rennline bumper shocks?

Pfitz911 · 05-16-2018, 05:28 AM

Hi gents
Can someone confirm that the rennline bumper shocks offer the same weight savings (approx) as the euro ones. Looking to save weight by replacing the US spec shocks.
Is it worth doing front and rear? These rennline shocks are much cheaper than the euro units??
Thanks in advance

roblav · roblav's Garage

A bumper shock's purpose is to raise the spring rate at full bump. Personally, I'd look for bumper shocks that fit suspension design / spring rate around the intended use of the car (significantly lowered / track car) rather than to lower weight. Koni designed them for race cars many decades ago, and (AFAIK) they still make them in different effective spring rates. I've used them on my formula cars.

jac1976 · 05-16-2018, 07:10 AM

I believe the OP is referring to the shocks/tubes in the actual bumpers.

75 911s · 75 911s's Garage

When you say "euro units" do you mean Porsche brand euro crush tubes? I can't answer whether they are the same weight as the official Porsche tube. I don't see how they could possibly weigh much more as the Rennline units are extremely light and well built. I bought both the front and rear impact tubes. The difference in the crush tube vs the hydraulic US impact tube is dramatic.

One thing I noticed was that on my car, I had to drill the ends out of the impact tube mount on the car. Both ends of the Euro tubes are larger thread. The bumper side studs will fit through the bumper, but you need new hardware as the studs are larger. As I mentioned, the chassis end of the tube mounts on the car need to be drilled out larger to accommodate the larger crush tube stud and you will need new washers and lock-nuts.

Helix8 · Helix8's Garage

I recently replaced MY84 rear impact bumber shocks with the Rennline units - spoke to Rennline about weight of their units (approx 1lb each) before ordering. I do not know what the Euro versions weigh but if steel constructed then should be about the weight as RL. I did not weigh the RLs before install but are considerably lighter than OEMs. I’ll try to weigh the OEMs and post. Additionally, I had no fitment issues as it was plug and play on my install

75 911s · 75 911s's Garage

Quote:

Originally Posted by Helix8

I recently replaced MY84 ... Additionally, I had no fitment issues as it was plug and play on my install

That's interesting. Here's a side by side of my 75 original hydrualic US impact shock vs the rennline. You can see the rennline is like a m14 and the original is m12.

You can see the other end in the shock above. The rennline bumper through studs are m10 vs m8 on the us hydrualic shocks.

I guess they went bigger for the SC and carrera? I always thought the shocks were all the same.

Jonny042 · Jonny042's Garage

I bought a complete set of these for my lightweight 3.2 Carrera project - havent fit them yet but did compare them to the stock units from an 85:

Rear bumper shocks:

Note the studs on the two sets do match in size. The weight savings isn't huge, but I for one want to maintain some semblance of bumper integrity on my car - no fiberglass for me! So every pound counts.

I briefly considered going with a fiberglass bumper blade but the stock one is very strong for it's weight - only 16 pounds. Don't believe the fiberglass suppliers claimof "Saves 18 pounds!".

Pfitz911 · 05-17-2018, 01:17 AM

Thanks gents
Ive just realised these are a crush tube? so not a shock as such. Any impact is a one time use for these...??
I think Ill order 4

Flojo · Flojo's Garage

Quote:

Originally Posted by Jonny042

The weight savings isn't huge, but

... someone drilled holes in the tubes...

dg567 · 05-17-2018, 11:34 AM

Quote:

Originally Posted by Jonny042

I bought a complete set of these for my lightweight 3.2 Carrera project - havent fit them yet but did compare them to the stock units
I briefly considered going with a fiberglass bumper blade but the stock one is very strong for it's weight - only 16 pounds. Don't believe the fiberglass suppliers claimof "Saves 18 pounds!".

I bet the blade with bumperettes and accordions, and the smaller quarter panel extensions are heavy together.

75 911s · 75 911s's Garage

I get close to 9lbs for the front shocks. So if the Rennline are 1lb each, then by my calculations that's roughly 7lb savings for just the front end.

Pfitz911 · 05-17-2018, 03:13 PM

Duane
Helpful as always mate
Thanks all. I'm heading to the US next month (from Oz) and I plan on stuffing my suitcase with as much gear as I can!!

ScottArizona · 05-17-2018, 03:30 PM

Quote:

Originally Posted by Flojo

... someone drilled holes in the tubes...

Can you explain? 6lbs seems low for oem bumper shocks. Are you saying these 6lb shocks were drilled out to make them lighter? I thought oem us shocks were more like 9lbs. Thanks!

Jonny042 · Jonny042's Garage

Quote:

Originally Posted by ScottArizona

Can you explain? 6lbs seems low for oem bumper shocks. Are you saying these 6lb shocks were drilled out to make them lighter? I thought oem us shocks were more like 9lbs. Thanks!

I think maybe he was suggesting it could be done to lighten the rennline/euro mounts even more.

QueWhy · 06-09-2018, 10:37 AM

Quote:

Originally Posted by Flojo

... someone drilled holes in the tubes...

This is my plan. Drill a hole in each of the front shocks, empty out the fluid, compress them, set screw to keep them where I want them, modify bumper and/or accordions, swap the stock SC smile for one from a 964.

I've seen a few bumper tuck threads and while not as prevalent among 911 owners as it is with the E30 crowd I think it looks good.

06-09-2018, 12:54 PM

Quote:

Originally Posted by QueWhy

This is my plan. Drill a hole in each of the front shocks, empty out the fluid, compress them, set screw to keep them where I want them, modify bumper and/or accordions, swap the stock SC smile for one from a 964.

I've seen a few bumper tuck threads and while not as prevalent among 911 owners as it is with the E30 crowd I think it looks good.

I'll be interested in seeing how this works out--I'll be deciding on bumpers pretty soon myself.

Larmo63 · 10-22-2019, 11:56 AM

Doesn't anyone just make a replacement aluminum bar? Hollow?

Super lightweight? No shock needed for track cars.

Bill Verburg · Bill Verburg's Garage

Don't know why they call these shocks
they are steel crush struts that the bumpers mount on that is why they are so light

Dmitry at Pelican Parts · 10-22-2019, 01:37 PM

Quote:

Originally Posted by Pfitz911

Hi gents
Can someone confirm that the rennline bumper shocks offer the same weight savings (approx) as the euro ones. Looking to save weight by replacing the US spec shocks.
Is it worth doing front and rear? These rennline shocks are much cheaper than the euro units??
Thanks in advance

Send over a PM to Russ at Rennline and he'll be able to give you all the necessary info.

Driven97 · 10-22-2019, 05:16 PM

Quote:

Originally Posted by ScottArizona

Can you explain? 6lbs seems low for oem bumper shocks. Are you saying these 6lb shocks were drilled out to make them lighter? I thought oem us shocks were more like 9lbs. Thanks!

I think he's suggesting someone drilled them and drained the hydraulic fluid, explaining why they are lighter than expected.

I swear I saw at some point some company who made aluminum crush tubes, but Google Fu fails me now. Don't think aluminum saved a notable amount over the Euro crash tubes.