Dynamic front end settings

[bcarrot28]

What is a good starting point on dynamic camber/castor on front end of a swartz? Wanting to check mine and make sure I'm not completely out of the ballpark.

[drgracer392]

Castor we use Left +3.5 , and right +6 is our standard. Camber Left 0 to 1 positive, and right 6 to 7 negative.Make sure you set them with the car at attitude (dynamic state).

[bcarrot28]

That leads to my second question. What is considered dynamic state? Rf at full travel, Lr at full extension, Rr at 2" compression and Lf fully extended?

[Ghopper]

That leads to my second question. What is considered dynamic state? Rf at full travel, Lr at full extension, Rr at 2" compression and Lf fully extended?

bcarrot28 - you have a good question. No one is racing at 2" RR compression, maybe they hit a hole for second to get that travel.

Given many cars run similar motion ratios on 3 corners...if you wanted corner entry under braking, then RF at your ~2000-2400lbf displacement value, LF compressed -1", RR -1", LR minus 0.5-2" from full extension. This is the only time your LF has significant load.

[billetbirdcage]

bcarrot28 - you have a good question. No one is racing at 2" RR compression, maybe they hit a hole for second to get that travel.

Given many cars run similar motion ratios on 3 corners...if you wanted corner entry under braking, then RF at your ~2000-2400lbf displacement value, LF compressed -1", RR -1", LR minus 0.5-2" from full extension. This is the only time your LF has significant load.

https://media.tenor.com/images/d38767bea06936e854b7190269138851/tenor.gif

Sup, Ghopper: long time no see

[bcarrot28]

bcarrot28 - you have a good question. No one is racing at 2" RR compression, maybe they hit a hole for second to get that travel.Given many cars run similar motion ratios on 3 corners...if you wanted corner entry under braking, then RF at your ~2000-2400lbf displacement value, LF compressed -1", RR -1", LR minus 0.5-2" from full extension. This is the only time your LF has significant load.Would that be where you would suggest checking/adjusting front suspsension? Also would you agree with the baseline settings suggested above?

[Ghopper]

Billet - it has been a long time since I have cruised the site!

@bcarrot28 - I would start by calling Audie Swartz. He as the most data on his cars across many customers.

If you want tune and track your own variation, then I would only set the front end with setup rods at or near an operation condition like discussed above. This will keep you consistent in your notes and relative changes. Final camber/caster/toe number vary by tire combination and average roll angle of the chassis.

Please hit subscribe for more ambiguous answers. :)

[billetbirdcage]

My suggestion would be document what you have in the dynamic state as far as caster/camber and toe but also toe while turning. Check a few positions, like straight, 10/15 degrees left and 20 right as well as 40 and lock. That way if you make a change you can see what all you changed so you have a better idea why or what effected the difference. Meaning you may changed one thing (lets say caster) but also changed the toe when turning right, so did the change come from the caster or the toe or both. This just helps you decipher what is actually going on.

[ZERO25]

There sure seems to be alot of contradictory info out there on these dynamic numbers. Our shock builder is telling us to tune our rr on its 3" number. Who do we trust these days? smh

[Ghopper]

If your shock builder is your overall setup guru, then you should listen to them as their advice only works in a package. Just don’t use the rubber travel indicator on the shock as a guide for load number setting.

For context, as a front end setting discussion, if the back of the car is +/-1” you won’t see much of a caster change for the tolerance we measure in.

[MasterSbilt_Racer]

My rr shock rubber won't move 3" in 3 races.

That said,

I agree, you have to put the whole package together. If not, you are the guy who asks 10 racers about an adjustment and winds up doing a little of each suggestion. Those guys are lapped traffic.

My cars would be undrivable if the rr ever compressed 3". That doesn't mean someone else's car wouldn't work.

[manwplan]

Castor we use Left +3.5 , and right +6 is our standard. Camber Left 0 to 1 positive, and right 6 to 7 negative.Make sure you set them with the car at attitude (dynamic state).

6-7 camber at attitude on the RF is not even close on any dirt late model

[Punisher88]

6-7 camber at attitude on the RF is not even close on any dirt late modelI feel like they are taking into account the car is set up at attitude. Which takes camber out if your going off ground zero level. Once the car bars up your reducing the camber read from the ground. If you leave the car on a jackstand level to the ground I'd imagine it would be much higher with just the rf raised up to max travel.

[MasterSbilt_Racer]

6-7 camber at attitude on the RF is not even close on any dirt late model

In reference to the ground, after chassis roll, that wouldn't be a terrible place to be.

[Ghopper]

Assuming 5-7deg body roll.......wait.....Want to make this easier? Not Hoosier or anyone else is going to give you much data other than the starting number from the chassis builder (when the car is ready to load in the trailer).

This is the lowest cost solution: Solid rods near an operation condition and measure camber relative to the chassis. Pick a number. Go to your test track. Sweep a few RF cambers keeping other variables as fixed as possible. Rate driver subjective feedback (thumbs up/down). Keep few objective metrics (tire temp, tire pressure, wear observation, lap times preferable in segments). Steering traces would be nice, note that spring rate changes with camber. This is the best you can do without a more advanced test-rig to remove variation of vertical loads with each configuration.

Some shock travels attached. The RR in this example is a completely linear spring rate (225). Note that I made a scatter plot with Liftarm travel on the X, shock corner on the Y. This conceals shock velocities, but gives you an idea of where most of your time is spent. Longer liftarm numbers are under braking, shorter are under throttle.

(edited - this image attachment tool is not good...)

[Kromulous]

One thing about a pull down rig thats always stumped me is, why do they pull it down with the wheels straight? or do they do it in a dynamic steering condition? A dirt car is very rarely straight at full or 90% hike, down the straights. I watched one being worked on once, and the bump steer, camber, wheels weights etc were all down with the wheels dead straight, to me thats about as bad as doing things from ride.

[billetbirdcage]

image attempt #2

Ghopper, attached images don't work here, you will need to upload to imgur or something like that and post link.

also if you want the link to show up, put and before and after the link

[Ghopper]

Billet - is this the '90s?

Figured it out. There is a size limit. Under 60kb seems to work. Above 100kb is out.

[ZERO25]

My rr shock rubber won't move 3" in 3 races.

That said,

I agree, you have to put the whole package together. If not, you are the guy who asks 10 racers about an adjustment and winds up doing a little of each suggestion. Those guys are lapped traffic.

My cars would be undrivable if the rr ever compressed 3". That doesn't mean someone else's car wouldn't work.

My shock guy's main cars are xr1's. His car has won alot of big crate races the past couple of years.My posts about lower rr deck heights came about because I noticed his cars and a couple national drivers cars were setup that way also.

Obviously, we have a b/g and have tweaked on his setup quite a bit but we havent got there quite yet.

[TheJet-09]

I apologize for hi-jacking the thread, but hopefully it's also relevant:

When checking bump steer on the RF, are you starting at ride height, or starting at a compressed point less than ride height? Or, in addition, would it be bad to toe in some (maybe 0.020") during the first three inches of compression (out at the hub), as long as it was back to zero and started to toe out from there?

I messed with it quite a bit and got this (eliminating the initial toe in), as of now:

1" - 0.008" out
2" - 0.035" out
3" - 0.084" out (this point is roughly 1 3/4" of shock compression)
4" - 0.150" out
5" - 0.233" out
6" - 0.332" out (this point is roughly 3 1/2" of shock compression)

The toe out numbers are the total measured at that point (not the difference from the previous spot). I can't go any further without modifying my gauge somehow, most definitely the plate the dial indicator measures off of. And I did search some prior threads on the subject (some very beneficial info), but I didn't come across a concrete number on where to start (compression wise).

Any feedback (like if those numbers seem realistic, or off somehow) is appreciated. Thanks!