Of Gears, Ratios and Gearheads

[Bagstr 288]

Hey Gang,

Mountain Season Set-up,

Up on Redonda Ridge Saturday, a discussion on traction and gearing ensued. All were agreed the MT43 is a significant advantage. Often I notice that many riders are using a larger rear sprocket than my 14/48 set-up. Ben and I discussed how a super low 1st gear can be helpful in the knarley tracks; 13/52 or 14/52 etc. I am currently running 14/48 and can see how being less concerned with clutch work as you ascend a slow technical section would allow one to concentrate on the line vs traction.

In that vein I ran a few numbers and compared published ratios used on the KTM 530 & my 690R.

Starting with Primary Drive ( tranny output ) then Final Drive ( countershaft and rear sprockets ) and finally the total ratio of the two. Numbers can tell you anything you want to make them, but I found support for creating a few more motor revolutions per wheel rotation.

KTM 530 EXC - Primary Drive 33:76 = 2.30, Final Drive 13:50 = 3.84, Resulting in 1.67 Overall 2.30 x 3.84 = 1.67

KTM 690 Enduro R - Primary Drive 36:79 = 2.19, Final Drive 14:52 = 3.71, Resulting in 1.69 Overall 2.19 x 3.71 = 1.69

The 690 being a multi-platform motor and greater torque starts with a higher Primary Drive output.

My seat of the pants judgement is that the bike would be easier to control on tough tracks with more motor turns per wheel rotations, i.e. super low 1st gear. This would make 2nd and 3rd the most used choice on the trail, holding 1st in "reserve". Matching the numbers of the more hardcore moto ( 530 EXC) gives me confidence to swap out the rear 48t for a 52t.

The price to be paid will be on the few pavement sections where I may be limited to 55mph vs the 60mph I can currently cruise.

Finally, I plan on needing to add a couple of chain links and will use master links with clips instead of riveted links. This way I can easily swap back to the shorter chain for the Dez season. Has anyone had trouble with removable master links?

Please comment if you see flaws in my ruminations.

[bikeslut 1]

I have not had a problem with clip style master links... yet... I prefer rivet style on highpower bikes... of which I currently don't have one

as far as chains go... get a chain and set of sprockets for each type of riding... swap out the whole set based on season... same time you swap out the rubber

Yeah; at Jacumba this week, my 15-52 geared DRZ did pretty well on most of the climbs, and I can save the clutchwork for lifting over an obstacle, or saving some wheelspin

I can still do 75 for short stretches even with that gearing and less motor than KTM guys have

[paulmbowers 236]

Have a look at the chain adjusting blocks. On the finest motorcycle ever made in the history of the universe, the 2003 KTM 525 MXC, the blocks have a short and long portion on either side of the axle.

This is designed to permit a two-tooth change in the sprocket without fussing with the chain. I change my front fairly often. Flipping the block gets me close to the right tension, but I still fine-tune.

I wouldn't run two master links. The wear on that short section will be different than the rest of the chain/sprocket combination.

Flipping the blocks + adjustment should do the trick.

[ADV Bum 205]

I have different sets of wheels with different sprockets. I usually run 14-48 most dualsport. I have a more aggressive rear with 50/51 sprocket. Street set that I go to 15 / 45. I have the chain set so that I can run these with using the wheel adjustment. I would play and see if I could set the chain so that multiple set ups can be achieved. To many masterlinks.

[ADV Bum 205]

Fakename, nice.

[Crawdaddy 96]

I have two rear wheels for my 520....one has a knobby on it and one has a trials tire.......both have 50 or 52 teeth on the rear sprocket (I don't recall).......my usual formula is pretty simple.......14 up front in the winter........13 up front Spring/Summer/Fall........I don't really care if the 13/50 or 52 limits me to ~50-60mph......

If I'm on a ride with substantional road content I'll leave the KTM at home and ride the WR250R......that's my ADV bike......it won't get there quick, but once up to speed it'll hum along smoothly/effortlessly at ~60-70mph even though I've lowered the gearing by swapping the stock 13 front for a 12.......(gearing is now 12/43)

[Beezzz 6]

KTM 520 Creeper King, 13 x 50. You'll forget to do any clutch work. Your big bike will never quit.

Remember that you are adding more torque power in the exchange.

I changed my KX250 to 12 x 50 to creep river beds and it added so much torque it was unridable in tight single track. Went back to 13 x 50 which I like for creeping and softened the torque, but the tight ratio tranny tops out the speed in the desert too quickly. I would rather creep easily than ride at high speeds.

[650hucker 0]

I think it comes down to torque more than gearing...My 650 has the stock gearing, and easily pulls 85 in 4th gear...but put it in first and it'll climb anything with what feels like 400 RPMS...You can literally feel the bike jump, or lug forward with each revolution....

But on my 426, it'll still hit 75...probably not now with the new gearing...I run 13/53 and it's still NOT in the powerband on most climbs and requires a lot of clutch work to keep it in the powerband. But this is a high-revving race bike.

[Spaugh 1]

get a 50 tooth rear and 13+14 fronts and swap fronts. A 450 EXC with 13/50 will still go over 90MPH. I assume the same is true for the 690. DID chains, ironman sprockets. munnracing.com for cheapest ironmans.

13 tooth fronts cause wear on the front chain slider so watch it over time.

52 tooth rears cause wear on the rear chain slider so watch it over time.

14-50 is the ratio that will have the chain rubbing the least on your chain guides.

[650hucker 0]

get a 50 tooth rear and 13+14 fronts and swap fronts. A 450 EXC with 13/50 will still go over 90MPH. I assume the same is true for the 690. DID chains, ironman sprockets. munnracing.com for cheapest ironmans.

I thought they're high speed estimates were extremely low...As mentioned, my 426 with 13/49 would hit 75+

[Spaugh 1]

Its a wide ratio 6 speed.

I know Tree runs a 13/50 on his 525 and he says he looks down at the speedo during races and sees 90+ often. I run 14/50 on mine and have looked down during races and gotten up to 97MPH. They would probably break 100 on pavement.

You can run 13/50 comfortable even in the desert. The only reason I run a 14 is so my arms don't fade as fast.

[Bagstr 288]

"Flipping the blocks + adjustment should do the trick." FN

Yes, that is the ticket. Luckily All American ( when Brent was still there ) cut the length for the 14/48 set with the blocks in the long position. I have about 5/8" shorter adjustment which I will cross my fingers in hopes if fits the 52.

Thanks for all the comments. It certainly is nice having the whole Team behind me when I make a change.

I'm sticking with the 14 front to save on chain wear. Possibly, I can use the 15t this summer when I'm on the road.

P.S. Hoss, I hope to have the Donor MT43 off this afternoon. I will let you know when it is available.

[darylhunter 1]

Here's a link to a gearing spreadsheet I did some time ago.

I'd originally developed it to help select gearing when I was racing my GSXR-750 and later made a version for my '06 Husky TE-510.

TE-510 Gearing

I have versions for an '06 TE-450 as well as my '07 GG TXT-300 Pro. Funny that 4th gear on the Gas Gas is lower than 1st gear on the Husky

Still have a version for the GSXR and my '99 R1 lying around somewhere.

[Bagstr 288]

"14-50 is the ratio that will have the chain rubbing the least on your chain guides." Spaugh

Mmm..I may go back to MotoW and swap for the 50. The Chainguide was a concern and you don't know if it's a problem until the thing is installed. At that point it is tough to return the sprocket.

14/48 = 2.19 x 3.42 = 1.56

14/52 = 2.19 x 3.71 = 1.69

14/50 = 2.19 x 3.57 = 1.63

Plus the 50 will help with turning the blocks. And the 13 can be installed for a tough run.

Thanks Spaugh and Gang

[ADV Bum 205]

I was able to drill another set of holes in the chain guard so that I could adjust it with the larger rear sprocket.

[Spaugh 1]

14/48 = 2.19 x 3.42 = 1.56

14/52 = 2.19 x 3.71 = 1.69

14/50 = 2.19 x 3.57 = 1.63

By the way dave, as someone who practices math for a living, yours is killing me.

What do you think Daryl? 2.19 x 3.42 = 1.56?

I'm just messin with you buddy, I know what you meant.

[TrophyHunter 15]

http://www.advrider.com/forums/showthread.php?t=569034

Some DR fun.

[darylhunter 1]

14/48 = 2.19 x 3.42 = 1.56

14/52 = 2.19 x 3.71 = 1.69

14/50 = 2.19 x 3.57 = 1.63

By the way dave, as someone who practices math for a living, yours is killing me.

What do you think Daryl? 2.19 x 3.42 = 1.56?

I'm just messin with you buddy, I know what you meant.

I saw that and wasn't going to point it out but, yeah, I think you'll that 3.42 / 2.19 works out to 1.5616...., but I knew what he meant

What I did when constructing my spreadsheet was to look in the shop manual for the various ratios.

For the TE-510, the primary ratio was 63:23 or 2.7391 to 1, the secondary ratio (which is your countershaft and rear sprockets) was 50:14 or 3.5714 to 1, and the individual gear ratios for 1st through 6th gear. 1st gear for example was 28:14 or 2.0 to 1.

I multiplied these together to come up with an overall ratio: 2.7391 x 3.5714 x 2.0 = 19.5652 to 1.

Then I figured out the circumference of the tire and did some math with inches per mile, seconds per hour, etc.

Then there's a table where I take the RPM of the engine and do the math to find out what speed will be produced.

So for 1000 RPM it works out as:

(1000 RPM / 19.5652 (overall ratio)) x 85.4 in (tire circumference) x 9.47 x 10^-4 (in/mile*min/hr constant)= 4.1 MPH

The spreadsheet has evolved over time and I haven't always been good about version control and internal notes/comments so if anyone does catch some oddity, please let me know and I'll take care of it.

The bit at the bottom dealing with the sprocket spacing was from when I'd adjust wheel base by selecting from a batch of sprockets to try to shorten or lengthen the wheelbase as desired to improve turn-in performance or stability while keeping the desired overall ratio. That was for roadracing and most folks won't bother with it for dual sport bikes.

I've got a mathcad worksheet somewhere too with this stuff in it. Might be able to find it if anyone is interested. Worked all this out once for a comparison of pulling capability between the 6.0 l diesel and V10 gas motor in my F-250.

[paulmbowers 236]

That makes my head really hurt.

[Crawdaddy 96]

That makes my head really hurt.

+1

Heading to the mountains? Drop a tooth up front and be done with it

[starpal2 0]

personally i dont mind using the clutch to get around i kinda prefer to use a little slip to get the exact amount of power i want/need. its not the best on the clutch bu im pretty good at replacing them. plus i can still go as fast as i want in the desert. plus if you are geared really low and you are using that to say get over a rock and on the other side of a rock theres a slippery hill needing a little more rpm out of that back tire you are going to have to change gears on your way up. with a closer to standard gearing you can use the clutch to navigate the rock(s) and still have enough gear to pull up the hill. just my own observation...

[Spaugh 1]

I agree with crawdaddy.

However 325lbs. = 325lbs.

260lbs. < 325lbs.

Thats the really important math.

[Bagstr 288]

Hey, what can I say, I was a History Major! Division, multiplication, what's the difference?

Regards the 265 vs 325lbs, I feel lucky not to be on the 440lb twin out there.

[paulmbowers 236]

You have a 440lb twin? Does he look just like you?

[650hucker 0]

Well all I know is that even with the gearing fixed, my bike will stick suck until I fix the clutch

440? That had to be interesting...I'm happy to choose between 240 lbs wet and 355 lbs wet when I take off for a ride :rtfm: