Handling question after switching to ZZS tyres

[rgrigsby]

I've recently switched to ZZS tyres having run CR500's and Kumho V70's for years. Northampton Motorsports set the car up a few weeks back and I've just completed my first track day at Donington on Monday.

Whilst the track day was a lot of fun, the handling of the car wasn't great. Throughout the day the car suffered with mild under steer in the mid to high speed corners and huge under steer in the low speed hairpins.

I didn't have the tools to make any significant changes during the day so tried adjusting tyre pressures but I wasn't able to improve the situation.

Likely as a consequence of the under steer the front tyres seemed to over heat and grip levels fell of a cliff about 10-12 minutes into a session making things even worse.

It's a bit of an open ended question but any suggestions welcome, here is the data about the setup from Northampton Motorsports which all seems pretty sensible.

Corner weights

 

           Left       Right

Front   135       132.5

Rear   134.5     141

Front camber -2.3

Front Toe -0.06

I've measured the rake and it's set at 15mm.

Tyre temps after the cool down lap were in the low 30c range.

Any thoughts?

[Simon.Rogers]

Rob.  Its all in your damper settings.

Call us some time!
 

[StevehS3]

#1 Those numbers look like ride height rather than weights. Do you have the weights as well? 

[rgrigsby]

#3 definitely corner weights, without the driver in though. Total car weight was 543KG with about 25l of fuel in.

[graearea]

what pressures were you running?

[aerobod - near CYYC]

Another possible issue is that the tyres are not getting hot enough if they are only just over 30C after the cooldown lap. The increased understeer after a while may be due to the rear tyres getting warm enough, but the fronts are still too cool (due to cooling air on the straights removing too much heat after braking and cornering). I find I normally need 50C in my AR-1 tyres after a cooldown lap to have had optimum grip during a session, not sure what the minimum advisable temp for ZZSs are for optimal grip, though.

[rgrigsby]

#5 tried a few different levels, 18psi hot to start with then up to 22psi hot later in the day. The higher pressures seemed to prolong the point at which the tyres overheated but didn't help with the understeer.

[aerobod - near CYYC]

I think with the higher pressure, it may have prolonged the time it took for the rears to get up to temp. To overheat the tyres you would need them up to 90C or so, I'm not sure what the exact spec is for the ZZSs is, but an R-Comp tyre like the ZZR will be in the optimum grip range for a temp range from 70 to 105C or so, so a high performance summer tyre like the ZZS is likely 50 to 90C or so, then knock off about 10 to 15C for the temp drop during the cooldown lap.

[Tom_Arundel]

LSD?

Anti-roll bars?

More toe out?

[rgrigsby]

Titan LSD, no front anti-roll bar (I'm running the Freestyle inboard suspension), rear anti-roll bar is fitted but is on the softest setting. Toe is pretty much parallel.

Talking to a very helpful person at Meteor it seems I'm not alone in suffering with under steer on the ZZS, I've got a few things they have suggested to try but will likely not be on track again until next year.

[BenF]

To give some impartial advice - it's NOTHING to do with damper settings!

James' observations sound right, with the tyre temps.  Only thing I'd say is that higher pressures usually help warm-up, because the energy is going into a smaller contact patch.  So usually warm-up is improved but then peak grip is lower once up to temp.  Normal practice with racing tyres was to put in an extra 0.5-0.8psi to see a noticeable difference in warm-up, but this was with tyres which were already in blankets at 80degC

Being a road tyre, I'd expect the ZZS to work well at a 50-60degC.  Racing tyres tend to work well at 80-100degC, but they are higher working range.  30degC at the end of the inlap does seem low.  Also depends exactly on how you're measuring it.

I'd consider trying a stiffer RARB setting.

Plus, is there much preload on the LSD?  On my R300K with CR500s and the wider rear tyres and LSD, it understeered loads in the low speed.  The main thing which helped was going to the 6" rear tyres, after which the balance was way better.

[Dave Hardcastle]

I run 15" ZZS on a R400D. Avon Motorsport recommend the following pressures;

13" & 15": 18-21psi check cold, for road

13": 22-27psi check hot, for track

15": 21-24 check hot, for track

[rgrigsby]

Thanks Dave, i have seen those numbers in a deck from Avon, after the track day :(. Lots of things to try out next time.

[Simon.Rogers]

Ben

I am sorry but I know Rob's dampers  - I have serviced them.  I could make the car go backwards into the corner or push straight on just by adjusting his 3 way Nitron's.

I would not need to change any other settings.  I would be happy to demonstrate if anyone ever felt the desire.  You just need to know what affects what.

Now I am not saying it is the damper settings and that it is not anything else. I know how Rob drives and I know he can drive well.  What I wanted was for Rob to let me know the numbers he is running and I can look at the damper plots to get a good ball park feeling if this is correct.

 

[BenF]

duplicate post

[BenF]

Simon, you might know Rob's dampers, but what are your qualifications regarding vehicle performance?  Happy to compare if you come clean about your engineering degree and job experience and I'll do the same.

I know that sounds a bit harsh, but in my time in motorsport I've come across so many salesmen pushing bogus cures for handling, it ceases to be a joke.  If you can genuinely justify why on earth dampers would have such an effect on handling, please explain - and I'd be happy to give my side of the story (which is based on being a customer of damper suppliers for over 2 decades - and also someone who had to technically evaluate the performance of dampers, from simulations and 7 poster tests, through to actually running them on racing cars)

[Wrightpayne]

Do you have a before and after geo settings of the work NMS undertook?

With different tyres and a suspension set up, potentially a lot has changed so may take some time isolating the cause.

[ScottR400D]

#16 Ben, you've reminded me of the old joke "2 weeks ago I couldn't spell 'engineer'. Now I are one!"

To be fair it's not hard to find Simon's track record (literally) with 7s and it seems clear he has a good idea of what makes them handle properly. 

[BenF]

Scott - I'd never heard that joke!  Actually on returning to the UK from Germany, it's been a bit disheartening to find that even some technicians are calling themselves engineers!

I agree that Simon has done some great stuff - e.g. the I.R.S conversion as discussed recently on here and in LF

However on this topic, the claim to use dampers to change car balance has been pretty comprehensively debunked for asphalt-based motorsport - with the assumption that baseline settings are in the ballpark.  You still hear this kind of stuff spoken about in more amateur motorsport (I even worked with an F2 engineer a couple of years ago who was claiming this) but it has no credibility any more.  In fact, in my years working away from top-line motorsport, I've heard all manners of claptrap spoken on this subject.

The danger with homeopathic remedies is that for 7s, even if they are just a placebo, but they can result in people parting with hard-earned cash for things which don't really work.  That's also the problem with using subjective feedback as proof - when told a change is going to improve things, people tend to concur.  It does not mean the change worked - that needs to be backed up by some kind of science.

Of course you can cure a handling balance by doing a disproportionately large change (going to an extremely high damping at the rear can be used to move the mechanical balance rearwards on corner entry, but this is only having an effect on the turn-in phase), but these solutions often have large side downsides and that's why they are not commonly used.

[Simon.Rogers]

I have never claimed to have a Motorsport Degree.

What we do have is significant experience driving cars and motorcycles along with analysis of any adjustments and changes to springs and dampers using a dyno across a wide range of vehicles with multiple national championships including BTCC level.

I don't wish to get into some sort of argument over who is more qualified.  All I wish to do is help Rob out. 
 

Rob. You know where I am. You can call anytime.

[KnifeySpoony]

TBH I don't think we have enough info to really diagnose the problem. Is the understeer during corner entry, at steady state, or on exit? Damping can make a difference on transitions for sure (ie more of a factor on entry/exit), but certainly the relative roll stiffness front to rear will be the primary determinant of handling balance. Hence I would look at spring rates and ARB. And also agree about tire temps - if you're not even getting heat in the tire than all bets are off regarding suspension.