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Hi guys. Most of you know this, I'm sure, but recently I realized just how big a difference tire size makes with regard to gearing and the overall power delivery and speed of the bike. I was running a Maxxis IT 100-100-18 with 13/47 (stock) gearing for a while now when I got a flat last week. Since that was the second pinch flat I got in a relatively short period of time, I decided to go with a bigger tire with harder rubber. I liked the Maxxis, so I went with the IT Dessert 110-100-18 and a heavy duty tube. THE DIFFERENCE IN GEARING AND POWER DELIVERY IS SIGNIFICANT! Trails where I would use 2nd gear with the smaller tire, I now have to use 1st. And trails where I would normally use 4th, I can now go the same speed in 3rd.

I noticed the same effect last year when I simply replaced a worn out tire with a new one of the same size. Just the wearing out of the knobbys made a huge difference on gearing.

With the larger tire that is made of harder rubber, coupled with the heavy duty tube, there is also a significant weight increase. I don't care about a couple extra pounds, but the extra weight added to the wheel also affects the power delivery. So, in short, the larger circumference plus the heavier weight, really affects the power delivery. I don't like the change. There was a significant decrease of power off the bottom.

In light of this, I'm gonna drop a tooth on the front sprocket from the 13t to a 12t and hope that I can get the gearing and power back to what I like. Anyway, just thought I would share this with everyone in case some of you didn't realize the significance of tire size as it pertains to gearing.

Another KDX rider that I know uses the 110 size tires and a 12 tooth front sprocket to make up for it. I personally would consider using a tooth or 2 larger rear as not to slow the bike down to much. But fronts are cheaper to replace.

6 Riders wrote:But fronts are cheaper to replace.

Are they ?

On a 12/48 combo for each rotation of the rear sprocket the front sprocket makes 4 rotations and because of that wears 4 times as fast ;)

DIY, you have a valid point, mine was more $12 for the front $40 for the rear......

One of the reasons I didn't purchase a rear sprocket to go with my new chain this season is because a rear was $40 and the front was $13. The front sprocket is what bears all of the torque from the motor and they wear out faster...

The other reason being my rear sprocket cleaned up rather nicely on my uhhh "wirewheel"

Does going up a size on the rear tire, thus raising the rear end of the bike somewhat, change the front rake enough to make a significant change in handling? I went to a 110/100-18 from a stock 100/100-18 and it seemed to change the handling significantly. It would climb anything I put in it's way, but seemed to make the front end wash out quite badly. I always wondered if this was what was happening.

Yes, it will change the handling of the bike in a few different ways. Rake/trail, weight, centrifugal force, and overall height of the bike, all affected by the choice of tire, will alter how a bike handles.

As for the whole sprocket issue, your better off going up a few teeth in the rear vs dropping one on the CS if you are already running a 13t. Going to a 12t creates more wear on both the CS sprocket and chain. That indicates more friction/wear which means you are actually wasting some power as well as longevity. I also don't know why you guys are spending $40 on rear sprockets when you can get a good steel one for $20. I know the chain becomes the expensive part when going up on the rear but it is well worth it. I have two years now on my 13t Renthal CS/48t Primary Gear/RK X-ring combo with only one adjustment and many years of life left. Do it right, do it once!

How many links are needed for a 13/49 combo? I am about to replace my chain/sprockets soon, and I have a 110/10-18 rear tire already.

JasonK94Z wrote:How many links are needed for a 13/49 combo? I am about to replace my chain/sprockets soon, and I have a 110/10-18 rear tire already.

E series or H? They use different length chains. I personaly bought a 120 link chain for my E, that was also the shortest length available at the time I bought it...(Regina chain) and simply cut it to length. The cost was negligible compared to trying to find a 110 link chain, about $5.00 IIRC.

6 Riders wrote:

JasonK94Z wrote: I personaly bought a 120 link chain for my E, that was also the shortest length available at the time I bought it...(Regina chain) and simply cut it to length. The cost was negligible compared to trying to find a 110 link chain, about $5.00 IIRC.

not too mention that after a certain amount of chains you can use all the little pieces to make one new one FOR FREE

6 Riders wrote:

JasonK94Z wrote:How many links are needed for a 13/49 combo? I am about to replace my chain/sprockets soon, and I have a 110/10-18 rear tire already.

E series or H? They use different length chains. I personaly bought a 120 link chain for my E, that was also the shortest length available at the time I bought it...(Regina chain) and simply cut it to length. The cost was negligible compared to trying to find a 110 link chain, about $5.00 IIRC.

Sorry, H series.

Stock is 108 link chain. I'd bet that 112 links would be required, but if you are wrong, you would be buying another chain. Go with 115-120 and chop a link or 3 off.

diymirage wrote:

6 Riders wrote:

JasonK94Z wrote: I personaly bought a 120 link chain for my E, that was also the shortest length available at the time I bought it...(Regina chain) and simply cut it to length. The cost was negligible compared to trying to find a 110 link chain, about $5.00 IIRC.

not too mention that after a certain amount of chains you can use all the little pieces to make one new one FOR FREE

REALLY! At first I defended you now Im sure your a new breed of dutch. The whole thread I never would of thought of that but in a sense yes you could just never thought of it.

ICRage42 wrote:

REALLY! At first I defended you now Im sure your a new breed of dutch. The whole thread I never would of thought of that but in a sense yes you could just never thought of it.

its kinda like the Seinfeld episode where they want to take NY soda cans with no deposit to MI where they can get 10 cents a can
it never works out because gas is to expensive
with the chains the problem is the master links
now, if I could just figure out how to "re-revit" the links I remove I would be in business

Maxxis IT 100/100/18 lists as 26.5" tall
Maxxis Desert IT 110/100/18 lists as 27.0" tall

That means to get back to the same overall gearing you need to step from 13/47 to 13/47.89, not even a full tooth on the rear sprocket.

I'm sure a lot of the difference felt is due to better traction more than gear ratio change, especially if ridding softer soils where the knobs dig in anyway. I remember one weekend were I started off on a very worn Trekmaster II, and that night changed to a new one, same tire, same size. The next day on the same sandy trails it felt like I needed to ride 2 gears lower, as the bike was actually hooking up and not just blowing through the gears with tire spin. Add in the fact that a Desert IT weighs a ton and you've added even more hookup and resistance to spool rpm up quickly.

Mathematically to get 3rd gear to be the same speed/rpm as 4th with 13/47 gearing you'd need to switch to a tire that's nearly 33" tall.

diymirage wrote:

ICRage42 wrote:

REALLY! At first I defended you now Im sure your a new breed of dutch. The whole thread I never would of thought of that but in a sense yes you could just never thought of it.

its kinda like the Seinfeld episode where they want to take NY soda cans with no deposit to MI where they can get 10 cents a can
it never works out because gas is to expensive
with the chains the problem is the master links
now, if I could just figure out how to "re-revit" the links I remove I would be in business

Or like the pizza idea where you make your own pie. "You get your mushrooms, your pepperoni, your olives, your cheese, you put it all together and you SLIDE it in the oven!! I tell you, people really want to make their own bike chains!"

Gotanubike wrote: Or like the pizza idea where you make your own pie. "You get your mushrooms, your pepperoni, your olives, your cheese, you put it all together and you SLIDE it in the oven!! I tell you, people really want to make their own bike chains!"

well, just for the record, I REFUSE to buy pizza from a certain place that makes them but expects you to bake them
that's not happening, if im paying a pizza place for a pizza it better be piping hot
if I want a home baked pizza ill buy a frozen on and give it to the wifey

now, about the chains, think about it, if you need a 108 link chain and buy a 120 then you get 12 links for free
that means that if you buy 9 chains you get 9 times 12 is 108 links for free, that is one chain for free, that's a return on your investment of 11 cents on the dollar

Check out this website I just saw. You select your bike and it loads your stock gearing with a chart that tells you your speed at every 1000 rpm

Customize your rpm range / tire size / sprocket sizes / chain pitch and # of links then displays results for the different combos...The difference really seems quite negligible. You would need to go down from a 47 to a 40 rear to reach 100km/h in 6th gear at 6400rpm

http://www.gearingcommander.com/

adam728 wrote:Maxxis IT 100/100/18 lists as 26.5" tall
Maxxis Desert IT 110/100/18 lists as 27.0" tall

That means to get back to the same overall gearing you need to step from 13/47 to 13/47.89, not even a full tooth on the rear sprocket.

I'm sure a lot of the difference felt is due to better traction more than gear ratio change, especially if ridding softer soils where the knobs dig in anyway. I remember one weekend were I started off on a very worn Trekmaster II, and that night changed to a new one, same tire, same size. The next day on the same sandy trails it felt like I needed to ride 2 gears lower, as the bike was actually hooking up and not just blowing through the gears with tire spin. Add in the fact that a Desert IT weighs a ton and you've added even more hookup and resistance to spool rpm up quickly.

Mathematically to get 3rd gear to be the same speed/rpm as 4th with 13/47 gearing you'd need to switch to a tire that's nearly 33" tall.

Thanks for this reply. Sorry I haven't been on the forum in a while to see all this activity. I have a question for you: How are you mathmatically figuring the gearing? Also, I just wanted to mention that the difference I've experienced is definitely not due to the tire hooking up better. The used 100/100 actually hooked up better than the new 110/100 (most likely due to the harder rubber of the IT Desert). Maybe the weight of the heavier tire makes a bigger difference than we realize.

I went out riding today for the first time with the 12/47 gearing. I do like it better than stock with this bigger tire, but I think when it comes time for new sprockets, I'll go a hair higher with 13/49.

For the calculations I am using a spreadsheet I made up some years back. Uses transmission gear ratios, final drive gear, primary drive gear (crank to clutch), tire height calculations, desired rpm, etc etc. Lots of variables to play with.

PM me an email address and I will send a copy.

Screenshot of the YZ version