28 replies to this topic

[Barry Boor]

To those who know about these things, this will be an easy one to answer, but a very important piece of information for me.

I know that tyre sizes are usually measured by wheel size and width but what I really need to know is what was the diameter or rolling circumference of the actual tyre? The fronts are not so important but the rears are.

Anyone?

[Gerr]

What are the dimensions that you have ? Do you know the tyre brand and pattern?

[Barry Boor]

I don't have any details at all. I don't need to be too specific; any car; any tyre manufacturer; it doesn't matter as long as it is accurate.

[Ian McKean]

Originally posted by Barry Boor
To those who know about these things, this will be an easy one to answer, but a very important piece of information for me.

I know that tyre sizes are usually measured by wheel size and width but what I really need to know is what was the diameter or rolling circumference of the actual tyre? The fronts are not so important but the rears are.

Anyone?

In 1961 they were using 15 in diameter wheels, and I think probably 5.0 section at the front and 6.50 section at the rear. I think the profile then was pretty much 100%, so the circumference would have been 25 in at the front and 28 in at the rear. But I expect Doug will produce some data from BRM or somewhere to prove me wrong!

[Don Capps]

Well, according to the 1961 issue of Autocourse....

Dunlop D9 or D12 500x15 front and 600x15 rear across the board.....

[Gerr]

Some data at this site:
http://www.sascospor...ts/products.htm

[Gerr]

Thanks Don and/or Autocourse,
Sascosports' chart gives a diameter of 24.8 inches for the 5.00-15 and 26.6 for the 6.00-15.

[Barry Boor]

Thanks for the info, Ian. However, my school maths tells me that a circumference of 28" gives a diameter of about 9". I have a feeling they were a bit larger than that.

Apologies for that!

Assuming, of course, that you meant diameter, that sounds about right. But I'll await confirmation from other sources. If 28" is correct, that would require a 1/32nd scale rear tyre to be 7/8ths of an inch in diameter.

Which is good news because I have a lot of tyres just that size already!

[Barry Boor]

I have a book that purports to carry 32nd scale drawings of some cars. The Sharknose is one of them. Scaling up the tyres, the sizes seem to match a 28" diameter rear. I must say that anything smaller would seem to be too small but obviously I bow to superior knowledge.

[Don Capps]

Barry, Keep in mind that the aspect ratio of these tires is pretty tame so a tire/wheel diameter of 28 inches is probably pretty much on target.

[Peter Morley]

If you go to Vintage Tyre supplies website (vintagetyres.com) they give dimensions for Dunlop Racing tyres.

pre-65 F1 cars are obliged to run L-section tyres (later cars would run M section which are lower porfile).

500 x 15 fronts & 600 x 15 rears would be about right, but 550 & 650 are also acceptable since they would have run the bigger tyres on the faster circuits.

I'll copy the table but it is likely to come jumbled.

Thing to bear in mind is the Historic Racing tyre is considerably wider than the original!
Maybe all the original tyres I have have shrunk with age, but an original late 50's 500 x 15 Dunlop Racing Tyres is about 2/3rds the width of a current Dunlop L-section 500 x 15 (but the original tyres might well have been R5 section!)

Here are the dimensions - not sure what units the diameter etc are

Size Tread Rim Width Diameter Overall
Width Tread
Width
L Section
500L10 CR65(wet) 3.5 498 165 120
500L10 CR70(dry) 3.5 498 165 120
450L12 CR65 4 540 175 118
450L13 CR65 3.5 560 167 115
550L13 CR65 4 608 199 128
550L14 CR65 4 631 198 128
450L15 CR48(R6) 3.5 609 156 102
500L15 CR65 4 631 187 120
550L15 CR65 4 659 204 128
600L15 CR65 5 684 224 135
650L15 CR65 5.5 706 239 142
600L16 CR48(R6) 5 708 201 122
650L16 CR48(R6) 5.5 729 227 130

[JtP]

The cars in 61 would have run R5s. The R6 came out in early 62, Clark complained that he did not like the original tyre and stayed on R5s till they were modified in his book "jim Clark at the Wheel".

The lower profile L(iirc) section came out in early 64 using 13" rims and the cars had to have the suspension reset to take them. Photos taken in early 64 show some really strange wear patterns on the front.

The R7/ CR65 came out early in 65, but again was not liked. The tread was then redesigned, it looked the same but had wider tread blocks and one less tread band.

The M section appears in 66 (iirc) and after that the world goes mad with Dunlop, Goodyear and Firestone having a tyre war. Sectional ratios became so awkward to deal with, that tyres were then marked with the actual size of rolling diameter and width

[Barry Boor]

Thanks for the input, everyone.

I think I have enough info to be going on with now.

[Ian McKean]

Originally posted by Barry Boor
Thanks for the info, Ian. However, my school maths tells me that a circumference of 28" gives a diameter of about 9". I have a feeling they were a bit larger than that.

Apologies for that!

Assuming, of course, that you meant diameter, that sounds about right. But I'll await confirmation from other sources. If 28" is correct, that would require a 1/32nd scale rear tyre to be 7/8ths of an inch in diameter.

Which is good news because I have a lot of tyres just that size already!

Embarrassing

Gerr's 26.6 in sounds about right, which suggests that the rears had a slightly lower aspect ratio than the fronts (24.8).

Peter Morley's table, I notice, gives 3.5 in for the 10" tyres rim width. I shouldn't think many people put racers on 3.5" Mini wheels, I suspect 4.5" was the minimum. Then again when I rallied my Saab 96 I had some CR65's and then some other strange handcut Dunlop which nominally were for a minimum rim width of 6" but I (and the works for that matter) ran them on the 4.5" rims and they seemed to work pretty well. Blomqvist was third fastest on the all tarmac Sutton Park stage on the RAC in IIRC 1973 on these 4.5" rims against lots of works cars with more power, wheels twice as wide and wider track/lower C of G than the Saab 96. That's genius for you!

[Barry Boor]

Rather than start another thread, I wonder if anyone can fill me in with tyre sizes used by the main protagonists in the first 2 years of the World Championship - 1950-51?

[Gary Davies]

Barry, a bit of information, from the Profile booklet, written by David Hodges, on the Alfa158/159.

It quotes the tyre details as "Pirelli; front, 5.50 x 17 or 5.50 x 18; rear, 7.00 x 18 or 7.00 x 19 (nominal sizes)"

[Barry Boor]

Are these not actually wheel sizes?

I am looking for tyre outside diameters.

[Gerr]

Barry,
That is the tire size.

With a Dunlop R5, 5.50-17, mounted on a 4 inch wide rim, it would have an inflated diameter of 28.1 inches, an inflated o/a width of 6.5 inches and a tread width of 3.8 inches.


A 5.50-18 Dunlop R1, 4 inch rim, the figures are 29.8, 6.7 and 4.1 inches.

A 7.00-18 Dunlop R1, 5 inch rim, 32.1, 8.8 and 5.4 inches.

A 7.00-19 Dunlop R1, 5 inch rim, 33.3, 9.0 and 5.4 inches.


According to my old Dunlop handbook.........

[Barry Boor]

Excellent! Thanks, Gerr.

[Wolf]

I have a rather daft question, and have excavated this thread to ask it without littering the TNF too much.

As some might know, I'm foolishly fiddling with the idea of designing my sportscar-cum-cyclecar, but have been bewildered by tyres. To improve on power to grip ratio I have tried to go the sensible route and reduce grip, but can't find suitable tyres. Any modern tyre that would fit the aesthetic mould (not being too wide, and not too grippy) is rated too low on speed (usualy T, which means 190kph, whereas I'd need something more akin to V, or even W).

The only other route would be historic racing tyres- something along the line of 5.00x15 front and 6.50x15 at the rear (that would be R6, wouldn't it, but I figure R5s could be even better). Any chance of getting those at a sensible price? And what about the durability (I'd hope to feed through them sligly over the power of '61 Ferrari)? Thanks in advance.

And to justify digging this dear old thread, here's some info on Dunlop tyres Barry might find interesting (dunno where I picked it up, so can't give proper credit) :
http://members.atlas...wolf/dunlop.jpg .

P.S. Barry- Since You asked about '61- how about doing two Monza 'specials'? Moss' Walker/works car and Innes' Walker/UDT-Laystal (thanks Roger, I forgot to thank You in Lotus 18 thread). Itr'll definitely add some colour to the grid.

[Peter Morley]

Dunlop Racing tyres aren't so badly priced - they are a similar price to what I have to pay for my Subaru road car, when you consider they are specially made for a very limited market I don't think we can complain (and without them we would be stuck - so we must encourage them to continue).

Michelin did make some historic racing tyres a few years ago under the Englebert name, I think they might be larger diameters (e.g. for earlier cars) but I think the remaining stock was being sold off quite cheaply.

And Blockley are looking at expanding their range, worth looking at them as well.

If price really is an issue and you aren't going racing seriously you should be able to find some used Dunlop racing tyres - either at a race meeting (ask the tyre fitters) or via adverts, I wouldn't suggest racing on old tyres but road use should be OK (and I think Dunlops are now labelled so that they are legit for road use).

Another advantage of old race tyres is they will have gone hard so you should have even less grip!

And you can re-cut them when the tread looks a bit thin - but of course that is not encouraged!!

[Wolf]

Thanks Peter- the price inquiry was because I was googling around a bit: most sites don't list the price and I stumbled upon a site which sold the tyres for almost Ł250 (presumably, apiece). It seemed a bit steep, to say the least.

[Peter Morley]

Something like Dunlop 4.50 or 5.00 x 15 are around 125 pounds each.
(500 pounds a set compares well with 800 euros for my Subaru!).

vintagetyres.com list prices - but they might not be the cheapest around.

[Bonde]

Wolf,

Would your car be able to use modern motorcycle tyres?

[Wolf]

Anders- I've decided for normal suspension (hopefuly, I'd get Elise parts), wouldn't bike tyres be at disadvantage with normal camber angles?

[Wolf]

I've also found Longstone tyres with seemingly reasonable prices, and listing tyre dimensions which might interest Barry. BTW, MC Plans lists basic tyre size (e.g. 6.50 R15) for most cars, and if they don't scale drawings could be used to extract those.

As an aside, I've found that Bridgestone Potenza tyres might yet prove to be the best compromise for my purpose (175/55 R15 and 195/55 R15 have 270kph rating)- easily obtainable and reasonable price.

[paulhooft]

And to justify digging this dear old thread, here's some info on Dunlop tyres Barry might find interesting (dunno where I picked it up, so can't give proper credit) :
http://members.atlas...wolf/dunlop.jpg .

Do you have a better quality scan of this JPG:
PLEASE
Paul

[Wolf]

Unfortunately not, Paul, but I've tried improving readability by increasing contrast (by 50%). Hope this helps:

[Wolf]

Sorry for littering this thread, but I've just fiddled with the visual design of my car- it seems my last attempt was OK, but the small niggling thing was that either I could fit in it or the steering wheel, but not both. I'm not very satisfied with the result, but this way even engine will fit in it (but the car has grown taller- to whopping 26.5").

So, I'd welcome comments- from nostalgic point of view, naturally. The comparison is with old Lotus Super 7 (the top red line is actually the top of my head). I'd hope to outperform his 'older' brother with the same engine.