understeer

[710]

I PMed Kevin, Darren and Steve about the understeer on my car. I received some very good suggestions from all three. The thread became longer than I though, so it was suggested I post the info so others could see the (exellent, like usual...) feedback.

So the following is my initial email to them, if they want, can they please copy and paste their replies? I have not posted their replies for confidence reasons...

Hello Darren, Kevin, TrackDemon,

Another long winded email from me…

First, Darren, thanks for the info about the brake lights, last year I think. Sorry I didn't acknowledge your email, I’ve been snowed under with work and I barely know what day it is just lately. I really would like to get a third brake light eventually. Thanks for the suggestions.

I have question for you about NSX understeer:
I did a search for “under steer” and understeer and came upon the this thread
http://www.nsxcb.co.uk/forum/viewtop...ighlight=steer
In the last post there, you said you can throttle steer. Can you do it at low speeds on a small road/roundabout, safely?

I have used my car everyday since I bought it in December, it is my daily driver. The Yokos on the rear went , I have replaced them with S03s. the Yokos on the front are still good, but maybe old since the car has spent it’s whole life in someone’s garage. Do old Yokos go off?

The car understeers too much for my liking (even when I had Yokos all round). For example, on a wet round-about it understeers disconcertingly. Here in Belgium the traffic is not too heavy and we can still drive very fast. I easily do 160kph (100mph) for 30 minutes each way to work. And part of the route has lots of roundabouts. It’s easy to drive very “sportily”, if you know what I mean, as police and cameras are practically non-existent (that’s why I live here, in the French part). Anyway, I have had the NSX over the limit (only in a safe place with plenty of run-off, though, not in the dry like http://nsxcb.co.uk/forum/files/nsx_sideways2.jpg but in the wet, the speed is lower…by the way, in that photo, I notice you are listing to the radio...bored, were you?) a lot. It’s the understeer that I need to change. I drive in rallies here in Belgium (Escort Mk2) and my other road car is a Cosworth Escort. So I, like all other guys, think I know how to drive a car… I mention all this, to give you an idea of my driving style (and also to brag, and to say how we don’t have any police or cameras here, hehe…). But it is the car, not me. It understeers too much.

I made a better rear antiroll bar for the Cossie (among many other things), to get less understeer, it worked, but putting a front LSD also helped, so that’s completely different than an NSX. Also I have rebuilt the Cossie extensively, but I don’t want to do that to my NSX. It’s almost good enough the way it is. If I can cure this understeer, it will be PERFECT. How can I do it without extensive work?

Of course, my Cossie and NSX are road cars so I don’t need a rally type oversteer on them, but I think the understeer on the NSX needs fixing a little. I understand the stock NSX LSD (currently with 35,000miles on mine) is not so tight, so that can’t be the main reason why it understeers.

Have you had experience with the “NSX” understeer? Do slightly wider front tyres help, or should I go straight to putting a stiffer rear antiroll bar on it? Can I move(modify) the current rear antiroll bar links to increase the rear stiffness or does it need more that that?

The funny thing is, the Ferrari 308 and the Lambo Uracco (the only other similar cars I’ve driven) also understeered like the NSX does. It can’t be a mid-engined thing, the polar moment is less so the front tyres should have an easy time turning the front. What is going on? It could be the LSD, but my NSX LSD is really “loose” compared to my other cars.

For the moment, I will leave the stock 1991 wheels on, but do you know if the wider fronts on later year NSXs where put there by Honda to counter some of this understeer? But the rears were also made wider.

Did the change to the rear toe setting (newer years) reduce the understeer (by reducing the rear grip, while saving on tyre wear…)? This reduced rear toe setting is interesting, though. Do any of you think that is effective for reducing understeer?

The car has not been crashed and an alignment check showed the car is perfectly aligned…stock for 1991.

Also, I have looked on nsxprime, but they talk about new antiroll bars reducing the body lean/roll, and the paint quality of the bars etc. Of course, but that’s not what I’m after.

Have you tried to reduce your understeer, if any? And what, for heavens sake, do you do on a wet circuit on a slow sharp corner? Throw it around? But on a circuit, you know what’s coming, so you can throw it a little. On a roundabout or public road, it may not be what you think it is…

One other point, I have not disconnected the ABS yet, and the stopping distance seems much longer than I would expect on a car like this. Is this due to high weight of the car, or is it just the ABS? Strange, I have heard the NSX has good ABS. Maybe with ABS disconnected, I wouldn’t be able to stop the car quicker, but I think I would. Maybe the high weight of the car is also to blame for the understeer. That spare wheel is like a bag of cement!
The car seems so absolutely competent, maybe I expect too much of it on a corner and under braking..

It’s a great car but it will take me another year to be confident enough to take it on the track. I have a lot of respect for you guys, taking it on the track.

Anyway, can you please give me your thoughts about this? Also please pass this mail on, if you know someone who might have had the same understeer problem.

Thanks
Peter

[ctrlaltdelboy]

Hi Peter

wow, thats quite a lengthy PM there!

I'll have to dig into my memory banks a little to answer your questions, as I've barely driven the NSX in the last year - it's been almost completely off the road for various bits of work, the most recent being the gearbox which came out in July and the new one is due to go in next week.

anyway, I've never suffered from understeer in the nsx, the opposite in fact - oversteer has been the beast that I have been fighting to control since I have owned it.

taking into account the mods that I did almost immediately upon purchasing the nsx - track strength sways, 225 front tyres, H&R sport lowering springs and bilstein shocks (and removal of spare) I'm not really in a position to compare. Although perhaps this in itself is in a way the answer - with the mods described I have never had understeer, so I guess they may in themselves be a cure to understeer?

when you look at the changes that each of these mods does to the handling of the car you can certainly see that they would each contribute in their own way to reducing/eliminating it.

I have enjoyed immensely playing with both low speed power induced oversteer as well as the more scary higher speed oversteer both power and inertia induced, and have built up quite a knack for it in the nsx, but more recently in my daily driver the S2000, however it sounds like your nsx may currently be some way from being setup in a similar way to both of mine.

not tremendously helpful I'm afraid but I hope this is of a little help to you nonetheless.

[710]

So this is my next email to them, in response to their suggestions. You will find their responses to my first post (I hope) in following posts. So it will not be in order...


Hi Kevin, Darren and Steve
Thanks for your ideas. You have given me some excellent feedback and a “feeling” of your situations. It’s given me a lot to think about.
Darren, “not tremendously helpful” you say. On the contrary, you were all very helpful. I appreciate it very much.

What all of you describe is different to what I have. For example, on one long 2nd gear, constant radius wide motorway entrance, I can slowly apply the power and as the speed increases, the understeer increases and I can easily plough the front off the road if I want (in the damp and wet, I won’t get the speed up that high yet, to do that in the dry). Slow smooth application of power during this just pushes (ploughs) the front further. While all this is happening, I can turn the steering wheel (exactly what you described, Steve) to the extreme and just drive around ploughing like crazy, and must reduce the gas to live.
If, while it’s ploughing, I sharply and suddenly let off the gas, the back end should come around and say hello, shouldn’t it? It does not.

In December we had snow in the Ardennes. I was there with the almost bald rear tyres (I was waiting for the S03s). I practised for about 3 hours, just going up and down a twisty but very wide safe road. The roads were slippery (wet with a little slush), and I could drift the car, with or without power. That’s gone now since I put the S03s on the back.

On the other hand, I am convinced the car is not bent, I know what that feels like (and I inspected the car thoroughly), so now I will check the tyre pressures (excellent suggestion, Steve, I had missed that…duh) and see what that does. I also ordered new S03s for the front, to match the back and loose those front Yokos. They are old, I believe, even though they feel OK when I stick my fingernail into the rubber and I measured the hardness with my tyre hardness gauge. I really don’t know about those front tyres. I’m baffled. So, like we do with a computer, I will change the tyres and see the difference between old and new.

Then I will stiffen, very slightly, the rear anti-roll bar by clamping a tube or other lump of metal on the arms (temporarily, of course). I considered disconnecting the front antiroll bar, but I don’t want the car leaning anymore anyway…

Darren, you say you are doing your gearbox, I have noticed the big gap between 1st and 2nd, are you putting in the Japanese gears? Or is it just a rebuild? I have decided to leave this wonderful car (except understeer) stock for a while. In the future I would like 17 fronts and 18 rears (not with 35 series or 40 series tyres, there are too many holes around here) and then I will do the diff to compensate for the increased wheel size, and the japanese gears while I’m at it…
So I would really like to see your gearbox in pieces, to learn a little. Is that possible?

Kevin, did they put harder springs on the rear of later year cars? That would give a little more oversteer, I think. Well, they have a full blown test bank to try these things…

Steve, you’re right about Spa. I can’t imagine coming down the hill in front of the pits, then into eau rouge, and then over that hill. My balls suddenly are not so big when I think of doing that. The speed! No way. A few years off yet, I think. You guys who do that, well, respect…

Thanks again
Peter

[ctrlaltdelboy]

Peter

first off, I reckon there is something seriously wrong with the setup of your car - it should not be handling the way you describe.

re my gearbox - JDM short gears plus OS Giken LSD 1.5 way plus OS giken 4.4 R&P

I'm at Nurburgring over Easter bank holiday weekend 25th to 28th March testing it out - feel free to come and meet me if you have time, you are welcome to check my car over and come for a passenger lap or two.

details on this organised trip are here
http://www.s2ki.com/forums/index.php?showtopic=250916

[710]

Yes Darren, I have checked, it's 2.5 hours drive for me, I will meet up with you for a day. Also, will you have dinner with some friends, rather, have you organised anything? I can stay the evening and drive back later.
Peter

[ctrlaltdelboy]

yes Peter, there's a Saturday night meal organised - just casual.
I suggest you register on that forum and add yourself to the attendees list - get Ben to reserve you a place for the meal

[trackdemon]

This was my reply....

Hi there Peter, glad your enjoying your NSX.

Phew! Thats a long post, don't know where to start so I'll just cover the points as I see them.

Firstly I'd say that the NSX is not really a power-oversteer type of machine "out of the box": as you say the diff is too loose (done specifically to make the car a bit more friendly on the road I suspect). It can be made to powerslide - especially in the wet - but it's certainly not something I'd recommend on the road, as you need a lot of room to gather the ensuing slide. On track, this is much easier to manage and as its not easy its a good challenge and satisfying to get right. My technique:

On a slow corner I brake until about 30% into the corner (using a late turn-in point) to help keep some weight over the front end and aid initial turn in. Once the nose has started to turn in an aggressive stab of throttle will normally start the rear of the car sliding, from then its just a case of balancing throttle output against opposite lock, although I don't tend to apply any more than a full turn of lock if possible as it becomes much more difficult to straighten up after that. Also, the steering doesn't really have a strong enough self-centreing action to help with winding off the opposite lock. It takes practice but its good fun! The key for me is to provoke the slide early using a stab of throttle, once the rear has started to slide it seems easier to balance than if your simply using excess throttle on exit.

On a faster corner (say 50mph / 3rd gear) I find you have to be fairly brutal with the car to get it to oversteer, basically requiring large throttle inputs to break traction. You can actually get some cool angles of drift doing this - the hard part is catching it when it comes back. Because my car has power steering this is even more difficult as once onto full lock the castor angles drop off and feedback decreases - really you have to predict it through the seat of your pants, probably easier with manual steering. Practice makes perfect, but definately one for the track!

I'm surprised you're finding a lot of understeer with your car. I've had the tracking "straightened" on my car a little to prolong tyre life, with little discernable effect on handling balance - which is superb in my opinion. I'm running Yoko's on the front, Michelin Pilot Sports on the rear and with this setup its just about ideal for the road - approaching the limit I encounter a little stabilizing understeer, which is well communicated and easily mitigated by adjusting the throttle, a really nice and useable setup that inspires confidence. Assuming you're NSX is standard and hasn't been messed about with I can only guess why its understeering - these cars don't normally understeer much at all.

Do you turn in on the brakes, or on a trailing throttle? This is my normal technique when road driving as it shifts some balance to the front and therefore aids turn in (as well as allowing me to decelerate more readily if necessary) - driving this way I have not encountered significant understeer at all.

The only time I've encountered heavy understeer has been on track when aggressively applying a lot of lock (in an attempt to unbalance the rear) - the quickly applied loading seems to break front traction and it doesn't come back until you get off the throttle. I normally turn in very progressively, in an attempt to "hook up" the fronts before getting onto the throttle and powering through - again this seems to work for me. If you're using both of these techniques already then it must be something on the car.

Check tyre pressures - the NSX is quite sensitive to pressures so it may be fun to adjust these until you find a balance you're happy with

My car is running the 2nd gen tyre sizes: 215/45/ZR16 f & 245/40/ZR17 r. These should be roughly equivalent to what you are running so I'd expect the balance to be broadly similar. Personally I wouldn't suggest changing tyre sizes.

So in summary no I haven't tried to reduce understeer on my car - in fact I've actually introduced a little more by running a "higher performance" tyre on the back. I simply don't see there being a problem, and with 60% weight over the back wheels I'd rather not be encountering oversteer on the public road anyway so thats a good balance.

This does make me think though: perhaps with you're racing experience of cars which are setup to oversteer you're perception of a car which understeers is somewhat different to mine? I regard my car as well balanced on the basis that it only oversteers when provoked or on the very edge of grip (a limit I only explore on a circuit), as such the only slide I tend to encounter on road is understeer. This is never of the "plough on" nature you describe and is easily quelled - for me being able to "lose" the understeer easily is the key to why I say the NSX doesn't understeer. Ultimately the only way to prove this would be for us to swap cars and draw our own conclusions - not really practical with you in Belgium!

The NSX brakes are not the best in the world by any means, but I rarely have an issue with the ABS - in fact the cut-in point is fairly well telegraphed and I can actually brake pretty much up to the point where ABS would cut in and stay there. As someone who considers himself to be fairly easy going on brakes be it on circuit or on road I'm probably not the best person to ask about this. I wouldn't personally disconnected the ABS, but again this is just because I haven't had an issue with it.

I do urge you to take your car on track sometime though - I'm constantly amazed and how fantastic (and fast) a "mere" 3.0V6 is round a circuit, humbling some much more dramatic machinery, certainly through the corners at least. Perhaps there are airfield type tracks where you can explore you're car safely (SPA may be a bit intimidating if its the first time you've taken it on track!)

Hope to catch you for an NSX meet in the future!

regards,
Steve

[Ciaran]

Hi Peter,

Unlike Darren and possibly Steve, I don't have any mods on my 95. Having run two track days last year and enjoying a few years in Formula Ford (many years ago, & a good deal lighter!!) I would have to agree that the NSX is not naturally an understeering car.

I played with toe in's last year to increase tyre life, but back on track (& only there) there was some understeer(i.e zero toe in/out - fronts). However before the next trackday, I got the toe in's set back to the original Honda settings, i.e. early 90's & pre court case, and the difference on track was quite noticable.

Also I would agree, that tyre pressure plays a big part, I would normally run about 35/36 psi in the rears for a track day, and probably leave the fronts at 32/33.

In theory this should give me even more understeer, which would be fine, as I like progressive u/steer, but not with this car.

I think a spin in another car is a vital first step.

Ciaran

[jaytip]

Hi Peter,
i noticed in an earlier post that you mentioned that in the future you wanted to fit 17/18 but did not want the 40/35 profile tyres? i think that with those size rims you would have to go with those size tyres to keep the TCS happy.
i could be wrong though :?:

[ctrlaltdelboy]

TCS?

whats that then? :lol:

useful gadget here