25 replies to this topic

[cheapracer]

Does anyone (Peter L?) know the basic starting point for a Sprintcar or Speedcar's basic front alignment settings such as caster, KPI etc?

RH wheel of course - yes for my beam axle, I need to start making the uprights.

I was thinking around 2 or 3 degrees KPI and 5 degrees caster and around 30mm trail - but looking at my base materials today I can achieve just about any settings.

I have never had anything to do with beams before so any input appreciated :-)

[McGuire]

Ford employed front beam axles as long (1903-48) and successfully (ha) as anyone. In their specs they were all much of a muchness with 4.5 to 9 degrees of positive caster depending, zero scrub, and 2 or 3 degrees of Ackerman at 20 degrees SA. Not exactly rocket surgery.

Sprint cars evolved directly from that Ford hardware with their own specs optimized for turning left -- for example, dirt sprinters might run 8 degrees KPI on the left and 12 on the right; also caster splits, either welded into the spindle bosses or via a split, adjustable axle. No reason for any of that on a road car, of course.

[Lee Nicolle]

They do sem to vary quite a lot. From looking at modern Sprinters most seem to be fairly standard with about 4 deg of caster on r/f and l/f standing straight up though some have more. Some seem to have positive camber on l/f but most seem to be straight up. That is really the same as my 42 y/o Super Modified. Except it weighs half as much!!
Also presuming the car has powersteering you can go more ofcourse though on a midget be careful otherwise it may well be quite twitchy.
All the components can be bought out of the US suppliers [and a lot seems to be coming from China now anyway] It is hardly worth making the hardware as it is quite cheap and proven and easy to buy.
XXX Sprint chassis is made in China but I have no idea if they do midget stuff.

[Wilyman]

Does anyone (Peter L?) know the basic starting point for a Sprintcar or Speedcar's basic front alignment settings such as caster, KPI etc?

RH wheel of course - yes for my beam axle, I need to start making the uprights.

I was thinking around 2 or 3 degrees KPI and 5 degrees caster and around 30mm trail - but looking at my base materials today I can achieve just about any settings.

I have never had anything to do with beams before so any input appreciated :-)

cheapracer,
While not able to contribute any figures re your cars front end your query brought a smile to my dial.

I built a backyard super mod back in the '60's. Flat head Plymouth motor, clutch only, no gearbox
I had a mate fabricate a straight tube front axle to take a transverse spring. I decided on a 'heap' of RH - camber, the LH less so. The caster was taken care of at the spring mount on the chassis. Once again the measurement was hit and miss allowing 'heaps' of positive. I also ignored the Ackerman meaning that both wheels were at the same angle at full lock.

The front transverse spring mount was offset to the left at the chassis. This also had crude adjustment for weight jacking.
The front spring had a fixed pivot on the L side with a 'sliding' leaf on the R side. Some used the normal shackle here.

If you've managed to read this far you are wondering how did I arrive at the above angles etc? I can only answer that I read a lot of speedway magazines back then and also mentally noted what the 'guns' were doing with their cars. So I must have been close yeah?
One of our 'party tricks' was with the weight jacker wound up the left front wheel could be raised easily by hand
With all these mods it went fairly well but now, 40 odd years later I ask if it all made much difference? Ah, well it was fun.

[cheapracer]

Thanks guys, nice story Wily :-)

I was worried about zero KPI creating shimmy with a chunk of trail - thought a little KPI may dampen that.


The older beams ran a bit of caster to offset the common positive static camber I would have thought?

I got my guess from needing possible shimmy damping of 2 or 3 degrees KPI and around 5 degrees of caster to retain negative camber gain for a modern tyre.
With those mild settings and light steering I figured I would retain feel/weight through trail.

[Johan Lekas]

...I got my guess from needing possible shimmy damping of 2 or 3 degrees KPI and around 5 degrees of caster to retain negative camber gain for a modern tyre. ...

(Since I'm also interested in beam front axles I can't keep my mouth shut)
Sorry I can't answer your original question cheapracer only pose more questions:
- Does not Caster+trail give the same (shimmy) damping as KPI+scrub radius?
- And what good does KPI really do except reducing scrub when mechanics prevent scrub reduction in any other way?

/Johan

[cheapracer]

- Does not Caster+trail give the same (shimmy) damping as KPI+scrub radius?

- And what good does KPI really do except reducing scrub when mechanics prevent scrub reduction in any other way?

/Johan

- Shopping trolleys and old cars prove otherwise.

- Stops shimmy I hope. (KPI is also a foregone conclusion/packaging problem for Mc Struts).

When I get there I may even try negative KPI which gets a camber gain in turn.

And don't get the impression I know what I'm doing, this is a total 'wing it' and see what happens - but I enjoy the challenge along the way.

[Fat Boy]

- Shopping trolleys and old cars prove otherwise.

- Stops shimmy I hope. (KPI is also a foregone conclusion/packaging problem for Mc Struts).

When I get there I may even try negative KPI which gets a camber gain in turn.

I know of at least one very successful endurance racing car with zero KPI. Shimmy isn't an issue.

Interesting you mention 'camber gain in a turn', because zero KPI coupled with a moderate amount of caster can lead to too much camber in a turn. With the aforementioned endurance car, you have to really be careful, as both an engineer and driver, with low speed understeer. It's very easy to put the inside edge of the tires to cords. Because of this, I'd recommend at least a small amount of KPI to keep the steer camber in check.

[Ross Stonefeld]

This probably has an exceptionally obvious answer but when you say inside edge of the tire, mid-corner, do you mean the right hand side of the tires in a right hand turn or the side of the tires closest to the center of the vehicle or something else?

[Fat Boy]

This probably has an exceptionally obvious answer but when you say inside edge of the tire, mid-corner, do you mean the right hand side of the tires in a right hand turn or the side of the tires closest to the center of the vehicle or something else?

Actually, it's a good point and probably not obvious. It is the inside tire that takes the brunt of the scrubbing and inside edge wear.

[cheapracer]

I know of at least one very successful endurance racing car with zero KPI. Shimmy isn't an issue.

Interesting you mention 'camber gain in a turn', because zero KPI coupled with a moderate amount of caster can lead to too much camber in a turn. With the aforementioned endurance car, you have to really be careful, as both an engineer and driver, with low speed understeer. It's very easy to put the inside edge of the tires to cords. Because of this, I'd recommend at least a small amount of KPI to keep the steer camber in check.

Thanks FB, I don't suppose you know what amount of trail they run?

[Fat Boy]

I don't have those numbers on this computer, but from memory (uh-oh), I think it's about 65mm. The wheel has a lot of offset.

[cheapracer]

I don't have those numbers on this computer, but from memory (uh-oh), I think it's about 65mm. The wheel has a lot of offset.

Thats interesting, I was thinking of using around 50mm earlier but as often mentioned I was worried about getting shimmy.

Guess I could always throw a steering damper on if needed.

Thanks heaps

[mariner]

THis may be a dumb question but is the car intended for dirt or track(pavement) use?

Thjere is a lot of data available on dirt sprinters because they are the most popular in the USA. However I think that maybe pavement sprinters/modifieds might use different set ups.

[cheapracer]

THis may be a dumb question but is the car intended for dirt or track(pavement) use?

Thjere is a lot of data available on dirt sprinters because they are the most popular in the USA. However I think that maybe pavement sprinters/modifieds might use different set ups.

Fast road and race intention.

Just interested to compare some baselines as a guide for a starting point - testing will follow.

[mariner]

There are a number of chassis articles in Circle Track magazine which as it caters for US dirt and pavement cars probably has more about solid axle cars then any other periodical!

Here is a link to the wonders of a pavement supermodified, I dont know if the claim of being able to get into an IRL filed at Pheonix is true but I have seen an ancestor of these cars at Oswego and they CAN accelerate.

http://www.circletra...cing/index.html

Anyway lots of chassis links at the top left of the page, I do'nt claim to be able to validate any of the info.

[Greg Locock]

Although the thought of zero caster sounds odd, it so happens the car I am working on (circa 1960 Fairlane or Park lane) has zero castor.

Presumably their only interest was lower parking efforts, as this thing weighs 3500 lb and has manual steering.

[Lee Nicolle]

Although the thought of zero caster sounds odd, it so happens the car I am working on (circa 1960 Fairlane or Park lane) has zero castor.

Presumably their only interest was lower parking efforts, as this thing weighs 3500 lb and has manual steering.

A lot of cars of that period had little caster, rag crossplys really did not need much coupled with positive camber. Give it a bit with radials and a small amount of neg and it will handle and steer a lot better with minimal increase in steering effort. Unusual for a barge not to have power steer, it may actually have some road feel in the steering!

[cheapracer]

Although the thought of zero caster sounds odd, it so happens the car I am working on (circa 1960 Fairlane or Park lane) has zero castor.

Presumably their only interest was lower parking efforts, as this thing weighs 3500 lb and has manual steering.

If I remember from my Chilton service and labour guide correctly the front wheel drive Oldmobile Tornado had negative caster.

I like old Fairlanes

[Greg Locock]

I misled you, it's actually one of these

http://www.remarkabl...ford-00072.html

[cheapracer]

Even cooler!!

[Peter Leversedge]

Hi "cheapracer", sorry I have not replyed to you but I have been in Autralia for the last 3 weeks and away from my computor.
If I remember correctly my Ozcar had about 9 KPI with power steering, caster 4, 0 toe in , very little ackerman and just set it on the right side as the left just goes along for the ride and a lot of the time is amost of the ground. Caster is on late type cars is something you can play around with and find out what the car likes as it easy to adjust.
KPI lifts the RF of the car as you turn the wheel to the right, tranfers weight to the left rear and helps straighten the car up
Like the '56 Fairlane Wagon, I had a '55 Sedan years ago [round park lamps, 6 volt instead of 12 and a non dished steering wheel]
272 Y Block V8 under the hood [not one of Ford's better engines]

Edited by Peter Leversedge, 08 April 2010 - 10:33.

[cheapracer]

Thanks Peter, thought you might chime in eventually

9kpi over 4 of caster? - you ran a chunk of static camber then to balance that imbalance out or just 'dug' the outside shoulder in? - dirt/clay I presume....

[Lee Nicolle]

If I remember from my Chilton service and labour guide correctly the front wheel drive Oldmobile Tornado had negative caster.

I like old Fairlanes

So do early Valiants. There is others also. Why who knows

[Lee Nicolle]

Even cooler!!

Leadsled!!. They really look trick these days. US Models had power steering advailable. Us Aussies were tough and did not need that new fangled stuff!!
Actually we semed to get all the basic models sourced out of Canada. At least Cussos got the V8 unlike the Chevs and Pontiacs which were all 6s until early 60s.
Peter, while the old Y block was never great they were not a bad engine. They were the best we had in Oz until early 60s when GM eventually got V8s in our cars.
We have one running in Classic Supermods and it can be bloody quick.

[Greg Locock]

Oddly enough the main part of the job is sliding a modern HPAS rack and pinion in. The PAS and steering gear that was available originally does not appeal to the owner. I've also tidied up the kinematics a bit, so it is basically running a modern front end geometry wise, should handle about the same as a Falcon wagon when we get the springs and shocks sorted. I'm always in two minds about major rebuilds of old cars, but as he points out, when you rescue one of these things that is rusting apart it's either that or turn it into razor blades.