If I unscrew the small screw on the shock collar does that unlock it and allow it to turn to add preload to the shock? Also if I turn it one revolution clockwise how many pounds does that transfer to the opposite front wheel?
i have discovered that my left front wheel is 100 lbs lighter than the right front wheel after doing corner balancing. So I am adding preliad to the right rear shock.
Thanks!
On my Intrax shocks there is a screw to lock the rotation in side hole pictured but I don’t remember there being one on top. I didn’t use the stops to lock the ring in place because the weight of the car was enough to keep it from rotating. When the car was on jacks the rings could easily be moved by hand. Unfortunately I don’t know how many rotations are required to get specific pound changes. I believe the changes are more complex than that because when you adjust one corner it has an effect on all of them (obviously more on the cross corner.
If I unscrew the small screw on the shock collar does that unlock it and allow it to turn to add preload to the shock?
Yes, exactly.
Also if I turn it one revolution clockwise how many pounds does that transfer to the opposite front wheel?
Well it depends on the geometry of the chassis. If the corner you are adjusting is light, then maybe not very much. If it is heavy, then a lot. Imagine a table that has a three legs 28 inches long, and one 27 inches. If you add 1/2 inch to the 27 inch leg, it is still short and the majority of the weight will remain on the opposite diagonal.
i have discovered that my left front wheel is 100 lbs lighter than the right front wheel after doing corner balancing. So I am adding preliad to the right rear shock.
This is not unusual even after carefully adjusting ride height, camber, and tow. Your approach to pre-adjust the light side so that the ride height does not change significantly during corner balancing is reasonable, however it may or may not be worth the trouble -- I could not tell you with certainty. My suggestion is to try a full turn, redo the entire chassis setup from start to finish, and see how that affects the starting weights for corner balancing. It is often difficult and time consuming to get everything perfect.
@schneller …. Why not make the shock adjustments while it’s on the ‘flat patch’ (on the scales)? You can then do the adjustment ‘live’ and you can see the difference and the end result. You can sit in the car while someone else makes these final adjustments….
You are welcome. I think I misunderstood your question, but it looks like you are on the right track.
I should add that if your car has fixed length pushrods in the rear, it is correct to make the corner weight adjustments at the rear spring adjusters so that you will end up with something besides zero rear spring preload. The front springs should maintain equal preload amounts on both sides after setup because if not, then threshold braking would be compromised.
If your car has adjustable pushrods all four corners, then I would suggest setting the target preload, and then making all adjustments for ride height and later corner balance with pushrods only. For example, in the factory setup, this would maintain 0/+4 turns of preload on the rear/front damper springs.
Another suggestion is to split the corner weight adjustment between left and right or even all four corners using pushrod adjustments. For example in the case the car has fixed rear pushrods, if you need one full turn on the right rear, then you can use -1/2 on the left rear and +1/2 on the right. (Same example with adjustable pushrods in front and rear: +- 1/4 turn on each corner.) This is subject to discussion, because at full droop there would be -1/2 turn on the left which means the spring would not be in contact with the perch if the car becomes unweighted. I probably would avoid more than one full turn negative at the rear, however with adjustable pushrods, you don't have to alter the spring preload to corner balance the car.
Rod, Thanks for the feedback. Thats what I am planning on doing. I will let you know how it goes.
Good info! Thank you. I am learning the double wishbone suspension by the seat of my pants. This is my first time working with it. I'm used to McPherson struts prevoiusly. I do think I have adjustable pushrods on all 4 corners. I will check. I will experiment with cornerbalancing with the coilovers vs the pushrods. I really want to get it balanced.
I have noticed that my Radical SR3 XX with Hankook tires on the track is prone to oversteer. I think the majority of cause is driver focused by carring too much brake pressure into the corner. Have you seen that in your car? To mitigate low to mid speed oversteer , I have read in the owners manual that you can add up to 10 clicks of rear shock rebound which will make the car more stable under braking. For a more noticable change you can add toe in up to 5 degrees to the rear wheels. Right now my toe in on the rear is 2 degrees. Im considering increasing to 4 degrees and see if that makes it less prone to oversteer. Have you had any experience incresing shock rebound or rear toe in to improve handling?
@schneller … regarding your reply to @davidf above and the oversteer your experiencing… Reading between the lines it sounds like turn in oversteer, and as you mention this can definitely be induced by too much trail braking. I would suspect once you’ve completed your chassis check that you are going to find your car has too much chassis rake. In my experience this is the biggest factor that influences turn in oversteer. For the XX chassis I was told to keep the chassis rake around 2mm lower than the previous RSX chassis. That means the target range for chassis rake should be between 12mm and 16mm (I was told 18mm at a maximum).
Given you’re new to the Radical chassis’ you might not have any experience doing this (I certainly didn’t!), and as a result this is going to be a fairly steep learning curve as Radical suggest using ‘drop heights’ to calculate the chassis rake. The issue I suffered with this approach is that I was using Avon tyres (very soft for sprint racing and time attack) and the drop height tables that Radical provide are only valid with Dunlop or Hankook tyres (there are two different tables). Their method is reasonably well described in the Radical Handbooks available in the resource section of this forum.
The method I started using after getting advice from people who were running the Radical Cup teams in Australia was to get a baseline by literally measuring the chassis ride heights while the car is on the flat patch. I use a laser level under the car (while it’s up on th flat patches) and also set the corner scale levels with this so that the ‘level plane’ is the same for the scales and car (while it’s on the scales). I can then simply measure from the chassis at 4 locations down to the laser ‘plane’. The four points I was told to use are the left/right corners of the cars floor pan immediately behind where the front splitter bolts up into the front of the steel chassis (right behind where the crash structure is mounted), and the left/right corners of the cars floor pan right in front of the aluminium flap that the rear diffuser sits on. The target dimensions I was given were 80mm at the front, and 70mm at the rear (and within a mm or two of these from side to side at each end of the car). By doing this, and then checking the chassis rake using Radicals method (by putting some new Hankook tyres/rims I have here ‘spare’ on the car and using the Radical Hankook Drop Height Table) I correlated that this set-up gave me about 17mm rake on my RSX chassis. I have since done the same on my new XX chassis and got very similar results.
I normally check the chassis rake (now using both methods to cross check) before doing the final corner weight adjustments, and when I make those adjustments I try and always only adjust the rear spring perches (on RSX with fixed pushrods) or rear pushrods (on the XX). This is similar to the advice @davidf provided above.
For corner weights I target less than 10kg delta in weights across the front wheels, and less than 2% (of the cars total weight) delta between the ‘diagonals’ (addition of LR and RF compared to addition of RR and LF). I was told to always prioritise the front delta… opinion seems to be that this is the most important. I’m 95kg’s with helmet and suit (~210 pounds) and can normally get to around 7 or 8kg delta on the front before I reach the 2% diagonal limit.
I have noticed that my Radical SR3 XX with Hankook tires on the track is prone to oversteer. I think the majority of cause is driver focused by carring too much brake pressure into the corner. Have you seen that in your car?
On my car or any car, if I hold too much brake while turning in or even off the throttle for certain type of turns like the esses at COTA, I can spin. But this is driving error. Also if the bias is too far rear, you can lock up even a little and it makes braking in a straight line very difficult. So it is hard to say if something is not set correct, or driver inputs but certainly this car will not allow heavy on brake at turn in. Coming off the brake at turn-in is what you want for all cars, but it is a matter of timing and feel.
The factory setup has worked well for me on many tracks. I do not find big problems with chassis geometry at factory setup, but I have found issues with tire pressure, and for certain tracks it is necessary to tune damper settings.
In high speed corners at the limit is where I can best evaluate the setup of the car, and particularly tire pressure which is always the first thing to suspect. I recall a very valuable lesson at COTA where we tested tire pressure at 28 and then down in 1/2 psi increments until I was at 26 psi with fresh tires. At 27-28, I could confidently get through the carusel at full throttle throughout. At 26 and 26 1/2, I felt a lot of high speed oversteer and I had to lift slightly to avoid crashing. I want that balanced confidence in these high speed corners where a full lateral load has balanced traction between front a rear tires. That does not mean that 27-28 psi is always right, but for that day and track with a factory setup, it was right and I confirmed it with another car and driver who had a similar experience. Camber also makes a big difference in target tire pressure.
To mitigate low to mid speed oversteer , I have read in the owners manual that you can add up to 10 clicks of rear shock rebound which will make the car more stable under braking.
I went the other way last year at Sebring because in the hairpin braking zone the rear was bouncing and locking up, so I wanted less rebound damping to keep the rear tires in contact with the track surface. It worked and my lap times improved. So even with less damping I had lots of confidence in braking throughout all braking zones.
The more tow you add, the higher the tire temperature. On a hot day that can really rob a lot of traction once the tire overheats. Sometimes adding tow is useful on a very cold day for short sprint race.
It is difficult to analyse what the car is doing without comparing downloaded data at the same track. Many times an issue is tire pressure. My experience with over three years with three different SR3s says to trust the factory setup.
Rod, what is your opinion on making all of the ride height and corner weight adjustments with pushrods only (for Radicals that have adjustable pushrods all four corners)?
@davidf … G’day David, I’ve now made some adjustable pushrods for the rear of my RSX, so now both cars have them. My setup is now ‘normally’ done using the pushrods to adjust height/weight… but i try to make the adjustments at the rear end only. I set the pre-loads (4 turns in the front on 110N/mm springs, and 1 turn in the rear on 100N/mm springs) and adjust the pushrods to keep as close as I can to 70mm rear ride height as described in my previous post)… last time that gave me 18mm rake (RSX) with Hankooks, which drops to 15mm with Avons fitted (front Avon tyres are same diameter as Hankooks, but Avon rears are 6mm (3mm radius or ride height) smaller)
I’d suggest you see where you are at in terms of ride height next time you’re on the flat patch… would be another good reference point for us all. I’ve been told that 2-3mm rake adjustment can make a huge difference on turn-in and mid-corner performance (less effect on corner exit with more/full throttle)… it might also help with what you are describing above with mid corner high speed balance…?
@schneller comment re increasing rear rebound to help reduce turn-in understeer…. Also points to rake being on the high end (and maybe marginal). What the increase in rebound stiffness does is that it stops the rear from lifting as quickly as the brakes are applied, and maintains more weight to the rear end for a fraction longer (by stopping the weight transfer that happens when the pitch changes)… lower rake does the same thing, but means the weight transfer is always lower… while the rebound adjustment provides a momentary effect… the rake still changes/the weight still shifts just more slowly. With lower rake the car doesn’t pitch forward as much (starts flatter and stays lower…. therefore less weight transfer).
Ron, A couple quick stories during my break from pre season prep on my SR3:
Story 1 involves a good race driver and new SR3. The driver complained of oversteer during trail brake at turn in, particularly right hand turns. It was so bad that he had to compensate by braking very early in a straight line and then getting off the brake before turn in. His lap times were poor and his frustration level high. His coach who drives full time Indy Lights and the race team former IndyCar engineer did not have a solution after several chassis setup adjustments. The problem was a bad left rear brake caliper that stuck and grabbed the rotor. Rebuilding the caliper solved the problem. Nobody suspected a bad caliper because it was a new car.
Story 2 involves a pro driver who rented an SR3 1500 at VIR to practice before a major IMSA LMP race. The race team set up the car with some sort of modification to improve driving performance. I don't know for sure, but I think the adjustment was ride height/rake; I do remember that the setup was not the factory spec. The race team asked him how the car handled and he said that it was very difficult to drive, unpredictable, and unbalanced in high speed corners. Later on that day he drove my car, and said that mine is a much better setup and gave him much greater confidence in high speed corners. He also said that my car is almost too balanced and that he had some difficulty getting it to rotate on turn in. The race team asked about my setup and I told them it is the factory setup. They took both cars back to the shop, took measurements on my car, and copied it to the rental car. The next day the pro driver said that the rental car was handling much nicer and he had a lot more confidence throughout the entire track, so he could drive faster.
Rod,
Great advice. Thank you for that insight and experience. That will save lots of trial and error on my part.
I have a laser that I can set up to project a level plane when the car is on the flat patch. That makes total sense. Im familiar with the measuring points you described so it should be a straightforward procedure to get the front and rear ride heights and subsequent rake accurate
I will let you know how that goes.
this car will not allow heavy on brake at turn in. Coming off the brake at turn-in is what you want for all cars, but it is a matter of timing and feel.
David,
Thanks for the info. I think this may be my problem with oversteer rather than chassis setup. I am trail braking after turn in to adjust weight balance and grip. With that technique I have experienced some spins that surprised me. Just so I am completely clear: You are completely off the brake after turn in?
I appreciate the info. Previously I was driving a GT3 with traction control and ABS. The Radical has been a learning eperience in chassis weight balance for me!
Thanks!
