suspension tech guide?

[MrVaper]

Hi everyone. Have a kbs mk7 with Quadrini rear that I've been slowly getting fixed up and have autocrossed a little bit last year. When I bought it, it was totally unbalanced with one side sitting an inch higher than the other.. Have it more or less corner balanced, put some new Hoosiers all around now and it runs very well..it's a lot of fun!

I can't help but think there's still a LOT of room for improvement though (understeer like a pig), and just looking at all the possible adjustment points makes my head spin.

What would be a good place to start to understand the handling better? I'd like a better idea of how the suspension geometry works, these panhard rods, how to adjust things like the roll center in the rear..and so on.

On a somewhat related note, do they make threaded tubing that you can adjust with a wrench..seems it could be handy
-Ben

[skt]

Hi Ben,

Most people on here don't realize F5s actually have suspension so you probably want to take your question over to formula500.org as there will be more people who autocross F5s there. As far as the MkVII goes there are a lot of adjustments you can do to change the balance including bellcranks (stiffen the rears, use the upper set most likely), raising the panhard on the axle, increased front camber, increased front caster, and throttle of course. I have not autocrossed an F5 before so can't comment on the specific setup for it.

For road racing I would recommend starting at about 1.5 deg negative camber (camber gain is crap on KBS), 3.5-4 deg caster, 1.75" front ride height, 1.875" rear ride height, relatively loose front bellcrank pivots and about 10lbs on the wheel to push down the rear pivots. Bumping rear tire pressure a few psi may also help (try maybe 11frt/12rear cold for oversteery goodness). Get the front corner weights as close as possible with loose pivots all around and let the rears fall out where they may. 4 lbs difference on the front is a lot more noticeable than 15 on the rear.

KBS is also very sensitive to ride height/roll center height adjustment. Moving the front up is more understeer, moving the rear down is more understeer. I prefer to move the front at the track, especially if I don't have scales available as it upsets the balance less if you just equally change the shock. Having run a MkVII for a few years I would recommend getting the panhard all the way up on the bottom of the axle tube if it isn't already there. All kinds of asymmetry but helps with the roll. We ran the front higher than what is above but it really depends on how your bellcranks are set up front to rear. Also be very careful that the shocks are running true and not binding.

I think people are typically running higher caster for auto-x and obviously tire temps/stability are different than road race.

[jim murphy]

As you read thru ALL the threads both here and at Formula500.org you will accumulate the setup for autox but here is some of what makes the car work in autox:
1. 7.5" wide rear tires mounted on 8" - 8.5" wide wheels on the front for max front grip.
2. Quicken the steering ratio by shortening the steering arm next to the upright and install a 9.5"/10" diameter steering wheel to catch the rear better.
3. Change the final drive from RR 3:1 to about 4.5:1 depending on the motor's peak HP RPM.
4. Re-tune the clutches for the faster acceleration to keep the motor in its peak HP RPM.

The rest are in the threads - start reading and find another FM driver nearby to go learn from.

Used to live in Jax, FL back in the early 1970's - raced karts at the 103rd Street Track.

Jim
Been messing with these cars since 1982.

[captaineddie1975]

Another site you should definitely look at is www.f500.US which has a lot of good info about clutching among other subjects. Clutching is vital to good performance on these cars.

[MrVaper]

Thanks for the replies and your time with the answers. Have started getting in some of the clutch components, new rubber pucks and so forth. As hard as it is to find concise technical information in a book from Amazon, it will be pretty rewarding figuring this out and being part of the F500 community.

I've heard a couple folks mention caster- what would be a practical way of adjusting this on the front of a KBS? Planning on picking up tune to win to get a better idea of some of the theory behind handling in regards to suspension and chassis. Any other good ones?

Have reached out to a couple FM drivers in the area..pretty far and few between but looking forward to meeting up.

Jim- think they're still doing their thing on 103rd..that side of town hasn't seem to have changed as much as the Southside

Until next time
-Ben