Low Versus Higher Profile Wheels
by Lorne Goldman

For the last two decades, tyre sidewalls have been shrinking and rim diameters growing. In other words, the cushion of air between the harder parts of your Morgan and the road has been reduced. This has affected the handling and comfort of all cars, but none more so than Morgan classic, with their simple vintage suspensions and their use of a treasured traditional design made for other tyres.

How did this all come about? Examining it gives clues to the ever-increasing expenditure of newer Morgan owners with suspension and steering "upgrades"..even as, for the most part, roads worldwide have improved in the last few decades.. 

What a Racer Needs in Tyres

It is race cars that began this movement in the low profile direction. But automobile racing is a specialized sport, done on specialized surfaces, a specialized environment, using specialized cars specifically altered and/or designed for this game and venue. With few exceptions, racing surfaces are made and maintained to a much higher and consistent standard than a road going vehicle encounters. As well, comfort is a much lower priority in sport than it is in travel.These elements mitigate the need for race track suspension. The primary goal of racing is to win and all other considerations, such as safe and enjoyable transport are secondary..even forced upon participants by rules.  Lastly, the support infrastructure is meters away at all times. In these odd circumstances, the few pros of low profile tyres make sense.

But to emulate something that is functional in another environment only makes no sense...especially when the car that adopts them is not redesigned to accommodate them. I am reminded of the first space-age days of the 1950/60s. The exitement, then about rockets more than race cars, spawned a trend to exaggerated car fins, though they added weight, altered aerodynamics, and very dangerously added to impact risks without providing any compensatory functional benefit.  Happily, the Factory avoid these fins, even at the peak of the rage for them. I imagine it was less sensitive to buyer tastes in those days.

Alleged Pros
to low profile tyres
   Improved steering response
   Higher top end speeds and mileage  from lower rolling resistance
   Improved sidewall stability under braking
   Room for bigger brakes
   Less camber distortion when cornering.
 
I used the word "alleged" to wan the reader that there are articles that refute many of these factors. But the needs of a road driving person are far more complex than that of racer. Comfort..the absorption of road anomalies that racing compeitors do not need. As well, a road driver meets a far wider variety of road surfaces than a racer ever will, without the nearby support or skills the racer has at his/her call.  
 
Cons
to low profile tyres
   Less of a progressive breakaway (tyres break away more suddenly
   More susceptable to sidewall damage and tyre failure

   Added unsprung weight
   More susceptable to tram tracking
   Harsher less confortable ride 
   More critical to tyre pressures
   More road noise
   More unsprung weight. In fact, both the wheel and the tyre weight theoretically increases. I have not checked this out, but a dealer can do so for us.

Anyone who imagines even 5mm+ less air does not make a NOTICEABLE difference is dead wrong.  And Morgans have lost  5 times that or 25mm of air cushion between rim and ground!  No wonder new car owners are fixated on aftermarket  "upgrades".  

WATCHPOINT: Easy to confirm if there is a Morgan dealer or friend around with another compatible (suspension and tyres) Morgan with a different rim diameter. Simply take your car on a mildly anomalied road for a short test drive. Then swap wheels and test the different combol on the same drive. Which was better? Frankly, you will understand all you need to know after a few meters, not kilometers. 

So why did the automobile market move in this direction? Aesthetics and a lack of understanding of the consumer is the only answer. 

But why did Morgan followed in this direction? They have not compensated forthe loss of air with a redesign of the car. (Aside from ever wider wing widths, the infamous fetish of Charles Morgan, the functional effects of which require another article) whether by instinct or wisdom, the company has steadfastly refused to alter the perceived design dynamics which have carried the car 'til this point from the mid-1930s. Yet, illogically, Morgan HAS moved from 14 inch to as much as 17 inch rims with its most powerful Classic models while keeping the same overall diameter..putting themselves between a rock (the needed traditional design) and a hard place (modern customer tastes and the road).



I have attempted to offer a visual of the changes in the adjacent diagram. (Those who argue with my iffy artistry need only precisely compare its tyre bands/ side walls and rims diamters to confirm.)
Yet during most of this journey, (saving the last example which has a wholly non-Classic chassis, braking and suspension), the overall wheel/tyre diameter has not changed and neother has the design of the car, its steering or its suspension been altered to meet the challenges. Merely the ratio of air to metaI is altered. Curiously. the recommended factory tyre pressure remained the same throughout these diameters. Admittedly, increasing the pressures would better protect the rims, at an additional risk to the driver safety and comfort.

What does it mean? Automobile wheel air to metal ratios are not (yet) a subject of legislation.  And with former skills levels and autombile understanding declining in the community, the importance of aesthetics to sales has increased.. The complaints and warnings on the internet about low profile tyres on other more knowledgeable forums is growing.  Examples are given often. Questions why earlier models  of many marques were more comfortabl are asked more often. A "google" reveals scores of such complaints. In fact, this article was spawned by them. I merely recognized their issue in the complaints I receive on the GoMoG Help Line. It is easier to make a Morgan with smaller rims handle well and be comfortable than it is with the newer models.

Sizing

When selecting a wheel/tyre combo with any existing car you have, you should always select the size with the closest to factory overall wheel/tyre diameter, regardless of the rim size. You can use a calculator like this one to calculate the difference in overall diameter from your stock wheel to the new one. I have found that staying within .8% of the original is good. I like to stay with 0.3% or less whenever possible. For Morgan Classic owners, this calculation is made easy by simply looking to earlier years with their smaller rims and adopting their tyres specs as well.  

The tyre size you use with whatever wheel diameter you pick can be juggled with a little bit to achieve the right overall diameter.

Sidewall & Overall Size Considerations

With wheel diameter increases come a decrease in sidewall size in order to maintain the same overall tyre+wheel combo size. It's important to stay as close to the stock tyre+wheel combo size as the overall wheel size affects gearing.

Smaller wheels improve acceleration at the expense of top end, and taller wheels decrease acceleration while theoretically increasing top speed (though in practice top speed is limited by power and drag long before tyre size..so for most cars, and definitely for Morgans, this factor is irrelevant. Increasing tyre size usually also hurts top end acceleration and top speed as it decreases the engine's ability to overcome the air drag holding the car back).

In any case, making the overall wheel/tyre combo taller or shorter will again affect suspension geometry. I don't advise this, especially for a road car. You can change it a small amount without any real adverse effects but try to stay as close as possible when choosing a new  combined size.

Additionally, the big "gotcha" with sidewall size is that the smaller the sidewall, the less protection your probably expensive rims will have from the inevitable pothole or road debris. If you keep the same wheels with lower profile tyres, the only route to more protection for your rims is increased pressure, which will prejudice safety, handling and comfortt, thusly prioritising the rims over yourself. 

Small sidewalls are very stiff, great for cornering "feel" but terrible for ride quality and  straight line stopping and acceleration  (more on that later). Stiffer sidewalls do not give any additional grip.

However, as a result of an increase in wheel diameter, the weight distribution of the wheel+tyre combo worsens - as the heaviest part (the tyre) is now further away from the center of the wheel - a no-no as it robs precious power from getting to the road. Many guys spend so much time focusing on the wheel weight but never even think about thedistribution of the tyre weight and its effect on the entire weight distribution of the wheel.

WATCHPOINT: Never make the mistake of choosing a tyre by its weight. Usually a tyre's weight is directly proportional to how much reinforcement is inside the tyre. Cheap tyres are often lightweight, but only because the manufacturer saved on the sidewall reinforcement. And cheaper tyre go out of round (square) because they are so cheaply made inside. Choose tyres based on tread and compound - never by weight. DO consider the weight of the tyre when picking the size of your wheel, however. Getting confused yet?

Larger sidewalls allow better ride quality, better straight line launch, braking and do not necessarily decrease grip though they do work to prevent a sudden (aka losing it!) rather than gradual break from the road. But they may make the car handle less precisely. In other words, the sidewall flexes so the steering response will be slower and you get a lot more "roll" in the bends. Too big of a sidewall can cause excessive tyre temperatures due to a lot of flexing about and possible failure in race conditions so it still is ideal to keep relatively low profile sidewalls on performance applications as we mentioned earlier. As mentioned, Morgans successfully used 14 and 15" rims for decades. Still do. 

You will notice that drag racing slicks always have very tall sidewalls. You never see low profile drag slicks. This is because when a drag car launches, the tyre actually deforms and ripples up to create an even fatter patch of rubber on the ground and to generate 'bite' into the ground. The smaller the sidewall you use, the more likely you will spin your tyres off the line. Taller sidewall tyres can generally bite harder both under braking and acceleration. Yet as modern Morgans become more powerful, their sidewalls are shrinking. So again, this doesn't make sense.

Choices

Yes. These market factors have reduced the neighborhood availability of 14/15 inch tyres. But Morgan Classics are a vintage design and the offerings from vintage tyre suppliers have increased, rather than diminished.  It makes no sense to own a Morgan unless you treat it right. 

COMMENT:

Hi Lorne,

Finally someone speaking the truth about low profile tires, especially where a Morgan is concerned.
My thoughts 100%.

Like you, get tired of hearing how bad Morgan suspension is. Or hearing how things break due to lack
of suspension when the going gets tough. I can imagine nothing worse than low profile tires.

Thanks for your articles on gomog.
Cheers
Win

The Problem With Large Wheels by David Finlay for MSN February 19, 2018

At a press event several years ago I had a pleasant chat with the UK marketing director of a certain car company. Despite his title, he was German, and he expressed amazement at the British enthusiasm for choosing large wheels and low-profile tyres from the options list. This was much less common in his home country, where, he told me, wheel sizes are on average at least an inch smaller than they are here.

Not that he was complaining about it. There’s a lot of profit in persuading people to pick the large-wheel option. It usually adds several hundred pounds to the price, in some cases a few thousand, and you can bet your life that the manufacturers are paying the wheel and tyre makers only a small fraction of that.

The usual reason for upgrading to larger wheels is that they look better than small ones. If that appeals to you, and you’re prepared to spend money on achieving it, Fair enough. But there are a few problems. For a start, there’s a greater risk of damaging a larger wheel against a kerb. They’re also more expensive to replace. Most of all, they frequently make the car much less pleasant to drive. 

This isn’t always true. Back in 1997, Subaru sold a car called the Impreza Sport. The only technical difference between the Sport and the GL was that the Sport’s wheels were one inch larger. You might not think this would make much difference, but it did. The GL was a pleasant car to drive. The Sport was glorious. That small change in wheel size sharpened up the handling almost unbelievably. More commonly, though, the optional wheels and tyres make little difference to the handling and have a devastating effect on the ride quality.

It’s not the wheels themselves that cause this. It’s the fact that you have to fit lower-profile tyres to them so that the circumference remains the same. If you didn’t, there would be space issues and the gearing would go to pot. Lower-profile tyres have smaller sidewalls (the sidewall being the part of the tyre you can see around the wheel when you’re looking at it side-on). Since there is less rubber, it can’t be deformed as easily, so shocks which would otherwise be absorbed by it are passed through to the suspension instead. Suspension is set up to deal with a particular wheel/tyre size. (As Morgan never changed their suspension when they changed wheel size), the suspension is no longer able to cope as well as it did before. It does not damp the shocks coming from the road as effectively, so those shocks are transferred to the rest of the car and, ultimately, to you.

This is noticeable in all cars, but in some more than others. The first-generation Audi Q5 and its close relative, the Porsche Macan, were set up on the assumption that they would be fitted with 18-inch wheels, and were very comfortable when that happened. In each case, fitting 20-inch wheels instead was a disaster. An obvious contrast was apparent within the Porsche range. By the time the Macan was launched, all 911s came with 20-inch wheels as standard, and their suspension were set up accordingly. It may seem strange that a company could make a sports car with a more comfortable ride than an SUV, but that’s what Porsche did.

Like the 911, the current-generation Renault Scenic and Grand Scenic MPVs have 20-inch wheels too. Also like the 911, they were designed from the start to run on them. The shocks transferred through the low-profile tyres are adequately absorbed by the suspension, and the occupants do not suffer.

There’s little sign that other mainstream manufacturers will follow Renault’s example, but perhaps some day they will. Until then, I’ll always choose the smallest wheels available. My car may not look as good as one whose owner went for the large-wheel option, but it will be far more comfortable to drive.

WIDE VERSUS NARROW TYRES

Newer owners are not going to like the following comments. When choosing tires for your vehicle, you might believe that picking the widest tire is best. However, that may not be the case, especially with Morgans. There are advantages and disadvantages to both wide and narrow tyres. When determining which kind is best for your vehicle, it’s important to think about what you want out of the tire and also about your car itself.

CONSIDERATIONS

Car weight — For some vehicles, buying a wider tire is not realistic because the weight of the vehicle will put insufficient pressure on the tire. If you were to mount a wide tire on a car that was too light, you run the risk of loosing traction and slowing the car. If you mount tires that are too wide on a vehicle that is very light, you will experience wheelspin, which can damage other internal systems in your car. So make sure you purchase the appropriate tires based on the weight of your vehicle. Morgans are close to the the lightest cars in the world. 

Traction — Having more pressure per square inch or a wider contact area are two options for creating greater traction for your car’s tires. With wide tires, you have a broader contact area, while skinny tires create more pressure per square cm. There’s no way you can have both options, so it’s best to find a balance based on what kind of roads you will be driving on and other conditions that will affect your vehicle. Always tune and set up your Morgan for the roads you enjoy the most. 

Wet condition driving — Wide tires are better for driving in wet weather since they have sipes, which help to trap and remove water from the contact surface. Narrow tires have sipes as well, but since they have a smaller surface area, they have less of them. One positive aspect of narrow tires in the rain is that when going through puddles, the higher contact pressure moves water out of the way. However, tyree technology has moved ahead. You can buy narrow tyres that give amazing control on wet roads and puddles. 

Dry road racing — If you’re mostly going to drive on streets with dry asphalt, you should consider going with wide tires. For this type of road material, the increased surface area provides better traction than having more pressure at a sacrifice to speed..

Fuel consumption — The less friction your vehicle produces, the lower your steering effort, which also means less fuel consumption. Wide tires provide for more friction, making your vehicle consume more fuel, whereas narrow tires cause your car to consume less fuel because they have lower amounts of friction.

Comfort - Narrower tyres are more comfortable and make less noise.

Stopping - Wider tyres stop faster.

These features must be carefully studied for Morgan owners more than most other vehicle owners considering how unusual Morgans are. Morgans are extremely agile and light cars. If you wish larger, fat tyres, buy another sports car. Aesthetics are only as good as long as they affect performance and handling. Wide tyres on Morgan's kill a LOT of the fun. One of the tragedies of the new Morgans (Aeros, CRX) is that they sacrifice performance and spped by ignoring the reality of these cars and have fit them with much wider tyres as today's owners choose looks over reality.