Tramlining - ways to help?

[RoadRacer]

I'm only 100 road miles into my car, and just had it aligned to the specs below, based on the manual suggestions.

alignment.jpg 2021-03-01 13.30.50.jpg alignment1.jpg

Before alignment, it was hardish to turn while parking, given my 285/30 front tires I wasn't surprised. I could have coped with it, but after alignment the car is pretty light steering, and much easier at parking speeds. BUT it's also very light when driving, darting all over the place to the point that it seems unsafe to drive quickly.

Looking up "online" many call this tramlining, but I'm not convinced that's the right description. It may be caused by a grooved road surface, but to me it was also happening on smooth roads. I'd describe it more like being blown sideways by the wind, or a passing semi. Very twitchy.

Since I couldn't find a thread here on this subject, here we are.

First I'm going to try lowering tire pressures and see if that helps at all. I haven't checked what the alignment shop put in yet, probably 35-40lbs in there. Then I was wondering about how I could play with caster or toe, to see what helped. Camber wouldn't be involved in my mind.

Anyone played with this? Suggestions?

[Brastic]

Your tire pressure is way to high and would cause the driving you are experiencing. The rule of thumb is 1psi for every 100lbs of vehicle weight. That is at least a starting point. For reference, most Cobra drivers are in the 21-24 psi.

[RoadRacer]

Your tire pressure is way to high and would cause the driving you are experiencing. The rule of thumb is 1psi for every 100lbs of vehicle weight. That is at least a starting point. For reference, most Cobra drivers are in the 21-24 psi.

I just checked with my POS autoparts store pressure gauge, and it says 20lbs in the fronts, 40lbs in the rears (the new tires just added). I'm waiting on a new proper gauge and then I'll set up correctly.

[FF33rod]

Mine were up close to 40 when I first drove - courtesy of the tire shop. When I brought them down to 23 it was so much better. However, I'm still not happy with it at highway speeds, gets twitchy so still some work to be done.

Steve

[Brastic]

In you alignment report I noticed that "0.05" of toe is positive. I know that you want 1/16" negative toe. I just do not remember if that should be a negative number of not. For one of my cars, I set it toe out for better short course turn in. It was great at the autocross, and scary on the freeway.

[RoadRacer]

In you alignment report I noticed that "0.05" of toe is positive. I know that you want 1/16" negative toe. I just do not remember if that should be a negative number of not. For one of my cars, I set it toe out for better short course turn in. It was great at the autocross, and scary on the freeway.

Thanks, I appreciate your help. According to Wikipedia,

Negative toe, or toe out, is the front of the wheel pointing away from the centreline of the vehicle. Positive toe, or toe in, is the front of the wheel pointing towards the centreline of the vehicle.

But this is worth confirming myself, this is one thing I should probably be able to measure (not the numbers, but whether I'm pointing in or out)

[RoadRacer]

I found this, which confirms my thinking that toe-in (positive number, wheels closer at front) is better for stability. Which is what you're saying too, Brastic. So I will make sure this is what I got from the alignment.

http://www.ozebiz.com.au/racetech/theory/align.html

My thinking is that, even if I have it right, I may try more toe-in and see how it feels. Trading some tire wear of course.

[lance corsi]

From my understanding, positive toe-in for highway driving. Caster is what makes your wheels return to forward after a turn. Less caster=dartier, more caster=stability. Too little caster<5 deg. Too much caster>9deg. Also, other factors such as pwr steering, large tires, heavy vehicle all play a role in the ease of steering.

[MPTech]

Are you running PS? A Heidts valve can allow you to dial down the assist.

[RoadRacer]

Are you running PS? A Heidts valve can allow you to dial down the assist.

No power steering. Everything is as raw as possible

[AC Bill]

When you get your tire pressure corrected, and you are still finding it darty, adjusting the tow angle is the key to solving the issue..

[sread]

I think you will end up adding a little more castor to get the stability you are looking for. I'd go with about 5 degrees to start

[Big Blocker]

The specs you posted are about as close to perfect for a non-power assisted car in your weight range.

Unfortunately, most tire shops I've dealt with love to look at the tire, notice it states on the tire that max pressure is xx pounds and then inflate to that pressure. They rarely ask what pressure you want to run.
The rule of thumb here has always been 1 pound of air pressure for every 100 pounds of vehicle weight - adjustable from there after some driving and tread wear checks. Driving thru some fine dirt in a parking lot will show you the tread "footprint" and then you can adjust from there.

FWIW, my MK-II with a 5.0 powered engine weighed in at 2165 pounds with 1/2 tank of gas, Mr. Tubby (me) not in it. I ran 21 up front and 23 in the rear and got perfect footprints.

As far as toe-in goes, 1/16" is the starting point. I ran 3-1/2°+ caster with my manual car and tracking was flawless with a set of Nitto 555's, 275x35x17 in the front. My 20:1 ratio rack made up for no PS . . .

Also FWIW, "tram-lining" can be caused by tire tread patterns. I had a Mitsubishi Outlander that tram-lined a bit on grooved roads, switched to new tires when the old one got to the wear date - new ones didn't do it at all. No other adjustments other than replacing the tires.

Doc

[RoadRacer]

The specs you posted are about as close to perfect for a non-power assisted car in your weight range.

Unfortunately, most tire shops I've dealt with love to look at the tire, notice it states on the tire that max pressure is xx pounds and then inflate to that pressure. They rarely ask what pressure you want to run.
The rule of thumb here has always been 1 pound of air pressure for every 100 pounds of vehicle weight - adjustable from there after some driving and tread wear checks. Driving thru some fine dirt in a parking lot will show you the tread "footprint" and then you can adjust from there.

FWIW, my MK-II with a 5.0 powered engine weighed in at 2165 pounds with 1/2 tank of gas, Mr. Tubby (me) not in it. I ran 21 up front and 23 in the rear and got perfect footprints.

As far as toe-in goes, 1/16" is the starting point. I ran 3-1/2°+ caster with my manual car and tracking was flawless with a set of Nitto 555's, 275x35x17 in the front. My 20:1 ratio rack made up for no PS . . .

Also FWIW, "tram-lining" can be caused by tire tread patterns. I had a Mitsubishi Outlander that tram-lined a bit on grooved roads, switched to new tires when the old one got to the wear date - new ones didn't do it at all. No other adjustments other than replacing the tires.

Doc

Thanks Doc, this is helpful. I got sidelined by a bad fuel pump, but I just took it out for 20 miles on a different road and yes, it's darty as hell. So now I can focus on this a little, checking pressures and toe first.. wanna make sure they did do toe-in, not toe out

[RoadRacer]

ok, an update.

I checked the tire pressures. I already had 20.5 in the front tires (I've had these a while), but the new rears were set at 35psi and 50psi.

So they are now set at 22.5, just a smidge over the fronts (no idea why I think they should, I haven't done corner weights yet). I took nearly 30lbs out of the passenger rear LOL.

I also checked the toe-in - yes I have toe-in. I can't measure the amount, but the printout has the number. I just wanted to check it was toe-in, not toe-out. Here's how I checked:

checking toe.jpg

The difference was 1" over 4 feet, FWIW. Like 63 1/16 at edge of front tire, and 64 1/8 4ft back from that (measuring under the car).

[j33ptj]

An easy way to see if you get full contact with the tyre to the ground is using some chalk. Draw a chalk line across the width of the tyre and than roll it forward so the chalk makes contact with the ground. If there is a mark on the ground which is narrower than the tyre, this means that the tyre is over inflated, if there are more prominent marks on the outside of the tyre than the tyre is underinflated. If the mark on the ground is just abt the same as the tyre width, the tyre pressure is correct.

Usually this is around 30psi/2bar in my experience with different cars.

[j33ptj]

PS you may want to check if your "Ackermann angle" is set up correctly:

https://en.wikipedia.org/wiki/Ackerm...ering_geometry

http://racingonthecheap.com/recommen...andling-guide/

[Big Blocker]

James,

From post #15, 1" difference is waaay to much. Measuring toe is a relatively simple task. Strap a yard stick or other similar straight piece of material horizontally to your tires. Bungee cords make great restraints to hold a 2 x 4 cut to the proper length ( long enough to just stick out past the tire diameter - Eg; 23" tire, 26" 2 x 4 ) to the tire. Make sure you are NOT on the lettering but rather a smooth place on the side wall. Measure from outer edges to outer edges in front - repeat for back edges.

Difference is your toe measurement.

From your post above: 63-1/16" front should be 63-1/8" rear. That is 1/16" toe-IN.

Doc

[RoadRacer]

James,

From post #15, 1" difference is waaay to much. Measuring toe is a relatively simple task. Strap a yard stick or other similar straight piece of material horizontally to your tires. Bungee cords make great restraints to hold a 2 x 4 cut to the proper length ( long enough to just stick out past the tire diameter - Eg; 23" tire, 26" 2 x 4 ) to the tire. Make sure you are NOT on the lettering but rather a smooth place on the side wall. Measure from outer edges to outer edges in front - repeat for back edges.

Difference is your toe measurement.

From your post above: 63-1/16" front should be 63-1/8" rear. That is 1/16" toe-IN.

Doc

Don't worry, I probably wasn't clear. I wanted to be SURE of toe-in, so I exaggerated my measurement by measuring it scaled-up over a 4ft length. So I magnified the toe-in dramatically by my measurement method. It's not an inch toe-in.


BTW, my first impression is that the tramlining is a LOT better by reducing the rear tire pressures. I wasn't expecting much difference but it's driving a lot better. I only noticed minor tramlining over some quite extreme backroad undulations.

[RoadRacer]

Just to update here too (more on my build thread) but I've now got my own alignment kit and have set caster to 7deg.

Although I have to say - the alignment kit instructions say to do the common 20deg left, 20deg right, then double the camber measurement. But I've also read many sites say times 1.5 - and even more (reputable sites) that say use the camber difference directly with no multiplier. In the end I have to believe the alignment kit people, but it's hard to find a straight answer on caster measurement.

Why am I so suspicious? Well, I'm now at 7deg with manual steering, and although the car drives much better than the 2deg it started with, the steering is still very light. Where is this "heavy steering" I hear about?

So next, I'm in line for a bump steer kit, and I may wind even more caster on to continue my experimentation. I need to be able to trust the car the way I drive it