Any drawbacks to widening track width

[sam 74]

I'm going t replace my a arms and was thinking about widening the track width a little, what would the pros and cons of doing this be?

[Ron Sutton]

The car will run flatter (less roll angle) and work the inside tires more.

How are you planning to do it in the front & rear?

[sam 74]

I'm going to redo the a arms on the front I have't figured out the rear yet, this was just an idea I was kicking around since I'm redoing the front, if it isn't a good thing to do to the front there really isn't any point to figure out the rear. I should also add that the track width out back is a little wider due to the wheel backspace, so would widening the front to be similar to the rear be of any benefit?

[Ron Sutton]

I was asking "how" because if you're widening the front track with spacers, the scrub radius increases. The positive benefits of the wider track width outweigh the negative benefits of the larger scrub radius. But if you're doing it by making the control arms longer, there is no scrub radius change, so no negative ... all positive.

In fact, there is a second benefit ... in that longer control arms provide less geometry change during travel.

In the rear, the method of achieving the wider track width is less important. You can run spacers, but I suggest you don't use more than an inch, as you'll be risking breaking the studs. Proper offset/back spaced wheels is the better route.

You want to keep the front & rear track width relatively close to each other. The ratio of front to rear track width is a important key to handling characteristics. If you made the front track significantly wider ... without increasing the rear track width the same amount ... you are making the car handle "tighter." Conversely, if you the rear track significantly wider ... without increasing the front track width the same amount ... you are making the car handle "looser."

Personally, I use track width as a suspension tuning tool to balance the handling of track cars, but I never let the front & rear get more than 1" different either direction. If you do, the car starts getting too much diagonal roll angle.

[astroracer]

I'm going to redo the a arms on the front I have't figured out the rear yet, this was just an idea I was kicking around since I'm redoing the front, if it isn't a good thing to do to the front there really isn't any point to figure out the rear. I should also add that the track width out back is a little wider due to the wheel backspace, so would widening the front to be similar to the rear be of any benefit?

Making the track wider by modifying the control arms (pushing the corners out) will significantly impact the steering geometry. Making the track wider by adding spacers has no impact on steering geometry. Make sure you keep that in mind when designing the arms AND your new steering geometry. :)
Mark

[Ron Sutton]

Making the track wider by modifying the control arms (pushing the corners out) will significantly impact the steering geometry. Making the track wider by adding spacers has no impact on steering geometry. Make sure you keep that in mind when designing the arms AND your new steering geometry. :)
Mark

Hi Mark,
Can you expand on the significant impact that would happen to the steering geometry?

In my experience, if the upper & lower control arms are both lengthened the same amount (more or less) ... and the pivot points stay the same for the control arms & inner tie rods ... the only things that are required are longer tie rods & lowering the tie rod at the spindle arm a small amount. Bump steer actually improves with longer arms due to the lower angle changes.

Did you incur some different results on a project? Thanks for sharing.

[astroracer]

Hey Ron,
I was just making the point so he is aware. Steering points need to be considered as part of the equation when doing the design work.

[RobNoLimit]

At first I would say all positive. But, I'll let you know that there is a point that may be too far. - depending on where your driving it. If your doing a lot of narrow track autocross, width can start to be a negative. My truck can barely fit through some of the lanes and gates of the tighter coarses. Now, it is wider than most, and really stable on big tracks, but Maier's Mustang can run a line that I can't even consider on a tight coarse. Also, I learned this from Ron, Matching the front and rear width is important. Initially the C10 was 2 1/2" wider in front that in the rear. There was no way to tune the push out of it. I bandaided the situation with additional toe out, but this has it's downsides. After some discussions with Ron, I changed the rear hub stance to net a 1/2" difference and the push is gone, I run only a small amount of toe out, and the truck is more stable at speed. Corner exit is also better. If the UCA and LCA are lengthened the same amount, lengthening the tie rod to fit will get you pretty close. Changing the tie rod end to a rod end, and using a stud and spacers at the steering arm to adjust the bump steer will dial it in.

[CA B4C]

Two points I haven't seen discussed yet are the effects on wheel rate and Ackerman. For the academic portion of this discussion, on a rear steer front suspension, increasing the front control arm length would tend to move the Ackeman convergence point behind the rear axle which wouldn't be all bad. However, on a front steer setup, the convergence point would move forward of the rear axle and may cause an issue with the inside tire draging during a turn. On the second point, given all other things remain the same, the motion ratio change would tend soften the wheel rate. Again, I'm not sure what kind of car we're talking about, and the intended changes may be slight and the effects may not be significant.

[Ron Sutton]

Wow ... this turned into a good discussion.


Hey Ron,
I was just making the point so he is aware. Steering points need to be considered as part of the equation when doing the design work.
Gotcha. Good point. I thought you may have seen some bad situations with longer control arms.


At first I would say all positive. But, I'll let you know that there is a point that may be too far. - depending on where your driving it. If your doing a lot of narrow track autocross, width can start to be a negative. My truck can barely fit through some of the lanes and gates of the tighter coarses. Now, it is wider than most, and really stable on big tracks, but Maier's Mustang can run a line that I can't even consider on a tight coarse. Also, I learned this from Ron, Matching the front and rear width is important. Initially the C10 was 2 1/2" wider in front that in the rear. There was no way to tune the push out of it. I bandaided the situation with additional toe out, but this has it's downsides. After some discussions with Ron, I changed the rear hub stance to net a 1/2" difference and the push is gone, I run only a small amount of toe out, and the truck is more stable at speed. Corner exit is also better. If the UCA and LCA are lengthened the same amount, lengthening the tie rod to fit will get you pretty close. Changing the tie rod end to a rod end, and using a stud and spacers at the steering arm to adjust the bump steer will dial it in.
Excellent advice & tips. Good point on the "too wide" possibility ... specifically for tight AutoX tracks like many Goodguys layouts.


Two points I haven't seen discussed yet are the effects on wheel rate and Ackerman. For the academic portion of this discussion, on a rear steer front suspension, increasing the front control arm length would tend to move the Ackeman convergence point behind the rear axle which wouldn't be all bad. However, on a front steer setup, the convergence point would move forward of the rear axle and may cause an issue with the inside tire draging during a turn.
If dynamic toe out (static toe, bump steer & ackerman combined) is the priority ... which is usually the case for track performance ... adding or subtracting a little bump out can fix this. If ackerman itself is a priority ... which is usually the case for daily street driving ... a little TLC (or shimming) at the centerlink to add or subtract some ackerman effect would be the better solution.


On the second point, given all other things remain the same, the motion ratio change would tend soften the wheel rate. Again, I'm not sure what kind of car we're talking about, and the intended changes may be slight and the effects may not be significant.

You're on point for sure. If we leave the springs in the same place & move the ball joints & wheels outward, we're reducing the MR, making the spring act softer. Of course whether it's significant or not depends on how much we move the BJs & wheels. If it is significant, we may want to increase the spring rate to get the wheel rate back ... assuming it was right before.

If we switch to coil-overs ... and move the mounting points out the same amount as the BJs ... we'd be increasing the motion ratio & wheel rate. We'd need to do the math & take that into account when ordering springs.

As a side note: Coil over or not ... I always like getting the shock out closer to the wheel. This reduces the shock's responsiveness delay and provides better control of the wheel (and grip of the tire) over irregular surfaces.

[sam 74]

This s a lot of good info, I have a 74 olds cutlass, front steer, I'm thinking I may just try and matchup my front track my rear, this way I only have to move everything out a little bit, maybe 1 or 1.5 inches at most. I'm thinking I may just try spacers at first to see how i like it then if alls well I'll build new uppers and lowers and ditch the spacers. Can anyone recommend a spacer to try out, looks like I'll need 1.25 spacers.

[j-c-c]

" I always like getting the shock out closer to the wheel. This reduces the shock's responsiveness delay and provides better control of the wheel", that sounds odd, is that what you meant to say regarding "delay", seems speed might change but not time.

[Ron Sutton]

" I always like getting the shock out closer to the wheel. This reduces the shock's responsiveness delay and provides better control of the wheel", that sounds odd, is that what you meant to say regarding "delay", seems speed might change but not time.

Hi J-C-C,

All shocks have a delay before they actually work, and by work, I mean provide resistance through hydraulic action. We think of this resistance as "control" of the suspension. I think of it more as the shock is "influencing" the suspension. All shocks are "reactionary" in nature and there are different factors that determine that reaction time.

Conventional twin tube shocks have the most delay (slowest reaction time) because the piston is simply sitting in the shock oil with no pressure ... until it moves. Once the piston gets moving, the oil going through the orifices & ports creates pressure & resistance ... and the shock can react to influence how fast that wheel & suspension move up or down.

In mono-tube, nitrogen gas charged shocks, the nitrogen pressure provides "some" pressure that makes the piston react quicker. It's still not at 100% until the piston moves, but the difference in reaction times is significant. A gas shock has a quicker reaction time.

Regardless of shock design, the closer we get the shock to the wheel, where its travel is closer to 1:1 compared to the wheel, the quicker (in time) the piston reacts & shock influence starts. The farther away from the wheel, the more time it takes to travel the piston far enough to react.

Make sense?

[bovey]

" but I never let the front & rear get more than 1" different either direction. If you do, the car starts getting too much diagonal roll angle.

^^^^^
Is this 1 inch rule the same for solid axel and IRS set-ups?

Thank you,
Bovey

[Ron Sutton]

^^^^^
Is this 1 inch rule the same for solid axel and IRS set-ups?

Thank you,
Bovey

Hey Bovey !

I don't know if I can call it a rule, because there are cars that run the track width difference greater than 1". But I find the car rolls unevenly when we do ... so I don't.

If the front track width is significantly narrower than the rear, the car rolls more onto the outside front tire on corner entry. This plants that tire harder & frankly reduces the load & grip on the outside rear tire. This is a good tuning tool to free up the entry & middle ... like all things ... to a degree. If you go to far, it's hard to keep the car from being loose on corner entry just after initial turn in. I find the things we have to do to fix the entry, end up hurting the car in the middle roll-through-zone making it tight or pushy.

If the front track width is significantly wider than the rear, the car rolls more onto the outside rear tire on corner entry. This plants that tire harder & frankly reduces the load & grip on the outside front tire. This is a good tuning tool to tighten & grip up the entry & middle ... like all things ... to a degree. If you go to far, it's hard to keep the car from pushing on corner entry just after initial turn in ... and it really wants to push in middle roll-through-zone.

So like most tuning strategies, it works ... but running too much track width difference either direction can have negative effects. Then you have to "tune around" these effects ... which is sometimes easy to do & sometimes harder than Chinese arithmetic. Whether the car is IRS or solid axle in inconsequential.

[sam 74]

Ron, I just found an issue with the car and wanted to run this by you, I measured the difference between the front and rear wheel in relation to each other to determine what size spacers are needed exactly. I ended up finding that the passenger side needs 1 inch more for the spacer to make the wheels square to each other. I need 1 inch on the drivers side and 2 inch on the pass side, this is on the fronts. It turns out the problem comes form the rear axle tube on the pass side being 1 inch longer than the driver side, the rear was installed a long time ago at a shop no longer in business and I don't want to get into trimming down the longer axle tube since tha also will effect axle length, everything is square with the rear end and the car rides straight, it's just the one axle tube is a tad longer than the other requiring me to run a 2 inch spacer on that side to make the front rim and rear rim square to each other and only 1 inch is required on the driver side to do the same, wil this be ok or do I have a big problem here?

[bovey]

Thanks. When you spell it out it makes sense. However, it's on the list of things I did not know to think of before reading your posts. This particular comment really resonated with me as I look at a lot of PT cars with really deep dish rear wheels and positive offset front wheels. I was questioning the different wheel offsets and how that would affect tire scrub, thus handling, but never did I link it to how the suspension would roll onto the tires as you mentioned above, that is of course if the tracks are different.

Forgive me as I speak beyond my education level with that last part...

Your posts answer and many questions and they create. That is a good thing, but it does mean a new thread is coming...

Thanks again,
Bovey

[Ron Sutton]

Ron, I just found an issue with the car and wanted to run this by you, I measured the difference between the front and rear wheel in relation to each other to determine what size spacers are needed exactly. I ended up finding that the passenger side needs 1 inch more for the spacer to make the wheels square to each other. I need 1 inch on the drivers side and 2 inch on the pass side, this is on the fronts. It turns out the problem comes form the rear axle tube on the pass side being 1 inch longer than the driver side, the rear was installed a long time ago at a shop no longer in business and I don't want to get into trimming down the longer axle tube since tha also will effect axle length, everything is square with the rear end and the car rides straight, it's just the one axle tube is a tad longer than the other requiring me to run a 2 inch spacer on that side to make the front rim and rear rim square to each other and only 1 inch is required on the driver side to do the same, wil this be ok or do I have a big problem here?

Sam, the picture is not completely clear in my head, so I'm going to ask you to state things differently.

With no spacers anywhere ...
Which side of the rear end housing sticks out longer? ... and by how much more?
Does the front end have equal dimensions to the WMS with no spacers?

What spacers are you running on each side of the rear end?
What is the track width in the rear with spacers?
What is the track width in the front without spacers?

[Ron Sutton]

Hey Mr. Bovey,


Thanks. When you spell it out it makes sense.
Good.

However, it's on the list of things I did not know to think of before reading your posts. This particular comment really resonated with me as I look at a lot of PT cars with really deep dish rear wheels and positive offset front wheels.
For track width purposes, none of that matters but the end result measurements. Of course the wheels are loaded differently and that requires a well designed wheel.

I was questioning the different wheel offsets and how that would affect tire scrub, thus handling,
To achieve less scrub radius ... and a wide track width ... requires longer control arms & deep back spaced wheels. This is how I design all serious road course cars, rules permitting.

but never did I link it to how the suspension would roll onto the tires as you mentioned above, that is of course if the tracks are different.
For even or uneven roll angles, the track widths front & rear are the key.

Forgive me as I speak beyond my education level with that last part...

Your posts answer and many questions and they create. That is a good thing, but it does mean a new thread is coming...

Thanks again,
Bovey

:lol:

[sam 74]

Ron, the passenger Side axle is longer by an inch, the front end is factory and unchanged. Everything on the front measured out ok, my concern is this, to get the outter edge of the rim on the front to match the outter edge of the rear I need a 1 inch spacer on the front drivers Side and a 2 inch spacer to do the same on the front passenger side, so I was wondering if that would cause any issues. There are currently no spacers installed.

[Ron Sutton]

Ron, the passenger Side axle is longer by an inch, the front end is factory and unchanged. Everything on the front measured out ok, my concern is this, to get the outter edge of the rim on the front to match the outter edge of the rear I need a 1 inch spacer on the front drivers Side and a 2 inch spacer to do the same on the front passenger side, so I was wondering if that would cause any issues. There are currently no spacers installed.

I'm sorta clear on it now. i still don't see why you need different spacers in the front. But it doesn't matter.

First, running a 1" spacer on the front is risky, if you're loading it hard. The 7/16" studs will break if loaded hard. 1/2" studs are marginal, 5/8" are preferred. But to run a 2" spacer is seriously asking for trouble. I'm not saying guys haven't done it. But as we see on the internet all the time .. guys are often willing to do risky things. I wouldn't.

On another note, safety aside, moving the wheels out 1" on one side & 2" on the other side will make the car handle differently on left & right turns. Lastly, by using spacers, you're increasing the scrub radius, so that's not the way to test this.

You can add a 1" spacer to the rear axle face on the "short side" to even them out. But for the front, you'll want to either make longer control arms or leave it be, depending upon the track difference front to rear.

[sam 74]

Thanks Ron, you addressed the concern I had with the 2 different spacers, I use the car mainly on the street but I want to do the occasional track day or autocross, but since I drive my kids around in this car from time to time I want it to be safe first and foremost.