XRAY - Model racing cars

I can't seem to get my car to handle with 350cst shock oil.

What ends up happening is the car is too reactive initial steering input, has a mid corner push and then oversteers on power out of a corner. The tighter the corner the worse it is for both the mid corner understeer and exit oversteer. It doesn't not oversteer on power through sweepers unless the sweeper tightens towards the end.

Spring changes have no effect on the problem and the ONLY geometry change to have an effect is removing the spacers under the rear upper link on the inside. Its only a small effect and not enough to fix the problem.

The only thing to fix this problem has been 400cst oil and foam pieces in the shocks (which was good for 2runs before they needed to be rebuilt as the car got twitchy again) and the forward holes in the steering knuckles for more ackermann. I am going to be testing with heavier oils and 3 x 1.1 pistons to see what happens.

What I think is happening is the car is rolling/pitching too fast which is causing the understeer and oversteer and probably explains why geometry and springs have no effect on handling.

Alot (if not all) of Alexander Hagbergs setups are with 350cst oil and 4 x 1.1 pistons. Question for Alex, have you ever experienced what I am experiencing? Would you able to make a detailed video or pictures of you building the shocks so we can see exactly what you do? (oil height, amount shock is pushed into body when building, amount of shaft showing when fully extened etc etc)

How I build shocks.

When I build my shocks, at full extension, the distance between the bottom of the assembled shock body and the lower shock mount is 9.5mm. I got this number as the manual tells you to have 1mm of thread showing.

Next, I fill the shock up with oil, remove the air (shock pump speeds up things), ensure there are no remaining bubbles, top the shock up so the oil is level with the top, insert the bladder working it down with a 3mm driver to remove the excess oil and at the same time push the piston up so that the top of the shaft is just touching the bladder but not enough to push it out. I then wipe off the excess oil without bumping the bladder and screw the shock on. Finally I check to make sure there is no air in the shock, if not, then its goes on the car. The shocks have 0 rebound this way.

Regards

Josh Kemp

A few things I should mention,

I started with the Asphalt kit setup, I have tried various tyres and the usual setup suggestions that are made for the T4.

I keep seeing people mentioning the same problem in exactly the same circumstances but changing shock oil is never recommended.

Since I don't know what level of traction you're running on, or the tyres or your current setup, I'll just post the things that have helped my T4 to be awesome... I race on low-medium grip tarmac, on Sorex32 tyres in the UK.

Springs. The kit ones give too much understeer. Try 2.5 on the rear, and either 2.7 or 2.5-2.8 on the front. The 2.5-2.8 on the front seem to make the car more consistent without costing lap time.

Bodyshell. I found the Speed6 to be loads better than the LTCR on every track I've been to, in all conditions. It has a much more consistent balance through the corner for me. Mount it a few mm off the front bumper for a touch more steering.

Belt tension. I run the front belt in the tightest position and the rear in the loosest. This helps a lot with traction out of the corner as it sends more drive to the front and less to the rear.

Chassis flex. I remove the inner-most topdeck screws from both the front and rear bulkheads. This gives more traction on the power at the expense of a bit of turn-in (but you'll have plenty of turn-in with the suggested springs).

Gear diff. I run 1000cst in most conditions. If you go thicker it will give understeer on turn-in and oversteer on the power, which is what you're experiencing.

Steering brace. This is a simple carbon plate going across the two steering posts. You can make one from a bit of spare carbon, or cut up a T3'12 floating servo mount. It gives a more consistent balance through the corner (less turn-in but more mid-corner) and makes the car easier to drive.

Shocks should be fine at 350cst and 4x1.1 pistons.

Daleburr - sorry to highjack the thread, but would you suggest the kit springs for say, a higher grip tracks where you are looking to tame steering input, or is that a detrimental way to help this?

Dale,
Do you use the standard front driveshafts or the ECS shafts ??

I use ECS shafts on the front (52mm), as for me they sound smoother on track. I don't think they're essential, as I've seen plenty of drivers do quick times without them, I just don't like the 'ratcheting' noise of the standard shafts at full lock. Maybe its down to car setup or driving style.

I never race in very high-grip 'traction roll' conditions so can't say what the kit springs would be like. When the grip comes up a bit on outdoor tarmac I might go up a spring on the front to tame any oversteer. This is fine as long as you're not getting traction-roll. If you're traction rolling, I believe thicker oil and softer springs all round is the way to go.

Many thanks, sounds like I have a lot of testing to do...