“An eight lac rupee motorcycle and it hasn’t got upside down forks!!!” is one of the first things you will hear when you tell someone how nice Honda CBR 650F is. Honestly it is one of the nicest and most welcoming big bikes you can buy in India today and yet, the lack of upside down forks among other things repels far too many potential buyers (or critics). It was the same story with Yamaha R3 and now half of the automobile media is crying about Bajaj not putting USD forks on the Dominar. So what is the big deal with upside down forks!
For starters, they are better and the reason they are better is quite straightforward. The front section of a motorcycle works like a lever under braking or under any sort of stresses. Centre of the wheel is the point where force is acting and it is being applied on the triple tree (or yoke). In a conventional setup, the thinner stems are held by the triple tree with fatter sliders connecting to the wheel axle. In an upside down fork setup, the fatter sliders are held by the triple tree while thinner stems connect to the wheel axle. The latter serves four obvious advantages:
- Stronger and fatter slider section is dealing with the forces instead of the relatively weaker stem which is more likely to bend.
- Higher fraction of the entire fork length is made of overlapping fat slider tubes and inner tubes.
- Reduced unsprung weight as the heavier sliders and fork oil has moved up and less material is moving with the front wheel.
- Sturdier front end with relatively better feel and feedback with increased stiffness.
So there are clear advantages of an upside down fork setup. However, they don’t come without their disadvantages which are not very apparent at the first glance.
The biggest problem faced by most people who have motorcycles with upside down forks is because of the oil. When the fork seals fail, and they will someday, the oil will drain out quickly. Also in case of a standard fork, even when the seal starts leaking, you can continue to ride and you will just have a ring of oil around the stem and maybe a bit more dripping along the sliders. In case of an upside down fork, the oil drips down onto the brakes and wheels and pretty much every other place that shouldn’t be getting lubrication.
Another related issue arises because of the position of the seal. Dust on the stem is often the prime culprit when the fork seal fails. In our country, dust is omnipresent. Lower part of the fork is more likely to accumulate dust while riding when compared to the upper part and that makes the seals on upside down forks more likely to fail for a comparable right way up fork.
The performance gains aren’t really very significant and often you will find upside down forks on premium motorcycles which in any case have often got better built suspension than their upright counterparts. In all probability, you are paying for technology you won’t use just because track machines and those awesome off roaders have them. So the next time you crib about the lack of USD forks on a motorcycle, you better have the skills to use the gains. (P.S.- They look cool though.)