Trials tire: Fail

[porterdog]

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...

Kind of a failed experiment, (un?)fortunately. The final track setup we wound up with was ~.45miles; I put in about 200 laps (103mi), all 3rd/4th gear. It had never been ridden hard before, and the tall grass provided amazing traction. Running both front and rear at ~8psi didn't tear anything up and the traction never degraded. I could detect overfast steering sometimes (again, I contend that this is geometry related) but it wasn't much of an issue. More next time I ride dirt.

[KarlP]

Maybe come up on compression a couple of clicks in front?

I take the forks are flush with the tops of the triple clamps.

[porterdog]

Maybe come up on compression a couple of clicks in front?

I take the forks are flush with the tops of the triple clamps.

Correct on the fork position. You're suggesting INcreasing the compression damping?

[KarlP]

Yeah, maybe it is diving a bit when you come off the gas into a corner.

Not steering right is NOT in your head.

I usually have to make final sag adjustments on the trail. I set it to a universally accepted number and then ride. It does not feel right, so I'll stop and adjust, 1/2-3/4 turn one way or another, until it "feels" right. Get home and measure again. Yup, still at that universally accepted number. I have no explanation.

I'd try both, small sag adjustments and increasing front compression damping.

Beats changing a tire again....

[Julien D]

Cool. Sounds like it was ok overall. The quicker steering could be increased traction on the front with your new front tire, no? I'll take your word for it anyway, since you're the one on the bike. It's really strange though. My bike seemed to handle better all the way around after switching to the mt43. The little bit of push in the front is easy to contend with, I just move farther forward in the tight turns than I used to.

I'm interested to see what you find next time you're out in the dirt! You know, the ultimate solution could be a set of MX forks up front

[porterdog]

You know, the ultimate solution could be a set of MX forks up front

....or a pumpkin!

[jcnes]

Not to necro-post in this thread, but there were a lot of questions about how much larger diameter trials tires are in general, and the Pirelli MT-43 is specifically, than a standard knobby. I asked Pirelli, and they responded that the outside diameter of the MT43 (4.00P-18) is 700mm. For comparison, a Pirelli MT-16 rear tire (110/100-18) is 684mm. With an overall difference of 16mm, that means that the MT-43 will raise the rear of your bike up 8mm, or a little over 5/16". The difference is likely even smaller if you run the trials tire lower than the recommended 10-12 psi. Anyway, I was working on a fork swap, and wanted to see exactly what difference the MT-43 made to my geometry; turns out, not a huge amount.

[ohgood]

Not to necro-post in this thread, but there were a lot of questions about how much larger diameter trials tires are in general, and the Pirelli MT-43 is specifically, than a standard knobby. I asked Pirelli, and they responded that the outside diameter of the MT43 (4.00P-18) is 700mm. For comparison, a Pirelli MT-16 rear tire (110/100-18) is 684mm. With an overall difference of 16mm, that means that the MT-43 will raise the rear of your bike up 8mm, or a little over 5/16". The difference is likely even smaller if you run the trials tire lower than the recommended 10-12 psi. Anyway, I was working on a fork swap, and wanted to see exactly what difference the MT-43 made to my geometry; turns out, not a huge amount.

I've ridden a few bikes with mt43, but I buy the shinko sr241 (Trails Tire is the label, but it's a TRIALS tire pattern) because it's incredibly cheap and works exactly the same. The kdx -loves- trials tires. Excellent traction, excellent cornering both on and off road, and a very long wearing tire. The only time it doesn't perform 100% is in mud (doh!) and in downhill conditions with heavy pinestraw coverage. The rest of the time it's my favorite rear tire.

Also, just get it close to a dirt bike wheel and it hops on all by itself- it's that easy to install.

The concerns about height and stuff are... nitpicking at best.

Enjoy the ride

[chippy]

I had this same issue with my Honda CRF250x. After I installed a Kenda Equilibrium 4.50x18, the handling suffered. (awesome tire - a trials/endure hybrid. Incredible traction) To correct the issue, I installed a Kouba link to the rear and raised the fork tubes to level the bike back to the same front/rear attitude. (I had measured the bike before putting the BIG tire in the back) Now it handles like before, with a lower seat height as a bonus! Traction and performance on the steep mountain terrain is well worth the effort. This thing is a mountain goat. I see that Kouba offers several links for the KDX ( I have an awesome KDX200) so the same mods can be done to it as well. I am not sure that I want that tire on my KDX though, it is a blast to ride with a knobby. Just point and squirt!
My buddies have run trials tires on their KTM's for years with good results, but have switched to the Kenda as well. Downhill braking and cornering is much better with the Equilibrium.

[Marylander]

Just pair up the kenda equilibrium or similar with a goldentyre gt216aa 90/100, which is a very fat front tire, to make the geometry the same as with standard knobbies.

[chippy]

That's a good idea, I'm just not sure you would gain enough height. That Goldentyre is an awesome front tire. Are they available here in the U.S.?

[Marylander]

I bought the GoldenTyres from these guys, in eastern PA: http://ajppa.com/golden-tyre/ (I think they may be the sole US distributor, dunno).

I just went out to the garage and did a quick height comparison between the kenda equilibrium and a dunlop d952 110/90:
kenda 25.5"
d952 24.5"

And the goldentyre gt216aa 90/100 and a d952 80/100:
gt216aa 26.75"
d952 25.75"

So, looks like no difference at all geometry wise. Now, these measurements aren't super precise as I was holding the bikes up and measuring by myself (measured the radius x 2). I've got the kenda and the goldentyre on my kx250 and that thing is crazy tall for me now (I'm not quite 5'7").