SCCA CAM-C Thread

[SteveW]

I'm sorry, flat ride has(d) its place, but that place does not involve a stopwatch. Forget flat ride & cut your rear spring rate... A ton. If it was not good on rough pavement, it's just a simple lack of compliance. Don't make this tougher than it is.

I hear you but my wheel rates are not out of line with other national level setups for categories where springs are free.

One of the problems I had on the bumps was the Viking rebound curve is progressive and the shocks were jacking. I improved the situation by softening the rebound. The solution might be as simple as a revalve.

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[TeeLew]

I hear you but my wheel rates are not out of line with other national level setups for categories where springs are free.

Tune your car; not theirs.

I'm not going out of my way to be a dick (it tends to come naturally). You felt a real issue in your car and the answer is apparent. I know there is a tendency on this forum to be concerned about flat-ride and to always be stiffening the rear springs. I think it's common to want to put rear spring on the car to reduce understeer, which it does. Spraying WD40 all over the rear tires would fix the understeer as well, but it's not the best approach.

I know Brian was a big proponent of flat-ride. I agree it works, but I don't agree that it's a desired thing in a performance application. Maurice Olley was who was the first to recognize the advantages in ride of a rear stiff car. He was a 1950's GM ride and handling engineer who was an absolute genius. The thing is, it was 70 bloody years ago and we don't have the same problems Maurice had. Maurice was trying to make big 50's and 60's sedans go down the new interstate system with crap dampers and chewing gum bushings. Limit handling was never a consideration. Unfortunately, Flat Ride is also mentioned in Race Car Vehicle Dynamics, by the Millikens. They don't say it must be used on a racecar, but mentioning it seems to be tacit approval. Even RCVD was only written at the beginning of the damper revolution (early 90's from experience in the 70's and 80's). They talk about damper end-eye bushings and all sorts of things we'd never use. Just because they mention it, doesn't mean you have to do it! In reality, it's biggest positive effect is felt at constant speed on a big, undamped land-yacht cruising down the road. The difference in damper and bushing technology alone makes FR approach mostly a moot point IMO, but when the goal involves a watch, it should not even be a consideration. Having said all this, I know several OE engineers and they almost always end up with a rear-stiff car to satisfy the ride evals. It has dickey-do to do with handling.

The problem with using Flat-Ride is exactly what you're running into. We end up over-constraining the problem. So we either compromise the front spring, making it lower than we need to for a stable corner entry or compromise the rear spring by making it stiffer than we want for good grip. Either way, we don't have enough understeer in the car and to truly go fast, a car *has* to have a little understeer. If you don't have just a little push in the car, then you can't be aggressive enough with your inputs to be able to run the best line or induce the correct rotation in the car. I've used the word, "You" here, but I really mean anyone, because, regardless of what *anyone*, including Harry Hogg from _Days of Thunder_, *loose is not fast*. The trick to going fast is to have the least amount of understeer possible without eliminating it or compromising the stability of the car. A guy can spend a lifetime trying to figure out the best way of doing that.

Set spring front spring rates for entry stability. Choose your rears based off how much you can carry without losing bumps compliance or powerdown. If you want to use ride frequencies to choose the spring, then my personal rule-of-thumb keeps the rear in the range of 80-90% the Fn of the front. At this point, you'll have some handling balance. Tuning balance using only springs is like trying to whittle a stick with a chainsaw. You've got a lot of tools available, don't be afraid to use them. Toes, cambers, ride heights, ARB's, tire pressures, dampers, etc. all shift balance and they can be much more efficient at doing it without the unwanted loss in compliance and grip.

Obviously, I don't suggest you make some big change before an important event, but if you're doing a test/tune day, why not take a chance? I'm specifically going lower than I like so I can find the floor. I've got 650's and 500's (for the stock position) in the garage. I'll run them both before the winter is out. That doesn't mean I'll stick with them, but I'm going to try them. It's not *that much* work and I'll have felt the compromises in a way which a spreadsheet cannot give.

I'm done now. I'll shut up.

 

[SteveW]

What I saw in the results from Nats makes me want to try a different way of making my car better. I'm very happy with how the car ran yesterday on the good, smooth lot. Time to target an event on a different surface in a few weeks to get more input on how the changes are working.

Fortunately, this change didn't cost me anything but the time and effort with the parts and pieces I have collected over the years for this car.

 

[djcodeman]

Saw em on fb marketplace here

 

[mavisky]

OK, I somehow completely missed this thread. Used to autocross with SCCA over a decade ago back in Indiana in various cars and classes, but just got back into it this year with the Atlanta region in my GT350. This was from my latest outing.

New tires worked as well as I thought they would.

New setup is rotatable 19x11 Apex wheels with 305/30-19 Khumo V730. I'd read some reports that these tires like crazy low hot pressures, and I can confirm that based on the 6 runs I got today and monitoring the sidewalls, this is accurate. Best times came with 30.5psi in the front and 27 psi in the rear.

I'm lucky to have a consistently fast local driver in my class in his modified 2014 GT and with the PS4S I had run during my first few events I was typically between a second and a half to 2 seconds behind him as he's on a set of 305 Falkens. With the new setup I was actually beating him until his very last run where he edged me out by a mere 0.087 seconds. My fastest time of the day caught 3 cones (2 minor slalom cones and one that probably cost me more time than it would have saved in raw time) but I did put down a faster raw time with a 65.732. Car is still on stock camber at the front and only slightly more than stock in the rear after lowering so I know I can dial in more front grip with a set of camber plates which could solve some of the understeer I'm fighting and really boost the car ahead in the standings. Time to pull the trigger on the next set of mods. (also looks like Brent, Jordan, and I all need to update our vehicle profiles to list the correct tires, oops)

At the end of the day I was in the top 20 on PAX even though the second heat was able to pick up a couple of seconds compared to our morning times. Typically Brent and his 2014 are top 10 in PAX so the second half got a major advantage on us in today's runs as he was only 15th with a number of cars he normally beats sliding ahead due to the better surface temps and cleaner surface in the 2nd half of the day. Feeling good as this means with a little more front turn-in from a set of camber plates I should be able to fight it out for top 5-10 PAX finishes in our fairly competitive Atlanta region events.

 

[seabee133]

If your ever looking for another spot to run, look at Red Hills Region. We are in south georgia, so a few hours drive.. typically we run in moultrie.. Always looking for more Cam-C

OK, I somehow completely missed this thread. Used to autocross with SCCA over a decade ago back in Indiana in various cars and classes, but just got back into it this year with the Atlanta region in my GT350. This was from my latest outing.

New tires worked as well as I thought they would.

New setup is rotatable 19x11 Apex wheels with 305/30-19 Khumo V730. I'd read some reports that these tires like crazy low hot pressures, and I can confirm that based on the 6 runs I got today and monitoring the sidewalls, this is accurate. Best times came with 30.5psi in the front and 27 psi in the rear.

I'm lucky to have a consistently fast local driver in my class in his modified 2014 GT and with the PS4S I had run during my first few events I was typically between a second and a half to 2 seconds behind him as he's on a set of 305 Falkens. With the new setup I was actually beating him until his very last run where he edged me out by a mere 0.087 seconds. My fastest time of the day caught 3 cones (2 minor slalom cones and one that probably cost me more time than it would have saved in raw time) but I did put down a faster raw time with a 65.732. Car is still on stock camber at the front and only slightly more than stock in the rear after lowering so I know I can dial in more front grip with a set of camber plates which could solve some of the understeer I'm fighting and really boost the car ahead in the standings. Time to pull the trigger on the next set of mods. (also looks like Brent, Jordan, and I all need to update our vehicle profiles to list the correct tires, oops)

At the end of the day I was in the top 20 on PAX even though the second heat was able to pick up a couple of seconds compared to our morning times. Typically Brent and his 2014 are top 10 in PAX so the second half got a major advantage on us in today's runs as he was only 15th with a number of cars he normally beats sliding ahead due to the better surface temps and cleaner surface in the 2nd half of the day. Feeling good as this means with a little more front turn-in from a set of camber plates I should be able to fight it out for top 5-10 PAX finishes in our fairly competitive Atlanta region events.

 

[mavisky]

If your ever looking for another spot to run, look at Red Hills Region. We are in south georgia, so a few hours drive.. typically we run in moultrie.. Always looking for more Cam-C

I live well north if Atlanta so it take me the better part of an hour just to get to Atlanta Motor Speedway. Moultrie looks like about a 4 hour drive for me so would have to be an event where I came down the night before realistically.

 

[WItoTX]

Man, I had a question on RT660's that I was about to post on this thread. However, I found an old post by someone else, around page 30, and it answered my question. I have kept reading from there, and WOW there is so much info on this thread, I don't know that I will need to answer another question. I am currently reading around post 600. Discussions of adding concrete to the trunk. Thanks to everyone who provided much more detailed information than I would have ever expected!

Sort of related, I took 1st at the PCA/BMW Autox two weekends ago, on a gocart track. I had really struggled to put the power down out of corners in prior events, and tried a wildly different tire pressure (RT 660's), from 28-26, to 34-32, and it made a massive difference, putting me in 7th overall. The EVO is north of 500 HP, and every car ahead of me is an autox veteran. I'll take it.

There is more time I left on the track. But I will take it. Also have a list of tweaking to do this next year.

 

[Dana Pants]

You are always welcome to do whatever you want, but I don’t thing going sideways through the lights is faster.

 

[WItoTX]

You are always welcome to do whatever you want, but I don’t thing going sideways through the lights is faster.

Agreed. I also needed to cut it a little harder than I did. My last run I cut it right where I wanted, and it was REALLY fast, but I hit a cone (1 of 5 on the track LOL).

 

[WItoTX]

Since I know there are several Texas guys on this thread, who all is making it to GrandSport this weekend for the two day divisional? There is only 53 entries so far, and 8 are in CAMC. Should be great competition!

 

[NightmareMoon]

I was registered but had to cancel. I love that site tho and would be there if I could be.

 

[mavisky]

Added a set of Steeda camber plates before this weekend's double header event. Dialed the camber up to as much as I could get on the factory strut openings for now. Amazed at how much turn in the car has now and ended up dialing the tire pressures back to 27 front and rear are very well balanced now. The car rotates nicely as needed and I really needed the extra grip as the course was very technical. I didn't lay down the fastest raw times of the day for my class, but the other drivers either DNF'ed or picked up a cone on their fastest pass so ended up taking the win in CAM-C for Saturday's event.

Also tried out a new helmet mounted camera view. Doesn't give the best course view, but much better idea of what I'm doing inside the cabin. I need to re-mount the mic as it seems like the connection isn't 100%. Also still having issues with the GoPro maintaining GPS connection so I lose the cool track map overlay as well as the speed monitor it normally provides. Anyone have any advice on this.

 

[kz]

27 psi on what tire ?

 

[mavisky]

27 psi on what tire ?

Khumo V730 in 305/30-19.

I know some guys in lighter cars run these as low as 24. Based on sidewall rollover I could still drop a little more if I wanted. Will have to wait til next year's test and tune to see though.

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