4WD handling problem

[chrispattinson]

I have a handling issue with my 4WD car, and wondered if anyone has a suggestion.

Just been trying the car on a smooth tarmac surface, with worn minispikes on, therefore there isn't much traction.
The car is setup to the best of my ability, on a setup station for angles and toe in and steering throw etc., using a vernier to check tie rod lengths etc. I threaded string through the centre points of the car to get the left right balance correct.
The car: CAT 2000 with Novak 4.5 brushless.
The problem:

When the car is rolling, it tracks straight.
When the car accelerates hard from a standstill, it pulls right.
When braking (one way unit fitted) it dives left.

The only thing I can think it might be , is if I have balanced the car (left right), but added the weight too much to one corner. I dont have the required 4 scales to check the load on each tyre. If anyone has any suggestions as to why the car is behaving this way, or how I can get the weight distributed evenly, I'td be appreciated.

Could this be down to the offset drive train on the CAT (the belts dont run exactly straight, they are angled), but I doubt that the tiny angle, would affect it this much.

I have checked chassis tweak, everything seems flat and true.

Thanks in advance, Chris Pattinson.

[Nick Goodall]

Chris, i think it's just something the Cat has always done, remember back in 1994 through to 1999 or so we didn't have the crazy amount of power that's available now so it wasn't really noticed on track - and to be fair, most of our tracks are high grip so the car doesn't really have a problem once out running..... Stand still on tarmac is a pretty unfair way to judge it and i really wouldn't worry too much as it's unlikely the car will ever be in that situation when you're racing it?

I ran the Cat 98 at the Worlds in Finland 99 and we just couldn't generate any traction out of it hence being a great European based car on high grip Grass and astro, but not so great on the dirt or slippery stuff.......

That's just the way i see it but maybe wrong, but i think it's to do with the allignment of the drive train, it's actually quite a large angle if you look straight down from above.

[chrispattinson]

Thanks Nick, I'll go with your explanation. Other than this problem, I am getting there with the cat. I managed 13th in round in one qualifying round at the last regional, which is higher than I've done before in 4WD. Just getting the hang of it again.

[HKP]

Yes I agree with nick, its a trait of the Cat 2000. Look at the angle of the outdrives in relation to a straight line (such as the wishbons). You'll see they sit at quite an angle giving a torque steer effect. I had a similar issue running mine on loose surfaces.

[Northy]

Chris, your running a 4.5 :o :o :o

I only have a 6.5 in the Pred! :cool:

G

[super__dan]

I agree, it's the madness of the northern lads, 4.5 for 4wd and 3.5 for 2wd isn't unheard of :)

Having said that if the straight is long enough this weekend I am dying to try my 4.5 :D

[Lee]

Chris,

Check the droop, or shock lengths if there are no droop screws, if one wishbone drops further than the other then it will pull one way under power

[Jonny_H]

You could try adding a tiny bit of preload to the LF and RR shocks, to cancel out the loads put in by the driveshafts on acceleration.

Don't over-do it though, or you'll start getting asymmetric handling mid-corner.

[chrispattinson]

G / Dan

I run 5.5 in 2WD and 4.5 in 4WD. The motors are more than I'm ever going to need in either class, and I just dial out some of the throttle using the arc and the EPA on the transmitter. Not ideal I know, but an acceptable solution which enabled me to buy the fastest motors I would ever need, and a way of limiting (fine tuning) the power and top speed to the track. As someone that has raced for a few years now, I would like to think they are'nt too fast for me to handle, however I would not recommend these winds to a new racer.

Dan - get the 4.5 in. G - Get a 3.5. Then you lot might be accompanying me in the B final instead of your usual A final positions.

Johnny_H

Thanks for that suggestion. I dont think I will add pre load to different sides of the car as I feel it would comprimise handling more than I currently suffer. I may try it in practice, but I'm not sure how confident I would be of the car jumping predictably. On the higher grip available on the tracks I race on, Nick is probably right in that it wont affect me. As long as we dont have many starts on the "patio" grid at Bury in the future.