Renault 5 Turbo Owners

In the states FWD drag cars are running wheelie bars to keep the front end down. I bet the first FWD racer who did that just about got laughed off the track.

Fraser

Reply to
Fraser Johnston
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Reply to
Nom

Rover 600 !

Yes, really !

Reply to
Nom

My car !

Reply to
Nom

Rover 600 : "What went against the 600, though, was the overt Honda influence in the engineering of the car ? as was demonstrated time and time again in the past, Rover were not interested in producing a car that used wishbone suspension ? it allowed for too little wheel travel, which resulted in the inability to deliver a supple and well-damped ride"

Rover 800 : "Because of Honda?s insistence that the car would have a low scuttle which led to a low bonnet line, traditional McPherson struts would not fit, so a complex and expensive double wishbone arrangement was settled on, but in true Honda tradition, there was only a limited amount of wheel travel available"

Why do you think they're a good thing ?!?!

Honda use them in lots of their cars - none of which are renowned for their handling prowess. Same applies to the SAAB 900.

Peugeot use them in almost none of their cars - most of which ARE renowned for their handling prowess (complete with rear torsion bars).

Reply to
Nom

are you sure?

Reply to
Theo

Yep.

Fully-independent double-wishbone suspension, both front AND rear. It's a '94-'97 Honda Accord, remember.

The TI gets dual-chamber gas shocks too.

Reply to
Nom

Yep, remembered Honda's double wishbone fetish the other day. They don't bother with them so much now AFAIK.

They're the best suspension setup you can get. That's why almost every out and out sports car and race car has double wishbones all round. They cost and take up a lot of room, so they don't get used in many cars. Take a look at the bootspace in a Jag XJ compared to one of its rivals with Multilink suspension.

Handling != Grip. There's also the fact that Pug spend a lot of time on their chassis setup, make their own dampers etc., and tend to make cars that will oversteer if you want them to. Which is what makes the motoring press happy :).

Reply to
Doki

In article , snipped-for-privacy@jcis.com.au spouted forth into uk.rec.cars.modifications...

He did until they posted their first time.

With the wheelie bars taking up any movement as the front wants to rise, they can run the suspension softer at the front, for less chance of wheelspin, but without it turning into a soggy unmanageable pile of whatsits.

Reply to
MeatballTurbo

So why doesn't my Rover 600 have excellent suspension ?

The TYPE of suspension is meaningless - it's all about the setup.

My previous Pug 405 had noticably better ride and handling, when compared to the TI - and it used Struts front, and Torsion-beam rear.

Double bad-thing then !

I'm not saying it does. But the Hondas and SAAB, nor my Rover 600 or the Rover 800, don't have particularly good grip either :)

Exactly. Double-wishbone is no better than a strut setup on "normal" cars. As Peugeot have proved, it's perfectly possible to make a strut-setup better than a wishbone-setup (Honda). As bonus, the Pug's have a better ride too.

Reply to
Nom

We're talking about what a car can manage in a flat out 0-60. A pretty heavily modified one at that. McStruts will always give you a camber change as the suspension loads / unloads, whereas double wishbones can be set up to give you a lot more grip. If you built a car and tried every kind of suspension you could think of out on it, and spent ages setting each up, double wishbone would come out tops.

If you're interested in lugging wardrobes and pinching pennys, yes. If you're interesting in making a properly fast car, who gives a toss?

Suspension is 99% down to how well it's setup. Double wishbones are shit in your car. In a Jag you get a smooth ride and a proper suspension setup.

Reply to
Doki

Precisely my point !

Reply to
Nom

Not quite true. The book, Mechanics of Pneumatic Tires (commonly referred to as the "tire bible" in vehicle dynamics circles), has a lot of measured data from tests included on this, something that I've yet to see on any of the websites perpetuating this view along with those derived largely from it. Rubber is a special animal and doesn't follow standard Coulomb friction "laws." The book has an entire chapter specifically on that subject. Effective friction coefficient appears to be quite dependent on contact patch area. The book breaks up tire friction into about five different areas with their own mechanisms and dependencies. Granted, grip is still not understood very well and no complete theory exists to describe it all that I'm aware of, but one major part of that friction is extremely sensitive to contact patch pressure. One chart shows mu varying from about 0.7 at 20 kg/cm^2 to over 2.5 at around

2.5 kg/cm^2. That's only one part of the total effective mu of course, but there's definitely a dependency on contact patch pressure. This particular contributor to effective friction coefficient may be the largest (the particular friction force, not the contact pressure per se). I.e., contact patch pressure may very well be a first order effect but I have not read anything that explicitly states this as fact.

Regardless, contact patch pressure does influence effective friction coefficient.

This is approximately true, but it is not true enough to make the common generalization people make that contact patch area is independent of tire width. In an aircraft tire with thin rubber and little structural rigidity, the air pressure accounts for about 97% of the contact patch size (according to the book), so with an aircraft tire that's highly toroidal in shape with a nearly circular cross section you could say that contact_patch_area = weight/tire_pressure and be very close to reality. In that case you could say widening an aircraft tire might not effect the contact patch area significantly (I haven't seen a study on that though).

With automobile tires that picture it's not very accurate however due to their relatively flat static contact patch and heavy shoulder region. The book in two places states that air pressure generally is on the order of 85% of the support. However, even then, other data shows that the relation contact_patch_area = weight/tire_pressure is not very accurate. This is shown in charts where vertical deflection and contact patch length (and therefore area) do not change at anything approaching a 1:1 ratio as load is increased.

I.e., with the contact_patch_area = weight/tire_pressure formula everyone loves to quote as if it were a proven fact (it's only true for soap bubbles and balloons basically), if you double the load on a tire and keep the air pressure constant, the contact patch area (length) will also double. The book shows several graphs and charts of data from tests that show this is does not provide a very accurate picture at all in the case of an automotive tire.

Most of the data shows vertical tire deflection versus contact patch length. Vertical deflection over a range up to 2 inches (except at extremely low deflections) is nearly linear with load on all tires shown except one or two. I.e., if you double the deflection in that range you also double the tire load. Meanwhile, the contact patch width is shown also to be nearly constant (it's simply the tread width +/- 1 or 2mm at the most, even in a rapidly spinning tire.) So one can look at the length to determine how much the area changes. I.e., if one doubles the vertical deflection one is also doubling the load. If the contact patch length also doubles then so does the area.

So with this data it is possible to verify whether contact_patch_area = weight / tire_pressure. I'll supply some of that data if you're interested.

In case there is disagreement on that, there is also a chart showing actual gross contact area versus tire deflection for five different tires. Here is my best attempt at reading that data off the graph:

8.00x 14 bias ply Vertical Deflection(in.) Contact Area (in^2)

0.5-----20

1.00---30 1.50---42 2.00---50

If the relation contact_patch_area = weight / tire_pressure were correct and one were to assume that 0.5---20 was the initial state, the remaining data along with the percentage error would read:

0.5-----20 ---- (original test data--100% accuracy) 1.00---40 ---- 75% 1.50---60 ---- 70% 2.00---80 ---- 63%

They also tested a tire that was 0.5 inches narrower:

7.50x 14 bias ply Vertical Deflection(in.) Contact Area (in^2)

0.5-----21

1.00---35 1.50---45 2.00---53

Interestingly enough the narrower tire in this case had a larger contact patch over the entire deflection range than the wider tire did. If you compare different tires you will find tendancies that are not predictable and therefore this data can not be used to simply say "narrower tires have bigger contact patches" of course. Anything can happen. Much depends on the tire's construction, but this stuff is clearly much more complex than contact_patch_area = weight / tire_pressure.

For instance, Avon published data on their F-3000 tires. The vertical deflection on the front tire at constant load started low at 18PSI, then rose as air pressure increased to 24 PSI. However, at 28PSI the tire centerline actually sat lower than it did at only 18PSI. In other words, this particular tire had a larger contact patch at 28 psi than it did at 18 psi. (Reference provided upon request.)

Anyway, it appears from the above data that air pressure alone is not a reliable indicator of contact patch area at all in the case of automotive tires. The accuracy of the equation (contact_patch_area = weight / tire_pressure) ranged from 75% down to 63% and certainly did not change at a

1:1 ratio with load. (The equation is a good assumption for aircraft tires, however, due to their shape and balloon-like construction).

Some calculations done on the front versus rear Avon F-3000 tires showed that indeed, the rear tires quite likely had a larger contact patch. The area was not actually measured, however, but instead calculated according to vertical deflection which was measured.

That might be true and to me makes sense as the frictional power per unit area of a wider tire at a given force level would be lower, resulting in less heating. I haven't seen data on that nor am I privy to compounding, but it should not be ignored that contact patch pressure *is* an important part of friction, and tire width (among many other things) can definitely influence contact patch area. Contact patch size and pressure are not simply a two term function of air pressure. At least, they are not tied closely enough to make the common generalizations echoed in your post (I used to preach the same things. Unfortunately I did it without actually looking at any measured data as most people do).

It might be argued that one could simply use 85% (or some other constant) to modify the equation. In one reference in the book this was indeed done. However, that does not give an accurate enough impression to make these generalizations because the slope of the contact area or contact length versus tire deflection (load) in all data in the book clearly shows that area does not double when load doubles, etc.. Additionally, air pressure changes do not effect the contact patch as much as the popularily (and mis-)used equation describes either.

On the subject of wide tires, the five tires shown with actual contact patch area versus tire deflection (load) vary quite a bit in width. Tire construction plays a large part obviously. The 7.50 inch wide tire had a greater contact area than the 8.00 inch wide one did. There is no information on profile or anything else other than the rim size. But there was actually a pretty large difference in contact area between the two, and it went the "wrong way."

There is also a 5.90x15 bias ply tire shown. This is significantly narrower than the two aforementioned tires. In an effort to show an example of how contact area might change with tire width, the contact area for the 8.00x14 bias ply tire is shown in the third column, along with the percentage of area for the narrower versus the wider :

5.90x 15 bias ply Vertical Deflection(in.) Contact Area (in^2) Percentage(%)

0.5-----14----20----70%

1.00---23----30----75% 1.50---30----42----71% 2.00---40----50----80%

Note that the 5.90 inch tire is 74% the width of the wider tire, and the contact area is also 74% as large on average. An exact match in this case, but this is not enough to make any generalization other than it appears that tire width indeed does effect contact patch area. I.e., wider tires DO have bigger contact patches. More analysis would have to be done on that. I did some analysis on the Avon tires and the wider tires also appeared to have a larger contact patch, but the area change was not proportional to the width change as it is here. I.e., the contact patch area appeared to grow by less than half the width change. Additionally, the 7.50 inch tire was probably more similar to the 8.00 inch wide tire (same rim size at the very least) and had a larger contact patch, so clearly both scenarios are possible. Additionally, pumping up the front Avon tire to 28psi caused a larger vertical deflection than it had at 18psi, so anything is possible.

The basic trends in data I've studied so far do appear to be that increasing tire width increases contact patch size. In addition, contact patch pressure does indeed have a tendancy to increase grip. So the view that increasing tire width does nothing but change the contact patch shape, and not the total area, appears to be inaccurate. So there are likely to be two reasons that, very generally speaking, wider tires tend to have greater grip than narrower ones:

  1. The contact patch area is indeed larger, although it probably does not increases by the same ratio as an increase in width does (I.e., double the width and the contact patch gets bigger, but it doesn't double in size right along with the width.) Because of the larger contact patch area, the patch pressure is indeed lower which would tend to increase friction.

  1. Wider tires are likely to be constructed of a different compound to take advantage of the lowered heating at a given force level due to the greater surface area.

People argue about these two points, but it is likely that both are at play here. I do not know nor have I seen any information that shows which effect would generally be stronger. Friction in tires is not very well understood. People perhaps should note that if even tire engineers in the highest levels of Formula One are not absolutely sure how tire grip works, they might not know either, and a formula like contact_patch_area = weight / tire_pressure, which has just been shown to be grossly inaccurate, can not simply be assumed to be true and subsequently used to theorize much else about tires at all.

Todd Wasson Racing Software

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Reply to
J. Todd Wasson

Definitely. Now they laugh if you don't run wheelie bars.

Fraser

Reply to
Fraser Johnston

Top notch post there. A little difficult to digest in one sitting, perhaps, and not nearly enough insults for U.R.C.M, but damn fine nonetheless.

Reply to
Albert T Cone

Thanks :-)

Todd Wasson Racing Software

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Reply to
J. Todd Wasson

In article , snipped-for-privacy@jcis.com.au spouted forth into uk.rec.cars.modifications...

I've seen some of the "import nights" stuff on Men and Motors, and them Civics and CRXs don't half kick some arse when they run the quarter.

Reply to
MeatballTurbo

They aren't exactley standard road civics/CRXs with cheap standard suspension setups.

Reply to
MeatballTurbo

"Kubo, from Chino Hills, Calif., who recorded the quickest run in Pro FWD history during qualifying on Saturday (8.028 seconds), backed-up the record performance with a winning final round run of 8.055 at 180.79 in her APC Saturn Ion Quad Coupe. The victory over defending category champ Nelson Hoyos was Kubo's fifth career win and second in a row dating back to the finals in Pomona in 2003. "

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And that is just for one of the governing bodies.

I think there is also the IDRA series.

Reply to
MeatballTurbo

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