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Why do they still do that?

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faffi:
There is one thing that I never stop wondering about. Or getting annoyed about. And that is mismatched suspension between front and rear on motorcycles, where one end is soft and the other firm. Quite often with damping rates that do not match the springs. Yet this is more the norm than the exception. One must wonder why the bikes are sold like this, because I cannot for the life of me imagine their test crews would think this is a great setup.

No need to read any further unless you too is a nerd :grin:

I can use my 2017 V9 Roamer as an example. 6000 miles on the clock, so parts are not worn out. Over sharp bumps, like frost heaves, they both feel harsh, although for different reasons. But for the most part, when one end is OK, the other feels harsh.

The reason is that the shock absorbers have too soft springs and soft damping, whereas the front have the correct spring rate for a 200-220 lb rider, and they will allow fairly sporty riding, with damping set for control rather than comfort. But unlike most budget suspensions, spring rates and damping rates are reasonable.

The shocks are OK for a light rider riding solo, but too soft for a 200-220 lb rider. So they bottom out frequently over larger bumps, but do a reasonable job over smoother roads. One can up the preload, but that would not change that the spring rates are too soft. And the damping cannot control stiffer springs, and also adding more preload will ask more from the rebound than it can deliver. Still, as an economy alternative, I think they are acceptably matched, spring rate to damping, but too soft. IMO, any rear suspension must be able to carry the maximum allowed weight for the bike in reasonable control and comfort.

The fork springs, as mentioned, are quite firm, and well up to the task of supporting a full load. The problem, for me, is the unsophisticated damping. There is too much compression damping, likely chosen to reduce the rate of dive under braking, that make the front wheel skip over sharp bumps instead of absorbing them. I can forgive this, because most people prefer this over suppleness and rapid diving under braking. There is also quite a lot of rebound damping, which make it impossible for the front wheel to drop quickly enough into bigger dips. Again, the setup overall is an OK compromise. Not for racing, but for sporty riding, or riding with a full load. More comfort can be had by simpl changing to a little thinner fork oil than stock.

However, the real issue I have is again that the front suspension and rear suspension do not work together! If both ends were soft, like the shocks are, I could understand that. Same if both ends were set up on the firm side. But not like this. It does not cost any extra to have spring rates that mirror each other functionally, nor does it cost anything extra to have damping rates that matches.

What do cost is sophisticated valving that will allow the suspension to work over any kind of terrain, and I fully understand that bikes built to a budget does not have this.

cliffrod:
It’s a function of mass and inertia.  The loads created/imparted by braking are generally higher and more consistent on the front forks than the loads imparted by normal vertical loads imparted upon the rest suspension.   

When the surface is irregular and braking is required, the front suspension must compensate for both factors at the same time. 

By contrast, the rear suspension normally unloads during braking. This helps supplement the action of the softer rear suspension.

The factory “mismatch” is done as a means to address the needs of the average consumer within a given price point.  That consumer can then modify suspension to better match their actual weight, style and amount of use.  Even if manufacturers produced perfect suspension, they would have no way to know these specifics to employ them on a production scale.

Zenermaniac:
On my Roamer I changed to 5W (17.5cst @ 40c) fork oil as opposed to the factory fill Agip which is 7.5W (32cst @ 40c) and an air gap of 130mm instead of 120mm. The negative of this is a little more fork dive but I was after a little more plushness on ordinary road surfaces. Mission accomplished.  In my old age I’m a more sedate rider and no longer need sophisticated performance for canyon carving.

rocker59:

--- Quote from: cliffrod on May 07, 2024, 06:07:48 AM --- The factory “mismatch” is done as a means to address the needs of the average consumer within a given price point.  That consumer can then modify suspension to better match their actual weight, style and amount of use.  Even if manufacturers produced perfect suspension, they would have no way to know these specifics to employ them on a production scale.

--- End quote ---

This is the answer ^

All motorcycles are built to a price point.  They're also built to an "average rider".

Even a $5,000 Ohlins setup won't work for a 250 lbs rider, if it's tuned for a 160 lbs rider.

When I got my V11 Nero Corsa years ago, with its nice Ohlins suspension, I had to soften the compression and rebound on the front fork and replace the factory rear spring with a stiffer Ohlins replacement. 

rocker59:

--- Quote from: Zenermaniac on May 07, 2024, 08:36:32 AM ---On my Roamer I changed to 5W (17.5cst @ 40c) fork oil as opposed to the factory fill Agip which is 7.5W (32cst @ 40c) and an air gap of 130mm instead of 120mm. The negative of this is a little more fork dive but I was after a little more plushness on ordinary road surfaces. Mission accomplished.  In my old age I’m a more sedate rider and no longer need sophisticated performance for canyon carving.

--- End quote ---

On my Sport 1100 Carb, I had to do the opposite.  Changed out the spring and went up to 10wt oil in order to firm it up a bit. 

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