How to put your bike on a diet
The lower the overall weight of your motorcycle, the more acceleration you’ll get out of each horsepower your engine produces. But it doesn’t stop there. Weight removed from the areas not supported by a bike’s suspension – the ‘unsprung weight’ – has other advantages in terms of handling and suspension reaction.
The lower the unsprung weight (the combined weight of the wheels, tyres, brake calipers and other ancillaries), the less mass the suspension has to control, enabling it to react more readily to road conditions.
Lighter wheels reduce the gyroscopic effect produced by the wheels, making the bike easier to turn. But be careful – sharpening up the steering in this way can cause an already quick-steering motorcycle to become unstable over rough surfaces, something that can’t be eliminated with a road bike’s (limited) standard suspension adjustment.
So, if you’re thinking about shelling out on a massively expensive set of super-light carbon wheels, also put some serious thought into investing some cash in re-valved/uprated suspension to provide a wider range of adjustment.
When selecting the parts you’re going to use to achieve a weight reduction on your bike, get extra value by choosing components which will provide additional overall benefits. For example, if going for lighter aluminium sprockets, adjust the gearing of the bike to be suitable for your needs while you’re at it. Almost every area of performance can be enhanced while on a weight reduction program.
Things such as fancy anodised tax disc holders and carbon look-a-like bar-end weights will obviously do nothing towards achieving a weight reduction on your machine if they are merely additions rather than replacements.
If you’re really serious about wanting to trim your bike’s weight, begin with the parts that will have the biggest effect for the least expense – an exhaust is a good place to start – and then take things from there.
1. Most fasteners can be replaced with lighter aluminium or titanium items, available as kits for specific models, or individually. Some come in anodised colours, including chain adjuster bolts, wheel spindle nuts, caliper bolts, etc. A sweep through the bike should save around 1.5kg, but titanium isn’t cheap – an axle nut alone costs £20.
2. Standard brake systems are now so good that only the most serious race bikes and specials justify the cost of aftermarket/race set-ups, which shave only a few grams off the standard weight. But using six-piston calipers, for instance, allows the discs to have a narrower swept braking area and therefore be lighter…
3. A full disc and caliper job, using high quality parts, costs around a grand and loses about 250g – a whopping £4000 per kilo. But all the weight is unsprung so has a double benefit, plus any loss from the discs is vital as it is spinning mass that must be accelerated with the wheel, thus creating gyroscopic force that must be overcome to steer.
4. High-quality carbon front mudguards only shave about 250g which, when you’re looking at around £100 a throw, works out at some £400 per kilo saved. But they do look good and those grams come off the steering mass. Remember that if you’re bolting a carbon rear hugger to a bike, you’re actually adding a little weight.
5. A quality titanium exhaust system is likely to set you back a grand, but that’s pretty good value when you’re losing up to 10kg and gaining about 10bhp. The best end-cans in titanium or carbon-fibre represent around half that weight saving and should add around 5bhp. With twins, you’ll double the weight saving.
6. If you don’t carry passengers, then a lot of weight can be lost for not a lot of cash. Going over to a single seat unit will knock a couple of kilos off straight away, and you can lose more by taking off the pillion footrests (you’ll need an exhaust bracket) and any pillion handles. Keep all the bits so you can get the bike back to standard when you sell it.
7. Wheels represent the largest proportion of a bike’s unsprung weight – lighter wheels mean better suspension reaction plus faster steering due to less gyroscopic effect at the front. A typical pair of sports bike wheels tip the scales at 12kg. Carbon-fibre wheels are 7kg, magnesium composite wheels are 9kg.
8. Save a third of the weight of your steel sprockets with hardened aluminium alloy replacements and get your gearing sorted at the same time (eg for better acceleration). There’s also a choice of a smaller-pitch chain, with even thinner and lighter sprockets. OK, you’ll only save a few hundred grams, but racing sprockets look cool for £35-45.
9. Redesign your braking system, firm up its feel with braided hoses and lose weight at the same time – most of which will be unsprung. Run two lines from the master cylinder (one per caliper) to junk the stock unions/splitters and banjo bolts. With less (and flex resistant) line, you’ll have better braking feel and less fluid in the system, too.
10. If you’re not bothered about getting the maximum range from your fuel tank, you can save around 5kg by under-filling your bike by a gallon each time you visit the petrol station! This is sprung weight, so won’t give a major handling improvement – but if it’s that extra 1mph you’re looking for, it’s worth considering.
11. If your bike already has lightweight clip-ons, there’s only a small advantage in fitting aluminium GP-style bars (about £120). Steel tubular items can easily be replaced with weight-saving aluminium tubes for £15. Don’t be tempted to go for ultra-light bar-end weights unless your bike is for track use only, as you’ll suffer from heavy vibrations.
12. Save money and lose weight at the same time by knocking the meat pies and burgers on the head. Lose half a stone (3kg) and you’re looking at the reduction value of a £450 end-can; another pound and you’ve got a carbon front mudguard. Your weight, of course, will come from the sprung total, so you’ll have to adjust your suspension to suit.