About rain tire

[KMUTT BlackPearl team]

Hello every one. We are from Thailand and this is my first post on this web board.

I have a question about rain tire. I have 2 choice on 13-7.5 and 13-6.5 Hoosier. Could you please recommend for my team.Which size is
suitable for wet racing on car weight around 300kg.

[M. Nader]

Isn't that your call to make? an educated guess perhaps. (although there are better factors to judge from)

Both will do fine with you weight, my honest advice would be to just select one and see how it goes if you don't have a criteria to select for.

[MCoach]

If you don't have enough information to select one for your car, neither does anyone else.

Sorry, it's really about that simple on this end of things.

[Claude Rouelle]

One suggestion and one question

Why don't you dress the list of criteria that would qualify and quantify what a "good " rain tire is.

300 kg with or without driver?

[M. Nader]

Originally posted by Claude Rouelle:

300 kg with or without driver?

I don't think that really matters as a first year team which i think they are

[Claude Rouelle]

"I don't think that really matters as a first year team which i think they are"

Just depends if this team is and/or want to be aware of the level of challenges they want to face.... Do they want want to start with a 300 kg car in 2014 and be at 150 kg in 10 years while at that time the best cars will probably be under 100 kg (same rules)? Or they want to start with a 225 Kg car and be at 150 kg in 3 or 4 years. Setting realistic goals start with an evaluation of existing cars, understanding trends which seems to make cars quick (information is available statistics are very clear) and simulate. And shoot high. Playing small doesn't help anybody.

[M. Nader]

Once they get to grips with what is needed to make the whole thing work, their improvement steps will be much bigger.

We did as you say and were careful of our weights and how the car is and eventually we ended up with an incomplete, unsafe car, that was fatter than we intended. sure we did good in the design event (and could have done much better if not for some documentation problems), but lost out everywhere else.

But i would also agree that the car alone, for a first year team should be around the 250kg mark. 300 isn't bad for a first year as long as it finishes all events.

[Claude Rouelle]

M. Nader, KMUTT BlackPearl and FSAE / FS newcomers need to be realistic.

300 kg first year car was already too heavy 10 years ago. Go figure now. Not when most automotive engineers receive at least once a week an advertising email for new weight reduction methodology, seminars etc...

Energy consumption and emission reduction control as well recycling impose huge weight reduction challenges to car and aircraft manufacturers. Learning how to make a light, good, reliable car in FSAE will help you not only to get more points in the competition but to find a good job where you feel you make an engineering difference.

I have seen too many new teams where a realistic low weight was not even part of the design goal list....

Sorry but at 300 Kg wherever you come from, whatever your experience or your budget I will say that your best is not good enough.

Back to rain tire: what does define a good rain tire?

[Owen Thomas]

what does define a good rain tire?
I would venture that a good rain tire for FSAE is one that does well in wet conditions while not terribly overheating in dry or damp conditions.

In the case of KMUTT's question, since they're both the same compound, the decision would have to come down to which one fits the rim better. I'm no expert, but would have to guess that a 7.5" wide rain tire on a 6" rim is going to overheat faster and not really give much extra grip in the wet compared to a 6.5" on the same rim.

At this level, it really just comes down to hand waving anyways. Realistically I would say it won't make a difference, and you should use whichever rain tires you can get.

[MCoach]

Originally posted by Owen Thomas:
I'm no expert, but would have to guess that a 7.5" wide rain tire on a 6" rim is going to overheat faster and not really give much extra grip in the wet compared to a 6.5" on the same rim.

Why would say that this tire would overheat compared to the other tire? I'm curious about the reasoning behind your answer.

[Claude Rouelle]

Let me put you on track wit at least some elements of answer

- Are there any differences in dimensions, especially loaded radius? If you want to keep the same ride height (I do not say you have to) will you have to change your spring platform position and / or your push / pullrod length?

- What are the difference if the tire construction stiffness (at least vertical stiffness)

- What does define a good rain tire pattern? Why?

- Should you use a different tire pressure and why?

- Is there a ideal tire temperature zone on a rain tire as there is one on a slick tire?

- All tings being equal should you run a wider or a narrower tire in the rain?

- Where would you find good explanation on how does a rain tire work...?

[Zac]

Originally posted by Claude Rouelle:
Let me put you on track wit at least some elements of answer

- Are there any differences in dimensions, especially loaded radius? If you want to keep the same ride height (I do not say you have to) will you have to change your spring platform position and / or your push / pullrod length?

- What are the difference if the tire construction stiffness (at least vertical stiffness)

- What does define a good rain tire pattern? Why?

- Should you use a different tire pressure and why?

- Is there a ideal tire temperature zone on a rain tire as there is one on a slick tire?

- All tings being equal should you run a wider or a narrower tire in the rain?

- Where would you find good explanation on how does a rain tire work...?

Ideally you want a narrower tire with a larger OD and a fairly minimal tread pattern. Practically, your rain tire options in FSAE are pretty limited.

The molded rains are generally designed for much heavier cars running at higher speeds. That means heavier constructions, deeper tread depths, and much higher amounts of void than you really want. Ultimately you end up with a heavy tire with poor footprint engagement when you put it on a lightweight vehicle.

The hand-carved intermediates are a better option, but those kind of limit what changes will really be seen in construction/dimensions. The compounds will also be pretty mediocre for wet conditions.

[Owen Thomas]

Originally posted by MCoach:
Why would say that this tire would overheat compared to the other tire? I'm curious about the reasoning behind your answer.
The reasoning there is that the larger tire body on a (relatively) small rim would deform more, working the rubber. Additionally, you get that extra slip area that may or may not be loaded properly. I think you could set up the tire pressures such that these issues wouldn't be a problem anyways, though. I'm not really sure, since these effects might be totally negligible compared the extra material for heat conduction/dissipation.

Basically, I have no idea what I'm talking about, but was trying to say it would be goofy to put a wide tire on a narrow rim.

[MCoach]

Originally posted by Owen Thomas:

The reasoning there is that the larger tire body on a (relatively) small rim would deform more, working the rubber. Additionally, you get that extra slip area that may or may not be loaded properly. I think you could set up the tire pressures such that these issues wouldn't be a problem anyways, though. I'm not really sure, since these effects might be totally negligible compared the extra material for heat conduction/dissipation.

Basically, I have no idea what I'm talking about, but was trying to say it would be goofy to put a wide tire on a narrow rim.

You at least got a smile out of me http://fsae.com/groupee_common/emoticons/icon_smile.gif

From what I would expect, the larger contact patch of the tire would distribute the load more and lead to lower tire temperatures. There may be some merit to your answer, but I am equally inexperienced and have no way to confirm or deny your theory. I hope that those with better understanding chime in on this bit...

[Claude Rouelle]

I think you will find a lot of answer to your questions in the downloadable document especially on rain tire friction mechanism page 59 and onward.

Excellent document from Michelin.

http://downloads.optimumg.com/images/GRIP.pdf

[theTTshark]

Water is very good at absorbing energy from its surroundings. Unless it is raining really hard, tire temperature is your hardest objective to achieve with wet conditions, and your second being water evacuation.

Give yourself less rubber to heat up, a lower tire temperature target, and your starting pressure is just a function of your starting and target temperatures. Your choice of either an "intermediate" or "full wet" tread cut just depends; 1) Do you have money for both 2) Does the inter have a soft enough compound (if cutting from slicks) 3) No matter how good the driver is, hydro planing should be avoided.

And thank you for that Michelin document Claude!

[Claude Rouelle]

TheTTshark

One comment and one question

1 I have experienced rain tires running at a core temperature above 70 deg.C. First time I saw that was in early 90's in heavy rain. It was in Japan with development tires. At pit stop tires were literally smoking. I was amazed. At that time, I did not think it was it was possible... I learnt a lot that year.

2. "Give yourself less rubber to heat up" If you want more heat / more temperature in your tire (rain or slick) do you prefer more or less compound?

[theTTshark]

Originally posted by Claude Rouelle:
TheTTshark

One comment and one question

1 I have experienced rain tires running at a core temperature above 70 deg.C. First time I saw that was in early 90's in heavy rain. It was in Japan with development tires. At pit stop tires were literally smoking. I was amazed. At that time, I did not think it was it was possible... I learnt a lot that year.

2. "Give yourself less rubber to heat up" If you want more heat / more temperature in your tire (rain or slick) do you prefer more or less compound?

My racing experience is not very extensive Claude, and I've only had to deal with rain on a hand full of occasions. So have you found that water evacuation is the most difficult? I've never dealt with that very much, always seems like I've struggled with temps.

So are you asking about the ability of the tire with more mass to retain more heat? I hadn't thought about that predicament before. So then if it were me, I would start by weighing how soft is my compound, how long the straights are, and ambient temps. In dry conditions I would want the bigger tire to keep the tire more thermally balanced (gets hot through the cornering sequence and cools down the straight). In the wet though it would just depend. If it wasn't very cool or very wet I would want more tire, but as the amount of water increased and/or temperature decreased I would want less width. I think the benefit of having a quicker heating tire in the wet would outweigh the negatives. With a smaller width you could also potentially have more contact patch due to less water having to be evacuated and thus less grooves. But I could also be completely wrong here. This is a very interesting problem. Someone should give me a racecar, Paul Ricard test track, and a plethora of tire sizes/compounds/thread patterns and I'll get back with the results in a couple months. Hah! Or of course, Claude could drop some knowledge on me.