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Lowering the Center of Gravity on My XR400R

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So, I've been doing some work to help lower the center of gravity on my XR400R.  It's a great bike, but heavy, especially when its in the sand.  Since lightening the bike gets difficult without modifying stuff like the frame, I've been trying some other techniques.

 

First I added a lowering link that seems to have lowered the bike about an inch when measuring the seat height.

 

Second I've compressed the rear shock a bit to gain maybe another half an inch, making sure not to go too far where I would damage the shock.

 

Thirdly, I went from running an 18" rim on the back down to a 16", but the tire I'm running is taller and actually provides the same outer diameter.  So maybe a quarter inch or so if I run the tire on a little lower air pressure.

 

So my next question is, has anyone run into problems with lengthening their chain and sliding the rear tire back on the swing arm?  Right now looking at my chain adjuster on the rear axle, I'm at 19, but I see on the adjuster it goes up to 40 if your chain is long enough, and of course if it still sits on the swing arm.  

 

A problem I see is possibly messing with the control of the bike. 

 

Anyone have some good advice on this matter?

 

Thanks!

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So, I've been doing some work to help lower the center of gravity on my XR400R. It's a great bike, but heavy, especially when its in the sand. Since lightening the bike gets difficult without modifying stuff like the frame, I've been trying some other techniques.

First I added a lowering link that seems to have lowered the bike about an inch when measuring the seat height.

Second I've compressed the rear shock a bit to gain maybe another half an inch, making sure not to go too far where I would damage the shock.

Thirdly, I went from running an 18" rim on the back down to a 16", but the tire I'm running is taller and actually provides the same outer diameter. So maybe a quarter inch or so if I run the tire on a little lower air pressure.

So my next question is, has anyone run into problems with lengthening their chain and sliding the rear tire back on the swing arm? Right now looking at my chain adjuster on the rear axle, I'm at 19, but I see on the adjuster it goes up to 40 if your chain is long enough, and of course if it still sits on the swing arm.

A problem I see is possibly messing with the control of the bike.

Anyone have some good advice on this matter?

Thanks!

I rode a xr400 transplant.

AF Cr250 chassis xr400 guts.

It was a decent ride.

Sadly this was before camera phones.

I don't know what all they had to do, but it handled nice for a old style thumper.

I considered building one for a play bike.

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The best thing you can do to lower your center of gravity is to learn to ride standing. Especially in sand.

Moving the wheel back in the swingarm lengthens your wheelbase, makes the bike more stable, makes it harder to loft the front wheel unintentionally, better for climbing.

Doing all these mods to try to make the bike feel less heavy and make you happier with it is telling you you probably ought to be on something lighter, you just don't want to listen.

And neither did I for a long time. A year ago I gave in to the fact that my xr is too heavy for me, to continue riding the kind of terrain I enjoy. So I bit the bullet and bought KTMs version of an xr, the 300.

Edited by Trailryder42

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The best thing you can do to lower your center of gravity is to learn to ride standing. Especially in sand.

Moving the wheel back in the swingarm lengthens your wheelbase, makes the bike more stable, makes it harder to loft the front wheel unintentionally, better for climbing.

Doing all these mods to try to make the bike feel less heavy and make you happier with it is telling you you probably ought to be on something lighter, you just don't want to listen.

And neither did I for a long time. A year ago I gave in to the fact that my xr is too heavy for me, to continue riding the kind of terrain I enjoy. So I bit the bullet and bought KTMs version of an xr, the 300.

 

 

 

I understand what you're saying, but I really love my bike, especially the low maintenance and bulletproof engine. And the cost of a new one is just not an option right now.  I used to ride it in more dirt but since I've moved to Oregon, I have been taking it out in the sand a lot.  I've been needing to customize the bike to my riding style for awhile now.  I am a lot lighter than the previous owner.  I feel like a suspension upgrade may be in my future, once I save up.

 

I've added a pumper carb to give it a little better response on the throttle which actually helps a lot in sand.  It gets going fine out on the open dunes and can climb anything, but I'd still feel a little better if the bike sat a bit lower and had the weight a bit lower as well.

 

Riding standing up does put my weight on the pegs and lowers the center of gravity of me and the bike, but that's usually not a problem when I ride. 

 

But extending the rear wheel seems like it might be an easier way to lower it a bit more, just wanted to hear if anyone had tried it and experienced any problems with such a change.

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Lengthening the wheelbase will make seat height higher, not lower. All you have to do is follow the angle/line from the swingarm bolt to axle to see that. Slight, but it does.

For now, set rear sag to 4-4.5 inches. Set compression and rebound clickers to suit for the terrain you're riding. Sand requires a little stiffer compression. Overly soft suspension causes wallering about in sand.

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Hi

I want to lower mine too. First I would try by the rear sock.

I have loosen the the nuts that stay above the spring right? Or is the opposite?

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Hi

I want to lower mine too. First I would try by the rear sock.

I have loosen the the nuts that stay above the spring right? Or is the opposite?

Yes, the nuts above the spring adjust rear sag, how much spring preload is on the shock. Screw them up the shock body for less preload and make the rear end sag more with your weight. With no weight on the bike and the rear suspension completely extended, measure from the rear axle to someplace on the fender. Then sit on the bike and have someone take the measurement for you again. Adjust the nuts/preload so that measurement is 4-4.5 inches less that your first measurement.

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Yes, the nuts above the spring adjust rear sag, how much spring preload is on the shock. Screw them up the shock body for less preload and make the rear end sag more with your weight. With no weight on the bike and the rear suspension completely extended, measure from the rear axle to someplace on the fender. Then sit on the bike and have someone take the measurement for you again. Adjust the nuts/preload so that measurement is 4-4.5 inches less that your first measurement.

Thanks, will do so

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I added 2 links to my chain a couple years ago (110 links total) and ran the adjusters on the back 3rd of the settings. It made very little to no difference. I actaully just went back to a 108 link chain. No problems but really, no help either.

 

From my experience, and this kinda goes against the grain here, if you have heavy fork springs in, make sure you still get about 35mm free sag on the forks and about 60-65mm rider sag for sandy stuff. The forks riding to high in the stroke will make for a squirley front end. Sounds backwards but it's to soft and "springy" way up in the stroke to handle well in soft stuff.

 

On forks - I run 5wt oil at 115mm from top / 35mm free sag / 60-65mm rider sag / .42 springs (set pre load for 35mm free sag and adjust spring rates for rider sag) past 70mm rider sag, go heavier, less than 60mm rider sag, go lighter.

 

Shock - Also 35mm free sag but more importantly, 105mm rider sag. Dial in rider sag 1st on the shock then see what your free sag is and adjust from there. Less than 35mm, go lighter, more than 35mm go heavier.

 

I weigh about 170 - 175 with no gear on.

Edited by michigan400

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Thanks, will do so

 

 If you are lowering for effect, you're not going to be able to stay within the recommnded settings.  You're going to have to remove preload, make the spring softer so it sags MORE and lowers the seat.  

 

Yes, the nuts above the spring adjust rear sag, how much spring preload is on the shock. Screw them up the shock body for less preload and make the rear end sag more with your weight. With no weight on the bike and the rear suspension completely extended, measure from the rear axle to someplace on the fender. Then sit on the bike and have someone take the measurement for you again. Adjust the nuts/preload so that measurement is 4-4.5 inches less that your first measurement.

 

 He's trying to lower the bike. Setting normal sag is not likely to be relevant. 

Edited by MindBlower

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 He's trying to lower the bike. Setting normal sag is not likely to be relevant.

True, Unless it's not currently set to sag at least that much, which he has given no indication of.

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Hmmmm here is somthing to think about....seiously considerall the modifications the would be required......

 

wht about lowering the engine in the frame....keep the rear swingarm pivot but move all the others rotating the engine down.  i am talking like 2-3 mm.

 

I heard on some CR500AFC conversions this is a trick they do to make the bike feel lighter.    front down like 1/4" 

 

its not rocket science I make engine mounts out of 1/4" aluminum plate regularly.  even bent ones the plate bends pretty easy in a vise.

 

something to think about....its just welding steel! but be smart about it

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Hmmmm here is somthing to think about....seiously considerall the modifications the would be required......

 

wht about lowering the engine in the frame....keep the rear swingarm pivot but move all the others rotating the engine down.  i am talking like 2-3 mm.

 

I heard on some CR500AFC conversions this is a trick they do to make the bike feel lighter.    front down like 1/4" 

 

its not rocket science I make engine mounts out of 1/4" aluminum plate regularly.  even bent ones the plate bends pretty easy in a vise.

 

something to think about....its just welding steel! but be smart about it

 

I've actually thought about lowering the engine but that seems like an extreme amount of work and a tad out of my expertise.  I'd probably end up screwing something up.  Another thing I looked into was if they ever made aftermarket aluminum frames for these bikes.  That could shave off quite a bit of weight as well but again, more work than I would like to put in and over my head for sure. 

 

I actually took my bike out last weekend and some of the little changes I've made really made a noticeable difference.  I've got a few minor adjustments left but the bike feels lighter already, especially in turns, and the front end wasn't slipping as bad.  I'm thinking a wider FAT paddle tire on a smaller 16" rim may be a great final addition.  Lowers the bike 1/2-1 inch maybe while also improving stability and traction.  

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You can drop the height by switching to a flatter profile tire.

I went from a Kenda Trackmaster II 760 to Kenda Millville tires. The back was an inch taller.

Not just having new knobbies, the profile is different.

The Trackmaster is U shaped, while the Millville is rounder. Look at photos of the rear tires.

Dennis Kirk has a great tire size guide. I finally know the difference between a 4.5 and 4.6 isn't just 0.10.

I have a 4.0 trials tire, which is tall as 4.00 tires are 100% tall as they are wide.

Edited by Kev_XR

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It's been awhile, so not trying to bump this, but I just wanted to let those who are interested know of the changes I made and how it turned out.  I threw on a rear fat tire from Bykas as well as had them convert a rear tire to fit my front.  This lowered the bike a decent amount, most notably on the front end making it easier for me to keep my weight forward.  I also installed a lowering link from Kouba that claimed to lower the bike about 1 inch.  I then ordered a new tank and shrouds set for a XR250M (which wasn't release in the US).  With a few custom brackets I was able to mount the tank fairly easily.  This was more for looks but I have noticed it helps reduce the top heavy feel, probably due to it holding slightly less gas as and holding more gas lower on the frame.  All in all I like how far it's come and am pretty happy with my XR400R, which looks almost unrecognizable now.  Thanks for all your help and input!

Dirt Bike.jpg

Edited by Foxmann250
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I take it you are trying to lower the center of gravity and not actually lower the bike so you can reach the ground?  If that is the case then getting rid of that big bulbous XR tank and installing an ALoop kit will help a bunch, sort of what he did in the thread above, but already set up and with a much nicer seat.  I can't believe this hasn't been suggested.

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Foxmann that looks great. I have never heard of running a fat tire on front but we don't ride dunes here either. Get flotation in a good way?

Here is my bike with the "lower" center of gravity and shaved down aloop seat. My plastics are somewhat torn up from competition.

skiatook17_3.jpg

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