Front end/rear wheel mods...your thoughts?

[the mole]

This started on another thread, thought it might generate some interesting responses if we got input from different riders who have tried it. Particularly interested in objective analysis if thats possible. We all think our own mods are great, especially after spending the money!

Quote from: Mdow on July 24, 2008, 06:58:51 PM
i just think its funny they used the same wheel and could have just easily added a second disk and didn't.


The mole:
You're working on the premise that 2 discs are better than 1, and thats not necessarily true, especially on a lightweight bike thats not very powerful.
You need 2 discs if:
1. A single disc just doesn't have enough power. If you can't either lock the front wheel or get the back off the ground then you need more power, but I think the single disc has enough power for the weight of the GS (even if its loaded).
2. You have a problem with brake fade. You'll get fade on a long steep downhill when heavily loaded, or if you ride it like a race bike, as in accelerate flat out, then brake hard, then repeat that for the length of a race. If you ride on the road like that, you need more than 2 discs, you need a brain transplant. I don't believe the single disc is going to fade, because the bike just can't accelerate fast enough that the brake is going to get too hot.

Suzuki paid engineers to figure all this out, and they didn't put on the extra disc because it would be:
1. More expensive.
2. Heavier, so reducing performance and economy.
3. More complex to maintain and service.
4. Increasing the unsprung weight, which is detrimental to handling.

There are similar arguments about fitting a bigger back tyre. I did a lot of miles on big Guzzis and Ducatis in the '80s, and most of them had 120 or less rears, and they handled well. You might need more rubber if you've got a LOT of horsepower, but this does not apply to a GS! If your bike is not handling right you're not going to fix it with  a big back tyre. Look at your riding skills first, then get your tyres and pressures right for the riding you're doing, then tweak the suspension. A big tyre will mean more unsprung weight and the contact patch moves further as you lean, so if you're making less than 80hp don't worry about it!
In fact, I reckon that if you "blind tested" two identical GSs, one stock and one with a 120 rear you'd get a lot of riders preferring the handling of the 120. We're all conditioned to think the wide tyres are cool because thats what the big bikes and racers use. For them its a necessary evil to deal with the horsepower.
My 2 c worth!


The Buddha

Posts: 14256

   Re: Front end swap
« Reply #33 on: July 25, 2008, 06:50:17 AM »
   Reply with quote
Excellent point about the twin brakes not needed, and how 1 disc can be as effective - as in you lock up with 1 disc, that all the braking you need, and plenty of us have locked it up ... so we know its powerful enough.
The 2 aspects you have not considered is - brake pad + disk life and twisting action by the single brake.
The GS has a static pad which takes all the wear, 3-4-5-10 times more on it. Brake disc gets eaten the same way. A dual piston, dual caliper will wear evenly, make a lot less heat and hence wear out a lot less. Not just 1/2 as less, somewhere like 4-5 times less.
The single disc also twists the forks and we put on thicker fork braces or do various things to keep it manageable. A twin disk will not twist, it will only bend the forks as a unit inward. far better. A fork brace upgrade on a GS is very very noticeable, on a Kat (that uses the same brace BTW) you wont even know.
Wider rear - OK you are right here, its a lot of pain or little pain depending on what your threshold for pain is, its mostly for looks. Maybe tire life, but then you'd be running hard touring tires and not the gummy supersport tires.
Cool.
Buddha.

[ecpreston]

I track my GS in stock form. Well, ok, with Sport Demons (130 rear), EBC HH front pads, and a front stainless line. Pretty darn stock. I'm winding down my first full year of it, so I have plenty to learn, but I work the bike pretty hard.

Brakes:
I've done a handful of track weekends and the front rotor still looks new. I finally went through a set of front pads for the first time recently. And the brakes have enough power that I can outbrake most anyone (it's usually the only chance I have to pass!) and of course easily bottom out the front suspension. They are very predictable as well. Would I "upgrade" them further? Never. This "twisting of the front forks"?.... I see the potential, but do not feel it. There is NO street situation that should overwork them. Another disk would just be adding more cost and adding the worst kind of weight, both unsprung and rotating.

Wheels/tires:
Let's see, a couple thousand street miles and close to a thousand track miles on this set. The centers are near full tread and the edges are maybe half and look all marbled/shredded. I THINK the rear was starting to feel a little unpredictable last time, so I ordered a new set just in case. They are a good match for the bike IMHO. There's still a very slight edge of unused tread since the pegs ground out before the tread runs out. One weekend I did at CMP recently, it was 103 deg out. If I was ~3/4 leaned and went full throttle in 3rd, yeah, I could get the rear to step out. Other than that, it's on rails, they never show signs of overheating. The front can handle quite a bit of trail braking. They also perform quite well cold. And in the wet. While others are scared of their big track tires not being up to temp, I'm passing them. On the street, the only time they've slipped a little was because of gravel, water, manhole cover, ice. Nothing any tire can do about those evils.

Suspension:
It's soft. No news there. I put some 15W oil in the front and keep the back clicked to 6. I have yet to upgrade as I'm just starting to really feel the limits of it. I'm probably 210lbs with gear on. If I move around too fast on the bike, it tends to get bouncy. But it's predictable and has been a great teaching tool. If I'm smooth and move just right, I can more than keep up in chicanes. And it doesn't bottom out in longer corners. Advantages include not being too upset by track seams and bumps, I just run over them. Last weekend at VIR Patriot my favorite corner was the last of a chicane that went something like this: Just past apex I'm already full throttle, finish standing up the bike just in time to run over a curb, front end pops up and wobbles, I bring my weight up off the seat just a little so the rear jump doesn't slap me in the nuts, whole bike jumps over to about mid track, back to full tuck, maybe a little wiggle from the rear, full throttle all the time. It did this exactly the same way 100 times (well, except when I accidentally went too far and ended up on the the INSIDE lip of the curb or the grass). So yeah, the suspension keeps up ok. It was also one of the few places I could pass the "real" sportbikes as most of them get pretty upset by the curbing.   

Engine (you didn't ask, but just a few comments):
I stick to the smaller tracks because the straightaway closing speed of any modern sportbike on me would be unsafe. But on a small track, I can keep up and pass less experienced riders. Hard braking from 90, 100 is about all the excitement I need. But I can do a trackday without adding any oil, it's held up for hours at 7-10k RPMs in 100+ deg heat, and it shows no signs of stress. I just checked the compression and the valve adjustment to affirm this. I use synthetic oil and plan on changing it and filter once a year. The stock gearing makes it pretty easy to stay in the powerband. I get 35MPG ON TRACK! It's enough to have fun, and there's no safe street behavior that should require more. 

In conclusion , the idea, to me, of upgrading any of these categories for street use is kind of silly.   

[the mole]

I track my GS in stock form. Well, ok, with Sport Demons (130 rear), EBC HH front pads, and a front stainless line. Pretty darn stock. I'm winding down my first full year of it, so I have plenty to learn, but I work the bike pretty hard.

Suspension:
I have yet to upgrade as I'm just starting to really feel the limits of it.
In conclusion , the idea, to me, of upgrading any of these categories for street use is kind of silly. 

Thanks, interesting post and congratulations on the fun you're obviously having out there! Nice to see someone focussing on their own skills first.....You've kept it light, simple and inexpensive and now if you do any mods you'll know enough to make a good judgement on how they work.
Sounds like your fun-per-dollar factor is right up there.

[The Buddha]

You must be a light weight. Some of us Porkers easily over power the GS suspensions on the street ... the wonderful pothole riddled streets ... you dont happen to have some of those on your racetrack do you didn't think so. Those things are murder on stuff. In street bikes is where you need to upgrade first.
Cool.
Buddha.

[ecpreston]

heh yeah... you're supposed to AVOID the potholes! Most definitely it bottoms pretty easily on driveway lips, big pavement seams, and unlevel manhole covers. Eh, no big deal.

[commuterdude]

the soft front end is the only thing I don't like about my GS.  It is always surprising to me how easily it will bottom out. 

[dgyver]

The Kat rotors are smaller in diameter than the GS rotor. Larger diameters have a greater rotating mass, not saying the 1 larger is more than the 2 smaller. I have not calculated the difference in rotating mass of the 2 smaller rotors compared to the 1 larger rotor.

The GS caliper is a poor design. Sadly, Suzuki continued to use this design on other bikes but did use 2 calipers instead. Having a static pad operated by 2 pistons on 1 side is not a reliable design. They would have been better off having opposed pistons, sounds like the rear caliper.

The GS pads will wear unevenly, have additional wear to them and to the rotor. Having less stopping power will cause the rider to have to brake longer and harder at times. This will add additional heat the rotor increasing the potential to over heat and wear out faster. Increased hand fatigue and less throttle control should also be considered.

I only use 1 finger with my Kat brake setups. These do have EBC HH pads and dual braided brake lines, no crossover. They have a very predictable response and feedback.

The Kat setup uses 2 calipers with dual opposed pistons. This is 4x the pistons than the GS.

Yes there is more weight with the dual calipers but the return is well worth it.

The weight of the GS is comparable to most recent GSXR's, which have dual 4 or 6 piston calipers. Acceleration and HP mean nothing to braking.

Fork flex can be noticed, especially under braking, with the small 37mm tubes. The single rotor will flex the forks. A fork brace will help but not eliminate the flex.

Under sprung suspension is bad. Anyone over 120# can notice this on the GS. Bottoming out a suspension, especially under braking, is very dangerous. At 220# in gear, I was bottoming out my TLR on the street. After having the forks rebuilt, it made the bike handle like it was on rails. I may ride hard but not that fast (anymore) on the street, the track is different.

The GS is a low budget motorcycle. It does what it was designed to do. Of course it could have been designed with better parts but then it was also designed over 20 years ago.

Not everyone rides to the limit of the GS, having extra stopping power and better control is like having a little extra insurance. Having better suspension and brakes is like wearing gear; you wear it hoping nothing will happen but when you do need it, you will be glad you have it. 

[The Buddha]

Ecpreston - Ha ha ... funny.
Commuter - you not used to the clack noise yet ... yes pitiful.
Dgyver - well said. TL was bad too. BTW Japan designed the best suspension (with the cost compromise in mind) ... and put them on bikes just ~1 size too big.
Cool.
Buddha.