Nitro-C5

I put up a post a few weeks back regarding changing the Toe on my car when I do Auot-X.

Small refresher: Car has T-1 Bars, Bilstein Shocks and Z51 Springs and was pushing pretty heavy on the auto-x. I'm running 1.8 camber in the front and 1.2 in the rear with 7 degrees castor. Also using Khumo Victoracers.

To get the car to turn in better I should put some Toe Out in the front and Toe In (in) the rear. I received a few post that gave me different measuments on how much Toe would change with the turning of the Tie rod ends. I decided to turn the front and rear both 3/4 of a turn Clockwise which according to the advice should have been about 1/8 inch on each wheel or 1/4 total toe change front and rear. After doing this I have tested the car (granted I'm not on my race rubber nor at the track), but in a parking lott and it seems like the car is pushing even more

Questions:
**Did I turn the Tie Rods the right way? If clockwise in the front as you look at the tie rod is Toe Out then the same clockwise should be Toe In in the rear correct?

**With 3/4 of a turn approximately how much toe did I change? Did I make too much of a change or not enough?

**Maybe I'm not pushing the car enough to really see the difference, could that be the problem?

All comments are welcome.

Thanks,
Rick

RAFTRACER

OK first off the front T1 bar is far from ideal for autox. My suggestion would be to install a 30 mm Z06 or Z51 bar on the front or use front Hotchkis bar (32 mm). The T1 bar is ok in the rear , it will free up the car on corner entry.(I use that bar in the rear currently). On a roadcourse you dont want to only run the T1 bar in the rear because this will make the car very corner entry nervous.

Next, I dont know about the information you were given. I align these cars for competition daily and 1/4 turn of the tie rod is .08 +/- .02 ". So if you just turned both sides 3/4 turn you REALLY put some toe in it. Additionally if the car is tight (understeer ) adding toe-in to rear will make the car more tight. Have you carefully analyzed when the car pushes ?? Is it corner entry, mid corner, or corner exit ??? Does trailbraking help with the push or make it worse ???? My guess is with toe that for autox you should be between 1/8 and 1/4 " toe out in front , and 1/8-1/4 " toe-in in the rear. Individual preferrances may vary here.


The tie rods on these vehicle all have right-hand threads , so tightening it shortens the overall length , and looseneing it lenghtens the overall length. for more toe out in front , you would want to loosen the tie rod to the tie rod end. for more toe-in in the rear you would additionally want to loosen the tie rod to tie rod end. This may seem odd , but thats because the front tie rods are fore of the wheel centerline, and the rears aft of the axle centerline.

Driving techniques and styles can promote a vehicle to a push condition for sure, and so can "over-driving" the course. If you are heavily trail-braking the car on the corner entry this can generate push. Remember , your front traction can only be 100%. You cannot 100% brake and 100% turn. You need a 60/40 ,70/30 split---- reducing brake pressure and feeding steering wheel---- Always trying to maintain 100% tire usage. This is not easy and does take alot of practice.


Hope this helps.

TedDBere

Sounds like you turned it too much. One flat is approximately 1/16th inch toe. 3/4 turn would be about 4 flats or 4/16ths per side for a total of 8/16ths toe-out, or 1/2 inch!

Put your car on a level surface,make sure the steering wheel is straight, and take a straight edge against the tire at the front of the rim, perpendiclar to the ground, and drop a line to the floor...mark it with a pencil. Do the same for the back of the rim. Do all four wheels and measure the distance between the "opposite" marks. The difference between the distances will be your total toe in or out.

I've never seen more than an 1/8 inch toe-out used in autocross. FWIW

RAFTRACER

I've been known to run more to in the front than that . Additionally I have seen some REALLY fast cars use in excess of .35 inch out in front.

TedDBere

I'm just saying I've never seen it...but I have now! I'd listen to Raftracer, he really knows what he's talking about! Were those fast cars with greater than 1/4 inch toe out Vettes?

Nitro-C5

Thanks for the info.

As far as changing the bars is concerned that is not an option. I do everything with this car including High Speed Schools coming up and even trips on Charlotte Motor Speedway. I don't want to change the bars back and forth for different events so really looking just for some Toe advice in regards to the handling. I know that T1 bars in the front are not optimal but this is more of a hobbie for me that I enjoy...I don't have a lift so changing bars frequently would not be something that I would want to do.

Right now I'm leading the SCCA SM2 class in the Carolinas so the car will perform, but what it is doing is pushing in mid corner especially when I lift off braking and go to the throttle which is why I thought that increased Toe Out in the Front and Toe In in the rear would help me get the power down to accelerate out of the corners. I rode with my buddy in his 100% stock Z06 and it did not push at all in mid corner at the same speed I was carrying. I ended up beating him only becuase I've got so much more power and was able to overcome the handling problem.


So regarding the Tie Rod ends then I should be adjusting just opposite of what I was told..in other owrds I should be turning Counter Clockwise to add Toe Out in the front?? I was told by (2) different drivers (both of who race on a national level) that you would turn Clockwise in the front to add Toe Out??? Can anyone verify this?

XPC5R

Sounds like too much, really need toe plates or string to check after the adjustment. Given where the car is pushing (mid corner, throttle on) I'd say reduce the front to 1/2 turn on each tie rod, and put the rear back to zero. With just those changes, see what the balance is like. That much power really wants some toe in therear, but only after you get the front to turn in and hold.

Also look at your tire pressures, and play with lowering or raising the front pressures to get max mechanical grip out of them. Also check rake, as the nose needs to be 1/4 to 1/2 in. lower (check at the jack points) to make the T1 bars driveable.

Sorry if the earlier directions were overkill.

Solofast

Increasing toe out actually increases understeer. You have taken it to new level, but it was instructive to learn the lesson. I didn't really understand this at first either and didn't think it was so, but after a few long discussions (over more than a few beers) with folks who do suspensions for a living, and helped design the suspension on your car and mine, convinced me and I now believe.....

Increasing toe out actually is used to help improve initial turn in, not to reduce steady state or mid corner understeer.

First think about understeer and oversteer as which end is generating higher slip angles, not in terms of push or loose....

If you think about it that way (this is what they used to convince me), if a car understeers the front slip angles are larger than the rear. To generate lateral acceleration with an oversteering car you need to get the car yawed, and then you can generate lateral acceleration. If the car is understeering, as fast as you can turn the wheel, you will generate lateral acceleration. Thus, more understeer actually gives you faster turn in. That is because there is no time lag in getting the car yawed so that you can generate the lateral acceleration with the back tires, so this is faster response. Many folks mistake the effect of incresed toe out as making the car looser because now the front end turned in quicker (and generated a high yaw rate). That high yaw rate is what we generally percieve as oversteer, Also, the high yaw rate is now a "happening thing" and the car is really rotating so much that the back end got loose later in the corner.

Another way to look at is that as the car leans on the outside tire, that tire is not pointed in the direction of the turn, so that gives more understeer. Similarily, with the rear, more toe in at the back of the car generates more understeer, and more toe out in the back generates more oversteer.

Mid corner (or steady state) understeer is best treated with softer front roll stiffness (bars or springs). The understeer in transition from braking to power and as you power on is best addressed with softening the rebound on the front shocks. Or you could do the opposite in the rear, stiffen the rear rolll stiffness or stiffen jounce control on the shocks in the rear....

Put the toe back to 1/8 or so toe out and soften the front shock rebound.

Don't be suprised if you end up running more front shock on higher speed events. In solos you are in first and second gear and can generate bunches of torque. That extra lifting of the front end will result in more understeer in the transition to power. On a road course you want more high speed stability and will want more front end rebound than on an autocross course. That is one of the fundamental differences between a low speed and high speed setup.

OOPS, my bad, I just looked and saw you were running Bilstiens.....No adjustment available,,,,, This kind of thing is why folks get adjustable shocks... More tuning available.

You can make big changes in roll stiffness with these cars by changing the sway bar bushings, or changing the front bushing preload. Change to rubber if you want to soften the front bar, or open up the preload on the front rubber bushing and you can probably get there without yanking the whole bar. Or, you can increase the preload on the rear bar bushing (if it is rubber) by putting a wahser or two between the rubber and the mount.

Try some more softness in the front bar that way and you can probably get there... After you fix the toe...

Nitro-C5

Thanks everyone for the great info

Recently put on the T1 bars and the Poly Bushing on so I really don't want to make any other parts change right now...so for the next few races I really want to see if I can live with the parts and adjust what I can to get the car to perform abit better.

The Rake right now is set where the back is about 1/4 higher than the front and I changed both front and rear tie rods to 1/4 clockwise. This "should" give me about a 1/8" total toe front and rear based on the different information that I have received. Since I have never ran any toe changes at the track this should at least let the car turn in quicker and help put the power down...going back to my (2) original questions can anyone give me a definative answer on the following:

1) Can we confirm that while looking at the Tie Rod that turning Clockwise does in fact add Toe Out in the front?

2) I've gotten alot of different numbers on this but does anyone have a quick answer on how much total toe that a 1/4 turn on the Tie Rods will give me? Based on variying information I'm guessing about 1/16th per side or 1/8" total toe...does this sound about right?

XPC5R

clockwise (the same direction you loosen the jam nut) will lengthen the tie rod, and create toe out in the front. The same adjustment in the rear adds toe in.

dmtnt

Some good info in this thread!

If you have or can borrow two levels or other straight-edges, you can easily measure toe. Just place the levels on each front wheel and measure the distance in front and back. The variation is your toe. I picked up a set of toe plates for around $50 and they make the job very easy.

astock165

WOW, that makes me rethink everything. So, if a car seems to have good initial turn in, but then understeers as you transition to throttle in mid turn and exit, what would the toe setup be for that? Nuetral?

Have others found this to be true as well?

TedDBere

Think of it from a suspension compression point of view. When you compress the front suspension the tire will toe-in due to the geometry. When you relax the front suspension the tire will toe-out. This is due to the position of the tie rods.

So in Autox when you initially turn in, the outside suspension compresses and the inside one relaxes. The amount of compression and relaxation will vary from set-up to set-up depending on your bars, springs and shocks/settings. If you have the front toed-out the outside tire will move towards neutral as the suspension compresses and the inside tire will toe-out more in the direction you are trying to turn. You are therefor attempting to give your car the turn-in characteristics you are looking for to make it drive fast for you.

If you have too much toe-out the outside wheel never gets neutral, or if you don't have enough then it toes in. What you want it set at depends on where it is and what you want the car to do compared to what it is doing.

Good luck.

ghoffman

As Solofast did in his excellent post above, I want to share a tip I use for something much more mundane, i.e. which way to turn the tie rods.
What I do is think of it not in terms of clockwise-counterclockwise but use the jam nut as a guide to "close the gap"-"expand the gap" thinking. First of all, I always use a white marking crayon to mark the "up" position of the tie rod at start. Loosen the jam nuts and then if in the front end you want more toe-out, you would rotate the tie rod in the direction that would increase the gap between the nut and the rod end. For more toe-in, back the nut off from the rod end a full turn and close the gap. Similarily, the opposite is true on the back but since the tie rods are behind in a "rear steer" position the opposite is true. This way, whether I am doing this front or rear, from under or over the car, I don't get confused.

Gary Hoffman
Hardbar.net

John Shiels

mvitacco

Great Stuff: So that's why circle track racers take the ackerman out
of the car. I've done bump steer measurments on both stock C4's
and C5's and could not measure any so I would not assume
toe changes in bump. However, if there is ackerman there will be
added tow out in turns, believe this is actually called TOT? I fould
my car handeled best in both slow and fast corners with 0 toe in the
front with good turn in response consistant with all stated above.

Autocross is totally different becuase it is all transents. You
tune for their initial turn in response, there is less
concept of steady state cornereing. I would not want to drive a car
with AX settings on a road course, but that's just me.

so who has the mole in GM? (and what else can we learn today?)