Advice on quick tuning on race day

[Vertigo35 81]

Hi,

so this year I will be running my M05 (fwd) at local races. The local track is indoor tarmack, very slippery. The only tyres that work there are Schumacher minipins. The problem is we don't have access to the track before the race, so a lot of testing is not possible before races.

If I list the settings I can *quickly* change between race rounds :

- tighten/losen ball diff

- change rear camber

- change damper springs for stiffer/smoother

- adjust ride height

Could long-time racers explain quickly what each setting does, or when I should adjust these ? For example, if I observe oversterring at the first race round, what should I do ? Also, what would be a good starting point for a very slippery surface (tight diff, soft springs ?)

Thanks a lot guys 😉

 

[sosidge 624]

Start with kit settings, make one change at a time, don't change anything after the first run as track evolution is huge at the start of the day.

I've run minipins on gym floors in the past, setup is normally similar to outdoor tarmac, you don't need to do anything extreme.

Also minipins wear very quickly and usually fresh ones are a lot faster, especially if you are running the narrows.

[Vertigo35 81]

Thanks a lot @sosidge for some useful advice 

On outdoor tarmac I think I am getting a bit of oversteering already (loosing the rear in wide, high speed turns, when the car takes some roll movement).

Among the "quick mods" I listed above, what would you modify first to improve that ? I tried stiffer rear springs, without significant effect.

[sosidge 624]

Stiffer front springs, not rear.

[Mad Ax 9325]

Assuming the club is of the friendly variety, talk to other racers.  Ask others what they're doing.  They've probably got a baseline setup that will be close to what you need, and in my experience, people are happy to share that.

Also don't be afraid to think outside the box, if the rules allow.  Some people run a lot of weight in the back of an M-chassis car to keep the tyres on the ground.  A few grams over the front doesn't hurt either.

I'm no racing expert, but in my experience, assuming your car has a reasonable (book) setup to start with:

90% of tuning is tyres.  If you've got the wrong tyres, no amount of tuning will help.  Check if you'll need additive and tyre warmers as they make a huge difference.  I only discovered within the last 12 months that it's common to run split compounds - hotter on the front, cooler on the rear.  The fronts will heat up quickly, the rears much slower - see note below about caster hubs.

6% is springs.  Soften for more grip, stiffen for less grip.  (This sounds counter-intuitive if you've read too many boy racer magazines that insist you need to add stiffer springs to unleash the handling potential of your compact hatchback).  Generally you want to go soft at the back and stiff at the front.  Ask what springs everyone else is using.

4% is radio setup.  Set your EPA so maximum input will get you around the tightest corner, and no more.  Expo can help smooth out your inputs on a long straight but IME it makes the car harder to predict when transitioning from small corrections to big inputs.  I went from running lots of expo a few years ago to very little these days.

Grip-roll is a serious problem with M-chassis cars.  It may be different if your surface is low-grip, but where I race (tarmac or carpet) we generally apply a layer of tyre glue around the outer shoulder of the front wheels to stop the cars flipping over in the corners.  Depending on track abrasion and temp, we have to reglue every 1 - 4 heats.  However, too little grip at the rear can also cause grip-roll, if the back end slides until the car is 90 degrees to its direction of travel and then digs in to flip it over.

You may find that handling drastically improves after 2 or 3 laps.  This is probably because the tyres are taking a while to warm up.  Toe-in rear hubs will cause the rear tyres to scrub and warm up faster, aiding rear-end stability (assuming they are allowed in the rules).

Generally we run our M-chassis diffs as tight as we can.  Mine have old style gear diffs which I pack with Blu-tac.  On a hot, grippy day I'll have to repack the diff every 2 heats.

In 2020, a fast racer said to me "after a day of setup, my car is really twitchy and hard to drive, that generally means it's at its peak potential and will give me the best laptimes."  In 2021, another fast racer said to me "I strive for the setup that makes the car easy to drive.  You want the car to be as balanced, neutral and well-mannered as you can, so you can focus on getting the best lines and not making mistakes."  I'm probably paraphrasing here, but the point still stands.  Those are two totally opposite directions you can take when setting up a car.  For me, the latter is true - a neutral setup lets me focus on my race.

I don't really know what all the other stuff like adjustable camber and Ackerman do, no doubt it makes a difference if you're trying to get the top spot in the A-final but I try to have mine set as neutral as possible.  Start with a neutral setup and focus on learning the track.  Not making mistakes is worth 10 times more than tweaking a good setup.

[Vertigo35 81]

Thanks a lot @Mad Ax, this helps a lot ! 

[dlruk 13]

Are you cutting and gluing the TC pins onto smaller Mchassis wheels? Can't tell from the photo. I race TC and now Mchassis on a wood floor. With TC the narrow pins work better than the wider ones. Wear rate is bad as mentioned above. Never tried indoor tarmac (where is this track?) but on indoor wood the grip changes so much throughout the  night as dust etc is cleared up that setup changes are almost pointless.

 

We have only recently started running Mchassis but have gone with the Tamiya rally blocks to keep costs down and easy to fit. My M07 and M05 were pretty terrible in their normal (club winning) outdoor setups. The next visit all I took was just the M05 having put in a very loose kit gear diff, no other changes other than lowering it to about 4mm (smooth floor) and it was much better. Yes you get the odd bit of oversteer but just keep on the power. We have been using additive which helps quite a bit even without warmers

 

Stiffer front springs and a tigher diff will all lead to more understeer. If you have enough front grip/turn in then go that route. I do the opposite for the slippy wood floor as otherwise it just barely turns in, I don't mind snap oversteer occasionally, just keep the power on to pull it straight

[Vertigo35 81]

Thanks, this will be quite helpful, too, and I might lower the car a bit (from 6-8 to ~5mm) before saturday's race 

The track is a large indoor gym with polished concrete floor. I'll try and take pictures.

My wheels are full-size TC wheels, with mods on the chassis to keep ground clearance low and enough suspension travel.

see https://www.tamiyaclub.com/forum/index.php?/topic/97466-the-m-chassis-topic/&do=findComment&comment=933448 

[dlruk 13]

Hmm cunning and yes far less hassle to be able to use TC sized ones instead of cutting and gluing the tyres with a bit removed.