| Author |
Message |
Rob Schermerhorn (Rexrcr)
Member
Username: Rexrcr
Post Number: 599
Registered: 11-2002
| | Posted on Friday, May 23, 2003 - 7:59 am: | |
Bob,
Going to full slicks, Pirelli or other brand, will be a dramatic improvement. Depending on a number of factors, I have seen as much as 7 seconds per lap on a 1.7 mile track! Your mileage may vary. Is your car a former Challenge? Or have you converted it?
If I assume it's former Challenge, or even conversion, your springs and dampers are not even close to optimized. You will gain a huge chunk of grip and drivability even if you go with the non adjustable solution I proposed. Yes, it's a compromise to cost, but a big improvement non-the-less. If you have experience with proper race cars, you'll really appreciate this modification. If this is the first time racing with DOT race rubber, then you'll have a learning curve. You may feel you don't like the new settings as it reduces roll a lot, responds much faster, more kart-like. But you'll eventually gain confidence and see your lap times drop.
As for dampers and adjustability: You state that you can really feel tire pressure changes. Then assuming properly valved dampers with good range of adjustments, you'll feel shock changes too. A suspension damper can be considered a "suspension timing device" in that chassis attitude changes that occur over time like roll, pitch or combinations thereof, are influenced by damper characteristics. You can "slow" the combination roll-pitch event with rebound increase on the damper that is extending and/or bump increase on the damper that is contracting. In general, adjust rebound to control events like these as rebound controls the sprung mass of the chassis. Thus you gain control over if and when the chassis pushes on corner entry or lose on corner exit/power down. You gain an additional powerful tool to improve drivability. Bump settings control the unsprung mass of the suspension (wheel, tire, 1/2 control arm, 1/2 spring & shock, etc.). If you look at a damper dyno force/velocity curve, in general, you'll see much more force in rebound than in bump, as the chassis has much more mass than the wheel/tire/hub.
You won't feel shock changes if the baseline valving is incorrect for the wheel rates and/or mass of the chassis. You won't feel shock changes if the shock's range of adjustment is very small (amazingly common). You'll get confused if the dampers are not responding in force-matched pairs (also common). You'll get confused with three or four-way adjustable dampers where "high-speed" and "low-speed" adjusters actually influence each other. Another difficulty is the common assumption that adjuster settings react linearly, i.e. four clicks is "two damping units" greater than two clicks. Not so in many cases.
I'm not trying to scare anyone away from adjustable shocks, they're a very powerful tool for racers and OEM's. It's just that just like any other aspect of life, knowledge is power and ignorance is not bliss. I understand that most racers just want to go out to the track, not break anything, and have fun. But then they get frustrated at not winning, and don't know why. Then the frustration continues when they realize they need to "go back to school" to learn what the f*#^'s going on. I sat in on the technical seminar held at SCCA's National Runoffs last September. The tent was SRO as the topic was "Tuning your racecar for best performance." Who wouldn't want to get this information? But 45 minutes into a very dry presentation, filled with technical terminology and poor analogies, eye's glazed over and the tent emptied out. I'm sure their thoughts were, "Learning this sh#t is too much work, I have to go back to work on my racecar..."
So in conclusion, there's no easy answer. It's a fun problem to have though.
If cash is an issue, just bolt on the slicks, do temps and pressures to optimize as best you can, and have fun droping a couple more secconds. If you want more, I've given you options. |
billy bob (Fatbillybob)
Member
Username: Fatbillybob
Post Number: 264
Registered: 8-2002
| | Posted on Thursday, May 22, 2003 - 10:59 am: | |
Yes Rexrcr,
I'm taking baby steps but having fun. I about ready to do the several thousands dollar thing you mentioned some months back. Are you still working for Morris or somone else? Anyway, I just ran kumho Victoracers 245 front 275 rear with stock 348 suspension settings 30psi fronts and 32 rears @ Laguna with even tire temps and wear pattern at my pace. Does that mean I'm reaching the limits of what I can achieve with my current set-up since the tires are a mirror of the actions taken that weekend? If yes then if I went to the Challenge specs with more negative camber I basically could put more force into the turns ,i.e. go faster, to get the even wear once the tire temps were ballanced? |
Rob Schermerhorn (Rexrcr)
Member
Username: Rexrcr
Post Number: 596
Registered: 11-2002
| | Posted on Thursday, May 22, 2003 - 9:21 am: | |
quote:post them when I get home tongiht
http://www.ferrarichat.com/discus/partsandservice/Robert_Schermerhorn/technical_reference_books_i_keep.htm |
Sean F (Agracer)
Junior Member
Username: Agracer
Post Number: 147
Registered: 2-2003
| | Posted on Thursday, May 22, 2003 - 9:09 am: | |
Carrol Smith wrote several books about racing. Tune to Win is one of them and I can't remember the rest. I'll post them when I get home tongiht. One of them specifically talks about suspension and such.
Come back tonight and I'll try to get you the synopsys from each book.
Rob is 100% about shocks. There is a big difference b/w the $500/set bilsteins and the $4000/set Ohlin's. A friend helped me a lot with setting up my FF2000 car including rebuildig the shocks, new springs, etc. and playing with it all to learn what exacly would happen when you changed things (this is also well documented, but there is nothing like experience). He also would only use the Penske oil for our shocks and it was like $100/gallon.
The other thing you have to also factor in is the weather. The car will act very differnt in hot versus cool weather. It's amazing how one set up can work on week when it's 75� out, then a month later, it's 95� and the car is crap.
Then of course there is the abrasiveness of the asfault. I used to race at Heartland Park Topeka and at Gateway in St.Louis. The surface's are light years apart, Gateway being much more abrasive and hard on your tires.
I'll post those books when I get home tonight. There is a lot of good info. While they won't make you an expert, it will give you a good foundation to start from. I know it did for me. |
Rob Schermerhorn (Rexrcr)
Member
Username: Rexrcr
Post Number: 593
Registered: 11-2002
| | Posted on Thursday, May 22, 2003 - 7:42 am: | |
quote:99% of people buy stuf like rollbars and shocks with absolutely no clue as to what they are doing
Agreed. It's a huge subject, complex kinematics, makes peoples brains hurt. What's interesting is that engine design is just as complex, but more people do it (well or otherwise) IMO because it's easier to feel in the @ss-o-meter, driving in a straight line. |
Rob Schermerhorn (Rexrcr)
Member
Username: Rexrcr
Post Number: 592
Registered: 11-2002
| | Posted on Thursday, May 22, 2003 - 7:38 am: | |
quote:the shocks really did not adjust that much to make a difference
Yes, this is the case for many manufacturers. They know only 0.01% of their customers will dyno their dampers.
A friend just for fun dyno'd his mountain bike shocks ($$$) and found the knobs did nothing, placebo effect only. He called the manufacturer and they said, "Oh, you dyno'd the shocks?"
Bilstein adjustable do have good range, their real race dampers have huge range. Koni have less range, in general, though I have not seen dyno sheets for their newest four-ways they just came out with.
Adjustability is determined by the hydraulic circuits internally. It's quite a challenge to build robust hydraulics, not cavitate at high damper velocities, and be reasonable to manufacture (the consumer is so used to seeing shocks for $100 each, they don't understand why one could cost $3000 each).
I could go on, but...
You want to know how to make your 348 quicker around the track? You posed this question a couple months ago and I offered a couple options.
There are no easy answers specifically, but yes, you do want a low CG, so you lower the chassis. But then you're right, you can mess up bump-steer, camber gain may be wrong for the tire you run, etc. You're right again, everything is a compromise. That's why it's suspension, SYSTEM.
So, to specifically answer your question of "...where ... do you start...?", you have three options:
1. Start reading (see my article on technical literature), buying parts, talking to experts about suspension tuning, and testing.
2. Buy an aftermarket suspension system and hope they developed it well, not just marketed it well.
3. Keep doing what you've been doing, which is fine, 94% of racers (even pro's) do it your way. |
billy bob (Fatbillybob)
Member
Username: Fatbillybob
Post Number: 263
Registered: 8-2002
| | Posted on Thursday, May 22, 2003 - 12:24 am: | |
Hey Rexrcr,
Are you interested in posting some posts on suspension tuning? 99% of people buy stuf like rollbars and shocks with absolutely no clue as to what they are doing. I understand about the parts of the suspension but not how they really work together. Everything is a compromise. Adding a stiffer spring sometimes mess up how the shocks work. Lowering a car can screw with bump steer. So where the hell do you start when you are trying to go fast around a track? First eprhaps you can tell us if there are any absolutes like lower to the max but no bump steer or must have adjustable shocks. Personally, I have never really felt a handling differnece in lap times with adjustable shocks. Either I'm not a good enough driver or the shocks really did not adjust that much to make a difference. I've used off the shelf Konis and Bilsteins. I therefore have uses the set it and forget it mode. |
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