Which slicks?

[AntA35]

I need to put some slicks on my Gp1 Dolomite Sprint for racing in the JD Classics series this season, yet I have never used slicks before and I haven't a clue which brand, which compound and type that I should be looking at.

The regs don't subscribe us to use any particular tyre, however one would assume I should be looking for a radial slick of a medium to harder compound for use in endurance racing that would suit the car.

Any suggestions, or does anyone have any experience of trying different types/brands/compounds?

[Mike Bell]

Originally Posted by AntA35

I need to put some slicks on my Gp1 Dolomite Sprint for racing in the JD Classics series this season, yet I have never used slicks before and I haven't a clue which brand, which compound and type that I should be looking at.

The regs don't subscribe us to use any particular tyre, however one would assume I should be looking for a radial slick of a medium to harder compound for use in endurance racing that would suit the car.

Any suggestions, or does anyone have any experience of trying different types/brands/compounds?

I would ring BMTR and speak to Peter in their Motorsport dept. They are UK Avon suppliers and should be able to advise what is available, which is more important these days than what you actually want. They also service a lot of the race meetings, which is very handy. Most historic touring car series require crossply slicks, so would be nervous about fitting radial in case not acceptable at some point. Dunlop also supply, btw.

[AntA35]

Thanks Mike, I will be sure to give them a call. As for the regs on cross ply or radial, it just seems to say tyres according to App K.

App K says:

"Unless otherwise specified in Appendix K and within the limits of availability and practicality, the width, external diameter, general appearance and tread pattern of tyres must be consistent with those fitted to the car or similar cars during the relevant period. All relevant regulations in respect of bodywork and rims must be respected and competitors are responsible for ensuring that the tyres chosen are compatible with the rims used."

Furthemore specific to the period:

8.2.5: Periods H1 and HR onwards may use slicks and wet tyres. T, CT, GT, GTS and GTP cars may also use tyres marked with «E» or «DOT» approval in accordance with the appropriate standard of the country in which the competition is taking place with a minimum external diameter as set out in Article 8.4.2.

The period in question is Period I, through to the end of 1981. The question I guess becomes, were crossplys or radials used in Period? Or maybe both?

[SAMD]

I 'think' (although I do stand to be corrected) that radial slicks are a fairly recent fenomynone.

[phoenix]

Originally Posted by SAMD

I 'think' (although I do stand to be corrected) that radial slicks are a fairly recent fenomynone.

I believe the phenomenon that is the radial racing tyre dates back to the 70s when Pirelli introduced the P7 - first as a treaded road tyre and then as a competition tyre in slick and treaded patterns. Lancia certainly used them for Group 4 rallying/racing (Stratos) in the mid 70s, Group 6 racing later in the 70s and Group 5 in the early 80s. I think Porsche used them too for the first Turbo race cars.

[Mike Bell]

Looking back at the thread discussing JD Classic series, the date radial slicks were introduced into racing was questioned. Peter M thought they were used in F1 from early 80s. It may be worth asking scrutineer John Hopwood via MRL for clarification, but my 'gut' feeling is that for touring cars the requirement for period profile, appearance and width will mean crossplies. Always happy to be proved wrong though....

[phoenix]

Originally Posted by Mike Bell

Peter M thought they were used in F1 from early 80s.

Michelin were the first radial tyre manufacturer in F1, commencing with Renault in the 1977 season. The first Grand Prix win was a year later with Reuteman in a Ferrari 312T. First driver world champion on radials came in 1979.

[AntA35]

It's all interesting stuff and completely new to me. Mike, I take your point... its worth me putting a call into John to hear from the scrutineer directly.

What are the discernable performance gains of one over the other?

[Mike Bell]

Originally Posted by AntA35

What are the discernable performance gains of one over the other?

Not having had the opportunity to try radial, can only guess that as they will likely be lower profile etc., a direct comparison would be difficult?

[FastDB2s]

Originally Posted by phoenix

I believe the phenomenon that is the radial racing tyre dates back to the 70s when Pirelli introduced the P7 - first as a treaded road tyre and then as a competition tyre in slick and treaded patterns. Lancia certainly used them for Group 4 rallying/racing (Stratos) in the mid 70s, Group 6 racing later in the 70s and Group 5 in the early 80s. I think Porsche used them too for the first Turbo race cars.

The 1st possible use of radial tyres is some 20 years before in the 1950s, Dunlop Duraband tyres were tested & raced ?? on the works D Type.

[Peter Mallett]

Originally Posted by phoenix

Michelin were the first radial tyre manufacturer in F1, commencing with Renault in the 1977 season. The first Grand Prix win was a year later with Reuteman in a Ferrari 312T. First driver world champion on radials came in 1979.

Blimey, "switch to Michelin, let's get things moving" was in 1977? I feel old!

[phoenix]

Originally Posted by FastDB2s

The 1st possible use of radial tyres is some 20 years before in the 1950s, Dunlop Duraband tyres were tested & raced ?? on the works D Type.

Indeed, but they weren't slicks. The Pirelli Cinturato dates back to 1952, The
Michelin X to 1948 and was first raced at Le Mans in 1952. It's hard to find an accurate date for the first appearance of the Duraband (Dunlop RB1) but I haven't found a reference pre 1959.

[phoenix]

Originally Posted by phoenix

I believe the phenomenon that is the radial racing tyre dates back to the 70s when Pirelli introduced the P7 - first as a treaded road tyre and then as a competition tyre in slick and treaded patterns. Lancia certainly used them for Group 4 rallying/racing (Stratos) in the mid 70s, Group 6 racing later in the 70s and Group 5 in the early 80s. I think Porsche used them too for the first Turbo race cars.

Correction to the above, Renault raced on Michelin radials, including slicks, in sports prototype racing - including Le Mans - as early as 1974.

[AntA35]

Blimey, some of you guys scare me with what you have stored away in your grey matter!

Just to help bring some closure on whether there is a choice of radial or cross ply slicks.

My research has led me to understand that indeed the first part of the answer comes down to more a question of what tyres are actually available from any of the manufacturers for your size wheels and application? My current research suggests the tyre size of preference for my car that was run in period are unfortunately not manufactured today. Therefore one has to resort to finding one that is close. This inevitably means a loss or gain in diameter and/or loss or gain in tread width.

From what I understand on the question of cross ply or radial, this comes down to how much camber one can dial into the suspension. With the Dolomite I wouldn't be able to get enough camber into the rears to make the radial tyre work as it should, so the answer for me at least is that I cannot get any perfomance gain from using a radial tyre anyway and the use of cross ply tyres will achieve the best/safest performance for the car in its application.

The questions I now need to resolve are what make, what compound and what size! However this will be a case of trial and error and one I am looking forward to discovering over the coming seasons.

Thanks for your help!

[Mike Bell]

Good luck with getting some tyres. With Avon, touring cars tend to run on A24 compound.

When will you be out with the Dolly?

[phoenix]

Originally Posted by AntA35

.....My research has led me to understand that indeed the first part of the answer comes down to more a question of what tyres are actually available from any of the manufacturers for your size wheels and application? My current research suggests the tyre size of preference for my car that was run in period are unfortunately not manufactured today.

I think, to be able to assist you in any constructive way, you need to tell us the wheel size you have to run - which you have not stated so far. So, give that and maybe more complete advice will be forthcoming.

[phoenix]

Originally Posted by AntA35

From what I understand on the question of cross ply or radial, this comes down to how much camber one can dial into the suspension. With the Dolomite I wouldn't be able to get enough camber into the rears to make the radial tyre work as it should

How much negative camber can you achieve on the rear of your car? I have used radials that need only a degree to a degree and a half to give proper temperature gradients, whilst some radial tyres need 4 degrees plus to work.

[FastDB2s]

Originally Posted by phoenix

Indeed, but they weren't slicks. The Pirelli Cinturato dates back to 1952, The
Michelin X to 1948 and was first raced at Le Mans in 1952. It's hard to find an accurate date for the first appearance of the Duraband (Dunlop RB1) but I haven't found a reference pre 1959.

Sorry I got it wrong, it was the Dunlop Stabilia & tested on a C Type on April 5th to 11th 1954, according to Norman Dewis, the worlds first radial low profile racing tyre, a 6.5 x 17, equivalent of a 6.50 x 16 Dunlop R1.
They were then tested again on April 24th on XKC401, the 1st D Type with a 142mph lap of MIRA, then as far as I can tell at Le Mans in 1954.
Your right though, they weren't slicks.

[AntA35]

Originally Posted by Mike Bell

Good luck with getting some tyres. With Avon, touring cars tend to run on A24 compound.

When will you be out with the Dolly?

Mike, I tried to get some tyres for last weekend but they didn't arrive in time and when they did arrive they were far too small in diameter. So we went with the road tyres instead. Funnily enough everyone else in the Group 1 category were also on Toyos so nothing was lost to each other on the track through tyre choice.

I was at the Donington Historic Festival in the JD Classics race. After lots of "breathing" issues in qualifying, we eventually went better (found 7 secs) in the race after we had taken the airbox off. We still have lots to learn and do with the car, having been freshly restored, but it would appear many others in the series are in the same situation so we are all growing together.

I will attempt to get some slick tyres for Brands Hatch at the end of the month, if I can find the appropriate size... will you be there?

[AntA35]

Originally Posted by phoenix

I think, to be able to assist you in any constructive way, you need to tell us the wheel size you have to run - which you have not stated so far. So, give that and maybe more complete advice will be forthcoming.

Hi Phoenix, I run 13 x 6 inch rims. The tyres that were used in period were 550/185 - 13 and I still have a set that were on the car from 1979, essentially measuring 550mm external diameter x 185mm tread width (Dunlop Racing). I can find some the correct width but not diameter, or correct diameter but not width.

As for camber I will have to ask but I don't believe it to be much more than 0.5 a degree.

Any help or guidance would be most appreciated...

[Mike Bell]

Originally Posted by AntA35

As for camber I will have to ask but I don't believe it to be much more than 0.5 a degree.

Any help or guidance would be most appreciated...

Unless your solid rear axle is bent (literally or otherwise ) you are not going to have any camber on rear. Would guess 0.5 to 1.5 neg on front?

Yes, Toyos a good choice, grip and cost wise! Have just done 6hrs on a set at Snetterton and they are ready for more....

Saw some pics of your car- it looks great. Will be out at Brands, so see you there!

[phoenix]

Originally Posted by AntA35

Hi Phoenix, I run 13 x 6 inch rims. The tyres that were used in period were 550/185 - 13 and I still have a set that were on the car from 1979, essentially measuring 550mm external diameter x 185mm tread width (Dunlop Racing). I can find some the correct width but not diameter, or correct diameter but not width.

As for camber I will have to ask but I don't believe it to be much more than 0.5 a degree.

Any help or guidance would be most appreciated...

If you want/have to stick to 6" rims and the overall diameter of 550mm there are a couple of choices I have found that come quite close. Ventus F200 radial from Hancook in the size 160/550/13 has the correct overall diameter, a tread width of 164mm and a section width of 183mm. Avon offer their crossply ACB10 in a 7.0/22.0/13 size but minimum rim width is given as 6.5" on their website. A better fit for your wheels might be their 7.0/21.0/13 which has a tread width of 182mm but is smaller with a 523mm diameter.

Might be worth trying some Formula For 1600 rear tyres if you can get some cheap. They are the right size, though you had best check with Avon that they are safe to use on your heavier car.

Their may be similar tyres from other manufacturers. There is a wider choice of radials in the 160/530/13 size.

[FastDB2s]

Originally Posted by Mike Bell

Unless your solid rear axle is bent (literally or otherwise ) you are not going to have any camber on rear. Would guess 0.5 to 1.5 neg on front?

Yes, Toyos a good choice, grip and cost wise! Have just done 6hrs on a set at Snetterton and they are ready for more....

Saw some pics of your car- it looks great. Will be out at Brands, so see you there!

Sprints had independant rear suspension, ANT - you need to speak to Ken Clark

[phoenix]

Originally Posted by FastDB2s

Sprints had independant rear suspension, ANT - you need to speak to Ken Clark

Yeah, right.....

Maybe one has?

[Mike Bell]

Originally Posted by FastDB2s

Sprints had independant rear suspension, ANT

What! Not when I worked for a Triumph dealer, they didn't

Pic here

(Other marque specialists are available...)