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Anonymous
| | Posted on Sunday, April 14, 2002 - 06:16 pm: | 
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it defies all my natural born logic when i see all these people talking about skinny tires.. Why do we air down? to increase tread contact.. So why not get as tall and as thick as you can fit? Offset rims take care of the turning radius. so what gives? |
Matt M
| | Posted on Sunday, April 14, 2002 - 06:36 pm: |
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It all depends on what you're doing.
Going through not too deep snow, skinny tyres (as we call them in the UK !) can cut through the snow easier and down onto fimer ground, same goes for not to deep mud (provided there is a firm base beneath) Whereas fat, wide tyres will just slip around on top getting nowhere fast.
I've seen a Citroen 2CV (for those of you who don't know the car - it's an awful small, cheap French thing, with what look like bicycle tyres) go where a Jaguar couldn't (and many other cars for that matter)
But if you're running on sand, or rock crawling, that's a different matter.
Matt |
Milan
| | Posted on Sunday, April 14, 2002 - 10:16 pm: |
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Even in snow and mud it depends what type and how deep and what's underneath. I found that the vehicle's weight has way more to do with how much traction you get out of a particular tire width than people think. A light vehicle will make narrow tires look awesome. A heavier vehicle can greatly gain in traction by using wider tires. There is such a thing as too-narrow which will cause you to not have enough surface area covered by tread and you will skid as you would with too wide a tire.
For example my full-size Bronco (about 4800-5200 lbs gutted - I can't remember which number is right) does really badly on 33x9.50 BFG MTs. Those same tires seemed much "grippier" on a 3800 lbs Jeep TJ. Yet the TJ has way more traction in all conditions except clay like mud with 12.50 width tires. So did the Bronco. The Disco seems to slip a lot on pavement and off-road with the crappy 235s. And I know in some conditions it's not the tread design but not enough width.
I think on the Disco you could easily help your traction by going to 11.50-13.50 width over the narrow 235's. But this goes against the grain of most roverites. Plus running wide tires has to be done with the right components as they do strain axles and steering more. I'm going with 265's once I can and I think 285s or even 315's would be great but too big from the strength/strain perspective.
Let me repeat myself that the only place I have seen the narrow tires work wonders was in clay or any very thick, sticky mud and that's probably why in most of the Camel Trophys and many of the British and South America events they seem to do so well. |
Curtis
| | Posted on Monday, April 15, 2002 - 12:36 am: |
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anonymous,
Although I would find it somewhat entertaining to kick you in the balls for posting anon on this topic, you have some good logic IMO.
Most people I know who run skinny tires do so because they think it looks better. Yeah - there are certain circumstances that they work better. Still, the name of the game is contact patch and skinny tires don't make sense in that regard.
Curtis |
Ho Chung (Ho)
| | Posted on Monday, April 15, 2002 - 01:04 am: |
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very hard to see but the length of this "contact patch" is what really increases and makes difference in the fwd movement, rather than the width of the "patch".
so, skinny or wide, as long as they are tall, you still hvae a pretty good contact. |
John Lee
| | Posted on Monday, April 15, 2002 - 01:30 am: |
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The contact patch theory has a certain appeal to it because the size of the cotnact patch can be quantified and the theory has a certain intuitive appeal. However, I have always believed that the greater traction from airing down comes so much the greater size of the contact patch from airing down but rather the greater pliability of the tires. If you actually measure the difference in contact patch between a soft tire and a hard tire, there is not that much difference in actual contact patch area. The bulging sidewalls don't touch the ground (a good thing because the sidewalls are relatively weak) on an aired down tire; the contact patch merely becomes longer and more pliable on an aired down tire.
An aired down tire is substantially more pliable than a pumped up tire and thus conforms to the irregularities of the trail better than a pumped up tire. This conformity greatly enhances traction, much more so than from the increase in contact patch. This effect is easily proved. If the size of the contact patch were dispositive, a pumped up wide tire would have the same traction as an aired down skinny tire (assuming equal contact patch), even though the wide tire was pumped up and harder than the aired down, pliable, and skinny tire. |
PerroneFord
| | Posted on Monday, April 15, 2002 - 02:12 am: |
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John
Have you measured the difference in length of a contact patch between a tire at normal pressure and one that is aired down? While the width of that patch will not be much greater, as you mentioned, the length can often be twice as much if not more. Since tractive force is generally applied in this direction, it seems this would be the more important measurement.
Pliability is indeed important as you have stated and this theory gets proved every weekend at drag strips all over the country.
Just a thought...
-P |
Steve (Oz93discov8)
| | Posted on Monday, April 15, 2002 - 07:00 am: |
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I used to have 205 80 R16 Michelin XPC's and had a lot of traction problems. Went to 245 75 R16 BFG A/T KO's and noticed a huge improvement - got a second set of wheels with 245 75 R16 BFG M/T (pre KM) and went to another level again. I think the width helped and the bit of extra height helped but tread pattern also helped. |
Simon E. Arenas (Simon)
| | Posted on Monday, April 15, 2002 - 09:43 am: |
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Milan, 265's are not the way to go... I have them and I sink til my frame floats on top of the GooMud we have in South Florida.... as soon as I can get rid of my 265's I'm going with 235's it is a taller tire than the 265's and it fit just right for the discos...
for a Disco to have good traction in this kind of enviroment I have to go with things that I just wont do... 35 inch (minimum)tires and HUGE body lift....
Simon. |
Marc
| | Posted on Monday, April 15, 2002 - 10:02 am: |
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Simon,
I think 238/85 and 265/75 are almost the exact same height, but the 265s are (obviously) about an inch wider. Am I wrong? |
gp (Garrett)
| | Posted on Monday, April 15, 2002 - 10:16 am: |
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yeah you are right. but again it depends on the tire maker. they vary from company to company. but in regards to the 265/75/16 cooper discoverer s/ts i have they are a good inch + wider and the 235's are 31.9 where the 265's are 31.76. hardly noticable. |
Kyle
| | Posted on Monday, April 15, 2002 - 10:25 am: |
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This COnvo can go on and on but what it comes down to is ground pressure. In many situations a skinny tire will hook better then a fatty because there is more ground presure per square " of contact area.... In botomless shit you are fairly screwed either way. Thats what the winch is for....
Kyle |
Simon E. Arenas (Simon)
| | Posted on Monday, April 15, 2002 - 10:54 am: |
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Kyle.. do you know the malaleuca tree?
that's all we have to winch from here... for those who don't know about it this tree is basicly a huge cork...
now you would say PULL PAL... right... but do you really want to use it in a bottomless shit? how many times can you use it until you start loosing it... do you need a winch to pull it back from that shit...? I haven't used it, but face it,in the south you need floatation and for a 4600lbs + gear truk you need BIG meats and a winch not just the winch.. how long can you drag your frame until you get pist at the truck, at the red necks in 44 SS, at the red necks in little samys with 38 boggers etc..
I already faced the cruel truth... Discos suck ass in the goo. you can say the "driver" I say well true... but how can you compare drivers when the first 6 feet in the trail you are sucked in the goo? a good driver would just get out of the truck because there is nothing else to do and a bad driver will keep digging his grave...
my post was and stil is, my "opinion" if I have to choose from 235 or 265 after having the 265's for 2 years is I choose the 235's because it doesn't have the rubbing issues of the 265's it is taller and if you think the 265's are going to help you in bottomless shit it aint going to happen.
marc. they are not the same. a tire calc might be good with numbers but different brands make different interpretations ... I say compare both in your local tire dealer. the futuras that I run are different.
Simon |
RVR OVR (Tom)
| | Posted on Monday, April 15, 2002 - 10:59 am: |
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This convo can go round and round, especially when we compare the tires that most folks put on their Discos: 245/75, 235/85, 265/75. There is little difference between them in height or width to make a substantial difference in performance. When a tire is 1" taller overall, you gain only 1/2" clearance for anything, as that height is divided in half. Also, on digging deeper into the mud to gain traction, maybe in some rare cases, all the traction you need can be found 1/2" deeper, but I doubt it. Also, by many standards, all of these tires can be considered skinny.
I have wheeled in 265/75 AT's vs the stock 235's. I couldn't notice much of a difference in traction when all the underpinnings were free from hang ups in both cases. I would contest that in slick rock type stuff (moab), maybe the extra inch in width would make more of difference than in loose dirt or mud. I didn't have the pleasure of that comparison.
Tom |
gp (Garrett)
| | Posted on Monday, April 15, 2002 - 11:03 am: |
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well with the little knowledge i have about tires i am hoping that my 265's are close to the performance of the 235's, but better on road characteristics. with a load range of C i am hoping to have a nice on road ride. since most of my driving is on the paved roads and realistically 10-15% is on trails. |
niall forbes (Forbesn)
| | Posted on Monday, April 15, 2002 - 11:12 am: |
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Regardless of skinny or fat, all tires will have the exact same size of contact patch given the same vehicle weight, tire pressure and I assume sidewall stiffness. It is only the shape of the contact patch that is different.
As long as you're not at one extreme or the other, the average person will probably notice little difference. |
Milan
| | Posted on Monday, April 15, 2002 - 11:16 am: |
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I should add some more info.
Simon, the 265 is probably the biggest I will go for other reasons not because they are the best. If your trail has a hard bottom, then it really depends on the mud. If it's thin enough for you to cut through with the wide tires, you'll also have traction. I think that if you can cut to the bottom with 235's you can cut to it with 265's as well - in our mud. Your experience is obviously different. We also have a lot of muskeg and the skinnies get you sunk. Fat tire seems to work better in our environment everywhere almost regardless of conditions (except for that clay as I mentioned earlier).
I also agree on the skinny patch going long and in the direction of travel. But if you take the same height tires and air them down to have the same length of the contact patch, the wider tire's patch will also be wider and more tread on the trail will mean more traction. All, the patch , the contact pressure and the flexibility of the tire will play a role in how much traction you have. Even more will probably be determined by the tread design and tire compound. Best way to tell is doing something similar to what what Steve did. Change little or not at all in tread design, just go wider. See if it improves. Then change your tread. I went the other way. I changed tread design first and then with the same tread, I upped the width and height of the tire. The difference was amazing even in places where the height did not play any role but the width pulled me trhough with more tread grabbing at the surface.
As far as contact pressure goes, like I said, you can also have too much pressure, so you brake loose because there's not enough tire allowing the pressure to get to the ground.
I also think, that slick rock or hard surface might benefit the skinnies in some situations but we do a lot of climbing on off-camber surfaces and laterral traction is very important and aired down skinnies just don't work as well as wider tires.
Lastly, on pavement, I don't air down, so wider than stock is again better in most situations, IMHO. I don't think 1 or 2 sizes taller tire will have much more bigger contact patch than a 1 or 2 sizes wider tire will. And even if it did, I think the wider contact patch would again work better where lateral loads are applied like in cornering. I also found that in snow & on ice, if you have tires that are too skinny for the application, they will slide even more than wider tires that supposedly float on top of the snow and never dig to the bottom. The wider tread just seems to make up for that by grabbing at any available surface/snow and pulls through. And if you do slide, the sliding is better handled thanks to the width again.
I'm trying to be as descriptive as possible because I'm only going by personal experiences and they may not hold true for all conditions or for everyone. I have, however, seen a couple of the theories not working, so I just go by what works even if it may not make sense. |
Simon E. Arenas (Simon)
| | Posted on Monday, April 15, 2002 - 11:23 am: |
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with minimum modifications 235's fit a lot better than 265's
they stuff better
they don't fuck with your turning radius
they are a bit taller
when I went with 265's I though they would help me get better traction here in sotuh florida.
Simon. |
Milan
| | Posted on Monday, April 15, 2002 - 11:25 am: |
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niall's, comment is a prime example of the theory being sound and true but the reality being different. Given the same criteria (pressure, vehicle weight, sidewall stiffness, etc.) the contact patch will be the same. Where things brake down is the fact that with bogger tires that hold more air you should run less pressure. Then your patch and sidewall flex will change by default. |
Robert Mann (Oldscout)
| | Posted on Monday, April 15, 2002 - 11:28 am: |
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Why skinny tires?
Simple, Our axles are too dam weak to handle serious meats! |
Simon E. Arenas (Simon)
| | Posted on Monday, April 15, 2002 - 11:44 am: |
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I forgot about that Oldscout!! hehehe..
if you are into modifying the crap out of the disco then sure get 44 super swampers.. cut the shit out of the disco etc etc etc..
but if you are happy with your all around 4x4 truck then get what fit best in your rig.
to me 235's are the best choice.
Simon. |
Moe (Moe)
| | Posted on Monday, April 15, 2002 - 02:23 pm: |
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Go large and don't look back, or leave the Disco at the trailhead
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