Bump stop compression?

[Rimmer]

After replacing the coils with air bags in the rear of the Defender I have to increase the bump stops.

Anyone reccommend how much extra to allow for the bump stops compressing please?

Tod.

[steveG]

Not 100% sure, but on standard bump stops I'd allow at least 12mm. They seem hard as hell but throw half a defender at them dynamically and I'm sure they'll deflect a bit.

Are you just going to pack them, or use longer stops? I've got the orange poly extended ones from Paddocks front and rear on the County (Isuzu) and find them very good. They've got a bit more give than the standard ones if you do happen to bottom out hard. I've allowed for about 25mm compression on them before my front coils bind. Pretty sure that hasn't happened yet.

Steve

[rick130]

FWIW the front bumps stops (are they the same ?) will compress 20mm easily.

[uninformed]

Is it because of your shock length or the bag?? If the shock you could relocate the top mount. Either way, I would err on the side of caution. 25mm MINIMUM. A mate that has been know to put pretty much every LR (except FC's and modern RR/Disco's) through their paces told me they will easily compress more if landed hard on. He had something in the engine bay 40mm clear when resting on the bumps. This got kissed once or twice...

[Rimmer]

Thanks gents,
So 25mm seems conservative enough.

I've asked Firestone what they reccommend in regards to relying only on the internal bump stop within the bellows?
See what they say and will post up.

[Rimmer]

It's the bags Serg. I've got 45mm left in the shock before they bottom out.
In saying that I've got ~20-25mm of room to play in reducing the spacer that the bags are mounted in too, if I want to chase every bit of travel/compression.

What sought of margin would you guys leave in regards to having the shocks bottom out?

This is the bag I've used. Same as Tim.:)
W01-358-5426, Firestone Reversible Sleeve Air Spring, Firestone Air Bag 5426 - TruckSpring.com (http://www.truckspring.com/products/Firestone-Reversible-Sleeve-Air-Spring__W01-358-5426.aspx)

Got heaps of available travel/droop, I'm just within the lower end of the bags design height when the vehicle is at "standard ride height" so there is plenty of room to move there. (Reducing the spacer in the bag mount would get me further into the design height too.) 190mm according to my measurements. Lots more than whats available from the shock anyway.

I reckon I'm pretty close to being on the mark here. Feel free though If any of you think I'm ****ing into the wind.
Always open to constructive criticism.:)

[roverrescue]

Just go crazy ;)
Poly Performance JEEP/TRUCK & BUGGY*::*Shocks & Accessories*::*Shocks*::*Bilstein Shocks*::*Bilstein Bump Stop - 4X4 Off-Road Parts, JK Synergy Suspension Systems, Fox Racing Shox, Beard, CNC Brakes, Johnny Joints®, Currie Enterprises, Edelbrock, Pit (http://www.polyperformance.com/shop/Bilstein-Bump-Stop-p-28434.html)

Steve

[rick130]

Just go crazy ;)
Poly Performance JEEP/TRUCK & BUGGY*::*Shocks & Accessories*::*Shocks*::*Bilstein Shocks*::*Bilstein Bump Stop - 4X4 Off-Road Parts, JK Synergy Suspension Systems, Fox Racing Shox, Beard, CNC Brakes, Johnny Joints®, Currie Enterprises, Edelbrock, Pit (http://www.polyperformance.com/shop/Bilstein-Bump-Stop-p-28434.html)

Steve

I'm waiting on an email/quote back from them ATM for something else :D

[Bush65]

It's the bags Serg. I've got 45mm left in the shock before they bottom out.
In saying that I've got ~20-25mm of room to play in reducing the spacer that the bags are mounted in too, if I want to chase every bit of travel/compression.

What sought of margin would you guys leave in regards to having the shocks bottom out?

This is the bag I've used. Same as Tim.:)
W01-358-5426, Firestone Reversible Sleeve Air Spring, Firestone Air Bag 5426 - TruckSpring.com (http://www.truckspring.com/products/Firestone-Reversible-Sleeve-Air-Spring__W01-358-5426.aspx)

Got heaps of available travel/droop, I'm just within the lower end of the bags design height when the vehicle is at "standard ride height" so there is plenty of room to move there. (Reducing the spacer in the bag mount would get me further into the design height too.) 190mm according to my measurements. Lots more than whats available from the shock anyway.

I reckon I'm pretty close to being on the mark here. Feel free though If any of you think I'm ****ing into the wind.
Always open to constructive criticism.:)
I don't understand exactly what you mean by design height, or where this is in relation to your 190mm figure.

Do you have Firestone's charts for that air spring - I haven't been able to find them, but do have charts for the same bellows, but with a slightly shorter piston. By my reconning design ride height for your spring would be somewhere about 11.5 to 14 inches - a good bit more than 190mm (7.5").

The spring rate changes as the air spring extends/compresses and changes rapidly near the extents of travel (compressed this has a lot to do with the shape of the piston). Set up at the recommended ride height, rate is low for normal road use. Set up for a largish ride height (e.g. off road use) the force to compress those air springs to close to minimum height is enormous and you would most like never hit the bump stops.

The following pics are a small part from a spreadsheet I made for my applications. These pics show the dynamic changes when static spring load of 1750 lbs and ride height is set at 9", 12" and 13". These are for the shorter piston, you would need to add about 1.25" (32mm) to these ride heights for your piston. If your ride height is 190mm then this is not an issue.

Stock coil springs in defenders are about 10 to 10.5" front and 11 to 12" rear. In my case I can have a low air spring height for on road and 2 off road heights. I'm considering making my own pistons to reduce the compressed forces (for better articulation), but this is not a low priority at the moment.

[Dougal]

I bargain on 50% bump-stop compression. I have not done any work to verify this, but it seems to keep my engine and axle casing apart. Just.

[Rimmer]

Thanks John,

No I don't have any charts unfortunately.

The 190 mm was what I had left in travel to reach the bags max rebound length 19.43". (The bags bottom out at 6.78", well before the shock.) This is while the bag was at 12" and my ride height, what I considered standard. (~125 mm bump stop clearance.) Bag pressure 45psi.
The bags design height of 12" - 15", you were pretty spot on with your reckoning.
Your input and advice is greatly appreciated!

My original reckoning was trying to aim at getting closer to in the middle of the bags design height, 13.5". After reading and interpreting those charts and graphs, it would seem my feeble mind was overlooking a whole set of other variables as well.:bangin:

I'll keep persevering.:)

Hope I've explained myself a bit better this time too?

[Bush65]

OK, I now understand what you meant.

If you set your normal ride height to 13.5" you will find that the pressure of the entrapped air will have risen greatly to compress the air spring fully. Also as the rolling lobe of the bellows is forced out by the bell shape at the bottom of the piston, the effective area increases. This means that the force exerted by the air spring (force = pressure x area) is very high near full compression, much higher than experienced with coil springs, so less likely to hit the bump stop hard.

If you start with a lower ride height the initial volume of air is less, and the difference to the fully compressed volume must be less, so the pressure doesn't increase as much.

Having said that, you are on the right track by allowing for some bump stop compression before your air spring bottoms out.