Bumpsteer

[7uptruckracer]

I know its rarely talked about. What is everyone spec on bump steer these days especially with the cars traveling more. I have seen Rockets at .063/1" wheel Travel. Warrior is at .020/ 1". What is everyone elses. I have run the Rf on a car at .072/ 1". We worry about static toe and most of us agree the LF is as close to 0 as possible. What are everyones thoughts on the topic because we have also been sliding Racks back for more ackerman too. I have a car to do here soon to see where it is and where I want to put it. Its on normal tires 1300-1350 so we don't really have to worry about hard tires unbalancing the heat front to rear. I've always gone with running higher RF bump because it helps stability but is this wrong for what we are trying to do now? Especially with the lockout stacks and bumps I know on asphalt when we bump the cars we run as close to zero ackerman and bump as we can because the bumps load the tires so hard. Thoughts?

[fastford]

i have always run between .020 and .050 per inch , a lot depends on the track im setting up for , also with the rt frt travel were getting now, close to 4 inches sometimes, we have to go back to the drawing board. i never liked the feel of a lot of akerman , but like i said, with the travel were getting now, it may take a combo of both....

[billetbirdcage]

I know its rarely talked about. What is everyone spec on bump steer these days especially with the cars traveling more. I have seen Rockets at .063/1" wheel Travel. Warrior is at .020/ 1". What is everyone elses. I have run the Rf on a car at .072/ 1". We worry about static toe and most of us agree the LF is as close to 0 as possible. What are everyones thoughts on the topic because we have also been sliding Racks back for more ackerman too. I have a car to do here soon to see where it is and where I want to put it. Its on normal tires 1300-1350 so we don't really have to worry about hard tires unbalancing the heat front to rear. I've always gone with running higher RF bump because it helps stability but is this wrong for what we are trying to do now? Especially with the lockout stacks and bumps I know on asphalt when we bump the cars we run as close to zero ackerman and bump as we can because the bumps load the tires so hard. Thoughts?

IMO, It depends on several things but I'll try to cover just a couple of the major ones:

1. How much Ackerman does the front end have in it. If the car has a ton built into it, then you can lean towards a lesser amount and vice versa.

2. This sort of goes with the Ackerman. Are the steering arms different lengths left to fight and how much different is the placement of the tie rod end inboard or outboard of 90 degrees to the snout. I personally hate different length steering arms, but is sort of the norm in many LM spindles but some have more difference side to side then others. Think about what is happening when you turn Left?

3. How much is either side traveling? if your using more travel then you can back it down some and less travel then you will likely want to increase it some.

4. What tires your on and the surface. You already covered this.

5. What is the track surface like? Does it build heat in the tires or easy on tires. This sort of relates to #4.

6. Is the car inherently tight or loose? It can also be used as a tuning devise to tighten/loosen the car at different places on the track. However with the RF down and ass up, it's not as useful as it once was because the attitude is more consistent all the way around the track, IMO.

Personally, I have more ackerman in my front ends then most and no toe in when turning left and still run least in the upper limits mentioned here. Is this correct? Might not be but it works for me.

[Austin34471]

IMO, It depends on several things but I'll try to cover just a couple of the major ones:

1. How much Ackerman does the front end have in it. If the car has a ton built into it, then you can lean towards a lesser amount and vice versa.

2. This sort of goes with the Ackerman. Are the steering arms different lengths left to fight and how much different is the placement of the tie rod end inboard or outboard of 90 degrees to the snout. I personally hate different length steering arms, but is sort of the norm in many LM spindles but some have more difference side to side then others. Think about what is happening when you turn Left?

3. How much is either side traveling? if your using more travel then you can back it down some and less travel then you will likely want to increase it some.

4. What tires your on and the surface. You already covered this.

5. What is the track surface like? Does it build heat in the tires or easy on tires. This sort of relates to #4.

6. Is the car inherently tight or loose? It can also be used as a tuning devise to tighten/loosen the car at different places on the track. However with the RF down and ass up, it's not as useful as it once was because the attitude is more consistent all the way around the track, IMO.

Personally, I have more ackerman in my front ends then most and no toe in when turning left and still run least in the upper limits mentioned here. Is this correct? Might not be but it works for me.
To add on to this.. you'd be hard pressed to find a racing tire that deflects more than a dirt late model tire. Maybe a top fuel dragster tire deforms more (maybe). So with the tire carcus as twisted and deformed as it is, sliding across a non smooth dirt surface trying to change the direction of a 2300# car with god only knows how much downforce... how much will the RF actually know that the spindle snout is turned 20 thousandths further to the left than the LF? How much weight is on the left front anyways? Which direction are we actually turning the steering wheel in these cars? Why do some race cars run anti Ackerman?? Lots of questions we need to answer before we decide to go with 20 thousandths of an inch or a half inch of bumpsteer or Ackerman

[7uptruckracer]

They might deflect but you have better contact patch compliance then ever and the camber gain they run these days loads the inside of the tire very hard and that camber thrust stretches the contact patch tight so the tire doesn't roll or fold in up upon itself. I know what you are saying but if static toe matters which is does to an extent then bump definitely does and it can be tuned per tire

[fastford]

also with the left front tire staying loaded more these days, there is a lot to be gained in this area, especially with up to 4 inches of travel in the right front. that .020 turns into .080 at full dive, but as i said above i feel bump steer and akerman have to be looked at more in a combo since now.

[7uptruckracer]

Yes and I understand they move the racks back which helps both ways you turn and bump can be one wheel at a time then include static toe. We turn left more then we use to and can correct the car with that kinda input with the new way we do things. I guess what I'm wanting to know being I know the ballpark specs and what people are trying is am i correct in thinking the more RF bump will add mid corner stability or entry whats the thought here? Most cars are setup to travel closer to 5" where as 4" use the be the standard