Author Topic: Lotus 79 Setup Notes  (Read 727 times)

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Offline Tiago Lapa

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Lotus 79 Setup Notes
« on: February 16, 2010, 19: 43 »
Notas do Volker Hackmann

There’s two kinds of adjustments, set and leave ones that you can use at every track, and track-specific ones. Let’s start with the former.

Tire pressures: 10 psi (which is the lowest possible value) at the front is an easy pick. At the back, it’s either 11 or 12 psi. I usually start with 12 which offers more side grip in fast corners, but at some tracks 11 might give slightly better traction off slow corners.

Toe in: I like the handling of 0.0 on both ends of the car, so I’m leaving it at that.

Brake bias: I like 38% and always leave it at that; if you don’t use throttle under braking, you’ll need a few percent more than that, but the car will still be very difficult to handle on entry due to the excessive engine braking.

Camber: It seems like the Lotus doesn’t like a lot of it, I couldn’t find any further grip increase by going past -1.0¬? at both ends of the car.

Caster: I generally like the feel of high caster in all kinds of cars, so that’s what I use.

Shocks: Not sure why, but all soft appears to work best. Maybe the simulation of chassis and wheel oscillations is fubar in iRacing, maybe the softest shocks are actually still quite stiff, or maybe the springs and / or tires already do a lot of damping work on their own, could be any of these.

Steering ratio: This is a completely personal setting, choose whatever gives you a steering sensitivity that you’re comfortable with. Considering that a lot of people complain about the steering being too sensitive, this will most likely be a high setting, as lower settings would increase sensitivity even further.

ARB arms / ARB diameter: With the fairly stiff springs that we run, there’s no need to have an anti-roll bar to reduce body roll, there isn’t any excessive amount of that anyway. You could think about using it for adjusting the low speed balance (stiffer / thicker sway bar = less grip at the respective end of the car), but I haven’t found the need to do that anywhere, so just set them to all soft.

Differential: This is in fact comprised of 4 different settings: clutch plates, preload, drive ramp angle and coast ramp angle. What I want the diff to do is being open on the coast side, so the car turns well on entry and in the center of the corner, and locked on the drive side, so you can get it to rotate on exit and to prevent the unloaded (i.e. inside) rear tire from spinning on exit, which would compromise your drive off the corner. Another welcome feature of having more lock on the drive side than on the coast side is that you can lock the diff on purpose by continueing to apply some throttle while going into corners. This would result in an understeery handling, which can be useful in corners where the car notoriously wants to oversteer on entry.
To accomplish this, I set the drive ramp angle to the lowest possible value (=maximum lock), and the coast ramp angle to the highest possible value (=minimum lock). Adding clutch plates or preload would increase diff lock on both the drive and the coast side, which I don’t want. There is already enough lock on the drive side from the ramp angle setting alone and I want the diff to remain as open as possible on the coast side.

Now let’s turn to the track-specific settings.

Ride heights: (they’re set by adjusting the spring perches, but the values of the spring perches don’t matter as long as they’re set to the same values on both sides of the car, just look at the ride heights instead): This is a very important setting, as it determines how much downforce you can get from the wing profiles under the car. The lower the car, the higher the downforce, so you’ll want the ride heights all the way down to 1.0 inches everywhere except of Daytona. The downside of running low ride heights is increased drag, and that’s why you want higher ride heights at Daytona, about 2.0 inches. That’s the only exception, though, everywhere else you’ll be way off the pace if you don’t make use of all the underwing downforce you can get.
Due to the shape of the wing profiles, the car does not require any rake angle to work, which is different from cars with a flat untertray.

Wings: The undertray produces more front than rear downforce, so you will generally need low front wing angles with fairly high rear wing angles. The wings also produce less downforce for the drag than the undertray, so they’re generally set to low settings…get the downforce you need from the undertray first. I run 2¬? of front wing angle (which is the minimum) and 8¬? of rear wing angle at most tracks. At tracks with shorter straights you might want to run slightly higher wings, especially if this gives you more confidence in a certain fas corner, or if it allows you to run a fast corner flat out that would have required lifting with lower wings. The highest I’ve run was 5/10 at Laguna which has really short straights.
If you don’t run low ride heights, you will lose more front downforce than rear downforce, and therefore you will no longer need a significantly higher rear wing to keep the car balanced. At Daytona, I run 4¬? rear wing angle, with 2¬? on the front wing.

Wickers: These devices, also known as Gurney flaps, increase the downforce and the drag of the wings. For some reason the car appears to be faster with the largest available wickers on the car, rather than by trying to generate the same amount of downforce with a lower or no wicker and a slightly higher wing angle instead. The exception here would be Daytona again, where you want to remove everything from the car that adds drag.

Springs: You want those as soft possible for two reasons: Firstly softer springs increase mechanical grip, and secondly they allow the downforce to lower the ride height while the car is travelling at speed, which then increases undertray downforce even further. At some point the car will bottom out too much on the straights and scrape off speed, though, or on severe road bumps in certain corners which may result in a loss of control (e.g. in the uphill at Lime Rock). I usually start with 1000 lbs/in springs, and have ended up with 800 to 1200 lbs/in at every track except Daytona where I ran stiffer springs due to the banked corners.
You could also run stiffer front than rear springs to tighten the car up (or vice versa to loosen it up), especially in slower corners, but personally I’ve found that the handling with equal springs on both ends of the car to be just fine.

Bump stop gap: You can limit the suspension travel by lowering the bump stop gap at the respective corner of the car. If the suspension exceeds this travel, it will start to compress a rubber spring (the bump stop), which has an increasing spring rate as it is compressed further. If your rear suspension hits the bump stop, the car might just spin out due to the loss of mechanical grip, and this is something you definitely want to avoid, so I always set the rear bump stop gaps to the highest possible value.
The front bump stop gap can be very useful, though. As the highest suspension travel is achieved in fast corners (due to high downforce and high centrifugal force), this can be used to tighten the car up in the fastest corner(s) of the track, while the slower corners aren’t affected at all. As the Lotus is usually looser in faster corners than in slower corners, this is great thing to have: By setting up the bump stop gap correctly you can run a rather loose car that turns great in medium and low speed corners, while the front bump stops will prevent it from spinning out in the fastest corner(s) of the track, where it might be completely undriveable if it wasn’t running on the bump stops. If you’re at a track without fast corners, or if the fast corners are easily flat out even if the front end runs on the bump stops, you can also lower the front bump stop gap to prevent the car from bottoming out too much on the straights, which might increase top speed slightly and / or might allow you to get away with running softer springs. I mostly use it to fine tune the handling in the fastest corners, though, and therefore there are tracks where I run a low bump stop gap setting (such as 0.3 inches or less), as well as tracks with the highest possible value or something close to it. If you lower it too far (such as running a negative setting), the handling can become a bit bouncy, though.

Final Drive Ratio: This is the same as diff ratio, it affects the overall ratio of all gears. There’s no benefit to choosing one over the other, apart from maybe having a wider selection of gear ratios in the relevant range that you need. I’ve found this to work quite well with the medium setting which is 3.444, and I think that’s what most other people run as well, so choosing the same one might useful if you want to compare your own setup with other setups. At most tracks top speeds will be very close too, as the car gets very quickly from 0 to 140 or 150 mph even on short straights with what I call the standard aero config (lowest possible ride height, low wings) due to its good power to weight ratio, but after that it won’t gain much more speed due to its high drag, the car never exceeds 165 mph.

Gear ratios: The first thing you need to think about is how many gears you actually want to use during normal driving. The car has 5 gears, but I only use 4 at most tracks, or even 3 at some. That’s because of the long shifting delays in the Lotus, on the one hand they make it difficult to go all the way down from 5th to 1st gear before a hairpin, and on the other hand less can also be more during acceleration off a corner. If you use more gears this keeps the engine closer to its optimum rev range (I’d shift up at about 11000 RPM by the way), but every additional upshift also means having no drive at all for 3 tenths or something close to that. 5th gear is set for the longest straight, the car makes the most horsepower at 10600 RPM, so you’ll want that somewhere in the middle of the straight. 1st gear is usually for starts as you don’t need it for normal driving, as explained above. 2nd, 3rd and 4th gear are more or less trial and error, you want to hold the revs high enough in the corners to get a decent acceleration on exit, you don’t want multiple downshifts in braking zones that are too short for it etc.
For the race, you usually have to run a taller 5th gear to keep the oil temperature down, it shouldn’t exceed 120¬?C continously, and sometimes making your 4th gear taller might be useful as well. Either to help you keep the temperature down if you use it a lot, or simply to make sure that the gap between the gears doesn’t become to big…there’s just not a lot of power down there at 8500 RPM, so you don’t want to drop that low after an upshift.

Fuel: 2.1 or 2.6 gallons for qualifying, the tires need 2 or 3 laps to really get up to temperature at most tracks, so I want enough fuel for that and about 2 further laps on the hot tires. As the race distances vary, race fuel loads also vary depending on the track.