RRH

I'm not sure there is any other way to get round a damp roundabout in an MX5 is there

tony95

4x4=scandanavian flick

CrisPDuk

All 4WD cars understeer to a certain extent, it's an unavoidable side effect of putting drive through the front wheels. True with proper geometry settings you can reduce it, but without resorting to trick transmissions (evo/skyline style) you'll never get rid of it.

finchyboy

Hope it wasn't may mobile hairdresser Tracy !!

2000TLondon

Hmm, not the response expected, I think!

All manouvres should be done in safe enviroments, and I believe the OP's point is if someone were to enter the roundabout, the drift would soon become a bang.....

However, as I learnt from driving my old MGB roadster (held together by goodwill and duct tape) it's very easy to get the right RWD car into a slide, although doing it in front of people generally made me feel like a bit of a tit!

2000TLondon

Hidden secret? I've seen a hundred posts from you telling us how every car magazine in the world regularly votes it car of the week, car of the month, car of the year, car of the decade, etc etc etc!

HankScorpio

Yes, I've posted it before but everybody loves it:

Clicky

I've shown it to a lot of people and everyone has said how cool it is and how they wish they could do it.

I think the tosser comment may be a bit green tinged...

CrisPDuk

It was well worth you posting it again Hank too, cheers

Dream Weaver

Nothing wrong with a bit of drifting

Leslie

Crispduk,

Mine was actually very neutral with the Cheltenham suspension set up and the steering rack spaced on its mountings so that there was no change at all in the lock when the suspension moved up and down. A standard setup was shocking in that respect. It was a classic Japanese STi 1994 model. It was an absolute joy to drive in the wet especially on deserted roundabouts! The handling on fast bends was outstaniding and totally predictable and progressive. It was tweaked up to 300 BHP and did not understeer at all if you entered the corner applying power progressively as you started the turn. It reminded me of the Mk1 Lotus Cortina with the A frame located back axle which I sorted out for cracking the diff with the torque being fed along the axle housing from the wheels. That was one of the best handling road cars I ever drove, especially for its year.

Les

Tripple'O G

Gave my R33 GTST a run last night.....in the wet and with a drifting diff on it ....so so so much fun....

"Officer, if I don't practice, how will I know what to do if it steps out on me?...."

CrisPDuk

Les, change in the amount of lock required based on wheel movement is not understeer, it's called bump steer, which can indeed be dialled out in the manner you detail. Understeer is the tedency of a car to try and go straight on even when you are applying lock.

If you want to experience the difference, you should try my Legacy turbo back to back with my X4x4 when it's raining The scoob understeers slightly, but bumpsteers quite a lot (stock suspension). The Sierra understeers dramatcally, but doesn't bumpsteer (Bilstein/Eibach suspension, compression struts & blade ARB, BIG iron V6 in the nose)

In the scoob, a firm but delicate grip on the wheel as you go through the corners is all you need

In the sierra the understeer is countered by giving it a bootful and letting the 30F:70R torque split sort it out You think an MX5 looks scary on a wet roundabout

Leslie

Crispduk,

Bumpsteer is the situation where as the suspension is compressed, the geometry of the steering arms causes the steering lock to change such that the wheels toe in or out depending on the steering geometry. In a corner where the weight transference towards the outside and the subsequent depression of the suspension causes the outer front wheel to toe out, it is equivalent to steering away from the corner and the result is understeer. The inner wheel on the corner will also decrease the lock since the inner suspension movement upwards on the inner side will also move the lock on the inner wheel away from the corner in relative terms and will increase the understeer effect. The demonstration at Cheltenham during the setup quite clearly shows this on a classic Scooby.

As you say, by spacing the steering rack vertically differently in relation to the front wheels can be done to alter the effective radius of the steering arms and in the case of the Scooby it is possible to get rid of the change of lock with suspension movement entirely. The change in steering lock of each wheel is independent to the other one.

Some car manufacturers will deliberately engineer such geometry to make the car appear to be more stable in a straight line and less likely for the back end to slide out, although it will understeer as a result. They probably dont expect drivers to go round corners fast enough for it to make a significant difference and it covers any defects in their suspension design.

Apart from poor design causing adverse wheel camber changes while cornering, so called bump steer is the major cause of understeer.

Suffice it to say that after the bump steer was removed from my Scooby, the cambers were set up, and when I fitted solid rear anti roll bar links, the car's handling was changed out of all recognition into an outstanding machine in the wet or dry through the twisties.

Incidentally, several years on the racetracks taught me how to steer a car!

Les

CrisPDuk

But that isn't the only cause of understeer, understeer can be caused by the mass of the car acting against the steered wheels and trying to continue in a straight line. It can also be caused by pushing to much power through the steered wheels causing their effective grip to be reduced, thus again bringing the first point into play.

To use the example of my XR again, with the numerous suspension mods, it suffers from practically zero bump steer, but driven wrongly can still understeer like a pig because of the vast (the cologne V6 weighs more than my scoobs engine and driveline*) amount of weight over and ahead of the front axle.


*The old V6 may be heavy, but the noise it makes knocks spots of the scoob

Leslie

Well Crispduk, I never said that the only cause of understeer was bumpsteer such that the wheels toe out when the suspension is depressed, merely that it is a major cause.

Of course weight distribution has its effect and also the loads induced into the front wheels by drive power, centrifugal force on the weight of the engine as you say, badly designed front suspension geometry causing the wheel cambers to tend towards positive either due a combination of body roll and suspension movement, and the extra loads on the outside tyre due to the effect of the anti roll bar if fitted. But I still maintain that bump steer is a major cause. The cars weight acts on both front and back wheels of course and the tendency towards over or understeer depends on the combination of suspension characteristics and whether the car is front, rear, or all wheel drive and the percentage of torque applied to front or rear wheels through the centre differential in a four wheel drive car as well as the weight distribution of the car.

One of the really good demo's of an oversteering car was the original VW Beetle with its awful rear suspension which induces gross positive camber on the outer rear wheel in a corner due to a combination of body roll and the roll centre making the wheel lean outwards. It was even more breathtaking in the wet. The early Porches had a similar problem although not quite as dramatic which led to the well known "Zwischen" method of driving them with the use of a light or nil amount of power applied through the twisties.

I do have a bit of experience with suspensions Crispduk, since I used to design and build my own racers from scratch and although I could never afford to buy an engine from the star engine builders, there was no car that could out corner mine in our class of racing, including the works cars.

I used to find it fascinating to get the car set up in Gerards bend at Mallory which was long enough to be able to experiment with inducing under or oversteer with various combinations of power and steering lock.

Les

fwdnutz

stop whinging WINDYBOY! takes skill and presicion to do a roundabout Drift in traffic! thumbs up i say keep life interesting!

CrisPDuk

It all boils down to our interpretations of the term understeer Les, I was taught that understeer is what happens when a car drifts outside of the arc it's front wheels are creating, which as you say is usually down to poor suspension design and/or poor weight distribution.
In the scenario you are relating the car is following the arc described by the front wheels, it's just that poorly designed steering geometry is preventing the steered wheels from pointing in the direction indicated by the steering wheel. Two completely different phenomena as I was taught, but admittedly both can result in embarrassing bonnet/hedgerow interfaces when taken to their ultimate conclusions.

Speaking of ultimate conclusions, you omitted to mention the most notorious (and lethal) iteration of the rear engine/swing axle drive chassis concept, the Chevrolet Corvair*

*For those interested see 'Unsafe At Any Speed' by Ralph Nader, a book I would call an 'entertaining' read

Leslie

Its a fine point Crispduk and I agree with what you say about the arc indicated by the steering lock and the arc created by understeer.

I would say that "understeer" can be applied to both cases since the car is not following the intended arc. Either the front wheels have a greater creep angle due to loads on them or adverse camber causing a greater creep angle or even loss of grip completely, or as in the case I quoted, the effective reduction of steering lock due to the bump steer. The final result is the same really, the car does not steer where you were hoping it would. It all seems the same when you are hanging onto the wheel except that loss of grip is likely to be a bit more final in the eventual result! Difficult to counter as well.

So as you say its all down to interpretation.

Thanks for the warning about the Chevvy Corsair, did not know about that one, remind me to avoid it!

Les

CrisPDuk

Shall we just agree to differ on a question of semantics then

Doesn't stop me being envious of you having been in a Lightning & I haven't (yet).

Do a google search on Corvair and look how many Owners Clubs there are stateside Makes people who join the Austin Allagro OCs look almost sensible

There is one other famous owner of the automotive equivalent of Jennifer Lopez's ****: the Mercedes Benz Gullwing 300SL

Leslie

Yes of course CrisPDuk, we were saying essentially the same thing anyway looking back on it.

Yes I was lucky to get that trip so I had better not tell you about the trip with the Red Arrows at the Plymouth air display and where I was allowed to do some of the formation flying.

Les

CT_dunmow

In my opinion the guy (or girl, women are as filthy as men) is cool. I got the thumbs up the other day from some white van trio who witnessed the claasic scooby tail kick from a wet junction, they bloody loved it and incidently so did i!

Go on slag me off for that!

pheunos

Was it a dark blue Mk1 MX5 by any chance???

kingofturds

iTrader: (1)

CLSII

Ha ha ha ha ha....that made my night