Best Track Set Up

[Baz 421]

Yep, so what the wider rear track does in this example is reduce weight transfer to the front. That means more grip at the back.

 

More grip at the back = less likely to oversteer!

[Batfink 201]

Toffee. A set of wheels doesn't make that much of a difference. IMO a 1.6 with either wheels still handles the same.

 

And on the snaky back end under braking, i'd hazard a guess something else was awry.

 

Certainly i've experience many a snaky rear-end under heavy braking on 1.9's, down to the common faulty compensators, but this is no where near as common on a 1.6.

 

When I swapped my car from 14" to 15" speedlines the difference through the steering was significantly noticeable. The car felt more grippy with 15's but turn in was not as nice and the car did not feel as nimble. Thats from driving one set, swapping and then going straight out again.

[DrSarty 90 1 Cars]

Fascinating conversation.

 

I would reitterate the point that the driver's style/antics/courage/guts has a lot to do with it, so the 'best' suspension set up for either one track or one driver may be incompatible with another. You really have to get out there and find what suits YOU.

 

I seem to remember a Mitsubishi Galant driver in 'WRC', possibly Tomi Makinen (sp?), who drove a car that almost everyone else struggled with; it was set up solely for him and his style.

 

Food for thought perhaps. Ultimately you may find that YOU are quicker on standard suspension, or possibly something that someone else finds downright dangerous.

[Cameron 16]

Yep, so what the wider rear track does in this example is reduce weight transfer to the front. That means more grip at the back.

 

No, the weight transfer is increased at the rear, reducing grip. The reduced weight transfer at the front increases front end grip.

What you're looking for is for the tyres to be as evenly loaded as possible, for the reasons I explained earlier about tyre behaviour.

[Rippthrough 98]

No, the weight transfer is increased at the rear, reducing grip. The reduced weight transfer at the front increases front end grip.

What you're looking for is for the tyres to be as evenly loaded as possible, for the reasons I explained earlier about tyre behaviour.

 

 

Why exactly would a wider rear track increase weight transfer at the rear?

[Cameron 16]

Also, I think that the roll characteristics of trailing arm suspension (that camber increases +ve in roll) reducing the contact patch area coupled with the increased load on that tyre will reduce rear end grip even more. This is where the stiffer springs come in though, as body roll and therefore camber change is reduced.

[Cameron 16]

Why exactly would a wider rear track increase weight transfer at the rear?

 

Can't be bothered to explain again! Have a look back a few pages.

[Rob Thomson 6]

No, the weight transfer is increased at the rear, reducing grip. The reduced weight transfer at the front increases front end grip.

What you're looking for is for the tyres to be as evenly loaded as possible, for the reasons I explained earlier about tyre behaviour.

Nope, because you've got a wheel in the air and therefore one rear tyre is taking 100% of the rear load in both examples. But the knock-on is less weight transfer at the front, which probably does mean more front grip.

 

My other point is that your diagrams show more load remaining on that one rear tyre (ie. less weight transfer to the front). Of course the mass of the front/rear ends of the car don't change, so that weight transfer affects the handling balance (in this case in favour of understeer).

[Baz 421]

What you're looking for is for the tyres to be as evenly loaded as possible, for the reasons I explained earlier about tyre behaviour.

 

Boll0cks!! Why? It does not matter one iota what the inside rear is doing, whether it's on the ground or not means FA, there's next to no load on it either way, that's just physics, so if it lifts off the floor, who gives a ....! Under cornering that wheel isn't helping, so why are you looking for it to be on the floor? If you're trying to make a setup that keeps all 4 wheels on the floor, you're sacrificing something else for the compliance needed for that, ie. bodyroll, or, more importantly, ADHESION! (Grip!) Which to me, is not sacrificial! Where as lifting a rear, unimportant wheel, is!

[kilauea 7]

From my limited knowledge, I'd say this four wheels loaded theory requires a s*it load of downforce too. Which your not going to generate in a 205 (without making it much faster and bolting a dirty big wing on the top!).

[Cameron 16]

Nope, because you've got a wheel in the air and therefore one rear tyre is taking 100% of the rear load in both examples. But the knock-on is less weight transfer at the front, which probably does mean more front grip.

 

My other point is that your diagrams show more load remaining on that one rear tyre (ie. less weight transfer to the front). Of course the mass of the front/rear ends of the car don't change, so that weight transfer affects the handling balance (in this case in favour of understeer).

 

You're right actually, in both cases the inside rear wheel has been lifted so you are actually gaining a slight bit of load on the outside tyre. Weather that's a good thing or not depends on the camber angle when you've lifted the inside wheel.

 

And yes, you should get more front end grip from a wider rear beam.

 

oll0cks!! Why? It does not matter one iota what the inside rear is doing, whether it's on the ground or not means FA, there's next to no load on it either way, that's just physics, so if it lifts off the floor, who gives a ....! Under cornering that wheel isn't helping, so why are you looking for it to be on the floor? If you're trying to make a setup that keeps all 4 wheels on the floor, you're sacrificing something else for the compliance needed for that, ie. bodyroll, or, more importantly, ADHESION! (Grip!) Which to me, is not sacrificial! Where as lifting a rear, unimportant wheel, is!

 

No, it doesn't work like that. As I explained earlier the relationship of grip to load isn't linear, I can't find a decent graph or diagram to show but it looks like this:

 

 

There is a key down the right hand side showing the colours that represent different loads, ignore all the other stuff, just focus on the shape.

 

You can see that as load increases, grip increases. BUT the relationship isn't linear (as I keep saying), so if you double the load you don't double the grip! What this means is that if you have one tyre carrying all the load it isn't as effective as both tyres sharing the load. The key point is that tyres are most efficient when lightly loaded. If you had the inside wheel on the floor, even if it was only very very lightly loaded, you would still have more grip on that axle than if it was lifted in the air.

Edited December 31, 2009 by Cameron

[Rippthrough 98]

Can't be bothered to explain again! Have a look back a few pages.

 

That's increasing diagonal weight transfer more than anything though - because of the now even stiffer rear roll rate compared to the front - that extra load on the tyre isn't necessarily enough to offset to reduced camber change induced by that stiffer roll rate, so we can't definitively say that means less rear grip without modelling the whole tyre and suspension system as one...which means we're probably back to a touch more understeer as well as the bit induced by the extra weight transfer...

Edited December 31, 2009 by Rippthrough

[Cameron 16]

Yeah, you're absolutely right it's very difficult to say without modeling everything. That's why I was only questioning the wider rear track. If the increased roll rate were enough to offset any negative effect caused by the wider track then surely having the same roll rate on the standard track width would be even better?

 

This is where I've been mis-quoted, annoyingly. I'm not questioning the spring / roll rates, I'm only questioning the track width.

[Rippthrough 98]

But to get the same roll rate on the standard track you'd have to run stiffer torsion bars, which would bring in problems of its own, higher peak forces on the tyre carcass for one.

[Cameron 16]

True, but surely it's nothing that would make the tyre dangerous as the increase is only slight. I mean people are running huge anti-roll bars without killing tyres.

[Rippthrough 98]

Oh it's not dangerous, it just reduces the grip on anything but billard-smooth tarmac, as you can see by your tyre loading graphs up there

[andyjstone 5]

I bet evo rich wishes he never asked the question

[Cameron 16]

I'm starting to wish I never said anything..

those tyre loading graphs don't show anything about road surfaces though.

[Rippthrough 98]

I'm starting to wish I never said anything..

those tyre loading graphs don't show anything about road surfaces though.

 

They show what happens if the peak force on the tyre carcass is higher....

 

 

Cornering is anything but steady state, the best mental image you can have is of everything vibrating at different rates....

[evo rich 0]

I bet evo rich wishes he never asked the question

[Cameron 16]

It isn't so much to do with the carcass though, it's more the behaviour of the rubber isnt it?

[Rippthrough 98]

It isn't so much to do with the carcass though, it's more the behaviour of the rubber isnt it?

 

 

Well, the force has to go through the carcass...