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BMW G450X Project, Part 2

We take on a build on the BMW G450X in an effort improve this unique off-road dirt bike

May. 26, 2010 By Dan Paris
We'll cut right to the point: Life with the project BMW G450X has been a series of ups and downs. We've been learning a lot about the bike, riding it on the trails and MX track, and addressing some issues.

We've got this bike working very well. In fact, every time we tweak something the bike works a little better. But little things, like complicated service issues and the short life of some components, are driving us nuts. If we didn't like the bike we wouldn't worry about it so much, but the bike is working really well and we like it. We like the BMW's 'freak factor' in the pits, we like the strong and smooth powerband and we like the suspension set up. Here's where we are at so far.

The wide-ratio transmission drove us nuts. Bonkers even. We absolutely, positively had to lower the gearing. We could have dropped a tooth off the front sprocket, but since we also wanted the bike to turn better we installed a two-tooth larger rear sprocket instead. This moved the rear wheel forward and still allowed us to use the stock o-ring chain.

The BMW is slower than the other 450s, even in high-power setting. This giant muffler is a big part of that. It is very restrictive, not all that quiet and weighs a whopping 9.49 pounds!

This titanium Akrapovic slip-on muffler weighs a mere 4.7 pounds, complete with spark arrestor insert! It bolted on in five minutes and gave the engine a completely new attitude at all points in the powerband.

The Akrapovic quiet core and spark arrestor is slick. With it in place the bike is quieter and better sounding than stock. With it out the bike sounds ratty and doesn't even run quite as well.

We also tried a Yoshimura titanium slip on. It was fussier to fit than the Akrapovic and heavier, at 5.48 pounds with spark arrestor. But we prefer it over the Akrapovic for a couple reasons. The Yoshimura pipe is tucked in better than the Akrapovic and provides slightly better bottom and mid-range power.

The Yoshimura spark arrestor design isn't as slick as the Akrapovic, and is more difficult to remove and install.

Always use this! With the quiet core in place we measured the Yoshimura muffler at 93.5 dbA. With it out we measured 111 dbA! We're not going to lie to you and say the bike doesn't run stronger with it removed, but in the real world we simply can't stand that much noise. We had the technicians at Budd's BMW reprogram the EFI settings and now have a BMW that pulls like a 450F should.

The BMW is crazy-sensitive to suspension adjustments. Our bike has much stiffer fork and shock springs and heavier valving than stock. We raised the fork 5mm in the triple clamps, set rear sag at 95mm and have the rear wheel pushed forward nearly as far as it will go without hitting the tire on the swingarm. This bike now turns great. Stability? Not what it was before the changes, but the little bit of headshake at speed is worth the vastly improved cornering habits.

We can't stress this enough. If the spring rate is too soft and the rear sag isn't exactly 95 mm the BMW becomes a tank. If sag is too little the bike headshakes badly. This is the fussiest motorcycle we've tested for chassis set up, ever.

The 45mm Marzocchi forks blow seals with alarming regularity, especially on the MX track. They never bottom harshly and with whatever valving and spring rates the BMW Canada race team came up with they work surprisingly well. But they weep or outright puke oil at the slightest provocation.

Our bike has 22.7 hours on it as of now. In that short time we have had to replace front and rear wheel bearings, which are undersized despite the giant hubs, and new swingarm bearings. The unique swingarm bearing design of the BMW places a high load on them, which causes a quick wear problem that is multiplied by poor seal design.


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