The rule for stock class bump stops is...

A suspension bump stop is considered to be performing the
function of a spring. Therefore, the compressed length of the
shock at the initial point of contact with the bump stop may not
be increased from the standard part, although the bump stop
may be shortened for the purpose of installing non-standard
shocks. Bump stops installed externally and concentric with the
shaft of a shock may be drilled out to fit a larger diameter shock
shaft. Bump stops may be substituted for the purposes of installing
non-standard shocks.

The question I have is if any auto-xers have tried running stiffer front bump stops to trick the car into thinking it has stiffer springs. The Z contacts it's stops at about 1.5 in front wheel travel so we are using the bump stops in almost every corner, even with a very stiff FSB.

mike

 

Bump stops mean what they say.........stops. They give a little, but not much at all. Get stiffer strings if thats what your after.

 

1...You have to run stock springs in SCCA B-stock

2...Bump stops can be designed to compress a lot. The stops in the Z compress over a 1.5in range and are also progressive. Bump stops are often used in street cars so that the designer can run a softer spring for ride quality and then use a progressive bump stop to control severe compression or cornering loads.

I'm looking for input/opinions from experienced STOCK CLASS auto-xers before I spend the time and money testing different durometer bump stops.

 

Bump stops must be stock durometer.

 

I don't think I'm over-interperting the rules here.

Bump stops may be substituted for the purposes of installing
non-standard shocks.

I can't find a rule anywhere that says the substituted bump stops must be stock durometer. I can't use the factory bump stops with my shocks and there is no way I could match their stiffness exactly with aftermarket parts.

mike

 

The key to the solo rules is "if it does not say you can then you cant". It is not a matter of it does not say they have to be the same hardness, the key point here is it does not say they can be different hardness. If you are in doubt write a letter to the SEB and ask.

From the solo stock class rules:


Alternate components which are normally expendable and
considered replacement parts (e.g., engine and wheel bearings,
seals, gaskets, filters, belts, bolts, bulbs, batteries, brake rotors,
clutch discs, pressure plates, suspension bushings, drivetrain
mounts, etc.) may be used provided they are essentially identical to
the standard parts (e.g. have the same type, size, hardness, weight,
material etc.), are used in the same location, and provide no
performance benefit. The allowance for use of such replacements
does not include camshafts, differential covers, or ring-and-pinion
sets, nor does it authorize the use of piston rings having different
configurations (e.g. “Total Seal”) from those of the original.

Hardware items (nuts, bolts, etc.) may be replaced by similar items
of unrestricted origin. Safety wire, threadlocker compounds, and
locking nuts are permitted. These allowances are strictly to allow
components to be replaced from alternate sources other than the
original manufacturer. They should not be construed as an
allowance to replace components with those which could be
considered a ‘higher performance’ alternative. Parts available as
replacements through the dealers parts department, the factory, or
any other source which do not meet standard part specifications
(e.g., hardness, size, etc.) are not legal in Stock Category, except as
specifically provided elsewhere in these rules.

If a modification is not specifically authorized in this or previous
sections of these Rules it is not allowed. It is not permitted to use
illegal parts even if they have been set to stock specifications.

So what is keeping you from using the stock ones? I have never seen a stock bumpstop that could not be fit to an aftermarket stock legal shock.

 

Eh, I see where you're coming from. I may have to send Doug an email with pics and get his opinion.

I have Ohlins DA shocks. Before anyone says they're not made for the Z, you're right. (not yet) I am a fabricator by trade and I made what I needed to adapt a set of Ohlins to my Z. The shocks satisfy all of the rule requirements as far as length, system of mounting, etc. The reasons I can't use the stock bump stops are....(this is had to describe w/o pics)

rear...The factory bump stop "snaps" into the upper mount around where the shock shaft bolts. I chose to invert the Ohlins so the upper mount is now a stud on the end of the shock body. My bump stop is now on the bottom, still concentric to the shock shaft. The shock meets all of the requirements in 13.5.

front...The bump stop also "snaps" in concentric to the shock shaft. The front is SLA with a coil-over so I had to mount the shock in the factory position, but to adapt the 16mm shaft to the 12mm mount I had to make a threaded adapter. I ended up with a shock that has the same overall length and stroke, but a longer shaft and shorter body. As a result the factory stop contacts the shock body over an inch later and will allow, in extreme bump,
the upper ball joint to hit the inner fender. So, I installed a different bump stop, still concentric with the shock shaft, that is the right length to keep anything from hitting and still satisfy 13.5.
Therefore, the compressed length of the
shock at the initial point of contact with the bump stop may not
be increased from the standard part

I hope this all makes sense. It does to me, but I built them.

 

TriPoint builds an inverted 28 series Koni for the RX8 and the still use the OE bump stop... Got any pics?

 

The only pics I ever got around to taking are of the rear shocks and they are analog. I'll scan them and see what happens.


I've changed the upper mounts a bit since these pics were taken, but close enough.