Ricardo 37 Posted June 15, 2009 Report Share Posted June 15, 2009 Hi ! I have an 1998 Kadett 2.0, and I've been racing in track days and autocross/solo with it. I'm now trying to make it faster in corners and want to share with you the modifications and also my doubts! This is the car: In the picture the suspension was original, with modification just in the tires that I was using(slick), and the front camber. The Set Up was: Front (Mc Pherson) original springs - 100lb original shocks camber: -1,5 toe-out - almost zero rear (twist beam axle) original springs - 170lb (stronger than the front one... I think that's becouse of the mechanical advantage - position of the spring) original shocks camber: 0,5º toe-in +3º (something was not ok with the axle... I think this was what caused a lot of understeer) Here some pictures of the car: turn-in (rear wheel lift): the turn-in was good in my opinion apex of the corner: lots of jacking effect, body roll and understeer another one from the apex (inside view) here we can see the amount of camber loss with the excessive body roll I have on youtube some onboard vÃdeos that can show how the car behavior was: fast lap (2 minutes and "almost" 15 seconds): Please wait a few moments for Video to Load! funny ride on the rain with TERRIBLE tires (LOTs of understeer here... just some oversteer in turn-ins becouse of the rear brakes that were a little stronger): Please wait a few moments for Video to Load! That's was how the car was ! Now I did some modifications: The Set Up now is: Front (Mc Pherson) eibach springs - 125lb very strong shocks camber: -2º (it was -1,5º, but with the change in the ride height became -2º) toe-out - almost zero rear (twist beam axle) original springs with 1,5 coil cutted-out - 210lb (got more 40lb now) very strong shocks camber: -1º toe-in: zeroº sway bar: now has a 16mm in the place of the original 14mm (I got the larger one from another car similar to the Kadett... like a "Kadett wagon" lol ) My first event with the new suspension was a Pro-solo (autocross) last month, and a took first place ! I'm going to put an onboard video in youtube soon the car was very neutral with a little bit of understeer, i think that's becouse the circuit was very slow with short corners ! Now I'm going to make PU bushings to the rear bar, expecting that this could bring me some strongness to the sway bar. The front sway bar I don't know if I am going to put PU bushings, becouse I'm afraid that this can causes understeer. I have no doubt that the car is a LOT better than stock, but I still have some ideas of how I can make it even better. Here are my doubts: Doubt 1: The front a-arms are paralel to the ground, so I think that I don't have much camber loss with body roll, and still a good roll center heigh (less jacking and less wheight transfer througth it). But I think that I have a problem with the roll stifness, becouse of the bigger distance from the roll center to the center of gravity that now I have. I don't know if you are understanding me... I'm been a little bit confused here, but my point is: the RC moved down more than de center of gravity did, so now there is a bigger couple (is this the name?). Conclusion: Now I need more front roll stifness to compensate this and my springs are only 25% stronger than the original. Question 1: Are this 25% stronger front springs sufficient to compensate the bigger distance from the CG to the RC? I'm sorry, but I don't have a recent picture of the car in a corner yet. But it now has very less body roll, I think it's becouse of the reduced jacking effect and also the stronger shocks. Doubt 2: How much caster should I adjust? I think that the more I could get is better to improve the camber gain in corners, but it won't bring me less traction? Doubt 3: I don't have larger sway bar available to put in the rear axle, and my question is: If the PU bushings don't give-me my desired oversteer (inside rear wheel at the floor), how could I get more rear wheight transfer? Stronger springs could give-me that (inside wheel a little bit at the air)? Doubt 4: how can I find the rear roll center height? remembering that it's a "twist-beam axle" thanks guys Quote Link to comment Share on other sites More sharing options...
Rich Posted June 15, 2009 Report Share Posted June 15, 2009 Welcome to WIM I take it the Kadett is the equivalent to our Vauxhall Astra? Those photos on oem suspension look scary with that body roll Have you fitted any aftermarket kits so the castor or camber can be adjusted? BTW I embedded your videos as well Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 16, 2009 Author Report Share Posted June 16, 2009 Welcome to WIM I take it the Kadett is the equivalent to our Vauxhall Astra? Those photos on oem suspension look scary with that body roll Have you fitted any aftermarket kits so the castor or camber can be adjusted? BTW I embedded your videos as well Thanks, it's my first post here ! I'm enjoying the forum, I wish I could be a good member and participate a lot ! Our Kadett here is equivalent to your Astra. Here are the pictures of ours: This is the "Ipanema", it's a kind of Kadett wagon. (My rear sway bar is from this car) This is a Kadett 1998 like mine (here Kadett has began in 1989 and last till 1998) In 1999 arrived here the Astra, this, I guess, is like yours. It's true, my car had a lot of body roll and that was scary !! I changed the springs and shocks but I'm still using the original strut. I prefered not to use camber plate, because I use the car in the streets and I was afraid that the rigid strut top could not be good in severe street use. So I modify camber and caster in other way, I can't adjust them at the track. Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 16, 2009 Author Report Share Posted June 16, 2009 I found a picture from my car in the solo event. But the car is stopped at the start lane: Than I decided to get prints from the video that a friend of mine did, and realised that the car still has some body roll. I think this roll is caused by the new CG and RC heights that I mencioned in the first question in the first post. Some more rool stifness in the rear like I said in my third question probably would help too. I'm waiting for your opinions guys ! []'s Quote Link to comment Share on other sites More sharing options...
Tony Posted June 16, 2009 Report Share Posted June 16, 2009 Interesting project....... I'll try and help after work, things are much to busy at the moment Quote Link to comment Share on other sites More sharing options...
CIH Posted June 16, 2009 Report Share Posted June 16, 2009 The Kadett you have was replaced over here approx 1993/1994 with this Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 16, 2009 Author Report Share Posted June 16, 2009 Interesting project....... I'll try and help after work, things are much to busy at the moment thanks ! Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 16, 2009 Author Report Share Posted June 16, 2009 The Kadett you have was replaced over here approx 1993/1994 with this We had this car here, it was called Astra "Belga". Quote Link to comment Share on other sites More sharing options...
Tony Posted June 16, 2009 Report Share Posted June 16, 2009 Before we go into the glorious world of suspension/ chassis dynamics i would like to ask the obvious, what castor do you currently have? It's very apparent from the images there's little to no camber migration and little to no castor sweep, hence the back end cocking a paw. I think in desperation you are trying to use the Geometry calibration (cambers and toe) to improve the corner-apex issue but in truth your nearing a drift set-up, without the drift. Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 18, 2009 Author Report Share Posted June 18, 2009 The stock caster where set between +1,5º to +2,5º, but actually my caster is around +1,5º. I'm thinking in changing it, but I don't know what graduation should I adjust. This is one of my doubts, like I said in the first post: "Doubt 2: How much caster should I adjust? I think that the more I could get is better to improve the camber gain in corners, but it won't bring me less traction?" Also I'm afraid of overloading my power-steering system with excessive caster. "I think in desperation you are trying to use the Geometry calibration (cambers and toe) to improve the corner-apex issue but in truth your nearing a drift set-up, without the drift." lol You're correct. My preference is the grip on the front tires because the traction is there. So I want to concentrate the more wheight transfer I could in the rear axle. My ideal is to stop increasing it when the inside rear tire lift off the ground (just a little bit - almost nothing) on steady-state cornering. But how can I get this behaviour? I changed my sway bar 14mm to a new with 16mm and still don't happened the "wheel lift". Stronger springs will bring-me that? "Drift set-up whithout the drift." <- I liked this sentence. Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted June 18, 2009 Author Report Share Posted June 18, 2009 Fell free to correct-me if I'm wrong in my thoughts. []'s Quote Link to comment Share on other sites More sharing options...
Tony Posted June 18, 2009 Report Share Posted June 18, 2009 As a base you need a castor of around +4d, this will help the cambers migrate during transition. Another aspect of this would be the inner wheels extended castor sweep, this will reduce the rear cocking a paw. The power steering can cope with such a high castor by the way Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted July 2, 2009 Author Report Share Posted July 2, 2009 As a base you need a castor of around +4d, this will help the cambers migrate during transition. Another aspect of this would be the inner wheels extended castor sweep, this will reduce the rear cocking a paw. The power steering can cope with such a high castor by the way Yeah, I'll probably try +4º caster. Do you think that more than +4 will bring me geometry problems or just the problem with the steering system? Sorry, I can't understand what you mean with "reduce the rear cocking a paw". Quote Link to comment Share on other sites More sharing options...
CIH Posted July 2, 2009 Report Share Posted July 2, 2009 stop the rear lifting off the ground heh heh! like you're picture That's a nice car by the way. Is it the 8 valve or 16v ? I read that the VW golf guys like the rear to lift to reduce understeer though ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 2, 2009 Report Share Posted July 2, 2009 4 degrees won't cause any problems, add plenty of negative toe it should be happy days. Quote Link to comment Share on other sites More sharing options...
Ricardo 37 Posted July 4, 2009 Author Report Share Posted July 4, 2009 stop the rear lifting off the ground heh heh! like you're pictureThat's a nice car by the way. Is it the 8 valve or 16v ? I read that the VW golf guys like the rear to lift to reduce understeer though ? exactly ! the rear lifting off the ground is what reduces the understeer ! and I wanted to keep this, but now with the new setup the rear isn't lifting this week I'll try another rear sway bar (again lol) oh, it's the 8v with 130hp and 20kgf.m []'s Quote Link to comment Share on other sites More sharing options...
Tony Posted July 4, 2009 Report Share Posted July 4, 2009 removing tyre contact to encourage oversteer is not the way to go. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 4, 2009 Report Share Posted July 4, 2009 Didn't think you'd approve Tony! That 8valve is probably the same as the SRI130 we got in Cavaliers over here. Very nice little engine, overshadowed by the 16v XE no doubt. Quote Link to comment Share on other sites More sharing options...
Tony Posted July 4, 2009 Report Share Posted July 4, 2009 Didn't think you'd approve Tony! That 8valve is probably the same as the SRI130 we got in Cavaliers over here. Very nice little engine, overshadowed by the 16v XE no doubt. If a car on track wants to get anywhere fast then it needs all it's wheels on the ground...... Look at the work that went into bazza's car to stop this happening, if i recall it took second last time out Quote Link to comment Share on other sites More sharing options...
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