F1 chassis tuning guide

[ChrisWells]

After taking 18 years off I have returned to the sport. My previous rig (an early 80's Schmidt GP chassis with a TZ750) had virturally no chassis adjustability, so I just rode it.

My new rig is a 2007 CSR F1 (locally made tube frame that copied 06-07 F1 GP suspension geometry) and is fully adjustable at all 3 wheels. I have 3 race weekends under my belt now (and 3 new tropies for my mantel ) and have figured out the basics of how to drive it. Now I'm wondering if I can tune a bit of the push out of the front end in certain corners (or is that something I should correct soley by having the passenger try to get his weight a little more forward).

Anyway ideally it would be nice to find a tutorial on how to go about setting up your chassis for different tracks. If that does not exist then I would appreciate responses or links to any bits and pieces of information I can absorb and hopefully put to good use.

Thanks,
Chris

[steve-e]

You will hopefully get more response here Chris.k

What adjustments does a CSR have to start us off? (when I say us I mean the experts, not me )

[ChrisWells]

Well the front and rear suspension is 5 link with adjustable length links. I haven't touched the front as I presume the builder (and former driver) set it up so the front tire has no camber or angle (from straight and level).

On the rear I use the top link which is oriented fore and aft to adjust the chain tension (and if I need a bit more adjustment there is a similarily oriented bottom link). At my first race the builder and former owner was there and advised a single turn change to the top link oriented across the chassis to change the camber as that track ran counter-clockwise. (It seemed to help as I set the lap record ). I don't think the toe-in is adjustable on the rear but I'll check.

On the chair I believe both the toe-in and camber are adjustable but I haven't touched them yet. I seem to be getting pretty consistent wear across the chair tire with slightly more wear to the outside of the tire (at least for clockwise tracks).

This is what I have gleaned from the internet so far (plus those LCR diagrams in your download area):

- Chair wheel camber and toe in are generally increased for circuits with tighter right hand corners, but this will reduce top speed.

- Measure tire temp to determine spread across available tread.

- Set tire to 1.1 bar when at operating temperature and measure again when cold to obtain optimal cold pressures.

[ChrisWells]

A picture of my chassis:

[steve-e]

For understeer is the chair wheel adjustable front/back? Moving the chair back can make quite a difference with the amount of grip on the front, as can of course softening the front suspension, especially if the push is as you open up and the front runs out of travel. Moving the chair of course trades off drive out of corners which is why the quick guys tend to move the chair forward and go further through the corner loading the front up before unloading it (probably without knowing why they're doing it - some of them).
If you're getting push on both lefts and rights go in harder

That should at least provoke someone to respond

[ChrisWells]

Hmmm, interesting suggestions. By "go further through the corner" I gather you mean carry more speed into the corner causing the front suspension to load up more before getting on the gas a little later on the exit? The push was most pronounced on 3 different sharp (1st or 2nd gear) right handers which turned 120-190 degrees and led out on to a straight. On 2 of those I was following some sage advice I received when I started racing: "Don't try to make up a lot of time in the slowest corner, it will end badly!". Also both of them are very quick transistions for the passenger (from the 2 sharpest lefts on that track). I think my passenger might be more enthusiatic about trying to get a little more forward than with trying to make an even quicker transition.

If we can move the chair wheel back a bit then what symptom should I look for if we have moved it too far?

Also I imagine dialing up the toe-in a little should help reduce the push a bit? Again how do I know if I have too much toe-in? (Will the rig tend to veer right on the straights? Will my lap times increase due to the increase tire scrub?)

So things to do:
- figure out how much of my front suspesnsion travel I'm using
- figure out adjustment options for my front suspension (from memory small changes to spring preload look possible)
- figure out if the chair wheel is adjustable fore/aft

[steve-e]

Also I imagine dialing up the toe-in a little should help reduce the push a bit?

Hardly ever noticed any difference to be honest on the bikes I've been on it's not a huge one from a basic set up, that's one for near the edge.

If we can move the chair wheel back a bit then what symptom should I look for if we have moved it too far?

It's a gradual thing depending how far you move it, but you will lose drive out, you're taking weight off the back and putting it on the front. It will just be like having a cold rear (not a cold seat ) It's surprising how much difference it makes when the bike is well set up, if it's way out to start with you might not really notice. On that note I'd be interested to know wheel weights on the corners of slideys now with the 4 strokes in. I know when I passengered Yangi years back he put the bike on scales to find out the weight on each corner once, something car racers do all the time but sidecar racers are far too knowledgeable to admit to needing to know

Come on people someone join in You all know what it's about and he's in Canada, he's not going to be turning up at Brands in 3 weeks and beating you all

[Alan Richardson]

Chris, i've had an LCR this year and this is what I did. Sidecar wheel toe in, 3 to 4 mm measured over 1 meter. Sidecar wheel towards the rear (if adjustable) Brake bias about 55% front, 45% rear. Camber on all wheels, go by the tyre wear. It pretty much speaks for itself, i.e. get all tyres wearing as flat as you can. Dont bother pi**ing about with temperature guns, etc. Shock absorbers. Set the front soft (ish) and the rear harder. Dont be scared to go quite hard on the rear. Sag front and rear about 20mm to 25mm, although in my opinion it's not too critical. Re-bound and damping slowish, but not too slow. Ride height, about 70mm for an LCR so I would jack yous up ang go from there. More height allows you to 'steer' the back wheel under power more easily. Also remember understeer can be caused by slow in, fast out too. Trying to 'power out' of a slow corner when a higher entry speed will lead to higher exit speed. This takes time (been there, done that ) so it's something to consider. You can make set up as difficult as you like but believe me, it is not rocket science. Get the basics right and concentrate on getting into the corners gradually faster. NEVER (and i mean NEVER) go into a corner on the brakes!!!! This sort of chassis will not like it. Get off the brakes early and drive it through. If you get the back coming round or the chair wheel up, keep a steady throttle. Do NOT shut off! You may get advice from others on here that will contradict what i have just written, but this basic advice stood me well this year. I have been faster than i have ever been and i'm older than ever now!!! (57) Your choice, good luck.

[Marci]

Hmmm - this explains some of the odd handling on our outfit at our last round when we moved the chair wheel forward... Didn't know any of that! How it translates to something a fraction of the size, I'm not sure, but lots of valuable info there from all of ya... ta muchly...

[scud2]

Check the ride height (with the riders on-board.) it should be 65 front and about 75 rear, although this can be altered to suit. The camber can be checked with a camber gauge and should be; 0deg front, 1/2 to 1deg negative rear and 2deg positive side. We check this using a pyrometer after every run, this allows for minor adjustment and compensation for wear. You MUST set ride height first as this will throw the other settings out if altered. Toe in for the sidecar is usually around 3mm/meter but if you are on a tight clockwise circuit, you can go a little more radical with this (we have run up to 9mm at times) if you increase toe-in you should also increase the camber to negate the "snow plough" effect down the straights.
Starting with all new tyres is ideal as you are on an equal footing all round. The position of the chair is used more for balancing grip/steering and i would start with it as central as possible at the beginning.

Dropping the ride height at the rear (slightly) can improve drive. As for the black art of suspension, this would take up volumes.

[ChrisWells]

Ok a bit of an update:

I was a little busy at our last race (exiting the end of a 1/2 mile straight upside down in the first practice on Saturday, affecting repairs & recruiting a stand in passenger before the race that afternoon, filming this most of Sunday: http://www.youtube.com/watch?v=GNritwnjZnc , and then running the final with a gimpy passenger and an underprepped sidecar) so I didn't get to do much on the tuning front.

I did confirm that our chair wheel is not adjustable fore/aft. I few questions on some of the suggestions:
1) How is "ride height" measured at the front and back? I'm assuming the height of the underside of the chassis above the pavement? Are the suggested heights with or without crew & fuel aboard? (oops I see someone already said "with crew")
2) Is the "sag" how far you need to jack that end of the chassis off the ground before the wheel lifts off or how much the suspension compresses when you add crew weight?
3) Assuming about 65mm ride height with about 20mm of sag (once I figure out what that is) at the front, does it not make sense to soften up the front suspension to use "most" of the travel (or harden it up if it is bottoming out)? Ideally I suppose that would be done with the spring rate but I'm probably stuck with pre-load (and possibly damping) adjustments for the forseeable future.

Steve: next spring as I get it all back together I will let you know the weight.