TR4 Tyre Pressures

[Rob Clarke]

Good day to all,

 

Sorry to turn to what is probably a well worn subject for the seasoned reader, but folowing a quick search of the Forums I couldnt find what I was after. I am probably looking too deep into this as usual, but I would appreciate any thoughts on reccomended range of tyre pressures for my project TR4 to be on the road soon (this year I hope!). I am keen to keep the car as original as possible, apart from front anti-roll bar and a bit more poke from the engine, and I have all the period advice regarding recommended tyre pressures. However, tyres are very different today to what they were back in the day, even radials. The handbook recommends different tyre pressures for each make / type of tyre that were on the market back then. I have bought a set of 165/15 Blockley tyres (with tubes on my original wires), that look just right, good price too - I can recommend you look these up if not already. I am also new to TR'ing, so I will be struggling to know initially what is a good set up, and not. Any advice welcomed.

 

Cheers,

Rob

[stuart]

Try 24F 26R to start and see how happy you are with it.

Stuart.

[John Morrison]

I run 24 fr 28 rr,

and up the rears to 30 for a full load, and or sustained motorway speeds.

John.

[Motorsport Mickey]

Oh and front anti roll bar...get used to enhanced understeer.

 

Mick Richards

[Steves_TR6]

Oh and front anti roll bar...get used to enhanced understeer.

 

Mick Richards

Unless you add a rear arb as well, but hardly original !

[peejay4A]

28 front and 26 rear suits my car and driving style. A tip from the dearly departed JF which works for me.

[Motorsport Mickey]

^ +1 The higher front pressures helps combat the anti roll bar.

 

Mick Richards

[mike3md]

Interesting, at the weekend in conversation with a well known TR specialist they were suggesting that the fronts should have higher pressures than the rear, on the basis that the normal weight distribution is front biased (unless you are fully loaded for a 2 week camping holiday!)

 

I think most would normally put less air in the fronts.

 

 

Mike

[North London Mike]

+1, same conversation, higher front pressure is not intuitive (after ten years and a few laps the other way round)

 

MIck: You seem to favour the higher front pressure. LNK does not have a front anti roll bar, would you still recommend ??

[Rob Clarke]

Thanks all, got a few different ideas and pressure balances for me to try here. Hopefully the understeer inducing anti roll bar will make the car act a bit closer to half a lifetime experience driving front wheel drive euro boxes! My armchair logic was convincing me that the front bar would act to stabilise the front of the car against the influence of the mighty iron lump of an engine and make it handle a bit more neutral. Which would make a standard suspension set up TR4 handle more predictable, with or without a front anti-roll bar?

 

Rob

[Motorsport Mickey]

Rob,

 

You have a PM. (Private Message). Go to the small triangle to the right of your name on the top right of the page and click on it, select the Personal Messenger item on the left drop down and click on it for a message.

 

Mick Richards

Edited March 6, 2017 by Motorsport Mickey

[Motorsport Mickey]

+1, same conversation, higher front pressure is not intuitive (after ten years and a few laps the other way round)

 

MIck: You seem to favour the higher front pressure. LNK does not have a front anti roll bar, would you still recommend ??

Hi Mike,

 

The standard handling on a TR4 is set at understeer, the fitment of a front anti roll bar takes you to UNDERSTEER.

 

The early TR4 has a positive camber vertical link (the later and TR4a is negative) and this allows the tyres to "tuck under" with the side forces which is why number one mod is to fit different length top wishbones to induce negative camber (on competition cars up to about 2 deg depending upon how the suspension is set).

On a standard suspension set up the handling of the car can be influenced greatly by adjusting the tyre pressures, often very crude because you change the handling by making either the front or the back handle worse which allows the balance of the car to be changed and conversely the handling as a whole gets better.

Increasing the front tyre pressures helps prevent the tyres tucking under preserving the tyre footprint and gives increased grip reducing the understeer even upon cars without an anti roll bar. On a standard roadgoing TR4 with live axle I always favour a higher front wheel tyre pressure.

The "live" axle cars of course control their rear wheel angles themselves presenting a more vertical tyre profile, but have their own problems with "bump" oversteer and other maladies all of which can be modified.

I've written a small article on bump oversteer and curing it on the front suspension which is available to any who want it (over 200 forum users have so far) just send me a PM with your e mail address and I'll send it.

 

Mick Richards

Edited March 6, 2017 by Motorsport Mickey

[Rockie51]

Thanks all, got a few different ideas and pressure balances for me to try here. Hopefully the understeer inducing anti roll bar will make the car act a bit closer to half a lifetime experience driving front wheel drive euro boxes! My armchair logic was convincing me that the front bar would act to stabilise the front of the car against the influence of the mighty iron lump of an engine and make it handle a bit more neutral. Which would make a standard suspension set up TR4 handle more predictable, with or without a front anti-roll bar?

 

Rob

Just out of interest, does anyone have any figures for the front/rear weight distribution for TR4 and 4A? The "mighty iron lump" is in fact located entirely behind the centre line of the front wheels and I have often thought that with 2 passengers on board the distribution must be close to 50/50. I have never been keen on antiroll bars for a road TR especially on Oz roads, because hitting a bump with one wheel transfers some of the impact to the opposite wheel, further unsettling the car. Having said that, my weekly reading of Autocar leads me to think that your roads may be worse than ours!

[Motorsport Mickey]

In standard trim 52/48%.

 

Mick Richards

[Rockie51]

How about with this lot on board? (still learning about posting images!)

 

 

 

 

Edited March 7, 2017 by Rockie51

[Motorsport Mickey]

How about with this lot on board?

 

What sort of trailer do you tow

 

Mick Richards

Edited March 7, 2017 by Motorsport Mickey

[littlejim]

Mine (4A) when I first got it, used to understeer into sharp corners, then snap into oversteer.

During the refurb I found a fair bit of toe in on the rear wheels, which I changed with shims to zero toe in.

Now it just goes where I point it.

[stuart]

FWIW it also does depend a lot on the size of rim/tyre combination fitted as well.My figures were for 195/65.

Weight distribution on my solid axle 4a (As shown on MOT Brake roller test) with 1 chunky MOT tester on board and around half a tank of fuel and an empty boot is exactly 50/50.

Stuart.

[peejay4A]

+1 195/65 here too.

[North London Mike]

Hi Mike,

 

The standard handling on a TR4 is set at understeer, the fitment of a front anti roll bar takes you to UNDERSTEER.

 

The early TR4 has a positive camber vertical link (the later and TR4a is negative) and this allows the tyres to "tuck under" with the side forces which is why number one mod is to fit different length top wishbones to induce negative camber (on competition cars up to about 2 deg depending upon how the suspension is set).

On a standard suspension set up the handling of the car can be influenced greatly by adjusting the tyre pressures, often very crude because you change the handling by making either the front or the back handle worse which allows the balance of the car to be changed and conversely the handling as a whole gets better.

Increasing the front tyre pressures helps prevent the tyres tucking under preserving the tyre footprint and gives increased grip reducing the understeer even upon cars without an anti roll bar. On a standard roadgoing TR4 with live axle I always favour a higher front wheel tyre pressure.

The "live" axle cars of course control their rear wheel angles themselves presenting a more vertical tyre profile, but have their own problems with "bump" oversteer and other maladies all of which can be modified.

I've written a small article on bump oversteer and curing it on the front suspension which is available to any who want it (over 200 forum users have so far) just send me a PM with your e mail address and I'll send it.

 

Mick Richards

Mick

 

You have a PM

 

Thank you

[dougal]

Hi

 

As a standard road car you are never going to get it to handle very well on a 195/65 tyre. also if you are on wire wheels you shouldn't really fit tubes into 65% profile tyres.

 

The tyre pressure problem is a nightmare, because on top of all the considerations that have been discussed here there is also the carcass to consider.

 

Here is Michelin they recommend different pressures depending on the tyre. However the only one they currently make is the XAS http://www.longstonetyres.co.uk/page/165hr15-michelin-xas.html

 

here is Pirelli a bit more where we want it today. and that recomendation will be for the Cinturato http://www.longstonetyres.co.uk/page/165hr15-pirelli-cinturato-ca67.htmlprobably thew best tyre for a TR4 (either that or XAS)

 

 

 

An d then here is Dunlop with different speed or loaded recommendations. sadly Dunlop don't make any historic road tyres.

 

[stuart]

Interesting that for a solid axle 4a its listed with 6.95X15 which was quite a large tyre for its day and yet on some lists 5.90X15 for IRS cars.

Stuart.

[Alec Pringle]

The only 6.95x15 tyre I've ever seen mentioned in factory documentation was the Goodyear GP, and that was listed for TR4, TR4A live axle, and TR4A IRS.

North American market and 4.1 diff are also mentioned in conjunction with the Goodyear GP.

 

That sounds logical enough, the first Goodyear race tyre, RR1, had proved itself in N American sports car racing for 3 seasons before the TR4 came along, and presumably the street version GP was fashionable . . . . . especially after Goodyear decided to challenge the Dunlop monopoly in F1, 1964.

 

A 3.7 diff with a 5.90 tyre wouldn't be so much different from a 4.1 coupled to 6.95 rubber.

 

Cheers

 

Alec

[dougal]

yep it suprised me, and it seems funny they all mention it.

[Alec Pringle]

The logic seemed to be that some at least of our North American friends were undiscerning when it came to handling, and that the 'bigger is better' cosmetic view prevailed, along with the greater ride comfort offered by the larger dimension rubber . . . . .

 

Cheers,

 

Alec