Rear Suspension Springs 15.4 or 15.9 mm

[Cairo1966_W110]

Hello Everyone,

I will start a project to renew the rear suspension on my W110, it's sagging a bit and the shocks definitely need replacing.

As for the springs, the original spec is 15.4 mm diameter wire (part number 1103243004). But these are getting hard to find. I can find "drop in replacements" but the wire is 15.9 mm diameter. And these are significantly cheaper, I think just because of supply and demand, manufacturer is the same.

15.9 mm diameter (0.5 mm thicker than spec) would give a stiffer ride, according to theory.

Anyone have any comments on whether to go for the 15.9 mm ones? Will it make a big difference. We have very rough roads where I live, so my thinking is to go for it, but I wanted to gather opinions before jumping.

[Frank Reiner]

Originally Posted by Cairo1966_W110

15.9 mm diameter (5 mm thicker than spec) would give a stiffer ride, according to theory.

The difference in wire diameter (15.9-15.4) is .5 (one-half)mm, not 5mm!

Anyone have any comments on whether to go for the 15.9 mm ones? Will it make a big difference. We have very rough roads where I live, so my thinking is to go for it, but I wanted to gather opinions before jumping.

The spring rate will be about 13-14% greater. Stiffness is proportional to the forth power of the diameter of the wire.

[Cairo1966_W110]

Originally Posted by Frank Reiner

The difference in wire diameter (15.9-15.4) is .5 (one-half)mm, not 5mm!

Good catch, indeed half a mm.

Originally Posted by Frank Reiner

The spring rate will be about 13-14% greater. Stiffness is proportional to the forth power of the diameter of the wire.

High school physics lessons coming back. I guess 15% more stiff could be better for rough roads? It's hard to image how that increase would feel.

Price difference:
15.4mm 209EUR
15.9mm 77EUR

[bracurrie]

I had a W110 with the stiffer springs and I thought it was better than the standard springs. It wasn't harsh at all and handled undulations better.

[Cairo1966_W110]

New springs, suspension and other associated rubber parts have all been replaced, the project was finished last night. I can report that I do not notice any difference in ride stiffness (I went with the thicker spring, 15.9mm), mainly because the old shocks were so worn out. Some of the rubber pieces that support the rear axle/differential where rock hard. She glides along now. So, in conclusion, I would say not really much noticeable difference. Like bracurrie said, the ride is not harsh and bumps and undulations are smoothed out.

One further tip that might be helpful to someone redoing an old suspension, is to have on hand several sizes of the rubber rings which sit at the top of the springs, between the spring and the body mounting location. The reason is that these greatly affect the ride height, and even though I bought what I thought was correct, because the old ones were so worn out, I had to get substitutes to raise the rear and lower the front based on what I originally purchased.