Not at all. In order to understand why, let’s take a look at the average straight axle and leaf spring set up. The weight of the vehicle contacts the axle at two points under the leaf springs – one point of contact on the left side of the vehicle, and one point of contact on the right.
The rubber spring in a rear SES kit, however, contacts the axle at a secondary point of contact. In other words, the rubber spring rests on the axle just inboard of the leaf springs. By adding a secondary point of contact, we’re reducing the stress at the original point, and actually spreading out the load to four points of contact on the axle, not just two.
Instead of the sudden jounce of a solid bump stop when the suspension bottoms out, the progressive spring rate of the rubber spring provides soft acceptance (uptake) of the load.
Will the rubber spring hurt the axle? Not in the least. All in all, the hollow rubber spring actually reduces stress on the axle by sharing the load with the existing (leaf spring) suspension while it absorbs road shock.
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