Jump to content

XR200R Weight Reduction

Recommended Posts

Several members have posted their conversion projects on this forum; the most popular seem to involve stuffing an XR200 motor into a MX chassis. I have one of those in my garage and while it is a good bike I thought I could make some improvements in my search for a more “perfect” bike for the type of trail riding I currently ride. A long time riding buddy and I have been fussin with riding dirt bikes since the mid sixties and thru the years our riding and priorities have evolved, and the bikes have ranged from open class MX bikes used in the desert to Trials bikes. Also during this time we have had a variety of XRs in our stables and the power delivery of the XR200 engine seems to suit the type of trail riding we currently like to do. During this past year we have been attempting to define an ideal bike for our use on technical trails in the PNW, we started by riding different types of bikes in side by side comparisons, and evaluating the results to find what we thought suited our riding style and terrain. I tend to focus on improving suspension and he focuses on light weight, as a result we have some lively discussions, and different bikes. At this point I’m just a recreational rider that likes single track along with some tight technical stuff, plus mountain trails with switchbacks and stair steps. My friend has a really cool Montessa Trials bike (Honda owns Montessa and this bike has a Honda 250 EFI Unicam engine); while it has one of the best engines for trail riding attempting to make the chassis trail worthy would require a lot of work including suspension upgrades. This engine would be my engine of choice for a trail bike. The 450 bikes just have too much power and weight for tight woods. MX bikes have a nice chassis but too long a wheelbase for tight trails. Two strokes are short on good low speed torque but I like their power delivery and light weight. Mini bikes have the light weight but lack enough tractable power; but most important is that the ergonomics of the cockpit are terrible for an adult on a long ride. So let’s get started.

As you can see from the following list there are a lot of compromises in defining the preferred characteristics for my ideal trail bike:

Quick steering requires steep rake, 26 degrees is about right; anymore and you lose good turning on tight trails, any less and stability is reduced.

10-12” of suspension travel; a lot of trail bikes have much less than 10 and MX bikes have more than 12. The trade off is that long travel raises the seat and CG, both of which I think should be low on a trail bike.

54” wheelbase; any longer and you lose the tight turning needed for technical trails and switchbacks, any shorter and the bike get squirrely.

200 lbs dry weight; low weight is nice when you must lift the bike back onto the trail.

Disc brakes; for the progressive feel and water resistance.

Low center of gravity; makes the bike easier to flick left/right in those tight woods.

Trials tire for traction, and to reduce the impact to trails. (Trials tires weigh 1 lb more than a knobby but you can offset the weight by using the Nuetech Tubeless system.)

Here are a few published weights (dry & wet) and my weighing (curb weight is with some gas):

Model Published Weight

82 XR200 216 dry 222 curb

82 XR200R 222 dry 227 curb

RM125 w/XR200 engine 218 curb

90 XR200R 216 dry 231 curb 218 no gas

CRF230 249 wet

  • Like 1

Share this post


Link to post
Share on other sites

To keep cost under control the chassis of choice will be an 86, or newer, XR200R. It fits all of the above criteria except for weight, brakes, and suspension travel. Next is how to change the weight, brakes, and suspension.

My proposal is to adapt CR80/85 Showa USD forks, these will provide 10.8” of travel with cartridge dampening. These forks are smaller in diameter than full size USD forks so should be more flexible, I don’t expect a lot of harshness. Finding a suitable 21”wheel was a problem, and my solution was to have Buchanan lace a 21” Excel rim to the CR80 hub. The Excel rim is one of the lightest available which is in keeping with the goals of this project. However this is not a cheap solution.

The rear is a bit easier; I selected a late model XR250R swing arm for weight saving, the disc brake, and compatibility with the XR linkage ratios. Honda XRs use a linkage ratio that is approximately twice that of other bikes so sticking with XR stuff makes life easier. But I want to use a CR85 shock for weight saving but the linkage ratio required for this shock is half that used by the XR shocks. If I go this route my solution is to adapt CR linkage to the XR250 SA and the XR200 chassis.

Rear wheel is the next item. The stock XR200R (and the XR250 drum brake wheel) is a 30 pound anchor, I have an 89 RM125 rear wheel that weighs 25 pounds w/ tire but it uses a 20mm axle and the XR250 SA uses a 17mm axle. Fortunately the bearings can be swapped out for ones that fit the XR axle.

Projected weight savings from stock:

96 CR80 front end w/ 21” tire 6.4 lbs

Renthal handlebars…… 1.0 lbs

03 XR250R AL swing arm 3.4 lbs

84-85 XR250R linkage 2.1 lbs

CR85 shock…………. 1.5 lbs

RM125 rear wheel…… 4.7 lbs

FMF Q muffler……… 1.0 lbs

Trials tire +1.0 lbs

NueTech Tubliss 1.0 lbs

TOTAL 19.1 lbs

If my weights are correct I can build a XR200R with cartridge forks and disc brakes that will weigh under 200lbs wet without gas!!!

Share this post


Link to post
Share on other sites

Very interesting Chuck. You've put a lot of thought into your project. I'm looking forward to the final product. I may utilize some of your ideas on my 200.

The late model 96-04 swing arm is is a 3.4 lb weight savings over the steel XR200? That's great, plus you get a disc. How do the lengths/widths compare? The brake cylinder would be a weight gain of what, 1/2lb? You are still under or right at 200lb's.

I'm very interested still in how the CR 85 forks work out as well.

Shaving a few pounds off an already light bike plus getting more performance.

Sounds like a plan! :thumbsup: I have a lot more q's but don't want to ask on the forum, OK to PM you?

Doug

Share this post


Link to post
Share on other sites

This is cool. I hope this thing rides properly and you don't end up with a cobbled turd on 2 wheels. But if you do that's part of learning what will not work. It seems like you have done your home work and I look forward to seeing & reading more about this in the future.

Will the conventional CR80R front forks fit into the 1986 XR200R tripple tree or will you need to modify the CR80R triple tree to fit the XR frame?

Share this post


Link to post
Share on other sites

I didn't use CR80 conventional forks, I used the CR80/85 Showa USDs. I put them on a few weeks ago. I was frustrated with the harshness of the stock forks; I changed oil and springs without getting the rid I wanted. My benchmark is a RM125 with 46mm conventional cartridge forks and I couldn't get the stockers close. I put on the CR80 USDs a couple of weeks ago and while the action was better they were also harsh on the initial hit, I fussed with the clickers and then change the oil to Honda Pro cartridge fork oil and wow, much better. I found a chart of oil viscosities and the the Honda, Yamaha and a few other "5wt" oils measure in the 15cSt range but a lot of the oils are heavier which would stiffen high speed damping. Here is a part of the that chart showing the viscosity of some of the "5wt" cartridge fork oils at 40 C.

Spectro Fork Oil (5wt) 21.7

Bel-Ray HVI (5wt) 20.75

Bel-Ray Fork Oil (5wt) 20.5

RockShox (5w Medium, Hydracoil) (Torco) 19.9

Spectro, Golden Spectro Cartridge Fork Fluid (85/150, Very Light) 16.9

Showa SS7 (5wt) 16.9

Showa SS05 (Stock Fork) 15.90

Maxima Fork Oil (5wt) & Bicycle Fork Fluid 15.9

Racetech (Motorex) (Light US1) 15.2

Kayaba (Zero-One Fork 15.10

Honda Pro HP Showa/Kayaba Fork Oil (5wt) 15.0

Yamaha 01 Fork Oil (Kayaba) 14.57

Torco RSF Light (Purple) 14.5

As you can see ther is quite a range of viscosities.

Today I installed RaceTech Gold Valves in the forks and will be able to report on their performance in a few days. Next are stiffer springs, due in a week or so.

Installing CR80 forks on the XR200 took a lot of planning but in the end was easy. The 86-91 XR200 forks measure 33 3/4" from the top of the caps to the center of the axle, the CR80 USDs measure 33 1/8", 5/8" shorter. However with the increased travel the 90/90x21 Michelin M12 just touches the bottom of the fender. My fix was to slide the fork tubes down 3/8". The CR80 stem is almost too short to fit the XR200 steering head so I decided to use a XR250R stem that is a bit longer and a lot lighter. The CR80 stem measured 6 7/32" from the top of the lower triple to the first threads, the XR200R measured 6 1/4" and the XR250R measured 6 3/8". All use the same bearings but the CR and XR200 stems are steel and the XR250R is aluminum, so I went with the 250 stem. The problem is the ID in the CR lower triple is 0.006 too big for the XR250R stem, Loctite to the rescue. I used a high viscosity retaining compound rated for 0.020 gap and assembled the forks, stem, and triples (not on the bike) and let them sit 24 hours for a full cure.

The XR200R stem is welded into the lower triple, the other two stem press out the bottom of the lower triple.

The CR80 forks are a big improvement over the stock damper rod forks, but not yet as good as the 46mm conventional cartridge forks on another bike.

I pulled the rear spring and bottoming bumper from the shock and did some measurements on rear wheel travel. Stock linkage provided 2" clearance from the tire to the fender/seat support. When I installed the 84 XR250R linkage it dropped to 1 1/2", the XR250 rod is a bit longer than the XR200. This is good because an 18" Trials tire has a 1" greater radius than the 17" knobby. The XR250 linkage is aluminum and the XR200R is steel, a savings of 2lbs.

Got a go, back later.

Share this post


Link to post
Share on other sites

Man this is good stuff. Wish I were out there to see this happen. I will add 2 things to think about. #1 why are these viscositys checked at 40 deg C? That a little aver 100F. Maybe thats is considered (working) temperature. I was just thinking that you are in the PNW & never see 100F. Was the CST data from some technical data sheet on the internet?

Also it sounds like you know alot more about switching around these shocks, and linkages and S-arms. My cousin & I tried to install a 2004 TRX450R aluminum SA on a 1986 TRX250R and there were many issues with the linkage ratios. We never could get the travel action to work properly so we had to abandon the project. The idea was to lower the weight by using the modern aluminum SA. Anyway I hope this works out better for you. I admire your tenasity on this project.

Share this post


Link to post
Share on other sites

There are several temperatures for measuring the viscosity of automotive oils, the author of the chart used 40C and 100C (100C is the standard), I only posted the 40C values because they would be more relevant to shock damping than the 100C values. I found the link to the table in the Suspension forum and downloaded the PDf file but unfortunately I don't have the link. The cSt (centiStokes) is the unit of measure for oil viscosity.

Here is a link all about oils, will not about suspension oils it has a motorcycle focus:.

http://motorcycleinfo.calsci.com/Oils1.html

And yes the oil would be thicker at a lower temperature.

I'm not doing much pioneering because there have been many discussions on this forum about SA interchangability for the XRs with members posting SA pivot dimensions and success stories of using other XR SAs on the XR200. And adapting CR80 USDs to CRF150/230s is pretty common (same bearings).

Share this post


Link to post
Share on other sites
Very interesting Chuck. You've put a lot of thought into your project. I'm looking forward to the final product. I may utilize some of your ideas on my 200.

The late model 96-04 swing arm is is a 3.4 lb weight savings over the steel XR200? That's great, plus you get a disc. How do the lengths/widths compare? The brake cylinder would be a weight gain of what, 1/2lb? You are still under or right at 200lb's.

OK to PM you?

Doug

I will publish more weight data as I get further along, the XR200 swing arm weight is based on the weight of an 84 XR250 SA which is dimensionally the same as the later XR200s. I have a 95 and a 03 XR250 SA and have their weights. Actually I have too much stuff but that is another problem. I'll weigh each item as it comes off the bike and the replacement item. The lenght of all of the SAs are within a fraction of an inch, which is good for two reasons; it will keep the wheel base short and not transfer weight to the front (I'm taking about twice as much with all of the rear weigh saving.

I just found some more weight: I weighed the steel sprocket on the 18" rear wheel that I intend to use and it weighs 2.4 lbs, the new Renthal weighs .68lbs, a saving of 1.7lbs.:thumbsup:

You can PM me but I would like to discuss things on the forum because I feel that we all gain from the discusion and exchange of ideas.

Share this post


Link to post
Share on other sites

You could use an aluminum shift lever and I assume you already have an after market silencer. I thought about using the stock titanium header pipe from my WR250F on my XR200R. Those are similar in shape and it is so much lighter. Also you could remove the backfire screen in the airbox to shave a 1/2 pound or so. Maybe aluminum handlebar clamps too What about a more modern seat foam? Would that be lighter?

Share this post


Link to post
Share on other sites

Neat ideas, your suggestions make a very good point that the weight saving is a little bit here and a little bit there. ExploringWA found this on his weight reduction for a 230; he had to search for a lot of small weight savings to reach his goal.

I bend shift levers so often I didn't want to use AL. I have a FMF Q on another bike and it would save maybe 2 lbs, but I like the very bottom end power of the stock muffler with insert and wasn't ready to give that up for maybe 2lbs. In 1980 Cycle dyno tested the then new XR200R with and without the muffler insert, the insert had much more power below 3000rpm and only gave up mid range to no insert. Ti head pipe is a good idea but I gotta convince myself of what is the best size for my riding before committing. I have a XR200 motor with a Powroll pipe (1 1/2" vs 1 1/4"stock)and always liked its performance but this 90 XR200R with a stock muffler outpulls it in 6th gear rollons (with gearing and overall weights the same). I should run some more tests with a leaner main jet in the bike with the Powroll pipe because it was jetted for a SuperTrapp and I didn't do a rejet when I installed the FMF Q.

I'm considering swapping the rock guards for an AL skid plate, don't know what the saving might be but I really smacked the lower cradle down hard on a big rock during an uphill rock garden climb last week. If that rock had hooked a cradle tube it could have been a quick stop.

I recently pulled the backfire screen and the handlebar clamps are AL.

Share this post


Link to post
Share on other sites

Interesting video I suppose we need to wait for a Dirt Rider article to learn the details, wonder when that will available. If this project goes well I may be able to put #198 on my bike.:thumbsup:

Weight is up a few oz because I swapped the CR80 master cylinder for a XR250 unit so I could use MSR Grip Levers.

Went riding today and the Gold Valve literlly eliminated the harshness, same oil and level as before. Started with 4psi, then ran the tire pressure up to 9psi, and finally settled on 6psi. This is with a stiff sidewall Michelin M12 on a light bike. I fussed with tire pressures because the terrain was wet with tree roots and rocks. At this point the forks are better than a set of 46mm KYB conventional cartridge forks on my other bike. I'll keep the GVs, may put a set in my other bike. Gotta fix the rear, I set the shock on zero compression and max rebound but it still is lacking, not too bad if I stand up; I need to test it on some good whoops.

XR200R8-21-9.jpg

Here is a pic of the 21" Excel wheel on the CR80 hub.

CR8021Wheel.jpg

The CR80 steel stem:

96CR80Stem625x7875.jpg

And the XR250 aluminum stem that I transferred to the CR80 triple.

84XR250Stem6375x8.jpg

Share this post


Link to post
Share on other sites

Looking good Chuck. Will need to try it out soon. Are you going to take it to Tanuem Sat?

Share this post


Link to post
Share on other sites

I held off making reservations for Tanuem because I didn't know if I'd get the new parts in time for a test or if the test would indicate enough improvement, but todays ride was good inspite of the misty rain, slippery rocks, and slippery roots. Actually it was a very good test. So I didn't make reservations, shame on me. How about you? Are you free?

Share this post


Link to post
Share on other sites

No, still working,

Yeah I'm bummed. Get that bike ready though and we'll go out next week or two.:thumbsup:

Share this post


Link to post
Share on other sites
Installing CR80 forks on the XR200 took a lot of planning but in the end was easy. The 86-91 XR200 forks measure 33 3/4" from the top of the caps to the center of the axle, the CR80 USDs measure 33 1/8", 5/8" shorter. ... The CR80 stem is almost too short to fit the XR200 steering head so I decided to use a XR250R stem that is a bit longer and a lot lighter. The CR80 stem measured 6 7/32" from the top of the lower triple to the first threads, the XR200R measured 6 1/4" and the XR250R measured 6 3/8". All use the same bearings but the CR and XR200 stems are steel and the XR250R is aluminum, so I went with the 250 stem. The problem is the ID in the CR lower triple is 0.006 too big for the XR250R stem, Loctite to the rescue. I used a high viscosity retaining compound rated for 0.020 gap and assembled the forks, stem, and triples (not on the bike) and let them sit 24 hours for a full cure.

Here is a pic of the bottom of the CR80 stem that I removed to install the XR250R aluminum stem.

CR80Stem.jpg

The circle on the left highlites the stop on the very bottom of the stem that seats against the bottom of the triple. Next to the stop is a snap ring groove with a circular snap ring that locks into a grove in the triple to prevent the stem from pulling out; when pressing out the stem the grove in the triple is damaged, no problem. The circle on the right highlites the transition from the triple clamp boss to the smaller bearing boss.

The stop on the XR250 stem is big enough to seat properly against the CR triple but the mounting boss is 0.006" too small for the bore on the CR triple. . I used a Permatex retaining compound which is equivalent to the Loctite that I mentioned in my post, it is called "Bearing Mount for Worn Parts" and is rated for 0.020 gaps, 3000psi strength, and up to 300F so I can fail it with heat if I need to remove the stem.

Share this post


Link to post
Share on other sites

Time to start thinking out of the box.

You aren't running any numbers, so trim or completely lose the number plates.

Also, route the breather hoses from the carb to the top of the gas tank. Then ditch the kickstand and just lean the bike on a tree or lay it on the ground :-)

Run a smaller CR type front fender and trim the back of it off, lighter and better airflow for the motor.

You got stickers on your hand guards. Obviously you aren't beating the bark that hard. Lose the full wrap aluminum guards for stock style all plastic hand "guards". They work pretty well at dissipating the blow to your fingers and knuckles.

Lastly, stop eating burgers and drinking beer. That's the quickest way to drop 10 lbs from the whole rig.

- JMA

Share this post


Link to post
Share on other sites
Time to start thinking out of the box.

You aren't running any numbers, so trim or completely lose the number plates. Good idea, will save for later.

Also, route the breather hoses from the carb to the top of the gas tank. Then ditch the kickstand and just lean the bike on a tree or lay it on the ground :-) Excellent idea to help protect the engine from dirt ingestion and on my list. For me losing the kickstand would really be out of the box.

Run a smaller CR type front fender and trim the back of it off, lighter and better airflow for the motor. Also a good idea, but in the PNW we need water protection.

You got stickers on your hand guards. Obviously you aren't beating the bark that hard. Lose the full wrap aluminum guards for stock style all plastic hand "guards". They work pretty well at dissipating the blow to your fingers and knuckles. New handguards are only about a dozen hours old, give them a chance. Good idea, but my hand guards are all plastic Cycra Pro Bend II. I figured my trail riding speeds are low enough to forego the heavier aluminum bar type.

Lastly, stop eating burgers and drinking beer. That's the quickest way to drop 10 lbs from the whole rig. Excellent idea; if I also loss twenty pounds that would be a total of 40lbs for me and the bike. (I've already loss 10 lbs during the past year, maybe another 5-10 to go.

- JMA

What is interesting to me is all of the different ideas that people have to save weight that I see on this and other threads. To me weight up high on the bike is more important to lose than weight down low; that is why I used Renthal bars and an aluminum steering stem. That also makes the front number plate and fender candidates. The stock gas tank is 4lbs 5oz and holds two gallons for another 14lbs, sure would be neat if that weight could be down low like the BMWs.

Share this post


Link to post
Share on other sites

Just curious what your weight is that you put the bike on such a harsh diet. Looks like you built a pretty sweet little bike, I probably would have done 19" front and 17-18" rear if I was going to build a bike like this. Why didn't you weld the stem in? I take it you don't weld aluminum, nor do you know of any local places that do for a reasonable price? If you welded aluminum you could do an aluminum cradle and subframe.

Share this post


Link to post
Share on other sites

Good questions:

I didn't consider welding because the CR and XR250 stems are press fit, also with welding you have distortion issues that I circumvented by using the retaining compound. In one of my former lives I was a Tool and Die Maker and believe me the stem is aligned to the fork tubes better than I could have achieved with welding. Although I had a career in aerospace I prefer steel for motorcycle frames.

Don't be too quick to judge because all I have done is the 7lb weigh saving on the front, much more weight will come off when I do the rear. But I'm very happy with the results so far on the front end; going for another ride in the morning. The work on the rear has already started but nothing fitted to the bike, that is a few weeks away because of the brake master cylinder bracket and brake pedal.

I chose to use a 21" front wheel because of the stability it adds to the bike inspite of the high cost of having a 21" rim laced onto the CR80 hub. I will also migrate from a 17" rear to an 18" so I can run a radial Trials tire. Both of these tire choices are more related to where and how I ride than the possible weight saving from using smaller wheels.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×
×
  • Create New...