![[Datsun 1200 encyclopedia]](/wiki/upload/wiki.png)
| Revision as of 23:54, 31 January 2012 ddgonzal (Talk | contribs) (->Overview) <- Previous diff |
Revision as of 00:33, 1 February 2012 ddgonzal (Talk | contribs) (->Measuring Offset) Next diff -> |
||
| Line 37: | Line 37: | ||
| = Measuring Offset = | = Measuring Offset = | ||
| - | Wheel Offset is the difference between the flange and the wheel centerline. You don't need to know the width to measure Offset. | + | Wheel Offset is the difference between the flange and the wheel centerline. |
| + | |||
| + | http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/Offset/WheelOffset_A.jpg | ||
| + | |||
| + | http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/Offset/WheelOffset_B.jpg | ||
| + | |||
| + | http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/Offset/WheelOffset_C.jpg | ||
| + | |||
| + | Technically, you don't need to know the width to measure Offset. As long as you can establish the centerline. | ||
| # Lay wheel flat on the ground (outside face down). You can also do this with tire mounted if it is aired up. | # Lay wheel flat on the ground (outside face down). You can also do this with tire mounted if it is aired up. | ||
Revision as of 00:33, 1 February 2012
The Datsun 1200 stock wheel is 30 mm positive offset (mounting face is 30mm outboard of the wheel's center line). This offset perfectly centers the tire inside the wheel housing. Note that the offset number is not directly related to wheel width or diameter, but is just the measurement relative to the wheel centerline.
Contents |
Overview
What wheel offset is best? You often hear "I used such and such and it worked" but rarely give the suspension mods, tyre size, body modifications or disclosed if and how much it rubs. Actual measurement and details are needed. Let's start with a stock size tire and stock width wheels.
STOCK = 30 mm offset
+30 offset is optimum for Datsun 1200, as the wheel hub face is exactly -30mm offset in the middle of the wheelwell. So a 30 offset wheel will center the tire in the well, allowing the maximum width within stock bodywork.
+30 centers the tire (and wheel) in the wheelwell:
Less postive offset will move the tyre outboard:
Additional positive offset will move the tyre inboard:
The offset doesn't mean much without knowing the tire width. All offset will tell you is if the tires will be offset towards the vehicle centerline (more + offset) or away from the vehicle centerline (more - offset). But it doesn't say how far the edge of the tire will be from the body -- for that you need to know the tire width along with the offset.
Stock Offset| model | Wheel type | Offset | wheel width | Tire width |
|---|---|---|---|---|
| B110 | steel | 30 mm (1.18 in) | 4" wide wheel | 155 mm |
| B210/B310 | steel | 30 mm (1.18 in) | 4.5" | 155 mm |
| B210/B310 | aluminum | 25 mm (0.98 in) | 5" wide wheel | 175 mm |
From this table we might conclude:
- Using B210 wheels on B110 results in a 1/2 inch wider tread width (measured from outside-sidewall to outside-sidewall). NOTE: These still fit under unmodifed B110 fenders.
- B210/B310 Factory Steel vs. Aluminum wheels may have different widths, but have close to the the same overall width as installed. The wheels are 1/2" wider (13mm), but offset on each side is 5mm less. So the outside edges as-installed are less than 2mm further apart from each other than the narrower steel wheels.
- The option wheels came from the Datsun 610, so the offset is not specific to the B210.
Measuring Offset
Wheel Offset is the difference between the flange and the wheel centerline.
Technically, you don't need to know the width to measure Offset. As long as you can establish the centerline.
- Lay wheel flat on the ground (outside face down). You can also do this with tire mounted if it is aired up.
- Lay straightedge or straight sawn lumber piece across it, measure to the ground.
- Measure down to the flange back face
- Subtract the two measurements. Offset = (1/2 width) - (distance to flange)
- Zero Offset: The wheel is centered exactly over the hub face
- + Offset: The wheel is offset towards the inside of the car
- - Offset: The wheel is offset towards the outside of the car
The centerline can be the center of the overall wheel width, or the center of wheel rim width, or the centerline of the tire width. Either method will establish the centerline.
Offset Charts
1200 Sedan Wheel hub is offset -30 mm from centerline of the wheelwell. So +30 offset wheels will perfectly centered inside the fender.
A zero-offset wheel will be positioned to the outside of the Sedan as in this photo. Note that the wheel is flush with the body, but has an excess of clearance to the leaf spring.
(a +30 wheel would center the tire)
Face measure: ~80 mm (3-1/8 inch) +30 = centerline of well
Back measure: 140 mm (5-1/2 inch) -30 = centerline of well
Optimum offset: +30 for tires up to 175-wide front, 195-wide rear
No Body Mods
REAR SEDAN Tire size Min. Max. Offset 155/80R12 6 58 165/70R12 7 56 165/55R12 12 52 175/70R13 16 48 185/60R13 21 43 195/60R13 26 38
NOTE:
- At the min offset, the tire will be very close to the outer bodywork.
- At the max offset, the tire will be close to the leaf spring.
With Rolled Guards
REAR SEDAN Tire size Min. Max. Offset 205/45R16 23 29 205/60R13 24 27
With 1" Flares
REAR SEDAN Tire size Min. Max. Offset 205/55R14 2 25 215/50R14 5 22 225/50R15 8 18 235/45R17 10 17
Choosing Wheel Offset
When choosing aftermarket wheels, a small amount of positive offset is desirable. This preserves the original suspension design factors and loads on the bearings.
- Stock +30 offset works with up to 175-width tires (requiring 5" to 6.5" wide wheels).
- For wider tires, you must use less wheel offset to move the tire further outboard (away from the spring). But this may foul the bodywork.
The offset and wheel width work together to locate the wheel inside the bodywork.
Negative Offset "Deep dish" old-school wheels have lots of negative offset
Positive Offset FWD wheels typically have lots of positive offset Datsun 1200 stock wheels have a mild amount of postive offset
wheel offset and backspace diagram
Normal Width Tires
For tires from 155-wide to 175-wide (front) up to 195-wide (rear) use a +30 offset.
The rear wheel mounting face (face of the drum brake) is offset -30mm from the center of the wheelwell. So using a +30mm offset wheel perfectly centers the tire in the wheelwell. Just like the stock wheels (+30 offset). Those clever Datsun engineers!
SEDAN
It may be possible to get 215-width tires under the stock bodywork (with Rolling the Guard) and fender pulling. Club member orange-1200 reports he has 215/40R16 on 7" wide wheels. The tires rub with a heavier than normal load or when going over a bump.
TRUCK
matty has reported fitting 225/45R15 under the rear of his ute.
Narrow Tires
For skinny tires, you may wish to move the tire outward close to the fender, giving it a more full look. A +10 offset for 155-width tires or +15 offset for 165-width tires will do this.
Extra-Wide Tires
For tires wider than 175-wide (front) or 195-wide (rear), they will only fit by moving the into the fender opening. This will be OK for 185/205 by rolling the guards.
For even wider tires, use a very low profile tire so it won't go up and hit the fender lip, or better yet add fenders flares.
Here are some reports by club members indicating what offsets they have made work. Many of these place the wheel face outside of the fenders.
- Zero offset works well up to 6"-wide wheels.
- 6.5 and 7" wheels need to be tucked inside a a little more and so require +10 to +15 offset.
- 8" wheels need to be tucked outside to fit, so require -5 or more negative offset and will stick out past the bodywork.
FWD Wheels
NOTE that front-wheel-drive cars use wheels with highly positive offsets. This is to say that the mounting surface is far outboard of the wheel's center line, with the wheel tucking inside. Often they will fit the 1200 if wheel spacers are used to bring the mounting surface back toward the wheel's centerline.
wheel spacers
Offset for Wider Diffs
When fitting a wider diff, you can still fit the same tires if wheels with a different offset are used.
For example if the diff is 50mm (2") wider, use wheel with 25mm more positive offset. Then the tires will be centered in exactly the same place. 165 tires can work with +55 offset wheels.
Wider tires on +55 wheels will cause the tires to hit the leaf springs, but using less offset will push the tire outside.
NOTE: Because the offset is the measure relative to the centerline, and so is Track, the wheel and tire diameter are irrelevant to this diagram. So is the wheel width. The offset only specifies the centering factor.
Wheel & tire width do become important in figuring out if the tire will hit the bodywork or foul on the leaf spring. For tires too wide to fit inside the bodywork, you can either move the leaf springs inboard (difficult) or use a less-offset wheel to push the tire outside the bodywork. Small diameter tires will be OK, but large diameter tires will needs mods to the body such as cutting the opening larger and covering it with an overfender flare.