Dry Lakes Racers Australia

In my build diary the question of suspension and frame geometry has come up....I have started this thread so that it can be more fully covered ...im all ears to finding out the facts and diverse opinions of you my fellow racers.....I have tried both suspension and no suspension ( rear only) but its hard to compare as the bikes are very different and my speeds are relatively low ....reading the many threads on other sites is not really helpful as our racing is unique ...and the opinion is divided on Landracing .com both with the car and bike folks as regard to suspension...appears most of the big dogs in the siton bikes run suspension but most of those are short wheelbase stock framed bikes but one bike (the guppy) has run 250+ with solid rear. Personally I like a hard rear end and suspension up front but is it the best ?
What say yea?

cheers

While i prefer suspension
the only 2 bike comparo i have is the US and Aussie 750's
US bike has enough lead to bottom out the suspension , it runs mid 220's, not quite solid rear end but pretty close
some motor and weight combo on the Aussie bike running at Bonneville with a heavier spring and functioning suspension gave us the same speed within a mph or 2
Both can overpower the track in lower gears , suspension feels smoother on a rough track, but the end result is similar

I think with very high speed the pressure ridges and other sharp bumps like holes in the track are absorbed in the tire deflection , and suspension realy only deals with undulations that are not realy noticable at lower speeds

The Creek this year was the best I have seen it and its quite a launching ramp.
I can't imagine attacking it full noise without suspension car or bike.

......Relative to speed.....
HOW FAST ARE WE NEEDING TO GO ?......................300mph...sit on bike..
I feel its all about controlling the vibrations the frame is recieving..
Its a given ... No one in there right mind would have a ridged front end, as you would be recieving vibrations from an arm that is leading through to the steering head that would not only try to tear the steering head out , but would also be enough to make your eyes rattle out of your head..
The rear is different .. vibrations are travelling from the rear wheel forward back to the riders butt, if unsuspended (and as staytie pointed out in the other thread ) you will have a definite feel of hook up.. suspension will mask this feel..

The length and design of the chassis , determins the need for supension.. a wheel base of up to 1800mm (axle to axle)
is fine with suspension , but at 1800mm it will be needing to be carring a lot of weight..

To go 300mph I would think the wheel base will need to grow from 1800mm .Once you have gone past this point the need for supension will deminish but if you exceed past 2400mm suspension will have to go back on..


Reason being
From 1800mm out there will be enough vertical flex in the chassis to give good feel and grip ..but you need to be carefull
of horizontal flex (to much and you will be cracking chassis )
Once you have gone past 2400mm you will then be long enough to have a rear end recieving and returning vibrations
This is a bad thing... the chassis will be bouncey and will be prone to cracking, suspension will needed to be added to nullify this issue.

Chassis design is the key ..

.....................................SUSPENSION ... 6 of one ....half a dozen of the other..........

PS: This information is not written in stone.. design ,tube diameter and wall thickness are factors that will adjust the
answer ! There is also the idea of the rider sitting in front of the engine which will also adjust the answer
.. The variables can be confusing...

Ross ..

"There is also the idea of the rider sitting in front of the engine which will also adjust the answer" Thanks for your reply Ross I would like to hear what you have to say regarding rider in front of the engine as one design im very interested in is FF like a streamliner.
cheers

FF (feet forward ) for those that did not realise, was a solid rule and class in the 2006 rule book..
maybe because no one used it it was deleted..
but anyway... building a FF 300mph sit on bike would be an enginerring feet.. steering would have to be
something special.. to be able to sit IN it comfortably and have some sort of proper control, it would either have to be centre hub steering or leading link with twin steering heads (one steering head behind the other with double linked arms)
Problems that come to mind .... body control will go just about to zero.. building the needed rigidity underneath the rider..

Building a engine behind the rider bike sitting in the normal position would be much simpler and in my opinion would be more successfull..
the advantages ... as to a normal A bike... short chain.. engine weight already at the back wheel.. lower aero package
unrestricted exaust system.. unrestricted intake system... steering can be telescopic or leading link..(leading link will allow a tall front wheel ) riders seat and proper balance of controls would be simple.. easy to add weight front or rear..
would go fast in any color...

Ross..

So the Silverton boys were ahead of their time with their Leyland V8 powered bike?

I think the Silverton Boys are from a parallel dimension

I spoke to Ackattack about the suspension on his streamliner and if I remember correctly he said they had an inch of suspension movement.
I think he mentioned that arriving at the springrate was easy but getting the damper rates correct was very time consuming.

How about a rear engine kneeler--- like a road race sidecar.
You could make an amply strong triangle trellis to go between the riders legs and the exhaust can go forward through the frame.
Bones

Thanks everyone for the input sofar great stuff......well for my project only one thing yet is fixed and unchangeable ,15" wheels and goodyear landspeed tyres....the major design criteria, which body ( mine) orientation gives the most streamlined area and least frontal area in keeping within the rules...lots of research ahead.
Favouring a modified leading link design and if Ross is correct about wheel base then a suspended rear end will be needed as the wheel base will be in excess of 2400mm especially if twin engines are used....to bad dustbins are out of favour

cheers

BONES wrote:How about a rear engine kneeler--- like a road race sidecar.
You could make an amply strong triangle trellis to go between the riders legs and the exhaust can go forward through the frame.
Bones

Ask Wilso about his 3 wheeler build,,

The V8 bike was rigid both ends,,,,,,

Just say you were doing 150 mph but with twice as many deviation in the racing surface, or 75 mph with four times as many.

Motorcycle road-racing suspension these days is something special in itself. High-end rear shocks have low and high speed damper circuits, and separator valves that 'as much as possible' isolate the compression and rebound circuits from each other. I'll try to get some telemetry data off a friend who crews one of the top motogp riders. These bikes commonly do well over 200 mph these days. (lap after lap)

Sometimes you will see telly on-board footage, with a rear facing camera looking at the rear suspension working, it's quite amazing to see.

I really don't understand why it is perceived that LSR is any different to any other elite form of motor-sport? That it is thought the laws of physics that apply every where else in the world, don't apply on the salt.

Using treaded tyres, pumped up to whatever, (certainly beyond what they are supposed to run at) lead on swing arms, solid rear ends? Can someone please explain?

Anyway, as I said I'll try to get some data. I'm open to to doing some field research on the topic, on the salt.

Last year, our bike felt like it was running down a newly surfaced freeway. The only deviation experienced was soft salt on our last run when the bike bogged down, and I ended the run.

I've got to say we did pay attention to what was commonly said about slip etc, and geared far to tall, with only 2 runs after rookie licencing, it was obvious that our best speed would be achieved at beyond red line in 5th gear. So we let the tyre down to minimum recommend pressure, off the tyre warmers... (gearing change) and ran it like that.

I'm just providing anyone interested, with a different point of view for consideration.

Quote
Using treaded tyres, pumped up to whatever, (certainly beyond what they are supposed to run at) lead on swing arms, solid rear ends? Can someone please explain? quote

One word sums it up TRACTION.....im sure that road racers if trying to race on a very slick/ slippery track trying to get 400+ hp to hook up would do things differently as well. Sure the laws of physics don't change ...but road racing and LSR are like comparing apples to oranges.

hawkwind wrote:One word sums it up TRACTION.....im sure that road racers if trying to race on a very slick/ slippery track trying to get 400+ hp to hook up would do things differently as well. Sure the laws of physics don't change ...but road racing and LSR are like comparing apples to oranges.

Really?

Edit: one question is do you need 400 hp? Wheel spin is fine if you want to spin your wheels. Lead is fine if you want your rear wheel to be in contact with the racing surface 1/2 of the time of each bump. I believe Brett runs with around or less than 200 rwhp, and he is the fastest bloke on a sit on in this country.