Gearing for 2 extreme environments

Greetings,
In April of 2012 I will be shipping a WRR from the US to Finland to do this Russian ride Russian off-road people 2011: Dirt Again . As I'll need to ride the bike on-road 600 miles (985 km) to Moscow, then do the off-road tour of approx. 2500 miles (4000 km) and finally ride the bike back to Finland from Moscow, I am trying to learn which sprocket combination will allow me to do both high-speed highway AND low-speed off-road riding with just a CS sprocket change.
My riding weight is 220 lb. and my gear is at 50 lbs., and the off-road sections of the ride, as shown in the video, are pretty extreme, so I need gearing with real pulling power, yet be able to cruise the highways at a minimum of 120 km (75 mph) for hours on end.
Is this possible with just a CS sprocket change, or will I need to carry a spare rear sprocket as well?
I'd really prefer to avoid carrying a rear sprocket if possible due to weight and space constraints.

In the end, what I believe I'm looking for is the greatest degree between ratios by changing only the CS sprocket, and keeping the same chain length and rear sprocket size, AND within the limits of drivability of the bike.

Thanks for your thoughts on this issue!

ktm950se

I'd just pick a compromise gearing ratio and leave it like that for the whole trip.
Myself, I'd try 13/48 out and see how I liked it.

I'd prefer to not change gearing during the trip, but the variations in terrain are just so large, and the 250's engine only so powerful, that I think a single compromise gearing would be miserable overall.
If the bike was a 500 or more cc's I think one ratio would be sufficient, but not in this case.

Do you agree?

ktm950se

The hardest thing is gonna be keeping up at 75mph rather than the gearing for tight gnarly steep single track. 13/47 will work pretty well for both, but I found I didn't have as much engine braking as I'd like on steep down hills at altitude (10-12k feet) with it. Going up was no problem. But I was on the rear brake pretty much constantly to control my speed on the downhill due to the cliff face on the right making me not want to crash. Highway at 65-70mph was no problem. 75mph starts pushing it for comfort imo but thats partly the added vibes of the speed and wind resistance of an upright seating position on a dirt-ish bike than the motor itself.

So like I said on ADV, maybe run 14/47 for the highway ride and bring a 13T and a 12T for the gnarly stuff, or just compromise with a 13/47 all the time and deal with the slight extra vibes and slight less downhill braking assist (which I only noticed because it was a couple miles of downhill on a loose shale/gravel road bed).

It's a 250cc bike, and it's gonna rev some at 75mph, which is 100% normal.
If it didn't, it wouldn't get out of it's own way or it would have an 8-speed transmission.
I believe that once you get over that, the bike will do just fine. :)

The stock 13/43 gearing is too tall, even for street use in my opinion, and it comes geared so tall, you can afford to gear it down some and still have plenty of top speed.

I have set up with the following:

14 /49 highway. With a 120/90 D606 on the rear this is pretty close to stock gearing. With a stock size tire you give up about 3 or 4 mph top end on the hiway. Right now I have the 120/80 MT21 on the rear and it does give up a bit of top end but is just fine on the hiway at 65 to 70.
13/49 for nasty off road

This with only a counter sprocket change.

A 112 link chain is needed. It coveres the range needed for the two sizes of counter sprocket.


You can check out gearing combinations on GearingCommander.
http://www.gearingcommander.com/


I watched the video of those rides . That is some tough riding ! Go for it And post up your trip report in here. I would love to see it!

Thanks everyone for your thoughts.
I'm still processing a lot of info, but I'll post back soon as to how the bike will be set up.
And a ride report will certainly follow!



ktm950se

2nd what YZETc said...except I may choose 13/46 or 47 for me.
Tire choice would be a bigger concern.

>"2nd what YZETc said...except I may choose 13/46 or 47 for me.

My choices are 13x47 and 14x47. Countershaft sprocket change only.

TwilightZone wrote:

>"2nd what YZETc said...except I may choose 13/46 or 47 for me.

My choices are 13x47 and 14x47. Countershaft sprocket change only.

How many links of chain go with this combination???


For the suggested combo ( 14/49 and 13/49) It ends up with a good position on the rear wheel chain adjuster. It leaves pleanty of adjustment as the cahin wears to tighten it up. Plus you end up with near stock gear ratios when using the larger counter sprocket.

If you use a D606 rear tire the 14/47 combo would result in slightly taller gearing than stock. That might help you for the hiway miles. But you need to pay attention to length of chain and where it falls in the rear wheel chain adjuster.