We see this query requested and answered each day in on-line boards with respect to wheel-and-tire packages, particularly relating to lowered vehicles.
The solutions typically present conflicting data as a result of diversified alignment, journey top, spring charges and coil-over packaging. Having the precise mixture of elements in your automobile is simply half the battle. Dialing all of it in optimally is essential to maximizing efficiency.
Since our Triple Risk ND-chassis Miata serves as our major take a look at mule for tire testing–see elsewhere on this concern–we needed to have the ability to match widespread motorsports-oriented wheel-and-tire packages with out vital internal fender contact. Once we first put in a set of RedShift Competitors dampers, we went by way of a bevy of spring charges to discover a mixture that supplied a spread of suspension motion appropriate for observe use with out compromising streetability.
A good bit of observe testing helped us decide the perfect spring charges for our setup: 10K fronts together with 4K rears. (In customary items, that will imply 560 lbs./in. fronts and 224 lbs./in. rears.) This mixture supplied the quickest lap instances together with avenue manners that we might stay with.
However we nonetheless had an issue: The equipped bump stops have been too brief for our wants and allowed for extra rubbing than we’d like.
What’s a Bump Cease?
For any given street or observe, the spring charge will largely decide the suspension journey–assuming it’s correctly damped and doesn’t enable any bodily contact. Stiffer springs enable much less journey, which accommodates lowered journey heights, which in flip presents each dealing with and aero advantages.
However there’ll at all times be a bump in some street extreme sufficient to exceed that damped spring, so we would have liked one thing to restrict the journey and forestall the shock from bottoming out in excessive conditions. That’s the place the aptly named bump cease comes into play.
Consider bump stops as items of rubber or equally tender materials that act as progressive-rate springs. They arrive in all sizes and styles. They’re normally discovered on the damper’s shaft, however they may very well be positioned elsewhere in a suspension setup.
In most setups, bump stops float on the damper shaft and act as progressive charge springs when engaged. Pictures Credit score: Andy Hollis
In OE functions, they’re sometimes very lengthy and have sufficient spring charge to offer easy engagement all through the suspension’s journey. Relying on the applying, a car would possibly nicely typically have interaction the bump stops, however on this case, that’s an excellent factor: Image these bump stops performing as progressive charge springs when engaged.
In motorsports, the place journey is rather more restricted, bump stops are extra of a fail-safe that forestalls the damper from internally bottoming out. In addition they forestall physique contact–like, say, a tire hitting an internal fender. A shorter, stiffer bump cease permits extra use of the linear vary of the first spring, however that’s on the expense of a extra abrupt change of charge upon influence.
Our RedShift coil-overs shipped with pretty brief, stiff bump stops. We then added a spacer to restrict compression journey to only shy of tire-to-inner fender interference.
To measure how a lot spacer our bump stops wanted, we first measured journey with our tires and Flyin’ Miata Kogeki wheels in place. Pictures Credit score: Andy Hollis
To make that spacer, we eliminated the spring from the coil-over, disconnected the anti-roll bar, pushed the bump cease down onto the shock physique, and jacked up that nook of the suspension till contact was made. After decreasing that nook of the suspension, the place of the bump cease confirmed us how a lot unusable journey we would have liked to get rid of.
Then we merely minimize a bit of Delrin rod. The excellent news is that this method labored fairly nicely to get rid of all physique contact. The unhealthy information is that this setup did so on the expense of complete suspension journey.
So, how might we achieve again suspension journey? To take care of journey top when a stiffer spring is put in, the coil-over have to be adjusted to compensate for the decreased static deflection.
With a one-piece damper, the decrease perch is moved downward, which might go away the spring free underneath excessive extension conditions. With a two-piece design, like our RedShift items, the efficient physique size will be adjusted so the spring stays tight on its perches. A aspect impact of this method is that droop journey is decreased in favor of bump.
Since we have been making small, incremental modifications and had loads of out there journey, we initially modified the physique size. By the point we established our remaining spring alternative, although, we had eliminated virtually 1 inch of damper rebound journey, which interprets to almost 2inches on the wheels. Furthermore, we had elevated the potential for bump-induced tire contact by that very same 1 inch, necessitating a good larger spacer.
We initially minimize a big spacer from Delrin, however putting in helper springs allowed us to decrease the underside spring perch and regain shock journey. Pictures Credit score: Andy Hollis
This method labored nicely on observe, however a extra elegant answer beckoned: helper springs. These low-rate add-ons match beneath the first springs to take up any slack but have simply sufficient charge to maintain all the pieces in place underneath full droop. This additionally helps preserve the tire in touch with the street floor.
With helper springs in place, we might now modify journey top by way of the decrease spring perches, simply as you’d with a conventional, solid-body coil-over, after which use physique size adjustment to dial in bump journey. Consideration have to be paid to minimal thread engagement on the damper physique, nonetheless. In our case, we nonetheless needed to run a small spacer even with the physique size maxed out, however we acquired again most of our droop journey.
With our fundamental journey heights and suspension journey sorted, the automobile was now prepared for remaining nook weighting and an alignment test.
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