tire pressure

[mct340]

Has anyone got any data for tire pressures when autocrossing?

Given that :
the Elan is light (compared to most)
the tires are cold (autocross- no warmup)
the tires are soft compound (Toyo Ra-1 185/60 r13's on 5.5" rims)

I will have it figured out in a couple of months but shortcuts wouldn't hurt.
I've been running 30psi so far but am hesitant to go less....
Thanks,
Mike

[Fitz]

[quote="mct340"]Has anyone got any data for tire pressures when autocrossing?

Given that :
the Elan is light (compared to most)
the tires are cold (autocross- no warmup)
the tires are soft compound (Toyo Ra-1 185/60 r13's on 5.5" rims)

I will have it figured out in a couple of months but shortcuts wouldn't hurt.
I've been running 30psi so far but am hesitant to go less....
Thanks,
Mike[/quote]

Probably no help at all, but in Roadsports circuit racing we run Yokos AO32R's at 20 lb/sq.in (cold), so don't think you should worry too much about dropping a little. Ours go up to about 24/25 hot.

Good luck.

Fitz

[rgh0]

Fitz

I run my Yoko A032R soft compound at around 28 psi cold on my Elan and around 33 to 35 psi hot in for historic racing. I find lower pressures lead to overheating and the tyres loosing grip after about 4 laps or have I got something else wrong with my setup ? What is the rest of your suspension setup like such that it enables these lower pressures to work ? Whats "roadsports" circuit racing.

I run 175 x60 on 5.5. inch rims with 150 lb/in front springs and 115lb/in rears and 7/8th inch roll bar. The suspension is 3/4 inch lower than standard. I also find the car less stable and harder to control the breakaway with the lower presures before they loose grip.

Rohan

[mct340]

Thanks Fitz, I'm gonna drop down to 25 cold for the next few runs and maybe try 20 if I get real brave. Got to get a laser pyrometer..... Always something.
Mike

[Fitz]

Hi Rohan

Nice to speak to you again. As far as I am aware, noone runs those sort of pressures over here. Now there may well be many reasons, like higher ambients etc. that make your situation different (Although that is a poor example as it would probable indicate a lower pressure..........).

Some guys who run 32R's on lighter cars like clubmans/kit cars run at 17 lb/sq in (cold).

I have never experienced the tyres going off through overheating, but then my indelicate inexperienced rear end would not be the last word in sensitivity!!

Yokos seem to me to be incredible tyres that give a relatively stable and progressive performance that differs little on various surfaces etc, and is also a decent tyre in damp conditions (with no standing water!).

I shall ask some of the guys at Cadwell this weekend.

Roadsports is the shorthand for sports cars that are road registered, licenced and have passed the Ministry of Transport annual test. They are allowed various improvements and tuning etc. but must keep standard carbs, bodywork, no lsd etc. My Historic Roadsports car, Rosey, is an S1 with approximately 170 bhp and weighs 640kg, so she is still quite entertaining and has an ability way beyond that of her overweight geriatric driver!

Will let you know what other more scientific brains think next week.

Presumably this is your quiet season, is it?

Best wishes, mate.

[rgh0]

Hi Fitz

I agree with your assessment of the Yoko's. I use new ones as my wet tyres and worn ones as my dry tyres. The compound is good and ages well which is important for people like me who need to get the most racing miles possible out of a set of tyres to keep the cost reasonable.

A number of guys here run lower pressures than me, not as low as yours but maybe around 20 to 23 psi cold for a light car.

I had my last race for a couple of months a few weeks ago. All the histoic racing is up North in Queensland and NSW for the next couple of months over Winter and a bit far to go for to many weekends.

Rohan

[twincamman]

well guys sorry to say auto cross is not racing----the tires don't have a chance to heat up and stabilize the air pressure-and friction for 2 miles or so to get the compound nice and sticky : -----run 5 to 10 more Pound's than normal for this application ---better turn in caused by stiffer side wall IS WHAT YOU NEED NOT WALLOWING AROUND ON THE FLEXING SIDE WALL with 10 pounds total pressure-- -ed

[rgh0]

Ed

What running pressures do you aim for in autocross tyres.

In racing I aim for hot pressures in the Yoko's 032R around 33 to 35 psi and Hoosier street td's round 30 to 33 psi. This gives good stiff tyre side walls, stable tread that does not overheat and good turn in and corner stability given the 60% profile and tyre widths I use of of 185/175 and rim width at 5.5. inches. I would presume you aim for similar pressures cold for autocross if running similar tyres and rim widths ???

Rohan

[Fitz]

Ed
You are obviously much more informed than I am. My original reply was just meant to suggest that a small reduction in pressure might be considered as an experiment. But autocross patently does not offer the opportunity to reach the temperatures that circuit racing does. I wonder what the Toyo guys recommend.

Rohan, I am fascinated by your suggestions. What do your tyre distributors say? Over here ours would simply not recommend such pressures on such a light car. Interesting isnt it?

Regards to you both.
Fitz

[rgh0]

Fitz

The Yokohama motor sport distributor does not recommend a pressure versus car weight what they say is.

1. You should aim for about a 5 psi pressure increase for racing from cold to hot. I find 28 PSI cold gives me 33 hot. lower cold pressures give me greater increase.

2. You should aim for a nice even graining across the tyre tread. With lower pressure I get less graining in the middle of the tyre and more on the outside edges.

The Hoosier dealer here is pretty useless and has no real recommendations for the tyres he just charges about twice as much as for a Yokos !!

Rohan

[twincamman]

we use koyo 185 14 for our fv series here in Canada and start with 15 front 18 rear but the car is only 1050 with driver so with another[ 2000 lbs][ typo] and cold-- try 40 all a round to start vary up or down a pound at a time----testing is allowed ---find a paved spot lay out a course with Even left and right turns and experiment ed

[Fitz]

You really think you should go up from 15/18 lb/sq.in. to 40 for another 300lb!!!!
Wow, sounds like one hell of a jump to me. I would not have thought there is a tyre made that is designed to be inflated to a range from 15 to 40. But, I am not a tyre technician.
Have we not got a tyre professional here anywhere??

[twincamman]

no we are dealing with 2 different concepts here ---a pure race car and a street car in a gymkhana turning and sliding in to turns 10 feet or so apart -----high tire pressures are required for gymkhanas -having done both i offer my experience ------but you do as you wish --ed--

[twincamman]

I take the wheels and tires off the vee after a race meet of 18 -20 pounds-- crank them up to 36 pounds each put them on my daughter 65 vw bug [with a hot motor] and beat the snot out of the jap tuner cars-----of course you must know the other driving secrets too----consistency -smooth driving and gentle trail braking carrying speed onto the next corner and balance ---ed

[paros]

HI
Now I will horrfy you all - I use 13 and 14 psi cold with Yokohama and also Avon 6/21X13 cross ply slicks. About 2 degrees negative with the Yoki's. Pressures esablished at race - or practice - from measuring the temperatures and trying with a 5.5 rim to get a nice even taper across the tyre with the inside about 5 or 6 degrees hotter. At anything higher than 13 or 14 leads to high temperature in the middle of the tread. Breakaway lovely and progessive. Tyres are over 20 when hot by the way and the cross ply sensitive to half a pound in getting a nice even temperature.
Front spring 300 lb and rear 175.
Suggets to anyone buy a temperature probe and measure temperature about half a mm into the rubber in 3 places across the tread. Don't worry about the pressure just get the temperatures right. I usually find after a coolind down lap I am looking at about 70 degrees C.
Hope this helps rather than confuses
Richard