Toe in versus Toe out in the front suspension

[CB72]

I brought my car in this morning to fit the Cedar Ridge non-compliance rear beam bearings and toe links I ordered recently.
This off course requires realigning the suspension and the question came up with respect to the toe setting for the front?
The owner of the specialized shop who successfully raced many BMWs stated that toe in was required to ensure stability?
So far, I've only been running toe out in front but I must recognise that the stability of the car is not that great.
Driving on off camber roads for instance will require me to correct the steering effort one way or the other depending on the slope of the camber?
The remark from [MENTION=8251]tucsonsx[/MENTION] (http://www.nsxprime.com/forum/showt...sta-LE-or-s-Drive/page4?p=1989272#post1989272) in post 95 who states that the NSX had tires designed with inherent toe in makes me wonder if it's still the right thing to go with toe out in the front?
The fact that I'm running semi-slicks with only 25 mm offset might probably also play a large role in this respect?

 

[goldNSX]

that toe in was required to ensure stability?

Stability? Where? Straight at high-speed or during a fast corner?

 

[docjohn]

use the nsx recommended toe out...

 

[gleibig]

I was told to put my left toe and my right toe out.


Then shake them all about.

 

[CB72]

Stability? Where? Straight at high-speed or during a fast corner?

The stability is related to the fact that the car doesn't respond in a linear manner to the steering input.
In practice the car wanders requiring constant wheel corrections.
The following article explains this in further detail:
http://racetrackdriving.com/car-setup/track-alignment/

 

[goldNSX]

I'm too lazy to read, sorry.

Why don't you try toe-in, then toe-out and finally decide which one is better for you?

I'm with docjohn on this. The suspension geometry of the car has been designed for toe-out in the front. Why should toe-in be better?

 

[CB72]

I'm too lazy to read, sorry.

Why don't you try toe-in, then toe-out and finally decide which one is better for you?

I'm with docjohn on this. The suspension geometry of the car has been designed for toe-out in the front. Why should toe-in be better?

The car was designed with 15 and 16" wheels with specific NSX tires.
Today most of us run 17 and 18" wheels with tire widths that have nothing to do with the past including never heard off wheel offsets.
I won't try to repeat what's clearly explained in the text about the pros and cons of toe in vs toe out...
In the meantime, I will try some toe in and see how it works.

 

[docjohn]

let us know how it feels

 

[Mac Attack]

Scroll down to about 2/3 of the link below for a good explanation of toe:
https://www.paradigmshiftracing.com/racing-basics/step-by-step-race-car-setup-guide

As far as front toe, I used to run on the outer OEM recommended range of toe-out because that's how I liked it. However, I had to change it after removing ABS and going back to practicing threshold braking. Depending how much weight transfer you have, the front geometry toes-in with front dive during braking. It's enough to counter-act the inherent toe-out when braking due to the compliance and "slop" in the system. I like the feel and stability toe in gives me during this threshold braking, so now I set the front toe to zero. The other benefit is that it reduces drag and tire wear. A little toe-in won't hurt you in the front if you want to try it. It will definitely help improve stability on the off-camber roads you describe.

On the rear however, I recently installed TiDave's rear non-compliance beam bushings and have been playing around with toe-in. I have old tires at the moment, so I've even tried up to 12 mm of rear toe-in. Keep in mind the design parameter of the rear was originally 8 mm and that led to the class-action lawsuit with free rear tires and a revised lower rear toe in. For my current setup, I like about 4 mm of rear toe-in (0.36 degrees total).

 

[CB72]

Scroll down to about 2/3 of the link below for a good explanation of toe:
https://www.paradigmshiftracing.com/racing-basics/step-by-step-race-car-setup-guide

As far as front toe, I used to run on the outer OEM recommended range of toe-out because that's how I liked it. However, I had to change it after removing ABS and going back to practicing threshold braking. Depending how much weight transfer you have, the front geometry toes-in with front dive during braking. It's enough to counter-act the inherent toe-out when braking due to the compliance and "slop" in the system. I like the feel and stability toe in gives me during this threshold braking, so now I set the front toe to zero. The other benefit is that it reduces drag and tire wear. A little toe-in won't hurt you in the front if you want to try it. It will definitely help improve stability on the off-camber roads you describe.

On the rear however, I recently installed TiDave's rear non-compliance beam bushings and have been playing around with toe-in. I have old tires at the moment, so I've even tried up to 12 mm of rear toe-in. Keep in mind the design parameter of the rear was originally 8 mm and that led to the class-action lawsuit with free rear tires and a revised lower rear toe in. For my current setup, I like about 4 mm of rear toe-in (0.36 degrees total).

Great article!
I'm glad to see I'm not the only one trying to understand the pros and cons of suspension tuning.
I've agreed with the shop for 1 mm toe-in upfront and 4 mm toe-out in the rear just like you!
The urge to get this right comes from me following Cayman GT4s.
While from a power standpoint I can catch them on a tight course it's another matter alltogether on very fast tracks like Spa in Belgium where they slowly (?)crawl away turn after turn...
Of course, I'm getting older and only raced motorbikes in my life but I want to make sure I get the most stable platform to at least stay with them.
Thanks for sharing!

 

[gleibig]

let us know how it feels

Like warm apple pie.

 

[docjohn]

........in my pants............

 

[CB72]

Just to give you an idea of how fast a Cayman GT4 can go at Spa...
https://www.youtube.com/watch?v=xmcnbP8wxos

I've analysed the time differences against a very poor video taken from my own car with a heavy passenger on board and I loose 4 seconds from the exit of the hairpin at 0.13 until the 100 m braking panel at the end of the long uphill straight at 0.47.
My speed at that point is 240 km/h at a little over 8000 rpm in fourth.
No lack of power there!
The issue is the speed in the famous "Eau Rouge" a most difficult S to negociate with a very strong uphill incline that goes off camber where many famous racers lost their life.
From there on that I keep loosing time...
6 seconds at 0.59, and 8 seconds at 1.39. until I get locked up in traffic
I believe the GT4 is on slicks while I'm on semi-slicks, but no excuses, the driver is very good of course!

 

[CB72]

I picked up the car today.
The settings are for the front: 2.5 mm (total) toe-in and 2°30' camber.
The rear is 4.1 mm (total) toe-in and 2°30' camber.
The camber in the rear is at it's minimum as I didn't buy the offset Cedar Ridge bushings.
According to the shop the initial settings were far off?
In any case, I drove the car home under a slight drizzle and the result was quite amazing.
Despite the semi-slicks the car went straight as an arrow even on very poor roads with lots of camber changes and potholes.
Before the modifications the car would wander right to left without any warning making it quite scary!
In a roundabout the steering loads up very linearly with very good feedback on the amount of traction available.
All in all my confidence got a big boost allthough the roads remained wet.
Now is it due to the Cedar Ridge beam bearings or the new chassis set-up, who knows ?
My next track outing should clarify the matter but if the confidence stays at this level, the times should drop significantly!

 

[Mac Attack]

[MENTION=19738]CB72[/MENTION] I'm glad you like it.

That's the whole thing about front toe - Set it toe-in or toe-out based on what the driver wants. Throughout the course of a complete turn, whether you have toe-in or toe-out makes a negligible difference in the overall car dynamics. But, the feedback to the driver varies quite a bit. If you're more confident then you'll probably be quicker.

Also, extreme toe will have an impact on fuel economy and tire life, but that's a small price to pay in these cars for driving satisfaction.

 

[dquarasr2]

I picked up the car today.
.
.
.
According to the shop the initial settings were far off?
In any case, I drove the car home under a slight drizzle and the result was quite amazing.
Despite the semi-slicks the car went straight as an arrow even on very poor roads with lots of camber changes and potholes.
Before the modifications the car would wander right to left without any warning making it quite scary!
In a roundabout the steering loads up very linearly with very good feedback on the amount of traction available.
All in all my confidence got a big boost allthough the roads remained wet.

If as you state "the initial settings were far off", is it possible that the "before" being way out of spec caused the instability you spoke of before the recent alignment? Is it possible that toe-out within spec would be just as stable as your "after" toe-in? Do you have the "before" specs? I'd be curious as to what they were . . . .

 

[CB72]

If as you state "the initial settings were far off", is it possible that the "before" being way out of spec caused the instability you spoke of before the recent alignment? Is it possible that toe-out within spec would be just as stable as your "after" toe-in? Do you have the "before" specs? I'd be curious as to what they were . . . .

Good question!
The camber settings were not changed but the front toe moved from 2 mm total toe-out to 2.5 mm toe-in.
The rear toe-in went from 6.2 mm total to 4.1 mm.
I must mention that corner balancing the car required adding 1 1/2 turn of spring preload on one off the front struts but while this didn't improve the stability it might have offset the toe settings that were measured previously (at least left to right)?
Hence the comment from the shop manager?

 

[CB72]

[MENTION=19738]CB72[/MENTION] I'm glad you like it.

That's the whole thing about front toe - Set it toe-in or toe-out based on what the driver wants. Throughout the course of a complete turn, whether you have toe-in or toe-out makes a negligible difference in the overall car dynamics. But, the feedback to the driver varies quite a bit. If you're more confident then you'll probably be quicker.

Also, extreme toe will have an impact on fuel economy and tire life, but that's a small price to pay in these cars for driving satisfaction.

You are right, it's down to driver's preference but from a technical standpoint there must be a non linear zone in the steering feel with toe-out as the front outer wheel will first resist going into the corner until it finally points into the corner...
Absolutely negligeable in tight corners for sure but in long very fast corners it must deter the driver's confidence?
BTW if you are still looking for NSX type projects what about designing a "throttle blipper" to aid in the downshifts under braking.
The Cayman GT4 has this and if you watch them around the Nurburgring or Spa it sure helps.
Of course developping it for a non DBW car is surely more difficult...

 

[dquarasr2]

Good question!
The camber settings were not changed but the front toe moved from 2 mm total toe-out to 2.5 mm toe-in.
The rear toe-in went from 6.2 mm total to 4.1 mm.
I must mention that corner balancing the car required adding 1 1/2 turn of spring preload on one off the front struts but while this didn't improve the stability it might have offset the toe settings that were measured previously (at least left to right)?
Hence the comment from the shop manager?

Another thought: Sorry to belabor this topic too much, but what were your before and after caster values? High caster gives a car that ability to go straight (I LOVE cars that know which way straight ahead is.) If "before" caster was too low, that could account for some dartiness (is that a word? LOL)

 

[CB72]

Another thought: Sorry to belabor this topic too much, but what were your before and after caster values? High caster gives a car that ability to go straight (I LOVE cars that know which way straight ahead is.) If "before" caster was too low, that could account for some dartiness (is that a word? LOL)

The caster was not modified as far as I know and the values were 7°38' and 7°48' well within the NSX spec that states 8°+or-45'.

 

[dquarasr2]

The caster was not modified as far as I know and the values were 7°38' and 7°48' well within the NSX spec that states 8°+or-45'.

OK, I don't think being low but within spec on caster would have made an appreciable difference, so that theory is out the window. :biggrin:

I just noticed that in an earlier post you pondered an auto throttle blip to aid in downshifting while braking. I assume that with your track experience you know how to heel-toe and that you're just looking for the convenience and consistency offered by an automated system. Hell, banging off perfect downshifts is half the fun of driving a manual shift car.

 

[CB72]

OK, I don't think being low but within spec on caster would have made an appreciable difference, so that theory is out the window. :biggrin:

I just noticed that in an earlier post you pondered an auto throttle blip to aid in downshifting while braking. I assume that with your track experience you know how to heel-toe and that you're just looking for the convenience and consistency offered by an automated system. Hell, banging off perfect downshifts is half the fun of driving a manual shift car.

I sure do "heel and toe" but I'm not Ayrton Senna!
While I always do it going down from 3rd to 2nd, I find it more disturbing from 4th to 3rd when the speed is much higher.
As the placing of the pedals is not ideal, at least for me, I bought a set of 2002 NSX R pedals but the accelerator won't fit on my NA1...

 

[stuntman]

What was your alignment specs before when the car didn't feel stable?

Is it 100% better now? Your descriptions sound like a bad corner balance. With the car on jackstands, make sure the left and right spring perches are within 3-4mm of each other. You can achieve a good cross weight number but have the car sitting like a 3-legged table.

Front Toe-IN
-sharper, more immediate response at turn-in
-slightly more understeer mid-corner.

Front Toe-OUT
-less responsive, lazy turn-in
-more front grip mid-corner

Scroll down to about 2/3 of the link below for a good explanation of toe:
https://www.paradigmshiftracing.com/racing-basics/step-by-step-race-car-setup-guide

As far as front toe, I used to run on the outer OEM recommended range of toe-out because that's how I liked it. However, I had to change it after removing ABS and going back to practicing threshold braking. Depending how much weight transfer you have, the front geometry toes-in with front dive during braking. It's enough to counter-act the inherent toe-out when braking due to the compliance and "slop" in the system. I like the feel and stability toe in gives me during this threshold braking, so now I set the front toe to zero. The other benefit is that it reduces drag and tire wear. A little toe-in won't hurt you in the front if you want to try it. It will definitely help improve stability on the off-camber roads you describe.

On the rear however, I recently installed TiDave's rear non-compliance beam bushings and have been playing around with toe-in. I have old tires at the moment, so I've even tried up to 12 mm of rear toe-in. Keep in mind the design parameter of the rear was originally 8 mm and that led to the class-action lawsuit with free rear tires and a revised lower rear toe in. For my current setup, I like about 4 mm of rear toe-in (0.36 degrees total).

The Toe link up front is behind the wheel centerline. Assuming the toe link is parallel with the ground, the tires will Toe-OUT under compression in braking or cornering (the loaded tire).

 

[Mac Attack]

The Toe link up front is behind the wheel centerline. Assuming the toe link is parallel with the ground, the tires will Toe-OUT under compression in braking or cornering (the loaded tire).

I didn't need to bother with mocking up the suspension in CATIA or anything - When measuring the motion ratios for my suspension, I also measured the toe change. The front toes IN at my representative ride height. I don't remember the delta (it was a very small change), but definitely front was toe-IN with decrease in ride height.

I forget what the back did since I was more concerned with the front impact.

 

[Mac Attack]

Here's a good explanation of bump steer, measuring it, and then adjusting it from Longacre:
http://www.longacreracing.com/technical-articles.aspx?item=8162

Obviously I didn't perform any precise measurements, but the front was definitely toe-in on compression at my representative ride height. It was a small change, IIRC about a degree or two, and it surprised me because I was expecting to see the front toe-OUT.

Again, the reason I was paying attention to this is that I do not have ABS and prefer the stability and feedback given by a front toe-IN during threshold braking as opposed to a static zero toe up front or a static toe-OUT.