motorcycle suspension considerations

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weezilco

motorcycle suspension considerations

Post by weezilco »

I note from Don Noble's post in this area that the salt at Lake Gairdner is smoother than at Bonneville. How much suspension compliance is actually necessary to cope with what undulations there are?

Chris Fraser's bike http://www.dlra.org.au/events/speedtrials2004-013.jpg appears to have no suspension at all, other than perhaps the frame flex in this long monster.

I am hoping to do some manner of hub centre steering to minimise the leading frontal area on the bike I'm planning. If I can't get the scooter front suspension I want, I'll have to make my own hub centre arrangement. I have a couple of ideas for it, but it'd be nice to know if, for example, 150-200mm of vertical travel would be sufficient for the surface.

Thanks

Brian
hawkwind racing
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Post by hawkwind racing »

G'day
many racers run without suspension ,as the salt surface is quite smooth ,I recon that its a bit like running on a concrete freeway smooth but a bit bumpy and 150-200mm travel would be ample I also note that you want to decrease the "leading edge frontal area " ??? if you want to do this for aerodynamic reasons you need to decrease the total frontal area ( a silhouette of the total machine and rider looking front on ) to be of any benifit :wink: your total effort should be directed at reducing drag to a minimum as well as rolling resistance with 10-12hp traction will not be of any concern for you ,welcome to landspeed racing
Hawkwind
fastest busa in Captains flat pop. 200
Chris Hanlon
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Post by Chris Hanlon »

G'Day
Welcome aboard Brian. Congratulations it takes a lot of thought planning and commitment to even make it to Lake Gairdner, so keep at it, sounds like an interesting project. After riding Bobs small mini bike around the pits my thoughts are you will need some suspension, not much because the small dia wheels magnify the bumps. Also the layed back posture I would imagine would be much easier to ride with some compliance. Have you considered nitrous to give you another class and possibly beat those Americans but good also.
Hi Hawk, have you started on 2005 yet.

Seeya Chris
Home of the Worlds Fastest Ute

Endeavour to Persevere
Guest

Post by Guest »

Chris Hanlon wrote:
Hi Hawk, have you started on 2005 yet.


Yes Chris well under way ,busa is striped and mods being made I will be running 2 nitrous bikes for 2005 APS/F 1000 and MPS/F 1350 hoping to get both over 230+ hows the grey beast going ? next meets a long way off and the cold winter months aproach ( not like you sunny Qld blokes ) so not much gets done untill it warms up again
Gary
weezilco

Post by weezilco »

hawkwind racing wrote:G'day
many racers run without suspension ,as the salt surface is quite smooth ,I recon that its a bit like running on a concrete freeway smooth but a bit bumpy and 150-200mm travel would be ample


I don't know why I said 150-200mm... Being an American but having lived in Aus since 1996, I occasionally make a dog's breakfast of metric conversions on the fly. I am thinking about 50-100mm travel.

hawkwind racing wrote:I also note that you want to decrease the "leading edge frontal area " ??? if you want to do this for aerodynamic reasons you need to decrease the total frontal area ( a silhouette of the total machine and rider looking front on ) to be of any benifit :wink:


Is there no merit to a shape which is small in cross section in the leading edge but gradually expands, as opposed to a shape where the leading edge has the same cross sectional area as the largest part of the bike?

I was thinking that not having a steering head above the front wheel would give a more gradual increase in c-sect area from the nose with repect to the more rearward bits.

This is the sort of nose I'm thinking of, but the rider goes feet forward in my plan.

[/img]http://www.yacoucci.com/albums/album85/aug15_27.sized.jpg[img]

hawkwind racing wrote:your total effort should be directed at reducing drag to a minimum as well as rolling resistance with 10-12hp traction will not be of any concern for you, welcome to landspeed racing


Wild wheelspin wasn't one of the things I was sweating. :D

Thanks for the welcome. :)

-B[/img]
weezilco

Post by weezilco »

Hmm, that went wrong... and I can't edit posts...

one more time...

Image
hawkwind racing
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Post by hawkwind racing »

I don't know why I said 150-200mm... Being an American but having lived in Aus since 1996, I occasionally make a dog's breakfast of metric conversions on the fly. I am thinking about 50-100mm travel.

50-100mm = 2-4 inch aprox yes IMHO that would be enough

Is there no merit to a shape which is small in cross section in the leading edge but gradually expands, as opposed to a shape where the leading edge has the same cross sectional area as the largest part of the bike?

absolutly none as far as cross sectional area goes ,but the shape certianly does influence your CofD your total "form drag" is a combination of cross sectional area and coefficient of drag as I stated your cross sectional area is like looking at a silouete of the machine front on ,at subsonic speeds a tear drop shape with the pointy end at the rear is the optimal shape not the other way around
I would advise you to read the current DLRA rules as the pic you posted that type of set up could be used ONLY for a streamliner and not a special construction class bike though I am in the process of seeking some streamling rule changes for "special construction class bikes "
gary



.


]
fastest busa in Captains flat pop. 200
Guest

Post by Guest »

G'Day Weez
A picture tells a thousand words, now I get it. That design looks like it will work well..You really are going to get a crook neck trying to read the tacho.
How do you plan to shape the rear of the body?
Heh Hawk.
We did a dyno shootout day when we got back. (We were the drawcard) and have been in catchup mode at work since then. Plan is to attack 200 in 2005. This will require the sheetmetal intake in an attempt to move my max torque point up about 500rpm. There is nothing left in the heads to improve and I love the cam so much I'm hesitant to change it, but may have too depending on how the manifold works on the dyno. I have to change to a toploader gearbox as I destroyed the single rail on my last pass on Friday (remember the weakest link)
Everything else I do will be tidy up and detail work to fix some of the rough stuff done in the rush this year and make the bus reliable.
weezilco

Post by weezilco »

I've just spent a little time looking at the front suspension pictured above. Deceptively simple. I wonder how much lock that arrangement has... but it sure is LOW.

-B
weezilco

Post by weezilco »

The bodywork I plan will be in two pieces, sorta like this Rotator "Pursuit" bike with "Interceptor" fairing:

Image

Another fairing:

Image

It's pretty close to the shape I'm after.

Without its sidecar, this concept comes amazingly close to what I've sketched up, minus the "windscreen" part of the fairing as in the previous pic.

Image

I'd not employ this fellow's under-seat steering arrangement, though. Ridden a few under-seat bicycles and didn't like them much.

I have a copy of the DLRA rules in PDF. I'm now off looking for the part which makes weirdo suspensions as above illegal for Special Constructions.

thanks,

-Brian
Last edited by weezilco on Sun Apr 25, 2004 12:43 pm, edited 1 time in total.
weezilco

Post by weezilco »

Chris Hanlon wrote:Have you considered nitrous to give you another class and possibly beat those Americans but good also.


Nitrous could be lotsa fun. :) Wouldn't have a clue as to how N2O and 2-strokes co-operate, tho.

I'm more inclined to develop the bike over a few years into a full streamliner to eventually have a crack at the NSU BF-S 50cc record from 1956 at 121mph.. now where's that old 6-71, and do I have enough motor to crank it over? :D

Beat the Americans? Absofrigginlutely!

'Course, I do get a lil confused with flag waving exercises as I'm a citizen of both the US & Australia. ;)

Speaking of that, gotta hit the hay, the girlchild is an Air Force Cadet, needs a ride to ANZAC Day memorial thing at 5am...

seeya

-Brian
John Broughan
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Post by John Broughan »

I think that your proposed suspension travel is a bit excessive. You only need enough to stop the bike shaking your brains loose, which at your relatively slow speed will be a problem. I would think that 25 mm of travel from a static loaded position would be enough to flatten the harshness out. My car is pretty much unbearable under 50 or 60 MPH. Over this, no problems
John Broughan
Empty Pockets Racing
200 MPH club life member
weezilco

Post by weezilco »

Righty-o! I'll plan the suspension as if I were going to run on a graded unsealed rural road. Flat, but kinda washboardy. Got it.

I've driven enough unsealed roads in Aus at stupidly high speeds to understand the concept of getting up enough speed to 'skip across the tops' of the undulations. I suppose this occurs when the suspension can't quite rebound fast enough to follow every tiny bump.

To that end, I imagine that the 50cc bike will need a rather 'slow' suspension- long control arms with minimal travel but stiffish damping.

Sound OK?

Thanks again!

-Brian
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