inch wheel is actually 9 inches wide so if the offset were 0 the mounting surface would be right on the centerline and the backspacing would be 4.5 inches. With a positive offset the mounting surface moves off center 24mm or 1 inch toward the outer edge of the wheel. This will make the inner edge go more inside which will result in a 5.5 inch backspacing.
CENTERBORE
This is the diameter of the center of the wheel. The centerbore must be equal to or larger than the hub of the vehicle for the wheel to seat. If the wheels centerbore is the same as the hub on the wheel then that wheel is hub-centric and uses the hub to center the wheels. If the centerbore is larger than the hub then the lugs will center the wheel and that is lug-centric. When using a lug-centric wheel be sure and snug the lugs up slowly and tighten them in an opposite or star pattern.
BOLT PATTERN
A bolt pattern of 6x5.5 means it has 6 lugs and if there were a circle through the center of all the lugs the diameter of that circle would be 5.5 inches. On vehicles with an even number of lugs you measure from the center of one lug to the center of the opposite lug.
With a five-lug pattern, measure from the center of one stud hole to the center of the farthest stud hole, skipping the adjacent hole. The resulting measurement is slightly smaller than the actual bolt-circle diameter. |
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Last edited by Sanctifier on Sat Sep 16, 2006 9:37 am; edited 1 time in total |
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Sanctifier
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| Posted: Sat Sep 16, 2006 9:33 am Post subject: |
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This issue came up recently and caused quite a stink when I suggested that using bigger diameter
rear and smaller front tyres on Evo 4-6 would cause the viscous coupling (centre diff) to fail.
Matching Tires on Four-Wheel Drive And All-Wheel Drive Vehicles. Click Here
| Quote: | The ability of four-wheel drive and all-wheel drive vehicles to divide the engine's horsepower between its four tires is especially useful on loose or slippery surfaces such as sand and dirt, as well as on wet, icy or snow-covered roads. However it's important to remember that in order to transfer this extra power, the four-wheel drive and all-wheel drive vehicle's driveline mechanically connects the tires so they work in unison.
Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.
This necessitates that four-wheel drive and all-wheel drive vehicles use tires that are very closely matched. This is because different diameter tires roll a different number of times each mile as a result of the variations in their circumferences. Tire diameter variations can be caused by accidentally using different sized tires, tires with different tread designs, tires made by different manufacturers, different inflation pressures or even tires worn to different tread depths.
As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth.
 The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile.
The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile.
While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.
This makes maintaining the vehicle manufacturer's recommended tire inflation pressures and using "matched" tires on all wheel positions necessary procedures to reduce strain on the vehicle's driveline. Using "matched" tires means all four tires are the same brand, design and tread depth. Mixing tire brands, tread designs and tread depths may cause components in the vehicle's driveline to fail.
Mismatched tires or using improper inflation pressures for all-wheel drive and four-wheel drive vehicles can also result in immediate drivability problems. Some Control Trac equipped vehicles in 4Auto mode may exhibit a shutter on acceleration and/or a noise from the front driveline and transfer case while driving. Some all-wheel drive and four-wheel drive vehicles may exhibit axle windup or binding while driving. Some four-wheel drive vehicles (manual or electronic shift) with a two-wheel drive mode may refuse to shift "on the fly" into 4x4 Auto or 4x4 High at highway speeds.
Rotating Tires:
Because the front and rear tires of all-wheel drive and four-wheel drive vehicles perform different duties while accelerating, braking and cornering, tire rotation is important to even out, and maintain equivalent treadwear of all of the vehicle's tires to minimize potential driveline stresses.
If the vehicle is equipped with a matching road wheel and full-sized spare tire, they should be integrated into the vehicle's rotation pattern at the first tire rotation. This will allow all five of the vehicle's tires to share in the workload and wear at similar rates. In the event that a single tire is damaged and has to be removed from service, this will allow the tread depth equivalent spare tire to be used with the remaining three tires.
If the spare is not integrated into the vehicle's tire rotation pattern, it will not match the tread depth of the four worn tires on the ground when called into service. Additionally, if a single tire is replaced by the full size spare tire, hopefully the new replacement tire can remain as the spare tire until the other four tires have worn out and need to be replaced.
Replacing Pairs of Tires or Individual Tires:
There are several suggestions that have been offered to drivers who are replacing pairs or individual tires on their four-wheel drive and all-wheel drive vehicles. Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.
Regardless of the vehicle manufacturer's recommendations, the least stressful application is when all four tires are the same tire brand, tread design and equivalent tread depth.
Before buying pairs or individual tires for all-wheel drive and four-wheel drive vehicles, drivers should read their vehicle's owners manual or contact the dealer's service department for confirmation of their specific vehicle's requirements.
Matching Tires By Shaving Them to Maintain Equivalent Tire Tread Depths:
What does a driver do if one tire has to be removed from service when it and the other three tires have already worn to two-thirds to one-half of their original tread depth? Simply installing one new tire runs the risk of drivability problems or expensive driveline damage. Replacing the other three partially worn tires along with the damaged tire significantly increases the cost.
The Tire Rack can provide a solution by matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle by removing tread rubber from a new tire on a specialized machine that operates as a tire lathe. While this may seem counterintuitive, the value of the mileage sacrificed by the one replacement tire is considerably less than the cost of rebuilding worn driveline components.
The Tire Rack has offered a tire shaving service that has been primarily used for preparing competition tires for racetrack use. This same service can also be used to remove tread rubber from new pairs or individual street tires used on four-wheel drive and all-wheel drive vehicles to allow them to match the remaining tread depth of the other partially worn tires that will remain on the vehicle. In addition to providing equivalent tread depth to eliminate driveline stress, shaved tires will also better match the traction and handling qualities of the remaining worn tires.
While the cost of our street tire shaving service will range from $25 to $35 for each tire, it is significantly less than the cost of unnecessarily replacing the remaining two or three good tires with lots of mileage still available from them.
Here are recommendations from some of the manufactures that The Tire Rack currently serves for matching the tires used on their four-wheel drive and all-wheel drive vehicles. Additional recommendations from other Original Equipment Vehicle Manufacturers is pending.
Audi: As published in their vehicle owner's manual, "rolling radius of all 4 tires must remain the same" or within 4/32-inch of each other in remaining tread depth.
Porsche: Cayenne within 30% of the other tire on the same axle's remaining treadwear.
Subaru: Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth. |
| Sanctifier wrote: | BTW over the last few days, in heavy rain, I noticed that the rear of the Evo "pushed" at any speed over 30 mph. Even a white line was enough to cause the rear tyres to "skip" sideways.
It got so bad that it felt like suspension damage!.. but only in heavy rain  
When I checked, my rear tyres were BALD while the front still had reasonable tread depth.
Nope that didn't do my viscous coupling any good. Luckily I caught it in time.
Too much fun on the corners, I suppose.  |
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R. Mutt
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Joined: 14 Apr 2005
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Location: New York
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| Posted: Mon Dec 18, 2006 5:29 am Post subject: |
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way....I have to go for a ride with you over Christmas
Nice read btw
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Sanctifier
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| Posted: Mon Dec 18, 2006 8:11 am Post subject: |
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^ ^ ^ No problem padna.
... but trust me; it will be much more fun and even easier to drive by summer vacation. 
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Plex
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| Posted: Mon Dec 18, 2006 9:13 am Post subject: |
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| nice infor... |
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Silvermike
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Location: Chaguanas
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| Posted: Mon Dec 18, 2006 2:10 pm Post subject: |
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how is it that the "apparent offest" increases with rim width?
for instance a 7 1/2" wheel will need +52 offset to fit over the brembos, while a 81/2" will only need +32?
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Sanctifier
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| Posted: Thu Mar 19, 2009 3:38 pm Post subject: |
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| Silvermike wrote: | how is it that the "apparent offest" increases with rim width?
For instance a 7 1/2" wheel will need +52 offset to fit over the brembos, while a 81/2" will only need +32? |
To be honest... I haven't a clue! I'll have to check.
UPDATE: Here's more info on Off/Inset etc. by Tokyo Seven...
| Tokyo Seven wrote: | How To Choose Your Wheels Sizes by TokyoSeven:
On our website we list various wheels and sizes. Each manufacturer offer different designs and fitments. It is best to consult with your local professionals before making a purchase to be on the safe side. If you contact us we can offer some advice on what suits your car based on the factory stock standard setup. If you want to know about fitments with other aftermarket brand Aero Parts (Body Kits) then we will not be able to give you any advice since it varies on many factors as well as if your kit is an original and if it was fitted properly and if your chassis has not been in any accidents or warped and so on.
You can see the listing on our website for wheels as specified in the options as...
17x7J - ET49 4H-100
When broken down they each mean this...
17x7J - This is the WHEEL SIZE : 17" Size x 7" wheel width (7J)
ET49 - This is the OFFSET/ INSET or OUTSET
4H - This is the the HUB BOLT NUMBER (number of bolts on the wheel hub)
100 - This is for the P.C.D. (Pitch Circle Diameter)
WHEEL SIZE:
The 17 is the diameter of the wheel in inches from edge to edge, measured inside the flange with sizes ranging from 10 inch on the original mini's to 25+ inch on some recent demo cars as seen at events like Japan's Tokyo Autosalon and the Sema Show in the USA.
The second number (7J) is the width of the rim, again measured in inches between the flanges. The original mini used 4.5 wheels and sizes range all the way up to 12 as used on some supercars and professional race cars.
HUB BOLT NUMBER:
Number of bolts or studs, well it goes without saying that you can't fit a 4-bolt wheel onto a 5-bolt wheel hub or vice versa. Sounds obvious right?, but people have been known to fork out for an expensive set of alloy wheels only to find they've got the wrong number of mounting holes or worse yet looking a a 5 bolt setup on your car but not realising that there are a variety of options on how many types of 5 bolt setups there are.
P.C.D.:... (Pitch Circle Diameter)
The PCD, or Pitch Circle Diameter is the diameter of the invisible circle formed by scribing a circle that passes through the centre point of each mounting hole. If you've got the right number of holes, but they're the wrong spacing, again the wheel just won't fit. The PCD notation
Stud patterns and PCD values are typically listed in this notation : 5Hx114.3 This means a 5-bolt pattern on an imaginary circle of 114.3mm diameter.
HUB CENTER/ BORE SIZE:... (Centre spigot size)
This is a tricky one. The wheel bolts or studs are there to hold the wheel laterally on to the axle, but they're not really designed to take vertical load - ie. they're not designed to take the weight of the car. That's the job of the centre spigot - the part of the axle that sticks out and pokes through the hole in the middle of the wheel. It's the load-bearing part of the axle and the wheel, as well as being the assembly that centres the wheel on the axle. For the most part, the centre spigot on aftermarket alloy wheels is much larger than that of the car you want to put them on to. When this happens, the best solution is a spigot locating ring (also called a hub-centric ring) which is essentially a steel or hard plastic doughnut designed to fit snugly on to your axle spigot and into the wheel spigot.
Hub-Centric Rings are also available from TokyoSeven.com!
The image below shows the PCD (the red ring and mounting hole centrelines) and the spigot size (the blue ring). The spigot hole on an alloy wheel is normally covered up with a centre cap or cover.
OFFSET:
This is very important!!. Ignore this and you can end up with some nasty problems. The wheel offset is the distance between the middle line of the centre of the wheel width and the mounting surface of where the wheel bolts to the hub on the vehicle. The offset is described by the term "ET", which is from the German word 'Einpresstiefe' translated as 'insertion depth'. Most wheels have a positive offset which means the mounting surface is further outboard than the wheels centre. If you reduce the amount of positive ET on the wheel the the vehicles track is widened and vice versa if the ET number is reduced. Straying too far from the original offset can be detremental as fouling to the suspension and bodywork can occur as well as eccess strain on wheel bolts or studs.
The details and information here is only to be used as a guide for beginners to aid with your wheel selection process. There are more conditional circumstances which will come into play depending on the design of your car from the manufacturer, your cars particular history (ex-race/demo car or accident history etc.) so when in doubt please consult with a local professional who can inspect your car for a better detailed analysis and professional advice. TokyoSeven.com staff will endevor to assist you as much as possible when we can and within our limits.
This article was published on Thursday 19 March, 2009. |
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