Bigger rear tire and gearing
 

We've discussed numerous times the issue of using bigger rear tires on the KLX. I've been a proponent of using smaller tires that are close to the stock size to preserve the meager power supply on even modded KLX's. I've been using the Kenda 100/100/18 rear TrakMaster with excellent results. I have 14/47 gearing and a 300 cylinder with a full Muzzy exhaust. I've used this bike with this setup in Utah and Colorado on previous trips with no problems.

This recent CO trip I tried a Kenda Parker desert tire on the rear in a 110/100/18. The Trakmaster in the 100/100 is actually a tiny bit shorter than advertised while the Parker is a tiny bit bigger than advertised. Oddly it was enough to cause me to use 1st gear a whole lot more than on other trips with with the 100/100 Trakmaster. There was just the tiny bit of taller gearing that actually made a difference in what gear I could pull in really steep, tough conditions. These size differences don't sound like much, but it was that tiniest bit of increase just enough to affect gearing subtly. I even had to drop the DJ needle one notch, something I'd never had to do in the past on any CV carb equipped bike. What I really needed was to go to a 13T front sprocket, but I didn't have access to one at this point.

The trip and riding were still great, but I struggled a bit more with slower speeds having to go to first more frequently and more quickly when the bike was running higher up and on steeper grades. I just mention this to point out that rear tire size increase can really affect a bike's performance as it applies to gearing. If I'd gone to one of the 130 or bigger size tires that are often discussed here, performance would have suffered much more. Even when you gear down the bike some more, you're still trying to spin a bigger, more aggressive tire on a relatively small displacement, lower powered bike. In southern Utah/Moab type conditions, this 110/100 tire probably wouldn't have made as big a negative impact, but high altitude and really steep, rough conditions really took their toll. The tire tread design and traction were great. It just needed lower gearing at the very least.

I just mention this to point how important that discussion about rear tire sizes can come into play on our KLX.

Thanks TNC, good info.

Why did you have to drop the needle this time? Haven't you rode up there before without issue? And what were the symptoms indicating you needed to drop a notch?

Yep, never changed a needle position or main jet before on this bike in CO or on any CV equipped KLR600/650 in the past. It was because the bike was lugging more before having to be down shifted. I'll be honest that I was surprised that this slightly taller tire made this much difference, but apparently I was right on the cusp of perfect balance of jetting, power, gearing, and tire size on my past trips. Last year and the year before, I was able to run 2nd and 3rd gear on this bike in CO a lot more effectively. This Kenda Parker is also a 6-ply, heavier tire, which of course didn't help. Like I said, I don't think this would have been noticeable in Moab. At the high altitude, the bike was blubbering too richly because I was having to lug too much before going to a lower gear. Now, just dropping the needle didn't recover any real extra power, it just limited the effect of high altitude and lugging. It was not the ideal fix, but it enabled me to improve throttle response with this gearing setup.

When Darren and I were going by Montrose and Gunnison on the way over from changing camp from Silverton to Creede, I called a couple of shops to check on a 13T, but obviously that was wishful thinking. Truthfully, I think I'll just go back to the Trakmaster 100/100. I've had nothing but perfect results with the last 4 or 5 or those tires, so there was really no reason to try something else except out of curiosity. That's not a knock to the Parker. It's wearing extremely well, hooked up excellently, and looks like a great overall performer. They just don't make a 100/100 in it. In some reflection I would still probably benefit from a 13T on these CO trips. A 13/47 would probably be pretty neat for there, and I avoid high speed pavement as much as possible anyway.

currently waiting for my tires to wear, so i can get smaller tires...this was a big gas and hp guzzling mistake...:(...but, looking at how the tire still looks brand new after 2,000 miles, i don't know how long i'll have to wait...

http://bayarearidersforum.com/forums...ictureid=14514

I know you're aware that the application of sizing for off road performance and gearing versus pavement applications has some dramatic differences...but yes...there are still some notable similarities. Man, that's one huge tire you have there. It does look cool, however, in a kind of Hot Wheels sort of way.:D

And I thought the Pirelli MT21 130/90R-18 I was running for a while was big.

Attachment 11822

shown here in the middle

Attachment 11823

yeah...i wanted to play in the dirt with an sf...but, it didn't quite work out well...and, now i'm just stuck with these frankenstein tires...the bike goes, so no reason to swap out the tires....

Ahnh: How much worse is your mileage with the larger tires?

i was getting consistently 65 mpg (k&n, dj132 main jet, 15/39 gearing, 110/70-17 front and 130/70-17 rear)....now, i'm getting almost exactly 55 mpg with the only change being 120/70-17 front and 150/70-17 rear....

10 mpg loss....wonder if there is a formula to calculate my exact loss in hp from the mpg loss...

I was looking at the Shinko 705 but I didn't see any tube type for the front.

Shinko Tires