unijacko67
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| posted on 28/10/13 at 11:16 PM |
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Bouncy wheel spin
I can do a quick start, but if the wheels lose traction the wheels spin and seems to judder/bounce rather than just spinning out until gripping. This
happens in the wet or dry. I have lsd, watt's linkage , equal parallel 4 link bars. I've tried a few damper settings and a couple of
different spring rates. Is this just a common thing with the large hp low weight cars or can it be sorted. It's obviously loads worse in the
wet. I've just built the car as a total one off so still trying to get the rear springs and damping just right handling wise. Any ideas.
 
Description
[Edited on 28/10/13 by unijacko67]
http://www.kittenkitcar.co.uk
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owelly
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| posted on 28/10/13 at 11:30 PM |
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I had horriffic axle tramp during launches and dropping the tyre pressures sort of cured it. I say sort of, because then my rear tyres were running a
bit softvand getting too hot!
http://www.ppcmag.co.uk
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arrow-engineering
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| posted on 28/10/13 at 11:42 PM |
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move your bottom link bars up one hole, do the test drive, come back, if still not happy do one more hole up, if still not happy look in the internet
about instant centres and squat/anti squat. its very possible from looking at your set up that the power from your car is causing the back end to
lift under accel, when you actually want it to sit down and grip.
[Edited on 28/10/13 by arrow-engineering]
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unijacko67
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| posted on 28/10/13 at 11:50 PM |
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Thanks, I will try that and report back. I know it can alter how the car handles, but wasn't sure it could alter the way the power goes down.
Cheers. I think my tyres where a bit hard also Owelly as I had 30 psi in them dry (ao48's) and dropped it to 24 psi in the wet. Cheers
http://www.kittenkitcar.co.uk
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CNHSS1
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| posted on 29/10/13 at 03:11 AM |
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Id agree, its an anti squat issue. On the hillimbers, a lot of the GTE & Coupe Scimitars really go to tiwn with the trsiling arm angles for anti
squat, makes a huge difference!
I too agree you are possibly getting pro-squat. Get a copy of Allan Stanniforths Race and Rall car source book and all will be revealed.
Another issue could be the lsd. I suspect its either plated or atb/torsen? If plated (salisbury type) it could be ramp angles or preload settings
although usually there are pointers from other areas (corner entry/exit oddities and noises) but in a new build theres so much going on to be tweaked
its difficult to pin down.
ATB diffs such as quaifes, cycle the grip left to right across the axle as they move the torque across from the grippiest tyre until it slips and so
on. On sticky slicks, my old atb equipped car would leave 'pulsed' black lines off the start and feel for all the world like axle tramp,
but it wasnt.
Id run a video camera under the car and do some hard launches as you can learn a lot from seeing whats going on.
HTH
CNH
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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snapper
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| posted on 29/10/13 at 07:02 AM |
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Would suggest even 24 psi is high for such a light car in the dry
18 to 22 is a better range
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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owelly
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| posted on 29/10/13 at 07:36 AM |
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I run 16psi in the fronts and 20 in the rears. Also be aware that it's possible to over locate the rear axle with anti-squat. Good for launches
but bad for cornering!
http://www.ppcmag.co.uk
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unijacko67
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| posted on 29/10/13 at 08:18 AM |
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Great info thanks, looks like bottom link bar up a notch and test, tyre pressure also not good. the diff is plated, but I originally thought the ramp
angles would need machining as steep for my car weight.
Quote 'pulsed' black lines off the start and feel for all the world like axle tramp. This is exactly what it does, the black lines are
even left to right in the dry, about 12" line then miss a bit less then 12" line again. How do I know if I'm over locating the
axle?
Will test it tonight, thanks men.
http://www.kittenkitcar.co.uk
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owelly
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| posted on 29/10/13 at 08:45 AM |
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Jack up the car using one end of the axle and see if the other end lifts too! You may need to remove the springs or disconnect the coilovers. Unless
of course you're using the axle as an anti-roll torsion bar.
http://www.ppcmag.co.uk
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froggy
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| posted on 29/10/13 at 09:17 AM |
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I run 25in the back if mine with a lot of weight over them .my 4 bar set up uses very long arms running downhill towards the de dion at 5 degrees . I
don't have any traction problems but its mid engined
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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Oddified
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| posted on 29/10/13 at 12:00 PM |
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I run 18 - 20psi in the rear with federal rsr's, works very well. If i use them for a bit of rwyb i drop them to 12psi.
Link angles, damper settings and springs are all important but over the years i've found that high pressures and hard ish regular road tyres =
loads of axle bounce irrespective of other settings.
Ian
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britishtrident
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| posted on 29/10/13 at 12:32 PM |
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Tyre pressure is the most likely cure, however looking at the picture the mounting point for the lower link looks like it needs some triangulation
to stiffen it.
If you add ant-squat I would raise the forward ends of both upper and lower links rather than just the lower link.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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snapper
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| posted on 29/10/13 at 01:11 PM |
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From what you've said it sounds like LSD setup is the issue off its pulsing left/right
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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unijacko67
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| posted on 29/10/13 at 02:30 PM |
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quote:
Originally posted by snapper
From what you've said it sounds like LSD setup is the issue off its pulsing left/right [/quot
Its not pulsing left to right, cheers
http://www.kittenkitcar.co.uk
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unijacko67
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| posted on 29/10/13 at 10:00 PM |
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Tested it tonight by moving the front up on the bottom bar, 1 hole helped and two holes stopped it bouncing totally when I light up the rears. same
conditions and pressures as last night so that was the cure for that, I just hope that doesn't have a knock on effect on anything else as the
front was pretty good. I think I need less tyre pressure also so can sort that.
Darren Bingley who designed the suspension geometry had said to lift the bars as I've done tonight, but I thought he meant for the handling
rather than getting the power down and as I've been struggling with rear springs and shocks I didn't want to alter too much at once, but
happy with the results up to now. I've not tested it other than over enthusiastic launches and a bit of wheel spin lock to lock up the main road
through the gears but feels much more planted with no bounce. I will check the axle isn't over located tomorrow evening Owelly.
Just out of interest as my axle position is pretty critical as not much slip in the prop I intended to move the bar's up 1 hole and one side at
a time, altering the length of the link bar if nessasary to keep the axle in the original position, but found the first hole up only about 1mm tighter
and the third hole exactly the same as the lower hole so not sure if that means anything just thought it might be worth a mention.
Thanks again for all the pointers.
 
Description
http://www.kittenkitcar.co.uk
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Fred W B
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| posted on 30/10/13 at 11:12 AM |
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You could try asking Sebastion Vettel over at Red Bull.
Cheers
Fred W B
P.S. Don't bother asking Mark Webber
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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unijacko67
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| posted on 30/10/13 at 06:04 PM |
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I didn't really want to pester Seb seeing as he's just clinched the title again, that's why I've asked you chaps. 
Looks like there's only one way to find out.
http://www.kittenkitcar.co.uk
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