The old lakester suspension argument.......

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walkingpace
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The old lakester suspension argument.......

Post by walkingpace » Tue Jul 24, 2012 2:56 pm

I am soon to start laying out the chassis for my lakester build but before I do that I need to resolve this issue of whether or not to incorporate suspension. The rear end will be rigid, that much I am sure of, however I simply cannot decide whether to do the same on the front. The positives of a rigid front end are simplicity, and the ease of creating a streamlined foil like structure around the axle which blends neatly into the body, however the negatives seem to be repeated firm kicks in the backside from bumps and potential control issues on a slightly dodgy surface. It is on this basis that I have a few questions;

How good are LSR tyres at ironing out small bumps through sidewall flex?

Has anyone actually stuck a camera on good old fashioned leaf spring lakester front suspension to see what (if anything) it's doing?

Just how rough do we expect the surface at Omeo to be once it has been rolled?

I intend to maintain a few inches of ground clearance in any event.

To make matters more complex I have gone for an unconventional lakester configuration being front engined with the driver seated just in front of the rear axle. The drive shaft will be run very low in the belly with a chain drive then rising up through a tranfer case to the diff, thus allowing adjustable gearing whilst also keeping the driver low in the car.

Any thoughts or ideas on the suspension issue would be greatly appreciated.

As a side issue I have almost finished a 1/18 scale model of the car in balsa wood along with a tiny wind tunnel and plan on doing some testing this weekend. There will be photos.....

Dr Goggles
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Re: The old lakester suspension argument.......

Post by Dr Goggles » Wed Jul 25, 2012 10:16 am

Nice work building the model.

I have only driven without front suspension, so my opinion isn't fully informed but on a list of things I'd change in our car(there isn't much) suspension isn't near the top.

One of the only relevant parameters in this game is un-sprung weight, the response rate of any suspension system and the attendant damping need to be greater than for any other sport, because you are going faster. If the suspension can't track the surface, it is worse than useless.That's the theory. In practice we watched other cars develop over several years and watched as they screwed their suspension down to a point where it didn't really work.

Rear suspension might help you hook up, that is if you've got enough power to break traction, not really a problem unless you've got more than 300hp, there are cars( in the US) running solid rears with 900hp......

Many argue against front suspension because of their concerns about ride height and cars "lifting" at speed.

Comfort wise it might be the only thing you remember about making a pass, seriously it's kind of featureless and unremarkable.
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

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Reverend Hedgash
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Re: The old lakester suspension argument.......

Post by Reverend Hedgash » Thu Jul 26, 2012 1:34 pm

As the good doctor said I can only speak for our car that has no suspension but we didn't come to that conclusion from laziness. As Dr G said we witnessed most cars ever tightening theirs and with what we felt with drag being a more important issue than suspension being a lakester that the less in the wind the better. If you look at the SoCal bellytank it looks pretty but that amount of suspension gear in the wind must have knocked 10+mph off top speed.

A question you need to ask is where are you going to run it?

The Salt at lake Gairdner is usually in very good condition when a meet occurs when compared to venues like the the dry lakes in the states which due to salt mining and higher traffic can have a significantly rougher surface where the need for usable suspension increases.

We tested at Mangalore airport which was a great day but their were some bumps on the track that caused us havoc with me getting the car airborne due to them. (Minor) The bottom of the car scraped the ground when I landed so there was enough flex in either the tyres or the axles themselves (front supported narrowly in the middle allowing a long slenderness ratio which means they could flex more than if supported at the ends)

For me if the future of the car was Gairdner only then I would have no hesitation to say go with none. If your future plans are more worldly then maybe some extra consideration is required.

For your information our front axle is not steel against steel, we sandwiched some high density rubber in the axle clamps. Our thoughts here were not so much to facilitate movement in the vertical sense but to reduce vibration.

The tyres are tall and although under high pressure there is of course a lot of rubber between the ground and the wheel so some absorption should be there.

My experience of driving is that it is bumpy as hell just toodling around the pits, etc, but when you get on the track and the speed starts to pick up everything quietens down a lot as it gets into a different frequency.

The biggest bumps in the end are the longer dips caused by the creek location and major deviations in the surface of the lake probably introduced by thermal factors. At the speeds we are doing these long shallow dips and hills start to become more noticeable ( and maybe a reason to run the track the opposite way...)

It takes so long to build a car and get it going maybe build it without to start with and get on track and then install it later if you deem it necessary. What is built can be unbuilt; that is the beauty of steel.

My thoughts, can't wait to see the pictures and model. There are some good virtual wind tunnel programs available now too.

Dik
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walkingpace
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Re: The old lakester suspension argument.......

Post by walkingpace » Thu Jul 26, 2012 8:23 pm

I think Dr Goggles makes a good point about the sprung vs unsprung weight issue. My front end is a cast iron I beam so it's bound to cause trouble for the suspension hitting bumps at high speed. Mounting the front end on rubber blocks seems a good idea though.

I think my best bet is to build it without springs but to make the front end height adjustable through about 2 inches. I'm building for Gairdner and I'm a huge fan of keeping things simple.

Your knowledge amd wisdom are greatly appreciated!

BIG GAZ
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Re: The old lakester suspension argument.......

Post by BIG GAZ » Fri Jul 27, 2012 2:42 pm

I am interested the sprung/unsprung weight issue. My thinking has always been that the less unsprung weight the better. Since going to Bonneville in 2010 and speaking to a number of actual racers it seems that golden rule doesn't always apply. There are a large number of cars (admittedly sedans) that have the ballast loaded or bolted directly onto the diff housing. Since my car, after all the mods only came up to 1,440kg I need to add in about 600kg and trying to distribute that amount of weight is not easy, space wise, so I am in two minds about bolting another 100-150kg to the diff as that is about the last space I have. Based on 'expert' advice I was looking at about a 52% front and 48% rear balance.
Is this the concensus of opinion on sprung/unsprung weight solely for landspeed?
GAZ

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JonB
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Re: The old lakester suspension argument.......

Post by JonB » Fri Jul 27, 2012 6:38 pm

Less unsprung weight will let a wheel follow a bump better.

More unsprung weight will reduce "road noise" type vibrations by making the tyre part of the vehicles suspension work harder.

A pretty flat surface with small irregularities at high speed will feel smoother with a greater unsprung weight.

A wheel with higher unsprung weight will take a bigger bump to leave the ground, a lighter wheel will get back on the ground quicker.

Cheers
jon
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grumm441
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Re: The old lakester suspension argument.......

Post by grumm441 » Fri Jul 27, 2012 8:38 pm

Hey Walking Pace
Welcome aboard
what Goggs and Headgash didn't mention is that the front axle in question is not a cast
unit and is a fabricted thick wall tube axle. so it has a certain amount of flex that you wouldn't
get with cast unit
G
They make it
I make it work

BIG GAZ
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Re: The old lakester suspension argument.......

Post by BIG GAZ » Fri Jul 27, 2012 10:33 pm

Jon- Yeah, yeah, yeah, I know all that. But is the salt different? If we were talking potholes I would Definately agree. And I know that at our sorts of speeds depressions or the creek could be considered a long pothole. But if you have plenty of rebound left in the spring as you hit the bump or hole then the comparatively heavier car would compensate for the heavier unsprung weight... Maybe? The fast cars, eg Hooleys Studebaker don't seem to suffer any ill handling from the higher unsprung weight. Any ideas?
Gaz

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