Technical Tyre size is confusing me...

[KungFooPanda]

Hi guys

The 100hp needs four new shoes. The tyres on there at the moment are sized at 195/50 R14- but when I look at the Blackcircle Web site it recommends 195/45 R14 .

I'm Lowering the Panda with Vogtland springs and Bilstein B6 shocks, but I've been advised to go with the (45) rather than te (50) because of maybe making contact with speed bumps with the body of the car.

I've no idea about the technical stuff with ride heights and tyre sizes! Could you explain why a (45) would be better than a (50) please. The (50) seem to be cheaper and you have a far more extensive range to choose from.

Cheers

 

[KungFooPanda]

EDIT... R15 that should me not 14 rim size

 

[Pugglt Auld Jock]

For any given size a 50% aspect ratio tyre will be slightly bigger in overall diameter than a 45%. The aspect ratio being the relationship between the cross sectional width of the tyre (in effect the tread width) and the height of the sidewall. So a 195/50R14 means it's suitable for mounting on a 14" diameter rim and will have a cross sectional width of 195mm with a sidewall height 50% of that tread width. The 195/45R14 will have a sidewall 45% of the sectional width so it's a slightly smaller overall diameter. I'd have thought, if the main concern is regarding ground clearance then the 50% aspect tyre would give marginally more ground clearance? Just by way of comparison, the standard "cooking" 169 model Pandas (the model made up to 2012) came on 80% aspect tyres - 155/80R13 on ours. Back in the day that was a common size to find on things like Ford Cortina, Hillman Hunter and Avenger and many other medium size family saloons. The Mk1 Lotus Cortina was considered a bit special on it's 5.5J rims with 165/80R13 Pirelli Cinturato tyres. I saved up all my pennies and bought a set for my 1966 Cortina GT - thought it looked "the bee's knees". Today's most common size is a 205/55R16 which is fitted to stuff like the standard Vauxhall Astra and many others - Makes the old Pirellis I so coveted look positively geriatric!

 

[KungFooPanda]

As always my friend - A brilliant write up and easy to understand, thank you. I would have thought, like you that a 50 aspect has a higher side wall so giving further clearance to the road surface.

I'm not bothered about great cornering in the 100hp as its going to become my daily drive soon to work and home. I'm looking at the Michelin CrossClimate+ tyres from ATS as they have a couple of offers on at the moment. As well as getting topcashback and 7% off by using my Lloyd's bank card.

What's your take on these shoes for the old gal Jock

 

[koalar]

15" were standard and 14" winter tyres

from the 100HP owners manual

"Note - Available at common retailers: alloy rims 5.5 J x 14ET32 with winter tyres 185/55 R14 80T (M+S)"

 

[Pugglt Auld Jock]

As always my friend - A brilliant write up and easy to understand, thank you. I would have thought, like you that a 50 aspect has a higher side wall so giving further clearance to the road surface.

I'm not bothered about great cornering in the 100hp as its going to become my daily drive soon to work and home. I'm looking at the Michelin CrossClimate+ tyres from ATS as they have a couple of offers on at the moment. As well as getting topcashback and 7% off by using my Lloyd's bank card.

What's your take on these shoes for the old gal Jock

Thanks for the kind words KungFoo.

I don't have any personal experience of the CrossClimate tyres but Michelin tyres in general have pretty much been up there with the very best you can buy for many years. I've read a couple of reviews of the CrossClimate and it seems to be rated very highly so if you're getting a good deal on them I'd have no hesitation in buying them.

All season tyres in general are made with "softer" tread stock so will wear a bit more quickly than a typical summer tyre. Personally I think this is no bad thing unless you are doing stratospheric annual mileages. Rubber hardens (oxidizes) with age and heat (sunshine) which renders it less able to grip the road so well. When I was young and impecunious - not that I'm exactly rolling in cash now - I was very impressed with a set of Chinese made tyres which seemed to show almost no wear. Eventually I had to chuck them due to the rubber cracking and splitting even though they were only about half worn, but long before that I'd become aware that when it rained the car behaved as if I was driving on ice! The understeer on roundabouts had to be experienced to be believed. I'd much rather have a softer compound tyre which gripped the road well, especially in the wet, even if it wears out a bit more quickly. Many of us don't cover really high mileages so durability is not such an issue but it's worth considering that the older a tyre gets the less grip it will give you, especially when the road surface is damp/wet. This is one of the reasons I'd never consider a part worn.

 

[koalar]

all things equal

when comparing tyres I go for the tyres with the lowest decibels. 2 decibels makes a difference if you change all four

on 155/80/13 cars the toyo nano is hard to beat. Economy, wet grip, sound, wear and cost. Never looked at the bigger sizes yet.

All the specs are easily available. Its worth writing a few down. Then comparing whats important to you

for me its wet grip and noise.

 

[DaveMcT]

The standard tyre for 100HP is 195-45-15. 195-50-15 gives a slightly taller side wall but instantly noticeable ride improvement. The road handling was obviously much better as I was replacing a set of ditch finders, but it was noticeably more comfortable.
Larger tyres make the speedo under-read which was great because it now read correctly. No kidding myself its reading fast - its not.

 

[Troubles with 500c]

I would plum for the higher profile tyres to gain a more comfortable ride.

More tyre wall should protect your alloys better when you hit potholes.

 

[Pugglt Auld Jock]

I would plum for the higher profile tyres to gain a more comfortable ride.

More tyre wall should protect your alloys better when you hit potholes.

Whilst I could have had 16, or even 17, inch rims, fitted with "rubber bands", I intentionally bought the version of my car which had the "less trendy" 15 inch wheels and 185/60R15 tyres for both those reasons but mainly because I prefer the more compliant ride. An unexpected bonus has been that it was easy to buy a standard 15 inch steel wheel and fit it with a 185/60R15 tyre which dropped very neatly into the spare wheel well in the boot so I wouldn't have to rely on the ridiculous bottle of gunge which came with it as standard.

Here's a pic of the N/S/R wheel complete with it's new Falken tyre which I had to fit due to an unrepairable puncture in the original Bridgestone:

I'll be replacing the other 3 Bridgestones - which I've not really liked very much and are now 6 years old and down to under 3mm - with Falkens in the next month so they have time to "run in" before we head off down to Devon some time when the good weather comes back. I'm looking forward to seeing how the Falkens perform.

 

[TagSouth]

The change in profile means that the circumference of the tyre will be slightly smaller on the 45 profile than the 50 profile.

That means that your speedometer will tend to over-read. It will also make the car slightly slower in each gear. The difference is about 10%. Tyre size calculator

 

[Adds80]

Hi guys

The 100hp needs four new shoes. The tyres on there at the moment are sized at 195/50 R14- but when I look at the Blackcircle Web site it recommends 195/45 R14 .

I'm Lowering the Panda with Vogtland springs and Bilstein B6 shocks, but I've been advised to go with the (45) rather than te (50) because of maybe making contact with speed bumps with the body of the car.

I've no idea about the technical stuff with ride heights and tyre sizes! Could you explain why a (45) would be better than a (50) please. The (50) seem to be cheaper and you have a far more extensive range to choose from.

Cheers

The 45 or 50 is the hight of the tyre so 45 is shorter then a 50 195 is width and 14 is wheel size

 

[DaveMcT]

Speedo reading on 195-50-R15 tyres is about 3.5% slower when compared to the 45 section tyres. It actually makes the speedo more accurate than standard (speedo over-read is reduced).

See - https://tiresize.com/tyre-size-calculator/
195-45-R15

Diameter 556​

Width 195​

Sidewall height 89​

Circumference 1748​

Revs per km 572​

195-50-R15

Diameter 577​

Width 195​

Sidewall height 87​

Circumference 1808​

Revs per km 553​

 

[koalar]

Speedo reading on 195-50-R15 tyres is about 3.5% slower when compared to the 45 section tyres. It actually makes the speedo more accurate than standard (speedo over-read is reduced).

See - https://tiresize.com/tyre-size-calculator/
195-45-R15

Diameter 556​

Width 195​

Sidewall height 89​

Circumference 1748​

Revs per km 572​

195-50-R15

Diameter 577​

Width 195​

Sidewall height 87​

Circumference 1808​

Revs per km 553​

side wall height

195/50/R15 87mm
195/45/R15 89mm

don't get it. Can someone explain, love the title because its confusing me now

I suspect the calculator is wrong

which puts in doubt other online resources

 

[DaveMcT]

My mistake I mis-typed the numbers.

50 series with 195 tyre shows 97mm side wall height.​

45 series with 195 tyre shows 89mm side wall height.​

​

Its easy enough to check the URL, but 195 / 100 x 45 = 87.75 and 195 / 100 x 50 = 97.5 so pretty close.

 

[irc]

side wall height

195/50/R15 87mm
195/45/R15 89mm

don't get it. Can someone explain, love the title because its confusing me now

I suspect the calculator is wrong

which puts in doubt other online resources

They look wrong to me too.
5% of 195mm is 9.75mm, not 2mm.
Which throws out the circumference and revs/km figures.
Unless I've forgotten how tyre aspect ratios work... always possible, haven't really thought much about tyre sizes since the 90s.

Edit: reply beat me to it.

 

[DaveMcT]

It's confusing because the side wall is only part of the wheel radius and its based on the tyre width and they mix inches and metric. So a 185 that will fit the rim would need to be a 55 (ish) aspect to do the same job as a 195-50

Throw some numbers into the calculator to see how it changes.

 

[koalar]

thought I would have a play with the online calculator with a tyre I know

155/80R13

Diameter 22.8"

Sidewall 4.9"

Circum 71.5"


4.9 + 4.9 + 13 = 22.8 top + bottom Centre

71.5/π = 22.8 circumference / pi = diameter

doesn't the bottom deflect especially on the narrower tall tyres.

shouldn't the circumference be significantly smaller on a narrow 80 profile tyre.

when I look at the wheel it doesn't appear round but flat on the bottom

never really thought about it too much as I always install fitment original size tyres

obviously I am missing something.

 

[DaveMcT]

You could pump a tyres to 60psi (as they do for storage to avoid creating permanent flat areas) and measure spindle centre height. Then drop it to normal running psi and measure again. That would give the true rolling radius compared to tyre overall radius.

With the tyres we are talking about, the correct running pressure should create the same size contact patch, regardless of tyre aspect ratio. The slight loss of radius (and percentage increase in rolling speed) should be the same for both tyres. Basically ignore it.

 

[koalar]

You could pump a tyres to 60psi (as they do for storage to avoid creating permanent flat areas) and measure spindle centre height. Then drop it to normal running psi and measure again. That would give the true rolling radius compared to tyre overall radius.

With the tyres we are talking about, the correct running pressure should create the same size contact patch, regardless of tyre aspect ratio. The slight loss of radius (and percentage increase in rolling speed) should be the same for both tyres. Basically ignore it.

I was trying highlight the fact the online calculators aren't always correct

I was just playing with 155/80R13 which comes back with 22.8" in the calculator you linked to 22.1" in another http://www.wheelcalc.com/

one site I was on gave different results depending whether you worked in imperial or metric.