Suspension tuning tips

[ashdricky]

Hi I am currently building a 1978 gs5/650 with the intention of road racing. with that said, I need some suggestions regarding period-correct suspension setups. What forks were used by the guys who raced gs bikes back in the 80's? did they keep the stock ones and just change the springs? or swap them out entirely?

 

[GregT]

The smaller GS's were mainly raced in Production classes around the world as far as I know so vey little was allowed to be changed.
Nowadays the first move is to have a look at the rules of the organisation you'll be racing with and see what is allowed.
Go along to one of their race meetings and ask questions too....

 

[TheCafeKid]

+1. Have a look at te rules for whatever class you plan on/are allowed to be running in.
Most of these would have been run in production class, save for the factory works/factory backed privateer teams who had the cash to use/build custom one off bits.

Since it's likely you'll be in some sort of VinMoto or VRRA class, there likely won't be much you're allowed to change. But you probably CAN use the best of the vintage, and/or modern upgrades that relate to safety...

 

[Big T]

I don't think many racers changed their forks in the 80's

Some new springs from Progressive or Sonic, a fork brace and some emulators (if allowed) should be the hot set up

Plus, changing the fork seals and checking for slop

 

[ashdricky]

What is an Emulator? I have been considering progressive fork springs, but am not sure if they can be installed as the forks I have are from an 83 650GLX and have Schroeder valves on the top to adjust air pressure i assume.

Competition rules:
We are building this bike to be my entry in a contest between myself and a couple of others, the goal being to see who can build the "best" vintage sport bike. If all follow schedule we will debut our bikes at the local father's day auto show. Following visual inspections and voting from the crowd, we are then supposed to head up to Toronto the following day to do some track runs. I believe my main competition will be an late 70's cb750. with that said we have only come to the agreement to use period correct components, with the exception of, electronics and brakes (in case OEM parts are no longer available). This is really all the information I have as far as 'Rules' go.

 

[hampshirehog]

Ceriani were the forks to run in this part of the world back then. I doubt you'll find any now though.

 

[Tim Tom]

What is an Emulator? I have been considering progressive fork springs, but am not sure if they can be installed as the forks I have are from an 83 650GLX and have Schroeder valves on the top to adjust air pressure i assume.

Competition rules:
We are building this bike to be my entry in a contest between myself and a couple of others, the goal being to see who can build the "best" vintage sport bike. If all follow schedule we will debut our bikes at the local father's day auto show. Following visual inspections and voting from the crowd, we are then supposed to head up to Toronto the following day to do some track runs. I believe my main competition will be an late 70's cb750. with that said we have only come to the agreement to use period correct components, with the exception of, electronics and brakes (in case OEM parts are no longer available). This is really all the information I have as far as 'Rules' go.

Well since the rules seem to be fairly loose, I would rebuilt the forks with modern springs and cartridge emulators. It seems more like a bet for bragging rights than a sanctioned vintage race series.

http://www.racetech.com/HTML_FILES/EMULATORGV.HTML

I would give Racetech, or some another reputable suspension tuning company a call and work up something that works for what you need. IE: the outside appearance of a vintage bike. I would do the same for the rear, and get it dialed in to your size, weight, and style.

Also be sure to get some good modern rubber on there. There are a few favorite 'Road Racing' GS tires, I believe the Avon RoadRunners and Pirrelli Sport Demons get high reviews.

 

[wera racer]

I can't speak to the smaller GS, but I race a GS1000 in WERA and AHRMA. I installed Race Tech springs and emulators when I did my build. The springs were way too firm when I raced them for the first time at Barber in October, but Race Tech had a tent there and their great guys spent a half a day (for free!) dialing me in with lighter springs and adjusting the emulators.

I can highly recommend them based on their customer service and know-how.

I installed Ikon shocks on the rear and am happy with them, but if I had more $ I'd run Werks.

Good luck!

Here's mine at Barber...

 

[jaywelchy]

Great pic .. like to see guys running the dinosaur's

 

[trippivot]

looking good there!

 

[ashdricky]

WERA_RACER, judging from you photo your suspension set up must be working. I think emulator cartridges are the way to go, I checked out race tech's site and I'm not sure if I need special springs to use the emulators or not?

 

[gs58]

I know someone who put the whole GS1000 front end in a 550 race bike. I don't know if the 1000 has better specs than the 550 though. He just used it because he had it.

 

[gs58]

WERA RACER - whats the purpose of the shield between the headers and the engine? Heat reduction, or oil catcher?

 

[speedyandypandy]

I don't think many racers changed their forks in the 80's

Oh yes they did, just read books/articles/info about old racers, pro and amature, they changed what they could.

Ceriani were the forks to run in this part of the world back then. I doubt you'll find any now though.

They do pop up on evilbay, but not cheap

I know someone who put the whole GS1000 front end in a 550 race bike. I don't know if the 1000 has better specs than the 550 though. He just used it because he had it.

I think you will find the GS1000 stanchions have a bigger diameter, maybe a wider front wheel axle and better brakes(I'm just guessing, but it's like that on the hondas, big cc CB's have wider than small cc CB's and I excpect the GS's is the same), and that's a good thing.

Normaly a class will allow upgrade's that where allowed back in the day, and/or use stuff form the right period, even if the bike your replica is based on didn't have that spesfic part. You can use Brembo calipers, even if the original used AP Lookheed. It's also normal that brake parts are allowed to be upgraded beyond the era, because of safety reasons.

 

[ashdricky]

Thanks Speedy that is definitely useful,I got a used set of Ohlins last week and need to find a shop to rebuild them. they aren't the most cosmetically appealing.

 

[GregT]

In my experience the single biggest mistake with these things is to overspring the rear. The lightest springs you can get away with and decent damping makes a lot of difference. Too much rear spring and they want to swap ends under brakes because the rear end just tops out immediately.
We haven't gone to emulators on our 1000 yet as the rider uses the front end "pop up" to encourage weight transfer...and he's doing pretty good without them.
Andypandy...the Euro rules allowing brake upgrades beyond the period are by no means common in the rest of the world...and IMO, good thing too.
again IMO it's not a safety issue as what can be Waay better brakes can overstress areas of the original frames - under race conditions.
Again away from Europe most race organisations have a max stanchion diameter which reflects what was available in the period.

 

[John Kat]

I can't speak to the smaller GS, but I race a GS1000 in WERA and AHRMA. I installed Race Tech springs and emulators when I did my build. The springs were way too firm when I raced them for the first time at Barber in October, but Race Tech had a tent there and their great guys spent a half a day (for free!) dialing me in with lighter springs and adjusting the emulators.

I can highly recommend them based on their customer service and know-how.

I installed Ikon shocks on the rear and am happy with them, but if I had more $ I'd run Werks.

Good luck!

Here's mine at Barber...

Nice lean angle
What's the rating of your front springs?
Is that a V&H exhaust you have?

 

[speedyandypandy]

In my experience the single biggest mistake with these things is to overspring the rear. The lightest springs you can get away with and decent damping makes a lot of difference. Too much rear spring and they want to swap ends under brakes because the rear end just tops out immediately.
We haven't gone to emulators on our 1000 yet as the rider uses the front end "pop up" to encourage weight transfer...and he's doing pretty good without them.
Andypandy...the Euro rules allowing brake upgrades beyond the period are by no means common in the rest of the world...and IMO, good thing too.
again IMO it's not a safety issue as what can be Waay better brakes can overstress areas of the original frames - under race conditions.
Again away from Europe most race organisations have a max stanchion diameter which reflects what was available in the period.

How is not getting better safety equitment a good thing? Frames can be made stronger, no worries

I might have been a bit unclear:-s, the master cylinder can be upgraded, the calipers must stay original(but there are ways to make them perform better), same with the brake discs, they can't be full floaters, in some of the classes half-floaters are allowed.


Suspension wise your experience with "over springing" the back sounds like a person who doesn't no how to set up a bikes suspension from the start:?:

Bigger stanchions, did I say they could be outside the right era? But even in the 70ies you had bikes with 40mm stanchions, and I know of atleast 1 street bike with 39mm stanchions.

Ash : Watch Twist of the wrist suspension set up and read some of Tony Foale, you can do far worse than listen to them.

All: Oh and a bit of a warning, don't use old cast iron discs on a race bike, they are prone to crack during hard racing.

 

[TheCafeKid]

How is not getting better safety equitment a good thing? Frames can be made stronger, no worries

I might have been a bit unclear:-s, the master cylinder can be upgraded, the calipers must stay original(but there are ways to make them perform better), same with the brake discs, they can't be full floaters, in some of the classes half-floaters are allowed.


Suspension wise your experience with "over springing" the back sounds like a person who doesn't no how to set up a bikes suspension from the start:?:

Bigger stanchions, did I say they could be outside the right era? But even in the 70ies you had bikes with 40mm stanchions, and I know of atleast 1 street bike with 39mm stanchions.

Ash : Watch Twist of the wrist suspension set up and read some of Tony Foale, you can do far worse than listen to them.

All: Oh and a bit of a warning, don't use old cast iron discs on a race bike, they are prone to crack during hard racing.

Here's the deal with what he was saying with the rear springs.
If its sprung too stiffly in back and the damping is too soft the spring by nature will too out under hard braking causing the rear end to go light because of the force of the spring wanting to rebound to hard/quickly.
The rear damping set up must be compliant as to let the rear end "bounce back" quickly enough to take the next bump cleanly, but not so fast as to upset chassis. When leaned over, the suspension is not nearly as efficient as when upright, and the rebound circuit must be able to control rebound (obviously) or the rear will step out. Some talented racers you will find are both on the brake and throttle at the same time to effectively shorten the front end geometry to turn in and corner more quickly. If in this action the rear is too stiff it can break traction and down you go...

As to the original post, you certainly can make the frame stiffer, but there are trade offs... By making the frame more rigid it cannot act as secondary suspension while in mid corner causing a loss of front end feel. The bike will want to stand up and lay back down repeatedly on an undulating surface. A stiff frame is helpful in many situations, but making it overly stiff can be worse than having flex in it. Ask Burgess and Team Ducati about frames being too stiff to tune. They'll tell ya all you wanna know. Hahaha

 

[GregT]

Thanks for the clarification Kid.
Andy - I build and maintain these old race bikes for a living...From what i've read and heard of the Euro scene the brake and suspension rules are more liberal than here in New Zealand or Australia but conversely we can use 17 inch wheels in the pre 82 class where as I understand it most of the Euro classes are limited to original sizes or 18 inch.
Both approaches have their points...
What I like about the Southern Hemsphere approach is that the bikes retain the handling quirks which make them difficult to ride at the limit...and fun to watch
I am firmly of the opinion that period brakes only should be used - no problem using the best of the period though. Having to ride to the limits of chassis and brakes is part of the atmosphere of the period and should be continued IMO