Race chassis

[husaberg]

Bimota and others just used to rengle the steering stem so it wasnt at 90 degrees.
From what foale says trail is more likely to be felt than rake.
Do this with a set of adjustable of set offset yokes like Kosman and others used to de would be far cheaper.

you could combine the insert like koosman used to do with ones to change the angle as well.

[jato]

another long-shot question - would anyone have some ball-park specs of swingarm pivot to front sprocket and if possible the rear axle's position in relation to them... I'm building a clutch housing for an engine that will eventually be raced and want to have clutch cover screws above and below the swingarm pivot. murphy will have me choose the wrong place for the screw boss and foul with the pivot. gsxr 1000 specs would be ideal as the bike will be similar size and performance. cheers

[jellywrestler]

I am sure the older readers can remember this i don't know his last name but at the time it was super trick.
I am not sure how the the rear suspension works because it looks sideways in the pic but not mentioned in the blurb.

Some will know who Sean is I bet?

used to stay with Nado in chch often, good man, did a few perkies and always had fridge full of piss that he received but didn't drink.....
he tried to sell that bike to me at one stage but i didn't want another bevel duke, been there done that.n haven't seen him for nearly a year.

[husaberg]

used to stay with Nado in chch often, good man, did a few perkies and always had fridge full of piss that he received but didn't drink.....
he tried to sell that bike to me at one stage but i didn't want another bevel duke, been there done that.n haven't seen him for nearly a year.

Cool small world, was he working for Air NZ?

[mr bucketracer]

For jello boy

[Orengo98]

Hi to all!

My name is Joan, I'm an engineering student from Barcelona.
I finished reading the ESE team Thread, and now the Race chasis one, wow, lots of information! Thank you to all the contributors.

Lately, I've been thinking on building a flat track bike, with a Bultaco center port motor which as I read, it seems that Frits has some experience with!
The idea that I have is to design a tubular frame around the motor, with twin shocks to retain the classic feel of the bike.

I've been doing some research and all flat track bikes have similar specs, 25º rake, 100 mm trail and around 1340 mm wheelbase. This seems to be the "industry standard" for flat track. Those are the specs of the Indian FTR 750, but the Bultaco Astro is very close to that too. Maybe is room for improvement, making the fork more vertical?

I would like to ask for your opinion on a topic talked here before, the lateral "suspension". It's been stated before that lateral flex, under leaning conditions, acts like a lateral suspension. I suppose this is of vital importance in flat track, as the track is not so flat hahaha compared to a road racing one, and the angles the bikes reach are considerable. I noticed that a lot of "farmers" like champion frames, have rectangular section swingarms, those have a lot of section inertia under vertical loads, but not in lateral loads. Do you think this is done for easiness of manufacture, or to help with lateral "suspension"?

My idea was to make a frame like the Yamaha champion frame:



But reading an article about the FTR 750 on cycle world, I found this:

" The chassis is made of steel tubes of modest diameter. This will look spindly to those accustomed to beefy aluminum sportbike chassis, but if chassis flex is important on pavement (which ideally is smooth), think how much more so it is on dirt, which is rough."

"one resembled popular aftermarket flat-track frames in having a single large downtube descend a short distance from the steering-head, then join a pair of tubes to form a cradle under the engine. A pair of tubes continue the cradle vertically behind the engine, with the swingarm pivots incorporated into them."

a picture of that frame for reference:



So my question is: Do you think that a design with double downtubes from the head tube, like the champion one, would be too stiff for a flat track bike?

Thank you in advance

[husaberg]

Hi to all!

My name is Joan, I'm an engineering student from Barcelona.
I finished reading the ESE team Thread, and now the Race chasis one, wow, lots of information! Thank you to all the contributors.

Lately, I've been thinking on building a flat track bike, with a Bultaco center port motor which as I read, it seems that Frits has some experience with!
The idea that I have is to design a tubular frame around the motor, with twin shocks to retain the classic feel of the bike.

I've been doing some research and all flat track bikes have similar specs, 25º rake, 100 mm trail and around 1340 mm wheelbase. This seems to be the "industry standard" for flat track. Those are the specs of the Indian FTR 750, but the Bultaco Astro is very close to that too. Maybe is room for improvement, making the fork more vertical?

I would like to ask for your opinion on a topic talked here before, the lateral "suspension". It's been stated before that lateral flex, under leaning conditions, acts like a lateral suspension. I suppose this is of vital importance in flat track, as the track is not so flat hahaha compared to a road racing one, and the angles the bikes reach are considerable. I noticed that a lot of "farmers" like champion frames, have rectangular section swingarms, those have a lot of section inertia under vertical loads, but not in lateral loads. Do you think this is done for easiness of manufacture, or to help with lateral "suspension"?

My idea was to make a frame like the Yamaha champion frame:



But reading an article about the FTR 750 on cycle world, I found this:

" The chassis is made of steel tubes of modest diameter. This will look spindly to those accustomed to beefy aluminum sportbike chassis, but if chassis flex is important on pavement (which ideally is smooth), think how much more so it is on dirt, which is rough."

"one resembled popular aftermarket flat-track frames in having a single large downtube descend a short distance from the steering-head, then join a pair of tubes to form a cradle under the engine. A pair of tubes continue the cradle vertically behind the engine, with the swingarm pivots incorporated into them."

a picture of that frame for reference:



So my question is: Do you think that a design with double downtubes from the head tube, like the champion one, would be too stiff for a flat track bike?

Thank you in advance

Rickman build frames for the Bultacos with center and side port and the center port Zundapp.
there was a company in Western oz that built trail bikes with Ossa and similar engines to a sort of sprite/Rickman design they were called Alron i thnk.
Sprite also built frames for Bultaco as well.
if you google these names there are plenty of pics
https://www.google.com/search?q=rick...VvjPai1GrLEZZM

https://www.google.com/search?q=alro...9Nd-WucNqOXEZM




I dont think it would be too stiff

here is the trakmaster OSSA
But it appears trackmaster built single backbone and double backbone frames for the trackers but only with the opposite downtube. I would suggest more to do with weight than stifness.


http://www.vft.org/RouitMuseum/Galle...ck2Stroke.html

Champion built many of the 250 frames

it was probably more important that the available propriety or oem seats and tanks still fitted the frame.

[Grumph]

For flattracking, I'd suggest the rectangular section swingarms were more fashion than anything scientific.
Yes, they're stiffer vertically than horizontally - which matters in roadracing - but IMO not so much in flattrack.

Locally there's a wide mix of chassis being used. There are some US origin big bikes - and some ex motocrossers.
Depends what size track you're going to run on. 1/4 mile - or 400 meter - tracks, from observation, something quite flexible works well.

Look at the classic speedway bike chassis. Very basic - and quite flexible.

[Orengo98]

Rickman build frames for the Bultacos with center and side port and the center port Zundapp.
there was a company in Western oz that built trail bikes with Ossa and similar engines to a sort of sprite/Rickman design they were called Alron i thnk.
Sprite also built frames for Bultaco as well.
if you google these names there are plenty of pics

Thanks for your answer Husa! I didn't know about the Alron frames, very cool to see this bikes being modified so far away!

I dont think it would be too stiff

Thanks! so with a double down tube type frame it should work fine.

Champion built many of the 250 frames

Here the sport is very recent, and we don't have any champion frame around, also I think it would be very difficult to find one for sale to import.
This gave me the idea to try to build one, and maybe do something different.

For flattracking, I'd suggest the rectangular section swingarms were more fashion than anything scientific.
Yes, they're stiffer vertically than horizontally - which matters in roadracing - but IMO not so much in flattrack.

Locally there's a wide mix of chassis being used. There are some US origin big bikes - and some ex motocrossers.
Depends what size track you're going to run on. 1/4 mile - or 400 meter - tracks, from observation, something quite flexible works well.

Look at the classic speedway bike chassis. Very basic - and quite flexible.

Thanks for your answer Grumph.
I thought maybe thee rectangular section swingarms had something to do with "lateral suspension".
If not, I better do a round tube swingarm, as it's going to be easier for me to do.

Tracks here are 400m. So, would you think that what I have to aim for, is a longitudinally and torsion stiff frame, but laterally flexible?

maybe a very stiff frame, but with a more flexible swingarm?

While looking at speedway pictures, I see that when they counter steer, and by the effect of the rake, the front wheel is much more vertical.
So my theory is that in the front, I need a very stiff frame, with a stiff head tube, that could support well the torsion, and a flexible swing arm. Do you think this is correct?

[Grumph]

Flattrack is a funny discipline. So much depends on riding style. Whatever you build, be prepared to change it to suit yourself.
I'm not going to tell you what to build - though copying a known and popular chassis is a good start.

I've only ever built one flattracker - in the mid 1980's. It's come back to haunt me too. The guy I built it for was a good speedway rider who wanted to go flattracking. So i built him a bike with geometry he was used to and could ride.
He's tracked it down and is currently riding it locally. Bear in mind he's my age give or take - over 60. i rebuilt the engine for him and now in the off season it's back to be rewired properly.
It's quite different to nearly everything being raced here as it's radical geometry compared to others. I suspect that if you haven't ridden speedway you wouldn't like this one at all.
Based on an XR500 Honda. Forks have been played with to lower it. Still got the 23in front wheel too.

[husaberg]

Woods was another famous flat track frame and bike maker
the only bike i can remember that tried to do the styling was the FT500
Any re bike class that stops or limits the use of brakes has to be a good idea.
there is still a track in the USA that still has the jumps and left and right turns i think it used to be dominated by ex MX'er in the past.

As below every Road race pro that kenny taught to flat track was educated on a XR100 Honda rather than a XR750 Harley
i think it was a 1/8 mile track

[Orengo98]

Hi!

Been a long time, but been doing some progress.

Flattrack is a funny discipline. So much depends on riding style. Whatever you build, be prepared to change it to suit yourself.
I'm not going to tell you what to build - though copying a known and popular chassis is a good start.

Thanks for your tip Grumph! for the moment we started making a welding table to do some kind of jig for the frame, and started copying the Bultaco Bandido frame just to practice welding, tube notching and all that. Keep in mind that it's not a 100% accurate copy, some tubes need to be bigger in diameter and the radius on the curves are not the same, it was only intended as a practice, before doing a usable one. I attach some pictures.

Woods was another famous flat track frame and bike maker

Those frames are very nice Husaberg!

[philou]

Hello

the wheelbase in the technical sheets is given with what position of the chain tensioner?

[Grumph]

Hello

the wheelbase in the technical sheets is given with what position of the chain tensioner?

Usually with standard gearing a competent designer will ensure the axle sits in the center of any adjustment.

[jato]

This thread is a goldmine of information but it seems a lot of people have moved on from modifying/building race bikes... anyway i'm curious if builders always endeavor to have their tyre central to the swingarm pivot bearings - i'm (slowly) building up a bike and have noticed some sport bikes dont always have everything symetrical. from an engineering perspective i like the idea of equal loads throughout ,maybe the marketing people have so much sway we end up with things like an R1 or cbr swingarm . maybe i need to measure some GP bikes - i suspect they give a better insight .