2 Up Performance Riding

[Arrow]

This is my first official post on the board, although I have posted first in the "Welcome Forum".

 

I have been seeking an answer regarding the changes needed, if any, in throttle control during riding spiritedly with a pillion. As near I as I can tell, there does not seem to be much information out there regarding this technology. Given that the placement of weight on a motorcycle is critical to consistency and directly related to suspension set-up, it would be a logical conclusion to suspect that there are far more forces to compensate for given the added aft weight being applied to the rear of the bike. It is understood that there must be compensation in the preload of the rear shock to help the bike manage the added sprung weight, but how does this also impact the front suspension during heavy braking? These are all questions that I believe to be related.

 

So to elaborate, I am asking if throttle control must be altered in some way? It is established that the optimal weight distribution ratio in a turn is roughly 40/60. However, that ratio has been established on the principles of a solo rider and where his/her weight is likely placed. The amount of weight, say 140lbs, to the far aft section of the bike seems as though it would already alter the static balance of a bike. If this is the case, then it should, in theory, take far less throttle to achieve the 40/60 rule to achieve optimal traction. Since one must be on the gas enough to overcome the forces of cornering just to maintain a constant speed, and also give enough additional throttle to achieve 40/60, should there be much less roll on to achieve the 40/60 rule because there is a large amount of weight already added to the rear?

 

I have noticed that when standing the bike up out of a hard corner, that the front is already much lighter than when solo. I have had the front chatter excessively with a pillion aboard when it normally would not under solo conditions. This leads me to believe that the bikes limits were being pushed. The question is, was it my over aggression, suspension not set up properly or a force that cannot be compensated for as though it was just a much heavier rider sitting in the solo section?

 

If it CAN be compensated for through suspension, then that is another question. How? If it cannot be compensated for with hardware, then what must I change with the throttle to achieve maximum optimal traction? This question is based on clean dry pavement but it should apply over directly, as when solo, to hitting sand, gravel or the unexpected wet spot.

 

Thanks,

 

Ryan

 

 

[ktk_ace]

imho bad if not horrid idea to ride spiritedly 2up.

 

 

ride slowly and within the legal limit.

[YellowDuck]

You will get more technically competent answers I am sure, but one thing I can tell you for certain is that having a passenger aboard seriously messes with the bike's geometry and rear ride height. The added compression of the rear spring alters the swingarm angle, bike attitude (front to rear ride height difference), steering geometry (rake) and stroke position of the the suspension (more compressed in the rear, more extended in the front).

 

You can compensate for this to some extent by adding rear preload. All this does is extend the shock from its current, more compressed stroke position towards a more natural position, which also solves your basic geometry problem (swingarm angle and front rake) under steady state conditions (neither accelerating nor braking). You will likely find that if you add enough preload to restore the normal bike attitude with a passenger aboard you will have zero free sag left (i.e., with no rider aboard the rear suspension will be topped out). This is not an issue but when riding solo again you will want to remove the additional preload.

 

What the preload adjustment can *not* do is make the spring stiffer. To really set up a bike for performance two-up riding you would want a stiffer rear spring, but on most bikes swapping the spring out is a pretty big job so that's not really practical unless the bike is always ridden two-up. What I am saying is that there is really no way to optimize suspension adjustment for two-up performance riding unless you change the springs (at both ends), so don't expect to find a perfect setup with the stock hardware. With your passenger aboard you are always going to be compressing the rear more under acceleration even if you get the preload right - that is, you will have more backwards pitch - and you will also more front compression on braking. I'll bet you could remedy this somewhat by adding both compression and rebound damping at both ends, but that is still not the same as having the correct spring rates.

 

 

 

[rchase]

One of the trackday orgs that I ride with does 2up sessions in the last few sessions of the day. If you correctly adjust the sag on your suspension and have a particularly light passenger it's not too horrible. I have even been passed by 2up riders on much more powerful bikes. There's nothing quite like having the throttle completely pinned and watching two people on a much more powerful bike whizz by you on a straightaway.

[Pepsi Drinker]

This is going to come off as bragging, which I am not. This is just some factual information;

I ride a 600cc sportbike

I have about 20 years racing experience and have ridden well over a million miles in my life.

The last few years, I ride more miles 2up than I do solo, I ride at a very spirited pace on the best roads I can find. I am not WOT and I 99% of the time have a self imposed 70-75mph cap on my top speed, but even in the marked 30 mph corners I run about 70, so double plus is pretty common except on the straights where I just troll along at about 70-75

I also do several track events each year where I ride two up the majority of the sessions

 

As far as the bike set up;

I have .95kg/mm fork springs in the bike when I ride solo and 1.05kg/mm fork springs when I am two up-and add both compression and rebound damping to go with that stiffer spring. 30mm sag is set either way

The rear shock, I have an oe fresh shock with stock valving and spring when solo and an entirely different shock set up for two up, the spring is quite a bit stiffer, so much so the rare occassion I have ridden on it solo it sits topped out most the time and about bucks me off the bike. It also adds 5mm more rear ride height when two up. 35mm sag is set either way

Given that the suspension demands are very different, I opt to take the 30 minutes it takes me to make the switch so it is set up for how I plan to ride. I have found the weight of the passenger is every bit as much on the front as the rear or very near the same weight bias when the bike sits statically. I have no doubt some model bikes this will vary on- to atleast some extent. And of course when on the brakes, there is far more weight pushing on that front tire

 

As far as throttle control, I find I am actually on the gas harder and earlier since the engine doesn't accelerate as hard with the passenger and the extra, lets just call it 160 lbs with gear, on the back seat. Which actually adds some amount of traction at a spirited pace. Mind you I am not saying race pace. I do set tire pressures differently as well, adding 4psi cold more to the rear and 5 to the front to keep that same approx 15% of pressure increase at temperature.

Tires that solo would last me 4500 miles or so of street while riding two up only go about 3200 miles. I actually burned through a set of tires in Arkansas in 900 miles late last fall two up the entire time at a spirited pace, they had less than 400 miles on them when we left.

 

The local track I typically run about 3-5 seconds off my solo pace when she is on the back and am typically passing most the riders on the track even two up. Again we aren't racing, but we are moving at very quick clip and most of the people who join me aren't racers although nearly all do trackdays several times a year. I do end up having to keep my sessions shorter with her on back, her wrists and legs get sore under hard braking after several laps once past the first session or two but especially later in the day.

 

There are a few people I ride with regularly who ride two up often and are very quick, quick enough to leave most solo riders far behind through the technical stuff. Their wives love it, but there are others who bring a passenger and if the pace is upped at all they get stiff and tense and do all sorts of bad things. So it will much depend on the quality of passenger as well as the bike set up

 

I have no doubt that if I was riding a liter bike where the extra weight wouldn't make as big of a difference in acceleration my throttle application would still be earlier and more than riding solo.

[Arrow]

Thank you to everyone for the replies.

 

It would seem to me that heavy attention to suspension set-up is going to provide more stability than anything. I have the bike set up for solo riding and just increase the preload for the rear during 2-up riding sessions. I am not willing to change hardware to accommodate pillion riding because I don't have enough (sport) bikes to do so. I have full intentions on picking up another sport bike within a year and perhaps setting up my CBR at that point for dedicated pillion riding would make sense. I think that taking the bike to a shop and having them assist set up, as best as possible, within current hardware limitations for pillion riding would be a good idea. Changing out preload, damping and compression settings is not a big deal. 10 minutes to switch to 2-up and 10 to adjust back is more than reasonable to achieve a more planted feel.

 

I have also decided to purchase a pillion rider aid that will undoubtedly increase comfort and control. I seem to be unable to post a link but the product is called VINXXGRIP. There are several brands of tank bars out there but this happens to be the one that best suits our needs. There is a mount that clips to the gas cap area and a set of small handlebars twist, lock on and all with little obstruction for the actual rider. Many of the others do not seem to remove as easy when not riding together. It appears to be a 20 second set up once the actual cap connector is mounted. There may be other and better mounts that I have missed out there and would love to hear of one that would offer more stability, ergonomics and ease of removal than this one.

[Pepsi Drinker]

I have tried one of those gas cap mounted units and she doesn't like it at all, she prefers the handgrip rails that came standard on the bike as her wrists are at a slightly akward angle with the tank mounted thing. Not to mention she bangs her faceshield into the back of my helmet way too often in that position.

Although the tank grip unit has been favored by many first time passengers going at a spirited clip on the track, most of which have been trackday riders, although only by them not me as the rider.

 

That said, I also prefer her to hold on to the oe grips in the back so it allows me a little more freedom of movement instead of her arms firmly pressing on both sides of me to get around to the tank mounted grip.

 

Actually she typically has one hand palm down on the tank and the other on that rear grab bar and swaps hands depending on the direction of turn so I am able to lean my upper body unobstructed. Of course I am really moving all that far, but enough that if her arm was there it would definately be in the way.

 

Besides the suspension set up, it really comes down to working together with your passenger and them knowing how and when to move with the bike, or more often how not to move at all.