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Trials tire: Fail
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Posted by: porterdog---------------------

Everything people said was true- great traction, softer rear, low trail damage.... No one mentioned that it screws up your geometry so bad the bike is nearly unridable.

I put a Pirelli MT43 on my KDX a couple weekends ago, along with a Pirelli Scorpion Pro front. Had a chance to really try it out this weekend- in silt, in sand, 1st gear ST and 5th gear ATV trails.... I think I may take it off.

It raised the rear so far that my front end is skittish and unpredictable. I took out rear preload like mad, until the rear got all harsh and nasty, and even then the front-end was far from confidence inspiring.

How have others coped with this?

Posted by: wildman88---------------------

There is a guy in our club that runs trials on his KDX and loves it. I'm not sold and haven't tried it yet and didn't even think about the height. Very good point. Make sure your running low pressure. I have heard 4 psi is what they like. I'll make some calls and see what I can find out.

Neil

Posted by: julien_d---------------------

6-8psi in the rear, and make sure your forks are lowered down in the clamps as far as they go. I had no problems with the front end after putting the MT43 on. Lowering the rear by adding too much sag is a bad idea. That's going to make your problems worse.

the MT43 does bring the rear of the bike up about 1" over most knobby tires.

Posted by: porterdog---------------------

Quote:

Originally Posted by julien_d

6-8psi in the rear, and make sure your forks are lowered down in the clamps as far as they go. I had no problems with the front end after putting the MT43 on. Lowering the rear by adding too much sag is a bad idea. That's going to make your problems worse.

the MT43 does bring the rear of the bike up about 1" over most knobby tires.

I was running 10psi; the trails were pretty rocky in places. I like what the tire does traction wise, but the front end needs to work too!

Lowering the rear was all I could think of to put some rake back into the front end; my forks are already as low as they can go. About the only other thing I can think of to try is a to make a set of lowering links; I'll not be driven to a KX fork swap just for the sake of running a low-impact tire.

Stylistically too, it may not be my cup of tea. Oversteer on demand is part of the fun of riding a dirtbike and the trials tire, with it's combination of ultra traction and higher gearing make that a thing of the past...

Posted by: julien_d---------------------

eh, oversteering with the trials tire is easy cheesy. Just get enough spin and lean and it'll slide quicker than a knobby will. Give it a bit to get use to it. part of what you're feeling in the front end might be just push from the added traction. The trails tire does raise the bike a bit, but the lower pressure should let it drop when you sit on it. Like I mentioned, I did not notice any change in handling after changing to the MT43, but the front end on my KDX is sketchy anyway.

Posted by: wildman88---------------------

I run a steering damper. Made a huge difference on my top speed. And low speed roots and rocks.
Might be a relatively low budget fix. I think out of all the mods(I haven't done the 36mm carb) it was one of the best.
Haven't heard back yet from the club member.

Neil

Posted by: james.keaton---------------------

I think that I ride too much deep muddy areas to run a trails, but if I ever have any extra cheese than I may try one.

Posted by: porterdog---------------------

Quote:

Originally Posted by julien_d

...but the front end on my KDX is sketchy anyway.

See, I'd just gotten mine working a lot better than it was (from stock to XR4 springs+shimstack mod). It was actually the best dirtbike I'd ever ridden at that point- very confident.

Quote:

Originally Posted by wildman_88

I run a steering damper....Might be a relatively low budget fix.

LOL, you're kidding about the budget, right? I do have a Scott's that's not mounted ATM, but the KDX will be my second string/buddy bike eventually, so I don't think I want to pony up for the mounting hardware for it. Plus, I didn't feel like I needed one before the TT entered the picture.

I'll try less pressure next time, get a little drop that way, and think more about the lowering links. They're supposed to make the rear suspension a little better anyway....

Posted by: julien_d---------------------

I really think you'll be able to figure it out and correct it. The .75-1" ride height added by the pirelli isn't going to alter things THAT much so that you can't compensate. What exactly does it feel like? Front end push? Headshake?

It took me a couple rides to get used to the new feel of the bike when I switched. The very first ride the bike threw me promptly to the ground about 4 times in a row. It was hard for me to grasp not pinning the bike coming out of a corner. Rather than spinning, the rear tire would grab in hard and the unexpected bite caught me by surprise. And this was in some pretty slippery conditions. After some adjustment in riding style, I think I have much more control of the bike overall, especially in the tight sections. The traction is really unbelievable at times. I'm able to just tractor the bike up sections that I would normally have to go up wildly with the throttle pinned and rear tire spinning like mad. Doesn't matter though, I'm grinning the whole time either way I go up the hill, lol.

If you stick to terrain that is fairly wide open and fast and like sliding into corners, then I think any trials tire is going to be the wrong choice for you. It's not that they always suck at going fast, they do fine at speed if you run a bit more pressure, but a really good knobby would likely be a better choice in those conditions.

Posted by: placelast---------------------

I'll take the MT43 off your hands. Email me.

Posted by: jth---------------------

This is my second year on a Dunlap trials @ 10psi. I agree with all julian_d said. Sounds like you lowered the back dramatically with the sag adjustments (more than the tire would have changed it) and still have the issues.
Maybe your new front sneaker is giving you grief. I use a Maxis IT @ 12psi it feels good to me and I am very picky about tires.

Posted by: jth---------------------

julian_d
I two have landed on my head trying to power slide out of a corner. Still have not figured that one out. But sliding into corners and steering with the rear wheel using the rear brakes is much easier and way fun.

Posted by: sr5bidder---------------------

too its real easy to see where your kdx friends went when the trail splits......I used the unique tread pateren to see where jth was heading at Hatfield McCoys!!!!!

Posted by: mudpack---------------------

Yeah, next time try to keep up, okay?

jth

Posted by: sr5bidder---------------------

can't do it seems nothing works right anymore ...ballance ...brain... body... I still try to enjoy riding, but its getting harder and harder.

Posted by: Joburble---------------------

Yup, dragging up an old thread.
I see that running a trials tire is what some people are doing, very interesting. In regard to geometry can't you just put a lowering kit on the rear to sort it out.

I am surprised to see that people are running these tires on their KDX's are they any good in:
Deep sand
Slick slippery mud
Megga slippery wet clay

Is there an issue with punctures running them at such low psi?

Posted by: Tom68---------------------

Quote:

Originally Posted by Joburble

Yup, dragging up an old thread.
I see that running a trials tire is what some people are doing, very interesting. In regard to geometry can't you just put a lowering kit on the rear to sort it out.

I am surprised to see that people are running these tires on their KDX's are they any good in:
Deep sand
Slick slippery mud
Megga slippery wet clay

Is there an issue with punctures running them at such low psi?

Better than a knobby on wet rocks and logs not as good in loamy soil, absolutely crap when locked sliding into a corner or dragging the tail down a hill as they wont pack the dirt up like a knobby. Had no problems in mud.
Geometry wasn't a problem with my 250 and that included running dirt track with short front springs and no air in forks. Would have been hitting 130k's on the straight, of coarse it was pretty smooth.
I used a Dunlop D803 and it wasn't long before all the knobs were 50% torn.
Don't know about it being a new thing, had one on my IT250 in 1982, only thing I remember was clutching it out of a turn on small exposed roots and she hooked up and headed off without me.

Posted by: Patman---------------------

10psi in the stiffest trials tire on the market?! No wonder it wasn't working

The idea with a trials tire isn't to pump it up like a balloon, it's is a low pressure grippy, conforming tire that wraps itself to the imperfections of whatever you are riding over. 4psi maybe 5-6psi at the very most. Don't blame the most untrials like trials tire that was over inflated for the problem.

Posted by: mudpack---------------------

After reading this again, a thought occured to me.

Getting back to basics, how much air pressure were you running in your front tire?

Mud

Posted by: sr5bidder---------------------

I know not my question to answer, but I run 12psi in front dunlap 756 and 9 psi rear dunlap 803 trials

Posted by: _JOE_---------------------

Quote:

Originally Posted by sr5bidder

I know not my question to answer, but I run 12psi in front dunlap 756 and 9 psi rear dunlap 803 trials

It's Dunlop......

Posted by: sr5bidder---------------------

dunlop...got it ....for a while at least!!

Posted by: porterdog---------------------

I think Mudpack was asking me- probably everywhere from 10-15psi?

I took out some front spring preload and that helped a bit. I also think that whoever suggested that enhanced rear traction may be lightening the front may be correct to some extent.

Finally, while the TT does work well in terms of ultimate grip, I personally am not happy with the transition from grip to slide and back to grip- very abrupt, and not at all like a knob.

Personal preference!

I bought an '08 KTM 200XCW, so the KDX will be a buddy bike and I think the TT will work well for that.

Posted by: mudpack---------------------

Yeah, Porter, I was.
I asked because your symptoms are those of a tire that is over-inflated. If you have to guess what the pressure was, then you need to try it again with the proper inflation pressure in it....you may have been over-inflated. I hope this helps.
Enhanced rear traction only lightens the front under acceleration. Generally we aren't accelerating going into a turn.
Give your setup another chance, this time knowing the psi. Good luck.

Posted by: porterdog---------------------

Quote:

Originally Posted by mudpack

Yeah, Porter, I was.
I asked because your symptoms are those of a tire that is over-inflated. If you have to guess what the pressure was, then you need to try it again with the proper inflation pressure in it....you may have been over-inflated. I hope this helps.

Baby, I ain't new to this- first thing I did was drop the pressure and back off the compression in the front. Appreciate your input, though- truly. Seems to me it would take *gross* overpressure (17? 20?) to be over the line.

Posted by: Joburble---------------------

Unfortunately none of us know the full expertise of the other, so with best intentions it always seems good to cover the basics first and move on from there. I guess we are all just trying to figure out why the tyre made your bike handle so badly. Personally I would love to know so that I can give that type of tyre a try and make the adjustmets necessary to make it work for me.

Posted by: julien_d---------------------

Quote:

Seems to me it would take *gross* overpressure (17? 20?) to be over the line.

Wrong. The difference between 8 and 10 is enormous.

Posted by: julien_d---------------------

ugh, double post......

Posted by: mudpack---------------------

Quote:

Originally Posted by porterdog

It raised the rear so far that my front end is skittish and unpredictable.

This is a puzzling statement, especially coming from an experienced rider. Generally, raising the rear of the bike will increase front end bite.
I still feel there is something elso going on here that is being overlooked. If not an overinflated front tire, then something....
What other changes did you make when you put the trials tire on? Something else was changed...even though you may not be aware of it...we just need to figure out what it was!
(it may simply be changing trail conditions, too)

Posted by: porterdog---------------------

Quote:

Originally Posted by mudpack

Generally, raising the rear of the bike will increase front end bite.

While raising the rear will increase the weight transfer to the front it will also decrease the rake angle (thereby altering the trail as well...) which can make the front end twitchy same as raising the forks too far in the clamps. (Mine are down as far as they go, btw...).

I definitely *did* make too many changes at once; in addition to changing both the front and rear tires I added ~5mm preload spacers to the front springs (and since removed them). Chalk that up to excitement

Since then I bought a KTM 200, so the KDX got moved to backup status and I quit messing with it actively. It doesn't suck, far from it, but it wasn't what I was expecting. For those on the fence, the MT43 is cheap- give it a try; far more people like it than not! Further review of the Scorpion Pro commentary found a couple people saying they felt it would slide a bit on turn initiation and then bite, so my dissatisfaction may well be a combination of everything mentioned:

1. Geometry change increasing twitchiness

2. More weight on the front overloading the front and causing it to wash, exacerbated by the characteristics of the front tire.

3. Better hookup at the rear overlightening the front and reducing bite (this really isn't in conflict with 2 though it may seem so. Part of my initial complaint was a decrease in predictablitity; transitioning from throttle to brake to throttle while winding thru turns will obviously change the loading conditions on the tires.)

While the difference between 8 and 10 psi may well be "enormous" I can't run 8 psi at the front on our trails- there are too many rocks and I'd pinch flat and/or bang up my rims. I'll go as low as 11 if I know it'll be mostly sandy, and did try 10 out of dismay, but 13 is more the norm. 8 in the rear is no problem, especially with this setup.

I'll try the TT on the KTM in the spring just to see; this would of course mean that the KDX would get a more standard knob rear and I'll learn a little more. The benefits of this type of tire are really attractive- despite some vigorous hammering it still looks great, and there were plenty of times I was forced to stop mid-hill (pure sand or sand and rocks) due to either inattention on my part or another rider having trouble and I *never* had a problem getting moving again.

Posted by: Porkchop---------------------

I'm surprised no one has mentioned gearing.If the tire makes the rear sit .75" higher, the circumference is 4.712" longer than your knobby.If the bike sits 1" higher, circumference is 6.283" longer. This will increase your final drive gearing, decreasing how snappy the power delivery feels.
Considering that a trials tire has close to double the actual rubber contacting the ground, in a larger contact patch area at 3-5 p.s.i. pressure, this requires more torque, due to way more traction. Try a smaller counter shaft sprocket or a larger wheel sprocket to get your gearing back in line. Wrap a tape measure around your old tire that you liked, then measure the trials tire,do the math& find out the percentage of difference between the two. Gear down that % at the least, I would double the difference gearing down due to way more traction. I did this to my crf450x & the combo is the bomb in the woods, instant torque with massive traction & control. 12 tooth on the motor 53 on the rear.
My pals thought I had motor work done... all I changed was rubber& gearing, it was hoot to ride. Good luck& best regards, Porkchop...
P.S. HMMMM....PORTERDOG..sounds like a good micro brew.....
let me know how this works for you.

Posted by: samiam---------------------

I have always wanted to try a trials tire, but I am afraid that I will hammer my rim into silly putty with the recommended 4 psi. I imagine that you are running a Bridgestone UHD tube in that sucker...have you incurred any rim damage?

Posted by: Patman---------------------

Quote:

Originally Posted by samiam

I have always wanted to try a trials tire, but I am afraid that I will hammer my rim into silly putty with the recommended 4 psi. I imagine that you are running a Bridgestone UHD tube in that sucker...have you incurred any rim damage?

Have you ever watched a national or world level trials event? If anybody is going to hammer a rim it's those guys. Do some real research on the various trials tires and take in to account the terrain you ride. A stiffer tire might be better in mostly high speed open riding because it will move around less. A sticky soft tire like the Michelin will excel in slow, rocky, log crossing infested single track. Then to dial it in get a real tire guage, one that reads to within 0.5psi or better (they are out there mine goes to 0.1psi digital). Mess with the air pressure in 0.5 psi steps and you will find the sweet spot, provided you selected the proper tire for the use and not the cheapest tire you could find that looks like the others.

Another observation. These tires work great in some situations but for the same reason everybody doesn't use the same intermediate rear tire it might not work for everybody. Even the most experienced riders can not really understand how a new part really effects things without some practical knowledge of the product and how it really works. How many people that have tried a trials tire on a KDX actually ride trials? Well kids until you actually do it you don't have a freakin' clue no matter how great of a rider you think you are. It is a different world, speed to clear things is the typical solution for almost all off road / MX riders, this is not the case with trials. I've been there and done that and it will humble you to find out how much you rely on momentum and speed and how little real balance and skill most of us have. Now take a reasonably skilled trials rider and put him on a off road bike and cry as they make you look like a slow bull in a china shop. I've had the priveledge to ride with and attend schools from some seriously skilled national and international level trials riders and I still am amazed every single time. If you really want to cry go on a trail ride where somebody like Ray Peters shows up on his KLX650 then proceedes to spank you on the trail, a trail that you know and he doesn't!

Posted by: porterdog---------------------

PChop- no complaints about the power though I see where you're coming from.

Sam- No issues, though I won't run 4psi. Works great at 6-8. I did see some reference to UHD tubes needing more pressure than that to really bear on the bead of the tire hard enough so I went with a lighter HD tube. The Pirelli TT, (MT43) is a sort of hybrid; DOT certified with a stiffer sidewall than a *real* trials rider would probably ever use- for this reason I'm not too worried about the rear rim- the MT43 protects it pretty well and has a rep for acceptable run-flat capacity.

Posted by: Patman---------------------

I usually don't put a lot of faith in current magazine "tests" as they are usually just an extensive advertisement but this is a pretty good write up with decent information on the subject. Be sure to see all the little roll-over info they have inbeded in the pics.

http://www.dirtrider.com/features/1...ison/index.html

Posted by: Porkchop---------------------

The entire reason trials tires are designed with a larger aspect ratio,(a tall sidewall vs.carcass width) is to allow massive side wall flex, increasing ground conformity and contact patch area.Running too much pressure defeats the purpose of using this type of tire. Several friends have them on ktm 530's, they hill climb on exposed granite rock faces on some of the nastiest mountain sides I have ever seen, running 2 psi. They also use 3 rim locks. Granted hillclimbing involves little high speed
riding, so rim damage is minimal if at all. Use what works for you,these tires are ment to run darn near flat, it might be hard to believe but if you have more than 7 psi & your stuck in the"ditch of doom",so to speak,
drop that pressure down & you probably won't be stuck any more.
Best Regards, Porkchop

Posted by: Tom68---------------------

Quote:

Originally Posted by Patman

I usually don't put a lot of faith in current magazine "tests" as they are usually just an extensive advertisement but this is a pretty good write up with decent information on the subject. Be sure to see all the little roll-over info they have inbeded in the pics.

http://www.dirtrider.com/features/1...ison/index.html

Good find, pretty much how I found trials tires to be.

Posted by: samiam---------------------

"If you smack into rocks and nail square-edged bumps hard, you will pay in flat tires and in rim dings."

Eh. I'm out.

Posted by: Patman---------------------

Quote:

Originally Posted by samiam

"If you smack into rocks and nail square-edged bumps hard, you will pay in flat tires and in rim dings."

Eh. I'm out.

Exactly what I was referring to, using speed to get over things. Some changes in how hard edges are "attacked" results in no damage / flats while getting there in the same amount of time, usually with less crash damage as well

To each his/her own.

Posted by: julien_d---------------------

Quote:

Originally Posted by Patman

To each his/her own.

Less crash damage, less abuse to my old bones, and a bike that stays happy for longer since I'm not wringing the piss out of it all the time anymore just to get up a lil ol hill. Works great for me!

Posted by: julien_d---------------------

Quote:

Originally Posted by samiam

"If you smack into rocks and nail square-edged bumps hard, you will pay in flat tires and in rim dings."

Eh. I'm out.

I do that all the time. No problems yet. I ride some of the rockiest nastiest trails around. If I feel like haulin balls, I'll just up the pressure to about 9 lbs. I usually keep it around 6-7 and grin as I tractor up all the loose rocky hills while my buddies slide back down while spinning the rear tire the whole way. Pisses them off every time, I love it! All my buddies have dubbed my KDX "the John Deer".

Posted by: magicass---------------------

The Pirelli MT 43 trials tire is the best tire I have ever used. Riding pretty gnarly, rocky, rooty, steep, clay soil slippy leave trails (Vedder in Chilliwack).

Posted by: Porkchop---------------------

Good morning magicass, let me tell you pal, I would really like to bring my trials tire to
B. C. & follow you around any where you think is worth going. We resided in Bella Coola B.C. for a short time in 1967-68. I visited there in 1976, absolutely awsome the place is.Bella coola is, if memory serves me right, a 2 day drive 400 miles down a dirt road from the victoria hi-way. For those that don't believe in sasquach, spend the night camping half way down that road, which is pretty much manditory(there's a whole bunch of nothing except mountains, christmas trees & more mountains), no lodging . It may change the mind on that subject. In the middle of a very silent night, I woke up listening to the most horrific hair raising screaming sound the likes of which I have not heard since that night. To this day it still makes the few hairs on my head stand up. The jeep roads & single track in that region must be worth the effort of going there. The other night i reviewed my trek on map quest, & brought back many good memories of that trip. Best regards, Porkchop...

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Trials tire: Fail

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