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Tyre sizes on older cars

Started by gf, 03 May 2017, 01:33 AM

gf

Every few years it seems tyres on cars get bigger and fatter. Even after radial tyres came in they keep getting bigger. So why did the older cars have such small tyres? Was it some technological limitation?

ptashek

Quote from: gf on 03 May 2017, 01:33 AM
Every few years it seems tyres on cars get bigger and fatter. Even after radial tyres came in they keep getting bigger. So why did the older cars have such small tyres? Was it some technological limitation?

My bet is on increasing drive train efficiency, and therefore more power at the wheels which requires more grip, hence wider tyres.
Then you have high-speed handling requirements, and simple design cosmetics. Modern cars are bulkier than older ones, except maybe the largest US cruisers. They just look nicer with bigger rims and less rubber.

In the 1970s few cars, affordable by Joe Common, were reaching speeds in excess of 150kph. Even the fastest road going super cars weren't exceeding 290kph. There wasn't much to be concerned about in terms of the rotating mass of the tyre itself, all that rubber compressing and decompressing differently at speed, and all the suspension dynamics that come with it. These days 200kph is nothing special for most cars, and hyper cars go well beyond 400kph, hence less compressible rubber, and more rigid rim.

Here's a nice article that goes into a lot of tyre physics. It's fascinating how complex an element a piece of rubber can be :)
http://laroverket.com/wp-content/uploads/2015/03/tyre_as_car_component.pdf
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

gf

Thanks ptashek I think that answers my questions. Interesting article.

rumb

Speaking of tires, I just got new ones for my W108.  Decided to get white walls.  195/75R14. Previous tires were 205's, I felt they looked to fat and bulky.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

s class

195/75 is closer to the dimensions of the original tyres than 205s would be. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

rumb

I know.  I was royally pissed 20 years ago when I bought them and the tire shop put them on because that was what they had in stock instead of ordering the correct size without telling me.  #finalyvindicated
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

floyd111

My theory is simple: ruthless greed.
For the very same reasons car manufacturers were not applying readily available science, all along the board. The width of the car axles were much narrow then the width of the car, making them top-heavy. There is no good reason for that, except to save money.

The tyre-science you speak of is real, for sure, but to me, it smells like a lucky excuse the manufacturers could make. The wheels were very narrow as to not raise costs. Aesthetics related as well matching the much-too-narrow axle width. Seat belts were not installed for a century, crumple zones were absent, no interior padding, no ABS and scores more. ABS was invented in the beginning of  the 1900's, just like electric drive trains. A seriously uberpriced W116 set/corrected many of these standards, no doubt a result of a storm of liability  lawsuits around the planet.

djenka018

Actually... the tyres used to be much larger before the WW2, I would think to better mittigate road imperfections.
Look at the Beetle' 16", it took 50-60 years to get back to the same diametre again.

I would think that improvement of the roads brought philosphical approach that large tyres are vanity... and that 12" were jsut as good for a fraction of the cost.
Excess width of the thread, otoh and imo, became usable only with the common 3 letter acronyms that came in modern days (ABS, ESR, BSB, PTC, ECG...) as well as with improved water rejection paterns and synthetic compunds.
Vitamin C for SL... the SLC

ptashek

Quote from: floyd111 on 05 May 2017, 08:19 PM
My theory is simple: ruthless greed.
For the very same reasons car manufacturers were not applying readily available science, all along the board.

An invention comes by, industry catches up, the product becomes mainstream and cheaper as a result - it's an endless loop.
Look at it this way - thanks largely to Werner von Braun and the Nazi V-2 rocket programme, people went to the Moon. But it wasn't financially viable to do so in the 1940s even though, in principle, the technology to at least put people into low orbit was there.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

marku

I used to have a 1965  E type Jaguar and its tyres were Dunlop 185 x 15 and were tubed. It would do close to 150mph which I did once down the local highway. It was some time ago and I would think hard before doing it again. The ones you see now have usually had much wider tyres fitted. Even though mine had a limited slip differential it was really easy to spin the wheels.
1974 450SE silver green/bamboo velour/green vinyl roof

carl888

The profile of the tyres has decreased over the last 40 years is mainly due to three reasons:

1. Marketing, in that each successive model from a given manufacturer must be seen to fit a lower profile tyre.  Subjective judgements such as "It just looks better" also plays a part.

2. Increase in brake disc diameter dictating a larger rim.

3. Reduction in fuel consumption (Through the reduction in hysteresis)

The increase in width is partly to compensate for the reduction in the contact patch for the lower profile tyre.  i.e. as you decrease aspect ratio (Fit a bigger rim for a given circumference) the contact patch becomes reduced.  That's why dragsters have such massive rear wheels and a very high aspect ratio run with 10 psi inflation pressure.

Remember that the contact patch (Within certain limitations) has little effect upon the overall grip levels because the weight is spread over  a given area, less contact patch, more weight per cm2.  That's why you can get amazing braking ability from a bicycle despite its very small contact patch.

In days of old when I was testing tyres under controlled conditions it was impossible for us to increase grip levels by fitting lower profile tyres assuming identical tyre compounds.  Subjective analysis told us that the lower profile tyres "Felt" faster due to the stiffer sidewall improving handling, but the lap times told otherwise.  In some cases, the lap times were actually slower with the lower profile tyres.  Although these tests were conducted in 2002, I am yet to see any data since then to suggest that things have changed in this regard.

There's a push now for manufacturers to fit low profile tyres but decrease the width to reduce rolling resistance.  The challenge is to develop a softer compound to maintain grip with good wear characteristics to compensate.   

s class

Quote from: floyd111 on 05 May 2017, 08:19 PM
My theory is simple: ruthless greed.
For the very same reasons car manufacturers were not applying readily available science, all along the board. The width of the car axles were much narrow then the width of the car, making them top-heavy. There is no good reason for that, except to save money.

The tyre-science you speak of is real, for sure, but to me, it smells like a lucky excuse the manufacturers could make. The wheels were very narrow as to not raise costs. Aesthetics related as well matching the much-too-narrow axle width. Seat belts were not installed for a century, crumple zones were absent, no interior padding, no ABS and scores more. ABS was invented in the beginning of  the 1900's, just like electric drive trains. A seriously uberpriced W116 set/corrected many of these standards, no doubt a result of a storm of liability  lawsuits around the planet.

The market is, and always has been competitive.  If lower profile tyres were practical/available in the 1970's, MB, Ferrari, BMW et al would have used them, if they were beneficial. 

It is unsubstantiated to say that they passed off substandard equipment out of greed.  Tyre technolgy advances were real and significant in the 1970's and 1980's.  Consider the TRX system developed my Michelin, and implemented by BMW. 

I have driven many 116/126/107 cars with standard wheels, and period correct upgrades such as 15" bundts, pentas, Lorinsers etc.  In pretty much all cases, the standard wheel/tyre combination still provides the optimum balance between handling/braking/comfort.  Especially if something like Michelin XWX's are used. 

Putting my money where my mouth is, I have currently 2 sets of 15" bundts and 3 sets of 16" pentas lying in the store unused, while all of my 116's are on 14" wheels with 205 or 215 tyres. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

gf

I was watching some 1960s English documentary on car safety and they were cutting tread patterns out by hand for pre production tyre testing. It seems all safety testing of the 60s-70s was very crude.

midnitesunmerc

Super-low profile tires (tyres for the limeys, lol) may look cool to some and have some performance benefits but they are certainly more suited to places that have very smooth roads - in the real world there is apparently a booming industry in fixing bent and broken rims because there is not enough tire to protect the rim in case of sudden impacts from potholes, etc....

Also I have a friend on Facebook who is constantly sending me photos of old Detroit muscle cars that people have put modern wheels and rubber on and frankly, they look stupid...these cars were made to look right with older tires that have some meat on them and the new ones just don't look right in the old fender wells, IMHO....
1977 280SE Colorado Gold
1979 280SE Euro model (parts only)

s class

Quote from: midnitesunmerc on 16 May 2017, 10:12 AM

Also I have a friend on Facebook who is constantly sending me photos of old Detroit muscle cars that people have put modern wheels and rubber on and frankly, they look stupid...these cars were made to look right with older tires that have some meat on them and the new ones just don't look right in the old fender wells, IMHO....

Agreed completely.

Further to your other point, here in South Africa, the roads just aren't up to a standard where one can realistically use a low profile tyre. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL