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smirk-racing

Help tuning XV-01 for on-road use

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Hi All,

I have finally gotten my XV-01 all sorted out mechanically (bought it used, unfortunately it came with all kinds of damage and issues). 

Now I am trying to tune it for "rough on-road use", which is to say, normal asphalt and pavement, but often pretty rough, broken, covered in gravel, etc. 

The main problem I'm having is that the car has a strong tendency to spin out. For example, if I give it a lot of throttle, it will sometimes spin out in either direction while accelerating up to speed. More often, if I try to turn hard, it will do a complete 360, and then keep going. If I let off the gas and keep it going straight, I can recover and continue, but if I stay on throttle or try to turn, it will keep spinning.

How do I dial-out this tendency to spin out? So far, I've tried adjusting the spring pre-load front and rear (from lots of pre-load down to none at all) and nothing I tried made much of a difference.

In addition, when it turns, it tends to "skitter" or skip. I think the rear tires are hopping sideways a bit. Not sure if that is normal or not.

For reference, I am running a castle 2-pole motor with the torque dialed WAY down (almost to the point that I can't get the wheels to break loose on clean dry asphalt, which is about a 3 out of 10), and I have the punch control set to be pretty soft. All of this is to help make the car more gentle to drive.

I am running traxxas touring car tires (the ones that come on the traxxas 4-tec) but I also have foams and various other tire options.

Thanks in advance!

 

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I have spent a LOT of time getting up this learning curve this year being new to onroad/rally. First thing i will say is messing around with springs won't do much. The most powerful tools you have are tyres then diffs IME. If you have some other tyre options try them out just to gauge performance. I found most treaded scale looking touring car/road tyres (i have tried absima and tamiya) are garbage for actual driving. No grip. Like driving on ice. I have some rally blocks on my rally car, and the soft tamiya ones are ok, and cheap chinese ones that come with wheels off ebay can be better but quality is a bit variable. The best option i have found for more road baised cars in the fleet (but still rough tarmac eith loose chipping etc) are Schumacher SST tyres. Best thing about these is you can buy them in different compounds, so you can help the grip balance by putting softer white compound rear and yellow medium comoiund front. These are great and work on damp, cold tarmac i have been experiencing recently. 

Next is diffs. Get some 1 or 2 million cst diff oil and pit it in the front to lock it up almost. Put the kit 900 diff oil in the rear to leave it almost open. This should massively improve the situation. 

As for setup, despite broken tarmac i have been amazed at how well my FF03 with 6mm ride height copes, hardly ever tripping up over gravel bits, but low kerbs do catch the body so you will scuff that up. My rally car runs about 14mm ride height with 5-6mm droop front and rear and this floats alobg almost buggy like, and will happily jump off kerbs. Maybe try setting the car up around 10mm ride height (ie with battery on board ready to drive) and adjust the droop (the up travel from ride height to full extension) to around 5mm (you may need to put internal spacers in the damper to achieve this) and see how you go. You don't need a crazy setup station for all this. I use an old shelf board for a flat surface and slide lego bricks under the car until they just catch then measure the brick height. Do the same until the tyres are barely touching the ground and that's your full extension (ride height plus droop, so 15mm suggested in this case) 

 

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ThunderDragon, this is really helpful - thanks so much. I will start trying out some of these adjustments.

 

I am surprised to hear you're using 1M weight oil up front - that's definitely pretty heavy (although the gears are tiny). Currently I've built the car to stock (I replaced the diff gears with metal a while ago). 

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Just now, smirk-racing said:

ThunderDragon, this is really helpful - thanks so much. I will start trying out some of these adjustments.

 

I am surprised to hear you're using 1M weight oil up front - that's definitely pretty heavy (although the gears are tiny). Currently I've built the car to stock (I replaced the diff gears with metal a while ago). 

No problem. That thick front oil seems counter inutitive but it does work. My TT02 Type S with locked front diff and open rear diff will still oversteer on the throttle even with said Schumacher tyres, so although it sounds extreme it doesn't completely change things.

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24 minutes ago, ThunderDragonCy said:

I have spent a LOT of time getting up this learning curve this year being new to onroad/rally. First thing i will say is messing around with springs won't do much. The most powerful tools you have are tyres then diffs IME. If you have some other tyre options try them out just to gauge performance. I found most treaded scale looking touring car/road tyres (i have tried absima and tamiya) are garbage for actual driving. No grip. Like driving on ice. I have some rally blocks on my rally car, and the soft tamiya ones are ok, and cheap chinese ones that come with wheels off ebay can be better but quality is a bit variable. The best option i have found for more road baised cars in the fleet (but still rough tarmac eith loose chipping etc) are Schumacher SST tyres. Best thing about these is you can buy them in different compounds, so you can help the grip balance by putting softer white compound rear and yellow medium comoiund front. These are great and work on damp, cold tarmac i have been experiencing recently. 

Next is diffs. Get some 1 or 2 million cst diff oil and pit it in the front to lock it up almost. Put the kit 900 diff oil in the rear to leave it almost open. This should massively improve the situation. 

As for setup, despite broken tarmac i have been amazed at how well my FF03 with 6mm ride height copes, hardly ever tripping up over gravel bits, but low kerbs do catch the body so you will scuff that up. My rally car runs about 14mm ride height with 5-6mm droop front and rear and this floats alobg almost buggy like, and will happily jump off kerbs. Maybe try setting the car up around 10mm ride height (ie with battery on board ready to drive) and adjust the droop (the up travel from ride height to full extension) to around 5mm (you may need to put internal spacers in the damper to achieve this) and see how you go. You don't need a crazy setup station for all this. I use an old shelf board for a flat surface and slide lego bricks under the car until they just catch then measure the brick height. Do the same until the tyres are barely touching the ground and that's your full extension (ride height plus droop, so 15mm suggested in this case) 

 

Another amazing, quality response 👍

Gotta love TC and all it members-utterly superb bunch 😊

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Your basically going to need to dial out the front grip, 

before you do any of that, you need to make sure you have perfectly equal left to right camber settings. This doesn’t mean having equal length turnbuckles, that makes an assumption everything on the car is 101% perfect to witching 0.01mm which it is not. A setup station is only about $100 and it’s a life long tool in this hobby and can be adapted to most 1/10 on and off road vehicles. What it does it allows you to get perfect camber settings. This is done with the car in the station fully loaded up (battery etc).

up front less aggressive negative camber (so closer to neutral) is a good start, then firming you the front suspension to reduce roll up front. This can include fitting a stiff sway bar. In a rc car, in most situations a swaybay will typically remove grip. 

you probably want to remove too much body roll by limiting suspension travel either by shortening the shocks or limiting the droop. You might like a bit more travel/droop possible out back to try keep those back tires on the ground. 
 

you may want to consider moving to racing slicks that have temperature ratings, using a higher temp rating up front and a lower temp rating out back. What range of temperature you choose will depend entirely on the type of weather/conditions your playing in. 
 

the XV01 is a front weight bias vehicle much like most real cars, so managing that extra up front weight takes a little trial and error. It is a uncommon approach because rc cars that are mid motored are simply much easier to drive and therefore faster on the track. The drawback of mid motored rc cars is that they are much less dynamic and less rewarding to use, but front motored cars like the XV01 do need a little more understanding and work to get the most from them. IMO it’s well worth persisting, I have so much more fun with my xv01 than any of my TT,TB,TA chassis cars. (Exception my TA03F).

there is people who can’t get along with the xv01 due to either lack of understanding about vehicle handling or just expecting it to jump/handle like a mid or rear engine chassis which it’ll never do. It is a more challenging chassis in every aspect no question. 

Juls

 

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Juls1, thanks for this great info. Much appreciated!

11 hours ago, Juls1 said:

Your basically going to need to dial out the front grip, 

 

On that particular note, I'm confused about something. It is not the case that the car spins out during a really hard turn, rather while accelerating it will tend to spin out even with a small amount of left or right input (i.e. a gentle turn). That makes me think front grip might not be the issue, because if the front tires didn't have enough grip to make such a gentle turn, they'd hardly be able to turn the car at all.

Thanks for the tip on the set-up station - I will start looking at those.

 

 

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11 minutes ago, smirk-racing said:

 

Juls1, thanks for this great info. Much appreciated!

On that particular note, I'm confused about something. It is not the case that the car spins out during a really hard turn, rather while accelerating it will tend to spin out even with a small amount of left or right input (i.e. a gentle turn). That makes me think front grip might not be the issue, because if the front tires didn't have enough grip to make such a gentle turn, they'd hardly be able to turn the car at all.

Thanks for the tip on the set-up station - I will start looking at those.

 

 

Get the front diff oil really stiff. It was pull the car straight out of turns. 

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1 hour ago, smirk-racing said:

 

Juls1, thanks for this great info. Much appreciated!

On that particular note, I'm confused about something. It is not the case that the car spins out during a really hard turn, rather while accelerating it will tend to spin out even with a small amount of left or right input (i.e. a gentle turn). That makes me think front grip might not be the issue, because if the front tires didn't have enough grip to make such a gentle turn, they'd hardly be able to turn the car at all.

Thanks for the tip on the set-up station - I will start looking at those.

 

 

First port of call then I would free up the rear diff and stiffen up the front diff, just like others suggested. You might like to try some better tires as well. 
 

if the car loops out more going one way than the other then your camber settings are all wrong left to right. Setup station should fix this.

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ok might seem a stupid question but... are the tires glued?

running brushed or stock silver i could get away with not gluing the tires... but not so for brushless

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No stupid questions... but i've done plenty of stupid things, like installing diffs backwards (makes for a rather poor driving experience ;)

 

In this case, the tires are indeed glued... 

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Ok, did some testing and it feels like too much weight is being transferred to the front when I lift off the throttle leading into a turn. Which adjustments should I make to reduce weight transfer to the front?

 

thanks!

 

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59 minutes ago, smirk-racing said:

Ok, did some testing and it feels like too much weight is being transferred to the front when I left off the throttle leading into a turn. Which adjustments should I make to reduce weight transfer to the front?

 

thanks!

 

You need to reduce the droop at the rear. This is the amount by which the suspension compresses from fully extended to ride height with battery on board. As mentioned above you can measure it by stacking thin lego bricks under the rear gearbox until the wheels just touch the ground, then pull the blocks out, measure them, and drop the car a couple of times to settle suspension, then measure ride height. You want maybe 5-6mm of droop. On touring cars there are screws in the arms which act as down stops to adjust this. Not sure if the XV01 has these. If it doesn't the quickest way to test is to raise the ride height front and rear usibg preload collars to bring the ride height closer to full extension hence reducing droop. The other thing to try having had a quick look at the manual is move the shock location on the arms to the outermost position. This might help too. 

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7 minutes ago, ThunderDragonCy said:

You need to reduce the droop at the rear. This is the amount by which the suspension compresses from fully extended to ride height with battery on board. As mentioned above you can measure it by stacking thin lego bricks under the rear gearbox until the wheels just touch the ground, then pull the blocks out, measure them, and drop the car a couple of times to settle suspension, then measure ride height. You want maybe 5-6mm of droop. On touring cars there are screws in the arms which act as down stops to adjust this. Not sure if the XV01 has these. If it doesn't the quickest way to test is to raise the ride height front and rear usibg preload collars to bring the ride height closer to full extension hence reducing droop. The other thing to try having had a quick look at the manual is move the shock location on the arms to the outermost position. This might help too. 

Could you also stiffen up the front shocks to prevent so much weight transfer forward?

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2 hours ago, Jonathon Gillham said:

Could you also stiffen up the front shocks to prevent so much weight transfer forward?

That would definitely help too. Droop is a really powerful setting though. It's what i had to get my head around this summer learning about touring cars

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8 hours ago, ThunderDragonCy said:

You need to reduce the droop at the rear. This is the amount by which the suspension compresses from fully extended to ride height with battery on board. As mentioned above you can measure it by stacking thin lego bricks under the rear gearbox until the wheels just touch the ground, then pull the blocks out, measure them, and drop the car a couple of times to settle suspension, then measure ride height. You want maybe 5-6mm of droop. On touring cars there are screws in the arms which act as down stops to adjust this. Not sure if the XV01 has these. If it doesn't the quickest way to test is to raise the ride height front and rear usibg preload collars to bring the ride height closer to full extension hence reducing droop. The other thing to try having had a quick look at the manual is move the shock location on the arms to the outermost position. This might help too. 

If you have no droop at rear, no weight transfer will occur to the rear. I believe you mean take the droop out of the front not rear.

With the XV front motor bias all the weight is at front already. So droop screws need to be turned in clockwise at front to remove the droop.  you will only need 1mm travel maximum. This way, when throttle is released, the front will come up around 1mm.. which results in the weight being transferred to rear for grip.  

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Install the droop screws into the suspension arms if they are not fitted, limit the down travel of the rear suspension to your desired ride height so that the arms cannot extend when the rear of the car is unweighted. This will help prevent some of the weight transfer to the front of the car, you can install the droop screws up front but it's less neccessary when your only wanting to transfer weight to the rear, under acceleration the front will lift transferring some weight backwards, what your trying to avoid is having that weight taken away when you come off throttle, so the front suspension needs to be a bit firmer to reduce its ability to compress heavily under braking or cornering loads, thereby helping your back end staying hooked up. 

High grip situations are much different to typical rallying, but all of the tuning tools are built into that chassis, it virtually has all the adjustments of a TRF Racing touring car, but in a rally package, if your wanting to transfer from on to off road with the same setup, then your going to have to accept some compromises somewhere be it on the tarmac or in the gravel, your not going to have a perfectly setup car for both, but you should be able to balance out a ok setting for both scenarios with a bit of time and patience. If the intention is for the car to be on road all the time you might like to consider a XV01 Pro TC, and have a car for each scenario.. that's what I ended up doing. 

Juls

 

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