Quote:
I've had numerous sets of different wheels in differing sizes on my Dolomites. 185/55x15s on anything are awful, far too heavy making every response of the car lumpen. I can only imagine 195/55x16 being even worse, don't do it, Nigel!
On 13s I like 175/65 or 185/60, on 14s 185/50 seem best, but Michelins in 175/55 work well too, on 15s I've got away with 195/45s but much prefer 185/45s.
Obviously innumerable differences in terms or brake size, offset, vehicle height etc, but if you want to retain any feel and lightness of touch, those are what I'd recommend.
One of the concerns and/or interests that are commonly expressed about changing tyre sizes, are the variation in overall engine gearing and speedometer calibration.
It appears that your preferred choices of tyre size, are of circa 4•6% to 7•5% smaller external circumference, than the factory-standard 155 SR13 tyres; which is equivalent to a significant increase in final-drive ratio! Using some of your preferred tyre sizes on a Triumph Dolomite 1850, would be roughly equivalent to substituting a 3•89:1 final-drive ratio in place of the original 3•63:1 final-drive ratio, which might have been what you intended!?!
In a 14-page, A5-format magazine technical article [published in either the Automobile Association’s “DRIVE” magazine or Motor-Caravanners’ Club’s “Motor-Caravanner” magazine, but believed to be the former] dating from early-1992, I found a statement that for standard-profile tyres such as 155 SR13 (later re-designated 155 R13), the aspect ratio was
82%, which is consistent with the
82% &
83% that I found in various papers, that were published in a wheel & tyre industry engineering conference proceedings from the early-1980s.
175 R13 => 175/83 R13 – overall external circumference = 1949•9 mm
175 R13 => 175/82 R13 – overall external circumference = 1939•0 mm (5•62% larger than 155/82 R13) [Nigel’s tyres 1974/75~87]
175 R13 => 175/80 R13 – overall external circumference = 1917•0 mm
155 R13 => 155/83 R13 – overall external circumference = 1845•6 mm
155 R13 => 155/82 R13 – overall external circumference = 1835•9 mm
155 R13 => 155/80 R13 – overall external circumference = 1816•4 mm
185/70 R13 – overall external circumference = 1851•0 mm (0•82% larger than 155/82 R13) [Nigel’s tyres from 1987 onward]
175/70 R13 – overall external circumference = 1807•0 mm (1•57% smaller than 155/82 R13)
175/65 R13 – overall external circumference = 1752•0 mm (4•57% smaller than 155/82 R13)
185/60 R13 – overall external circumference = 1734•7 mm (5•51% smaller than 155/82 R13)
175/65 R14 – overall external circumference = 1831•8 mm (0•22% smaller than 155/82 R13) [MG-F & MG-TF space saver spare]
175/55 R14 – overall external circumference = 1721•9 mm (6•21% smaller than 155/82 R13)
185/50 R14 – overall external circumference = 1698•3 mm (7•49% smaller than 155/82 R13)
185/65 R15 – overall external circumference = 1952•5 mm (6•35% larger than 155/82 R13) [Nigel’s preferred future choice]
185/60 R15 – overall external circumference = 1894•3 mm (3•18% larger than 155/82 R13)
185/55 R15 – overall external circumference = 1836•2 mm (0•02% smaller than 155/82 R13)
185/45 R15 – overall external circumference = 1720•0 mm (6•31% smaller than 155/82 R13)
195/45 R15 – overall external circumference = 1748•2 mm (4•78% smaller than 155/82 R13)
185/55 R16 – overall external circumference = 1916•0 mm (4•36% larger than 155/82 R13)
195/55 R16 – overall external circumference = 1950•6 mm (6•25% larger than 155/82 R13)
I would be extremely wary of using ultra-low-profile 45-Series tyres on classic cars like the Triumph Toledo & Dolomite, whose suspension was designed to work in series with the vertical “spring-stiffness” & “damping” of 80-Series or 70-Series radial-ply tyres.
185/45 R15 => sidewall height = 83•25 mm
195/45 R15 => sidewall height = 87•75 mm
Several years ago, I came across the following on-line technical article:
Steve LaFerre, "Bottoming Out: With Aspect Ratios, How Low is Really Too Low?”, Tire Review, 22nd May 2008.
http://www.tirereview.com/bottoming-out ... y-too-low/
« In my lifetime tire aspect ratios have ranged from an 85-series to a 25-series. Did you ever clean the whitewalls on a 1952 Chrysler Imperial? Be thankful you didn’t. That’s why I like the new lower aspect blackwall radials. Not only are they easier to clean, they are radials, they handle astoundingly well, they give me a lot more grins per mile, as well as a low-rolling resistance gain in miles-per-gallon. »
« But many of us wonder how low a tire’s aspect ratio can go before we hit the point of diminishing return. To Michelin’s way of thinking, 25% of a tire’s section width is going to yield an 83 millimeter sidewall. “For everyday street-use tires an 80 millimeter sidewall height is our threshold,” says Mark Ludlow, a tire engineer for Michelin. »
« “Anything under that size is built only for racing or show cars. But we feel any sidewall that falls under 65 millimeters is more about show than go,” he says. “Think about the tire as an elastic, deformable subject working hard during cornering with virtually no slip angle available for it to do its job. A tire built to that size is simply too rigid. »
« “When the height of a sidewall is under 80 millimeters it just can’t deliver a normal regime of a slip angle because there is no elasticity or deformity available in a severe handling environment. Put another way, there is simply too little sidewall real estate for the work required of the tire. »
Given that a tyre of 80 mm side-wall height is considered the absolute minimum, for a modern or ultra-modern road car that is designed for use with low-profile tyres, I surmise that tyres of 83~88 mm side-wall height, would be of significantly too low-profile for 1970s vintage classic cars like the Triumph Toledo & Dolomite. Not only would I expect the ride to be unduly harsh, but road holding on uneven road surfaces, with bumps, corrugations & potholes is likely to be compromised, as well as being more susceptible to wheel & tyre damage.
On my 1974 Triumph Toledo 1300 “HL Special”, I wasn’t really planning to use 55-Series or lower aspect-ratio tyres on any size of wheel and I cannot ever imagine substituting a 16 inch or larger diameter wheel. Given that I seldom do more than brake gently & infrequently, I see no useful purpose in modifying the hydraulic brake system, other than to convert from the original single-circuit to a late-model Triumph Dolomite 1300/1500/1500HL dual-circuit system, which won’t alter the front or rear suspension’s un-sprung weight.
Although I have acquired some 7 x 16 inch Mercedes C-Class alloy wheels for use on my 1973 VW “1600” Type 2 Westfalia Continental motor-caravan (based upon the VW Kombi Type 23-517 model, having front & rear axle load limits of 1020 kg & 1270 kg respectively) as a substitute for the original factory-fitted 5½ x 14 inch steel wheels & Michelin XZX 185 R14 Reinforced tyres. For medium to large sized commercial vans, 65-Series tyres on 16 inch wheels, has been virtually the de facto standard for the past ten years or more, and 80-Series commercial-van tyres for 14 inch wheels are becoming progressively rarer and relatively expensive!
Since I first started driving the Triumph Toledo in May 1975, it’s been exclusively shod with either 175 SR13 (i.e. 175/80 R13) or 185/70 R13 tyres, on 5½ x 13 inch alloy wheels, of either 21 mm or 35 mm wheel-offset, so I don’t know what it would be like to drive on factory-standard 4 x 13 inch steel wheels and 155 SR13 (i.e. 155/80 R13) tyres.
The “original” 175 SR13 (i.e. 175/80 R13) tyre size is something of an expensive rarity these days [MyTyres.com list only two options! | HI FLY 175/80 R13C 97/95R commercial-van tyres @ £46•99 each or Maxxis MA1 P175/80 R13 86S car tyres @ £107•89 each | neither is highly rated for fuel-economy or wet-weather performance ] and even the 185/70 R13 tyre size is far from common now and probably destined to become rarer in the coming years.
175/80 R13 – 86S or 175/80 R13C - 97/95R | 2 results
https://www.mytyres.co.uk/search?sortCo ... iews=false
185/70 R13 – 86 T | 17 results
https://www.mytyres.co.uk/search?sortCo ... iews=false
Given that most small to medium sized modern cars, are now equipped with either 15 inch or 16 inch wheels, it makes sense to substitute 15 inch wheels, for which there is likely to be much more choice of tyres in the coming years, before the use of petrol-engined cars is eventually outlawed.
When I get around to completing the Triumph Toledo projects, I have a set of seven, MG 2000 Maestro 5½ x 15 inch cross-lattice style alloy wheels [31 mm wheel-offset], to which I have the option of fitting 185/65 R15, 185/60 R15 or 185/55 R15 tyres, in conjunction with either a 4•11:1 or 3•89:1 final-drive ratio. Although there are a few 185/55 R15 tyres available in a T speed-rating, most are of either an H or V speed-rating, which would be undesirable (if for no other reason than rolling resistance) on a road-going car, that is unlikely to ever be driven at speeds in excess of 70 mph, and typically driven at 40~60 mph outside urban areas. There were more than twice as many options for 65-Series tyres than for 55-Series tyres!
Checking on MyTyres.com, I found the following options:
185/65 R15 – 88 T or 88 H or 92 T XL or 92 H XL | 290 results
https://www.mytyres.co.uk/search?sortCo ... iews=false
185/60 R15 – 84 T or 84 H / 88 T XL or 88 H XL | 209 results
https://www.mytyres.co.uk/search?sortCo ... ologation=
185/55 R15 – 82 T, 82H or 82V / 86 H XL or 86 V XL | 132 results
https://www.mytyres.co.uk/search?sortCo ... ologation=
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I've also been looking at tyres and I can easily get 185/60/15s in a range of makes and speed ratings for sensible money. Toyo Proxes CF2s are £52 a corner and Falken Sinceras are £58 a corner. There are no name specials for under £40 a pop but i'm not THAT hard up! The tyres on the Dolomega currently are 185/60/14s, so i'd basically be lifting the car a 1/2", but no other change to aspect ratio or compliance from what I now have. I already have an electronic speedo, so calibration is only a matter of a single measurement (rolling radius in inches) a couple of quick sums and punch the result into the speedo.
The Carledo ran on 195/50/15s and I had to relieve the arches a little bit to get them in, but a narrower, higher aspect tyre might negate that a bit.
According to the following references, the standard rim-widths for 195/50 R15, 185/55 R15, 185/60 R15 & 185/65 R15 tyres, are 6 inches, 6 inches, 5½ inches & 5½ inches respectively, so using the tyre-industry “rule-of-thumb”, I would expect the actual installed section-width of such tyres on a 5½ inch wide wheel, to be about 5 mm greater on average for either 60-Series or 65-Series tyres than for a 55-Series tyre.
The same argument also applies to installations on a 6 inch wide wheel, where in general, the installed section-widths of identical tyres of the same size, will be circa 5 mm larger on a 6 inch wide wheel than on a 5½ inch wide wheel. This is one of the reasons why I elected to use an MG 2000 Maestro 5½ x 15 inch wheel of 31 mm wheel-offset in preference to an MG 2000 Montego 6 x 15 inch wheel of 28 mm wheel-offset; which I anticipate will give about 5½ mm greater clearance between the tyre sidewall and the outboard areas of the rear wheel-arches.
Tire Specs Explained: Rim Width Range
http://www.tirerack.com/tires/tiretech/ ... techid=198
Tire Specs Explained: Measuring Rim Width
http://www.tirerack.com/tires/tiretech/ ... techid=199
Range of Wheel Sizes for Given Tyre Sizes
http://www.tyresizecalculator.com/tyre- ... calculator
Tyres: 195/50 R15 => Wheels: 15 x 5½ minimum | 15 x 6 standard | 15 x 7 maximum
Tyres: 185/55 R15 => Wheels: 15 x 5 minimum | 15 x 6 standard | 15 x 6½ maximum
Tyres: 185/60 R15 => Wheels: 15 x 5 minimum | 15 x 5½ standard | 15 x 6½ maximum
Tyres: 185/65 R15 => Wheels: 15 x 5 minimum | 15 x 5½ standard | 15 x 6½ maximum
Tyres: 185/70 R15 => Wheels: 15 x 4½ minimum | 15 x 5 standard | 15 x 6 maximum
Tyres: 185/70 R13 => Wheels: 13 x 4½ minimum | 13 x 5 standard | 13 x 6 maximum
There will be significant variations between different tyre brands, but one might expect on average to have about 2½ mm less clearance on either side of a 185/60 R15 tyre than a 185/55 R15 tyre, when mounted on the same wheel.
By similar arguments, one might expect on average to have about 2½ mm more clearance on either side of a 185/60 R15 tyre than a 195/50 R15 tyre, when mounted on the same wheel.
For more detail, refer to my earlier discussion as follows:
Board index » The Triumph Dolomite Club » Dolomite-related [Start here!] » MG-Rover-Austin Maestro or Montego alloy wheels for Triumph Toledo & Dolomite
https://forum.triumphdolomite.co.uk/vie ... 94#p321555