Rear bump stops -- optional or necessary?

[Leon R]

You need to keep in mind that rubber isolators and springs are used in numerous applications!

Its main advantages are:

- High stiffness with relatively small size (not important or desirable on VX suspension, but great for motor mounts)
- Inherent damping, that is missing in metal springs (again, great for motor mounts, but shocks provide plenty of damping in suspension)

Its downside is:

- Deterioration over time (rubber gets harder/stiffer with age, until it cracks and becomes much softer)
- Varying performance (stiffness/damping) depending on ambient temperature (that should make our suspension MUCH stiffer in the winter)

Looking at our spring helper design, this is NOT your typical "bump stop"! It is designed to be relatively soft and to have a relatively long displacement!

But overall, rubber is NOT an ideal material for vehicle springs, especially for a varying climate vehicle with a considerable suspension travel. I am sure that Isuzu engineers were well aware of the above information. So why would they add this inferior component to their flagship vehicle?

Lets look at vehicle dynamics, why would you stiffen rear end? This isn't a tow vehicle and stock springs seem to be stiff enough own their own for normal driving. The only reason I can see is to make it safer during emergency maneuvers. Stiffer rear suspension also keeps the front end straight, reducing "plowing" effect in hard cornering. The downside is that you pay for it diminished rear end traction (especially when you hit bumps, right 89vette? ). But apparently, they were willing to live with it.

I suspect that they determined that they need more rear end stiffness, which could have been achieved by stiffer shocks, springs or rear sway bars. But some bean counter probably insisted on adding an additional section to an existing suspension bump stop, thus turning it into a "spring helper". In most cases, this is a cheaper solution.

This would also explain if people feel these "helpers" and complain about them more often in the winter months .

So while this was not a good solution, it was a solution to a problem that I am not sure many of us would want to experience...

My VX still has the helpers and it has been practically bumpy in the rear end, as of late . I am still not sure if want to cut them. I might remove them all together to test out the handling. This way, it will be reversible. Another solution might be to get new OEM helpers, if the original became too stiff.

[blacksambo]

You need to keep in mind that rubber isolators and springs are used in numerous applications!

Its main advantages are:

- High stiffness with relatively small size (not important or desirable on VX suspension, but great for motor mounts)
- Inherent damping, that is missing in metal springs (again, great for motor mounts, but shocks provide plenty of damping in suspension)

Its downside is:

- Deterioration over time (rubber gets harder/stiffer with age, until it cracks and becomes much softer)
- Varying performance (stiffness/damping) depending on ambient temperature (that should make our suspension MUCH stiffer in the winter)

Looking at our spring helper design, this is NOT your typical "bump stop"! It is designed to be relatively soft and to have a relatively long displacement!

But overall, rubber is NOT an ideal material for vehicle springs, especially for a varying climate vehicle with a considerable suspension travel. I am sure that Isuzu engineers were well aware of the above information. So why would they add this inferior component to their flagship vehicle?

Lets look at vehicle dynamics, why would you stiffen rear end? This isn't a tow vehicle and stock springs seem to be stiff enough own their own for normal driving. The only reason I can see is to make it safer during emergency maneuvers. Stiffer rear suspension also keeps the front end straight, reducing "plowing" effect in hard cornering. The downside is that you pay for it diminished rear end traction (especially when you hit bumps, right 89vette? ). But apparently, they were willing to live with it.

I suspect that they determined that they need more rear end stiffness, which could have been achieved by stiffer shocks, springs or rear sway bars. But some bean counter probably insisted on adding an additional section to an existing suspension bump stop, thus turning it into a "spring helper". In most cases, this is a cheaper solution.

This would also explain if people feel these "helpers" and complain about them more often in the winter months .

So while this was not a good solution, it was a solution to a problem that I am not sure many of us would want to experience...

My VX still has the helpers and it has been practically bumpy in the rear end, as of late . I am still not sure if want to cut them. I might remove them all together to test out the handling. This way, it will be reversible. Another solution might be to get new OEM helpers, if the original became too stiff.

Well put. Great analysis.

Between this inexpensive suspension solution and the genetic-weakling transmission we have, I keep coming to the conclusion that the VX was more styling and novel mechanics oriented than a serious performance vehicle. I think it looked so tough everybody thought it would perform the same way......it was more of a way ahead of it's time science-fiction project. It was a brave endeavor, and I still love mine for it being so.

[89Vette]

Well put. Great analysis.

Between this inexpensive suspension solution...

Lots of vehicles have these types of travel limiters. Unless I see a link to something showing Isuzu really considered this an "active" part if the suspension, I think you're stretching to make the assumptions you're making.

I totally agree with your assessment on analysis though!

[blacksambo]

Lots of vehicles have these types of travel limiters. Unless I see a link to something showing Isuzu really considered this an "active" part if the suspension, I think you're stretching to make the assumptions you're making.

I totally agree with your assessment on analysis though!

All you have to do is look at the cut-away drawings on the VX JDM brochure to see that the spring helper basically rides on the rear axel to know it had to be an active part of the suspension that was intended curbed body roll.

[89Vette]

All you have to do is look at the cut-away drawings on the VX JDM brochure to see that the spring helper basically rides on the rear axel to know it had to be an active part of the suspension that was intended curbed body roll.

Is there an online link? In the "Rear Suspension" diagram of this link we don't even see the stops pictured. That tells me they're not considered an active part of the suspension.

[blacksambo]

Is there an online link? In the "Rear Suspension" diagram of this link we don't even see the stops pictured. That tells me they're not considered an active part of the suspension.

Thank you for your request. VT Maverick recently posted the entire JDM brochure on the board, which depicted the cut away reveal of the rear helpers' close proximity to the rear axel.