Originial Tire Sizes?

Gary Gibbs · 08-09-02, 03:53 PM

What tire sizes were used on original GT40s:
Mk 1?
Mk 2?
Mk 4?
Mk 1 Gulf (68 - 69)?

Did the Gulf cars just go up on rear tire size with the larger flares?

Thanks
Gary

MK -IV J6 · 08-09-02, 04:06 PM

MK-IV 25X9X15 front
27X10X15 Rear
Goodyear Sports Car Specials

Gary Gibbs · 08-27-02, 11:21 AM

Info I found in David Hodges book:

GT40:
Front Wheel 6"
Rear Wheel 9"

Mk II:
Front Wheel 8", Tire 9.2" (Indy Museum)
Rear Wheel 9.5", Tire 12"

GT40P (FAV Car???):
Front Wheel 6.5"
Rear Wheel 9"

Mk III:
Front Wheel 6"
Rear Wheel 8"

J-car:
Front Wheel 8"
Rear Wheel 12"

Mk IV:
Front Wheel 8", Tire 25" x 9" (Mk IV - J6)
Rear Wheel 12", Tire 27" x 10"

GT40P (1968-69 Gulf Cars):
Front Wheel 10"
Rear Wheel 14"

Mk V:
Front Wheel 8"
Rear Wheel 10"

MK IV-J6:
As for the Mk IV does this seem correct for your car?

No other info on tires. I was curious as to the sizes and ratio of widths front to rear (leading towards balance). Obviously balance can be tweaked with sway bars and springs, but...

[ October 08, 2002: Message edited by: CCX33911 ]

MK -IV J6 · 08-27-02, 11:25 AM

Wheel size is correct. Tire size is Diameter/cross section/wheel diameter.

Neal · 08-27-02, 05:03 PM

I'm going to run BRM wheels 7x15 and 8.5x15. I'm thinking about using 215/60/15 (25" dia) and 265/60/15 (27" dia) BFG T/As for the street.

What 15" wheel/tire combos are you running?

08-29-02, 01:20 PM

Neal

Your choice on rim width seem slim. Which make of car do you run? Consider an 8 or 8.5 front and a 10 inch rear. The tyres you want will still fit but you should get better stability in driving. Also think of upping the front tyre width as you will get a better turn in.

Malcolm

Neal · 08-29-02, 02:43 PM

Thanks for the feedback Malcolm. The effective width is really 8" and 9.5" This is a NZ GT40 Replication car. I'll try 225/60 for the front.

gweitzel · 10-08-02, 07:18 AM

Hi all,
I am currently running 7x15" at the front and 10x15" at the back.
Tires fitted are BF Goodrich 205/60VR15 front and 265/50VR15 at the back.
These tires do not have a lot of grip.
Does anyone know what other tire choices I have for the road on these 15" wheels?

10-08-02, 04:12 PM

Sounds like you are running the original spec GTD tyres sizes. Snag is they no longer make the rear tyre and there are no real straight forward replacements out there. 15 inch rims are discriminated against. But does the government do anything about it? No....

Anyway. Some guys use Pirelli P7 275 55 15s as used on some Aston Martins. Not very common but they do exist. Cost maybe up to £300 per tyre. There isn't a front P7 to match but you can match the grip level by reading the small print on the tyres. The treadwear number is a good indicator of grip. The lower the number and the softer the compound.

The only other option I know of is to change the speed rating on the tyre and go to a lower speed rating. This may cause you legal and insurance issues and these may be different than in the UK. There are HR Comp TA tyres that will go on your rims but they are likely to have no more grip than your current tyres.

What ever you choose to do, if you change your tyres keep your current tyres in storage. If they have tread they are worth hanging onto for some future use.

If you find any good 15 inch tyres that are VR rated then shout about it as everyone would like to know.

This problem is why so many owners go for 17 inch rims.

Malcolm

gweitzel · 10-09-02, 02:07 AM

Thanks, Malcolm,
In Germany I can not run tyres with a lower speed rating, so this option is out.
A friend of mine works at Pirelli in Germany and I have already enquired about the tyre you mentioned.This tyre is obviously out of production for some time now and they could not tell me if and where there are any stocks left.
Does anyone know?
Are there any other suitable 15" tyres anywhere?
If I would change to larger wheels, where could I get them from and how much would they cost?

MK -IV J6 · 10-09-02, 09:51 AM

Hoosier makes very sticky DOT 15 inch tires
in the sizes you need.

Julian West · 10-09-02, 02:36 PM

Those of you that run 17", what rim/tyre sizes do you go for? There seems to be plenty of choice, right up to 315/35!

Gary Gibbs · 10-09-02, 04:29 PM

Wayne uses 245/45-17 front (8" rim), and 315/35-17 rear (11" rim). I will be fitting a set to a wide body CAV in a few weeks and will let you know. Anticipated 335/35-17 rear and same or 255 front.

Julian West · 10-10-02, 02:57 AM

OK CCX33911, thanks for the info. I'm sure the larger tyres give a huge footprint. Is it possible to overtye a GT40? or will the chassis dynamics cope with so much rubber?

Also, I'm concerned that such a wide, flat tyre will need very precise geometry & perhaps softer springing, as there is no compliance in the sidewall.. anyone got any experience of this?

10-10-02, 04:46 AM

The Pirelli 15 inch tyres I mentioned above have to be sought out. Andrew (and Roy?) got sets of rear tyres from Micheldever Tyres in Micheldever, Hants, UK. I think they made a batch for Aston Martin and none since. Seek and ye may find?

The Hoosiers mentioned above, if they are the same DOT tyres that I have read about, seem to be perfect. But when I spoke to the distributor, he said they were not road tyres but a "race" tyre as the 0.5 mm tread will disappear after one hot lap to leave you with a slick! A shame really. However if you hand cut the tread deeper, would that work? I don't know.

The Dunlop Post Historics may suit. The 4.75 10 by 15 (fronts) and the 5.25 10 by 15 (rears) do not say Not for Road Use on them. These have been used on some UK cars. They are not speed rated as they are cross plies. Therefore there is a case for them being legal.

Hope this helps

Malcolm

10-13-02, 07:02 AM

Someone could tell me were finding the 17" rims i saw on Brian Mc gees car at Le Mans Classic ? BF Goodrich slip too much ....

Brian Magee · 10-13-02, 03:49 PM

Hi Fred

My wheel centres are from a small batch of rims that Ken Saunders had cast using an original BRM wheel as a pattern. The rims are 17" which step down to 15" and bolt into blind holes in the centre from behind so that it looks like a one piece wheel. The stepped rims are no longer available so I have to treat my wheels with care as I will not be able to replace them.

Brian

10-14-02, 12:48 AM

He made them from castings from within the Enthusiasts Club so they are not off the shelf items but this does not mean they are not available but you would need to talk to the Enthusiasts Club for the right contacts. Sorry I can't help you more.

Malcolm

gweitzel · 10-15-02, 07:46 AM

Hi Malcolm, MK-IV J6,
I enquired about the Hoosier Tyres you mentioned at a place called frisbyracetyre:

I am enquirieing about Hoosier DOT Radial Tyres suitable for 15" wheels as
listed on your website, product codes 45500-45540.
I am looking for suitable tyres for a Ford GT40 Replica which has 7x15"
front wheels and 10x15" rear wheels.
1. Are these tyres street legal tyres?, what is the depth of tread?
2. Do you have these tyres in stock?
3. If so, can you ship to Germany and what would be the approx. freight
charges? snail freight is ok.
4. What are the different compounds listed? Do you have more details?
5. Are there any other tyres which you could recommend or supply? I am
currently running BF Goodrich 205/60 VR15 front and 265/50/VR15 rear but
these do not provide the desired level of grip.

Here is their reply:

The radial tires you asked about are competition tires only. They have 5\32's
of rubber on them and no real tread design, just two lines. When they get hot
they would pick up any object inthe road. Some of the guy's that have the
Shelby Cobra's use the Street TD, ut it is a bias ply tire, but it is not
speed rated, but it is capable of handling high speeds. The sizes that are
available are P225/50d15, P245/60D15 and a P275/60D15. We can ship to Germany,
we use UPS or FedX. I hope this helps you.

Thanks

Bob Schaefer

So this option seems to be out as well. 5/32" tread is 5mm in christian units-thats where you start looking for a replacement tyre on the road. I dont think that tyres without a speed rating are legal in Germany.
Were these the tyres you were referring to, MK-IV J6?

josvdp · 10-15-02, 08:55 AM

"5/32" tread is 5mm in christian units"

OBJECTION :

The imperial system is older than the metric as far as I am aware and I think the latter postdates Christianity by nearly two thousand years

I can't believe I'm writing this on a forum like this - I must be very bored at work today !