Suspension set-up

As promised, here is the long awaited round up of our suspension system. I know some of you have been itching to find out how we’ve managed to get the car to corner so well (despite the handicap of swing axles, crossply tyres and an almost stock ride height) So here it is in a nutshell:

Front Suspension

Balljoint beam with stock leaves, stock rubber bushes and a pair of Sway-A-Way adjusters
1 set of caster shims
2.5” drop spindles
Camber adjusters (2 degrees negative camber)
Tracking 5mm (3/16”) Toe-in
Formula Vee ‘adjustable’ anti-roll bar
Custom made Quantum ‘double adjustable’ dampers
Ride height: 2” lower than stock (note: front is set 1” higher than rear)
Wheels: 5x15” JGE Raders
Front tyres: Dunlop L500 treaded crossply historic racing tyres (120mm tread width)
Front tyre pressures: 22psi cold (25psi hot)

Rear Suspension

Stock ‘soft’ torsion bars and stock rubber grommets
Lowered to acheive the optimum camber (3.5 degrees negative camber)
Tracking 2mm (1/16”) Toe-in
Custom made heavy duty ‘adjustable’ Z-bar
Custom made Quantum ‘double adjustable’ dampers
Ride height: 3” lower than stock (note: rear is set 1” lower than front)
Wheels: 5x15” JGE Raders with 10mm wheel spacers to widen the track by 20mm
Rear tyres: Dunlop L550 treaded crossply historic racing tyres (135mm tread width)
Rear tyre pressures: 25psi cold (28psi hot)

One interesting thing to note is that our suspension set-up goes against all current thinking in Beetle racing, and has more in common with a formula Vee than an old Beetle Cup car (Formula Vees are single seater racing cars that use Beetle suspension, brakes, gearbox and engine. First raced in the 1960’s, these cars are now ‘state of the art’ bits of kit, capable of lap times similar to a modern BTCC Touring Car)...Here are some comparisons between ours and a typical Beetle Cup set-up:

See what i mean?....It’s like we’ve done the complete opposite ‘on purpose!’

There will be many ‘experts’ out there telling you that “we’ve done it all wrong!”....”The ride height is ‘too high”, “the springs are ‘too soft”, “we should use toe-out, ‘not toe-in’ on the front”, “the tyres are ‘too tall’ and ‘too skinny”, “we should use urethane bushes” etc. But then these are the same people that turn up at the Drags with a 2387cc engine with the largest cam and carbs and then get beaten by a bloke with a 1776!....The 1776 probably had a better ‘combination’ of parts. Not the wildest cam or largest carbs, but a selection of parts ‘that have been proven to work’.

It’s much the same with suspension, It’s not about having the lowest car with the stiffest springs and widest tyres....you’ve got to be cleverer than that! The ride height, springs, dampers, tyres, front and rear bars, front and rear cambers, caster, toe angles and tyre pressures of our car have been carefully chosen to ‘work with each other’ in order to get the most out of the car. A low centre of gravity IS very important, but it’s not the be all and end all. The Beetle chassis is a unique design and what works on a Honda Civic isn’t always going to work on a Beetle.

I remember Julian Lock (in the early days of the BeetleCup, when he was virtually unbeatable) saying “everyones lowering their front ends too much...when you lower the front too much, it screws up the steering and suspension geometry”.....and that’s always stuck in my mind.

I’ll try and explain our set-up in a bit more detail so that you can understand the reasons why we’ve picked a set-up that ‘works on-track’ but makes no sense ‘on-paper’....I’ll try and pre-empt your questions!

Q: Why would you go to the trouble of fitting axle adjusters AND drop spindles?
A: The disadvantage of drop spindles is A ‘the cost’ and B ‘the added unsprung weight’, but they make up for this by lowering the car ‘and more importantly’ keep the suspension arms at the factory angle (i.e pointing downwards) so that the suspension and steering work as they were designed to. The Sway-A-Ways are purely there to allow us to fine tune the ride height.

Q: Why have you chosen front Toe-in when Toe-out is better?
A: Toe-out IS known to be better for cornering grip, but it can also unsettle the car under braking, especially on wet or undulating surfaces. Imagine if you have to fight the car entering a corner....your mind is going to be on controlling the car, not on speed. We already have good front end grip, so Toe-in allows me to concentrate fully on getting the best exit...and it’s the exit speed that counts! All of our settings mentioned above are designed to make the car as easy to drive as possible.

Q: Why have you only lowered the car a couple of inches? the centre of gravity will be too high!
A: The historic crossply tyres that we have to use, work best with softer springs. If we lower the car any more, the car will bottom out or hit the bump stops, neither of which you want at racing speeds. Softer springs also offer better tyre grip than hard springs and allow us to ‘monster’ the kerbs without unsettling the car (see pic below). We’ve lowered the centre of gravity significantly by relocating items to the floor of the car, fitted a steering column that is 6kg lighter, adding polycarbonate side and rear windows etc. The car now only weighs 685kg (soon to be 635kg) so body roll is minimal, despite the soft springs. The reason why the car is 1 inch higher at the front than the rear is because it improves straight line and cornering stability. (you’ll see this time and time again if you look at rear engined cars throughout history. It’s all to do with aerodynamics and the polar axis of a rear engined car)

Q: Why go for such skinny tyres? 125mm and 135mm!!
A: There are only a limited number of tyre sizes to choose from. Dunlop crossplys have narrower treads than modern radials and these are the widest tyres that we can fit under the wheel arches. We may experiment with wider tyres at a later date, but wider tyres ‘may’ not give us any more grip as the car is so light that the tyres may not be able to get up to the optimum temperature. Have you seen the front tyres on a Vauxhall VX220? They have very skinny tyres ‘presumably’ for the same reason (135 or 145mm) and they are known to be one of the best handling cars out there.

Q: Why go to the trouble (and expense) of having dampers custom made?
A: The Quantum dampers were expensive, but they have been built ‘to order’ to match the precise characteristics of our car, and having driven it, it’s proved to be money well spent, especially when you consider that they are rebuildable and should last the life of the car. They also offer adjustable bump and rebound and this is one of the key features of the car ‘adjustability’. This is why we have an adjustable anti-roll bar and Z-bar. Next season we will start to experiment with various combinations of bar settings, damper settings and tyre pressures to tweek the handling further. GAC that built the suspension are confident that we can find another 1 or 2 seconds, just from fine-tuning our current set-up. (race pics below Courtesy of www.mattsayle.co.uk)

When driving a car ‘on the limit’ the driver has to ‘manage’ the weight transfer, so that each tyre is doing its fare share. This means not overdriving the car and overtaxing the tyres. If you watch in-car movies of top drivers, they may turn the steering wheel fast and brake hard, but there are no jerky movements, everything is a smooth flow. The secret to our Beetles handling is that these dampers (combined with the soft springs and plenty of suspension travel) soften the weight transfer allowing the car to turn fast into corners without overtaxing the tyres.

When you corner hard, weight transfers to the outside tyres. If there is too much weight transfer or it happens too quickly the grip will suffer. Contrary to popular belief, there is nothing you can do with springs, dampers or anti-roll bars to reduce the amount of weight transfer, the only way that you can reduce the total weight transfer is to make the car wider or lower the centre of gravity. Apart from lowering the suspension, all that springs, dampers or anti-roll bars can do is ‘slow’ the weight transfer down. Our dampers act much like hydraulic rams, slowing this process down. Once turned into the corner, the car ‘gradually’ squats down and plants the tyres without overburdening them.

In the diagram below we have 2 Beetles, both are identical apart from the suspension settings. Beetle ‘A’ is heavily lowered with stiff springs and very little suspension travel, Beetle ‘B’ is our car with mild lowering, soft springs, plenty of suspension travel plus our Quantum dampers. For the purpose of this exercise, both cars weigh 800kg (400kg on the left and 400kg on the right) When car ‘A’ turns into the corner it’s low centre of gravity means that it transfers an extra 100kg to the outside tyres and loses 100kg from the inside tyres, this is quite normal and not a problem. When car ‘B’ turns into the same corner it transfers 120kg to the outside tyres (20kg more than car ‘A’) This is the higher centre of gravity working against it.

Car ‘A’ actually has an advantage because of this, but due to it’s limited suspension travel and stiff setup, car ‘A’ transfers this extra 100kg to the outside tyres ‘instantly’ as soon as the car turns into the corner. The driver of this car needs to keep his wits about him as this car could very quickly break traction or swap ends at that turning-in point. Car ‘B’ on the other hand takes nearly a second (or 100 feet at 70mph) to transfer the extra 100kg, so the tyres are better able to cope with the transition, it also keeps more of the cars weight on the inside tyres than car ‘A’ so the weight of the car is being spread more evenly over the four tyres for more of the time.

After a full second car ‘B’ shifts an additional 20kg to the outside tyres (higher centre of gravity remember) but it is more able to cope with this extra 20% as again its a slow transition. In addition to this, if both of these cars were to get into a slide, car ‘A’ will be much harder to control because there will be very little warning of an impending spin and the spin will happen very quickly. Car ‘B’ will react much slower, giving the driver more time to catch the spin and the car will be more forgiving, it will also be much easier to drive in the wet as softer set-ups provide better grip on wet surfaces.

So there you have it...A Beetle that can match a race prepped Mini Cooper S in the bends...who’d have thought it! But before you get carried away and use these suspension settings on your own car, bare in mind that this is a car that uses tyre technology from the 1950’s. The lack of body roll may also be, in part down to the fact these these tyres don’t generate enough grip. If we were to put modern grippy tyres on the car the weight transfer would increase and possibly unsettle the car enough to require us to run a fraction lower and stiffer.

This isn’t meant to be the definitive suspension set-up for your Beetle that will guarantee you trips to the podium. A cars suspension set-up relies on so many variables, such as the cars weight, weight distribution, centre of gravity, the cars relative speed to others, wheel size, tyre size, tyre type, driving style etc. If any one of these factors on your Beetle are different from ours, your set-up WILL be different....The best set-up for your car may be the complete opposite of ours, more like a BeetleCup or BeetleChallenge car (low and stiff). Maximising a cars handling is a bit of a black art, even the best teams in the world get it wrong (how many times do you hear Formula one drivers moaning about the cars set-up?)

If you want your car to handle well on road or racetrack (something similar to ours would be the better option for the street) speak to as many people as possible, go on the web, go and see the guys that race in the BeetleChallenge (the successor the the BeetleCup) They are a great bunch and they’ll be more than happy to spill their secrets like us. Visit www.beetlechallenge.com

Once you’ve gathered enough info, it’s up to you to choose a set-up that works for you, then make the necessary adjustments to get it right. Don’t be tempted to make adjustments straight away though...get used to the feel of the car first. It may surprise you to know that we haven’t touched the suspension yet...they are still the same settings that the car had when it was built! But now that i’ve spent 4 races in the car, I’ll be better able to ‘feel’ any improvements that come from making any changes to the car.

I hope we’ve proved a point..that there’s more to life than an EMPI anti-roll bar and a set of Koni’s! Go out there and try stuff out. If it works...tell everyone about it, then we can all go faster!

If after reading this you’re still not convinced that our set-up works, take a look at our onboard movies on youtube. Our straight line speed was poor (4th gear was too tall!) but it was able to make back some of that time lost in the bends. (more speed coming next year)

Highlights Movie:
http://www.youtube.com/watch?v=rARRdwc-tU4

Oulton Park (part 1):
http://www.youtube.com/watch?v=fZ949l650M0

Oulton Park (part 2):
http://www.youtube.com/watch?v=3TEkaJl_7M8

Mallory Park:
http://www.youtube.com/watch?v=IVbqyMg-4e8


In the next blog I will do a round up of our first season and share with you what we’ve learned.

Bye for now!

Ian