Gearing - Making the XR400 a better "adventure" bike


Well, I have an XR400 that I'm fairly happy with, but it's a little tiresome running any distance on pavement. I've geared it up to a 16 tooth front sprocket, and that helps quite a bit, but it's still a little buzzy above about 50mph for riding any distance. In an effort to do more road tripping in the future, I was looking for a different bike that might work for me, but I'm pretty much back to my XR as the best thing going. (Not so heavy, good power, simple to work on...) If it had a button start, that would be nice, but it starts well enough that I don't mind kicking it a few times a day. :)

Anyway, there is a giant XR400 thread on ADV that gave me the idea that I might use TRX400EX 1-3 gears in my XR transmission. A little microfiche surfing revealed that indeed a LOT of the internal parts do interchange between the two, and that if they fit, the EX gears would widen out the ratio in my trans by another 10% or so, which is more than one tooth on the front sprocket! Yes!!

I bought a 400EX trans and an XR400 trans off Epay, and decided to check it out yesterday. Unfortunately, I won't be swapping in 1-3. It looks like I could swap 1, 3, and 4, but 2nd gear dogs to 5th gear, and where XR has five dogs, the EX only has four. Not gonna work. I can still put in the 1st gear, which I'm going to do. That'll widen out the 1-2 shift a little, but it should still be pretty manageable if I go back to the 15 tooth front sprocket and run a 40 on the back. With that setup, I can still toss on the 16 tooth if I'm running a LOT of pavement, and I'll not have a super-tall 1st gear.

I've also given some thought to machining new 5th gears. Neither gear has internal splines, so that makes it easier. I may still go this route eventually, or at least do some design work and get a cost from a few sources. If I did that, I could make it compatible with the 2nd gear from the 400EX, and then I really could have a wider ratio trans, a lot like the old XR600 had. (I'm on the lookout for XR6 5th gears btw, to see if they can be modified to fit...)

Just wanted to document this all somewhere. I think this is one of the places where folks might be interested in a wide ratio trans for the XR4. I guess I could make this my bike thread... I'll work on getting some pictures up to show what I've done so far... Be interesting to see what others might have done to their XR's as well!!

List of mods to date: Home built aluminum rear rack, 2" PVC tool tube in front of the engine, UFO headlight (Better than stock, but not by much...) wolfman E-12 saddle bags, Passenger pegs from XR's only, Trailtech Vapor, home built Dualsport Kit, Moose handguards.

Older pic with tiny Moose ATV tank bags for saddlebags:

More recent, Stoney Pass near Silverton, CO

Taylor Mtn NM this spring (Yes, it snowed on our motorcycle ride, which was pretty cold...)

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Another big xr400 fan here too.

Everything about the xr400 works for me. Simple, reliable, tough, lots of torque, etc.... I was sorry to see Honda kill the XR in 2004, but I do appreciate that it is lacking in modern updates and that my priorities in a dirtbike are not typical.

I have done several long DS trips and multi day rides in Baja with lots of pavement. After lots of experimentation, I have decided that the stock 15/45 setup is the best compromise. Second best is to carry a 16 tooth CS and just do a quick swap for long highway stretches. That is what I did in Baja. But the 15/45 setup can handle 55-60mph well enough for my needs. I have done 45 miles at that pace. The RPMs are high but it is not hitting the rev limiter and within the motors design specs. Just a bit buzzy.

I have a lot of spare parts stored away and hope to get at least another decade out of my XR.

Your lightweight saddle bags look nice. That is one of my next mods.

Good luck



Yeah, I'm doing the 15/45 - 16/45 swap thing too. I figure if I toss in the EX 1st gear, I can run 16/45 all the time pretty much. If I could do 1-3, then 15/40 would probably work well, and if I could bump the OD on 5th gear just a bit, then I'd get rid of the buzzy 60mph thing, which would also be swell. :)

Looking at the big gearing chart on ADV, there's not a lot of inexpensive and reliable options out there... CRF230L is about the best simple bike, but it's a little underpowered for my taste. (Wife has one.)

I found a place that can make gears. I think I'm going to draw a couple up over the next week and see how much.

AZ ADVenturist

If you do ever decide to up the ante a bit, you might consider a DR650. Still air cooled simple & a great DS moto.
Nice pics, luv N.M.


Watching you from a ridge
Tagged for whatever happens. I'm rebuilding my XR4 to the 416 version, but I'll still carry that additional CS sprocket. But....yeah, a wide ratio? That'd be nice. Or all the way....six speed? heh.


I used to race a trx416. Thing was bulletproof, just lacked top-end pull compared to the twin cam motors it was competing against. I think mine hit the rev limiter around 45to 50 in fifth gear.


Well, I was hoping to get to this already, but I haven't, and now we're prepping for a Baja trip at the end of the month, so I doubt I'll have time.

I did some more number crunching and I'm on the fence now. Only 1, 3, and 4 will swap between the XR and EX. Swapping 1 gives me a lower first, but for riding singletrack, I'm usually up in 2nd, an only occasionally down in 1st. If I re-gear so 1st is the same as now, then 2nd is going to be 10% faster, which may be less than ideal, since it's already on the fast side. Grrrr.

I'm now starting to wonder about swapping 5th out of an XR600... They had a .84 ratio, instead of the 400's .93. The ratio change from 4th to 5th isn't much, a slightly bigger step there would do wonders for it, and not affect the lower gears at all. Or I could really widen it out and do 1st gear too...

Anyone with an XR5/6 trans laying around that can do some measuring and take a few pics??
I bet the centerlines are different. Sux that there seems to be no options to make the XR a better dualsport. :(
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Active member
Many years late to the party, but I've an XR400 I love for all the same reasons mentioned above, and in looking into addressing the same top end gearing dilemma stumbled upon not only this thread, but a similar one on ThumperTalk.

It's author seemingly solved some of the issues in using the TRX gears to lower the 1-3 gears so that you can run a higher final drive gearing to lower cruising RPM while maintaining stock-ish lower end gearing.

Screen Shot 2022-02-01 at 11.12.15 PM.png

Screen Shot 2022-02-01 at 11.13.17 PM.png

That thread hasn't been updated in a few years either, but the author posted that he was able to make the 'custom #1' combo work and has seemingly created a running, riding, operational bike; so there's reason to hope it'll work.

I'd already tracked down a complete TRX400EX bottom end to harvest the crank and e-start, which will necessitate splitting the cases anyway, so I went ahead and placed orders for the XR400 Falcon and XR400SM gears with hopes of combining them with the XR400r and TRX400EX gears to end up with the 'custom #1' gearing combo mentioned above.

XR400SM - 23451-MBV-000 /

NX400 Falcon - 23421-MCG-000 / *Which includes this encouraging review*
Screen Shot 2022-02-01 at 12.18.14 AM.png

I'll try and remember to report my impressions/results once I'm done and its back up and running in a few months in hopes it might contribute to a communal information repository to aid others down the line and hopefully keep a few more XR400Rs on the road as they're just such goldilocks bikes in so many ways.
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Active member
It seems this may actually pan out.

I placed orders for the requisite two gears mentioned above and they've both just shipped; hoping they arrive from Japan and the Netherlands by early next week.

It was about $125 USD for both of them, including international shipping, which is pretty cheap for a potential +/- 11.5% increase in gear spread if you're splitting the cases anyway.

Additionally, @GreyRider, who originally posted about this on, replied to my request for an update with the following encouraging response:

Screen Shot 2022-02-09 at 8.51.38 PM.png

It'll be a few months until my bike is up and running again to test and report for myself, I'm adding electric start from a TRX, sending the crank out to be rebuilt, boring the cylinder, lacing new wheels, etc., but this development is encouraging as I'm hoping the wider gearing and e-start help make the XR4 everything I hope it could be.


This is sweet info!!! I'll have to order up a few gears this spring!! (Procrastination DOES pay!!! :)

I haven't ridden much for the last several years, but I really need to get back on the bike. I have noticed that it's smoking a bit, so it's time to give it some love too. Might as well do a trans update as well as new rings and valve seals. Thinking about a 416 kit and stage 1 hotcam... Hotcam mostly as a way to get rid of the stock auto-decomp, which makes cold starting harder IMO.

Hmm... 10:1 piston might be even better, since I'm sure my cylinder would be fine with a light hone. That would at least make up for the 7000' altitude I live at, without necessitating premium, though it mostly gets premium anyway...
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