YZ-2 Straight line stability

Sean T · #1 17-10-2015

I've run the YZ-2 for two meetings now, but cant find why im have problems with straight line stability. under heavy braking at the end of the straight the car pulls to the left every time, then as soon as i come of the brakes it will straighten up. then under hard acceleration at the start of the straight it pulls to the right. if i feed the power or brakes in very gently then there's no problem.
Im running kit setup apart from shock oils and springs, weight under lipo & 20g in front of servo, all of the transmission is free running with the gear diff with 3K oil, all the suspension is free moving. I thought it was steering setup at first but now the cars been on a setup system its all fine running 0 deg toe. it was then setup with 1 deg toe in, but this has made no difference to the handling.
Im running on smooth astro indoors with Schumacher Blocks Rear/ Cut staggers Front.
Any ideas before i strip it down.

Sean.

shark · #2 17-10-2015

Double check the shocks are of equal length .
Also Spring collets are equal .

Sean T · #3 17-10-2015

I've gone through the shocks & spring all are equal, droop settings all checked. arms are all equal on setup board. Shocks have been swapped from left to right.

Sean.

discostu · #4 17-10-2015

Where are you racing it sean

discostu · #5 17-10-2015

It's gonna be some thing silly like a anti squat insert inserted wrong left to right maybe a caster insert up side down left to right pissibly a binding drive shaft seased bearing

Sean T · #6 17-10-2015

I've been running at FORCC.

Everything is free running. so was looking at the diff to be causing the problem. just going to start going through it now. just thought i would ask before i start stripping it down.

Sean.

discostu · #7 17-10-2015

The grip at FORCC is so inconsistent any way those block tyres as soon as the edges round off they are use less I'm assuming you are using cut staggers on the front as well

I suppose you are also running a too fast motor like a 7.5 or similar

discostu · #8 17-10-2015

Why do you thinks it's the diff

Is it binding

I assume you are running kit 3000 in it IMO is to soft I've always ran a minimum of 7 round there

Sean T · #9 17-10-2015

I've had the problem from the beginning with new blocks, cut staggers.
My thinking of the diff is that its one way when braking then the other when accelerating, the diff runs very free so going up in diff oil was my next plan. The buggy is otherwise all free moving so it only leaves the diff to be causing the problem.

Sean.

Allan1875 · #10 17-10-2015

For what it's worth, I always thought this car had torque steer and I just put it down to weight distribution.

It's only noticeable on medium to high grip.

It was always manageable and it was far less when I swapped the gear diff out for the ball diff. It's as if the gear diff diffs out under hard acceleration.

discostu · #11 17-10-2015

Yeah go up on oil

The car doesn't have torque steer unless you have some thing wrong

Good luck Sean ditch the cut staggers and go for non cut low profile it will be much easier to drive around there

Set your clutch correctly.

Allan1875 · #12 17-10-2015

Quote:

Originally Posted by discostu

Yeah go up on oil

The car doesn't have torque steer unless you have some thing wrong

Good luck Sean ditch the cut staggers and go for non cut low profile it will be much easier to drive around there

Set your clutch correctly.

So basically I had something wrong with my car then? Glad you cleared that up.

Stu is partly right, as I believe the reason for mine early on was the lower oil in the diff causing the car to diff out. I just preferred the ball diff in the YZ2. However, even with the ball diff the car still had a little torque steer, but far less than with the kit 3k in the gear diff.

I don't know much about the track you are racing, however Stu has mentioned that when the tyres get worn they are useless. Combine that with the gear diff and it will be a handful on the throttle.

discostu · #13 17-10-2015

Quote:

Originally Posted by Allan1875

So basically I had something wrong with my car then? Glad you cleared that up.

Yep give it a good check over.

Zippy G · #14 23-10-2015

I have a similar problem with my sons YZ-2, it pulls right under braking, I'v put it on the bench and gone through drive train etc, no problems.
Then I have moved to the front of the car, with the car on a stand I spin the front wheels, the left wheel spins for 4 times longer than the right wheel, so dad says dodgy bearings, yz-2 says no, dad says stub axle, yz-2 says no, dad says hub, yz-2 says no. Dad says AAARRRGGHH

LMAO!!!

I have since changed every part on that corner but its still the same, I have tried even changing hex pins and the hex's even rotated the wheels from side to side but still the same.

Any advice would be appreciated

Regards Sam

Allan1875 · #15 23-10-2015

Quote:

Originally Posted by Zippy G

I have a similar problem with my sons YZ-2, it pulls right under braking, I'v put it on the bench and gone through drive train etc, no problems.
Then I have moved to the front of the car, with the car on a stand I spin the front wheels, the left wheel spins for 4 times longer than the right wheel, so dad says dodgy bearings, yz-2 says no, dad says stub axle, yz-2 says no, dad says hub, yz-2 says no. Dad says AAARRRGGHH

LMAO!!!

I have since changed every part on that corner but its still the same, I have tried even changing hex pins and the hex's even rotated the wheels from side to side but still the same.

Any advice would be appreciated

Regards Sam

If it's rotating freely, that won't be causing it to pull under braking, there is nowhere near enough resisting force to cause that by the sounds of things.

danDanEFC · #16 23-10-2015

I hate ball diffs!

However, when I put a ball diff in it was even better, and much better coming on to the straight. I tried the gear diff again last week and the Ball diff is going straight back in.

xtreme-rc · #17 23-10-2015

Hi
There are a number of things causing this problem,
1 the tyres, from new , as the blocks wear they can have different grip levels,
2 the astro, if you watch the cars on the straights you will see them track to one side on different bits of the astro, this week ed commented that the car was pulling to the radiator side.
3 gear diff, will make the car unpredictable in certain parts of the track
What can you do, change the diff , as said the ball diff will certainly
Help, making the car easier to drive, keep the rear tyres sharp, we reckon 2-3 weeks before the go off and cause odd problems, the front tyres , low profile cut staggers unless mounted correctly will give inconsistent handling
Sounds a lot to do, but the track is odd and changes a lot
Hope this helps
Xtreme

Sean T · #18 23-10-2015

Problem seems to be resolved. well nearly, after a few emails & messages since my first post i came to the decision that the diff was the main cause of the problem. So gear diff changed to ball diff, the setup basically stayed the same from last meeting except more weight added under lipo & a bit more up front. Luckily when i got to the track only the astro was laid out so managed to run the car around the hall. there was a vast improvement in straight line stability straight away, then did some runs up & down the same bit of astro, fine one way then wandered to the right the other. so now its gone back to handling as last meeting. it now appears the weave in the astro is the main problem to my wandering & not so much the car setup. the ball diff has made a lot of difference over the gear diff, the car is a lot easier & consistent to drive now. The one thing i hadn't considered being the astro was causing me most of the problems.

Thanks to Les (xtreme-rc) post, astro is the devils carpet.

Sean.