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18"/21" wheels on DRZ125


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I swore, after sinking untold amounts of money into Honda XR50's, that I would never again spend tons of money on a little bike trying to make it a big bike.... BUT THEY'RE SO MUCH FUN!

 

Here's the short story:

 

I have a 2003 DRZ125 that has been a wonderful playbike (I have many other bikes) and I find it to be the most fun bike of the bunch when things get into "trials bike territory." After too many times getting it into extremely hairy situations I thought to myself "if this just had fullsize wheels and 10-15hp, it would be perfect!" 

 

I have been analyzing cost/benefit ratios of building the drz, or selling it and putting that money towards a different bike (trials bike, crf230, or bigwheeling/ fullsize wheels on my CR85 chassis XR100.) See my "what bike should I buy" thread here: https://thumpertalk.com/topic/1108894-crf230-as-a-gnarly-trail-bike-trials-bike-hear-me-out/ I was all set to sell it and then the light bulb went off! The biggest cost in the conversion was going to be custom spokes and new rims to fit my hubs, if I just use stock wheels from another bike (like the KX250 or KDX200 parts I have behind the shed) I will not need to spend anywhere near as much money to make things happen as I had originally figured on. There will be much more custom work involved and a lot more problem solving + headaches to make it happen, but the time I have, the money not so much.

 

Moving forward with the tiny bike on fullsize wheels thought process, I started mocking things up on the DRZ yesterday. I can see A LOT of work ahead, but it looks promising. Using my kx100 swingarm (I have a complete roller) I should have enough room to just squeeze in a trials tire, I will need to do some fairly minor modification to fit the KDX200 rear brake and then change the wheel bearings to some with a smaller I.D. to fit the kx100 axle through the KX100 swingarm and KDX200 wheel. Sprocket specialties has helped me before, so I'll have to call them to make a 428 sized sprocket for the KDX wheel. 

 

The front end will require a similar wheel bearing change to fit the RM85 axle (I have RM85 forks/ little wheel and rear shock on the bike currently) with either the KX250 or KDX200 wheel. I'll have to make a caliper bracket to run the big bike brakes, but luckily it is just a piece of 3/8" plate with 4 holes in it. I'd actually prefer to run the smaller brakes, but it looks like a lot less work to use the big bike stuff. Other than that, I'll need to trim the right side fork gaurd to clear the hub. The big issue with the front is that I have 11" of travel and only 8 1/2" of clearance to the fender. I could slide the fork tubes back down 1 1/2", but that still leaves things 1" shy and would absolutely ruin the handling. With the forks in their current position, I have a 64* head angle which is right where I was aiming for (63-66). So how can I reduce the available compression travel without reducing ride height?

 

All said and done this would give me a 51 1/2" wheelbase and 15 1/2" unloaded ground clearance. The fullsize wheels are surprisingly VERY close in weight to the drum brake/ steel rim/ steel sprocket 14"/17" stock wheels. Forks are lighter by about the same amount. Swingarm is slightly lighter. I'm sure I'll gain several pounds here and there, but I started with 176lbs dry weight, so I see no problem keeping dry weight under 190lbs.

 

Has anyone here pulled this off before? If I can make this happen, then I will move forward with building the engine, no sooner.

 

20141101_164402_zps0da7bb22.jpg

 

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For the front, my first thought would be to make some 1.5" spacers and put them in the front forks. I had to do that to an older bike I had since the front needed to be resprung and the new springs were a different length so to preload them properly you needed spacers.

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It looks like the KX100 swingarm won't accept the trials tire afterall. I was just measuring from pivot to axle but failed to measure from axle to the cross brace of the swingarm (where the linkage mounts.) So either way I'll have to lengthen a swingarm. That being said, it might be best to just use the DRZ swingarm and save the extra machine work of boring the KX100 pivots to accept the larger drz bearings/bolt. Not to mention I can weld the steel drz swingarm myself, I'd have to pay someone to weld the aluminum KX100 swingarm. Hmmm.

 

I need to get more of these things (mostly) figured out before I proceed. I know I can work around each individual issue, but I still need to figure out if it will make financial sense in the end. I know I could just bigwheel (19"/16") and it would be a nice improvement for much less effort/money, but I don't know if that will be enough improvement to justify even starting the project.

 

I should change the title of this thread to "18"/21" wheels on DRZ125: thinking out loud"

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Will you be running into the same clearance issue with the rear suspension when the shock bottoms out and the rear tire rubs to a halt inside the back fender ?  I suppose the lengthened swing arm might help that ? 

 

 

As far as I can tell right now, there won't be any clearance issues in the rear (once the swingarm is lengthened.) Just roughly mocking it up, I have 12 1/4" vertical clearance and only 10 1/2-11" rear travel. The stock DRZ swingarm is 1" x 2" x .065" wall which seems crazy thin even for a mini bike, even my XR50's were at least .095" wall. I still think that I will go ahead and lengthen it, but probably plate over the sides too.

 

Does anyone have a stock DRZ swingarm they want to sell CHEAP?

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Does anyone have a stock DRZ swingarm they want to sell CHEAP?

 

If you're interested, I've got a '03 swingarm that I had to cut off my DRZ (bolt, bushings, swingarm all fused together). I'll shoot you a PM with pics if you think it might help you.

 

I also happen to need a KX100 swingarm as my machinists screwed up my current KX swingarm and I think its toast, so I need a cheap replacement (I'm out the cost of the swingarm + the cost of the machine work + my time!).

 

Maybe we can work something out.  -Ed 

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Too bad you're all the way across the country, I have a DR200 (18" rear) swing arm and an unknown rear wheel that was mounted on it I'm looking to unload. Let me know if I can take any measurements for you.

 

Too bad indeed! I have a 1984 KX80 frontend (listed in your sig) laying behind the shed!

 

Do you have a DRZ125 around? I wonder if the linkage hooks up the same?

Edited by TheLetterJ
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I had one, some bastard stole it. I plan to get another, but it won't be for a few more months.

 

From what I remember, the DR-Z is just a miniaturized DR so the linkage should be very similar. The question is will it bolt in or are there other things that need to be changed in the process like the KX swingarm needs to be bored to accept the DR-Z bearings.

 

Maybe Bruce has an idea if the swing arm could be easily made to work for you. I would love to do a trade for that front end.

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I'm liking that front end in your pic. Did you just slide in the whole triple clamp assembly off of the KX?

 

Close, this frontend is off of a 2003 Suzuki RM85 (little wheel) with the tubes slid up ~1 1/2" above the triple clamp. The KX80 bigwheel (same as a KX100) frontend I have would have fit up just the same, but the 37mm Showa's (RM) were in better condition than the 36mm KYB's (KX) so I went with them. Either is a 100% direct bolt on.

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  • 5 months later...

Did I mention that I'm a slow builder?

 

I put the fullsize wheel part of the project on standby and decided to just bigwheel the bike for now. The 19"/16" wheels I have came from a '97 KX100 so they are the older generation which use smaller front brakes. The front rotor is not interchangeable with the newer KX100's. Because of that, I had to move my front caliper and ended up using a KDX200 complete front brake system and redrilling/tapping new holes in the caliper bracket. I also had to "clearance" the inside edge of the caliper to ensure it could not come in contact with the spokes. Handled. Moving on.

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For the rear end I decided that I didn't like the way that the KX swingarm had to be shifted to the left side in order to get the chain to align so I am using a stock DRZ swingarm. After lots of measuring, I made new wheel spacers for each side (1/2" heavy wall pipe) to center the wheel in the swingarm. With the wheel centered, the chain was now 5mm too far inboard. Coincidentally, the old steel 420 KX sprocket was 5mm thick... I cut it down to make a spacer (basically just a small ring with 4 holes in it) and then installed longer studs into the hub. With my 52tooth 428 conversion sprocket now bolted on top of the spacer, everything is now in perfect alignment! The plan is to make another spacer out of aluminum and weld the spacer and sprocket together so that the sprocket remains hub-centric instead of stud-centric. The KX caliper bracket would work as-is in the stock drz swingarm, but I'll be welding another piece of 1/8" plate to the locating tab on the swingarm making it form a "T" instead of the current "I" shape, that should make for a perfect fit.

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Next up was addressing the rear master cylinder. I tried and tried to find a location that would allow me to use the KX MC or even my RM85 MC, but kept running into clearance issues with the brake hose and the exhaust. My solution was to use an RMZ250 MC which is angled rearward, has an integrated reservoir, and has the brake hose exiting from the front instead of the top of the MC. I've got a clean little bracket fabbed up out of 1/8" plate and will be welding it up later today.

 

The brake pedal was not as bad as I had figured. I measured leverage ratios of the KX/RM/ and RMZ pedals and they were all 4.7:1, so that's what I went with for my new pedal. I cut off the top/pull rod lever from the pedal and then welded the back half of the KX pedal to the drz pedal. The KX pedal has 2 90* offsets that kick it out about 1/2" which was exactly what I needed.

 

Now onto the brake hose itself. With the little wheel swingarm, the stock RMZ hose is ~1" too long. I've been kicking around sourcing a BW swingarm for the bike anyway which would make the RMZ hose fit perfectly, so that is probably going to happen sooner rather than later now... besides, I haven't cut my new chain yet, so maybe I'll just wait until I get a BW swingarm. The stock rubber hose is also kind of large in diameter and doesn't like being bent into a tight radius, so the plan is to use a RMATV "Tusk" branded (it's actually made by Galfer but costs 1/2 the price of having a custom one made) SS brake hose for the RMZ to clean things up.

 

As soon as I get these last few things buttoned up and I take 1 lap around my cul-de-sac, I'm selling my DMC CR/XR conversion and using some of the proceeds to build the drz engine. I know it doesn't seem logical to get rid of a conversion bike that is PERFECT just to build another of the same class, but for some reason I just like my "yellow bike" better and it has much greater engine potential than my already built ~11hp xr.

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Nice work. Sounds like you made a lot of progress recently.

 

The plan is to make another spacer out of aluminum and weld the spacer and sprocket together so that the sprocket remains hub-centric instead of stud-centric.

Small bit of contention, when you make a custom sprocket, you're going to have to make all future sprockets a custom sprocket. I would leave it as a spacer and move on. The fractional difference in weight between aluminum and steel in this case isn't worth the hassle even if it's unsprung weight.

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My concern had nothing to do with weight, it's just that with the spacer on the hub, the sprocket is relying solely on the studs to locate it. The raised lip on the hub does not protrude far enough for my sprocket to ride on it anymore. It would probably be fine, I'm just concerned that sprocket might get pulled straight forward (instead of rotating) when it sees an extreme heavy load... remember, I'm 6'5" 220lbs and use this as my "rock" bike so it is VERY likely that I'll dump the clutch at near full throttle in high traction situations in order to clear an obstacle. That would screw me in a BAD way (not trailside repairable) if I broke those studs off while riding some remote single(no)track in BFE! By welding the sprocket and spacer together, the sprocket would now be hub centric again so any and all forces applied would be rotational.

 

I'm just going to run it for now, but even if it seems to be holding up, the thought will still be in the back of my mind... peace of mind is worth something. This is the first time since 2003 that the sprocket is being replaced, so I don't mind having to make a custom sprocket each time.

 

We had to leave my buddies ttr in the forest for 3 days because of a mechanical failure and it was not fun/easy getting us out, devising a plan to retrieve the bike, and actually executing it... well, it was kinda fun looking back, but stressful at the time!:

 

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A year later while on a trail clearing mission, we had to ditch the ttr AGAIN due to a hole in the case, this time we were able to retrieve it and got home at midnight:

 

20140823_125534_zps3327a037.jpg

 

Needless to say, more ground clearance (for him) and substantial skid plates/ frame cradles for both of us are extremely high on the priority list! I put my KX frontend on his bike and bought a set of ttr bigwheels off of another friend so it's getting closer.

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As long as the nuts are tight, you'll be fine. If the sprocket were out of alignment, the chain would move with it and if the chain were able to move the sprocket, it would get moved back into place when the wheel was 180 degrees rotated from before, if you could put enough load on it. But keep your nuts tight and you'll be fine. It's a DR-Z125, it makes 8 hp. This isn't a problem for a Hyabusa with 10X the displacement and 20-some odd times the power, it won't be a problem for you.

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