Tyres - What influences 'grip' the most? - Page 5

emjaya · 9 Dec 2005, 14:13 (Ref:1480487)

Quote:

Originally Posted by dtype38

Ok, so it seems I might not be going down the right route using 225s (8.85inch) wide tyres on 7" wide rims

...

But would anybody like to hazzard a guess at what's happened to the second tread ring on my front right tyre. It goes all the way round the tyre in a regular pattern and appears to be burst blisters from below the tread rubber. I did this sometime during a two day meeting at Croft on a warm dry day, but didn't notice it till I took them off the other day.

Sorry to come in late on this,but that line in your tyre looks like one of the layers of rubber extruded on in manufacturing was contaminated(speck of dust probably)and did not cure as well as the rest of the tyre.Being heated or indeed overheated caused it to separate from the layer beside it.

That's only a guess from someone who worked in a retread factory many years ago,but that's what popped into mind when I saw the photo.

Great thread,very interesting reading.

greenamex2 · 9 Dec 2005, 14:18 (Ref:1480491)

retro/tony - Couldn't agree more. We going up on pressure but the lap time keep increasing only to come down when the pressure does.

On my kit car I run 17-18PSI cold. It sound 'wrong' but it works. Bit odd to drive to and from track days though. I am also constantly worried about the tyre coming off or spinning on the rim until the are hot. Someone please assure me that will never happen!

HiRich · 9 Dec 2005, 14:32 (Ref:1480502)

Denis,
Well I run 14 & 16psi, as recommended by the factory. But that's 450kg (including driver) on four 6" rims. And I can run ACB super-soft as road tyres...

retro_msport · 9 Dec 2005, 14:35 (Ref:1480505)

Dennis... we set pressure high at the workshop... and drop them as we run the car at the track...(or increase if it gets colder or wet ... now you driving to a track, run road psi then drop at the track, and then pump them up again for the way home...

I would hate to drive a car with 10" rubber at 36+ psi... the tyre would look like the rear on a Harley Chooper and run on the center 2"

graham bahr · 9 Dec 2005, 14:39 (Ref:1480510)

Quote:

Originally Posted by retro_msport

Dennis... we set pressure high at the workshop... and drop them as we run the car at the track"

so do i its a sight easier to let them down at the circuit than blow them up!

graham bahr · 9 Dec 2005, 14:44 (Ref:1480517)

Quote:

Originally Posted by Denis Bassom

On my kit car I run 17-18PSI cold. It sound 'wrong' but it works. Bit odd to drive to and from track days though. I am also constantly worried about the tyre coming off or spinning on the rim until the are hot. Someone please assure me that will never happen!

ok the pressures low but so is the weight of the car.

i very much doubt they will come off the rim, you just have to see how much the bead breaker on a tyre machine sometimes struggles to get them off,

as for slipping, its quite common for drag racing big cc street motorcycles to run 2 psi in the rear tyre, they dont slip

R59 · 9 Dec 2005, 15:17 (Ref:1480543)

Quote:

Originally Posted by graham bahr

i very much doubt they will come off the rim, you just have to see how much the bead breaker on a tyre machine sometimes struggles to get them off,

Should have told that to the Toyo's on the front of Neil Armstrong's Civic when one came off on his n/s/f causing him to punt me off at Thruxton two years ago. He had 16psi in them for some reason (trying to get some heat in them so I was told!).

I ran at 38psi (wet) and 40psi (dry), and found them rise to 40-41 wet when hot, and 44 dry. Any lower, and laptimes went up. (Nova, 780kg)

But taking the weight of your kit Denis, I'm sure that you can run much lower pressures, and get away with it. What are they hot?

The proof of the pudding is in the testing!!

Rob.

graham bahr · 9 Dec 2005, 15:22 (Ref:1480548)

Quote:

Originally Posted by racing59

Should have told that to the Toyo's on the front of Neil Armstrong's Civic when one came off on his n/s/f causing him to punt me off at Thruxton two years ago. He had 16psi in them for some reason (trying to get some heat in them so I was told!).

Rob.

true but neils civic is a lot heavier than most kit cars

**dtype38** · 9 Dec 2005, 16:11 (Ref:1480592)

emjaya, thanks for that note... I was hoping that I wasn't the only one thinking "manufacturing fault", but it's a definite possibility considering it was on the right and therefore "less" loaded of my front tyres.

Either way.... that doesn't mean I'll be just writing off the experience and not change anything. There's been some very sensible advice so far about using wider rims to give better tyre wall support. Also that the only real way to set the correct tyre pressures is with proper testing and a good tyre temperature probe.

Just to reply to to Dennis on an earlier question, I quoted my tyre pressures cold. I'd expect them to be 8-10psi higher than that on track. And on that particular subject, lets not get all uppity about tyre pressures and the difference between racing and doing track days in a road car. It's horses for courses. I've done some track days in a road-going Jaguar XJS (1750kg) on 70 profile tyres and had to up the cold pressures to well over 40psi just to keep the tyres on the rims!

Anyway, when we run out of things to say about tyres in the dry, we can have a little chat about whether to put the pressures up or down when it rains

retro_msport · 9 Dec 2005, 17:08 (Ref:1480628)

Quote:

Originally Posted by dtype38

Anyway, when we run out of things to say about tyres in the dry, we can have a little chat about whether to put the pressures up or down when it rains

We dont ... we pack up and go home.... oh no thats in America

**dtype38** · 9 Dec 2005, 17:23 (Ref:1480634)

Or Rockingham

graham bahr · 9 Dec 2005, 17:31 (Ref:1480639)

Quote:

Originally Posted by dtype38

Anyway, when we run out of things to say about tyres in the dry, we can have a little chat about whether to put the pressures up or down when it rains

havn't we already done that one to death somewhere?

the answer was most go lower, some go higher and some leave them alone

**dtype38** · 9 Dec 2005, 18:02 (Ref:1480674)

I think

is the one you were looking for

Or perhaps we've done that one to

Anyone got anything else serious to say? Please?

graham bahr · 9 Dec 2005, 18:07 (Ref:1480679)

its cold and dark outside! seriously cold and i need to go out in it and work on my car, but its far to easy to stay in the warm posting on here.

**Tim Falce** · 9 Dec 2005, 19:01 (Ref:1480711)

Quote:

Originally Posted by dtype38

Anyone got anything else serious to say? Please?

On the subject of overheating, have the sidewalls gone a blue colour, I have had this on my 032's and on truck tyres that have overheated and find this good indication that they have got too hot.

graham bahr · 9 Dec 2005, 19:15 (Ref:1480720)

i'd forgotten about blueing but your quite right falcemob

**dtype38** · 9 Dec 2005, 19:42 (Ref:1480744)

Dennis didn't forget about blue. It was the first thing he asked (post #63) when I put up a picture of the tyre. As I said then, there is no discernable blue colour to the tyre. Looks completely normal... well except for the big trench I've now cut in one of the treads

Al Weyman · 9 Dec 2005, 19:56 (Ref:1480752)

I experimented with the pressures on the Dunlop Formula R's and agree with graham, Johnys figures just will not cut it. I set them orginally at 30 psi alround then onthe advice of a fellow competitor (dangerous you may say) with a similiar weight car who goes really well ;et the rears down to 28. Not bad results got a 4th but stll going off a bit. I tried loweringthem bown by 5 psi in the hope they would last better and put up with a bit of squirming at the start, did'nt work. So for the race I went up about 37 front 35 rear for the race. result was a disaster, by 6 laps they were finished witness by my excursions in to the Pembrey swamp. So I reckon the advise I originally got i.e. 30 front and 28 rear was pretty near the mark.

**Tim Falce** · 9 Dec 2005, 20:06 (Ref:1480758)

Quote:

Originally Posted by dtype38

Dennis didn't forget about blue. It was the first thing he asked (post #63) when I put up a picture of the tyre. As I said then, there is no discernable blue colour to the tyre. Looks completely normal... well except for the big trench I've now cut in one of the treads

Think he was talking about the blue on the tread, but I would have put any blueish tinge in that pic down to the lighting conditions of the photo and not necessarily the tyre itself

**dtype38** · 9 Dec 2005, 20:11 (Ref:1480762)

Assuming your setup is reasonable, I guess we'd have to say you've got a classic case of an under-tyred car. That is, with the correct settings of everything, they don't last a full race distance. That gets us into the realms of tyre management! So... do any of you guys deliberately drive below 10-10ths (

) early in the race so that you have tyres under you at the end. I've never even tried that myself... but then I've never done a race more than 20mins

Al Weyman · 9 Dec 2005, 20:17 (Ref:1480765)

Good point D-Type and something I think I am going to have to do. When I last race we were using Falken road rubber and it was a simple case of adjusting the pressures to get to what stage in the race you wanted the car to be at its best, new ball game entirely these Dunlops.

**dtype38** · 9 Dec 2005, 20:38 (Ref:1480781)

Falken road tyres???? I used a set of them on my XJS race car (215/55R16 or something like that). Raced a full season on them and you could have mistaken them for new ones! I've never come across a harder bit of rubber that wasn't called "Bakelite"

Al Weyman · 9 Dec 2005, 20:41 (Ref:1480784)

Quote:

Originally Posted by dtype38

Falken road tyres???? I used a set of them on my XJS race car (215/55R16 or something like that). Raced a full season on them and you could have mistaken them for new ones! I've never come across a harder bit of rubber that wasn't called "Bakelite"

Yeah great wer'nt they, I still have two sets on Camaro rims, dthey worked better than the ones we were using the year before and all times improved.

**dtype38** · 9 Dec 2005, 21:04 (Ref:1480803)

Oh, almost forgot! When we were talking about tyre pressures, and commenting that checking the temperatures across the face of the tyre is the only real way to set pressures... err... what sort of temperature are we looking for as "correct". I'm talking about the temperature you read with a sub-surface probe immediately after full race conditions. Also, is this temperature an absolute, or, a number of degrees above ambient? Oh, and are we looking at different working temperatures depending on the type and compound of tyre?

retro_msport · 9 Dec 2005, 21:27 (Ref:1480819)

The tyre manufacturer should be able to give you and ideal temp range for any given compound. if yours is hotter then your over working them and if the are under then your not working them... though this is rare as can be seen from the previous posts

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