Trials tire: Fail

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Trials tire: Fail

Post 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?

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...
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Post by KarlP »

Geometry and "too much" rear traction are two issues that have made me hesitate to try a trials tire.

If I could find a spare 18" rear wheel for my CR frame i might go for it.
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Post by canyncarvr »

What size is the Pirelli?

Just took a quick look...but I see only a '4.0 x 18'

No aspect ratio numbers on that tire?

Michelin is the same...

What IS the difference height-wise? Between what you generally run and the Pirelli?

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Post by porterdog »

>|<>QBB<
canyncarvr wrote:What IS the difference height-wise? Between what you generally run and the Pirelli?
The TT is about 1.75" taller on the diameter when compared to my no-longer-fresh 739.
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Post by skythrasher »

I have been running the D803 and don't have any problems. It is a bit taller than some of the low profile tires but not much. I can't tell much difference in it or the D756, or D739 that I have on the other rims. Both of the knobbys are 100/100-18. You might try dropping the fork tubes in the clamp some and see if that helps. Choice of tires and handling traits are person specific. What one guy considers golden the other may hate. Good luck.
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porterdog
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Post by porterdog »

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skythrasher wrote: You might try dropping the fork tubes in the clamp some and see if that helps. Choice of tires and handling traits are person specific. What one guy considers golden the other may hate. Good luck.
1. Good advice but.... they as low as they go.

2. Correct! I'd rather have a solid front and squirrely rear.
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Post by fuzzy »

How is your front susp? Setup for your weight, etc? Tire could be bringing out deficiencies.
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Post by Julien D »

Like I said over there, I don't have any problem with my front end after switching. I feel MUCH more in control of the bike over, although it does take a bit of seat time to get the feel of it. Like Fuzzy said, you need to figure out what's not right with the susp. and and take care of it. A .75" or so change in the rear isn't going to screw up the front to the point you can't make it right unless something was already not right.

First step at this point should be to re-set your sag properly, and give an accurate description about what the front end is doing that you don't like.
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Post by island220 »

I had same problem height and gearing went with 12-51 gearing and dropped forks about 1/4 inch and works great I also have the kx forks which makes the wheel base almost 5/8 of an inch longer. After dropping forks in triples she hangs the corners like a flat tracker I love it, I also messed with my clickers alot, did scottish trials and took 7th best I ever did and it was really tight, nasty, rocky you name it they had us ride over and through it.
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Post by firffighter »

It does take a bit to get used to how a trials tire "feels".

But, the MT-43 does not change the geometry of the bike enough to make your front end all of a sudden not perform like it should.

I have run my KDX's with many different rear tires including the M5B, VE-33, MT-16, Dunlop 756, Maxxix IT and probably others I cant remember. I have always run a 110/100, and switching to the MT-43 does feel different, but does not change the steering geometry enough to make a difference in fork performance.

Most likely what you are feeling is the trials tire grabbing traction in places you would not expect it too in comparison to your knobbies. This may be giving you a sense that the front is is vague, whereas it may be that you are getting traction and the front end is now lighter that it would be in comparison to a spinning knobby.

Also, if you are used to running a 100/110 knobby on the rear, the MT43 or even a larger profile knobby for that matter will feel different.

Like Fuzzy, mentioned, making sure your front forks are setup correctly and proper sag are a good place to start.

The MT43 does cause you to change your riding techniques a bit, but the benefits are well worth it. The MT43 has added to my confidence and allows me to nasty terrain faster. A great addition IMO.
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Post by porterdog »

>|<>QBB<
juliend wrote:... and give an accurate description about what the front end is doing that you don't like.

Hard to describe, but there were several things I noticed:

1. An increased tendency to 'fall' into turns. Coming into a bermed turn, I'd dial in some amount of steering, call it X, and get some amount of response, call it Y. Y was less than I needed to make it around the corner, so I'd add more steering, to, say, 1.2X. The problem is then I'd get ~1.7Y. I had this happen in a lot of different conditions, the aforementioned bermed turn, and also fast sweepers- dial in some steering, don't get enough turn, dial in more steering, then immediately have to take some out because all of a sudden my line was too tight. Frustrating!

2. A *signficantly* increased tendency to deflect off trail junk. Two weeks ago I rode on my old skins and had no issues getting the bike to go exactly where I wanted. The worn front 739 would sometimes tend to wash a bit when pushed hard, but it would climb right up and over small ruts parallel to my direction of travel. No longer. I suppose it could be the new front, but the Scorpion Pro is well reviewed.

3. An overall lack of feel and confidence from the front end- sometimes it would wash then bite, other times it would bite then wash. It never dropped me, but I was constantly fighting with it.

4. An increased tendency towards headshake. Again, I didn't have this issue before the tire swap, and predictably, getting my butt way back onto the seat helped quite a bit (aside from being uncomfortable).

The sag was set proper when I first took it out- dropping the rear was a defensive move to get some front end back. Like I said earlier, it helped a bit, but at significant cost to the rear action...

I'm not arguing with anyone about the traction; I rode up some really steep dry silty/sandy hills without any drama whatsoever- made me giggle like a little kid, but for those that are claiming that a .75" change in rear ride height is inconsequential, I'm not buying it- that's 100mm of rear rider sag to 80mm of rear rider sag. The way this bikes feels is like the forks are too vertical.
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Post by Julien D »

Sucks you are having all these problems. The trials tire is a perfect match for the tractor-like torque of the KDX engine. Please take our word that the higher ride height does not inherently cause all these problems that you have described. There IS something else going on with your bike, period. With the amount of users that have moved to trials tires, both pro and amateur, you would have heard this complaint before if it was a common result. Try to look at each issue respectively and make a diagnosis.

#1 sounds like difference in front tire performance, period. A front tire change makes a dramatic difference in handling characteristics. Take some time to get used to that as well and try varying the front tire pressure if possible.

#2 deflecting off roots and such? Does it feel like the forks are bottoming, or just too stiff to absorb the hit? Play with the clickers. Try a couple turns out and a couple turns in from where they are now and take note of the difference.

#3 Again, seems like a difference in front tire traits. However, since moving to trials I also feel the front end has more tendency to "push" when I'm on the throttle, and grab when I'm not. It feels to me like the rear is getting more bite, and lightening the front end when you're on the throttle like Fuzzy was saying above.

#4 I can't imagine a taller rear tire causing more head shake. Double check the front tire mounting and make sure there isn't any place where the bead isn't seated. Check around the rim lock as well and make sure it hasn't got the tire pinched further in or pushed out too far in that area.

#random tip - definitely try less pressure in the rear. If conditions permit, run down around 6-7lbs.


I hope you can work this out man. Like Fuzzy, I have much more confidence in my riding overall after switching to the trials tire. I have better control of the bike in almost all situations, and am just plain having more fun.

Again though, trials tires are not for everyone. If you like to keep the bike pinned and the rear wheel spinning it's probably not going to work out very well for you. If lugging the bike up a gnarly hill in 2nd while your buddies are spinning out on all sides makes you grin, then give it another shot!
Last edited by Julien D on 07:10 am Jul 01 2009, edited 1 time in total.
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Post by firffighter »

I'm going to agree with Juliend here.

And, yes the trials tire is a nice fit for the KDX. Seems like a perfect fit for me.

But, it is not for everyone, and if it does not feel comfy for you....




BTW, if you decide to get rid of if, give me a PM :wink:
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Post by KarlP »

Funny things do happen when you change geometry on a bike you are used to. At least for me, it does not take a big change at all to get me all catywhumpus (Technical term for screwed up).

I'd keep working with it a bit more. Seems you're obligated to anyway, unless you want to go through the trouble of changing that rear tire again already.

I get the impression the front is new, also?
I find new tires are wierd for the first few rides. I think they need to break in. Pressure too high? 8 psi ought to do it.

This is just me, but I like the S-12 best. I've used the Dunlop and Pirelli and others and just keep coming back to the Michellin S-12 front.

Good description in #1 up there. I could feel exactly what you were describing and that is frustrating.
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Post by fuzzy »

I love that front tire, too.
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Post by Mr. Wibbens »

Scorpion Pro is a dualsport tire

Ran one on my DR650

Looks like a good offroad tire but it could get pretty skittish at times.

Has nowhere close, the grip, of say a D756
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Post by TWMOODY »

Porterdog where are you riding with all the rock?
Mio loop?
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Post by porterdog »

Yes, Mio quite frequently as I have a friend with a place right near there. Lots of two-track stuff, too, also often in that same zone. The last place I rode was Tomahawk, and it was typical Michigan: Whooped out sandy single track, trees 6" off the trail, and rocks from egg- to bowling-ball sized.

Next weekend I'll have a good opportunity to check things out- I'm going to a friend's place, an old farm property, where we'll ride around the perimeter of a couple hayfields. Sounds rectangular, but it ain't! I'm going to take my spoons, my windex, my bucket, and my old 739s. I'll reset the sag as demanded by Julien [ ;) ] and ride the '43 at 8psi first. If I'm unhappy with that, I'll put the old 739 on and have another go...

Mr.W- the Scorpion Pro *is* DOT rated, but I'd hardly call it a dual sport tire. Dwight Rudder of TT offroad fame (7 times ISDE medalist or summat, see here: http://www.thumpertalk.com/forum/showth ... p?t=169897) highly recommends this tire, and while I'll grant that tire preferences are personal, an 8 time national enduro champion oughtta know some stuff...

In any case, if I swap to the old 739 and my front end STILL sucks, I'll put the old 739 front on and try THAT. If it comes back, I'll swap tires yet again (man is this gonna be fun) for the MT43.

One way or the other, I'll get to the bottom of it.
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Post by Mr. Wibbens »

Call it whatever you want, listen to whoever you like, it's a DOT street legal tire, or in simpler words a dualsport tire


The compound is pretty hard to be much use in anything but hardpack or asphalt

It's pretty vague on anything loose, and it'll wash out on you in a heartbeat

It'll last a very long time though, I had over 4,000 miles on mine and it still had half its life left

Granted the DR was 100lbs heavier than my KDX, I could take a corner 10 - 20 mph faster on the KDX with a 756 up front than I could with the DR with the Scorpion, at same air pressure
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Post by Julien D »

Mr. Wibbens wrote:

The compound is pretty hard to be much use in anything but hardpack or asphalt
First time i've heard anyone say that about this tire, out of a few dozen reviews, and that certainly doesn't mirror my experience with it. I feel like a billy goat running this tire. I just go wherever I want.
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