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Post by dannyboy on Apr 23, 2008 22:02:49 GMT 12
Do you mind sharing the secrets of the the front suspension setup? Or the rear too? Out on the track yesterday I was getting chronic understeer and am keen to rectify this. Hey zep tell me a few things about your car and I may be able to help wheel alignment? whats your camber and castor set at? tyres semis or road? tyre pressure cold and what is it when you come back in? what size tyres? what size rims? what are your shocks and springs like?
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Post by gordo on Apr 23, 2008 22:25:11 GMT 12
Do you mind sharing the secrets of the the front suspension setup? Or the rear too? Out on the track yesterday I was getting chronic understeer and am keen to rectify this. There's a heck of a lot of things that can cause your problem. Is it primarily on turn in/entering the corner, transition/in the middle of the corner and/or on the exit of the corner. Worse under power or about the same? Worse in tight corners or open, sweeping corners? The normal cause for lack of grip on one end of the car is higher roll resistance at that end - whether through too stiff springs and/or anti-roll bar. Tyre pressure/type/size will also affect the grip. Not sure exactly what combination you're using but it is common for lowering to be done for cosmetic appearance rather than real performance which may have resulted in over stiff front springs compared to the rear.. What I might suggest is trying varying the tyre pressures a little but I wouldn't use less than 28PSI cold and you may need to go close to 40PSI. You should also be using around 1 1/2 degrees of negative camber - depends on tyre clearance and may need slight slotting of the ball joint mount where it's bolted, increasing the caster by machining up new spacers for the top wishbone - just add the two stock spacers together and use that size - however this will increase steering loads. If not already used, see if you can fit the stock* or aftermarker rear anti-roll bar. When playing with sizes of 'roll bars, remember that they increase in stiffness by the FOURTH power - ie double the diameter and it will be SIXTEEN times as stiff! So a little goes a long way. If you have adjustable dampers (shocks), you can alter the turn in and exit to an extent. Softer front and stiffer rear will tend to improve transition grip on the softer end. If you have just fitted some strange dampers "as they are the right length", that will almost certainly cause problems - TJM or a local damper shop should be able to sort out some adjustables for you. However, I suspect you may have to change springs to settle things down a bit. Don't forget to make sure the wheels are aligned straight ahead - I used to use 1/16" ot zero toe in. You may also wish to try different driving styles and lines as that can make a significant difference as well. Hope that gives you something to think about. *One car had bad understeer on right handers - turned out to be a bent 'roll bar and was sorted by altering the spacer lenght on the drop link with the addition of a couple of washers.
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Post by mikuni on Apr 24, 2008 8:11:31 GMT 12
Can you explain the adding spacers in part to add castor more please? In my setup I wouldn't be able to add one in without removing the other so is this what you do?
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Post by dannyboy on Apr 24, 2008 10:25:10 GMT 12
Do you mind sharing the secrets of the the front suspension setup? Or the rear too? Out on the track yesterday I was getting chronic understeer and am keen to rectify this. What I might suggest is trying varying the tyre pressures a little but I wouldn't use less than 28PSI cold and you may need to go close to 40PSI. . are you insane or do you just want to see this guy hit the wall?? 40psi cold would be over 50 hot and would offer no grip at all even 28psi cold would end up at high 30's.
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Post by bulldog on Apr 24, 2008 11:41:37 GMT 12
Hey Dannyboy...was looking over your car at Tony's the other night....very nice.
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Post by dannyboy on Apr 24, 2008 12:32:47 GMT 12
Thanks Bulldog, it's wide aye!! we got it going yesterday after running a bearing at the track last time out, the loss of oil pressure after rebuilding was a tiny little piece of bearing shell stuck in the relief valve of the oil pump so had to pull the motor out again and strip down again but all is good now. Yours looks very good in the photos, you should be ready in a couple of months maybe?
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Post by mikuni on Apr 24, 2008 13:49:36 GMT 12
Dannyboy, I was driving back from auckland last week and I saw your car being trailered up just north of huntly. It was pretty exciting! haha
The funniest thing was that I was checking out the chaser/mark II that was towing it, thinking how it was so sweet then I realised that there was a bangin chevette attached to the back of it.
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Post by bulldog on Apr 24, 2008 13:53:23 GMT 12
booked in with Tony in two weeks and will take a couple of weeks to do the rear etc. So hopefully in a month!
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Post by gordo on Apr 24, 2008 20:09:16 GMT 12
are you insane or do you just want to see this guy hit the wall?? 40psi cold would be over 50 hot and would offer no grip at all even 28psi cold would end up at high 30's. Nope, as I said, "may", "close to". Back in the day, I was using 40+ with 155s and even then, it was scuffing a couple of inches up the sidewall during club races. However, as you may be pointing out, it will be something that requires experimentation, quite possibly less than the 28PSI depending on the tyres and weight, etc, of the setup.
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Post by gordo on Apr 24, 2008 20:22:36 GMT 12
Can you explain the adding spacers in part to add castor more please? In my setup I wouldn't be able to add one in without removing the other so is this what you do? Yup, there should be one large and one small diameter spacer on the pivot bolt, IIRC, they're around 4mm thick (check first). You could try using a double thickness shim in the front and remove the rear one. This will affect tight cornering more than sweeping corners and will increase steering loads a little. Something else I was thinking of that may have some affect is if the vehicle is lowered to the point where the suspension hits the bump stops when cornering, that will increase the spring rate and cause less grip at that end.
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Post by dannyboy on Apr 24, 2008 21:45:54 GMT 12
Hey Gordo sorry mate I was just rereading my reply and I sounded like a grumpy prick, i didnt mean to I just thought it sounded a bit high but I do agree that the psi could have a lot to do with it. I set mine cold at about 24psi and have about 31/32 after I come in but that is on good semi slicks with a good suspension setup and with camber at -1.5 and castor at +1.5
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Post by dannyboy on Apr 24, 2008 21:53:50 GMT 12
Cheers Mikuni, the ole grande is my tow wagon. It's even supercharged.haha
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Post by gordo on Apr 24, 2008 22:38:54 GMT 12
Hey Gordo sorry mate I was just rereading my reply and I sounded like a grumpy prick, i didnt mean to I just thought it sounded a bit high but I do agree that the psi could have a lot to do with it. I set mine cold at about 24psi and have about 31/32 after I come in but that is on good semi slicks with a good suspension setup and with camber at -1.5 and castor at +1.5 No worries, matey BTW, if you check your trademe listing for the BMW bottletops and slicks, you'll see I've bought them.
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Post by mikuni on Apr 25, 2008 0:40:24 GMT 12
I set mine cold at about 24psi and have about 31/32 after I come in but that is on good semi slicks with a good suspension setup and with camber at -1.5 and castor at +1.5 Do you get castor by using a similar method to gordon or do you do it another way? Thats pretty interesting, I think I may have a crack at that. My suspension certainly doesn't hit the bumpstops but I am looking at options for a stiffer spring rate, mainly in the rear to try and eliminate some of that understeer. I may look at a very slightly bigger anti-roll bar in the rear also but I'm not sure of the cheapest way to go about this. I know of a business that makes them but that could prove a little expensive. Do you guys just use offset upper balljoints and spin then around to get camber up from or the non-offset ones and slot the holes to allow movement? I'm not a big fan of slotting holes on such a vital component but I guess if its tested and works then I'll give it a try.
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Post by dannyboy on Apr 25, 2008 17:19:02 GMT 12
I set mine cold at about 24psi and have about 31/32 after I come in but that is on good semi slicks with a good suspension setup and with camber at -1.5 and castor at +1.5 Do you get castor by using a similar method to gordon or do you do it another way? Thats pretty interesting, I think I may have a crack at that. . I have adjustable camber and castor setup on mine, the bolts holding the arms on have a cam lobe type setup seems to work well. I do also have slots in the bolt holes for the bottom ball joint and can get some extra castor adj there, I have gone to a much stronger ball joint also.
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