M400 on the track... understeer to be precise!
Discussion
Yesterday I got to do my first track session with the M400 since Rockingham. It was one of those airfield days and the weather couldn't have been better... if a little hot!
Please understand (the likes of Mr Cundy) that I'm no racing driver and am learning as I go. The problem that kept cropping up was understeer which I was led to believe was a rare thing in any Noble. After some hints from the pros I kept a bit of brake on after turning into the corners and that helped keep the weight on the front.
Part way through the afternoon a very experienced Formula Ford champ (Ed Moore) came to a disused part of the airfield with me for a bit of instruction on how to get the back out and keep it under control. To his amazement, despite some determined efforts, all he got was understeer!?! He put this down to 2 things; the surface (an old runway) and the car being setup for 'safe road driving'. In fairness, we moved to a slightly different surface and he managed to get the back to let go but not without some heavy right foot. Needless to say, as soon as I tried it I spun... not once, but twice!
My question to you all is; do I have an exceptional car here or are they all like this? Ed did comment that the handling was fantastic and, when pushed, it was understeer that caused and problems and not oversteer as expected.
Second observation; after my 3rd session I opened the rear clam to check the engine and found a small amount of oil dripping from under the throttle assembly. In a moment of panic I called the factory and they assured me that this is normal after a hard session on the track and it was coming from the 'breather'. Has anyone else found this?
Thirdly; the only car to pass me during the day was a Caterham on slicks driven by a bloke who does an average of 2 track days a week during the summer... not all that surprising then :) I did have one slightly worrying moment though. On the main straight I noticed a TVR (Cerbera or Tuscan... not sure) pulling away from me under max acceleration!?! It may be that this was a 'special' but I really didn't expect to see that. Excuse the dumb question, but what's the best way of clarifying the power I'm getting out of my car? Is it onto a rolling road or is there some simpler way or finding out with some sort of ECU download?
Apologies for the long mail... you can tell it's a bank holiday ;)
Cheers,
Dom.
Please understand (the likes of Mr Cundy) that I'm no racing driver and am learning as I go. The problem that kept cropping up was understeer which I was led to believe was a rare thing in any Noble. After some hints from the pros I kept a bit of brake on after turning into the corners and that helped keep the weight on the front.
Part way through the afternoon a very experienced Formula Ford champ (Ed Moore) came to a disused part of the airfield with me for a bit of instruction on how to get the back out and keep it under control. To his amazement, despite some determined efforts, all he got was understeer!?! He put this down to 2 things; the surface (an old runway) and the car being setup for 'safe road driving'. In fairness, we moved to a slightly different surface and he managed to get the back to let go but not without some heavy right foot. Needless to say, as soon as I tried it I spun... not once, but twice!
My question to you all is; do I have an exceptional car here or are they all like this? Ed did comment that the handling was fantastic and, when pushed, it was understeer that caused and problems and not oversteer as expected.
Second observation; after my 3rd session I opened the rear clam to check the engine and found a small amount of oil dripping from under the throttle assembly. In a moment of panic I called the factory and they assured me that this is normal after a hard session on the track and it was coming from the 'breather'. Has anyone else found this?
Thirdly; the only car to pass me during the day was a Caterham on slicks driven by a bloke who does an average of 2 track days a week during the summer... not all that surprising then :) I did have one slightly worrying moment though. On the main straight I noticed a TVR (Cerbera or Tuscan... not sure) pulling away from me under max acceleration!?! It may be that this was a 'special' but I really didn't expect to see that. Excuse the dumb question, but what's the best way of clarifying the power I'm getting out of my car? Is it onto a rolling road or is there some simpler way or finding out with some sort of ECU download?
Apologies for the long mail... you can tell it's a bank holiday ;)
Cheers,
Dom.
The first thing I would check if you have not already done so is wheel alignment. This must be done on a 4-wheel aligment machine and the toe settings front and rear are very important to establishing the proper steering characteristics of the car. In addition, I found on my car that some of the camber settings as delivered were not correct (out of spec and not uniform side to side). Since camber is not adjustable directly, changing it requires some custom modifications which I am currently undertaking.
The next thing to check is tire pressure. Simple understeer can often be easily cured by increasing the front tire pressure and, if necessary, decreasing the rear pressure. Each pressure change should probably be limited to 2 psi until you get a feel for how it is affecting tire grip. It is also usually a good idea not to change tire pressure until the tire is at temperature equilibrium (that is, the tire should be "cold" ).
>> Edited by JLSELAN on Saturday 28th May 23:47
The next thing to check is tire pressure. Simple understeer can often be easily cured by increasing the front tire pressure and, if necessary, decreasing the rear pressure. Each pressure change should probably be limited to 2 psi until you get a feel for how it is affecting tire grip. It is also usually a good idea not to change tire pressure until the tire is at temperature equilibrium (that is, the tire should be "cold" ).
>> Edited by JLSELAN on Saturday 28th May 23:47
Dom,
You will be able to promote understeer on tighter bends, but the trick is not to allow it to happen in the first place. A slight pre-turn lift off the throttle, or a little less entry speed will do the trick (remember my original demonstrations on a similar type of track before you bought the car?).
Unfortunately, after the car's done a few laps with the front end pushing wide, the outer-shoulder of the tyre will overheat and it will need nothing short of a boot-full of throttle to change the car's atitude.
I doubt if there's anything wrong with the suspension geometry, although it may be worth checking that the tyre pressures read 20(f), 30(r) when cold.
The 3R will understeer less when provoked, mainly because it does without a roll, or sway, bar at the front. The M400 has a rollbar as standard and is stiffer and more stable on turn-in - especially on faster bends. For example, trail braking (as you learnt) is possible in an M400, a technique that's not safely available to drivers of most mid-engined cars.
If you want a chat, feel free to give me a call at the factory on Tuesday.
Simon
Simon Hucknall
Press Officer
Noble Automotive Ltd.
You will be able to promote understeer on tighter bends, but the trick is not to allow it to happen in the first place. A slight pre-turn lift off the throttle, or a little less entry speed will do the trick (remember my original demonstrations on a similar type of track before you bought the car?).
Unfortunately, after the car's done a few laps with the front end pushing wide, the outer-shoulder of the tyre will overheat and it will need nothing short of a boot-full of throttle to change the car's atitude.
I doubt if there's anything wrong with the suspension geometry, although it may be worth checking that the tyre pressures read 20(f), 30(r) when cold.
The 3R will understeer less when provoked, mainly because it does without a roll, or sway, bar at the front. The M400 has a rollbar as standard and is stiffer and more stable on turn-in - especially on faster bends. For example, trail braking (as you learnt) is possible in an M400, a technique that's not safely available to drivers of most mid-engined cars.
If you want a chat, feel free to give me a call at the factory on Tuesday.
Simon
Simon Hucknall
Press Officer
Noble Automotive Ltd.
A track day regular once told me that the best time to check tyre pressures is after a few laps when they are warm. The reason is that the outer tyres (eg the left side on a clockwise circuit) will be under a higher load on average, and will therefore be hotter and have a higher pressure.
If you equalise the pressures after you've done a few laps, you can make sure that, for that circuit, you'll have equal pressure left and right an have a better balance.
Of course when you're as poor as I am on the track it makes no odds
If you equalise the pressures after you've done a few laps, you can make sure that, for that circuit, you'll have equal pressure left and right an have a better balance.
Of course when you're as poor as I am on the track it makes no odds
ThatPhilBrettGuy said:
JLSELAN said:
The next thing to check is tire pressure. Simple understeer can often be easily cured by increasing the front tire pressure and, if necessary, decreasing the rear pressure.
Other way round surely?
Tire pressure and tire slip angle are closely related, and the slip angle dictates the maximum lateral force a tire can sustain before slippage. For pressures below about 40 psi in modern road tires, increasing pressure will increase slip angle and therefore improve lateral grip. Other factors complicate the equation immensley like acutal rubber characteristics, internal tire construction details, contact patch size, road roughness and temperature, etc., but, in general, increasing pressure will increase tire grip, reducing understeer/oversteer depending on what the driver desires. A very good book covering these subjects is Paul Haney's "The Racing and High Performance Tire". You can also do the following "thought experiment" to visualize this relationship: reduce your front tire pressure to 5 psi and try to negotiate a corner at 50 MPH (remember, this is a thought experiment :-)). You can certainly imagine that the front of the car will go straight on (severe understeer) because the tires do not have enough air pressure to support an adequate slip angle and therefore they cannot generate the lateral forces required to steer the car along the desired path.
>> Edited by JLSELAN on Sunday 29th May 19:08
>> Edited by JLSELAN on Sunday 29th May 19:53
Not sure I agree with that in this instance. Phil is correct I believe. The M400 runs corsas which have very stiff sidewalls so the air pressure is not needed to hold the tyre up, a higher pressure in this instance will lead to a smaller contact patch as poressure = force over area. If you leave the front tyres alone and increase rear tyre pressures to 40psi the rear will become more mobile, not less. The softer end (combo of spring, damper and tyre) will always have more grip as a rule of thumb. F1 cars run at well under 20psi.
domcross said:
Second observation; after my 3rd session I opened the rear clam to check the engine and found a small amount of oil dripping from under the throttle assembly. In a moment of panic I called the factory and they assured me that this is normal after a hard session on the track and it was coming from the 'breather'. Has anyone else found this?
Dom, I get this and so do a few others that I've spoken to but don't know of any problems with it. I guess it shows you're driving it properly!
I've put a canister on mine so the oil has somewhere to go other than the crankcase. If you're at Bedford tomorrow I'll show you, failing that I'll post a few pictures. Anthony
Dom,
Keep to the factory recommended pressures and you will get the optimum handling/roadholding from the M400 on road and track.
Only last week I drove down to Goodwood, tracked the car all day, passed everything (Ferraris, Lambos etc)and posted a best of 1m 26sec. However, I didn't slide the car once (well, hardly...) and the tyres had negligible wear after 500 miles (350 road/150 track).
But when I demo the car at Bruntingthorpe, slides are the order of the day and the tyres' performance does deteriorate v.quickly.
It really does sound like a change of technique is called for, rather than alterations to the car's set-up.
By the way, chances are that the oil you've seen in the engine bay is from the power steering reservoir breather (tell tail sign is if it's down the offside of the engine). Check the level of this after a track day, but it shouldn't give cause for concern.
Simon Hucknall
Press Officer
Noble Automotive Ltd.
Keep to the factory recommended pressures and you will get the optimum handling/roadholding from the M400 on road and track.
Only last week I drove down to Goodwood, tracked the car all day, passed everything (Ferraris, Lambos etc)and posted a best of 1m 26sec. However, I didn't slide the car once (well, hardly...) and the tyres had negligible wear after 500 miles (350 road/150 track).
But when I demo the car at Bruntingthorpe, slides are the order of the day and the tyres' performance does deteriorate v.quickly.
It really does sound like a change of technique is called for, rather than alterations to the car's set-up.
By the way, chances are that the oil you've seen in the engine bay is from the power steering reservoir breather (tell tail sign is if it's down the offside of the engine). Check the level of this after a track day, but it shouldn't give cause for concern.
Simon Hucknall
Press Officer
Noble Automotive Ltd.
micknall said:
Dom,
Keep to the factory recommended pressures and you will get the optimum handling/roadholding from the M400 on road and track.
Simon - The owners manual says 18 front, 27 rear.
You say 20 front and 30 rear earlier in the thread.
Which is correct?
micknall said:
By the way, chances are that the oil you've seen in the engine bay is from the power steering reservoir breather (tell tail sign is if it's down the offside of the engine). Check the level of this after a track day, but it shouldn't give cause for concern.
Dom, as Simon says the power steering reservoir will leak out through the breather during heavy cornering on a track. Like other owners I prevent this by filling the breather hole with a silver paper bung and strapping it in place with insulating tape before track events. The fluid normally splashes out over the inside of the clam and is easy to spot when you realise how it can happen.
--
Richard
And the contestants are... Dom, the oil under the throttle body is not from the power steering reservoir it's caused because the breathers from the engine are vented back into the air intake of one of the turbo's, this is to comply for emissions etc.
When the car's are driven hard on track the crankcase pressure rises and the oil etc being vented by the breathers doesn't drain to the sump instead it finds it's way into the intake through the turbo, intercooler and collects in the throttle body and for some reason all over the gearbox !, i've even had it come out of the air filter and run onto the hot exhaust on a very tight twisty track, not very clever !!!. The other side effect is really bad smoking on starting the engine after a hard track session until the oil is burnt off in the engine.
A race car has it's breather going into a catch tank , l have modified mine by removing the vent pipe from intake system which comes from the top of the oil swirl/seperator pot and connecting to a 1 litre catch tank, then blanking off the connection to the intake tee. The only side effect is having to empty the tank sometimes, l usually drain it after a track day, about a cup full of brown oil and water crap ( can't be good going back into the engine) but so far never require's draining with road use.
The other side effect of oil in the inlet system is oil reduces the octane level of the fuel, so l assume in theory ultimate power !
Kevin
>> Edited by kj-r on Monday 30th May 20:37
When the car's are driven hard on track the crankcase pressure rises and the oil etc being vented by the breathers doesn't drain to the sump instead it finds it's way into the intake through the turbo, intercooler and collects in the throttle body and for some reason all over the gearbox !, i've even had it come out of the air filter and run onto the hot exhaust on a very tight twisty track, not very clever !!!. The other side effect is really bad smoking on starting the engine after a hard track session until the oil is burnt off in the engine.
A race car has it's breather going into a catch tank , l have modified mine by removing the vent pipe from intake system which comes from the top of the oil swirl/seperator pot and connecting to a 1 litre catch tank, then blanking off the connection to the intake tee. The only side effect is having to empty the tank sometimes, l usually drain it after a track day, about a cup full of brown oil and water crap ( can't be good going back into the engine) but so far never require's draining with road use.
The other side effect of oil in the inlet system is oil reduces the octane level of the fuel, so l assume in theory ultimate power !
Kevin
>> Edited by kj-r on Monday 30th May 20:37
m12_nathan said:
Not sure I agree with that in this instance. Phil is correct I believe. The M400 runs corsas which have very stiff sidewalls so the air pressure is not needed to hold the tyre up, a higher pressure in this instance will lead to a smaller contact patch as poressure = force over area. If you leave the front tyres alone and increase rear tyre pressures to 40psi the rear will become more mobile, not less. The softer end (combo of spring, damper and tyre) will always have more grip as a rule of thumb. F1 cars run at well under 20psi.
I suggest that before you make the mistake of comparing F1 race tires/chassis set-up with the Noble street tires/chasis set-up (and make a tire pressure adjustment that could potentially endanger you and your car on the track) that you use a constant radius (200 to 300 foot diameter) skid pad to experience how changing tire pressure actually affects dynamic handling characteristics. You should have your answers after about 3 pressure changes and 30 minutes of driving.
I have done exactly that excercise when I set up my Nitron dampers with the help from Andrew Walsh. The contact patch is reduced with a higher pressure as pressure = force over area, that is very basic physics, if you disagree with that formula then I'd be interested to see your reasoning. On my BMW I start at 24PSI cold which equates to 32PSI after a few laps, and more and grip falls and the tyres get knackered.
Why are tyre pressures on an F1 car, or caterham, or saloon car not comparable with a Noble? There is nothing unique about how tyre pressures work on a Noble and I'd suggest that the factory guys have got it about spot on. All I was going is agreeing with Phil.
Forgetting tyre pressures for a minute - if your car is understeering you can soften the front end, either the damping, the spring rate or the antiroll bar to improve grip, do you disagree with this statement?
Dom, go and see Andy Walsh, best modification you can ever make!
Why are tyre pressures on an F1 car, or caterham, or saloon car not comparable with a Noble? There is nothing unique about how tyre pressures work on a Noble and I'd suggest that the factory guys have got it about spot on. All I was going is agreeing with Phil.
Forgetting tyre pressures for a minute - if your car is understeering you can soften the front end, either the damping, the spring rate or the antiroll bar to improve grip, do you disagree with this statement?
Dom, go and see Andy Walsh, best modification you can ever make!
m12_nathan said:
I have done exactly that excercise when I set up my Nitron dampers with the help from Andrew Walsh. The contact patch is reduced with a higher pressure as pressure = force over area, that is very basic physics, if you disagree with that formula then I'd be interested to see your reasoning. On my BMW I start at 24PSI cold which equates to 32PSI after a few laps, and more and grip falls and the tyres get knackered.
Why are tyre pressures on an F1 car, or caterham, or saloon car not comparable with a Noble? There is nothing unique about how tyre pressures work on a Noble and I'd suggest that the factory guys have got it about spot on. All I was going is agreeing with Phil.
Forgetting tyre pressures for a minute - if your car is understeering you can soften the front end, either the damping, the spring rate or the antiroll bar to improve grip, do you disagree with this statement?
Of course, your basic formula is correct physics, BUT it only strictly applies to a tire that is not moving and is therefore not generating lateral forces. That is, the formula applies only to simple elastic deformable bodies at rest. A tire on the road is neither. In fact the eleastic, hyperelastic and viscoelstic deformations a tire undergoes while cornering are enormous--just check out the close-in, slow motion coverage of F1 cars bouncing off the curbs at Monza to see how much deformation can be tolerated in that application. In addition, the size of the contact patch is only one of dozens of tire parameters contributing to ultimate tire grip, and slip angle is far more important until the tire actually slides relative to the road.
As for the BMW experience, typical tire pressure increasses on the track should be less than 4 psi. An 8 psi build up is excessive, which clearly implies that your starting pressures is too low. A low pressure will force the tire carcass to "work" too hard (too much deformation and flex) and the tire will be torn up in the process, as noted. Start at 28 to 30 psi and you will see a marked improvement in both handling and tire durability.
As for F1 tire technology, it is a closely guarded secret, of course, but you can be sure that internal construction details and rubber compounds are totally different from anything you can buy for a street or race tire. Add ground effects, low static weight and virtually unlimited suspension adjustability and you are in a completely different relm of vehicle dynamics compared to a road car. (I did note with interest, however, that Simon's tire pressure recommendations are the same that I use, which is about 2 psi above the factory recommendations).
My point is you cannot forget tire pressure--besides driving technique, it is the only handling parameter that you can change at the track on a Noble, and if the changes are not made correctly the consequences could be expensive. Ideally, yes, you want to reduce the stiffness of a front sway bar to reduce understeer, but if you cannot do that on the spot, the next best thing is to increase front tire pressure to increase the tire slip angle and consequently increase the ability of the tire to generate lateral forces before slippage.
But by increasing the front tyre pressure you are not only reducing the contact patch but also effectively incresing the front spring rate (tyre wall is considered part of the suspension), both of which will increase understeer.
Can you explain exactly what you mean by slip angle as I think we may be talking at cross purposes...
If you start Michelin Pilot Sport Cups at 28psi on an M3 CSL they'll soon get above 32psi and grip will reduce, you can ruin a new set of cups in 1 day by running them above 32psi.
Can you explain exactly what you mean by slip angle as I think we may be talking at cross purposes...
If you start Michelin Pilot Sport Cups at 28psi on an M3 CSL they'll soon get above 32psi and grip will reduce, you can ruin a new set of cups in 1 day by running them above 32psi.
m12_nathan said:
But by increasing the front tyre pressure you are not only reducing the contact patch but also effectively incresing the front spring rate (tyre wall is considered part of the suspension), both of which will increase understeer.
Can you explain exactly what you mean by slip angle as I think we may be talking at cross purposes...
If you start Michelin Pilot Sport Cups at 28psi on an M3 CSL they'll soon get above 32psi and grip will reduce, you can ruin a new set of cups in 1 day by running them above 32psi.
Car set-up is always a compromise--even in the F1 world--and generally the slight increase in front roll stifness resulting from a 2-4 psi increas in tire pressure will be more than offset by the improved tire perfomance.
Slip angle is a simple concept--when a tire is negotiating a corner, it is the angle formed by the difference between the direction the car is heading and the direction the tire is actually rolling. It is a measure of the tire deformation, produced by both the contact patch "squirm" and the sidewall flex. When rolling straight ahead, the slip angle is zero, but when you turn the wheel each tire on the car develops a slip angle instantaneously (since the car has finite dimensions, each tire follows a different path and the slip angles that develop are also different side-to-side or front-to-back). A tire cannot generate the lateral force needed to turn the car unless a non-zero slip angle develops (try negotiating a turn in a wagon rolling on 4 solid disks), and lateral force will increase as the slip angle increases and the tire deforms more as it "trys" to follow the path set by the driver. Maximum slip angles are very dependent on tire construction details, but peak angles between 5 and 10 degrees are not uncommon for road tires. Obviously, a tire with a stiff sidwall can only develop a relatively small maximum slip angle and will be viewed as relatively "unforgiving" compared to a tire with a more flexible sidewall even though the stiffer tire may generate higher lateral forces. After the peak slip angle is reached, the tire breaks away (loses adheasion) and the lateral force no longer increases. It is important to always remember that when a tire is operating below its maximum slip angle there is no relative motion between the tire and the road. As a result, the contact patch is always instantaneously at rest and the tire is essentially sticking to the road. That is the reason the actual size of the contact patch is relatively unimportant (to first order, friction force is independent of contact area) until the tire starts to slide.
On the subject of Michelins, unless these are R-rated or track only tires, I would be flabergasted if a factory represnetative (not a salesmen) would state without reservation that the tires will suffer excessive wear at pressures above 32 psi.
>> Edited by JLSELAN on Tuesday 31st May 03:11
>> Edited by JLSELAN on Tuesday 31st May 03:12
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