Tyres - What influences 'grip' the most?

[graham bahr]

Originally Posted by retro_msport

Dennis would you agree to this.. 9" rim with Dtypes tyres fitted, check temps to get pressure and camber setting right for the particular conditions, and then fine tune spring rates with temps and stopwatch

dunno about denis but i would agree, 225 is just miles too wide for 7 inch rim, and argueably inbetween ok and too wide for an 8inch

just to back up what i say,

i normally run a 200 on an 8 inch rim, i've ordered some 220's and so am now hunting around for a set of 9 inch rims.

[greenamex2]

Sounds like a plan but good luck getting some 9" wide rims on a budget!! If anybody knows where you can get budget (ie cheaper than Image) 9*15's with an offset around ET37 PLEASE let me know!

Now that I have to run on a budget I would do something like buy a COUPLE of the cheapest 8" wide wheels I could buy (secondhand/ebay/scrap yard), sling a couple of good condition tyres on them. Try them on one end of the car for half a practice then stick your normal combination back on for the rest and compare the feel and stop watch.

If they make that end grip/the other end slide then proceed immediately to the nearest wheel manufacturer and get the lightest wheels you can afford made.

Then you are going to have to spend a few more practice sessions with a tyre temp probe/gun fine tuning.

[Al Weyman]

I bought a set of Minilite lookalikes off eBay brand new I think he has more I can check if you like, they were Chevy spacing same as Jaguar 15 x 8 and a very reasonable price lot less than DT's, came complete with tube nuts and washers (chrome).

[TEAM78]

The widest rims Ive ever come accross at sensible prices is 8", 235 wide tyres fit fine onto 8" rims any way. As for running 225 on 7" rims, er no chance, widest on a 7" rim should be 215 really.
Have you considered compliance effects in the suspension? these can be large.

[retro_msport]

This would be what i was looking for on Dtypes car, thats what we run on the escorts .. 10"x 21.5"tyre on 10.5"x 15" wheels, heavy engine (cossie turbo) with an all up weight around 900kg. the wheels on that car cost £500 ... the joys of Fords being popular

[dtype38]

Great advice there guys... this really is very helpful.

If I might push my luck a little bit further and add a bit more about my options....

First off to mention is that the Jag Club sports car series has a rim width limit of 8" to keep costs down. Even then, I currently run in the "semi-modified" class which has a 7" rim width limit. If I move up to 8" I'll have to go in the "full-modified" which is pretty much an "anything goes" class. That could get a bit pricey but at the mo there's not much competition in it. That said, the SR & GT race series I run in doesn't have a rim width limit other than the tyres have to be list 1a, 1b, Historic or Post Historic. So long as the tyre is there you can have anything that fits. So..... if going wider on the rims is the only real option, I'll have to consider which type of racing I want to do.

Could be why one chap said I was "over-tyred" because he was running 205 tyres, but I can't remember if it was on 7 or 8 in rims. Anyway, Al, I think minilites are the cheapest option for 8x15s to fit mine as well. Falcemob got some 7x15s for his D-type very reasonably. That said, retro, do you have contact info for "Harry at Image wheels" please?

Back to the tyres though.... I've now cut away the tread face completely on that tyre, and the blistering goes well down into the tyre... deeper than the tread depth. The rubber is all granular which I thing means its got really quite hot. Guess that one's a gonner Anyway, I had a chat with chap who races the same basic setup as me and he said that I need to be careful not to under-inflate the tyres, or work them too hard early in the race. He said that with Yoko 008s this can lead to the carcass overheating and cause problems. That could well be exactly what has happened to mine.

Another interesting thing I just noticed as well, on all my tyres, is that I'm wearing the treads in a "saw tooth" pattern across the width of the tyres. The outer edges of the treads are worn more than the inner edges. On the outer half of the tyres I'd say the wear is about twice as much on the outer edge of the block than on the inner edge. Would I be correct in guessing that this means that not only are my tyres tucking under, but I'm sliding them as well?

PS. retro those look the dogs danglies on an Escort... but on a D-type?

[johnny yuma]

Speaking in ignorance really, never seen a D Type in Australia,only a replica some years ago.IMHO you need 38 to 44PSI IN FRONT TYRES,and maybe smaller diam ARB,and check the obvious ie toein/out,squareness and alignments generally,Ackermann angle if altered.Too much is going on at front,or the tyres are duds.

[retro_msport]

These are the ones I was on about



And if you look on this page you'll find the size guide that Harry uses so you can get the max size wheel under your arches
http://www.imagewheels.co.uk/pages/techincal_info.html

[greenamex2]

I'll try and get some pictures of my cars front tyres which demonstrate an extreme version of Dtypes wear pattern.

On the very inside of each tread block is a 2-3mm wide strip of TOTALLY unworn rubber. Image a brake pad that is overhanging a disc and you would get the idea.

The 100Kg lighter Pug 205's don't suffer from this despite being on a similar wheel/tyre combinations.

[Al Weyman]

I paid £75 each for the Minilites complete with studs and carraige and no vat.

[dtype38]

Johnny... with the A008R's I use about 3/4 degree neg camber all round, 30' of toe out at the front and 30' of toe in at the back, no ARB's, exceedingly stiff springs and virtually no damping all round, and about 27psi in the tyres. And that's 4psi more than I used to use in my old A032R's of the same profile I thought I might have been a bit over-inflated

Retro... very, very nice wheels. Last time I saw three piece D-type wheels they started around a grand a corner. The ones I use are one piece Compomotive at around a grand a set. I'll look into it though, cos you never know

Denis, what sort of things do you think could cause a "saw tooth" wear on the treads?

Al, when I've decided what sort of wheels I want, I'm going shopping for them with you!

[Al Weyman]

Sorry that should have read complete with tube nuts and washers.

[retro_msport]

Originally Posted by dtype38

Retro... very, very nice wheels. Last time I saw three piece D-type wheels they started around a grand a corner. The ones I use are one piece Compomotive at around a grand a set. I'll look into it though, cos you never know

)

I'll look forward to seeing your car with its new wheels then

[graham bahr]

Originally Posted by dtype38

Denis, what sort of things do you think could cause a "saw tooth" wear on the treads?

in my experience saw teeth saw teeth come about due to either geometry problems, or excessive tread block movement,caused by incorrect rim width or pressures, too soft a compound or overloading of the tyre, or in other words nearly anything!

[greenamex2]

In my case I am running on genuine road tyres, can't change my geometry significantly (Al's fault), have restricted rim width (8") and am probably overloading the front tyre.

Can't do much about the tyre other than switch them from front to rear each meeting to even out the 'abuse'. I could also change them more regularly but even the ridiculously cheap price we get them for is going to be difficult with the baby/wife.

One thing I could do is have them buffed lower. On the advice of another competitor (Pug 205) I had more tread left on them but having now seen their tyres they don't suffer the same as my car does.

About the only thing left to do to the geometry (within the rules) is increase the castor and increase the cars track. Given that increasing the track is going to cost money and could cause other problems we are delaying that and going for a castor increase.

I am stuck with the rim width.

Funnily enough the rears don't suffer half as bad. The tyre temp reading are about the some so I guess the problem is the way the heat is generated in certain parts of a corner.

[graham bahr]

Originally Posted by Denis Bassom

One thing I could do is have them buffed lower. On the advice of another competitor (Pug 205) I had more tread left on them but having now seen their tyres they don't suffer the same as my car does.

Funnily enough the rears don't suffer half as bad. The tyre temp reading are about the some so I guess the problem is the way the heat is generated in certain parts of a corner.

not suprised at either, buffing prevents the tread moving around as much, therefore the tyres cant chunk up or saw tooth as much, from what i've heard, buffing a new set of tyres down to half tread depth will not only mean they work better but also last longer than an unbuffed set

the rears wont suffer in the same way, afterall they dont have the load of trying to turn the car in and most likely whilst also on the brakes

[johnny yuma]

dtype38-don't hesitate to ramble on the D type nothing could be more interesting.I can't see 27psi is anywhere near enough pressure in the front tyres . I DON'T assume it is a genuine D but a replica so more options must be available re ARBs,springs,dampers etc but notwithstanding all that,and although by modern standards it is not a heavy car[although most is over the front wheels] current practice with your tyre/rim for those who are prepared to reveal the semi-secret world of inflation pressure WHERE HAPPY talk of 35-45psi.
As well you have biggish unsprung weight,minimal damping,noARBs..sounds unnecessarily primitive.Trusting you chuck it into tight turns and give it a bootful to break the tail loose and take the push off the front end!!!

[greenamex2]

Dtype - are your quoted pressures hot or cold?

[graham bahr]

45psi!!! that would certainly suggest tyres too wide for the rims to me

[johnny yuma]

this is a long standing discussion of the bleeding obvious.If you have 15psi you have useless grip.25psi is average noddy who checks pressure every 6 months.30psi is a starting point for dry road.I have never driven any car which wasn't better with 36 psi front.

[graham bahr]

johnny it seems to me your mixing up road and race cars, i know of NO race driver that doesn't check the pressures at least once at the start of a meeting, most several times, so i dunno where the six month bit comes in.

you also cant generalise on pressures put 36psi in the front of my car and understeer wont be the word for it it wouldn't even think about going round a corner

[retro_msport]

pressures are set with a temp gun... once the calculations are done we adjust the pressure accordinly... and this can be as low as 18psi C for a front engined RWD car of 55/45 weight split and all up wet weight of 820kgs

[car1]

Tread Pattern or Tread compound

[Tony Crossley]

Artificially high presure in a road car will make it feel great at 6 or so tenths. The steering will feel more immediate, it will feel to have a little less body roll and compliance. But as soon as you start to push it a bit harder it becomes awful and then the tyres shortly overheat and it becomes really awful.
I was driving a friends M3 CSL on track a month or so ago on road tyres (not the cups) and it was understeering afte a few laps. The tyres were clearly goign off. Checking the tyre temps shows the centre to be overheated. He had started off with normal road presure and maybe added a few psi "'cos that's what the trackday people say you should do." I presuaded him to drop the front and rears (that were also overheating in the centre) to around 4 or 5 psi less than road (cold). Subsequent sessions the understeer did not return even after extended lapping and the car was flying.

[jonners]

johnny - go back to Max Power please...