We see this query requested and answered every single day in on-line boards with respect to wheel-and-tire packages, particularly in relation to lowered vehicles.
The solutions typically present conflicting data as a consequence of various alignment, journey peak, spring charges and coil-over packaging. Having the fitting mixture of components in your automobile is barely half the battle. Dialing all of it in optimally is vital to maximizing efficiency.
Since our Triple Menace ND-chassis Miata serves as our major take a look at mule for tire testing–see elsewhere on this situation–we wished to have the ability to match frequent 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 via 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 one of the best spring charges for our setup: 10K fronts together with 4K rears. (In customary items, that may imply 560 lbs./in. fronts and 224 lbs./in. rears.) This mixture supplied the quickest lap occasions together with avenue manners that we may 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 highway or observe, the spring price 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 affords each dealing with and aero advantages.
However there’ll all the time be a bump in some highway extreme sufficient to exceed that damped spring, so we wanted 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 delicate materials that act as progressive-rate springs. They arrive in all styles and sizes. They’re normally discovered on the damper’s shaft, however they could possibly be positioned elsewhere in a suspension setup.
In most setups, bump stops float on the damper shaft and act as progressive price springs when engaged. Pictures Credit score: Andy Hollis
In OE functions, they’re sometimes very lengthy and have sufficient spring price to supply clean 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 a superb factor: Image these bump stops appearing as progressive price springs when engaged.
In motorsports, the place journey is far more restricted, bump stops are extra of a fail-safe that stops 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 price upon impression.
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 wanted to get rid of.
Then we merely minimize a chunk 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 may we acquire again suspension journey? To keep up journey peak when a stiffer spring is put in, the coil-over should be adjusted to compensate for the lowered static deflection.
With a one-piece damper, the decrease perch is moved downward, which might go away the spring free below 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 lowered 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 ultimate 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 fair 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 resolution beckoned: helper springs. These low-rate add-ons match beneath the first springs to take up any slack but have simply sufficient price to maintain every thing in place below full droop. This additionally helps hold the tire involved with the highway floor.
With helper springs in place, we may now modify journey peak through the decrease spring perches, simply as you’ll with a standard, solid-body coil-over, after which use physique size adjustment to dial in bump journey. Consideration should 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 ultimate nook weighting and an alignment verify.
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