Understeer Oversteer - one for the setup theory gurus

[chrispattinson]

Ooplers, I have a really strange handling problem to resolve. I am running a TRF501X. On a low grip surface (gym hall floor), I need to resolve the following problem:

Off power understeer, on power (breaking traction) oversteer.

When I drive the car into a corner, it will understeer, and I find myself getting on the throttle to kick the back end round. I've been having a think about this, and can't think of any setup theory that will resolve this (my one idea is it being an antisquat issue as it seems the steering is throttle sensitive, however maybe the oversteer is only occuring due to breaking rear traction, - but why doesn't it break frint traction?).

Hopefully some more knowledgable ooplers will have a better idea.

This problem occurs whether running a diff or one way, with different ackerman angles. I am currently running long wheelbase (to try and counter the understeer) and 1deg antisquat.

Thanks in advance for any ideas. Chris P.

[Southwell]

Dial in rotation. Slow down more into the corners. I found rather than trying to dial in steering changing your driving style helps more. It would seem by trying to get loads more steering you are making the back end loose, i would go back the other way.

Hope that made sense

[sosidge]

Not enough grip Chris.

[Mike Hudson]

well he did say its a low traction surface! as outhwell said slow down more into the corners, slow is fast

[DCM]

if it is all low grip, you need the car to roll, but you also got to expect it to slide a bit too

[sosidge]

Last time I drove your car Chris it felt very good so I'm wondering what has changed.

It could just have been a particularly low-grip day at Jarrow? Perhaps our carpet laying on Sunday spoiled the grip

Otherwise, here is what I am wondering...

Does this coincide with fitting the LiPos? Go back to NiMHs.

What tyres? When I last tried you car it was on Minipins - go back to those.

Are you still running that 4.5 in there? Try something milder.

I had a similar issue at first with my Durga on the slippy floor - felt disconnected from the track. Stiffening the car worked, particularly at the rear, stops the car over-rolling and becoming unresponsive, keeps a more optimal contact patch, stops lifting wheels. Try the bars and see if they improve it, if not, try some even stiffer springs. Are you still running the blue AE fronts in the middle arm hole and the silver AE rears on the outer arm hole? That seems a good spring setup.

[Body Paint]

Originally Posted by chrispattinson

Ooplers, I have a really strange handling problem to resolve. I am running a TRF501X. On a low grip surface (gym hall floor), I need to resolve the following problem:

Off power understeer, on power (breaking traction) oversteer.

When I drive the car into a corner, it will understeer, and I find myself getting on the throttle to kick the back end round. I've been having a think about this, and can't think of any setup theory that will resolve this (my one idea is it being an antisquat issue as it seems the steering is throttle sensitive, however maybe the oversteer is only occuring due to breaking rear traction, - but why doesn't it break frint traction?).

Hopefully some more knowledgable ooplers will have a better idea.

This problem occurs whether running a diff or one way, with different ackerman angles. I am currently running long wheelbase (to try and counter the understeer) and 1deg antisquat.

Thanks in advance for any ideas. Chris P.

I would say you need to try shorter wheelbase. If you shorten the wheelbase you will actually increase the amount of steering at initial turn into the corner, and, obviously give you more rear traction when you apply the throttle.

Also if your car is very light you could add a few lead weights towards the rear of the car, this will also improve "turn in" and give more rear traction.

All this assumes that you have a good base setup, which I would suggest would be a little softer than your normal setup.

[chrispattinson]

Thanks for all your input so far.

Sosidge - Im running the NIMH, I ditched the Lipos as the car wouldn't handle with them in. I'm running on spring rate lighter all round compared to when you tried the car, a legacy from when I had the lipos in - I think I'll try the silvers and blues spring setup again.

Southwell - How would I dial in rotation?

CH - I think I'll try this. Ive never ran short wheelbase, as I thought this would take away turn in, as more weight is ver the rear of the car. I don't undersatnad how it will increase initial turn in, however I am going to give this a try, it sounds like it could be the solution I'm looking for. - Im a big fan of your B4 grass setup from doughty.net a while ago, so I'll go with you on this one.

Thanks for all the suggestions guys, I'll be trying them (one at a time of course) to see what happens to the car.

[jimmy]

My 501X was great with lipos at worksop. I used the 3200 Trakpower lipo and in practice the car was terrible. I softened the rear dampers and ended up on kit (yellow) springs, 25wt losi oil and largest hole standard piston.
I added lead between the cells along the centre of the chassis - and about 20/30g on top of the front rear hinge pin brace just in front of the rear gearbox - this made the car feel really good with the lipo.

[Body Paint]

Originally Posted by chrispattinson

CH - I think I'll try this. Ive never ran short wheelbase, as I thought this would take away turn in, as more weight is ver the rear of the car. I don't undersatnad how it will increase initial turn in, however I am going to give this a try, it sounds like it could be the solution I'm looking for. - Im a big fan of your B4 grass setup from doughty.net a while ago, so I'll go with you on this one.

Thanks for all the suggestions guys, I'll be trying them (one at a time of course) to see what happens to the car.

Well the idea is that a shorter W/B will effectively move the weight in the chassis backwards. This puts less weight on the front wheels and more weight on the rear wheels. With less weight pushing the front wheels into the ground the grip will react faster, changing the direction the car is travelling faster, hence MORE turn in.

Without watching/driving the car it's difficult to say definatively, but, sounds like it shoud help

Rotation: This can be effected by just about everything you can adjust. One of the mor consistant ways to increase/decrease rotaion is anti squat, though this also alters the way a car jumps, have a read through the setup section of your B4 instructions about anti squat.

[rich_cree]

From my memories of running yokomo YZ 10's on polished wood....

Ackerman makes a big difference, softer foams in the front, less castor, running the car slightly raked (front lower than rear), diff tightness, wing angle all make differences.

[super__dan]

Whilst I agree with Craig I think for different reasons. As with many of our setup changes on model cars, what we change actually effects more than 1 thing, sometimes for the effect we want, sometimes not, sometimes the effects work together sometimes they balance out, sometimes one effect is more at high speed/grip whilst the other low speed/grip.

Anyway, on a 'real' car when they talk about short wheelbase, they are usually chopping the middle out of the chassis and the short wheelbase car will turn like a mother (Group B rally cars). We do it just by moving the hubs at the rear which as we know has an effect of moving the weight distribution over the rear wheels.

Anyway, off power I think that shortening the wheelbase certainly car aid steering (as a 'real' car) but as we apply it on power it can add traction. Both things you appear to want?

Lastly on low grip you can often get more grip but running a stiffer car (oil wise anyway) I think, becasue by softening the weight transfers quicker (harder?) and overlaods the outer tyre and you lose grip. The harder car will share the grip between all 4 tyres thus feeling like more overall.

What you really want in here is Cree.............................................. ....?

[super__dan]

And as if by magic he shall appear whilst I type. I look forward to being shot down in flames

[Welshy40]

What I found worked was Stu Woods setup, and of course a few other extras ontop. Stu's setting is perfect but I changed the springs due to the low grip at my track. Ok green associated springs all round but the same oil and pistons with a fraction of pack.

I race on a highly polished concrete flooring with almost zero grip with yellow mini pins. I added a roll bar on the rear, also a one way. I also put a 3mm washer on either side underneath the wishbone pivot block at the rear (in front of the rear gear box), and this gave a kick up angle on the front of the rear wishbones. This did make a big difference. Also angle of the shocks need to be the same front and rear.

I also had alloy rear hubs with three slots to raise and lower the hub as this helped on low grip surfaces. I also raised the rear tie rod height, and changed the angle so the tie rods were close to central instead of angled. You will need a longer set of screws for this. Experiment to find the best setting with the little blue alloy washers.

These little changes did change the handling, and made it more solid on low grip surfaces, and a doddle to drive with pretty much zero understeer or oversteer and a lot more easier to dial than the standard kit setting.

Hope this helps.

[Southwell]

Ackerman should make it turn pretty agressivley, but if you have any carpet sections you could struggle to stay consistant. I found the best way of getting the car to turn is change the way i drive the car, getting off the power whilst on full lock should make the back end let go so you can get round the corner better. Of corse having it setup so it actually lets you drive it like that is a completely different thing.

I personally would drop the ride height, not so much that it compromises jumping capability, play with the wheelbase, camber links and probably frost caster. Unless the car is absolutely awful try to keep changes to one or two changes per race or you will tie yourself in knots.

[Lee]

Originally Posted by Welshy40

What I found worked was Stu Woods setup, and of course a few other extras ontop. Stu's setting is perfect but I changed the springs due to the low grip at my track. Ok green associated springs all round but the same oil and pistons with a fraction of pack.

I race on a highly polished concrete flooring with almost zero grip with yellow mini pins. I added a roll bar on the rear, also a one way. I also put a 3mm washer on either side underneath the wishbone pivot block at the rear (in front of the rear gear box), and this gave a kick up angle on the front of the rear wishbones. This did make a big difference. Also angle of the shocks need to be the same front and rear.

I also had alloy rear hubs with three slots to raise and lower the hub as this helped on low grip surfaces. I also raised the rear tie rod height, and changed the angle so the tie rods were close to central instead of angled. You will need a longer set of screws for this. Experiment to find the best setting with the little blue alloy washers.

These little changes did change the handling, and made it more solid on low grip surfaces, and a doddle to drive with pretty much zero understeer or oversteer and a lot more easier to dial than the standard kit setting.

Hope this helps.

So you took a "perfect" setup and changed it

[Welshy40]

Yes as Stu's setup works fantastic on grass and outdoor surfaces, and worked rather well indoors on zero grip surfaces with green springs all round. I worded it a bit wrong didnt I, so thanks for pointing out my mistake.

Ok I just went further and made it work a bit better on the surface I race on, but I would recommend trying Stu's setting and if up to it try my ideas and see if they work for you.