Quote from: JB21 on December  3, 2020, 17:50

Quote from: AdamR28 on December  3, 2020, 17:24That was standard with the orignal Munter yep, so hoping it will be the same again!

Apec pads and Falken ZE914 tyres. Only the best. Snigger.

Nah you'll be sound with them on such a light car. I've had the 914s on my Celica 190, and just fitted a set of FK510's to my F30 330d. Falken are really underrated tyres.

They are decent tyres (especially in the wet), but if I'm guessing correctly, they've been borrowed from the bucket and are a good few years old now. They certainly won't be in any way sticky!

They're new uns, as I got hold of some 14" wheels. Have used the old version on track before and liked them (Hi @B.RAD !). It was a toss up between these and TR1s, so may try the Toyos  next time.

Well hello! Loving the thread mate, a thoroughly good read full of interesting insight, upgrades and tech thoughts. Can't wait to have a go in Mr Poo! (That sounds weird)

Those falkens are mega. Had them on my Westfield, 520kgs and 226bhp and they were great, very predictable and communicative (if not with the ultimate grip levels).

Gutted I can't be at Oulton with you but I'm looking forward to the updates 👍

The 914 is no longer made in '2' sizes, their model now is the ZE310. I cannot comment on them for track, but they're pretty good on a road car.  Secure in the wet.

The 914s are so good in the wet. I always wondered why people said to exercise caution on wet roads in a MK3, as the bucket always felt rock solid even in monsoon weather.

I did have the older Toyo's (T1R I think) on the front of another middy, and they were pretty shocking! The crap budget tyres on the back had so much more grip than them it would understeer at sensible speeds.

Yes Lee, I agree about the 914's, great tyres in my book!

You wanna try the FK510's, they have 90% of the performance of Michelin's PS4 at half the price. Epic tyre for the money.

Even my 330d with 560nm of torque struggles to break traction in the wet.

Just a shame they only make them in 17" upwards.

did you do the track day?

Yep! And mostly all good. Have vids, pics and stuff to write up when I can.

Oulton Park 5th December – First Outing!

(Note after having written this out – it's long, and maybe not that coherent as it was done in a few chunks.)

TL:DR: Car didn't break, is fast, is a lot of fun, oversteers a lot. Happy days!


Having not been on track for a while, and having a new toy to play with, I was pretty excited about this one. That excitement was slightly tempered by the fact that, in the past, I have given myself a hard time if things don't go 100% perfectly. Combined with December usually being absolutely manic at work, meaning high stress levels and lack of sleep, it meant things had the potential of going terribly wrong...

I've been reading Adrian Newey's 'How to Build A Car' book over the last few weeks, and while being an interesting insight into the world of F1, his single-mindedness and level of focus also struck a chord. Perhaps more importantly for me, the book also mentions his 'failures' – such as misunderstanding certain aspects of the car from time to time, and 'that' incident on 1st May 1994, for which he still feels partly responsible as one of the senior engineers on the FW16.

The book proved to me that even the very best make mistakes, so I could cut myself some slack and not everything had to go perfectly with a freshly-built car.

The weather was as you'd expect in the North of England in December – cold and wet. On the floor at least; we managed to escape rain for 99% of the day, and the track even ended up with most of a dry-ish line by the time dusk fell. It was, however, mostly covered in a mixture of cement dust and the contents of someone's sump by this point – this had meant a track closure of nearly an hour mid-afternoon. I guess this was the Yin to the morning's Yang, where everything went beautifully and there were no stoppages at all, despite the super slippery near-zero conditions and murky visibility.

A very good friend, @Maurici  (my 'race boyfriend' – his terminology, not mine), came along in his mx-engineinwrongplace  – meaning a pair of blue, RWD, Japanese sports cars with 1.8 litre engines and about 140bhp – but obviously slightly different!



I had a new FauxPro to get used to having lost my GoPro (I hoped it would immediately turn up having bought the new camera, which it should have done according to Sod's law, but it seems Sod is on holiday at the moment), and I cocked up the set up and it didn't record for the first session. This was a bit of a shame but not the end of the world.

First impressions:

1) This is a quick little car (nothing came past – all morning, in fact, and only one car all day! – and all manner of expensive stuff was easily dispatched).

2) The aero works (properly shat myself the first time I entered Island bend, and it oversteered quite strongly. And again at Druids. Yet understeer through the two low speed chicanes unless you meter it with the brakes.).

Here's a still from a video I took of Maurici heading past the pits... not on the brakes at this point, and the front of the car looks very low! There's also a lot of 'squirt' coming off the front corners of the car, and a reasonable amount of spray being sucked up into the air, as shown by the water.





3) Driving position and ergonomics are almost spot on (ended up removing the foam pad on the headrest, as that 10mm was too thick and pushed my helmet forward a touch).

Entering the garage after the first session I was feeling pretty chuffed. All the stuff I'd done seemed to be working just fine – water temp was stable proving the ducting works, the engine pulls hard to the red line proving the exhaust works (and sounds awesome!), the car drives straight and true (alignment all good), the mechanical handling / grip was excellent with tons of feedback (armfuls of controllable sliding about when wanted, but still fast enough to overtake everything), the 'rear view mirror' did the job perfectly, brakes not optimal – but fine, with no fade and enough feel.

A quick check around the car revealed that everything was still stuck on, I had burned about 200ml of oil (haha), next to bugger all fuel (started with nearly a full tank) and the brakes were getting to surprisingly high temps.

Front brakes: The green paint burns off at 500 degrees, the pink at 600.



Rear brakes:




I've said it before, but I'll say it again – these are Apec pads. Cheapo road pads from the local motor factor - you can do a complete car for under £40 – yet they work really, really well. 600 degrees is a fairly significant amount of brake temp, just have a look at what 'proper' brake pads are rated to.

(For reference, 500'C = 930'F, 600'C = 1110'F)







I'm unsure how well the Apecs will hang on when it's properly dry and I'm really pushing on, but I've never had these fade on me (other than 'green fade' when bedding in, of course) and have done plenty of track days and racing with them fitted to heavier cars with smaller brakes. They just tend to wear faster if they do get too hot, which produces tapered wear, and associated mushy brake pedal – which is enough warning to change them. A spare set in the van, changed over in ~10 minutes, job done.


I managed to get the FauxPro sorted for the rest of the day, but annoyingly even when you plug the external mic in the internal mic keeps working – so the sound is a bit crap. Maurici found a way to stop this by drilling the camera, destroying the internal mic – but I figured that was best done in the workshop than in the paddock with cold hands!

Speaking of – Maurici took the car out, got settled in the first lap, tried to push on a bit the second, stuck it sideways a lot, then came straight back in and declared it was too much of a handful for him. He is one of the people I would say knows how to handle a car – and the video below proves it (see 3:50 and 4:55 for proof) – so for him to agree with me that the balance wasn't there meant I should probably try and do something about it!


I went for the simple options: more pressure in the front tyres, and a bit of toe in up front. With hindsight, I could have disconnected the rear ARB as well / instead, but for now lets explain what I did do.

With the fraction of static toe out the car had initially, this means the inside front wheel creates scrub at initial turn in, resulting in an oversteer torque on the car. Changing that to toe in, means the torque on the car is then trying to make it understeer, settling down the initial phase of the corner.

I feel a diagram would be useful here...

The cross in the circle represents the centre of mass of the car, the point around which all forces operate. The arrows represent forces – straight ones are scrub due to the tyre pointing in a different direction to the car's motion, curved ones are the resulting rotation.



Now, the MR2 uses almost 100% Ackerman steering, meaning the inside front wheel turns more than the outside (for the same amount of steering lock). So when combined with toe out, this effect is magnified. With slight static toe in, this reduces the above effect at the very start of the turn-in phase, helping to keep the car settled.

The tyre pressure adjustment – this is a huge area and I am not one of the most qualified to 'lecture' about it, but below is my understanding of parts of the puzzle.

People do this sort of thing all the time without realising what is actually going on. 'Oh I've got understeer so I need more front grip and I'll reduce the front tyre pressure to give a bigger footprint'. Weellllll yes, part of the story. Ish.

Increasing tyre pressure effectively 'props up' the carcass of the tyre more, with three significant results: The effective spring rate of the tyre has increased, slip angle is generated more quickly, and optimum lateral load is generated at smaller slip angles.

Slip angle is the difference in direction between where the contact patch of the tyre is pointing and where the wheel is pointing, in degrees. The tyre physically twists up when you turn the steering wheel (it also happens at the rear, or else you wouldn't go round the corner, but we'll leave that one for now!).

Imagine grabbing a 1" square chunk of solid rubber, about 4" long, and pushing it onto the surface of a desk. Now, twist with your hand. The rubber will deform to a certain amount / angle, then the 'footprint' will start to rotate when it can't stick any more. This is what your tyres do – load is applied to them vertically, you twist them, until they can't stick any more. You can then imagine if your rubber is firmer, it will twist less before the footprint starts to rotate.

Road tyres generate optimum lateral grip at larger slip angles than track tyres – and from the above test, we can see why. The road tyre has softer carcass, so twists more. By adding tyre pressure, this stiffens the carcass, and you get your optimal grip at reduced slip angles. The slip angle also builds more quickly because of less twist in the tyre, so you get your optimal grip 'appearing' more quickly.

From the above, increasing tyre pressure will actually increase the rate / speed at which grip builds at initial turn in. It certainly gives the driver more feedback. And this is why lowering tyre pressure CAN be the wrong way to go if you need more grip, depending on what phase of the corner you need it...

So... what about mid corner? There is an optimal pressure at which the tyre will give you the most grip, which depends on a huge range of things. It can, however, be determined with a tyre temperature probe (not IR gun, which only takes the surface temp). Deviating from this either way will give you less grip.

Not knowing the optimal tyre pressure for my car on this day in these conditions, meant I'd have to completely guess at the correct value. So I didn't. But why, if increasing pressure has been shown above to build grip more quickly on initial turn in, and more front grip would give more oversteer, did I go higher with the front pressures?

The change in spring rate is important – 1psi will change the spring rate of the tyre by ~25lbs/in in most cases. On a softly sprung car, on road tyres - like mine - the deviation in tyre spring rate from pressure changes can have a huge input on the overall handling of the car.

This is another discussion for another day, but in short – if you stiffen one end of the car, that end will 'lose' grip relative to the other end of the car. It's why ARB adjustments work for adjusting under / oversteer balance.

The actual springs are only 106lbs/in, front ARB probably around the same again, and while I don't have data for the Falken ZE310 (obviously) I can see from a Hoosier FSAE (Formula Student) slick spec sheet that theirs are approx. 530lbs/in at 10psi, going up to 740lbs/in at 18psi. These tyres are designed for a 250kg car, and having had hold of a set before, I can say that the sidewalls are pretty supple – not far from a road tyre.

Adding 8psi to the front tyres on Saturday massively increased (as a percentage) the front spring rate, thus giving the front axle - as a whole system – a higher spring rate, and thus reduced front grip. And it reduced slip angle needed to get the car to turn in, and increased the rate at which the slip angle built. No wonder I like high pressures on track with road tyres...

To put some maths on that, because I love maths...

'Actual' spring rate: 106lbs/in

ARB spring rate: 100lbs/in (guessestimate – haven't measured an OE ARB yet)

Approx tyre spring rate at original pressure: 890lbs/in

Approx tyre spring rate with +8psi: 1190lbs/in

Increase in total spring rate from increasing tyre pressure: Going from 1096lbs/in to 1296lbs/in = 18%

(And the front of the car was scrubbing / grounding out under hard braking when hitting a certain bump, so I figured trying to keep it off the deck wasn't a bad idea - sometimes practical considerations can be just as critical as theoretical ones!)

Just for fun – lets do the same with coilovers, and a stiff ARB.

'Actual' spring rate: 270lbs/in (a 5kg/mm spring, such as MeisterR coilovers)

ARB spring rate: 180lbs/in (guessestimate – I haven't measured a Whiteline, for example)

Total spring rate before / after tyre pressure change: 1340lbs/in to 1540lbs/in = 15% change. Add in a stiffer tyre to start with (as most with coilovers and uprated ARB-shod cars would have), you can see the tyre pressure change isn't as significant as with a softly-sprung and squishy-tyred car.

Anyway, 'blindly' lowering or raising tyre pressure may or may not give you more or less grip. What it will give you is a change in the slip angle that generates the optimum cornering load, how quickly the tyre reaches the optimum slip angle, and the spring rate of the tyres (and thus axle) that you have played with. As they often say, a little knowledge is more dangerous than none at all (and I certainly don't know it all!) – but in general the old 'I'll lower pressures to add more grip' does work, just for different reasons than you think.

Part 2 to follow...

Now, here's something I get all the time – coming up behind a 'normal' car (eg. one with all the major bits still attached where the manufacturer intended) in my shitter, the driver in front assumes it's got buttloads of power because it looks crap, so they don't move over and keep the throttle buried on the next straight. The ensuing drag race is usually frustrating (and I lose, ha), but today it helped give some sort of indication of engine health.

Stuff Mr Poo is a bit faster than, in a straight up drag race:

- EP3 Civic: 197bhp, 1280kg (with driver) = 154bhp/ton

- 172 Cup: 170bhp, 1100kg (stripped out, cage, driver and passenger) = 155bhp/ton


Stuff a bit faster than Mr Poo, in a straight up drag race:

- E46 M3: 343bhp, 1650kg (with driver) = 208bhp/ton


It appears The MunteR2 sits pretty much in between these two 'sets' of cars. Obviously there are other factors involved, so this isn't all that accurate, but...

- Mr Poo: XXXbhp, 840kg (with fuel and driver) = approx. 180bhp/ton, therefore approx 150bhp (180 / 0.84 = 151).

Now obviously gearing and aero / drag plays a part, but I'm confident my 1ZZ 2-stroke is not putting out less than 140bhp. Happy days.

The reason I say 2-stroke, is that the thing used nearly a litre of oil, but only about 30 litres of fuel. This was really quite confusing. Not the oil consumption, obviously, but using such little fuel. I've still got two full jerry cans sat in the van! I think I need to get an AFR gauge in there to check it's running safely...


Now moving on from theory, to practice.

Three bolts holding the steering wheel on, he said. That'll be fine, he said.

Unless two of them drop out. Gulp.

In what is probably one of the scariest moments I've had on track – not helped by that Caterham bullying past at a wholly unsuitable place and time - this happened.


Now obviously there are worse times and places for the steering wheel to become non-functional, but it's not ideal. I did, however, get away with it.

I had half-intended to swap the steering wheel over to a smaller one pre-trackday, so I hadn't tightened the bolts properly, just nipped into place. Also turns out the bolts didn't QUITE reach the nylon part of the nut.

Lesson well and truly learned. However, even Adrian Newey isn't infallible.

One of the bolts was fished out of the cockpit, a spare dug out from the back of the van, 2 new nuts fitted, and out we go again.

I also decided to tweak the angle of the rear part of the floor, giving it a smidge more 'kick up' at the rear. This in theory should add some downforce (or reduced lift, at least) to the rear of the car. It seemed better - both in the car and on the video - but not sure if that was me driving differently, trying to keep speed going rather than just sliding about, or it actually had an effect.

The final session was great – lots of 'the usual suspects' kicking about, track prepped Clios, Civics, MX5s, various BMWs. All those sorts of cars that have been 'developed' for track days, driven by experienced drivers. You know, the ones that are actually reliable enough to still be running at the end, owned by people who haven't given up because it was a bit slippy earlier in the day, who know the final session is often 'the one'. The track was even nearly dry, ish.


If I'd have had the datalogger running, which I didn't obviously, it would have showed a best lap around 2:10. Which, considering none of the laps were clear and the track wasn't dry, is better than anticipated.

Here's a sketch of some data traces I did from memory / feel, because the datalogger wasn't running, obviously.

(Bugger, forgot to send these over to myself last night - will upload at another point!)



This is Munter (in the bone dry on proper tyres) vs MunteR2. The main things that stick out are:

- The wet bits of track really cause a huge drop in apex speed - 20mph through Island bend!

- MunteR2 is clearly a lot faster in a straight line, gaining around a second on each straight, and a huge gap in the drag up Clay Hill.

And just for fun, here's MunteR2 vs Lobster (my Westfield with the bike engine, on silly skinny road tyres and with terrible aero, hence not really having higher apex speeds despite the low weight).

(Again forgot to send this, will do it later)


So. What's next? Well, here's the to-do list. Aims and intended routes.

- Sort the aero balance. This was perhaps the first thing that struck me as 'awkward' about the car, and certainly Maurici agreed! Big Gay Wings (BGWs) are not really my style, and they do cause additional drag, so that leads me to playing with the floor...

My recent aerodynamics research revealed that there can be some significant gains from a proper diffuser. At the moment it doesn't have enough angle, and there will be air spilling in from the sides (high pressure down the sides of the car vs low pressure under the car = the air tries to go from an area of high to low pressure, reducing whatever effect it is having).

So I had a nosey for some documents which may assist with design, and stumbled across this absolute gem: https://www.racetechmag.com/2017/08/willem-toet-explains-motorsport-diffusers/

This gives me pretty much all the info I need to get designing and (hopefully) create something that will create downforce.

I do need to be a little careful of the exhaust proximity to the floor though, as shown it below it was slightly affected at the weekend...



As part of this job, I will raise the front of the floor by 10mm or so. This will reduce front downforce but therefore aid balance at higher speeds. Plus, it will help to stop it bottoming (especially once a passenger is in!). It was only the deflectors in front of the front wheels, but having them scrubbing as I hit a bump while braking on the way into Island, and all the way through Shell when the car is fully loaded up, was a little off-putting. If that still doesn't work, I can pack the bump stops or fit longer or stiffer ones.

Playing with ground effect in this way, especially with soft suspension, I'll have to be a little careful not to go too 'extreme' else a change in ride height can totally cock up any downforce – eg. hitting a big bump mid corner could stall the rear diffuser and lose grip... (IF any of it works!)
Another note on this subject, the rear of the car has a really 'turbulent' look about the dirt on it. I am wondering if the floor exit being 'in front of' the rear of the car hasn't helped in this respect, so extending the floor into a diffuser and having it exiting behind the bumper should help.



- Tweak the brakes. The front brakes are doing all of the work at the moment (check the wheel dust on the side-on photo below). With the car being so rear-weighted, there will be a gain – both in braking performance and pad life – if I can shift that rearwards. I need to do some maths surrounding line pressures, but it looks like I'll add the bias valve into the front circuit. I appreciate this isn't the normal place for it to go – but – this isn't a normal car and I'm not a normal kinda guy. The brakes also could do with a bleed, I always find there's bits of air dislodged after proper use, and the pedal feels that way too.

- Add extra rear ARB adjustment. I'm going to weld a bit of bar onto the ends of the rear ARB, so it has more adjustment in the 'soft' direction. Another handling balance tool for next time, if necessary.

- Attempt to keep air out of the passenger compartment. Now this is a funny one which confused me at first. The panel behind the seat, which is designed to keep air out from the area where the roof would normally bolt (which would end up like a parachute), is held in with gaffer tape as before. This time though, the gaffer tape has started to rip, indicating it's taking a fair amount of force...





With more thought this makes sense: 1) the levels of the front and rear openings to the cockpit on the MR2 are totally different to the MX5 – the MX5 has a higher front and a lower rear, the MR2 is the other way round.



2) I'm now firing a heck of a lot more air over the scuttle thanks to that big duct from the front bumper through the radiator. This has to go somewhere – and it appears that is into the cockpit and thus into that rear panel.

I'm thinking of some sort of additional deflector mounted to the bonnet, firing the ducted air up, sideways, or a combination of both. Needs more thought.



On that note, the bonnet – despite being single-skinned and pretty floppy – barely bobs around at all even at 100mph+, which proves there Is very little air entering the front of the car. Happy days.

- Probably more stuff I haven't identified yet.

- Oh yeah, that stupid aerofoil shape on the roll hoop? Was ok for most of the day, until the track dried and top speeds got over 100mph. Then it just started flapping about all over the shop, so much that it almost deafened me and I was scared it would fall off. So I ripped it off. I have a tentative plan involving some 3D printed wing 'chords' and thin sheets of Lexan, so let's see where that goes.

I've now booked Donington for 16th Jan, and already looking forward to seeing if my tweaks work as intended!





And the reason I used white correx for the scuttle? It acts as a board to write stuff on!

Thanks for the information and entertainment Adam.
Will need to mull over the former a ´bit´!!!!

Can you fit a ´tonneau´ cover over the passenger tub?

A silly big wing may not suit your style; it does work a treat though.

Lóve the whiteboard kill tally. Something to translate to car silhouettes on the quarter panel ;-)

Most of that (like the wind/rain) went over my head but its seems to have gone very well for a first drive!

The videos were more interesting than most track day videos too, feels like you are in the car for some reason....

I hope you were wearing your brown pants when the wheel started to fall off.

I was also going to ask about a tonneau cover. In the spirit of the car, could you glue some kitchen foil on the difuser under the exhaust?

(Still think it would look better all one, very bright, colour!).

Congratulations.

Nice one Adam didn't understand most of it but I read it all.

Got the datalogger info now:

Here's a sketch of some data traces I did from memory / feel, because the datalogger wasn't running, obviously.

You cannot view this attachment.



This is Munter (Blue trace - in the bone dry on proper tyres) vs MunteR2 (red trace, session at the end of the video). The main things that stick out are:

- The wet bits of track really cause a huge drop in apex speed - 20mph through Island bend! (Around 4300 feet, looking along the bottom of the image - where I have plonked the white vertical line). At this point, looking down the far left of the image, you can then see that the red trace (MunteR2) is pulling 0.86 lateral g, and the blue trace (original Munter) is pulling 1.17g. We can assume that they are taking the same radius, therefore this explains the difference in apex speed - 76.8 vs 96.6mph. Heading right down the bottom, at this point in the lap the red trace is 1.454s behind the blue one, and this steadily climbs through the lap. This is called the lap delta.

- MunteR2 is clearly a lot faster in a straight line, gaining around a second on each straight from looking at the delta (the red line drops down slightly as it goes along), and a huge speed gap in the drag over Hilltop (7500 feet) and up Clay Hill (10000 feet along).

- Druids (11000 feet) is also really slow compared, because it stayed wet.

- Cascades (2300 feet) dried out sufficiently for corner speeds to be matched.

Looking into the data more, I drove a 2:07.8 'continuous' lap (from Shell Hairpin to Shell Hairpin), and the best theoretical (puts together all the best sectors) on the day was a 2:04.1.

So, with all said and done, I think this car is capable of a 2.00 minute lap in the dry, even in current guise.


And just for fun, here's 'old' Munter (Blue trace - chose this one because it was also dry) vs Lobster (Red trace, my Westfield with the bike engine, on silly skinny road tyres and with terrible aero, hence not really having higher apex speeds despite the low weight).

You cannot view this attachment.

You can see the insane differences in acceleration from the angle of lines, which means massive differences in top speed - up to 25mph at points.

Another stark difference in the traces: With a low-powered car, the key is to maintain speed; so you brake later, rolling through the apex faster, and you can do this because you don't have all that excess power ready and waiting to spin up the rear wheels when you put your foot down.

The opposite of that is what I do in the Westfield - I am slowing down to minimum speed earlier, and in some cases a lower minimum speed, in order to get the car fully rotated earlier and take advantage of that extra acceleration, which is the optimum way to end up with a higher speed at the end of the straight.

Just looking at your speed graph and how smooth it is I can see you don't brake as hard as me, therefore carry more speed through the corners. Something i definitely need to learn.

Below you can see mine, lots of sharp drop offs where I'm braking to much. No idea what happend at shell, must have lost GPS.

This day/lap was in the middle of summer with temps around 25°,  roof off, on AR1's with bluestuff pads front, yellowstuff pads rear . Its actually the lap before the engine went pop 🙄

Very interesting Adam, thanks for sharing it.  You have driven a 2 on a track before though, yes?


Gary

Quote from: Gaz mr-s on December  8, 2020, 22:23Very interesting Adam, thanks for sharing it.  You have driven a 2 on a track before though, yes?

Gary

Very welcome!

Ah yes, completely forgot about the 3 Sisters evening. Oops!

Quote from: AdamR28 on December  9, 2020, 09:15Ah yes, completely forgot about the 3 Sisters evening. Oops!

Right..... so has the flat undertray increased your front-end grip, or is it in combination with the splitter?

None of this is guaranteed, and slightly hard to figure out due to so many other changes, but here are my feelings...

- The splitter itself does next to nothing. I intended it that way. I didn't want something huge sticking out for both practical (eg. not smacking it on stuff) and cosmetic reasons.

- The floor, however, is a massive gain to both drag reduction and either generating downforce or reducing lift. I'm not sure if it actually *makes* downforce, but my gut feel is that it does, from how the car feels and that photo of it heading down the straight. It definitely reduces lift though.

This is explained well in the video below:


I think the MR2 is a perfectly-suited car for this modification, due to the engine location and lack of hot stuff running all the way down the underside of the car.

So, that's what the Nappies are doing?  

The front nappies will be doing a little bit of lift reduction yes, but their shape and stiffness isn't good enough to produce downforce.

At the rear... It's more a cover to keep spray out than anything.

Quote from: AdamR28 on December  9, 2020, 10:41I'm not sure if it actually *makes* downforce, but my gut feel is that it does, from how the car feels and that photo of it heading down the straight. It definitely reduces lift though.

The whole car is shaped like an airfoil and moving forward through air creates less air pressure above than under. This results in a force opposed to gravity. Call it anything you like. Lift is most common.

The air passing underneath the car is affected by several other aspects: The road surface, the pofile of the underside, how the frontal air is directed, how the air passing through the radiator is directed, how air is ´extracted´ at the rear or not, the rake of the car etc.

A flat underside will reduce turbulence under the car thus speed up the air flow thus deminish the airfoil effect. As the latter is most commonly called lift, the effect of the flat floor is most accurately dubbed negative lift.
Basically most things done to the underside are counteracting the airfoil effect, thus negating the lift.

Now take rake. Thát creates a pressure drop by increasing more volume towards the rear of the car and although the resulting force counteracts the lift, it is different from the airfoil effect and you could dub it downforce.
Seems semantics but it does help understand what is happening.

The air vents in the bonnet are tricky ones. Although they reduce the amount of air pushed under the car by the pressure wave in front, thus reducing pressure under the car, it also affects the two air flows, thus affecting the airfoil effect. This may go either way although the effect of less pressure under is most likely the greatest.

All in all an übercool subject imo and I reallyREALLY appreciate the illustrative emperical efforts by Adam.

@nappies that is both yes and no. Just look under the front: There is a gaping hole allowing the air passing through the front to go underneath the car. This is already a totally turbulent flow. Imo the rear nappies are foremostly intended to keep the noise down.
What Adam has done is create a vent abóve, allowing him to close, smoothen the bottom and thát makes a lot of difference.
As I write; übercool.

Quote from: JB21 on December  8, 2020, 17:28Just looking at your speed graph and how smooth it is I can see you don't brake as hard as me, therefore carry more speed through the corners. Something i definitely need to learn.

Below you can see mine, lots of sharp drop offs where I'm braking to much.

I am actually generally pretty poor in terms of finding maximum braking. Know all the theory, but struggle to put it into practice! I tried to be last of the late brakers at Donington at a race meeting once - ended up through the gravel a couple of times. It is something I'm aware of and working on, but I find having a small margin for error comforting, especially on a track day. There are lots of people who *can* brake later than me, but this isn't the full picture so I've spent my time learning / researching other phases of the corner.


You need accurate datalogging equipment to see the subtle differences in braking traces. Something that has an accelerometer rather than using GPS speed. In general though, braking as hard as the car will allow is always a good thing, with a caveat - the driver must have the car under full control at the entry phase of the corner.

Something else that makes a difference is the suspension setup. If you just literally stamp on the pedal, the brakes will lock in any car (well, perhaps not something with shedloads of downforce) because there's not enough vertical load on the front tyres yet to allow the tyre contact patch to create enough torque to overcome the braking torque from the pads / disc.

It therefore follows that a stiff car will allow you to get to full braking effort more quickly, because it transfers weight forwards more quickly.

With a moderately stiff car, you can get from full throttle to full braking in around 0.3-0.35s. With the MunteR2 being on a soft setup, this is going to be more like 0.5s. At 100mph, that means having to start braking nearly 10m earlier, and the shape of the speed trace will be more 'rounded' at the tops of the peaks. Once you're on the brakes fully though, the steepness of the speed trace is unaffected, and in some cases can remain steeper because the car will be less upset by bumps on a softer setup.


Getting to corner entry phase, coming OFF the brakes is very important. Jackie Stewart is quoted as saying it's the hardest thing to learn. Here you are aiming to actually steer the car using the brakes, rather than the steering wheel. Turning the steering wheel introduces a slip angle to the tyres, which creates scrub - the tyres pointing one way and the car travelling another. This scrub reduces your speed.

If you can 'hint' the car into the corner (using a very small steering input) and then use weight transfer - via the brakes on entry - to get / keep more weight onto the nose, this will increase grip at the front (and thus reducing grip at the rear) and the car will keep rotating into the corner, with very little steering lock on.

On this note, if you jump off the brakes just before you turn the car in, or as you are turning in, this releases weight - and therefore grip - from the front wheels, just when you need it. Understeer. Safe, but slow. So, releasing the brakes smoothly is really important. Again with accurate datalogging, you can see what's going on in this area.

The holy grail is zero steering lock, with the car physically rotating around its centre of mass all the way through the corner, rather than being steered through, as the brakes bleed off and the power feeds in just as smoothly. In reality, what's possible for mere mortals is a series of steering corrections all the way through, the car transitioning from 'steering' to 'oversteer' conditions (and hitting everywhere in between) while you shuffle the steering wheel and increase and decrease pressure on each of the pedals, depending on which phase of the corner you're in.

The start of the main video above, with all the slides, is me trying to hit that stage, but just overcooking it slightly. Too much oversteer is also slow, as we all know, because that scrub I talked about is there in vast quantities - but you have to get the car out of shape a little bit for it to get close to its potential.

It therefore follows that, to hunt for 'the holy grail', you need to be comfortable with the car moving about under you... And you also need to be able instigate that consistently, with control; rather than simply reacting to what the car is doing. Many people never reach this stage for the reasons I'm about to explain below.

It is really important to consider the car and the driver as one. Bolting go-faster bits to the car does make the "car & driver package" faster immediately, but the car is then harder to drive and the driver will never get as close to the potential of the car as they would had they learned in a soft car. If you have a car that is now 5% faster because of the latest go-faster bits, but the driver can only exploit 80% of that performance, it will end up slower than a standard car with 90% of the potential used.

This is why I am a HUGE advocate of learning to drive on track in a soft car, with low power on cr@p tyres. The above 'system' happens at a much reduced speed (both in mph and the rotation of the car) and thus gives the driver more time to 'play' on the edge of grip. Think underside of spoon rather than sharp edge of knife. A faster car means faster corner entry with less time to react, a stiffer and grippier car means the whole thing transitions from grip to slip in much reduced time. If the driver hasn't learned the 'signs' in the slower, softer car, he or she will never learn them in the faster / grippier car because it will be scary when the car gets out of shape. This means they always drive well within the potential of the car, to avoid said scary moments.


That ended up a lot longer than I anticipated, but hopefully it all makes sense and may help a few people!

@AdamR28

The last part of your essay reminds me of something tiff said when he was doing a test on track for 5th gear.
He basically past a radical in a Mx/124. He observed that the driver was a novice under instruction and why were they trying to learn to drive on track in something that was practically a race car. They should be driving this he said.
Makes perfect sense.