When you weld the spider gears, it becomes a locked diff. This means at all times both tires are putting power to the pavement unlike an open stock diff. that only puts the power down through only one tire at any given time. You can run the diff on the street and some do. The only problem is understeer that is created when making sharp turns quickly. Not too desirable for road race where the course has sharp constant turns. The under steer while cornering is caused by the following. Because both tires turn at the same rate at all times, when you turn the outside tire must cover more ground than the inside tire. Thus, the inside tire will actually push the car against the direction you are turning. This should only really affect you when you attempt to make a sharp turn at a high rate of speed. The welded diffs are mostly used in drag and some open course racing. I would think for open races like hill climbing it would be ok. Once the spider gears are welded, the diff is just about indestructable. The diff is an R-200.