Increased front wheel dia and mass - Steering issues?

I believe the switch (circa late 50s) from wire to magnesium was all about unsprung weight.

I curious to know if the directional change (steering forces) are significantly altered between lightweight smaller dia road wheels compared the large dia steel/wire  rims fitted with high profile tyres? If so, what is the theory behind the change in force, and if so, was that behind the move to smaller dia steering wheels? Thanks.

(edit) To add some clarity - hopefully! Thanks

Edited by Wirra, 28 August 2019 - 06:57.

I understand the switch (circa late 50s) from wire to magnesium was all about unsprung weight.

 

I curious to know if the directional change (steering forces) are significantly altered between lightweight smaller dia wheels compared the large dia steel/wire rims fitted with high profile tyres? If so, what is the theory behind the change on force permitting smaller dia steering wheels? Thanks.

'Just a tad confused. Are you referring to actual steering wheels (in cockpit) shrinking, or the simultaneous switch from wire to mag/larger to smaller diameter front (steering) wheels?

btw, were the downsized wheels by choice or by regulatory mandate? I didn't start following 'til '60ish and don't have access to regs back then......

In either case, I don't think the downsizing of the actual steering wheel was due to less effort in steering (I assume the effort went up with the advent of wider, more gripping fronts), rather, an effort in downsizing the cockpit size (thus less frontal area) and rapidity in steering.

Edited by jimclark, 28 August 2019 - 03:15.

I would think that tyre compound and width would have a much greater effect than wheel diameter/weight/profile.  Given those were starting to change at about the same time as wire wheels were phasing out, the picture may not be clear as to what was causing changes in steering forces.

btw, were the downsized wheels by choice or by regulatory mandate? I didn't start following 'til '60ish and don't have access to regs back then......

The concept of regulating wheel diameters in major racing categories is a recent one. In F1 the Tyrrell P34 used 10" diameter front wheels and Shadow built a CanAm car with unusual low profile tyres. Of course, the teams had to persuade somebody to make the tyres...

***

A bigger spinning mass has greater gyroscopic effects making it harder to steer.

Larger diameter wheels require a bigger separation from bodywork in order to turn through the same angle.

Rack and pinion steering replaced steering boxes as the standard mechanism.

There was greater understanding of the effects of castor, steering reversibility, offsets etc.

Ackerman vs anti-Ackerman. I'm not sure when the consensus changed, but anti-Ackerman was the norm by the early 1960s.

I raced automobiles through all of the time frame that you nominate in your question. I also fully understand the physics that you question.  An effort to answer your two questions follow.

Road wheel/tire dynamics first.  You have to realise that the smaller diameter wheels were always mounted with tires that had a height of between 80 and 90% of width.  As wheels increased in diameter the tire heights started to dramatically reduce.  This along with reduced wheel weights due to material changes meant that the gyroscopic forces stayed within small changes and were imperceptable.  These changes aslo coincided with dramatic increases in wheel width which came about with the understandings that along with tire construction changes resulted in the oval contact patches with the road going from n/s to e/w relative to n being the front of the car.  Tire mu factors went from circa .8/.9 to 1.4 very quickly.

This more than anything increased steering loads immensely.  The biggest factor change to counteract this was bringing caster settings more upright..  All other changes had little effect on sterring forces other than the advent of power steering for some classes of cars.

Steering wheel diameter changes next.  The smaller the wheel diameter the smaller the circumference the shorter distance hands have to move to get a fixed degree of steering action.  Also smaller diameter provides for more accurate feedback though the wheel.  All this results in faster and more accurate responses which provides better lap times.

Hope this all helps your understanding.

Regards

...This more than anything increased steering loads immensely.  ..

 

Okay, I follow that

...The smaller the wheel diameter the smaller the circumference the shorter distance hands have to move to get a fixed degree of steering action...  

I agree with that but wouldn't the force required be greater? 

...Also smaller diameter provides for more accurate feedback though the wheel...

I'm having trouble accepting that, in fact, I'd consider the opposite to be the case, Wouldn't a greater feedback rotation or resistance give better feel of what was happening?

 

Steering wheel diameter changes next.  The smaller the wheel diameter the smaller the circumference the shorter distance hands have to move to get a fixed degree of steering action.  Also smaller diameter provides for more accurate feedback though the wheel.  All this results in faster and more accurate responses which provides better lap times.

 

Too small a wheel is going to be harder to turn now? Making those 'better laptimes' harder to reach. Don't forget the organic materials when engineering a car. 

Too small a wheel is going to be harder to turn now? Making those 'better laptimes' harder to reach. Don't forget the organic materials when engineering a car. 

It's definitely an issue of preference. Most drivers like a certain amount of weight in a wheel, but it's easy to go overboard. If we start at a 1975 Plymouth, which has absolutely zero steering feel, and then increase it linearly, we'll find a 'U'-shaped curve. Initially, it will provide more information and more control to the driver. Taken too far, it will act as a type of steering damper which resists changes in steering angle. Speeding up the steering will also make the high-speed steering sensitivity so great as to become unstable, particularly once the lash in the system will be a meaningful percentage of the total necessary steering wheel movement.

To revert to the first point raised in the OP (wire wheels vs. alloy), not only unsprung weight was a factor. Alloys are stiffer. In the case of Vanwall, both were used, even on a single car to suit the drivers preference, as seen here on the Zandvoort grid:
 

http://www.grandprix...es/vanwall8.jpg

On a general note this whole tire characteristics business is tiring .

A personal anecdote from daily driving my Triumph 2500TC: when changing from the original 175 x 13 tires to the fashionable 185/70 x 13 "wide" tires, I was surprised to experience less force required for steering. My explanation was the torque required to overcome the flexibility of the original tires (to twist the walls).

And yes, then I found the smaller steering wheel diameter from the cars' younger sis, the Dolomite, perfectly suited and a direct fit. The car still has the wheel (and 14" rims from a Stag and a rare aftermarket brand, mounted with slicks for track use).

 . . A bigger spinning mass has greater gyroscopic effects making it harder to steer. . . .

But larger diameter wheels spin slower reducing gyroscopic effects.

  Slightly off the subject maybe - but  the original  Ford GT 40s  used wire wheels (and I think raced at Le Mans with wire wheels)  whereas the car they were developed from (the Lola GT Mk.6) used alloy wheels.   Apparently Ford management thought a proper "sport" car should have wire wheels.  

Edited by Kelpiecross, 31 August 2019 - 05:06.

I have said this before, wire wheels are great flexible flywheels. There is heaps of pics around and you can see the wheel flexing, far more on the bigger dia sedan wheels.

Wheel dia came down on both road cars and racing cars and tyres got wider. Full size passenger cars went from 16 down to 13"and 14" by the early 60s Then started to go up again from the late 70s to the stupid 18 19 20 21" sizes  around now.

Most racing categories have  either made it or followed it. But F1 has had 13" wheels for decades,, oh and Nascar still use 15" steel flywheels. Though it seems they are a little lighter now.

For a racing car and maybe small capacity Sports Car probably 15" is the go. And probably a 25" tyre. Bigger sports cars and many tin top categories have seldom got bigger than a 27"  18" As a Sports Sedan runner I started off with  around 21" high13" rims and tyres, growing to rears at least 23".then went to 15" and later to 16" as 'fashions' changed, and as brakes got bigger. My car eneded up with 13" rotors inside 16" rims. Brakes were in effect GpA Commodore. Now most use 18" rims with it seems some with 14" rotors as do the Supercars. Though the tyres used are generally Sports Car tyres [on Sports Sedans]

With racing cars most have used 13" since the60s, some 5000s used 15". Unsure of the S5000s though I suspect they too are 15".

F1s though going to a bigger dia rim will have to build cars with suspensions!! Making them use tyres for one race too would be a very good idea. Not 7 lap tyres!

  Slightly off the subject maybe - but  the original  Ford GT 40s  used wire wheels (and I think raced at Le Mans with wire wheels)  whereas the car they were developed from (the Lola GT Mk.6) used alloy wheels.   Apparently Ford management thought a proper "sport" car should have wire wheels.  

I think that's a tremendous leap. It's much more likely they just used what they thought was the most reliable.

Lee pretty much hit the nail on the head. Wheel sizes are largely dictated by exterior concerns. Tires and brakes are probably the 2 biggest.

But larger diameter wheels spin slower reducing gyroscopic effects.

Only if the tire radius is larger. Often the rolling radius stays similar and we lose is sidewall height.

Then the question becomes - for a chosen rolling radius, tyre width and load rating:

 - Which is lighter - large diameter rim with low profile tyre or small diameter rim with tall tyre?

 - Which has the greater rolling inertia?

(Sorry - that's two questions isn't it? Darn - three now.)

My money is on the small rim, tall tyre.

I suspect you are deep into second order effects there, but I'm too lazy to work it out. Rubber isn't that much lighter than aluminium.

Then the question becomes - for a chosen rolling radius, tyre width and load rating:

 

 - Which is lighter - large diameter rim with low profile tyre or small diameter rim with tall tyre?

 - Which has the greater rolling inertia?

 

(Sorry - that's two questions isn't it? Darn - three now.)

 

My money is on the small rim, tall tyre.

Honestly, it's not a question which is even often asked. I suspect it would vary depending on the rims/tires involved. In most scenarios the wheel size (often the wheels themselves) and tires are specified in the rules.

With a small rim, the tire sidewall needs to be stronger. Like Greg said, rubber isn't much lighter than AL.

I seem to recall that Moss raced te Vanwall for a while with alloys on the front and wired on the back, saying that he preferred the "feel."

Edited by Bloggsworth, 05 September 2019 - 18:29.

I seem to recall that Moss raced te Vanwall for a while with alloys on the front and wired on the back, saying that he preferred the "feel."

I have read that as well. Could the stiffness of the wheel or the probably better cooling of the brakes (with wires) been the reason?

Check the photo Cavalier53 linked to in post 9. The wire wheels were on the front and the alloys on the rear. This became the standard fitment for Vanwall during the 1958 season, as the drivers generally preferred the steering ‘feel’ they got from the less-rigid wire wheels, and because (as stated above) front brake cooling was better with the wires.

I'm old and bits are, one by one, falling off, including parts of my memory - You are right.

Check the photo Cavalier53 linked to in post 9. The wire wheels were on the front and the alloys on the rear. This became the standard fitment for Vanwall during the 1958 season, as the drivers generally preferred the steering ‘feel’ they got from the less-rigid wire wheels, and because (as stated above) front brake cooling was better with the wires.

There could be so many differences between the alloy and steel wheels that it's tough to know *why* they used what they did. The deflection in a wire wheel would have probably been an influence. It's entirely possible there were slight different rim widths or offsets involved which were meaningful.

Several years ago I was running a GT1 and the tire guy accidentally mounted a front tire on a rear rim, which we put on the car without knowing. The wheels had the same offset and the rear was only 10-15mm wider. It gave a big(unexpected) gain in front grip and we ended up working the whole setup around using 'rear' rims on all 4 corners.

Wasn't that the idea(of several) behind the Acura LMP1 car(the Wirth one circa a decade ago) massive front tires, basically rears?

And I want to say when Tyrrell did their annual "well let's try something wacky" at Hockenheim(when it was long straights) they put fronts on the rears for less drag but Goodyear got a bit squirrely about it. 

A few years ago, early in the Pirelli era, there was as thing of the teams running their tires backwards? Like, lefts on a right rim and etc. Something about the construction or seam direction or something but there was a difference between whether a tire was faced in the 'correct' direction or not. I never entirely understood what difference it made, performance or feel, or how they even figured that out. Did someone go out on a badly mounted set one day and go "holy **** this is cool" ?

If memory serves, yes, that was the Acura move. I think it was the smaller prototype at the time, though? The equivalent of an LMP675 or LMP2. I also think that Arrows put Bridgestone rear tires all around at Hungary with Damon Hill (1998?) and were damned fast. That was a while ago, so I could be wrong.

Maybe we should have tried using rear tires all around. Our SNAFU was just the rim. We were still on front tires. A wider bead-to-bead changed the tire characteristics enough to have a real effect on handling. It was damned impressive.

I don't know about Pirelli's, but Goodyears used to be notorious for showing a pronounced tread splice if you ran them the normal direction and it'd rip the tread off if you went backwards. They were just absolute garbage. Lord help them if they aren't using Dunlop's IP for WEC. I'll find out here shortly.

Pirelli has changed their tire construction due to their time in F1. They now wind the rubber on the tire carcass with a ~1mm continuous strip of rubber like thread on a spool. There is no tread splice. It's pretty clever.

Oh my bad, I thought it was a rear in totality on the front. Your version is even wilder. Was there an explanation why the tire co didn't go with that format originally? 

After some digging, here's Hockenheim 1996 I believe. 

Loving the front A-arm too. 

And for anyone wondering about back-to-front Acuras, apparently they got out ahead of what became standard practice in LMP1. 

https://sportscar365...ire-revolution/

Oh my bad, I thought it was a rear in totality on the front. Your version is even wilder. Was there an explanation why the tire co didn't go with that format originally? 

 

 

That was just the original design. Wheel sizes were actually chosen for a different tire manufacturer, so maybe that played into it.

It was an ALMS GT1 car. I had done a different splitter and dive planes for that weekend. The wheel messed that test up. The track has mostly fast corners to the right and slow ones to the left. The drivers had said the car had better front grip, but when we had them do track maps, they specifically mentioned it in the slow lefts and said that was a bigger deal than the changes to the right. I thought that was really odd. Then the tire guy comes into the office and tells us he accidentally ended up with a rear wheel/front tire on the RF corner. The aero stuff I had done, which was a lot of work and money, was only a moderate gain. The wheel, a complete accident, was a really big deal. When we put them both together we had a better car.