Miata_Nut

Is it advisable to trim or cut the oem bump stops when using the Swift Spec-R springs with Koni Sport dampers?

I'd be using the top adjustment perch, of course, since Swift claims the springs will lower the car 1.2" front and rear.

I emailed Swift and this was their response:

"When we do our testing we do not modify the bumpstops.

So you do not need to modify your bumpstops, but users can modify their bumpstops to suit their subjective needs."

I was hoping for input from owners here that may have done some experimenting and could advise me either way.

Thanks in advance!

B serious

A 1.2" drop will put you close to the rear bumpstop (about 0.3" away). Front should still have lots of room.

I'd leave the bumpstop if you wanted a stiffer overall spring rate.

Plus...Swift factors bumpstop rate into their spring rate...just like Honda does.

The Konis won't mind either way. Try it with uncut bumpstops first. Its easy to cut them later.

I assume ride quality would be softer with cut bumpstops.

ZDan

If springs lower the car 1.2", I'd cut half that off of the bump stops so you only lose 0.6" bump travel. IMO they're for limiting travel under bumps, not ideal to be engaging them during "normal" hard braking and cornering as car balance will be affected (understeer on entry, possible oversteer mid-corner to corner exit).

B serious

Bumpstops for like....every modern car are part of the rate. Especially small cars with short shocks.

You engage bumpstop every day you drive the car. The stock ones are soft and progressive. They're meant to be used like a secondary parallel spring.

Available rear shock travel at stock height is ~0.88 to 1" before bumpstop. You lose ~0.7" of available travel with a 1.2" ride height drop (assuming a 1.73:1 MR).

Available stock front shock travel is like 1.13" (IIRC) before bumpstop. You lose about 0.71" of that by lowering the car 1.2" (assuming a 1.69 MR).

That's before you or anyone else gets in the car.

The bumpstop is like 1.5ish" long, IIRC.

The stock bumpstops are definitely part of the rate for hard cornering and braking.

They're progressive. So halving them will make the overall rate climb more steeply when they do become active.

Swift engineered the rates with the stock, unmodded bumpstop included, according to OP's email. Again...so did Honda.

OP can always tune it how he wants it. But it probably helps him to have a clear understanding of why or why not to cut the bumpstop.

All the above is considering the stock shocks. Do the Konis have a shorter body?

ZDan

I've just been through this on the BRZ. Running the stock bump stops with Swift lowering springs was an utter disaster as the car was *hard* on the bump stops statically. Any minor bump was like a small accident, BANG! And the front would be thrown up quite a way due to uber-stiff rate of combined spring and heavily preloaded bump stop. Cutting them down helped significantly.

I understand that the bump stops are active by design, but that doesn't mean you can throw away 1.2" of travel and expect things to be fine with the *same* bump stops.

Of course if the Konis do have built-in additional bump travel, might be all good. But same vs. same it only makes sense to shorten bump stops to regain some lost bump travel.

BRZ is a different application of course, but worth noting that the Swift springs did not come with bump stops while just about all other lowering springs for that car come with much shorter bump stops to replace the factory ones.

B serious

I get your point. I would usually shorten the bumpstops when I installed Koni/GC setups on integras and civics.

He's reducing 0.7ish" of travel. 1.2" of ride height.

Generally, the car will be more comfortable with shortened stops. But that may or may not translate over into handling.

Idk how Toyota designs their bumpstops. The S2000 bumpstops are quite soft to start with.

He will be sitting like 0.2 to 0.4" above the un-cut bumpstops with stock shocks. Again...not sure on the dimension of the Koni. Usually, they do not add bump travel...but I've never measured them for a S2000.

Car Analogy

One thing that jumped out at me reading this thread, is the difference between wheel travel and shock travel.

The car is lowered 1.2". That's effectively at the wheel. At the shock its roughly half that (based on Motion Ratio). This what B and some others have been saying.

So basically if you cut half the cars lowered distance off the stops, or .6", you would have about the same amount of shock travel before you hit the stops. But as B points out, you'd be altering the progressive nature of the stop. Similar to cutting a spring, you'd make it a lot stiffer.

So in addition to what B said about the effects, when you did hit the stop the effect would be more instant and dramatic. Instead of a gradually increasing spring rate, you'd have a sudden large increase, then increasing rate from there on, as more load to that corner was transferred.

So just like cutting a spring, proceed with caution, and make sure you know what you're doing. Its kind of a pain to fix it if you screw it up.

ZDan

Yeah, I blew it on skipping motion ratio. BRZ front strut was on my brain... If 1.2" lower means 0.7" at the damper, then I would start out removing about half that as a compromise between losing bump travel and avoiding a more abrupt transition once it becomes engaged.

If lowering would put him 0.3" from the bump stops at rest, that means he was 1" from the bump stops before lowering. That's a big change... Splitting the difference by cutting 0.35" off the bump stops would seem to be a decent compromise between hitting them all the time and maintaining some bumpstop height/compliance. Then again if there's really still ~1/2" of wheel travel before hitting bump stops, maybe it's fine to leave them as is...

For my specific case with the BRZ, they definitely needed to be cut to avoid constantly riding on them, which sucked pretty bad...

silenc3x

What about with Swift Sport? I know the drop isn't nearly as large, can I leave the bump stop as is?

B serious

We just went over all this...