Change of Tyre size ?

#1
Hi , I have been offered a set of Pirelli Cinturatos 185 / 70 / 14 for a good price. My question is as my car is a 72 2000 TC with standard wheels and is now shod with 175 / 80 / 14 would these be suitable or would I need to source a set of V8 wheels. Thank you in advance .
 

quattro

Well-Known Member
#4
Your car will be slightly lower geared (3.2%) if you use the 185/70, as they are slightly smaller in circumference (around 2.5").
 
#5
Your car, like mine, was designed to use 165/80 R14. My first P6 came with new 185/70 R14 tyres, which have almost the same rolling radius as the 165/80s, but they are unnecessarily wide and make the steering too heavy at low speeds. I replaced them with the correct 165/80s (Cinturatos, lovely tyres) and it was much nicer to drive: lighter, crisper steering, less road noise, a generally more agile feel. 175/80 R14 has too big a circumference and would cause the speedometer to under-read on a 2000. I have just fitted a new set of Vredestein Sprint Classics, 165/80 R14, to my current 1972 2000 TC and they feel just right.
 

Demetris

Well-Known Member
#6
Your car, like mine, was designed to use 165/80 R14.
I agree with what you say, but my only concern is that with the narrow tyres, under current traffic conditions, the wheels will have more of a chance to lock up under heavy braking, than with the slightly wider tyres.
 
#7
Hello,
At some point I will need to get new tyres and I looking at the Michelin XAS... Probably on the dear side but I guess are top quality and correct for period (launched in 72)
 
#8
I run Michelin Energy Save + 185 70 R14 tyres and haven't noticed any downsides at all. If they're heavy at low speeds it certainly isn't obvious. And they allow me to take corners at speeds that most modern car drivers don't dare.
 

GRTV8

Well-Known Member
#9
I went to the expense of the higher brand Michelin. As I used the car less frequently as in the 70's the michies went "off" even though they had heaps of tread.
I now run on cheaper [not budget] Kumho.
Still a good tyre and Im not so worried about them going off with age.
Just sayin.
 

Phil Robson

Well-Known Member
#10
...but they are unnecessarily wide and make the steering too heavy at low speeds......165/80 R14, to my current 1972 2000 TC and they feel just right.
My (non power steering) V8S has 'standard' 185s on whereas my early 2000 has 'standard' 165s on, which are significantly narrower. The 2000 is a delight to drive, but the V8 is really a bit heavy. Of course the cars' weights aren't too different.

I also agree with Demetris' comment about locking up, although in slippery conditions it could be argued that a narrower tyre will be better as the unit pressure on the road is greater.
 
#11
I also agree with Demetris' comment about locking up, although in slippery conditions it could be argued that a narrower tyre will be better as the unit pressure on the road is greater.
This is not quite correct. For the same inflation pressure, the area of the contact patch doesn't change with the narrower tire, i.e. unit pressure stays the same. What does change is the shape of the contact patch, which become longer and more able to get through the water/slush/snow to the surface of the road.

Yours
Vern
 

Phil Robson

Well-Known Member
#12
Ahh, I see - that makes sense.

Given that, how is it that my 2000 is still much lighter on the steering.... :confused: I don't think the tyre pressures are much different.
 

Demetris

Well-Known Member
#13
Given that, how is it that my 2000 is still much lighter on the steering.... :confused: I don't think the tyre pressures are much different.
As far as i remember the steering box is different between the two, and also the front suspension geometry is rather different.
Also the tread pattern and depth, compound hardness can affect significantly the steering effort.
 
Last edited:

Demetris

Well-Known Member
#14
This is not quite correct. For the same inflation pressure, the area of the contact patch doesn't change with the narrower tire, i.e. unit pressure stays the same. What does change is the shape of the contact patch, which become longer and more able to get through the water/slush/snow to the surface of the road.

Yours
Vern
Vern, i think that your approach is somewhat simplified. In practice the contact patch will become significantly longer, only if you allow for tread deformation i.e. by lowering the pressure. Wider tyres are not just a trend, they do actually produce more friction under normal conditions, otherwise we would still be driving around in 125s. However, i agree with you that narrow tyres have a better chance to get through the water/slush/snow to the surface of the road.
 

sdibbers

Well-Known Member
#15
Interesting discussion. My 1969 2000TC came new with the optional rostyle wheels. It has 3500 hubs (different offset compared to the standard 2000 hubs) and the kinked rear upper suspension link. So has the wider rims and 185 tyres. It did feel a little longer legged than my old car with standard rims (feels quicker now because of mods). The steering is also heavier on the 69. Which makes sense given the other comments.
 
#16
The area of the contact patch stays the same if the pressures are the same. So the contact patch becomes longer as the tire width decreases. The only way to change the area of the patch is to change the pressure, or the weight on that corner of the car. That's the theory. In practice, tires with very thick tread bands and/or very stiff sidewalls and tires that are so underinflated that the sidewalls are near touching behave differently, but a properly inflated passenger car tire follows the rule.

I wasn't suggesting narrow tires are superior, but they have their advantages when the first task is to dig for solid ground to grip.

Yours
Vern
 
Last edited:
#17
What an interesting discussion . Taking all the comments into consideration I have made my mind up and I am going to go for the Pirelli Cinturato standard size 165/80/14 . Why is it the 185 is so much cheaper ? Supply and demand I suppose. Thank you for all your inputs.
 
Top