18" ET 40 and lowering?
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01-17-2004, 03:50 AM
Join Date: Feb 2003
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#2
01-17-2004, 04:27 AM
4th Gear
Join Date: Nov 2002
Location: Kalamazoo, MI
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Since I started viewing this forum in 9/03 and later as a MCO/NAM member, I've copy and pasted valuable information into 61 pages of "MINI Stuff" for future reference. So I went back and pulled the following up for you. Didn't copy who and when this came out.
SMKKVK
PS My MINI technician at BJ MINI was against the use of spacers.
------------------
S-Lites Spacers and Wheel/Tire Theory
Rubbing aside, I would not go more than the 5mm spacers behind your S-Lites. Also, I wouldn't use an aftermarket wheel with a negative offset of less than 45mm. Here's why:
Reducing negative offset, whether by changing to aftermarket wheels or adding spacers, has both advantages and disadvantages.
Good:
- Wider track for improved handling
- Fills wheel openings for better appearance
- More inside clearance for springs or coilovers
Bad:
- Potentially adverse handling effects due to changes in steering geometry
- Shorter life of front suspension/steering components
- Shorter tire life
- Less outside clearance, possible tire rubbing at wheel opening lip
Let me try to explain some of these. In steering, each front wheel pivots about a vertical axis. If that axis is projected to the ground, the point the axis reaches the ground should be in the exact center of the tire's contact patch. Actually the point is in front of the center of the contact patch creating something called castor, but for this discussion castor is irrelevent so we'll neglect it. With the steering axis at the contact patch center point, the wheel will pivot neutrally about that axis. When we move the wheel outward with spacers, we move the center point of the contact patch outward relative to the steering axis. The result is that the wheel will want to pivot around the axis, or turn, when it is traveling straight down the road.
Think of what would happen if you mounted the front wheel of your bicycle on the outside of one of the front fork blades instead of between the two blades. With the wheel way out to the side, the bicycle would not track straight and would be difficult to ride. The only difference on a car is that there are two wheels connected through the steering linkage. So with improper offsets the left wheel wants to go left and the right wheel wants to go right, the force is equalized by the steering linkage, and the driver doesn't feel anything different at the wheel. But all that added force/stress in the steering linkage will contribute to tire and linkage wear, and can cause some strange results in cornering as the car's weight is shifted from the inside to the outside wheels.
The reason most aftermarket wheels have less negative offset is not for any performance reason; its because the makers want to fit as many different cars as possible from one common casting. The factory MINI offsets are high and for someone to produce a wheel specifically for the MINI would limit the potential market for that wheel to only MINIs. Tooling for a wheel casting costs hundreds of thousands of dollars, so a wheel maker wants to buy one set of tooling, cast one common wheel, and then machine different bolt circles and hub diameters to fit a multitude of cars. For cars with unusually low or high offsets, the resulting wheel becomes a compromise.
In my opinion, a little less negative offset can be a good thing; but a lot less negative offset can be harmful to both handling and durability. The offsets of the factory wheels range from 50 (S-Lites) down to 45 (7-Hole 15"ers). So I think you are safe with any offset between 45 and 50. I may try the 5mm spacers with S-Lites when I get my car. I am concerned however with the long term results of some of these aftermarket wheels with offset of 38-40. For those who have gone this route, I am curious to see in a couple years as the cars get some miles on them, if we get a lot of complaints of loose front ends, vibrations and shimmies, and costly front end rebuilds.
SMKKVK
PS My MINI technician at BJ MINI was against the use of spacers.
------------------
S-Lites Spacers and Wheel/Tire Theory
Rubbing aside, I would not go more than the 5mm spacers behind your S-Lites. Also, I wouldn't use an aftermarket wheel with a negative offset of less than 45mm. Here's why:
Reducing negative offset, whether by changing to aftermarket wheels or adding spacers, has both advantages and disadvantages.
Good:
- Wider track for improved handling
- Fills wheel openings for better appearance
- More inside clearance for springs or coilovers
Bad:
- Potentially adverse handling effects due to changes in steering geometry
- Shorter life of front suspension/steering components
- Shorter tire life
- Less outside clearance, possible tire rubbing at wheel opening lip
Let me try to explain some of these. In steering, each front wheel pivots about a vertical axis. If that axis is projected to the ground, the point the axis reaches the ground should be in the exact center of the tire's contact patch. Actually the point is in front of the center of the contact patch creating something called castor, but for this discussion castor is irrelevent so we'll neglect it. With the steering axis at the contact patch center point, the wheel will pivot neutrally about that axis. When we move the wheel outward with spacers, we move the center point of the contact patch outward relative to the steering axis. The result is that the wheel will want to pivot around the axis, or turn, when it is traveling straight down the road.
Think of what would happen if you mounted the front wheel of your bicycle on the outside of one of the front fork blades instead of between the two blades. With the wheel way out to the side, the bicycle would not track straight and would be difficult to ride. The only difference on a car is that there are two wheels connected through the steering linkage. So with improper offsets the left wheel wants to go left and the right wheel wants to go right, the force is equalized by the steering linkage, and the driver doesn't feel anything different at the wheel. But all that added force/stress in the steering linkage will contribute to tire and linkage wear, and can cause some strange results in cornering as the car's weight is shifted from the inside to the outside wheels.
The reason most aftermarket wheels have less negative offset is not for any performance reason; its because the makers want to fit as many different cars as possible from one common casting. The factory MINI offsets are high and for someone to produce a wheel specifically for the MINI would limit the potential market for that wheel to only MINIs. Tooling for a wheel casting costs hundreds of thousands of dollars, so a wheel maker wants to buy one set of tooling, cast one common wheel, and then machine different bolt circles and hub diameters to fit a multitude of cars. For cars with unusually low or high offsets, the resulting wheel becomes a compromise.
In my opinion, a little less negative offset can be a good thing; but a lot less negative offset can be harmful to both handling and durability. The offsets of the factory wheels range from 50 (S-Lites) down to 45 (7-Hole 15"ers). So I think you are safe with any offset between 45 and 50. I may try the 5mm spacers with S-Lites when I get my car. I am concerned however with the long term results of some of these aftermarket wheels with offset of 38-40. For those who have gone this route, I am curious to see in a couple years as the cars get some miles on them, if we get a lot of complaints of loose front ends, vibrations and shimmies, and costly front end rebuilds.
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