RE: Mark Hales on Technique: Shifting the weight about

[RobM77]

Debaser said:

Pity you deleted it, but I can understand not wanting to get into an argument. PH can be a bit odd sometimes.

Wish I'd saved it actually - it took me a while to get the explanation just right! However, yes, PH is a very strange place - there are lots of keyboard warriors on here. I try my best not to antagonise people.

[CABC]

RobM77 said:

Debaser said:

Pity you deleted it, but I can understand not wanting to get into an argument. PH can be a bit odd sometimes.

Wish I'd saved it actually - it took me a while to get the explanation just right! However, yes, PH is a very strange place - there are lots of keyboard warriors on here. I try my best not to antagonise people.

maybe we should all have to prove who we actually are? Especially on main social media sites, like Haymarket.

[RobM77]

CABC said:

RobM77 said:

Debaser said:

Pity you deleted it, but I can understand not wanting to get into an argument. PH can be a bit odd sometimes.

Wish I'd saved it actually - it took me a while to get the explanation just right! However, yes, PH is a very strange place - there are lots of keyboard warriors on here. I try my best not to antagonise people.

maybe we should all have to prove who we actually are? Especially on main social media sites, like Haymarket.

That could have two effects though. Yes, trolls are likely to back off a bit if their name is attached to everything (although not completely, as Facebook and Twitter arguments show!), however if someone gets nasty with me then I'd rather they didn't know who I was.

As an example, I also post on another forum who have it in their rules that you must use your real name. I was badly let down by an automotive company, so I posted very carefully saying that I'd been let down by 'someone' (no names mentioned!) and could anyone recommend anyone else? A few replies were made by others and between them they worked out who it was, posted it, and they were right. However, it was me who got threatened by the company for starting the thread!!

I also had a problem with this on PH many years ago, when I had my real name on my profile. I did some races in an uncompetitive car in a mixed category. The faster cars were, err, faster, but some guy decided to twist the facts and make me look bad. My small sideline of trackday instruction for novices dried up there and then and I've not done any since. The same thing happened to someone else I know in almost identical circumstances.

Edited by RobM77 on Tuesday 18th July 09:32

[NDNDNDND]

I think it's quite a pity you deleted your post Rob, I thought it was a very helpful post that helped clarify the mistake the Gemaeden had made - although given your reasons I can understand why you're shy of confrontation online.

Actually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

I'm actually quite pleased to see this thread free from any arguing - it seems much like a rational debate on an interesting topic. I'm also quite pleased that Gemaeden posted up his misinterpretation, as I've personally found it a good learning opportunity.

My own experience of weight transfer came after a tutoring session at Brands with Mike Wilds in my MX-5. Before my lesson, I'd been cornering in the traditional fashion - feeding in the throttle to the limit of the rear tyres while unwinding the steering away from the apex. Mike showed me how you can 'thump the throttle' as Mark describes before the apex, loading up the rear tyres enough that you could slingshot through the corner at full throttle. Felt amazing and was much faster!

Very pleased to see Mark writing articles for PH, and you can tell from the forum how it's brought all the petrolheads out of the woodwork!

[CABC]

NDNDNDND said:

Mike showed me how you can 'thump the throttle' as Mark describes before the apex, loading up the rear tyres enough that you could slingshot through the corner at full throttle. Felt amazing and was much faster!

i've been playing around with this myself. I guess you can 'thump' the throttle in a 5 as it's quite low powered, whereas something with 400hp would need a 'firm press', over a fraction of a second. Maybe Rob can help here.
I've been fortunate enough to be messing around with a Morgan too, and i have to say it's been great fun. You can feel rotation and the back bedding down far more clearly than in an Elise for example. Not saying that the Morgan is in anyway advanced, but on a smooth road it really is informative and a good training tool.

[RobM77]

NDNDNDND said:

I think it's quite a pity you deleted your post Rob, I thought it was a very helpful post that helped clarify the mistake the Gemaeden had made - although given your reasons I can understand why you're shy of confrontation online.

Actually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

I'm actually quite pleased to see this thread free from any arguing - it seems much like a rational debate on an interesting topic. I'm also quite pleased that Gemaeden posted up his misinterpretation, as I've personally found it a good learning opportunity.

My own experience of weight transfer came after a tutoring session at Brands with Mike Wilds in my MX-5. Before my lesson, I'd been cornering in the traditional fashion - feeding in the throttle to the limit of the rear tyres while unwinding the steering away from the apex. Mike showed me how you can 'thump the throttle' as Mark describes before the apex, loading up the rear tyres enough that you could slingshot through the corner at full throttle. Felt amazing and was much faster!

Very pleased to see Mark writing articles for PH, and you can tell from the forum how it's brought all the petrolheads out of the woodwork!

Maybe I was being a bit too tentative, sorry. In essence, Mark Hales is correct and it's a nice article.

What was being incorrectly asserted was that weight transfer and its effects were caused by the tyres of a vehicle. Tyres are indeed an unusual thing, and they behave differently to simple blocks of wood or bricks when sliding and moving around (more on this below). However, weight transfer is a much more basic phenomenon and applies whatever the tyres of a car are made out of.

'Weight' transfer occurs when a car changes its speed (e.g. accelerates) in any given direction, whether that be increase in speed (the car squats - think of a motorbike pulling a wheelie), a decrease in speed (the car dives, think of a motorbike doing a stoppie), or cornering (the car leans one way or the other). By the way, in physics terms cornering is also an acceleration (think of a car viewed from behind or in front taking a corner - it 'accelerates' towards the corner from that point of view). To put some numbers to this, if you imagine a car weighing 1000kg with a 50:50 weight distribution, then at rest on imaginary scales it would put down 500kg through the front tyres and 500kg through the rear. When braking hard for a corner, our imaginary scales might read 700kg at the front and 300kg at the rear. When backing off in a corner, this might be 550kg front and 450kg rear. In terms of cornering, on a right hand bend the left hand wheels might be bearing 600kg and the left hand ones 400kg. The two figures will always add up to 1000kg (the weight of the car), but it'll be distributed amongst the tyres differently. Both these effects are going to change grip levels, with the end with more weight getting more grip. So, when you brake into a corner, you're giving the front end more grip than the rear and you can use this to overcome the car's tendency to want to go straight on (Netwon's first law) and turn in to the corner, then once in the bend you can use this effect with more subtlety to control the car and also to enable you to accelerate as hard as possible out of the turn and stay on the best line. As Mark rightly says, it is critical to understand this and get it right when driving fast - in many ways, motor racing simply boils down to managing weight transfer.

The confusion was caused I think by something called 'tyre load sensitivity'. This refers to the fact that as you load a tyre up, the resistance that it is able to generate (e.g. against wheelspin when accelerating) reaches a peak and then tails off as load increases. If you had a car with wooden tyres, then this wouldn't happen, and it'd be 10 times harder to push sideways with 10 times the weight. Car tyres though don't respond like this due to the way they interact with the tarmac; it might only be 9 times harder to push them with 10 times the weight. TLS though is irrelevant to Mark's article, because he's simply discussing controlling a car using weight transfer as a tool to steer the car using throttle and brakes (see the paragraph above, not this one!).

Mark briefly touches on downforce generating cars, and this is relevant because they provide additional complications, such as the fact the wings and venturis etc work differently at different angles of lean and different yaw angles (angle of the car relative to the oncoming airflow; i.e. a sideways car loses downforce). This is a whole different topic.

The issue with track instruction (or any sports instruction) is that you need to understand the scope of what you're explaining before you explain it, and you also need to stick to the point, because you could spend all day diving down intellectual rabbit holes discussing tyre pressure, temperature, contact patch deformation etc etc. Mark was doing this very well in his article (unsurprisingly - he's an excellent driving coach). Incidentally, this is what I tried to do above by using colloquial terms such as 'weight transfer' and 'acceleration'. Technically speaking, it's 'load transfer', but most people understand it in terms of 'weight', so that's the word I used. Weight is actually a force/load, so I'm happy with that.

Edited by RobM77 on Tuesday 18th July 14:54

Edited by RobM77 on Tuesday 18th July 17:53

[RobM77]

CABC said:

NDNDNDND said:

Mike showed me how you can 'thump the throttle' as Mark describes before the apex, loading up the rear tyres enough that you could slingshot through the corner at full throttle. Felt amazing and was much faster!

i've been playing around with this myself. I guess you can 'thump' the throttle in a 5 as it's quite low powered, whereas something with 400hp would need a 'firm press', over a fraction of a second. Maybe Rob can help here.
I've been fortunate enough to be messing around with a Morgan too, and i have to say it's been great fun. You can feel rotation and the back bedding down far more clearly than in an Elise for example. Not saying that the Morgan is in anyway advanced, but on a smooth road it really is informative and a good training tool.

Mark would be far better qualified to discuss that one than me, as a TVR Tuscan champion and frequent driver of very powerful cars with low grip. I'm simply a physics geek who likes to race cars in his spare time. However, what I will say is that the best way around a corner is not always textbook or obvious in a given car, because of that car's particular strengths and weaknesses. A car that is visibly sliding at higher than optimal slip angles won't be generating as much grip as a car that isn't, but if that grippy car is harder to handle and wants to plough straight on, then it might not be able to drive an optimum line and come on the power early enough to get a good exit speed down the next straight, so a slidey technique may be faster. Note also that different tyres and surfaces all produce their own optimum slip angles - the tyres on a 250F behave quite differently to those on a modern slick shod grand prix car. This is just one example of a divergence from textbook technique - note that F1 drivers in the modern era often concern themselves with tyre temperature management as well as their mastery of the optimal theoretical approach to a corner - there's a very good Peter Windsor You Tube video on this - apparently it separates the top drivers to some degree.

Often these sorts of problems are dealt with by setup, but quite often they can lend themselves to driving techniques as well, on top of those setup changes. For example, the trick with setting up front drive cars is sometimes to reduce rear grip below what is optimal, because this allows the car to be driven in a way which results in it being faster overall. This also manifests in a slightly different driving technique for FWD - I used to aim to get a very slight amount of oversteer before the apex, because even though this was slightly slower through that phase of the bend, I could get on the power harder and sooner, which overall in terms of lap time was a benefit.

[RobM77]

NDNDNDND said:

IActually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

That thread touches on the same thing actually, and someone actually quotes the same data from Miliken and Miliken! As Stressed Dave rightly points out, that's tyre load sensitivity and a different topic. By the way, what he says about 'chemical bonding forces' is wrong; it's actually hysteresis of the rubber that generates the grip and that is also responsible for TLS.

[S. Gonzales Esq.]

RobM77 said:

NDNDNDND said:

IActually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

That thread touches on the same thing actually, and someone actually quotes the same data from Miliken and Miliken! As Stressed Dave rightly points out, that's tyre load sensitivity and a different topic. By the way, what he says about 'chemical bonding forces' is wrong; it's actually hysteresis of the rubber that generates the grip and that is also responsible for TLS.

I'd forgotten about starting that thread all those years ago - very interesting coming back to it with six years more experience.

All the physics still makes my head hurt, so I'm increasingly seeing the point of what Don Palmer said - essentially that it's more important to notice that there is something happening and to work with your experience of it, than to necessarily have an exact understanding of the science involved.

[CABC]

S. Gonzales Esq. said:

I'd forgotten about starting that thread all those years ago - very interesting coming back to it with six years more experience.

All the physics still makes my head hurt, so I'm increasingly seeing the point of what Don Palmer said - essentially that it's more important to notice that there is something happening and to work with your experience of it, than to necessarily have an exact understanding of the science involved.

i contacted Don 4 yrs ago but never managed to hook up!
Anyway, i guess your a fan? I like what i hear of his style and your comment above fits with that.
sometimes instructors just lecture and take things from their perspective. but i need someone to see things from my side and help me through the learning. ie a proper teacher/coach

[S. Gonzales Esq.]

CABC said:

i contacted Don 4 yrs ago but never managed to hook up!
Anyway, i guess your a fan? I like what i hear of his style and your comment above fits with that.
sometimes instructors just lecture and take things from their perspective. but i need someone to see things from my side and help me through the learning. ie a proper teacher/coach

I've never had individual coaching from Don, but have met him a few times and took part in an event he was running. I know lots of people that have used his services though, and if you want a coach in the field of limit handling rather than an instructor then he's probably your man.

[majordad]

I thought it good. Thanks

[NJH]

Excellent article. Dead easy to see weight transfer in action. If you have an old fashioned air freshener hanging from your rear view mirror just watch it pitch to the left when chucking the car round a roundabout, or pitch forward when on the brakes. Of course if you can get the air freshener pointing 90 degrees up straight out to the left then you are being a very naughty boy/girl indeed and need to perhaps slow down on those roundabouts

[Kawasicki]

RobM77 said:

NDNDNDND said:

IActually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

That thread touches on the same thing actually, and someone actually quotes the same data from Miliken and Miliken! As Stressed Dave rightly points out, that's tyre load sensitivity and a different topic. By the way, what he says about 'chemical bonding forces' is wrong; it's actually hysteresis of the rubber that generates the grip and that is also responsible for TLS.

tyre grip is complicated, some say there are two main mechanisms
mechanical grip...like a gear against a gear
molecular adhesion...Van der Waals forces

[johnfm]

Gemaeden said:

griffgrog said:

I think you're getting questioned because your asserting that Mark's article about weight transfer improving turn is incorrect - or a red herring as you put it.

In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.

Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.

Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.

If Mark had written what I have, turning most peoples beliefs on their head, and I had suggested some of what he had written was a misunderstanding I'm sure most people would choose to believe Mark rather than me as he is well known race driver and instructor and therefore seen as authoritative.

However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.

Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"

Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7

Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.

Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.

Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.

You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.

"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"

If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.

This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.

You note that weight transfer is responsible for this or that above, so how is it a 'red herring'?

[johnfm]

Great article.

I've just bought a Formula Junior. No aero, no LSD - so the article was really relevant.

[Gemaeden]

johnfm said:

You note that weight transfer is responsible for this or that above, so how is it a 'red herring'?

Okay. I've made mistakes before and no doubt I'll make more in the future, but hopefully I'll gain a better understanding from the responses I get.

I mentioned weight transfer being a red herring, as I didn't see it as increasing grip per se, merely distorting the sidewalls.

My reasoning was framed by looking at Formula Ford and such like non-aero friction circle graphs.

If putting weight on the nose improved turn in, then why is there not a scattering of plots showing good lateral acceleration at near maximum longitudinal braking g on such graphs?

Surely the increase in yaw rate would show up as lateral acceleration in this area.

What I see in these graphs is like a scribbled 'T' shape, whereas what I would expect to see is some fanning out at the bottom of the 'T' if grip were increased by weight on the nose.

Either I'm misinterpreting these graphs, which is of course possible or they don't show these plots as they are considered as noise. In which case, what is the point of them?

Hopefully now you can see my reasoning. I can't find any evidence in the data that I see for an increase in grip due to weight transfer.

If someone can show me the error of my assumption through data rather than theory, or anecdotal descriptions of feel, then I'll be happy to change my belief and stop upsetting people.

[Kawasicki]

Gemaeden said:

johnfm said:

You note that weight transfer is responsible for this or that above, so how is it a 'red herring'?

Okay. I've made mistakes before and no doubt I'll make more in the future, but hopefully I'll gain a better understanding from the responses I get.

I mentioned weight transfer being a red herring, as I didn't see it as increasing grip per se, merely distorting the sidewalls.

My reasoning was framed by looking at Formula Ford and such like non-aero friction circle graphs.

If putting weight on the nose improved turn in, then why is there not a scattering of plots showing good lateral acceleration at near maximum longitudinal braking g on such graphs?

Surely the increase in yaw rate would show up as lateral acceleration in this area.

What I see in these graphs is like a scribbled 'T' shape, whereas what I would expect to see is some fanning out at the bottom of the 'T' if grip were increased by weight on the nose.

Either I'm misinterpreting these graphs, which is of course possible or they don't show these plots as they are considered as noise. In which case, what is the point of them?

Hopefully now you can see my reasoning. I can't find any evidence in the data that I see for an increase in grip due to weight transfer.

If someone can show me the error of my assumption through data rather than theory, or anecdotal descriptions of feel, then I'll be happy to change my belief and stop upsetting people.

Good post. I think that maybe you are underestimating the balance aspect. Imagine 2 identical cars, both cornering at 1 g. One is in deep understeer, one is in more neutral steer. Which gives the driver more confidence and options?

[The Wookie]

Gemaeden said:

Okay. I've made mistakes before and no doubt I'll make more in the future, but hopefully I'll gain a better understanding from the responses I get.

I mentioned weight transfer being a red herring, as I didn't see it as increasing grip per se, merely distorting the sidewalls.

My reasoning was framed by looking at Formula Ford and such like non-aero friction circle graphs.

If putting weight on the nose improved turn in, then why is there not a scattering of plots showing good lateral acceleration at near maximum longitudinal braking g on such graphs?

Surely the increase in yaw rate would show up as lateral acceleration in this area.

What I see in these graphs is like a scribbled 'T' shape, whereas what I would expect to see is some fanning out at the bottom of the 'T' if grip were increased by weight on the nose.

Either I'm misinterpreting these graphs, which is of course possible or they don't show these plots as they are considered as noise. In which case, what is the point of them?

Hopefully now you can see my reasoning. I can't find any evidence in the data that I see for an increase in grip due to weight transfer.

If someone can show me the error of my assumption through data rather than theory, or anecdotal descriptions of feel, then I'll be happy to change my belief and stop upsetting people.

You're mixing up weight transfer and friction circle. You don't get big weight transfer to the front without using up the available friction of the tyre for lateral. Weight transfer effects for handling are more subtle and in the lower ranges of longitudinal acceleration

Basically you're confusing non-linearity of the tyre with actual available grip due to the combination of vertical load and friction coefficient. The mechanism you're talking about is only applicable to extreme tyre loads where the tyre effectively becomes saturated. The only time I've heard of this being a significant effect was in a heavy car with an extreme amount of aero that started losing lateral grip at high speed as presumably the friction coefficient was dropping off faster than the vertical force on the tyre was increasing. This happens in other friction systems too at the very extreme, such as brake pads.

[RobM77]

Kawasicki said:

RobM77 said:

NDNDNDND said:

IActually, I'd dug about and read up online a little myself, and was going to post this thread: https://www.pistonheads.com/gassing/topic.asp?h=0&... before I realised that you'd already added something yourself.

That thread touches on the same thing actually, and someone actually quotes the same data from Miliken and Miliken! As Stressed Dave rightly points out, that's tyre load sensitivity and a different topic. By the way, what he says about 'chemical bonding forces' is wrong; it's actually hysteresis of the rubber that generates the grip and that is also responsible for TLS.

tyre grip is complicated, some say there are two main mechanisms
mechanical grip...like a gear against a gear
molecular adhesion...Van der Waals forces

You're quite right, I'd completely forgotten about that rather bizarre aspect of grip!