You do not get a greater range of adjustability over a conventional fork. Ohlins (and everyone else) make conventional forks with full adjustability (rebound, compression, preload), as well as provision for radial-mount/monobloc disc calipers. Additionally, USD forks do not have better anti-dive. If anything, they are (very slightly) worse, since USD forks tend to have less "stiction" (resistance to compression due to side-loading of the fork sliders), and thus will dive more readily.


As noted elsewhere, when you reduce the amount that the fork can flex, those forces are redistributed to other areas of the frame. With the vast majority of Indian bikes, where the front forks are puny and the frames are welded mild steel, fitting a stiff fork USD or not will mean the frame is subject to greater forces (forces that used to be absorbed by the fork). The R15 is really not much more than an FZ in disguise, and has a single "backbone" to the frame. This means there is no side bracing to the steering head. Since the stock R15 fork is so spindly, replacing it with a stout performance fork means the steering head will be subject to higher side loads, putting stresses on the welds that the manufacturer never intended them to sustain. As slow and limited as they are, there really are no bikes sold in India (excluding the Duke) that could benefit from the addition of a heavier fork. You'd be far better served by fitting a conventional fork that had adjustability. USD forks also generally require a new set of triple-clamps, where a conventional fork could conceivably be fitted to the stock clamps (maybe with minor machining).

Second the recommendation for Tony Foale.

In general, the USD fork had one purpose (as hinted at by the anecdote of the GP test). USD really only does one thing: reduce unsprung weight. Mounting the thinner fork inners to the front wheel, with the heavier outer sliders fixed to the bike, means the front wheel assembly weighs less overall, and is thus easier to control with the suspension. It is possible to make conventional forks thick enough to virtually eliminate flex, though the thicker tubes of a USD do help significantly in that respect. Also, as I mentioned earlier, USD forks tend to have less stiction, since side-loading of the moving slider isn't as heavy due to the greater overlap of the fork assembly. The trade-off, which didn't really matter on the racetrack, was reduced overall suspension travel. That has been overcome to some extent with additional development, and USD forks are now available on motocross bikes that live and die on their suspension travel.

However, USD forks do have a couple of significant disadvantages as well. Due to being "upside-down" the fork oil sits right on the seals, unlike a conventional fork where the oil sits at the bottom of the slider as though in a tall narrow glass. Second, those fork seals are exposed directly to road debris and grime, since they are located down near the wheel hub instead of being up above the fender. Where a conventional fork can get away with a dust wiper and maybe two or three seals, an USD fork generally has four or five seals.

I was waiting for someone to mention the reduced unsprung weight advantage and finally @the mountain does it. Great. Reduced unsprung weight allied with greater rigidity and lower stiction can make a huge difference to the predictability of the front end.

Tony Foale was always the one to refer to when it comes to bike geometry and chassis dynamics. But do take a look at the Hossack design brought to life with the excellent 'duo-lever' front of the BMW K1300r. The aim has always been towards reducing unsprung weight, stiction and increasing rigidity and there are a number of ways to achieve them. Depends on the designer's approach and priorities towards tailoring the suspension characteristics. The Bimota Tesi is a case in point for hub-center steering for example. There is another good description at this website here that'll help you visualize how the different suspension systems function.

As an endnote, retro-fitting USD's on older models like the Pulsars and the ZMA will not yield all their potential benefits. And as @abhinmanyu31 rightly points out, could bring up dynamic issues that would be difficult to rectify or control.

The problem is that unless the rest of the bike is of equal sophistication, you won't be able to do anything with the slight advantage in unsprung weight and rigidity that an USD fork brings. The vast majority of Indian bikes are still using 1960s-technology frames, rear suspensions, and brakes. On top of that, they're all so puny that you'd go beyond the capabilities of the tires long before you reach the limits of even the fork on the Duke. Additionally, the typical indian road is so rough, poorly graded and uneven that unsprung weight becomes secondary, since no one can ride fast enough for it to matter.

Personally, I have always liked "alternative front suspension" bikes. My favorite is the Parker/RADD front end, easily the most radical suspension ever to be mounted to a production bike (I don't count the Tesi; it's a handbuilt custom).

Point Disagreed.



I remember the RD350 being advertised with "All New Telescopic Front Suspension System"

Upside Down vs Normal Forks

I am posting this because I've seen many reviews talk about having not having usd forks as a con with many motorcycles. Is this really an important consideration for a commuter or even something like the Bajaj Dominar?

Re: Inverted forks: why they are good

Some simple questions about the USD vs conventional forks:

Even if the USDs prove the performance benefits over the conventional forks, are they really needed on entry level bikes like the R15 which, most of the buyers use for daily commuting and do they really utilize the bike to its full performance potential all the time?

Is the little gain in performance really worth the purchase and maintenance cost which most of the audience expects to be low while buying a bike in countries like India?

Is the audience that requires the performance bump, large enough to compensate the sales figures that could drop from the price increase?

I believe there is some calculation based on the questions above that manufacturers do while putting something like that on the bikes that go on sale in India.

Re: Inverted forks: why they are good

The new CBR 250rr has em also another bike cb190 r has it, but Lower cc bikes will not get USD forks in India, I think cost of manufacture will be too high to handle. These really help in handling, if Honda did bring the bike,it would beat all its competitors cause its one of the best handlers.