Tire friction measurements and coefficients

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Tire friction measurements and coefficients

Postby jacco » Wed Sep 22, 2010 1:07 pm

As I have been finding out, the "grippyness" of the rear tire makes a huge difference on the track.
Most of the time my problem is that the rear tires are too grippy and unforgiving, resulting in deslotting (ie tipping over in cornes or lifting the guide out when accelerating). ie Aussie Retro F1 or 1/32 Plafit

As there are different tyres/donuts available, ie Alpha donuts I tend to use:
Piranha, Natural, SuperNatural, Wonder Rubber, etc

Does anyone have any ideas or recommendations on which tires are good for high friction and which ones for less and low friction? Also, any simple methods on how to measure it? (or is this another black art of gutfeel and trial and error?)

A tyre friction coefficient would be good.

thanks in advance,

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Re: Tire friction measurements and coefficients

Postby SlotBaker » Wed Sep 22, 2010 2:46 pm

I think it's mostly black art of gutfeel and trial and error and a bag full of experience.

There are so many variables to contend with. Track condition, ambient temperature, relative humidity, chassis design, body design (down force or not), motor performance, gearing, tyre compound, controller, others??

Going from my observations, trials and tribulations, reading plenty of stuff on the forums, and talking to plenty of good builders/drivers, there are a few things to try for the different handling effects.

Firstly, find out what limitations (if any) there are on tyre choice. Rules for the class etc.

For your example of too much grip, tiping in the corners and popping the guide out of slot;
- Try narrowing the tyre. Less tyre surface to grip.
- Use 'treated' tyres. Less grip
- Lower the centre of gravity (CofG) in the car if possible.
- Remove a bit of weight from the rear of the car. Allow a bit of tyre slip.
- Add weight to the front of the car. Holds guide down harder, and shifts weight balance from rear to front.
- Stiffen the chassis.
- Others??

For the opposite problem with too much slide in the corners;
- Widest tyres.
- Keep tyres clean.
- 'Fish' type compound tyres,
- More weight at the rear.
- Add weight up higher to raise CofG.
- Add some flex to the chassis if possible. (Wayne might sell you some :o )
- Others??

It can be a never ending task. If you get the car right this week, and don't use it for a week/month, you can pretty much start over again to get it right. Those racers who frequent the track 3~4 (or more) times a week will have a better chance of keeping the car handling right, as they can move the set-up whenever the conditions change.

What works for me, may not work for anyone else, so trial and error is where it's at.
Steve King

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Re: Tire friction measurements and coefficients

Postby stoo23 » Wed Sep 22, 2010 3:57 pm

Yeah,..I think Pretty Much what Steve said,.. :D

I must admit, of late, I have Not been tending to use the Alpha tyres, and in a real 'Black Art sort of way,..I'm Not Really sure why!!,..lol

I usually try different tyres, if what I had on the car seems not to be working agreeably, on the night.

Lately, I have been running the JK 'Big Daddy' Rears, but the other night, swapped to Normal JK's and after trying Alpha's on both the Other CanAm and one of the F1's, I opted for JK's all round.

As also suggested, Narrowing the Rear Tyres, can make a Big difference and if the Car Already has Too Much Lateral Grip, incrementally Reducing the Rear Width, may let you find the 'Sweet Spot'.
Also, the extreme inside of the Tyre on the Normal Alpha's, is Unsupported, (Unless running the Full width Hubs), so Can be Easily Trimmed, to end up with a Far Tidier Tyre IMHO.

The JK's, Like the Full Width Aplha's, support the Whole Width of the tyre.
I guess, it could be argued that like a Dragster, the inside edge of the Alpha's Will Grow, perhaps creating a Slightly Larger Rolling Diameter, one Can see eventual Distortion of the profile across the Tyre with time, so I guess it Is happening,..lol

Also as Steve mentioned, Cleaning of the Tyres can Help a lot, especially if/when you are running around in the Earlier stages of the evening!

The Track has Only relatively recently been 'Prepped' for the nights racing, so has a Maximum amount of Spray Goo on the track surface,..Often, creating a slightly False 'Indication' of the cars Handling, especially F1's.

Try running Brand New Tyres, as it takes a while for them to 'Bed In' and build up Grip and you will Now have a Nice 'Ready' set to change to if necessary as the evening progresses / tyres wear.
Pick the car up and 'Feel' the Tyres, during practice, are they Warm?, Sticky?, etc,..Go Give them a Clean and have another run,..etc

I have changed Type and style/brand of Tyre Mid Event, Heck Why Not !!!???
If you already have a nice set of slightly used 'Too Grippy' Rears, Trim a few millimeters off the inside edges and keep em in your Box to Try 'On the Night'.

I Rane Much Narrower Tyres on My older CanAm chassis, Especially at Area3 on Pete's last track there,..and Won !!,..so it IS Definitely Worth thinking about!,.. :D

Finally, Weight.
Heck, Unless the car is Already a Bit Too Heavy, Don't be afraid of Adding Weight to Aid in the cars 'Stability/driveability/traction' etc. At worst you may lose just a tad in acceleration/braking, but may very well Gain Heaps through the cars 'predictability' etc in the Turns!

Don't Ever be 'afraid' to Experiment,... :D

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Re: Tire friction measurements and coefficients

Postby jacco » Thu Sep 23, 2010 12:24 pm

Thanks for the reply Stoo and Steve.
I understand the car setup (Weight, CoG, flex, Tire width) has a lot to do with the handling, but what I really wanted to know is whether there is any understanding out there on which tires are good for high friction and which ones for less and low friction, possibly based on the material they're made off....

eg. it seems that Alpha Piranha tires (I used most) are high friction (As you confirmed Stoo).
What about JK, Parma, Pro-Track, etc tires?

ps: one handling consideration, is also the shape of the outside tire edges (edgy for tracking, round for sliding).

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Re: Tire friction measurements and coefficients

Postby fast_mick » Thu Jan 20, 2011 10:06 pm

Jacco as you probably worked out high traction = high friction (soft tyre). If you want to get bit more technical buy a durometer and start writing down results on times etc round the track with the various tires. You will then get a feel for what works and doesnt work and when you buy new tyres you can check the durometer reading for repeatability.