140mm - 120mm - 130mm

[Bagstr 288]

Tires and widths?? With limited raw horsepower, where is the sweet spot in traction? The Pro FIM is great at McCain but Blowsand? The biggish MT21 130 is a lot of weight to spin and roll. Never tried a 120mm wide. Over to MotoW they have a 350 XCW Six Days on display with a 110mm wide by 100% tall 18inch. KTM at least thinks that looks good so I am willing to try the close dimension 120mm Dual Sport tire. Fully realizing the compound and sidewall etc. is different. The Pro FIM is not going to hold up running down Motezuma Grade while on Dual Sport loops in the Borrego.

So this will be a test, less weight, less width. How will that do in the San Gregorio Sand River.

[Spaugh 1]

110's are the right size for a 350cc. 140 FIM is a special case meant to be ballon like run at low PSI to get good traction. Running a 130 knobby, even 120 is just going to rob the bike of power and make turning more difficult. Used to run 120 maxxis tires on my 540 and 300s for desert racing. The 350 and 200s get 110s.

[dirt dame 561]

I have had good luck with the IRC Battle Rally 4.50 on my 450. Works well on pavement, in sand, mud and on the rocks.

[Bagstr 288]

Mounted the 120/90-18 MT21. Looking forward to a test run later this week. Previously ran the 140/80 PRO FIM and a 130/90 MT41. Seems like small differences in width mm and height percentage.

[TrophyHunter 15]

I'll never be a racer but in researching this, my WR450 shop manual recommends a 110/100-18 for USA & CDN models......130/90-18 for Euro/Aus/NZ models.

Hmmmmm..??

[Spaugh 1]

I'll never be a racer but in researching this, my WR450 shop manual recommends a 110/100-18 for USA & CDN models......130/90-18 for Euro/Aus/NZ models.

Hmmmmm..??

Taller tire for big Americans?

^110 is a good tire. Bigger is not always better. Bagstr ride HIGH. Dtay!

[TrophyHunter 15]

So you're sayin' really tall with spinners. I'm on it.

[Bagstr 288]

My Math - As opposed to what Your math may be.

KTM 350 XC-W recommendation: 80/100-21 and 110/100-18 . Front 80mm tall Rear 110mm tall

PRO FIM 21 Inch 90/90 = 81mm tall

MT21 18 inch 120/90 = 108mm tall

MT21 18inch 130/90 = 117mm tall

PRO FIM 18in 140/80 = 112mm tall

Ignoring for the moment turning dynamics based on width and just thinking of rake/trail based on height -

Where 10mm = .39inch

The 120/90 is actually 2mm shorter than the stock 110/100 and the 90/90 is 1mm taller than the 80/100. A 1mm rear bias over recommended. Heaven only knows what KTMs springing bias is vs my sag settings. I would think one may feel the 9mm lowering of the rear going from the 130/90 to 120/90.

What do you think of my History Major math? Spaugh, Robertaccio

And Circumference = 2 Pi radius 80mm vs 81mm = 3.14mm difference Front

108mm vs 117mm = 28.26mm difference Rear

Edit: After some thought, my circumference calculation is highly suspect. 80mm for example is not the total diameter of the wheel, just the aspect ration height. You need an accurate radius, i.e. center of axle to top of tire, to get circumference. With that, there an important difference in height with different tire sizes.

[Spaugh 1]

I like the scientific approach for a minute i thought you were just rollin dtay.

thought you had a 120/100. Now i realize the errors of my ways. Forgive me, its lonely out here. Carry on.

[Spaugh 1]

So you're sayin' really tall with spinners. I'm on it.

For a 450, 110/100 is fine maybe 120/100 for desert riding. Less punctures and maybe better float in sand but they are heavy.

[bikeslut 1]

^{other than sand, I also like thinner tires for trail riding... they make my heavy bike feel less heavy while changing direction. They also accelerate faster (less rolling mass?) in my mind anyway}

[bikeslut 1]

and; I would love to take credit for the previous post font, as a way of messing with you old guys, but I really have no idea how it happened

[Goofy Footer 539]

Not to throw a variable in the math but it sure seems to me that different manufactures have their own interpretations of what a 120 width tire is.. Go to the shop and put a few tires next to each other - I'd be shocked they are all equivalent. I could be wrong but my experience so far as led me to never trust brand to brand equivalency.

[PastaPilot 17]

Your math is sound Dave. I like the buoyancy of the wider tires but after swapping a well used and worn 120 for a 110 I noticed right away how much taller the new tire was and after a couple rides I can tell it turns a bit better. Could just be the new tires though

[Bagstr 288]

Two Rides in with the MT21 18-120/90. Vs the 130 this quickens the handling and handles the sand better than the Pro FIM 140/80.

CID and I did a big loop yesterday with the whole gamut of pavement, sand rocks and slippery DG drops. I was particularly impressed with how the tire ( and the bike ) handled the rock steps approaching Pinyon Drop. Drive right up and over! Thank you very much.