Custom Mods That Can Hurt You and Your Motorcycle

Rider taking corner on motorcycle with custom modifications

Custom motorcycles have been a big part of my life for over a decade now. And when it comes to the common mods that many wannabe cafe racers, nouveau offroaders and future leather rebels want to make happen, there aren’t many I haven’t seen before. From firestones to pipe wrap and clip-ons to rearsets, I know them all like the back of my old, oil-stained hands.

Now the process of taking a factory bike to a custom one is pretty simple; a factory bike is usually designed to be useful and usable to as wide an audience as possible. And a custom bike has an audience of one single, solitary rider. You.

Now that’s cool and all, but the fact remains that as you reduce useability, you can sometimes increase negative traits and other issues that simply weren’t factored in by the OEM engineers. Usually this isn’t a big deal, but there are a few important examples where screwing things up can lead to a broken bike—or worse—a broken you. Let’s take a look.

Risky Custom Mod #1: Lowering the Bike

For a whole bunch of custom genres, lowering a bike—especially lowering the front end of a bike—is a super common practice. Be it a cafe racer, bobber, or brat, it’s hard to deny that a lower or ‘stanced’ bike looks hotter than microwaved shit. And the easiest way to achieve this on most bikes is to simply loosen the triple trees and move the top of the shocks up so that the rest of the bike drops down relative to the ground.

The tell-tale sign that this has been done to a bike is the way the tops of the shocks protrude upwards out of the top triple. Another common way to achieve the look is to cut the forks, thereby reducing their overall length.

A custom motorcycle from Bandit9 in VietnamImage via Return of the Cafe Racers.

So what’s the big deal here? If done right by someone who knows their own ass from grass, absolutely nothing. Yes, it will change the geometry of your bike, but unless you’re starting with a MotoGP bike or a motocrosser, this usually won’t take it outside of it’s engineering comfort zone.

But done badly (by you or by a previous owner), this mod can have two pretty nasty side effects. The first is reducing shock travel to a point where big potholes or speed bumps can see your shocks ‘bottoming out’—or the bike’s sump tearing itself open on a gutter, speed hump or even a deeper-than-expected pothole. And done really badly, the bike may even scrape dangerously during tight cornering.

Risky Custom Mod #2: Breathing Modifications

Hot rodding exhaust pipes and carbs are practices as old as racing itself. And in the bike world, a long exhaust can not only sound crap, it can add a ton of weight to a bike, too. So taking to it with a hacksaw and replacing factory air filters with something ‘faster flowing’ seems like a no-brainer, right?

Sure it is. But you have to understand that there’s a whole bunch of knock-on effects these mods will incur. And yes, you really have to be completely across to make sure your bike is still a happy little camper.

a close-up shot of free-flowing carbs on a motorcycleImage via Return of the Cafe Racers.

The first and arguably most obvious thing to do here is ensure the bike’s fueling is still properly adjusted. There’s no point making the bike ’breathe better’ if the air/fuel ratio doesn’t also change.

Keeping the air/fuel ratio stock will more than likely see the bike running lean—which, in turn, can mean the engine runs way too hot. And if it runs too rich, you can end up with a bike that’s hard to start and that burns through spark plugs.

A customised motorcycle with a short exhaust blows flames during high revs in a workshopImage via Return of the Cafe Racers.

Chopped exhausts do remove a lot of back pressure on the bike’s exhaust stroke, but most factory engines are set up to expect that pressure and might just produce less power at certain rev ranges if it’s not there.

The moral here is simple; when doing major carb or exhaust mods, take the bike to a professional dyno tuner and have them do their magic so you know the mods are helping things and not hurting them.

Risky Custom Mod #3: New Rubber

Of course, just swapping out tyres on a bike that have the same dimensions and general specifications as your old ones isn’t a big deal. Again, factories design in enough leeway here to make it safe as houses. But once you go off the beaten path by fitting tyres that are completely different sizes than specified, you’ve got to really have your wits about you.

a rear-view of a Honda Racer motorcycle with Firestone tyres fittedImage via Return of the Cafe Racers.

Most commonly, custom tyres can rub. This might be on guards, swing arms, frames or even on the inside of forks. And just in case you were in any doubt, this is bad. Not only can you lunch a new tyre in a few hours like this, but tyres can and have failed catastrophically at speed thanks to being worn away and overheating.

 an old Firestone Tyres poster on a wallImage via Return of the Cafe Racers.

Of course, anyone with a skerrick of custom experience will be shouting ‘What about Firestones!’ at their screens right now. Contrary to popular belief, these (and other) retro-styled tyres aren’t the death traps they are often made out to be.

C’mon people! Do you think Firestone would still be in business if their tyres were killing riders? Hells no. But what they can do is to give your bikes some seriously different handling characteristics—especially around corners. As with any new rubber on any motorcycle anywhere, the first 100 miles or so should be ridden with mucho caution.

Risky Mod #4: Fueling Modifications

No, I don’t think you are stupid—and yes, we all know that fuel is more dangerous than a grizzly in a honey factory. Anything to do with modding fuel tanks, lines, filters or carbs needs to be done with the utmost caution.

Unlike cars, motorcycles have the rather unfortunate feature of needing to have their fuel tanks directly above that hot, burny thing us pros call ‘the engine’.

A top-down view of a custom motorcycle fuel tankImage via Return of the Cafe Racers.

Needless to say, fuel leaks above or around an engine are a bad, bad thing, and many custom bike mods target a new tank as one of the first things on the list to change—as nothing improves a bike’s look as quickly or as thoroughly as a new tank. But in a similar fashion, nothing changes your private parts and legs as quickly as a fire placed right between them. Ouchy.

Risky Mod #5: Cutting Frames

I remember, as a kid, watching my Dad under our hillside family house as he cut away some random piece of support structure to make more space for his workshop. “It’s not a main beam,” he told me, inspiring absolutely no confidence in me and producing quite a few nights of restless sleep.

The same thing can be said for frame mods to motorcycles. While you may not be able to understand the intended purpose for a piece of tubing, that doesn’t mean it’s not important.

a motorcycle with no fuel tank fitted so we can see the bike's frameImage via Return of the Cafe Racers.

Equally as dangerous is angle grinding something off—only to replace it using your less-than-professional welding skills. Sure, it may “look fine”, but a bike’s engine and the forces put on a bike’s frame over thousands and thousands of kilometres of riding will be the ultimate test of your skills. Also, consider that you may sell the bike before the welds give way, meaning you could hurt someone else in the process.

Risky Mod #6: Swapping Handlebars

Chatting to my local customiser, they were adamant. “Changing handlebars is the number one thing we see done incorrectly. There are a lot of things they can get wrong. Not replacing cables or misrouting them. Not making sure the bar ends clear knees and tanks. Sadly, we see it all the time.”

The real issue here is that new bars involve modding electrics, brake lines, clutch lines, ergonomics, the dash, and sometimes even headlights.

parts of a motorcycle's handlebars laid out on a table ready for installationImage via Return of the Cafe Racers.

If done poorly,  you just may end up with a bike that’s harder to steer, has rubbing cables that could cause electrical or control issues, bars that dent the tank and most likely crush fingers, and a headlight that blinds oncoming traffic. Not great!

a detail shot of a custom Yamaha motorcycle that has been fitted with new handle barsImage via Return of the Cafe Racers.

Customize Your Bike with Care

In closing, I thought I’d just give you a few words of encouragement. Yes, bad things can happen when you mod motorcycles. But you could say the same thing about cars, planes, or even something as mundane as a guitar amplifier. And amazing things can happen as well.

Hell, it may be a bit of a long bow to draw, but if Orville and Wilbur Wright didn’t start messing around with bicycles and tinkering with dangerous machines in their garage, they may have never flown at Kitty Hawk in 1903. Just make sure you stay safe and do it the right way.