195/70R14

When you are working out the set up of a car it is a balance between handling and straightline braking. I think what road and track were saying is fatter tyres would have improved straight line braking - full stop!. however BMW were considering the derogatory effects on handling when fitting wider tyres. It is easy for a journalist to critisize what is there, but they don't have to consider how to fix that element, and the effects that fix might have on other features that BMW were trying to balance.

low profile tyres were all the rage in that period of the 1970s. Pirelli had just done 60 profile tyres on Porsche, and Porsche and Ferrari had just done fitting bigger tyres on the rear of a road cars. Then in 1974 all the megga low profile tyres such as the P7 and the TRX started to come out. Some of the bigger sports cars were going down the same route the luxury saloon cars so, ferrari started to fit 215/70R15 Michelin XWX, while Maserati and Lamborghini were fitting 215/70VR15 Cinturato CN12, the big Mercedes were 205/70VR14 and 215/70R14 for a special treat on the 6.3 cars. I can only think of the Silver Shadow and Aston Martin V8 that fitted anything bigger on the front, with 225/70VR15 Cinturato CN12 on the DBS V8 and 235/70VR15 Avon TurboSpeed on the Shadow. But lets face it that Silver Shadow wasn't know for its handling, but it certain ly could stop very impressively in a straight line (considering its weight).

So i think waht is interestig is what did BMW do with their cars. So i think BMW's continuation of the E3 was onto the & series, which continued to fit 195/70R14, but then 205/70VR14 on the top range models, and then i beleive they also offered 220/55R390 TRX, and the E9 turned into the 6 Series, which offered the same tyre choice. it woudl be interesting to know what changes BMW did at this point, stiffere anti roll bars, different camber and caster settings, stiffer springs, less travel in the suspension etc.

then it seems to me that in about 1986 (according to my books) the more sporting of these models when for taller rims and wider low profile tyres with 240/45R415 TRX. what adjustments did BMW make at that period? what were the press reports at the time. the Buzz was about low profile.

It is however interesting to note that at the same time the smaller sports cars known for their best handling Alfa, Lotus Elan were fitting 165R14 or 165R13, oh and guess what tyre the 2002 was fitting? yep well done; it is 165R13. I think it was only when Alpina pretty much turned it into a full blown racing car that it got fitted with the 185/70VR13 Pirelli Cinturato CN36 that it fitted wider tyres, but you can bet your underpants they had done a selection of other modifications to make them work well as a track car.

Incidentally Michelin do still make the TRX

Michelin TRX Tyres - Classic Michelin Tyres

Michelin TRX tyres - Tel: +44 1302714072 The classic range of Michelin TRX tyres, perfect for youngtimer classic cars. Michelin TRX tyres online.
www.longstonetyres.co.uk www.longstonetyres.co.uk

And they are great tyres.
 
I had TRXs with their ugly metric rims in my 6 series BMW. They prove that the optimistic view that BMW and their engineers know what they are doing and that every choice they make is an optimization is wrong.

That 6 model went from having E12 based suspension and steering in 1977 to E24 bits in the 80s, the weight of the TRX stock rims and tires caused thrust arm bushings to wear very fast, the steering develops a shimmy. The steering box opens up a play that cannot be fixed with the screw without risking unstable behavior. The L-bracket holding the steering against the chassis fatigues and cracks, and if not reinforced can put you in fatal hazard. Not only they got it wrong, they went backwards. My E9 has none of those issues.

I had to reinforce the bracket, rebuild the steering box, start using 740 bushings, and replace my rims with alloy Hartge rims for 15' non-metric wheels. The acronym TRX became a pejorative to E24 owners.
 
So that is one of the things about developing cars and tyres. the extra grip of those TRX tyres would have dramatically increased the amount of grip. it is a thing i often mention to people over tyreing cars. It dramatically increases the load on the cars components. So when they did that they were starting to learn that now they had developed ways of keeping enormous tyre foot prints all on the road during corners, that brought several counter difficulties and increased wear on steering components was a big one.
 
Dougal Cawley said:
So that is one of the things about developing cars and tyres. the extra grip of those TRX tyres would have dramatically increased the amount of grip. it is a thing i often mention to people over tyreing cars. It dramatically increases the load on the cars components. So when they did that they were starting to learn that now they had developed ways of keeping enormous tyre foot prints all on the road during corners, that brought several counter difficulties and increased wear on steering components was a big one.
Click to expand...
My point is that these engineers operate by trial and error, and it takes 5-10 years to realize these errors. Don Lawrence can summarize the 50 things that should be different in a coupe if they just knew then what he knows now. Paul Cain can provide the other 50.
 
@Dougal Cawley - i hear you, but BMW started supplying the e21 3 series with 60 series Pirelli P6 tires to improve the handling performance on those models in the late 70s - especially the iS versions. there are pros / cons about 70 series, 60 series and 55/50 series ... to me they all have their place for different reasons. if you have a stock car with a stock suspension, i buy your arguments. if you have an improved suspension on a coupe - its a 50-50 argument for the classic tire (whether CN36 for a 15" / P7 for the 16") ... if you have a very improved suspension + larger wheels, i think the argument for the 16" 50/55 series tires are a 75-25 argument for the modern tire.

just my opinion, but its NOT a black and white discussion if its not a stock car - there are 50 shades of gray added for the variables that come into play

and oh by-the-way - i HATE the TRX tires + wheels that went with them. a very expensive tire that just wasn't that good of a performer and virtually no other options. give me the cn36 or p7 any day of the week - i like the xwx as well, but only comes in 70 series.
 
Ha Ha! I think it is quite difficult to argue that the TRX were bad tyres. They did win formula one and the World Rally on that technology. However i do under stand that they were so good they often lasted so long that the rubber becvame old. As far as performance goes, that will be about the only critism that the TRX deserves they are remarkably clever tyres.

The real qualm with the TRX system is that is that the wheels are also clever and cant fit other tyres. they are millimetric for a reason. its not just becuase Michelin hate the fact that wheels are imperial not millimetric. Michelin do hate that, but the TRX wheels are different because the rim has a different clever profile to accomadate the clever bead technology.

people dont like TRX because tyre come at price tag and they occasionally go out of stock. the winge that they are difficcult to get is unfounded, becuase you can just buy them off of me or any of the other Michelin Collezione dealers world wide. But we post them everywhere. I met this Austrailian guy last weekend racing at Oulton Park. he had bought some tyres off us on Monday night and received them on the other side of the world on Thursday. Loads of companies in the UK seem to struggle with Europe no we have done the old Brexit, but we have worked our way round it we ship to Europe 2 -3 days no hold ups no extra duty. So they are accessible. but they do hurt your credit card and Occasionally they might be out of stock, but that is rarely more than a month.



I have always been carful to say when discussing tyre recomendations that it is for road cars.

And yes you can make modifications to the car to keep the footprint of a 225/50R 16 tyre on the road, but all those modifications make for a less pleasant road car, as does having an inch less side wall height. that is about a fith of the side wall.

I think it is fair to say that the E21 had diffierent geometry and steering. In fact a different car altogether. a late 1970s car with its geometry designed in the full knowledge that low profile tyres were out there and with the intention of fitting them from the get go.

And here is the other thing. They didn't fit fatter tyres to improve the handling. They fitted them to give it more grip.
 

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My '79 635CSi came with TRX tires but I didn't keep it long enough to get in trouble.
My '83 533i came with TRX tires that didn't grip worth sh*t in the wet. Thankfully I sold it before the tires got more bald and the crank position sensor went on vacation. I wouldn't have known what to do. CPS was on the bell housing (somewhere?) and I never saw it.
My '87 (E32) 735i (early production still with the 5 series chassis) came with TRX tires, a severely beat-up front suspension and steering AND a violent shimmy that no amount of parts replacement fixed. Wobbled so bad that the steering box mount had to be welded back on, but that didn't fix the violent shimmy. Truly a violent, frightening experience at 45 mph, and I've done a bunch of stupid stuff.

No fan of TRX, me.
 
Dougal Cawley said:
Ha Ha! I think it is quite difficult to argue that the TRX were bad tyres. They did win formula one and the World Rally on that technology. However i do under stand that they were so good they often lasted so long that the rubber becvame old. As far as performance goes, that will be about the only critism that the TRX deserves they are remarkably clever tyres.

The real qualm with the TRX system is that is that the wheels are also clever and cant fit other tyres. they are millimetric for a reason. its not just becuase Michelin hate the fact that wheels are imperial not millimetric. Michelin do hate that, but the TRX wheels are different because the rim has a different clever profile to accomadate the clever bead technology.

people dont like TRX because tyre come at price tag and they occasionally go out of stock. the winge that they are difficcult to get is unfounded, becuase you can just buy them off of me or any of the other Michelin Collezione dealers world wide. geometry designed in the full knowledge that low profile tyres were out there and with the intention of fitting them from the get go.
Click to expand...
TRX were bad because they are metric, which reduces choice and thus increases prices and variants to choose from.
The rims were ugly for the 635CSi. Formula I and World Rally were not won by an E24 so how does it prove any benefit to my car? The E24 is not a supercar or exotic car that justifies having to go to you to get tires, and for all I know you may decide to sell vintage Rolexes one day instead of tires and my supply chain is broken...
I put Hartge rims a long time ago, 740 bushings, a rebuilt steering box and the TRX days are just a bad memory.
 
Dougal Cawley said:
(snipped)
It is however interesting to note that at the same time the smaller sports cars known for their best handling Alfa, Lotus Elan were fitting 165R14 or 165R13, oh and guess what tyre the 2002 was fitting? yep well done; it is 165R13. I think it was only when Alpina pretty much turned it into a full blown racing car that it got fitted with the 185/70VR13 Pirelli Cinturato CN36 that it fitted wider tyres, L]

And they are great tyres.
Click to expand...
Dougal,
Many of my car friends are your loyal customers, and enjoy the excellent products you sell. I will come to you when I'm ready for a set of CN36's.

However, I think you are prone to some hyperbole when it comes to fitting larger/wider tires to vintage cars. Over 45 years ago I fitted slightly wider tires on my first BMW (195 to 205) and it improved road holding without any noticeable harm to wear and tear of the suspension. Until 2003 I routinely fit +1 or +2 sized tire/wheels on my many many BMW's, and all of these cars did over 100kmiles when I owned them, None that I can recall suffered from premature suspension/steering failure (IMHO).

An important and valid point you make is that bigger/stickier tires changes the driving experience. Taken too far this can ruin the vintage driving experience for some of us. In particular, I love the wonderful ride quality and forgiving handling that GT cars of the 1960-80's had, and am unwilling to lose it by going to a larger diameter wheel and low profile tires (and the extra weight is also a significant drawback for ride quality).

On my E9, I am still on the stock 14" wheel diameter (but with period correct 14x7 pre-BBS Mahle alloys). While this works for me, in no way does imply that going to a 15x7 or 16x7/8 and modern sports tires is wrong for other E9 owners. Yes, it changes the ride and handling, but it does IMPROVE handling/grip it's not a disaster in terms of accelerated wear and tear (although it does accelerate wear, which is rarely a concern on vintage cars). In point of fact, I have modern sporty tires on my XK120, and it makes the car much safer to drive and has not caused any problems suspension/steering in a decade of touring/rallying.

And finally, even if you stay at original size, the new tread compounds are vastly stickier/superior than those of the 1970's. Simply fitting new tires substantially changes the handling of the car from the original. A good example of this is an Avon CR6ZZ vs what you could buy as a road legal sporting tire in 1956 (when my Alfa was manufactured). Same for my 105 series Alfa, and etc. A modern all-season will run rings around a P7 from 1980).

In this context, I don't see why going +1 or +2 on rim diameter is such a bad choice. It's not my preference, but I think you overstate the drawbacks and risks for street-driven cars.

None of the above applies to racing vintage cars, where new race tread compounds often/regularly cause suspension/steering failures or original components. Every 1950's Alfa on Avon CR6ZZ tires is at risk of breaking a front hub because the forces far exceed the design capabilities of the original style hub. Every 105 series Alfa racing on modern R-spec tires should have the steering box checked yearly because the aluminum housing will crack and eventually fail at the input shaft bearing or 2 of the mounting bosses.

John
 
This is the Michelin Collection book from 2000. Showing liquidation stock of the 195/70VR14 XWX. they havent made a batch since then.

dimensionally it is 14mm taller and 8mm wider. So yes the difference is subtle. That is why untill Pirelli started making this 195/70R14 CN36 again the 205/70R14 XWX was the best tyre for you guys. I guess yes if you are prepared to sacrefice a bit of steering accuracy for the softer ride of the taller side wall then it is probably still the second best option

2000 XWX brochure.jpg




"On my E9, I am still on the stock 14" wheel diameter (but with period correct 14x7 pre-BBS Mahle alloys). While this works for me, in no way does imply that going to a 15x7 or 16x7/8 and modern sports tires is wrong for other E9 owners. Yes, it changes the ride and handling, but it does IMPROVE handling/grip"


Wider modern tyres do not improve your handling. The steering is not as precise the wider foot print picks up the uneveness of the road and creates tracking. the steering is slower and not as precise. The handling is not as progressive. A large reason for this is that lovely rounded shoulder of the period tyre. (be it the 2 proper period tyres XWX or CN36 and Avon CR6ZZ which, though not a period tyre does have a suitable rounded carcass, which was designed later to suit chassis like yours, but with a racing compound.)

handling.jpg


I think i have posted this highly technical diagram before, but what it shows is a period tyre as the car leans, its contact patch moves around the rounded shoulder of the tyre that way the size of the contact patch does not suddenly decrease when cornering. The second picture shows a modern tyre on an old car. so as it leans it lifts a large portion of tyre off the road, the car snatches a little and then you will get full grip again, and you drive round a corner like a 50p peice. The third picture shows how a modern car cleverly keeps all the foot print of a modern square shouldered, or wide tyre in contact with the road.

When i say modern car you could sometimes swap that for race car. With your race car you slam it on the deck, with stiffer springs, dampers and anti roll bars so the suspension doesn't travel as much, and then add adverse camber so the little bit the car leans actually puts all the footprint on the floor in the corners. Is this relavent to the road. well it makes it a horrible road car, but it is worth those compromises because driving on the track is nothing like the road. a race track is perfectly smooth and you are flat out braking or accelerating nearly all the time.

Tracking.
When you fit a modern tyre instead of a period tyre, the foot print is wide in relation to the width of the tyre. that is one of the clever things about modern car design in that they enable a car to take advantage of this feature which is not suited to an older car. One of the derogatory effects is the outer extremities of the foot print have more leaverage on your steering becuase they are further away from it. Hence it being heavier, but it also picks up the unevenness of roads and pulls at the stearing. that is tracking. a thinner rounded tyre does not track as much on motorways. (it doesnt go away all together. that is because opur motorways are rubbish)

Grip is different to handling. (sometimes it works against good handling. you can over tyre a car).
A wider tyre does give more grip in some circumstances, because the contact patch is pread over a greater area. however that is lost when you consider the effects of the diagram above. However straight line grip is better with a fatter tyre, less straight line wheel spin. better straight line braking. So ideal for point and squirt traffic light racing, but not for handling. However extra grip means when you are on the edge of available grip when it lets go it does it more suddenly.




"it's not a disaster in terms of accelerated wear and tear (although it does accelerate wear, which is rarely a concern on vintage cars). In point of fact, I have modern sporty tires on my XK120, and it makes the car much safer to drive and has not caused any problems suspension/steering in a decade of touring/rallying."

Can i ask what tyres you have on the XK120?

The best road tyres for an XK are the 185VR16 Pirelli Cinturato CA67. If you want a sportier tyre Michelin make the 600WR16 Pilote Sport which is also great, but a bit heavier. Pirelli actually make a great crossply for the XK now, The 600V16 Stella Bianca, as fitted to cars like the 250F in the day, but they are currently out of stock.

Jaguar XK Tyres - Classic Tyres

Jaguar XK Tyres. Buy your Jaguar XK tyres online. Jaguar XK120, XK140, & XK150 tyres. We offer Jaguar XK tyre pressures, original equipment OE. Classic Jaguar tyres, vintage Jaguar tyres.
www.longstonetyres.co.uk www.longstonetyres.co.uk


"And finally, even if you stay at original size, the new tread compounds are vastly stickier/superior than those of the 1970's. Simply fitting new tires substantially changes the handling of the car from the original. A good example of this is an Avon CR6ZZ vs what you could buy as a road legal sporting tire in 1956 (when my Alfa was manufactured). Same for my 105 series Alfa, and etc. A modern all-season will run rings around a P7 from 1980)."

The tread compounds of the current classic tyres from the top manufacturers particularly Pirelli are modern compounds that is why they give such incredibly good results in tyre tests, specially in the wet. Look at this test. perfect grip in braking in the dry. then nearly perfect in the wet. production wise modern tyres have no advantage over these tyre. However on your car these tyres have a massive advantage because they present the tyre to the road in a way that is appropriate to your car.
thats your car, not a totally different set of geometry of a modern car.

Reifen test AB Klassik table (1).jpg





"In this context, I don't see why going +1 or +2 on rim diameter is such a bad choice. It's not my preference, but I think you overstate the drawbacks and risks for street-driven cars."

No body said anything about risks. what i do say is it will not be as nice road car. A perfectly smooth race track is a different enviroment all together.


While i am being belligerant. i am going to bang on about TRX again. (but only a bit)

yes they have occasionally been difficult to get hold of. They do some times go out of stock for a month or 2

yes the fact you can only fit a Michelin must be annoying, because you have to buy them off a blood sucking leach like myself.

yes these weird obsolete, bespoke tyres do add up to a large credit card bill.

But none of that detracts from the fact they were and are a good tyre.
 
Dougal Cawley said:
Wider modern tyres do not improve your handling.
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Douglas, we simply disagree on priorities and semantics.

Where your vast experience is most valuable (IMHO) is helping us understand the tradeoffs between the different tires/sizes so we can become more informed consumers of your products.

For me, handling is a combination of many things, including ultimate lateral grip, reaction speed to steering inputs, precision wrt steering inputs, balance (over/under steer), braking behavior, acceleration behavior, behavior at the limit (& beyond), and so forth. Every tire size and type is a compromise across these many dimensions. The optimal balanced for 1 may not be so for another. This is particularly so when you consider the vast differences in roads, driving style, driving capability,and usage profile.

Here we are talking BMW owners, who tend to modify their cars quite a bit. Many have modified suspensions with shorter & higher-rate springs, camber changes, stiffer anti-roll bars (weight transfer bars), higher damping dampers, lower compliance bushings, etc. To me, this means tire selection should more of a bespoke process.

ADAWIL, for example drives on 7-8x16” wheels with 50/55 series modern sports tires. This works well for him, and I have no doubt his E9 will panic stop faster than mine, or that it provides a much quicker and more precise turn-in, or that his tires cost much less than mine. In contrast, my 16” BBS RS and Alpina sets are in boxes, and I’m on a 14” wheel that gives a more luxurious ride but requires earlier/larger steering inputs due to more flexible tire sidewalls.
 
"Douglas, we simply disagree on priorities and semantics."

not really. its physics.

Where your vast experience is most valuable (IMHO) is helping us understand the tradeoffs between the different tires/sizes so we can become more informed consumers of your products.

For me, handling is a combination of many things, including ultimate lateral grip, reaction speed to steering inputs, precision wrt steering inputs, balance (over/under steer), braking behavior, acceleration behavior, behavior at the limit (& beyond), and so forth. Every tire size and type is a compromise across these many dimensions. The optimal balanced for 1 may not be so for another........"

However the characteristics of the different carcass structures are determined by physics and not opinion. the optimal balance for a road car is not optimal for the track. The compromises you are prepared to accept for a track car do not make a good road car.

"............This is particularly so when you consider the vast differences in roads, driving style, driving capability,and usage profile."

Between road and track are criterior we can consider. We aren't about to change our tyres dependent on weather we are going on a motorway or a road. however they are more similar than one might think when comparing any road condition to a perfectly smooth race track, which is perfectly smooth and driven flat out, or hard on the anchors.

"Here we are talking BMW owners, who tend to modify their cars quite a bit. Many have modified suspensions with shorter & higher-rate springs, camber changes, stiffer anti-roll bars (weight transfer bars), higher damping dampers, lower compliance bushings, etc. To me, this means tire selection should more of a bespoke process."

These modifications are turning a car more into a track car and, as a result making it a less of road car. In other words a less pleasant road car, with a harsher ride, and heavier, slower, number steering and till you get up to warp speed, which on a normal road will tram line.
ie: be a compromised road car.

"ADAWIL, for example drives on 7-8x16” wheels with 50/55 series modern sports tires. This works well for him," well; he is prepared to put up with the compromises to its drive on the road so he can buy cheaper tyres, or because he likes the look of a 16" wheel, or because he likes to track day it. "and I have no doubt his E9 will panic stop faster than mine," yes; in a straight line, if it doesn't aquaplane. "or that it provides a much quicker and more precise turn-in," no it won't, that is the remit of the thinner foot print "or that his tires cost much less than mine." yep, maybe, If buying on price is the focus." In contrast, my 16” BBS RS and Alpina sets are in boxes, and I’m on a 14” wheel that gives a more luxurious ride" yes "but requires earlier/larger steering inputs due to more flexible tire sidewalls." no

Thinner tyres turn in quicker, and more precisely. and less tramlining.
Taller side walls give better comfort.
Rounder shoulders of a period carcasses give better progressive handling and less tramlining on an older car.
195-70R14 CN36 V 205-55R16 P7.jpg


If this car would have been better with a fatter tyre BMW would have fitted it.
 
Dougal Cawley said:
If this car would have been better with a fatter tyre BMW would have fitted it.
Click to expand...
Now I must strongly disagree. When an OEM makes their choice of tire/wheel size, it is a decision dominated with compromises that are biased towards do no harm and reduced cost rather than do the most good for a specific location/driver/application.

An example is the std E9 tire width vs what BMW used in the street going CSL. The original design was for a 195/70R14 yet BMW saw fit to increase this to a 205/70R14 for the more sporty CSL. On the e21 the OEM tire size ranges from 165/80 to 185/70, and up to 195-205 (Alpina) with the only difference being calibration of springs/dampers, wider wheels, and alignment specs.

And finally, taller profile sidewalls respond to steering inputs more slowly than low profile sidewalls. This is, as you say, just physics.

John
 
JFENG said:
Now I must strongly disagree. When an OEM makes their choice of tire/wheel size, it is a decision dominated with compromises that are biased towards do no harm and reduced cost rather than do the most good for a specific location/driver/application.

An example is the std E9 tire width vs what BMW used in the street going CSL. The original design was for a 195/70R14 yet BMW saw fit to increase this to a 205/70R14 for the more sporty CSL. On the e21 the OEM tire size ranges from 165/80 to 185/70, and up to 195-205 (Alpina) with the only difference being calibration of springs/dampers, wider wheels, and alignment specs.

And finally, taller profile sidewalls respond to steering inputs more slowly than low profile sidewalls. This is, as you say, just physics.

John
Click to expand...
Agree completely. Additionally, the tire technology limitations of the period are vastly different than today. BMW would probably make an entirely different choice in wheel and tire for the e9's if todays technology were available to them back then.
 
Dougal Cawley said:
If this car would have been better with a fatter tyre BMW would have fitted it.
Click to expand...
I have to take the utmost exception to that blanket statement. One only has to look at the Firestone mess of the late 1990's to see how that is false.

Ford fitted my 1994 Explorer with Firestone ATX tires. Why? They could get them for about half of what the comparable Michelin or BFG tires cost.
Those Firestone tires were garbage. No traction. No tread life. Very bad handling. On top of that - Ford had their pressure set to 26psi. Why so low? To try to give the Explorer 'truck' a car-like ride. Neither of the choices of tire or its pressure were based on the physics of anything - Ford did so because they could get them cheap and they wanted the Explorer to ride better than it really could.
Lives lost and lots of lawyers later.... we all know how that turned out.
I ran Michelin LTX M/S tires on that truck for 200,000 miles. I made the choice of what to install - and in direct conflict with what Ford had on their books as recommended fitment.

Next - I purchased a new GMC Yukon in 2001. It came with these same crappy Firestone tires (but at least GM set the pressure was back to where it should have been). Ok - not my favorite thing, but I didn't feel the need to spend $$ on a set of new tires when the truck was not needing them - as I thought anyway. I had planned on using them up and then switching to something better as normal.
But... things changed.....
After only two weeks and a couple of hundred miles into my time with that truck - I lost a tire on the freeway.
No warning, just blew out. Totally destroyed the tire.

GM would not deal with me for any warranty claim. They had me to go to Firestone for a warranty claim for anything dealing with tires.
Well - I did.... and they gave me a full set of Bridgestone Dueler H/L's (about $800 back in 2001) - and that was that.
To put it in perspective, retail price on the Firestone ATX was nearer $50... only a quarter of the price of the Dueler.
Why did they do that? Even Firestone knew their tires were not good. Better to send me out as a happy customer compared to loosing me forever and having me to go Michelin.
Drove that truck for 300,000 miles before letting go of it just a few years ago. Bridgestones - that was all that the Yukon saw.
My Escalade (that replaced the Yukon) has Duelers on it now as well. Not looking back....

OEM choice of tire is mostly an economic decision with just a limited amount of technical requirements thrown in.
For example, on my other cars - I do not install "P rated" tires on my Porsche... Don't need to on a 20 year old 997 with 160,000 miles when other tires are available and more appropriate.

Plus - For cars that are 50+ years old (like the E9 here), the tires available in 2024 are TOTALLY different than the tires available back when these cars were new - both in terms of quality as well as availability. That fact colors what I want to install as well as what I can install. For my Mustang, I really don't think I want to get a set of Polyglass Bias Ply tires..... even though that is what Ford has on the books for 1968.

I drove my 2002 for nearly 30 years with 14" Bottlecap wheels. Were those OE fitment on that car? Hardly.
Could I even find original size 13" tires if I wanted to? I don't think I could - and if I did.... they'd be both expensive and a compromise for what the 14" fitment gave me.

From there - YMMV as usual.
 
Dougal,

I don't have time to respond at much length to your posts, but while, yes, physics is physics, vehicle handling is not just physics, and arguments about handling are not just physics - they come with the priors that the person making the arguments brings with them, which may be stated or unstated and implied. There are a lot of things that you are saying that are technically correct but are all based on the assumption that the very best possible expression of a car is exactly as it was when it was brand new. There is certainly an argument to be made that this is desirable as one of multiple ways of approaching the dynamics of a car, but not that it is "the best." In addition you make arguments that because an engineering team made certain decisions when developing the car, it therefore must be the best possible solution. This is only true in the very limited sense that it is the best solution for the priorities they decided on at the time given all of the other limitations they were operating within (as someone else mentioned.) I did spend some years working as an engineer in the auto industry so I have a bit of firsthand familiarity with the compromises necessary in a production environment. .
 
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lip277 said:
Could I even find original size 13" tires if I wanted to?
Click to expand...
I got my most recent set of 13” tires from the UK. They were 185/70R13 sticky summer max-performance type for a 65 year old very light British OTS that does short tours and an occasional autocross. Shipping was surprisingly cost effective.

Those in the UK are spoilt for choices of tires for 13-14-15” wheel diameters. This includes vintage style and modern tires. We know Dougal has vintage style tires for all our old BMW’s.

For modern tires, here is an example:
Advan HF Type-D A008 sells for about $100 in a 185/70R13.
 
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