Tire width, contact patch, and biting edges

[Focus]

We all pretty much agree that rally tires grip better than snow tires which grip better than street tires. The general consensus is that skinny tires are better, but how skinny is too skinny? We also know that the big dollar race teams have different tires in different sizes for varying terrain and conditions. Driver skill is more important, but let's get technical just for the fun of it.

Let's pretend that some idiot, for some reason, wants to rallycross a front heavy, RWD vehicle. (Some people are blessed with AWD and nearly 50/50 balance) Skinny front tires would have weight on them, and dig in, finding more grip, but the weight isn't present in the rear to create that grip. Wider tires, but still with a chunky tread pattern, would have more edges to grab dirt with. Think about the paddle tires on dune buggies. I realize that true rally tires are only available in certain sizes, but aren't all competitive stage rally cars AWD these days? Does anyone have any info on what sizes professionally set-up RWD cars have run? Are they staggered for some conditions?

[Welacey]

Not all competitive cars are awd. Did you read the story of the 3rd place BMW junker, no crew and very competitive. It was a great story, forgot who posted it.

[Focus]

Yes I did read it, but there was no chat over what tires he had chosen. I think it even mentioned that it's been a while since a RWD car actually made competition.

[Focus]

Don't some people run truck tires that are wider? That Toyota with the cut-out fenders? Sean Andrews PR Supra (is that him?)

[hondamaint]

We run 245/60/18 and also 245/65/17 . I am sure there is a better combination but this is all we have at the present time. We may in the future try the narrow tires like everyone talks about, also maybe a smaller wheel so we can get rally tires. The reason we run these is they are free, not because they are the best thing for our car.

[Focus]

After riding in the pilot, it seems reasonably connected to the ground. How much does it weigh? The LTD transitions from understeer to rear sliding out, to just plain 4 wheel washing out into the dirt everyone else threw in the corner exit. I don't mind the sliding, but having grip for maybe three or four whole seconds out of each run would nice. That, and being able to get up that hill, lol. Currently wearing 195 width street tires.

[slowautoxr]

We all pretty much agree that rally tires grip better than snow tires which grip better than street tires.

I wouldn't make a blanket statement that rally tires grip better than snow tires. Tbone seems to prefer Winterforces over his rally tires. I like rally tires because they are much more resistant to debeading. I still wince whenever I slide across the ruts though. If you have 14" or 15" wheels there is a wide selection of rally tires. As it is, I'm currently on 13" wheels and the rally tire selection is very limited - as are snow tires.

As far as tire width goes, in loose soil I think narrow might be better. During the dry season, the track can become very hard - yes you can chirp the tires. During that time I imagine that wider would be better.

[hondamaint]

3620lb's. I would think a narrow set of snow tires or a set of mud tires would help. What size wheel so you have ? I know a couple used tire places ( I am a bubba ya know )that may have something cheap you could try, I can stop by and look if you want me to. I bought a tire for my Toyota truck last week because I had a blowout for $30.00 mounted and balanced, I have bought a set for less than $100.00 before.Also a good place to find used tires is a junk yard.
I agree with your thinking, tires are the first thing you should try to get.

[Focus]

(up two)Yes, that makes sense, but there's still no reference point. What size tires do you run, Charles? Maybe I should find someone who's rallycrossed something a little heavier and less balanced.

(above) I've got 14x6 (5.5?) on all corners, but the rear end that's going in (hopefully soon) will have 15x6.5's to clear the brakes. I have 15x7s for the front that I could use, or not.

[slowautoxr]

IIRC, my rally tires are 165/80-13. I got them on sale a bunch of years ago. Price is why I got them. My OEM size was 185/70-13. The only snows I can get are 175/70-13's.

[dirtdog]

Hey erik, it looks like your car need more bite, thats pretty obvious, the size is less important, than grip both front and back, i would stay close to the stock size but
make sure that you have a more aggressive tread.

dirtdog

[Focus]

Thanks for the input everybody.
Stock sizes are 185 and 205 on 14s, but with all the junkyard parts swapping i'm doing, it looks like i'll be running 15's. I'm seeing 185s through 225s that could fit. If I run a tire on it's maximum approved wheel width, is it more likely to de-bead? Minimum wheel width?

[tbone]

Another size consideration; rallycross is primarily a 2nd gear event. Consider OD to manipulate your gearing so you are on the power throughout second gear....and reaching the rev limit (or limit of practical power) by the end of the fastest section.(45-50mph)

IMHO, Winterforce snows are an excellent all-around tire. If you could only have just one set of tires/wheels, snows would be ideal.

Another consideration for rally tires are that most are "gravel" tires and not specifically suited for messy, muddy conditions. But are decent for intermediate loamy dirt and great on dry hard-packed.

Sloppy, wet & muddy event tires???? Now there's the question.

I've de-lugged some snows and can't really tell a difference in the mud.
I've thought about runnning the WF snows backwards for more aggressive approach to the nasty stuff......we'll see.

I've got a set of Silverstone s525m "mud" rally tires on my wish list.
These will be great in the mud and will be ideal for all but the dryest events at the SBRP.

[Focus]

Tire sizing based on gearing?! That's just one more thing I can't do, because the engine and transmission are apparently in a race to see which can break first. I'll need to replace both. Hopefully I can do that all at the same time. If anybody has any ford motors sitting around... (actually I should make a WTB thread)

[RUSSOM]

Another size consideration; rallycross is primarily a 2nd gear event. Consider OD to manipulate your gearing so you are on the power throughout second gear....and reaching the rev limit (or limit of practical power) by the end of the fastest section.(45-50mph)

IMHO, Winterforce snows are an excellent all-around tire. If you could only have just one set of tires/wheels, snows would be ideal.

Another consideration for rally tires are that most are "gravel" tires and not specifically suited for messy, muddy conditions. But are decent for intermediate loamy dirt and great on dry hard-packed.

Sloppy, wet & muddy event tires???? Now there's the question.

I've de-lugged some snows and can't really tell a difference in the mud.
I've thought about runnning the WF snows backwards for more aggressive approach to the nasty stuff......we'll see.

I've got a set of Silverstone s525m "mud" rally tires on my wish list.
These will be great in the mud and will be ideal for all but the dryest events at the SBRP.

Did you ever try them backwards?

Any risk of running a 185/75 snow or should I try to stay with something 70 or shorter for debeading reasons?

Thanks