Hello

[cliff.b]

Have just bought another Spitfire after a 40 year hiatus. It's a largely restored 1500 but bought as a non runner (Soon resolved). I'm sure I will have many questions and will raise them in the appropriate sections of the forum but I cant see which of those would cover tyres. It has what looks like original rims with brand new 185/70's on the back & 185/60's on the front.

Apart from the profile difference, these are far wider than I would have fitted in the past so just looking for any thoughts about their suitability and tyre pressures to use?

Any advice greatly appreciated.

 

 

[dougbgt6]

Cliff,

Try the search option, "tyres" will reveal  there's been  plenty of threads on tyres and debate about pressures. 185 does sound big. and I wouldn't use different widths .As to pressures my GT6 is supposed to have 26 on the back and 22 on the front according to the manual, but modern tyres need a bit more. I run at 30 and 28, but a Spitfire will be different.

Doug 

[cliff.b]

Thanks for your reply. The tyres are all the same width (185's) but the front ones are lower profile. 

[dougbgt6]

Cliff,

Sorry, yes profiles as well, I like to keep them all the same, what would you carry for a spare? (Although my modern has a completely different diameter spare! Ford recommended!)  

Others may think it's OK, but check out the search option.

Doug

[Gully]

1 hour ago, dougbgt6 said:

.As to pressures my GT6 is supposed to have 26 on the back and 22 on the front according to the manual, .

Doug 

Really?! That's interesting, as my orange owners manual for the Mk 3 GT6 says pre-1973 (ie. Rotaflex) 24 front, 28 rear, but 1973- (swing spring) 30 front and 26 rear. All based on 155/80 tyres. With modern tyres (I run 175/70 R13 on 5 inch rims) I set the pressures on my 1970 GT6 at 27 front, 30 rear - if I go as low as 24 on the front the sidewall 'slop' is really noticeable.

Gully

[dougbgt6]

Gully,

Just checked Haynes (Never wrong! ) It says GT6, 20 front and 24 rear, no mention of tyre type or year. My Euro manual says GT6s 20 24 for cross ply and 22 26 radials. The WSM says 20 24 is for a GT6 MK1 and the MK3 supplement gives tyre pressures for year types '71,  '72, and '73. 1 up, 2 up, or laden.  These vary between 24 30, 24 28, 24 34 and 30 26. (30 26? Really?!!)

From the WSM this makes the Gully-mobile a '72  which I think is correct!

 All very confusing and useless information because you don't run modern tyres that low. I run 28 front 30 rear, judged and set on how it's handling, which is almost the same as you. 

Doug

[cliff.b]

Reading all the above, I think that once the brakes are sorted I just need to take it out and see how it feels then experiment with the pressures.

 

Many thanks.

 

[Pete Lewis]

Its pretty certain the book pressure wont suit a modern tyre construction and higher than quoted is normal to gain handling but not so high as to wreck the comfort 

yes trial and error is the way to a liked preference /

 

Pete

[Gully]

13 hours ago, dougbgt6 said:

Gully,

Just checked Haynes (Never wrong! ) It says GT6, 20 front and 24 rear, no mention of tyre type or year. My Euro manual says GT6s 20 24 for cross ply and 22 26 radials. The WSM says 20 24 is for a GT6 MK1 and the MK3 supplement gives tyre pressures for year types '71,  '72, and '73. 1 up, 2 up, or laden.  These vary between 24 30, 24 28, 24 34 and 30 26. (30 26? Really?!!)

From the WSM this makes the Gully-mobile a '72  which I think is correct!

 All very confusing and useless information because you don't run modern tyres that low. I run 28 front 30 rear, judged and set on how it's handling, which is almost the same as you. 

Doug

Nothing like consistency! 😄 I'm intrigued by the reversal in pressures for the last models - have you ever tried the hard front, softer rear on your '73? 

Mine's a '70/'71 Mk 3, so even the WSM and owner's manual (extract below) don't align... Really is a case of going by feel!

Gully

[johny]

Ive always thought it strange having softer front when thats where the most weight is😵

[Pete Lewis]

the balance front /rear is all about steering reactions understeer /oversteer characteristics 

it is unusual to see the balance reversed which is the change from controlled rear  camber on rotoflex  wishbone to lesser controlled with a swing spring /axle

and dont forget in cold weather to check the pressures as cold air drops the pressures  same as hot increases 

if youre stored up then add 10psi to avoid flat sets , re adjust before  road use 

pete

[1969Mk3Spitfire]

On 14/04/2021 at 14:59, cliff.b said:

Have just bought another Spitfire after a 40 year hiatus. It's a largely restored 1500 but bought as a non runner (Soon resolved). I'm sure I will have many questions and will raise them in the appropriate sections of the forum but I cant see which of those would cover tyres. It has what looks like original rims with brand new 185/70's on the back & 185/60's on the front.

Apart from the profile difference, these are far wider than I would have fitted in the past so just looking for any thoughts about their suitability and tyre pressures to use?

Any advice greatly appreciated.

 

 

Congratulations on your purchase. I broke a 45 year hiatus last year by buying a Mk3. 

I believe that the car was originally fitted with 155SR13 tyres on 4.5J rims. These have a nominal diameter of 578mm.

185/70 will mount on a 4.5J rim but it has a nominal diameter of 590mm. 185/60 is not recommended for 4.5J rim. 5 inch is the minimum. Nominal diameter is 552mm.

Dimensions from ETRTO data book.

The Spitfire steering and suspension was not designed for lower profile tyre technology. If it were my car, I’d remove them.

 

 

 

[RichardG]

22 hours ago, Pete Lewis said:

if youre stored up then add 10psi to avoid flat sets , re adjust before  road use 

Now that's a great tip.  Never thought to do that but like the logic.

[Clive]

On 14/04/2021 at 14:59, cliff.b said:

Have just bought another Spitfire after a 40 year hiatus. It's a largely restored 1500 but bought as a non runner (Soon resolved). I'm sure I will have many questions and will raise them in the appropriate sections of the forum but I cant see which of those would cover tyres. It has what looks like original rims with brand new 185/70's on the back & 185/60's on the front.

Apart from the profile difference, these are far wider than I would have fitted in the past so just looking for any thoughts about their suitability and tyre pressures to use?

Any advice greatly appreciated.

 

 

(1) check teh date stamp on the tyres. That will tell you how old they are, so many people buy new tres early on in a restoration, and they are out of date before they hit the road.

(2) if the spitfire has 4.5j wheels those 185 tyres will be balloning, too wide for te rims. If the late 5j wheels, not quite as bad but not ideal

I have found that pressures are best found by experimenting. I have a rotoflex equipped spitfire, and find 24psi all round works well. Go to 30 and it feels skippy, softer and it wallows on the sidewalls. Of course, the tyre type matters, with most tyres expected to carry cars twice the weight of our little spitfires. 

 

[cliff.b]

10 hours ago, 1969Mk3Spitfire said:

Congratulations on your purchase. I broke a 45 year hiatus last year by buying a Mk3. 

I believe that the car was originally fitted with 155SR13 tyres on 4.5J rims. These have a nominal diameter of 578mm.

185/70 will mount on a 4.5J rim but it has a nominal diameter of 590mm. 185/60 is not recommended for 4.5J rim. 5 inch is the minimum. Nominal diameter is 552mm.

Dimensions from ETRTO data book.

The Spitfire steering and suspension was not designed for lower profile tyre technology. If it were my car, I’d remove them.

 

 

 

Thank you for your thoughts. Do you know if a 1978 1500 would be 4.5J or 5J? I was thinking 5J but could well be wrong about that.

[cliff.b]

8 hours ago, clive said:

(1) check teh date stamp on the tyres. That will tell you how old they are, so many people buy new tres early on in a restoration, and they are out of date before they hit the road.

(2) if the spitfire has 4.5j wheels those 185 tyres will be balloning, too wide for te rims. If the late 5j wheels, not quite as bad but not ideal

I have found that pressures are best found by experimenting. I have a rotoflex equipped spitfire, and find 24psi all round works well. Go to 30 and it feels skippy, softer and it wallows on the sidewalls. Of course, the tyre type matters, with most tyres expected to carry cars twice the weight of our little spitfires. 

 

Thanks. The tyres look and smell brand new but as you suggest, I will look for the date stamp.

I assumed a 78 was 1500 but as I just responded to another poster, I'm not certain about that and agree that they would be far too wide for 4.5Js. They don't look like they are "balooning" though. 

 

[cliff.b]

1 minute ago, cliff.b said:

Thanks. The tyres look and smell brand new but as you suggest, I will look for the date stamp.

I assumed a 78 was 1500 but as I just responded to another poster, I'm not certain about that and agree that they would be far too wide for 4.5Js. They don't look like they are "balooning" though. 

 

That should say assumed a 78 was 5J

[Clive]

1 hour ago, cliff.b said:

That should say assumed a 78 was 5J

From the factory, yes. Perfectly feasible that somebody has fitted 5.5j wheels. You shpuld be able to check by carefully looking for the small stamps on the wheels. Or by measurement, but that is tricky with the tyres on.

 

[cliff.b]

23 minutes ago, clive said:

From the factory, yes. Perfectly feasible that somebody has fitted 5.5j wheels. You shpuld be able to check by carefully looking for the small stamps on the wheels. Or by measurement, but that is tricky with the tyres on.

 

Do you know where these stamps on the wheels are located?

[thescrapman]

Should be in 2 places. One stamped inside rim, which I large letters.

other is on outside near centre of rim.

will say something like 4.5x13x16

[cliff.b]

43 minutes ago, thescrapman said:

Should be in 2 places. One stamped inside rim, which I large letters.

other is on outside near centre of rim.

will say something like 4.5x13x16

Many thanks👍