cloudy
|
| posted on 21/3/07 at 01:37 PM |
|
|
TRE Binding!
Sorry for my constant "need help" posts, I'm on the really safety crictical parts and really want to get it right...
Here's my problem - this is my suspension at full bump
The top joint bottoms out just past this point (before the chassis would hit the ground), so obviously I will set the shocks to stop it going this
far...
Problem is the TRE is binding here, is this a common problem - any idea's for a cure or is this just at the limits of this type of setup?
James
|
|
|
|
|
andyharding
|
| posted on 21/3/07 at 01:39 PM |
|
|
Your sump will stop the chassis hitting the ground 
Are you a Mac user or a retard?
|
|
|
02GF74
|
| posted on 21/3/07 at 01:49 PM |
|
|
Where is the shock? do you really think it will go that far?? How fitting about the shock without the spring and try again.
|
|
|
ecosse
|
| posted on 21/3/07 at 01:50 PM |
|
|
That looks like a lot of bump movement (3 -4"?) can't you just reduce the amount of travel you have (or is that pic misleading)?
Or if you need that much travel how about using a high misalignment rose joints instead of the tre's?
Cheers
Alex
|
|
|
Mr Whippy
|
| posted on 21/3/07 at 01:50 PM |
|
|
the upper ball joint looks like its at the limit also.
|
|
|
Ivan
|
| posted on 21/3/07 at 01:58 PM |
|
|
How much bump do you have in the photo? To me it looks a lot more than normally allowed (around 3" )with the sort of shock lengths we use.
With full left lock the TRE will be even worse and you deffinitely don't want the ball joint binding as that's just asking to break
things.
So set everything up to avoid the binding - if necessary lift the rack slightly and find a new sweet spot to avoid bump steer.
[Edited on 21/3/07 by Ivan]
|
|
|
cloudy
|
| posted on 21/3/07 at 01:58 PM |
|
|
It's a BEC middy - no sump 
It's going to ride quite low about 120-130mm so how much travel will I need in bump from rest at 120mm?
If I can solve by just putting shocks in so it hits the stops before this then that would be fine (shock mounts are not built yet)
|
|
|
zetec7
|
| posted on 21/3/07 at 06:31 PM |
|
|
Build the shock mounts to preclude this binding at full bump. That's a LOT of a-arm movement you're showing in the pic...you should NEVER
have your suspension travel that far under anythng but hitting-a-speed-hump-at 100mph circumstances...and if that happens, expect a lot more damage
than joint binding! Your setup looks great, just set the shock mounts to prevent this situation, and don't worry about the shown binding. It
should never happen with the shocks in place.
http://www.freewebs.com/zetec7/
|
|
|
Ivan
|
| posted on 21/3/07 at 07:25 PM |
|
|
quote:
Originally posted by cloudy
It's a BEC middy - no sump
It's going to ride quite low about 120-130mm so how much travel will I need in bump from rest at 120mm?
If I can solve by just putting shocks in so it hits the stops before this then that would be fine (shock mounts are not built yet)
The chances are that if you originaly set the ride height at the front at 120 - 130 mm (quite high) you will want to lower the car to 105mm at some
time so I would start out with 75 mm of bump so that if the car is lowered you would have 50 mm bump which should be adequate.
|
|
|
cloudy
|
| posted on 21/3/07 at 08:34 PM |
|
|
Thanks Ivan + zetec, I will check where 75mm takes me and see if I can get away with it
James
[Edited on 21/3/07 by cloudy]
|
|
|
cloudy
|
| posted on 21/3/07 at 11:24 PM |
|
|
OK at 105mm ride height I only get 25mm before it binds up!!
Looks like two options,
1) Move wishbone mounts to top of tubes at the bottom, and move tubes out. Move top mount tube up
2) Put on smaller wheels - these are 215/40/17, I don't really want to do this as the large wheels are a feature of the design...
edit - number 2 won't work the tyre is only 5% larger than a normal 195/50/15
Any good idea's?
James
[Edited on 21/3/07 by cloudy]
|
|
|
Ivan
|
| posted on 22/3/07 at 06:39 AM |
|
|
Your no 1 proposal should help but will of course influence roll centres.
Your options are limited to changing ball joint type or changing suspension mountings or changing upright.
I'm not sure - is this car your own design or is it a kit - if a kit the supplier should sort out this problem for you - if your own design
it's back to the drawing board.  That's the fun of doing your own design 
One other thing have you tested the rack location for bump steer or is it just placed in terms of theory - I would actualy test it as you may be able
to lift the rack without impacting too much on bump steer. Also lifting the attachment points of the wbones won't help your TRE problem as you
will lift the rack the same amount.
|
|
|
cloudy
|
| posted on 22/3/07 at 09:29 AM |
|
|
I've been playing with bump and if i start to raise it I start bringing the bump steer back 
It's my own design - back to the drawing board!
PS. Just a thought - are you suggesting 105mm from sump to ground or chassis rails to ground?
James
[Edited on 22/3/07 by cloudy]
|
|
|
Ivan
|
| posted on 22/3/07 at 11:31 AM |
|
|
Normally the car will be set up for the chassis to slope down slightly (12 - 25mm) to the front to cope with things like variations in passenger
loading and fuel levels etc so if you choose to go to 105mm chassis height at front (depends on where you drive and road quality) you would go higher
at back and again you have to make the decision on chassis height informed by sump protrusion from the chassis.
All those decisions are affected by things such as vehicle use, wheel rates ("soft" springs need more suspension movement and hence ground
clearance) wheight distribution fore and aft, normal driving loads etc etc so it is impossible for me to advise you as only you know the answers - you
just have to decide for yourself
Have a good look at succesful similarly configured cars and be informed by them - in your case Lotus Exidge or similar (Even Porsche RSR) Even talk to
guys in your area with radically lowered saloons and find out the problems bearing in mind that the lowering is likely to have been badly engineered.
|
|
|
cloudy
|
| posted on 26/3/07 at 12:06 PM |
|
|
As part of a solution to move the whole suspension up so I get the required ride height with the bottom wishbones flat - i would need to do this to
the bottom wishbone mounts
Can anyone comment on the safety aspect of this? Is it likely to be too weak?
|
|
|
Ivan
|
| posted on 26/3/07 at 01:58 PM |
|
|
I would hesitate to ever comend the safety of something like what you intend to do but can comment that repeating the gusset plates below the bracket
would add conciderably to the strength.
I recommend you pay or otherwise get an engineer to design these brackets.
|
|
|
cloudy
|
| posted on 26/3/07 at 02:17 PM |
|
|
That does defeat the point of a home designed chassis
I figure as long as I do it sensibly, it should be OK - what's not drawn is two runs of L section that join the two chassis tubes side to side
that form the steering rack. This should help dissapate the twisting moment.....
James
|
|
|
