When adjusting the front end settings on the alignment rack, should the car be aligned with the slick pressure at launch psi, or with he slicks pumped up to simulate spinning/full size?

My 23x8x13 slicks look WAY different at 20 psi than 7 psi.

 

just align it with regular wheels and tires. much easier

It doesnt matter if you have 5 psi in the tire or 50, the alignment does not change.

It doesnt matter if you go from a 13" wheel to a 30" wheel. the alignment does not change.

What does change the alignment a little is the hit when you shift weight and the front tires are loading the suspension.

 

Actaully it does change if you vary the overal size of the wheel.

A change of size of wheel changes camber measurements. A change in camber affects toe measurements.

 

Actually it absolutely does not. Just sit back and think about that for a few minutes.

 

I had my slicks and car aligned at 20 psi, car pulled straight as an arrow with the slicks at 6.5 psi

 

I'm not concerned with "pulling straight", I just want settings for maximum traction/straight line performance.

 

I have always been told to sit in the car while they align it as well. I wonder if this matters with a 150lb driver vs one that is 250+

 

I think that's more like corner balancing???

 

People typically corner balance the car as it would be at the track. Driver/fuel level.

 

That's what I do. I also sit in it during alignment....though reading the screen with me in and out rarely changes anything.

 

I have a buddy who weighs 300lbs and also happens to be a mechanic who specializes in alignments. I'll ask him, but I know with him out of the car vs in the car it's quite a difference in readings. I'll report back once I get the answer

 

Well hell ya it will. But I'm a mere Buck-40 on a bad day so the amount that the alignment flickers is marginal when I get out.

 

Hence the reason I stated racers who weight 150lbs vs those who are 250+ in my previous post. Not every racer is the size of a 13 year old lol. Personally I am a big guy, so I think next year when I go to get the car aligned I am going to do it with me in the driver seat and see if it changes anything.

 

I've found that having the front wheels slightly toed-in with a couple degrees positive caster helps get the car to leave the line.

I don't mean to run excessive caster or toe. I mean that when doing the alignment allow the setting to be at the furthest point in the green scale. Not outside in the red scale. Those who do alignments should understand the concept.

Weight has everything to do with how a car reacts after adjustments. The heavier the person and/or load the further off the settings will be.

Wheel diameter and tire size do alter the settings. Especially if both diameter wheels are present on the vehicle at the time of alignment. Next time use the smallest diameter wheel and tire combo with the tallest. See if you can get the car to pull straight after changing to all 4 same sized rims and tires.

 

Just Google search it, the wheel size and tire size does not change the alignment. I can't believe I'm having this argument. All that a wheel size changes is the relationship to the hub distance from the ground. Not the distance of the hub in relation to the suspension(example turning a collar to adjust to Spring height)

 

Better bleieve it. This is Honda-Tech. lol

Matt is right. Tire size doesn't matter. They mount the reflector to the wheel and align the car based on wheel data. How does the tire affect anything?

 

Tires do not matter just like everyone is saying, but having your car at race weight does. Some cars more than others depending on how much the height of the car changes with the weight and how well the bump steer is set. If possible sit in the car while its getting aligned take as much guess work out of the procedure.

 

I have given it some thought and I believe you may indeed be correct. I was thinking overall ride height and lever (wheel) size would affect camber. Now that I give it a little thought the actual spring position settings and their relation to the hub should be the only measurement that affects alignment readings.

I see some merit to your "argument" and now I would like to compare it in real world circumstances. Next time I align the car I am going put street wheels/tires vs drag wheels/tires to prove this in real world circumstances.

Maybe the fact that the newest most expensive alignment racks have air chucks for automatic tire pressure setting before alignment is making me assume things I shouldn't... Maybe too many books on suspension/steering theory have me thinking everything affects alignment.

Sorry to make you so hangry Matt

Can I buy you a Snickers?

 

Luck4rmkc, I have aligned with street tires then drag and it didn't change anything. the only time alignment changes is when suspension geometry changes. weight does. lighter drivers will not notice much diff, but heavier drivers will. weight of the car and location of weight in the car will change alignment and how the car reacts to the weight transfer.

 

Judging from the theories I've (and the rest of the vets) on this site have seen, I'm not surprised at all. :p

Wheel/tire size does not in itself change alignment. Not sure why that's even being debated as the wheel doesn't change suspension geometry. I'm assuming they are thinking along the lines that to fit a substantially taller tire/wheel combo, one must raise the car, which in turn, does alter the alignment. That's the only sense I can make of it. LOL

As to answer the poster, you align the car at full race weight with the idea that whatever you do, e.t./mph in the first 330 feet matter more than the last 330 feet. If you see no change in 60' and 330' times with different settings, then align it for what the car is doing at the end of the track to at least help fight rolling resistance at higher speeds where drag matters more. Usually, everything is always a sacrifice, and this is no different. But always keep in mind e.t./mph in the first half matter more so the emphasis should always be there.

 

Ok, so align the car as normal, got it.

Now, to throw another wrench in the works, corner-balance the car with 20 or 7 psi in the slicks? Again, 20 would simulate full "stretch" and 7 how it sits waiting to launch.

 

Don't align it as "normal" unless it's a street car you don't care about getting 100% performance from. If you align it to be where you want it as it's in a neutral/static state of suspension travel, it will be off when racing when you have weight shifting from load. You'll be out of toe and camber the entire way down the track which is counterproductive.

It totally depends how much suspension travel you will have (I was shocked to see how much my old car lifted up in 4th in a Go-Pro video) as to how you want to align it. It's all variable to your specific set of circumstances and only you can solve that. None of us online without access to your car.

In regards to the slick psi, it will not matter, as stated.

 

Tire psi does effect scaling.

Why are you trying to simulate what the car is doing going down the track when no one knows what it is actually doing? Why guess? Everyone I know scales the car the same way (race ready).

 

I'm not here to argue with anyone.

Knowledge is power. I'm here to learn.

I'm guessing the few times I encountered a difference in wheel diameters there was something else wrong with the tires that would keep the car from going straight.

 

good info....so what would be rough settings to start with? xxx camber? and xxx toe?