quick question to aussie teams

[The guru of guru's]

Can i get an indication of what wheel base and track that you guys are using? Also what type of motion ratio do you use?
Thanks for the help.
Cheers
Dave.

[The guru of guru's]

Can i get an indication of what wheel base and track that you guys are using? Also what type of motion ratio do you use?
Thanks for the help.
Cheers
Dave.

[PatClarke]

G'day Phantom http://fsae.com/groupee_common/emoticons/icon_smile.gif
Didn't you take a tape measure to Tailem Bend, or were you too shy to use it?
Successful cars range from short like UQ to long like Chalmers, and stop at every station in between. Design the wheelbase you need to achieve what you want to achieve.

Meanwhile back at the bellcranks, look at the available stroke available from contemporary bike shox, then consider the wheel travel required by the rules, and the motion ratio answers itself (almost) http://fsae.com/groupee_common/emoticons/icon_wink.gif
PDR

[Jarrod]

track widths ranged from 1050 to 1300, wheelbases from 1525 to 1750 from memory.
I sent Ash some shock data, consider that when discussing motion ratios. Custom springs aren't especially expensive.

[The guru of guru's]

Yeh...a tape would have been a help. Note to self: bring a tape next time. Thanks Pat.
Cheers
Dave.

[Kevin Hayward]

Dave,

Motion ratios are very dependant on the damper you wish to use. If you want to use an unmodified Fox damper for instance I would take note of what the successful teams use for the springs. This combined with a reasonable wheel rate will help you get a starting point. This worked for us in the first year and our motion ratios haven't actually changed dramatically since. This is despite now knowing what the dampers are doing.

I'm reluctant to put a value on this as it will start an almighty war between suspension people. However I think that the mountain bike damping rates seem to work with springs ranging from about 350 to 600 lbs/in. remember this is not a wheel rate ... surely nobody is running anywhere near this as a wheel rate http://fsae.com/groupee_common/emoticons/icon_smile.gif

The real bastard with running motion ratios in this range is there is less fluid motion and hysteresis is a bigger problem.

This is one of the reasons why teams start to go away from mountain bike shocks or start revalving to performance under increased shaft displacements.

As for wheelbase and track:

Wheelbase: 1750
Track: 1200 and 1150

No big secrets here. Most teams are pretty close in tracks with wheelbases between 1600 and 1800 ... well at least from what I can see

Cheers,

Kev

UWA Motorsport

[Ashley Denmead]

Jarrod,

Did you send that info to myself or Aaron?
we had custom springs made last year....definitly a good option if the spring rate you need isnt available off the shelf.

Hope all is goin well down clayton way....see you on the weekend at MoTeC http://fsae.com/groupee_common/emoticons/icon_wink.gif

ash

[Jarrod]

I sent it to someone I'm sure. If not I can send it again. I won't be at the seminar this year (went in 02 and the plane ticket to England cleaned me out about 5 times over) You should stop by the uni one night, have a couple of quiet ones.

[Frank]

suggestion:

if: you plan not to modify mountain bike shocks

then: dyno them first, and set your motion ratio to match your required damping rates (it might be a large motion ratio). I guess if you do this, the trade off is prefered damping rates VS the potential hysteresis problem, that kev just mentioned.


as for wb.. we're extending from 1525 to 1575 this year

[Ashley Denmead]

mmmmm alchamahole....sounds good jarrod, might come by and see what ur up to soon.

ash

[The guru of guru's]

Is it Monash's shout?

Thanks Jarrod for that data, are you guys still going to use the fox vanilla shocks or have you got something else in mind? We are looking into buying a set quite soon.

Dave.

[Big Bird]

Note for anyone who wants to buy Fox Vanillas here in Oz - you might want to get in pretty quick. Word is from Dirtworks (importer) that the new 2004 units are going to have some sort of MTB specific valving mechanism that will make them a lot harsher in their low speed response. To quote Bear from Dirtworks from a mail he sent me around two months ago:

"We have stock of shocks we keep specifically for FSAE use, as the latest valving set up, called Pro Pedal has extremely high low speed compression damping which would be, I think, rather unsuitable for FSAE usage - think of considerable wheel chatter problems & you'll have an idea. Once these are gone we cannot obtain stock of the more FSAE suitable shocks, so if you want something you would need to do it fairly soon, we have enough enquiries from Uni's at the moment to account for available stock about twice over".

Cheers all,

[Jarrod]

I discussed the same thing with bear, and after alittle research, the pro-pedal shocks would be absolutely useless on an fsae car unless it weighed about 600kg. The low speed damping is around double the current settings. (which I think is a little stiff anyway). The range of adjustment on compression is no better either.
Ghost considering there is no future availability for Fox shocks, we have decided to move on to other options. I think I'll leave it at that. We can sort this one out if you promise to tee me up next time i'm down your way. Any chance you'll be around this weekend big bird?

[Kevin Hayward]

Guys,

I don't think the problem with the compression stroke is in the actual rate. In fact we were chasing a little more compression damping. The amount of damping does depend on motion ratios etc so I don't think this is the case for everyone. Of course the adjustment in compression is just a preload adjustment on blowoff, hence no actual low speed compression rate change.

From what we have seen the main issue with the compression side is the hysteresis (much worse than on the rebound side). This is probably designed into the mountain bike shocks to help prevent pogoing while pedaling (I think this is the right mountain bike term ... not being a mountain biker myself).

The name pro-pedal suggests to me that more hydraulic friction has been added to increase pedalling efficiency ... could be wrong though. If that is the case then they are next to useless ... even more hysteresis. However if it is just a rate change then given the large rebound adjustment range you should be able to make mods to motion ratios to make them work. We run on the low side of rebound adjustment to begin with. What it will mean is even less shaft movement ... bit of a bummer.

The problem of MTB shocks : so light, cheap and easy to package but pretty ordinary fluid control.

Cheers,

Kev

UWA Motorsport

[The guru of guru's]

No worries Jarrod, you guys are welcome to come down anytime. I know Ash will fire up the bbq.
Cheers
Dave.

[jdstuff]

Kevin,
In response to hysteresis being designed into MTB shocks, you're basically right. I worked at a bike shop for about 4 years as a mechanic, so I've spent a lot of time working with MTB suspension. The pheomena that good MTB shocks are designed to prevent is called 'bob', which is when the suspension compresses slightly under each pedal stroke. When riding, this really robs you of forward motion because some of your pedal stroke is wasted and converted into suspension travel.

The newest MTB shocks actually have a concept similar to a blow-off valve on the compression stroke, prohibiting ANY compression until a given hydraulic pressure is achieved. The shock is then essentially a rigid link under light loading....great for eliminating pedal bob, a nightmare for our applications! These are actually refered to as "platform" shocks (just think of what the dyno curve would look like and you'll get the idea).

Anyway, probably not much help to the thread, but a little history lesson nonetheless.