Twins vs. Mono

[reddirtrider]

Nothing is infinitely stiff, and in a turn the bike + rider's center of gravity will be different distances away from each shock and its mounting points.

Somehow I just don't see how a swingarm that doesn't meet the infinitely stiff test will flex with a shock on each side and affect the handling dynamics, yet if it flexes with a mono it won't.

[liloaty]

Somehow I just don't see how a swingarm that doesn't meet the infinitely stiff test will flex with a shock on each side and affect the handling dynamics, yet if it flexes with a mono it won't.

Well, first off the mono swingarms are much stiffer than that dual shock swingarms. Second, even if the swingarm with a monoshock flexes, the shock is still putting its reactive force on 1 point on the frame. With 2 differing reactive forces, like in a dual shock setup, it can cause the frame to twist.

[reddirtrider]

Well, first off the mono swingarms are much stiffer than that dual shock swingarms. Second, even if the swingarm with a monoshock flexes, the shock is still putting its reactive force on 1 point on the frame. With 2 differing reactive forces, like in a dual shock setup, it can cause the frame to twist.

Ah, one of the pre-requisites to this discussion was that the mono swingarm and the dual shock swingarm are equally stiff. That's a very simple task, just use a mono swingarm for both applications.

As for the frame, once again the assumption is that it's stiff enough. If that's the case (and it's entirely possible) there is little difference as far as the geometries of the relationship between the wheels and frame.

The mono will always be easier to tune, but I just how a well designed dual setup is inferior.

[liloaty]

Ah, one of the pre-requisites to this discussion was that the mono swingarm and the dual shock swingarm are equally stiff. That's a very simple task, just use a mono swingarm for both applications.

As for the frame, once again the assumption is that it's stiff enough. If that's the case (and it's entirely possible) there is little difference as far as the geometries of the relationship between the wheels and frame.

The mono will always be easier to tune, but I just how a well designed dual setup is inferior.

OK - I'll give you the equally stiff swingarm assumption, but the frame assumption I don't agree with.

If frames were "stiff enough" then Suzuki, Honda, Kaw, Yamaha, Ducati etc etc wouldn't be pouring money into frame R&D like they do. I don't think its fair at all to say that a frame, for this argument, is infinitely stiff or stiff enough not to be twisted by unequal shock loads.

[reddirtrider]

OK - I'll give you the equally stiff swingarm assumption, but the frame assumption I don't agree with.

If frames were "stiff enough" then Suzuki, Honda, Kaw, Yamaha, Ducati etc etc wouldn't be pouring money into frame R&D like they do. I don't think its fair at all to say that a frame, for this argument, is infinitely stiff or stiff enough not to be twisted by unequal shock loads.

I'm not saying the mono isn't better, it's just I believe you can build dual shock units that virtually none of us could distinguish from a mono. That's my standard - that virtually none of us could tell the difference. (I'd say none, but I may be underestimating someone)

[tone]

Having done a few mono conversions on gs's etc here's my thoughts .......

A stock gs twin shock steel swingarm is lighter than something like a bandit 12 ally arm but no where near as stiff

Once you add the linkages etc there is a significant weight penalty but its gained back when you add the rest of the components, wheels tyres disc brakes etc & most of this is unsprung weight which can only be a good thing

The main advantage of mono arms is the rising rate linkage, twin shocks or cantilever mono shocks can never compare for quality of ride & keping the tyre in contact with the road

Twin shocks put the forces generated into two top mounting points that where never strong or stiff when new & after 20 or 30 years of use WILL be misaligned even if they were straight from the factory which is doubtfull at best

Ive had brand new unused frames on the jig that had the mounts up to 5mm out of horizontal with a 3 to 5mm differance in distance from the centreline of the frame, All of this puts strain on the stock rather weak swingarm & no matter what shocks you use they will be working at slightly differant damping rates because of it

Monoshock conversions when done properly put the forces generated directly into the strongest part of the main frame, above the swingarm pivot & up below the tank area, a little bracing here works wonders for handling

tone

[reddirtrider]

Having done a few mono conversions on gs's etc here's my thoughts .......

A stock gs twin shock steel swingarm is lighter than something like a bandit 12 ally arm but no where near as stiff

Once you add the linkages etc there is a significant weight penalty but its gained back when you add the rest of the components, wheels tyres disc brakes etc & most of this is unsprung weight which can only be a good thing

The main advantage of mono arms is the rising rate linkage, twin shocks or cantilever mono shocks can never compare for quality of ride & keping the tyre in contact with the road

Twin shocks put the forces generated into two top mounting points that where never strong or stiff when new & after 20 or 30 years of use WILL be misaligned even if they were straight from the factory which is doubtfull at best

Ive had brand new unused frames on the jig that had the mounts up to 5mm out of horizontal with a 3 to 5mm differance in distance from the centreline of the frame, All of this puts strain on the stock rather weak swingarm & no matter what shocks you use they will be working at slightly differant damping rates because of it

Monoshock conversions when done properly put the forces generated directly into the strongest part of the main frame, above the swingarm pivot & up below the tank area, a little bracing here works wonders for handling

tone

All true, but you're comparing a properly built mono to a stock setup. Use a good swingarm with the associated brakes and wheels, brace and align the frame, use quality shocks and it's an entirely different story.

Yes, the mono is easier to tune, and the rising rate linkage is great, but if you do all of this work to a GS to convert it to a mono, you have to be fair and do the same to upgrade to a decent twin shock setup.

I would be great to have the Yoshi bike with modern wheels and tires on a track next to a converted mono so we could compare them.

[tone]

All true, but you're comparing a properly built mono to a stock setup. Use a good swingarm with the associated brakes and wheels, brace and align the frame, use quality shocks and it's an entirely different story.

Yes, the mono is easier to tune, and the rising rate linkage is great, but if you do all of this work to a GS to convert it to a mono, you have to be fair and do the same to upgrade to a decent twin shock setup.

I would be great to have the Yoshi bike with modern wheels and tires on a track next to a converted mono so we could compare them.

True i'm comparing a mono conversion to a stock twin shock setup to a small degree, using a better/stiffer swingarm with twin shocks will show an improvement but the fact remains the top mounts are still pretty poor & that is where the problems lie plus you still end up with no proper rising rate

Putting a monoshocked gs & an upgraded twinshock head to head on the track is pointless as tracks are reasonably smooth & there will be little differance if any but try it on the road with all its potholes, off camber corners etc & its a different story

[LilTinc]

Putting a monoshocked gs & an upgraded twinshock head to head on the track is pointless as tracks are reasonably smooth & there will be little differance if any but try it on the road with all its potholes, off camber corners etc & its a different story

Tone,
Are you saying you think the mono set up would work better over real road type conditions or that the "twin vs. mono test" should be performed on real roads instead of a more uniform close course track surface?

[Mark M]

The main advantage of mono arms is the rising rate linkage, twin shocks or cantilever mono shocks can never compare for quality of ride & keping the tyre in contact with the road

The advantages of rising rate are greatly exaggerated for road and track use. Current sport bikes and MotoGP bikes use very little rising rate, less than 10% for the most part. That can be achieved with twin shocks that are moderately inclined forward a bit. I don't know where the GS models lie as I have never measured one out. Rising rate is excellent for dealing with load variations, but is a tuning problem if you are trying for really good track performance.

One of the biggest advantages is that it is hard to find top quality twin damper sets and it is easy to find very good single dampers. Even the premium Ohlins twin units are only middling grade compared to the high end mono units.

Mark

[LilTinc]

Mark,

It sounds like due to market demand that R&D on twin shocks has pretty much ended while R&D for monos has picked up. Correct?

I was tinking with all things being equal I was going to go with a twin shock set up as there would have been very little if any out sourced labor for the project. It's beginging to look like the cost of having the fabrication and welding done to my frame to accomodate a mono conversion may be easily offset by the lower cost of parts of the caliber I want.

Thanks all for the input.....however, the deal isn't sealed until the first cut is made.

[tone]

Tone,
Are you saying you think the mono set up would work better over real road type conditions or that the "twin vs. mono test" should be performed on real roads instead of a more uniform close course track surface?

yes imo monoshock setups work better in real world road conditions simply because the development has been consistant & ongoing for the last 20 years or so while twin shock development has remained static

Also imo any sort of handling package including modifycations or ajustments should be tested in the enviroment it is intended to be used in eg a perfectly setup track bike is truly horrible & uncomfortable on the road while a road bike setup simply cant hack it at the track the only exeption to this that i can think of is TT road race bikes

cheers tone

[nisom512]

Another item to consider is cost. A late model GSXR swingarm and shock can be had off eBay for around $100 and are high quality with a lot of adjustment possible. A set of ZRX shocks will be around $200-300 and a set of Ohlins is close to $800.

All modern sportbikes and roadracing bikes come with monoshocks, if there were an advantage to twinshocks then they would be so equipped. But the latest GSXR and MotoGP bikes all are monoshocked.

The late model monoshock style swingarms are also much stiffer due to their bracing.

Have to disagree with you on the weight matter reddirtrider, the last time I weighed it my bike is 450 pounds with a full tank of gas and the oil filled up (536 pounds is the listed stock wet weight) and a significant chunk of that weight savings came from the rear rim/tire/swingarm/rear brake/shock assembly.

WINNER!!!

[nisom512]

personally tho I like the dual shock look like has been said the mono is the new in. so you bought an old GS so why not be differnet and keep the dual shocks and have everyone else on the road riding mono rockets or what have you look at you and think what an old peace. and you can be thinking Heck yeah this thing is beautiful.

just my .02
Jake

[Mark M]

Mark,

It sounds like due to market demand that R&D on twin shocks has pretty much ended while R&D for monos has picked up. Correct?

Not really, a shock is a shock. But no one offers a current shock design combined with a high quality build for a twin setup. If they did, the cost would be double that of a mono, because the size is very insignificant in the cost.

The current top of the line Penske shocks offer ride height, high and low speed compression and rebound damping adjustments. In addition, they also offer numerous piston designs that will give almost any damping curve imaginable. They also cost around $1250USD... In the latest issue of MX Action mag there was an MX shock that offered adjustable bottoming control in addition to the above adjustments. Nothing we can buy for our GS's is even close and performance suffers accordingly.

I agree with Tone that a mono installation nicely braces up the frame above the swingarm pivot, but that can also be done with a twin setup if desired.

Mark