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Working on roll center correction solution

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  • So, i have done the first shakedown on the track, and man, how this new setup is great!
    The car has a very stiff springs and valve dampers, and it dont bounce around like before, and the suspension is more like a new car, then a old car, feels very nice.
    Out of the corners is very weard, because of im used to wheelspin, and the car now has a bunch of grip.
    With all things i have been thinking to go wrong, the least thing goes wrong, the damper shaft bent!!
    All the rest is 100% fine, very positive results, and a bunch of fine tuning to do, for now, the car is very understeer, but with the dumper thing, I do not have time to mess around the tuning, just the problem.

    Link for the onboard video: https://www.youtube.com/watch?v=KS_HLLRMsjw
    btw, it was shakedown of the new engine setup, and it is f great.
    Attached Files

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    • With this geometry you can have way less stiff springs and dampers as there is hardly any need to fight roll, in fact a bit of roll gives you more grip and also a bit more oversteer.

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      • Originally posted by Vinci View Post
        With this geometry you can have way less stiff springs and dampers as there is hardly any need to fight roll, in fact a bit of roll gives you more grip and also a bit more oversteer.
        I wanna try diffent spring rates, as its availyble to me, but now i need to find the problem.
        And i feel that the spring rates can be lowered by how the car handles.

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        • I have also downsized the anti roll bar from 25mm to 22mm and now 20mm. It should really not be as thick as with the stock geometry. I also have a Daewoo Lanos, and that has the 25mm anti roll bar as stock, which looks like a stab in the dark they did to improve the poor roll behaviour. It didn't help at all though, it handles like it doesn't have any anti roll bar.

          At the back I have replaced the axle for a Saab 9-3, which has a bit thicker torsion bar and anti roll bar, but I didn't really notice much difference. This was not the reason why I swapped it though, I actually swapped it for a clean slate to put different suspension on and it was fully rust free (from Spain). My old one was from an Astra MK3, and I cleaned it up to remove the rust, but some parts on the welds and overlaps already were quite thin. Then, I noticed the Saab axle, and my Lanos axle have a gusset on the vertical 'tower' where the hubs are attached.

          My suspension at present is actually all stock stuff, really soft, and I have got tons of travel also, as I have enlarged the tubs at the rear. I can go almost full speed over speed bumps if I want to, but the roll is virtually non existent. It handles syper predictable, precise, and it does that up to really high speeds without going out of control. With the stock setup, just a 20 degree corner between two straight stretches of road, going 80 km/h used to be a very dangerous practise, now it is just one steering input, and done.

          In a few months I want to hit Zandvoort with the car, just a few laps booked for 'touing' class to have a go at higher speeds without getting speeding tickets. Really wonder how she'll handle on track.

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          • So, finally I can make to a racetrack and test the car, the event is Meet Brazil Racing, its like a WTAC, in a anual 3 day event with regulation for tires and classes for different types of cars. About 100 cars compete, and this year, was in Tarumã Racetrack, available in Automobilista (fun fact).
            About the car, it was amazing, after the bent bumper rod, I make some changes and without the time to make a new control arm with rod ends, I just put the lower ball joint in the original position with some whashers to space a little. In my class, we run with street tires, +201 treadwear, that do not is a good track tire, I use the Zestinos Gredge 07R in 205/50 R15 for the best lap.
            What really amazes me is the fact that the tire was worn out almost flat across the contact surface, it is a new thing for me, really making good use fo the tire. Another really positive fact is, the car has 1.3 G os force in the corners, and before it make at most 1G in corners, so even with not so good tires, the car really feel great. The characteristics of this is 95% left turns and 5% right turns, so I can ajust the caster and camber on track, with some basic tools, this time i use about 3 degrees of caster (the limit of my camber plate), -3.5 / -5.0 degress of camber left/right, and 4mm of toe out. For the future I want to ajust the rollcenter even further and fabricate some lower control arm for that, some ajust on Bump Steer as well.
            And as you can see on the video, the car is F oversteering all the places, its because i changed the front of the car, and think the rear end just work well as before, but it is loose all weekend, with 0 degrees of camber, it destroy tires and I cant change this on the track, just dont have the knowledge to do so. For the future I pretend to refine more the car.
            I'm gonna throw some photos and the link of the video. (going to upload the photos to the Drive link as well.)
            Video Link: https://youtu.be/GNHk4P9tdls
            Drive: https://drive.google.com/file/d/13QC...usp=drive_link

            The lower ball joint in the moment.
            Click image for larger version

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ID:	527851 Just a random pic. Click image for larger version

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ID:	527852 The tire after the use. Click image for larger version

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ID:	527853 My rear tire after 1 day and half.

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            • Originally posted by Lucas1717 View Post
              after the bent bumper rod, I make some changes and without the time to make a new control arm with rod ends, I just put the lower ball joint in the original position with some whashers to space a little.
              I simulate on the car the whole suspension movement, and as the ball joint is inverted, he reach some extreme angles and put some bend forces on the dumper rod, I fixed, and now we can continue developing.

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              • Bit late to the party, sorry about that, been watching your progress with a lot of interest. Not too sure what to think of the stability in the video, it looks like it is quite a handfull to keep it on track, but what do I know, I rarely drive on track and maybe do'n't push it as hard as you do. Curious to see your further progress!

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                • The plan is add some camber in the rear, around 2 degress, and a bit of toe in, and I think that the rear springs has very high spring rate, and it is kicking on the track, you can see in the start of the video.
                  I'm planing more trackdays in november, we will see

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                  • Interesting reading. Lucas that car looks a handful! Great on a twisty track but too much for me.

                    What tyre pressures are you running? Rear tyre pressures are a really cheap and effective tuning tool for getting rotation in FWD cars, which you have loads of. Maybe try a 5-10 psi lower rear pressure for a short stint, you can use them as a spring rate tool, unlike coil spring suspension they are direct, there's no lag and less rising rate. It also changes the contact patch. Going through a range of pressures in steps can give you a clue about what direction and step size to go with the springs, but it will wear your tyres out faster if you do long stints at the extremes (although you have that issue already!)

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                    • Nice and construtive comment, but im gonna add one variable, im running the rear axle linked to the body do que car, it limites the “rebound” movement, so, wen I enter the corner, the outer rear tyre dont have any camber gain.
                      If you think in the front, if you dont have camber, you need high tyre pressures so it cant deform, right?
                      In my case, I find that, losing a bit of this link, and stayng on the 50 psi of pressure, give me one positive result, I imagine that the rear pressure can be lowered, but I will fall in to the tyre wear again, even in a couple of laps, I shows a lot.
                      As I say, my next test is put about 2 ~ 2.5 negative camber on the rear, so I can neutralize the severe tyre wear and give the rear more grip, and with it, securely lowering pressures, so the tyre dont deform on the corner.
                      Really thanks for the comment. Click image for larger version

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