Monthly Archives: July 2010

Suspension Frequency Calculator

Most among us are used to thinking in terms of springrate when talking about stiffening the car. Others that have been around a bit longer think in terms of *wheel rate*, taking into account the geometry of the suspension on the car’s setup. The next step is to think in terms of the relative wheel rate to corner weight ratio.

All that said, thanks to Rennie Clayton, I’ve added another tool to my way of thinking about setup on a car, which is the ability to calculate the frequency of your setup. This takes into account springrates, motion ratios, wheel rates, and the relative sprung and unsprung weights. I put all those numbers together in a small suspension frequency calculator, which I’ve prepopulated with the numbers for my Stohr DSR, down to the unsprung weights measured for the Shock Shop. It also includes an evaluation of your relative front-to-rear springrate bias, which is kinda nifty. Enjoy!


Updates Updates

We’re just under two weeks out from the last update, and have exactly three weeks until the car needs to be on track with its new parts. It’s getting a bit iffy, here’s the latest:

  • Shocks: The shocks are off to Chris Billings at the Shock Shop, who has been The Man for Stohr shocks for some time now, from what I can tell. He’s done JR’s, Farrell’s, and several other cars. Stohr says he’s the fellow that does the setups on most cars these days. My case is a bit odd in that my Penske 2000’s are not the same as the standard Ohlins, but Chris is confident that he can get the same results with these shocks that he does with the Ohlins. They arrive today, and we’ll eval from there. As part of sending the shocks off to Chris, he had me complete a worksheet for the “Critical Damping Analysis”. A couple interesting notes came out of this:
    • Motion Ratios: Since I’m converting my car to WF-1 bodywork, that means lowering the front bellcrank to clear the new front fender. I measured the front motion ratio before and after this change, and detected a slight decrease – from right about exatly 1:1 before, to somewhere in the neighborhood of about .95 after. The rear motion ratio is almost exactly 1:1 as well as I could measure (with the shock in the inboard/longer mounting position). Finally, the optional “low” motion ratio available on the front bellcrank appears to be somewhere in the neighborhood of about .85:1.In theory, that means that one might be able to quickly make stiffness adjustment by quickly changing bellcrank positions, but in fact, once you do this you have to reset all your ride heights, making it not much faster than just changing springs in the first place…
    • Unsprung Weight: This was fairly shocking to me, though it makes sense in retrospect. The unsprung weight on the front (wheel, tire, caliper, rotor, upright, 1/2 spring and shock etc) is a whopping 39.5 pounds, and at the rear, is 49.5 pounds. That means that nearly 180#, or approaching 1/4 of the weight of the car is unsprung weight!
  • Bodywork: Wayne is cranking away on the bodywork, and is hoping to have it ready to ship perhaps the end of next week, which will make things PRETTY tight in terms of being able to get it to Pat in time to get some paint laid up on it. With luck, if it can arrive by the end of next week (maybe!), then I could fit it over the weekend, and get it to Pat at the beginning of August. We’ll see.
  • Oil Pans: I’ve shipped my oil pan/pickup/baffle off to C&M to get double-checked before reuse, and have a second one on the way to plunk on the bottom of the motor that was previously the dry sumped engine. That engine will have to go out to have a new bottom case put on it, that doesn’t have the passage drilled out for the dry sump oil bypass.
  • Battery: The new VoltPhreaks battery is in place. Built-By-Bones made a nice little ally bracket for me, and it now occupies the same space that the old battery did, just with 12.8# less mass. The battery comes with a small button to turn the battery on and off, preventing discharge even when it’s hooked up. Kind of a neat idea I guess. Will report on its efficacy relative to the ol’ PC680 as the season progresses.
  • Misc: There are lots of little bits associated with this change. Stohr has sent a new airbox that I’ll be able to install to get a nice ram-air effect at speed. I’m changing to their
    small LED brake lights, since I can easily wire those up to the side of the spar down low, so the wing does not obstruct them anymore. The new body also means being able to remove that large chunk of aluminum that acts as the rear body support, which will be another pound or two out of the car. It all adds up!
  • Camera: With the CAM-FX packing it in, I splurged and ordered a PDR100 recorder from ChaseCam, along with their SS1000 video processor to be able to show front-and-rear video at once. This should be just all kinds of fun. Among the PDR’s features are auto-start and auto-stop recording, which means I won’t be able to forget to turn on and/or start recording anymore on the unit, which means no more forgotten video. Woo!
  • Header: No word yet from Rilltech, though they are hoping to have a few built in time.
  • WRD Diff: No update here either, cannot seem to get ahold of Lee Williams.


Midsummer Update

It was a very quick turnaround from June Sprints to the July 4 “Freedom Sprints N/N”, but we made it. Turned out to be a pretty uneventful weekend, but I’ll still do a writeup of the weekend.

Further, I’m getting towards having my writeup completed for The June Sprints.

Those races completed, there’s now a six week break until the “Great Salt Race” at MMP in the middle of August. After looking at the various cars, meeting the people, and seeing how
we did at the Sprints, we made the decision to stay in DSR. As such, it’s time to try and see if we can improve the competetiveness of the car, and that’s what the next six weeks are all about. In short, it comes down to reduced weight, more downforce, more grip, and maybe a touch more horsepower.

  • Bodywork: This is the biggie. Having talked about it for quite some time, I decided to update the car to WF-1 bodywork. The chief reason for this is that the
    1g bodywork that I have weighs a hefty 92#, versus the 60# or so that is more commonly seen. With the 1g body known to not cool quite as well as the WF-1, and the poor feed
    of air to the rear wing, we decided to have Stohr build us a new long-tail body in lightweight e-glass. Carbon was simply too expensive. Fully painted, the body shouldbe right around 60#, for a 32# weight savings, perhaps more.With this change comes the need to refactor a lot of tidbits, such as replacing the front bellcranks, and then smaller changes such as figuring out how to re-mount the camera, radio antenna, moving the oil cooler back (since I can remove the front oil duct), and several other fitment issues that I’ll detail as I get the bodywork and get to fitting everything.
  • WRD Differential: Primarily for the performance improvement we’ve decided to update to the WRD diff, but the 4-5# weight savings is significant as well. This is on order
    from the guys at WRD, and should hopefully be ready late month.
  • VoltPhreaks Battery: Replacing my PC680 is a Voltphreaks VPH300 (?) battery, for a weight savings of 12.8#. Nice!
  • Dry Sump Removal: In the name of weight reduction, we’ve decided to remove the dry sump. The wet sump pans seem to be functioning with superb reliability these days,
    so those having been debugged, we’re going to save the 15# or so by removing the dry sump system, and replacing it with the standard C&M pan/pickup/baffle.
  • Ti Header: Most folks I’ve talked to reckon that Rilltech’s Ti header is the best one available, so I’ve put an order in on one of those, once they become
    available again.

New Camera Setup

Unrelated to performance, but worth mentioning nonetheless, is the replacement of the video recording system. The CAM-FX has been trusty for a couple years now, but it appears that the vibration and speed of Road America was enough to finally kill it.

So, we’ve decided to replace it with a PDR100 and SS1000 from Chasecam, allowing us to use both cameras on the car, and have some fun front and rear coverage simultaneously. Among the interesting features are auto-start and auto-stop on recording, which should help prevent us from missing sessions due to me not turning on the camera anymore, which will be really nice to not have to worry about.

Those bits should arrive fairly shortly, and I’ll report on its efficacy from Miller.


Abort, Retry, Fail

After a superlative, educational, exciting, and amazing June Sprints, the Miss Liberty N/N at High Plains was almost always going to be a bit of a letdown. Sure enough, it, uh, succeeded in doing just that, so this will be perhaps a most brief of writeups.

In all, it was a pretty forgettable weekend. Paul Leonard was there briefly in his Radical, but packed up on Saturday after his engine developed a miss. This turned out to be clogged
fuel injectors, which Rilltech helped him diagnose a bit later.

Saturday’s race was therefore pretty lonely, with just me in DSR, next to Russ Lindemann in his FM in P2. I ran away quickly and just ticked off the laps. The weather was too warm for any significant laptime improvements, the car was handling only reasonably well, and running just the short course meant that it was just a matter of finishing the race to get my points. The one upside, by finishing, I was now qualified for Runoffs, another milestone met.

Sunday we were able to run the full course due to having a few more workers arrive and register. In qualifying I was near my previous bests, in the 41’s, as before. However, after qualifying, I noticed a large crack in my RF brake rotor. My spares/floaters still being in Fort Collins, and with no competition to run against, we just said “ah screw it”, packed up, and went home.

The only interesting tidbit to come out of the weekend is that I seriously began left-foot braking for the first time, running both Sunday sessions exclusively with my left foot. For the moment, it appears still to be costing a bit of time, as the amount of concentration required to teach my stupid left foot how to brake properly is distracting from driving hard, and completely at the limit. As well, shifting is not completely automatic. However, it’s progress, and perhaps as sessions go on, I’ll continue to improve with the left foot until it’s as subconscious as the right.

So, with that completely underwhelming weekend behind us, it was time to pull off the body, shocks, diff, engine, and start with the weight reduction program. On to Miller!