Understeer at Winton Raceway

[Sirois]

Hi everyone,

Firstly, this isn't about an MX5 but would really appreciate advice as I don't know where to go with this.

So, the car is a Mitsubishi Lancer FWD that I use purely at Winton Raceway.
It has MCA reds, Nankang AR1 205/50/15 tyres 30-32psi hot, 20mm solid rear swaybar, stock front swaybar.

What I have noticed is that the front tyres are not wearing at all on the outside, so much so that after 5-6 track days the outside is like new.
I thought that was running too much camber so I played around and here were my results:

+6 castor and -3 camber caused excessive understeer
+4.5 castor and -3 camber gave it a lot more front end grip however still understeered
+3.5 castor and -2 camber seemed worse than the above setup yet still the outside of the tyre has zero wear on it.

Going stiffer front shock settings gives more grip at the front end.

The rear is already very stiff, it lifts the inside rear wheel during brake trailing.


I don't think the AR1 tyres are so bad... from all the reviews I read they are pretty decent.
I am going to be lowering the front a tiny bit and raising the rear a bit (now the rake is as per stock, lowered about 1.5" all round).


So the problem seems to be that little of the front tyre is making contact with the road.
The suspension is stiff but does have roll. Springs are 9kg all round.

According to this article:
https://speed.academy/how-to-fix-unders ... up-tuning/

It says that with stiff suspension sometimes going stiffer front will end up giving more front end grip.


Any advice would be greatly appreciated as I am at a loss currently.
I have spoken to Josh from MCA many times and have followed all his advice and still the handling is poor.

[Magpie]

Have you tried a wider front tyre?

[Sirois]

No I've not tried.

I have considered going 225/45/15 AR1 fronts or 215/50/15 A050s but seeing as the wear on the current tyres indicates that the contact path isn't good I felt that going wider would make no difference if I am still only using a small section of the tyre

[Luke]

I could never make the AR1's wear evenly on my MX-5.
They would always wear a strange line about 3cm from the outside edge. When I flat spotted all 4 a join line was revealed under the canvas where they were wearing.
I still rate them the worst ever R-Spec I have used. I believed the reviews as well and call bull sh*t on them now. I know some here will probably argue against that but I have a comparison of times somewhere on this forum saying how much slower they were than other tyres I have used on the same car.

The one setting you have not told us is your front and rear toe settings. That will control your under and oversteer more than anything else. It can also highly influence inside tyre wear. Either way being FWD you will want toe out front and rear. Generally more on the rear than the front. How much will be trial and error depending on balance.

In all seriousness before you go chasing spring rates and sway bars further than you already have, try another brand of tyre as well.
If you are budget conscious and the regs for what every you are running in allow it, give the Nitto NT01's a go. Or go for the less aggressive Hankook RS4 which are just as fast as the AR-1 and will last twice as long as they are still a road based track tyre. Both available in 225/45/15 for circa $800. Nittos have 205/50/15 as well.

Now the dumb question, are you going fast enough around the corners to wear the outside???

[Magpie]

Have a search for the Honda called Mighty Mouse, this is a VERY QUICK FWD car. Rob has spoken a lot about the setup on his car...

Back to basics... :

1. The front's are being asked to do almost 3 times the work, accelerate, brake and steer. This is even more apparent on corner exit when the tyre has to take side load as well as acceleration forces.
2. Do you have a friction circle that you could post? Here is a recent one of my car (225/45/15 AR-1's)
   
3. How much bump/rebound travel do you have at normal ride height?
4. How much bump steer do you have?
5. At what point do the bump stops engage?
6. What are the spring rates?
7. If you are not getting any wear on the outside then this would suggest that you have no (or very little) camber gain. Negative camber could be dialed back, but it sounds like a suspension setup issue in that there is no camber gain.

Now the tyres...

1. It is no secret I run the AR-1's. Whilst they are not as fast as other R Specs they are faster than AD08R's.
2. They are sensitive to setup, just like any other tyre! With the fronts doing almost all the work they will heat up VERY quickly and heat is the enemy of ANY tyre. Here is data from 03/02/19. The tyres were almost at 110°c at times, not to mention 60+ in the cab!
   
3. I would suggest 29/28 hot in the front, maybe a little more in the rears. I have been able to still get good times from very worn AR-1's - https://www.facebook.com/mx5na6/videos/973246246199869/

In closing try and make single changes and then evaluate. Making too many changes at once makes it difficult to attribute if one of the changes worked or did not work. I would verify suspension travel including camber gain/bump steer (and if required make changes) and reduce the fronts to 28 hot.

Off topic but I should be able to provide some feedback on the AR-1's and slicks very soon...

[Magpie]

I still rate them the worst ever R-Spec I have used. I believed the reviews as well and call bull sh*t on them now. I know some here will probably argue against that but I have a comparison of times somewhere on this forum saying how much slower they were than other tyres I have used on the same car.

Here is your previous post on how slow they were- http://www.mx5cartalk.com/forum/viewtopic.php?f=30&t=77004

[Sirois]

1. I don't have a friction circle. I did measure my front tyre temps once and from memory they were in the mid 60C range on a 23C ambient day. Even though the outside of the tyre has near zero wear the temps were only slightly cooler on the outside (by a 5-8C from memory).
What is a good friction circle app to use?

2. There is plenty of bump/suspension travel and I am not anywhere near hitting the bumpstops.
By rebound I assume you mean droop? I never measured it however from visually seeing it, there must be about 10cm all round.

3. I haven't measured bumpsteer but everything is original equipment so I do not expect a huge amount. The car is about 1.5" lower than stock

4. Spring rates are 9kg all round. The front is Macpherson strut so the motion ratio is nearly 1:1, rear are multi link and I am unsure of the motion rate but obviously the 9kg spring is "less" at the wheel

5. Why would no wear suggest on the outside suggest no camber wear? Isn't the issue here that the tyre is not rolling enough on the ground hence not contacting the outside edge?
Either way though, this is a Macpherson front so there is little camber gain. The strut to LCA angle is less that 90 degrees so it certainly is not gaining positive camber, but should gain a slight amount of negative camber.


Toe settings are 1.2mm total toe out front and 2.3mm total toe out rear.

I know the AR1s aren't the best, but surely they must still generate decent enough grip such that they aren't the problem here?
When I say my car understeers, I don't mean it's at the limit, it understeers very very easily.

Another thing to note (not sure if this means anything or not) but even though there is little grip in the dry, when it rained on the track it gripped reasonably well (considering it was wet on semi slicks).
So, relatively speaking the wet grip is impressive but the dry grip is really poor.

[Sirois]

I have been thinking about biting the bullet and buying some A050s.

But I don't use the car for competition, just fun, so it seems like the AR1s should have plenty of grip for fun only.


Josh at MCA did recommend better tyres on the basis that at least that will be one variable that we can take out of the equation for the poor handling.

[Magpie]

1. I don't have a friction circle. I did measure my front tyre temps once and from memory they were in the mid 60C range on a 23C ambient day. Even though the outside of the tyre has near zero wear the temps were only slightly cooler on the outside (by a 5-8C from memory).

You really need to know this information as it will help with alignment settings as well as tyre pressures! An observation would suggest that the tyres were not up to temperature however no data makes it difficult, plus how quickly were they taken after the cool down lap? I have correlated my temps in the pits with the tyre temp sensors that are logged.

What is a good friction circle app to use?

To draw a G Plot (friction circle) you need an app that saves g forces. The friction circle is a very handy tool to see the limits of cornering/braking plus shows how much of the available grip you are using. There is a term called 'filling the circle', personally my target is to achieve at least 1.2g from when I brake to when I exit.

2. There is plenty of bump/suspension travel and I am not anywhere near hitting the bumpstops.
By rebound I assume you mean droop? I never measured it however from visually seeing it, there must be about 10cm all round.

I'll quote from a very knowledgeable person (you have spoken to his son) "there is no point having a conversation on suspension if you do not know how much bump/rebound travel you have with the car at normal ride height". As an example you have 10cm of travel, at normal ride height this is 6cm bump and 4cm rebound (droop). You have a 4cm bumpstop, therefore at normal ride height the bump stop will engage after 2cm of bump. Therefore you only have to transfer 180kg of weight to that wheel before the bumpstops engage. I would guess under braking you are transfering more than 180kg of weight...

3. I haven't measured bumpsteer but everything is original equipment so I do not expect a huge amount. The car is about 1.5" lower than stock

Again, advice given to me would be do not assume measure it yourself.

4. Spring rates are 9kg all round. The front is Macpherson strut so the motion ratio is nearly 1:1, rear are multi link and I am unsure of the motion rate but obviously the 9kg spring is "less" at the wheel

I'm no FWD expert but maybe stiffer in the rear or less spring in the front.

5. Why would no wear suggest on the outside suggest no camber wear? Isn't the issue here that the tyre is not rolling enough on the ground hence not contacting the outside edge?
Either way though, this is a Macpherson front so there is little camber gain. The strut to LCA angle is less that 90 degrees so it certainly is not gaining positive camber, but should gain a slight amount of negative camber.

Maybe I should have said that the no outside wear is that the car is not being worked hard enough in corners to make use of the current camber. It is not about the tyre 'rolling' (sidewall deflection) to make use of the camber it is about the suspension geometry and/or driving style.

Toe settings are 1.2mm total toe out front and 2.3mm total toe out rear.

I would have zero toe in the rear, maybe even increase front as it is the dríven end. Caster is FWD's best friend. That being said more rear negative camber to get the car 'loose' as well as a wider front tyre.

Rob Nguyen - It's not rocket science here... it's just due to weight distribution... fwd generally speaking is 65-70% front heavy. So you just wasting money and weight carrying a large wheel and tyre at the rear.
Stick a potentiometer on the rear suspension.. there next to zero activity. Cat would survived a few laps in your rear suspension no problem

I know the AR1s aren't the best, but surely they must still generate decent enough grip such that they aren't the problem here?
When I say my car understeers, I don't mean it's at the limit, it understeers very very easily.
Another thing to note (not sure if this means anything or not) but even though there is little grip in the dry, when it rained on the track it gripped reasonably well (considering it was wet on semi slicks).
So, relatively speaking the wet grip is impressive but the dry grip is really poor.

Based on this comment that you found you had more grip in the wet than the dry I would say driver error/style. Buying A050's will not fix driving style or setup issues, yes you maybe faster but the issues will still be there.
Having just used AR-1's in the wet I found they had MASSIVELY LESS grip than in the dry and I could very easily break traction (i do not have much HP). However a change in driving style, that is being more gentle on the application of brakes/throttle/steering I was able to do some reasonable lap times in the wet. Learning to drive in the wet is a skill that needs to be experienced, hence when it rains I like to go out

I also do not agree with "I know the AR1s aren't the best" as it would appear that you are attributing the blame to the tyres but have no evidence apart from lap times and perceived ' poor handling'. Most of us have been in this same situation, I am no exception, my build thread (and this forum) is littered with my mistakes of where I would lay blame on something but in reality I was wrong.

As I mention I am no FWD expert, nor a RWD expert for that matter. However your final comment about wet/dry conditions, at least in my limited knowledge/experience suggests driver issues. Toss the keys to an experienced driver and get their feedback as well as look at the setup you have and get a KNOWN/MEASURED baseline to work from. Using an experienced driver in your car removes the variable "YOU" from the equation however if money no object by A050's and let us know how it goes.

Another point to ponder... I tossed the keys to my car to a person I trust just after I got out of it. Despite the number of laps I have done in it over the years in 4 laps Trent was under my PB for the day! By the way Trent's only complaint was that he found the pedals difficult to heel/toe with! This is not the first time I have done this, on 05/08/12 at Morgan Park Chris O'Shannessy (SDT instructor) managed a 1:20.12 on 27/07/13 whereas myself a 1:22.66 on Layout E. Again on 24/10/15 Chris again was tossed the keys and asked to so me what the car could do, he managed 1:18.99 again on Layout E. On 21/03/16 I managed 1:18.22 and gone faster than the baseline set by Chris. 09/07/16 down to 1:15.04, 22/07/17 down to 1:12.90. My current PB is 1:12.459 for layout E.

Using other people to give an opinion can not be underestimated!

https://www.facebook.com/mx5na6/videos/1131488433682431/

[RS2000]

Why not, as an easy test mod, disconnect the front arb & see what happens.
Everything I've read about reducing understeer says soften front/stiffen rear.

[Sirois]

You really need to know this information as it will help with alignment settings as well as tyre pressures! An observation would suggest that the tyres were not up to temperature however no data makes it difficult, plus how quickly were they taken after the cool down lap? I have correlated my temps in the pits with the tyre temp sensors that are logged.
- I have recently bought myself a tyre temp gun so I can start logging accurate data in regards to this.
The first time I measured them it was within 1min of coming off of the track.

I'll quote from a very knowledgeable person (you have spoken to his son) "there is no point having a conversation on suspension if you do not know how much bump/rebound travel you have with the car at normal ride height". As an example you have 10cm of travel, at normal ride height this is 6cm bump and 4cm rebound (droop). You have a 4cm bumpstop, therefore at normal ride height the bump stop will engage after 2cm of bump. Therefore you only have to transfer 180kg of weight to that wheel before the bumpstops engage. I would guess under braking you are transfering more than 180kg of weight...
- I will measure bump travel and droop travel on the car.
Though I have never measured these, when I adjusted the suspension I was careful to ensure that travel was not hindered (i.e., I could see plenty of the damper rod that allowed for travel before the bumpstop).
With droop I am unsure how to measure it. Should I measure the total suspension droop, or just the suspension droop until the spring becomes loose?

I'm no FWD expert but maybe stiffer in the rear or less spring in the front.
- The rear has a whiteline swaybar and dampers set to full stiffness. Also the rear spring rate is by ratio stiffer than the front.
Through corners (at the very least during trail braking) the inside wheel lifts off the ground.
I know the fundamental principle is to stiffen the rear/soften the front to remove understeer but when I stiffen the front shocks I gain grip at the front.
And according to this:
https://speed.academy/how-to-fix-unders ... up-tuning/
There is an area where the front is stiffened to reduce understeer

I would have zero toe in the rear, maybe even increase front as it is the dríven end. Caster is FWD's best friend. That being said more rear negative camber to get the car 'loose' as well as a wider front tyre.
- I did run 0 toe in the rear before but found toe out works better and is recommended for FWD cars.
As far as tyre is concerned, as mentioned I may go 225/45/15 front and 195/50/15 rear. Or A050 215/50/15 front and 195/55/15 rear.


Based on this comment that you found you had more grip in the wet than the dry I would say driver error/style. Buying A050's will not fix driving style or setup issues, yes you maybe faster but the issues will still be there.
Having just used AR-1's in the wet I found they had MASSIVELY LESS grip than in the dry and I could very easily break traction (i do not have much HP). However a change in driving style, that is being more gentle on the application of brakes/throttle/steering I was able to do some reasonable lap times in the wet. Learning to drive in the wet is a skill that needs to be experienced, hence when it rains I like to go out

- Sorry, I meant I do have less grip in the wet, but not as much less as I’d expect.
To rephrase that I’d say that I was impressed with wet weather grip given they are semis but was really underwhelmed with their dry weather grip.
I certainly am not the best driver by far, and yes driving style may mitigate some of the understeer but 100% the handling of the car is not right.

I also do not agree with "I know the AR1s aren't the best" as it would appear that you are attributing the blame to the tyres but have no evidence apart from lap times and perceived ' poor handling'. Most of us have been in this same situation, I am no exception, my build thread (and this forum) is littered with my mistakes of where I would lay blame on something but in reality I was wrong.


- I meant, I know there are better tyres than the AR1s however I do not believe the AR1s are bad enough to cause this understeer issue. They should be good enough for a decent amount of grip.
To put things into perspective, my mom’s Mazda 3 hatchback on some all season tyres has an abundance more grip that my track car on semis and coilovers.
So I don’t believe this is a tyre issue.
I agree that yes maybe the A050s will mask the problem but the problem is still there.


I don’t know any professional drivers… I am pretty new to this. If I do have the opportunity I will ask someone though.

So what should be my next steps?
I will measure bump/droop travel. How much droop should I have?
Lower the front roll center and raise the rear slightly
Try a larger range of tyre pressures and start measuring tyre temps
Disconnect the front ARB to see the handling difference

Should I go 225/45/15 AR1s on the front? They are 225mm section width compared to 214mm section width of the 205s.
The 215/50/15 A050s are 229mm section width

[Sirois]

Also Nitto NT01 225/45/15 are on special currently for $221 each.

Is that a decent price, and a decent tyre to consider?

[Magpie]

So what should be my next steps?

1. Get a note book.
2. Set a baseline and note this down
3. Make single changes and evaluate
4. Rinse and repeat

Mind you this advice assumes that you can be consistent to remove the driver variable from the equation. The worst thing that can happen is that the driver has a good day, you have made changes and attribute the improvement to the changes and not the driver having a good day (regression to the mean).

[Sirois]

Thanks Magpie,

I am not timing my laps currently so really aiming for a more neutral handling car.

I try to limit adjustments but I only get out to the track maybe 6 times a year so do hope to try a couple of changes especially ones I cannot make at the track.

What is your take on understeer reducing with stiffening the front dampers?

[Magpie]

What is your take on understeer reducing with stiffening the front dampers?

With respect to a FWD car?

Dampers respond to shaft velocities, hence the suggestion to make sure the dampers are operating as designed. Personally the adjustment of dampers are for fine tuning and done when the rest of the setup is close to what you want. I make adjustment to the dampers based on track conditions and change spring rates if have done major changes (aero) or trying a different setup.

Experiment and try different things it is the only way to feel what 'bad' is really like.