XRAY - Model racing cars

Hi all,

Had my T4 2016 for a couple of months now, getting quicker all the time, the last couple of meetings in particular I have been plagued by rear end issues with new tyres.

I put on a set of new (scrubbed in) Sorex 32 last week and set a new PB, had I not been held up in traffic I would have been within 7-8 seconds of the outright track record so the performance was good however the rear was a bit loose on corner entry but I just about kept it together with only one tank slapper losing over a second.

I used those tyres again last night, same additive, same setup, track slightly cooler, front grip was good, rear on the initial corner entry was shocking and I kept spinning. When I didn't, the mid/exit rear grip was good but two qualifying runs and the final were ruined due to this

Using 5/6 run and 16 run (yes really!) old 32's in other runs and practise, the car was perfectly balanced front and rear, obviously the lap times were slower but it was balanced with none of this snap oversteer on corner entry

So, any suggestions? I presume with the new tyres the front grip is over powering the rear so I perhaps need to take grip away from the front? I noticed it was a bit better if I was gentler on the steering but couldn't keep this up. I do run quite soft springs but they seem to work there, perhaps stiffer might be better to stop so much weight transfer to the front which is unweighting the back?

I did stand the rear shocks up a hole and tried with no layshaft screws but didn't make much difference. I don't see other drivers changing their setup or having such issues with new/worn tyres. I have changed motor from a Thunderpower to a 24k from my GT12 for the last two meetings, it has a bit more drag (force to turn the rotor by hand) but not sure that would cause this issue alone, I turned drag brake down from 15 to 10% as well

This should link to my setup, diffs I have marked as Down position as per the manuals recommendations for initial asphalt settings, I see other peoples setup guides they have them in the Up position unless I am confusing this?

cheers

Darren

Hi Darren,

It looks like you have the arms moved forward on the front and rear. Have you tried going back to the kit setting of middle/middle? Also, it seems to me that you have a lot of droop. Maybe try .4mm less rear droop to see if that helps control the weight transfer to the nose when you get off-power.

I haven't run both diffs down in a long time, so I can't really answer on that one.

Hope that helps,
Robbie

Hi Robbie,

Sorry the setup sheet confused me with regards to the arms, I have both front and rear as per the manual, 1mm shim either side of the arm

Are you suggesting with the diffs I should have them in the higher position so the tab uses the notches at the bottom?

thanks

Darren

Usually all setups I see and my personal preference is diffs up position. This means notches point downwards.

In your setup rear diff seems too soft. This can cause very nervous and prone to spin car at turn in, especially if track is high grip.
Try 4000-5000.

Maybe you get a bad batch of tires? Do you have another new set to compare? Or put rear tires to the front to see if the car will be pushy now.

This is the track he's talking about, and it's medium grip;



My setup from last years Clubmans (what you see in that video );

Thanks for the advice everyone. I will try some of the suggestions, diffs up, slightly thicker diff oil etc

Skiddins, I was running it with the top deck raised and no screws but had gone back to standard for now, difficult to tell some changes on a club night as the grip changes throughout the evening. Last week I did a 24 309 with traffic (12.45 lap) for reference so a second off what you did at the clubmans last year but it was twitchy and then this week undriveable as mentioned on new(er) tyres

Mustafa yes I tried another set of new and it was the same.

Obviously I would like to get it handling and balanced well on new tyres, but ideally it would stay the same on worn as well. I had only just got it for the Clubmans at the track this year and I don't want to discuss my first visit to your WLRC as that was a disaster but improving slowly at Eastbourne

I will report back after the next club meeting

cheers

Finally had a dry mid week evening meeting! I used the car at a Sunday meet a week and a half ago and it was a bit better after a few changes, diffs up, less toe out, 4000 in the rear diff, old oil had leaked out again....not visible this time, no idea why, new ring and gasket, anyway....used the car last night and still fairly tail happy but I managed to resolve it

Firstly that set of tyres were definately suspect despite setting a PB on them, swapped them front to rear and it was better but still loose. I then loosen the rear belt tension 1 notch, improvement, tightened the front 1 notch, big improvement, now stable, tightened the rear back up a notch and still good. Did 3 more runs with different tyres, all good so seems like it was a combination of duff tyres and the more so the front belt being way too loose. I run the white ones and from new I had to have the front a notch tighter than standard/vertical if you follow, always been a bit loose.

So anyway, with a set of 2 run old tyres and with track conditions not being the best, I broke my PB by half a second, fastest lap 12.62 compared to 12.45 from my previous PB so slower track but more consistent. Started the A final 4th, up to 3rd out of first corner, got over excited and parked on the grass ended up last/8th, worked back up to 4th and ended up 0.6 off 3rd place but still on lead lap so happy with that. Fairly close lap times in qualifying as you can see in the photo! Think I had 2nd quickest lap in the final about 0.05 off

One thing I need to improve which is vaguely relavant to this thread is tyre prep. Car is great at the end of the run but the first minute/few laps it is loose. I was doing 10 minutes of additive with warmers at 52deg last night, striaght to track, warm up lap, sitting for maybe 20 secs. Not sure if I am heating too hot so they need to cool down or I should do additive sooner, make sure tyres are 100% dry then put the warmers back on for a few minutes, probably with new tissue to avoid a hot spot?

cheers all

Darren