Blowouts - What causes them

[Gentlefoot]

Competed in the 60 Lap ATC GP yesterday. Did much testing to ensure tyres would last. Did 21 laps before blowout on R3 front and 28 on R4 before losing the back and having to plant the accelerator (XFR) to get it back - this blew my fronts too.

Thing is, I never had a problem with the rear tyres during testing.

I'd planned a stop at lap 20 and one at 40 on R3s. I had good pace and when I pitted the first time I was up to 6th of 23! Came out in 8th. 17 laps into the second stint and the rear right blew sending me into a wall - fortunately right by the pit entry. I dropped to 12th.

This screwed me completely because I would either have to switch to R4 fronts to do the extra 3 laps, or pit again later. I figured I'd lose more time on the R4s so planned to pit on lap 55 (only 18 laps more) and then run a light fuel load and r2s for the last 5 laps. Unfortunately on lap 49 the rear left blew! Only 12 laps into the 3rd stint. Unfortunately it was in T1 so I had to do the whole lap on a rim. By the time I came out of the pits I was 15th. Gutted. Finished 13th in the end.

Wierd - I managed to do 28 laps on these rears with no probs but in the 2nd and 3rd stints they only lasted 17 and 12 laps repectively. I didn't drive any harder so wonder why they last less time in the 2nd two stints.

Any ideas on this would be greatly appreciated.

[Funnybear]

Does the arse end squirrel around a bit? Lateral motion (In real life) will cause a good deal a wear and tear to the tyres. If the car is moving sideways alot during the race (If you have a four wheel drift setup or an oversteery one) then the rears will generate alot of heat causing them to break down. Softening the rear suspension and increasing the the PSI might be two quick fixes . . . other than that . . . . dunno.

[Vain]

Did you observe something strange in F9-view? Like flat spots or excessive heat?

Vain

[nikimere]

Sometimes flat spots on the rear tyres are caused by the inside back tyre not having much downward pressure applied to it when braking and cornering at the same time. The inside rear wheel lifts almost off the ground but the tiny bit that is still touching the the ground locks up and thats how you get your flat spot. Every lap it flat spots on the same place until in blows.

[Jakg]

it could be the setup, i have 2 aston nat sets that both give the same times, but one can screw a set of tires in 3 laps, and the other one was going for 20 laps, tires on left were staying at 100 centigrade, and the rights were virtually stone cold, and yes this was on the XFR!

[B2B@300]

Well in a race there is alot more going on in your head :D and you may not be driving the same as you were in practise (even if you think you were :tilt:) i.e. your driving doesn't have too change too dramatically for tyre wear to increase significantly and this is very noticable in FWD cars, I've seen quite a few seasoned drives struggle with tyre wear in longer races in FWD cars :scratchch. So your not alone :) In real life this very issue is what sets the top drivers apart from the rest of the pack, it's not just fast lap times that win races but fast effecient laps that do :D

[colcob]

In my experience I always drive harder and heat the tyres more in a race then when testing, just because there is so much more going on and you are thinking about an awful lot more things that when testing alone.
I tend to find you do a lot more little lockups, more small losses of traction etc. even though you dont really notice it.
If your R3's lasted 21 before a blow out in testing then banking on doing 20 laps stints in race conditions was a pretty risky strategy.

[Gentlefoot]

Believe me, I drove hard in the 23 lap test and even overheated the fronts but no problem. In the race I lapped consistently within 1/2 a second each lap. They lasted 20 laps fine in the first stint, when you would expect me to be pushing harder while everyone is close. Second stint only 17 and third only 12. I assure you all I did not push any harder or change my setup. The tyres showed no unusual signs in F9. In addition, a fellow racer had the exact same experience. We tested together and neither of us had probs with rears. We used different setups for the race but suffered the exact same problem.

Only thing that was a bit wierd is during the second stint the car seemed to get very oversteery but after the pit stop handling appeared to return to normal as it was in the first stint. Final stint handling was normal and yet tyres only lasted 12 laps!!

I was thinking maybe rear body damage may have been the cause if some rubbing was happening but I would have thought this would have shown up in F9. I didn't have any significant contact with anything until after the first tyre blow.

The mystery continues. Clearly not many of us run these long races so maybe that's why no-one has experienced this problem. If it were a 20 lapper the problem would not have appeared.

[Gentlefoot]

colcob - it wasn't the rears that went after 21 laps - that was the front. I never had a rear blow in testing even after 28 laps! I don't know how much longer they would have lasted. yet stint three they only lasted 12! This is why I'm confused.

The fronts lasted the 20 laps in each stint as I planned. I did several tests and R3 fronts always went in the 21st lap which was why I was happy to take the risk. And I was spot on - R4s are 2 seconds a lap slower and the R3 fronts lasted the 20 laps in every stint. It was the rears that I had a problem with even tho they lasted 28 laps in testing.

[AndroidXP]

So, what exactly were the rear tyres showing? All cool and plenty of rubber left? Or was the rubber getting thin, although in my experience that's pretty hard in a FWD? Maybe the sidewalls were getting too hot (low tyre pressure) and they gave up? :shrug:

[Gentlefoot]

67% fuel at the start of each stint so fuel was exactly the same for all 3 stints so it can't be that

Kev - I know what you are referring to but this effect is far more subtle then the effect I experienced in stint 2. Also, it only seemed to happen on right handers. It was the rear right that blew in the 2nd stint. If the two things were related you would expect the rear left to blow.

[Grivage]

Did it definitely change the rear tyres at each pit stop?

If so it does sound quite strange. Would be nice to see a replay if someone has it? Only that will give us the full situation and hopefully an explanation.

[danowat]

Does indeed sound odd, I dont suppose LFS models punctures at all?.

Dan,

[Gentlefoot]

That's what I was wondering. Maybe there is some debris moddeling in the game where people can drag crap onto the track that can cause punctures. I had one or two instances where I put a couple of wheels on the grass myself.

I was pretty sure all tyres were changed at the stops but I will check on the replay tonight. Sure I looked during the stop itself. I always have F9 switched on.

Yes I do have the replay but 23 racers over 60 laps of a 1m:50s circuit makes for a damn big mpr file! Not sure where I could post it. It may be available on the ATC team website.

[Vain]

You're pointing me towards something... Is it possible that slight damage (minimal) caused slight changes to the wheel's geometry (toe, etc.)?
I did notice that when driving off the track the FFB sometimes changes permanently until you restart the race during my preparations for the Westhill-60-lapper. This might be due to minimal damage (not visible in F10) and may also have caued your tyre wear. I don't exactly recall wether the weird-FFB-feeling went away after a pitstop or not.
Can you review the tyre-values (camber, toe) in a replay?

Vain

[Theafro]

I had a similar problem on lap 39 (planning to stop on L40/42), although i'd set the 'change tyres if wear >' to 70% on the first stop, my rears didn't get changed. I assumed :shrug: , that they would last at least until the next stop, but near the end of the next stint they blew :(. after reviewing the replay, (a long, long, long proccess) it seems the first one went under braking, and the second blew after i lost the back end, the tyres were thin on the inside edges and stone cold.

My theory is, as the weight drops off the rear end, as fuel is used. The rear brakes tend to lock up a bit more, and the wear gets exponentioally higher as they thin out and cool down, combine these two factors and you get a slightly unpredicatable wear rate. add in the fact that we were racing, and I'm pretty sure that's the reason.

My solution, More front brake bias and more rear tyre pressure. and maybee keep a better watch out for flatspots early on while they're a little more obvious.

And i'm pretty sure the tyre wear check in the pits takes an average reading rather than the lowest point. Might be one to watch out for in future.

BTW good effort gentlefoot, a tough race for most of us.


URL of replay to follow.....

[colcob]

Hmm, its interesting, I tend to think that the theory of slightly locking the unloaded inside rear under trail braking is the best one.
I wasnt suggesting that you weren't pushing hard in your testing, just that in my experience, I just dont drive as tidily in a race as I do in testing, even if I'm lapping quickly during testing. There might just be an accumulation of micro-errors that you dont notice while racing hard that add up to a flat spotted rear.
It would be worth posting the MPR if you have some webspace big enough for it.

[Gentlefoot]

I found the more practice I had the smoother I became and needed less and less lock so I'd be surprised if I drove in such a way as to cause more tyre wear.

I had mine set to change if 60% worn so I will check tonight if the rears were indeed changed.

I've also noticed that toe can be knocked out in a collision but I ususally notice such things.

Afro - great race wasn't it. I was very surprised to see you still behind me after 30 odd laps. You were quick on those R4s man. I switched to R3s front!

[Vain]

I didn't talk about collisions. I talked about driving over a curb, or going over some gravel for 20 meters. That has caused permanent changes in the FFB for me several times.

Vain

[Gentlefoot]

Sorry Vain - I didn't read your post carefully enough. FFB changes? What wheel do you use? I've never had this happen to me. I use the Logitech MOMO.

[danowat]

Upload the reply to yousendit or something like that.

Dan,

[Vain]

I also use a Logitech MOMO (Racing).

Vain

[Gentlefoot]

Dan - I'll have a look and see how big it is tonight - the replay that is lol.

Vain - you got me worried now :)

[spankmeyer]

I've had few instances where I have crashed or driven over rough terrain with my car, causing the chassis itself to bend. No damage shown in F10 but I felt something had changed in the car through ffb and it got fixed when I did a pit stop without changing tyres or adding fuel. Quite far fetched, but I assume it can happen.

[Vain]

In theory this works this way: You drive off the track over a curb, you get a very short peak-load that shows in the F10 view as an orange flash, one tyre has a very small change of geometry and when the tyre was one of the front tyres the steering-forces cange due to this minimal change in toe, camber, or whatever.
At least that is what I figured. Might also have been a bug in LFS's FFB-code. :shrug:

Vain

[Gentlefoot]

spank - I've noticed this too.

vain - the only thing similar I've had is where the lower wishbone becomes damaged and the steering gets knocked out so you have the wheel at 45 degrees when driving straight. Which circuit did this happen at? Fern Bay by any chance? big kerbs there.

[Vain]

No, Westhill and Kyoto were the last I recall.
Note that the F10 view reported *no* permanent damage. Not the least. I didn't even see any flash in F10, I just figure it would have shown up if I viewed it.

Vain

[Gentlefoot]

Do you know if anyone else has had the same thing happen?

[Vain]

Obviously spank. ;)
And perhaps you. :D

Vain

[Theafro]

Afro - great race wasn't it. I was very surprised to see you still behind me after 30 odd laps. You were quick on those R4s man. I switched to R3s front!

I had a busy race!:schwitz: here's the .MPR :- http://theafro.budshovel.co.uk/

(BTW it might take a little while to update, you might just get a bad picture of me in the woods looking rough! damn easyspace!)

[NotAnIllusion]

You said it was your right rear that blew? Perhaps the one thing that constitutes to the blowout is the rain channel (or whatever else the long narrow thing is) in the long left hander before the long right hander to sector 3. On several occasions during the race my right rear got 'caught' in it in such a way it could have scrubbed heavily against the inside tyrewall. Over 20 laps it could add up to enough wear to cause the tyre to blow even though the F9 screen is showing no apparent signs of the inevitable.

Having said that, I ran with r3s at the front and r2s at the back with two stops on laps 20 and 40 respectively. I got caught in that slit several times, occasionally causing heavy sliding but I had no problems even though I pushed really hard towards the end of each stint.

[Gentlefoot]

Same strategy that I was planning then. I know the thing you mean just as you turn into the flat out left hander. I try to stay away from it but I did run over it a few times. Thing is, it was the right hand rear in the 2nd stint but the left hand rear that went in the 3rd stint. I'm starting to think the rears didn't get changed at the stop. Check it tonight and let you know.

There's you're replay then boys - see TheAfros post - same race

[Vykos69]

Is there a replay of the race? One could have a look at it, and analyse a bit...

[felplacerad]

hey gentlefoot i hope you dont mind me borrowing your thread.

tonight i'll be participating in an event in which i'm planning to drive the fxo. im not too familiar with fwds, and i think im going to be in alot of trouble. the races (1st 15 laps, 2nd 27, iirc) are going to be held on fe green. i've done some testing; my right front wheel is unpleasantly red (on the surface, not the inside) after only ~5 laps!

does anyone have some tips when it comes to fwd racing? obviously i should not skid the tyres too much, but other than that? :)

[AndroidXP]

I only have a bit experience from XFR racing but from what I know most people are turning way too much. They don't understeer extremely, but the same or even a slightly better radius could be archieved by much less steering.

Just try forcing yourself to steer less alltogether or alteast return the steering to lower angles after the initial impulse. If you're running a setup with locked or high diff, remember to use throttle AND brake while turning in, as this greatly reduces the initial push such a setup causes.

[Vain]

Higher tyre pressure, locked diff, good heat distribution (inner and middle about the same, outer slightly cooler), and never have the tyre scrub or squeal. When the tyres produce a scrubbing sound they are already on the way to overheat.

Vain

[Theafro]

I only have a bit experience from XFR racing but from what I know most people are turning way too much. They don't understeer extremely, but the same or even a slightly better radius could be archieved by much less steering.

Just try forcing yourself to steer less alltogether or alteast return the steering to lower angles after the initial impulse. If you're running a setup with locked or high diff, remember to use throttle AND brake while turning in, as this greatly reduces the initial push such a setup causes.

Definately, you've really got to avoid using too much lock, it makes the difference between lasting 5 laps and lasting 25, especially if it's a tight one with lots of braking/accelerating. Toe out can help, but it can give a slightly mushy feel to the front end.

BTW Replay url works now! :D

[Grivage]

Ok i havent finished watching it all yet but it doesnt change the Right Rear at the first stop but does change the Left Rear.

I can only presume that an incident or as discussed above the inside wheel going light and locking easier has caused the left to show as more worn than the right even tho the right is obviously taking much more load around the oval.

Im guessing that something similar may happen at the next stop but the left rear will not be changed and a similar result may occur.

Yup was right about the Left rear not being changed but also the spin you had caused by the 1st blowout did a lot of damage to the Left rear although not enough for it to be changed. I'd say you were unlucky tbh

[2nd EDIT] lol the roll on lap 44 also doesnt help the tyre situation tbh scrubs some more of that sucka [/Edit]

[Final EDIT] lotsa dirt on the tyres and scrubbing it off wore out the left rear along with the incidents mentioned above. Was a thoroughly enjoyable race to watch :) Even at the last stop it only changed 3 tyres so you were lucky in one respect after all the spins on the pit in lap to finish. You need to adjust your pit strategy with regard to the tyre wear. I know this will be changed in future but obviously this doesnt help you now.

The way i work it is this. for the first stop i woulda had the tyre value at 30 percent. for a third of the race it would change only the tyres which will not last to the end. Assuming as in this case it changes the lot the next one i would adjust it to 50 percent as this applies the same principle but only since the last tyre change. Not fool proof by any means as it assumes consistent driving etc etc but to date hasnt let me down yet.

Hope this is all clear [/Edit]

[Hallen]

I have had virtually new tires blow when I had a major lockup... I got cut off. Boom, the tire blew. Pretty realistic in a way.
I have also had tires blow just as I banged across a curb. The tires were getting thin, but had several laps left in them. I hit a curb too hard, the guy behind me who was on new tires hit me, we both rolled. I ended up on the wheels just before pit-in. He landed on his back. Race ruined for him:( .
I tried to push the tires too far. If you can do 20 laps in testing, then expect less in the race. Not necessarily because you drive any different, but because stuff happens and you need a bit of insurance. Plus, factor in that extra pit stop compared to driving an entire lap with a blown tire. That pit stop starts looking pretty good.

I have had good success on longer races by going with R2 tires and doing a 3 stopper instead of a 2 stopper. I also usually set my change tires setting to something very low. I figure it isn't worth the few seconds you gain by not changing the rears as compared to getting new rubber all-around.

I am not saying you did anything wrong... just stating my opinion.

[colcob]

I've not had the rears blowout, but I have had the strange experience when you have some kind of violence happen to the car, and it feels all wierd through the FFB but no damage is showing on the F10 view. I've always assumed that it was actually the wheel itself going slightly out out kilter as a result of being flung around by me and the FF motor.

[tailing]

You've got your answer imo, the fact you didn't change the tyres is almost certainly the cause. I've just finished a 4 round league in the XFR, 3 races just over an hour, the last a two driver team event 3 hrs long.
With the XFR you can't bank on the rears being able to last two stints even if they look to have more than half the tread still left after the first stint.
Our first race was KY Nat Rev, I did a one stopper and didn't change the rears, they lasted but not by much it seemed in the end and the handling was affected with the wear and the fact they cooled down.
In testing for the third race at AS Nat my left rear blew on the second stint when I didn't change them. It started locking up for T1 and kept locking on the same spot, I had at least a third of the tread left on the tyre display but after 3 or 4 laps it went. In the race I did change all tyres and finished but one of my team mates didn't and spun out, his tyre didn't blow but he spun cause he lost too much grip as they'd cooled too much.
In the final 3hr race Latch and I changed all tyres on each of our four stops and we ended up winning (against the likes of Chaz :D). We did stints of 27-29 laps with R2's all round at BL1. The extra time in the pits didn't really cost us and meant we had a nice handling car all race.

While the focus in the XFR is usually all on the fronts the rears are still important. From my experience your best to change them when you change the fronts because you do run the risk of flatspotting them. Even if you don't they tend to cool down too much, losing grip and getting quite taily.

[AndroidXP]

I've not had the rears blowout, but I have had the strange experience when you have some kind of violence happen to the car, and it feels all wierd through the FFB but no damage is showing on the F10 view. I've always assumed that it was actually the wheel itself going slightly out out kilter as a result of being flung around by me and the FF motor.
What I noticed is that a frontal crash, for example plowing through a tyre stack, may screw up the wheel caster, either making the FF lighter alltogether or in extreme cases inverting the caster so the wheel tries to pull in either direction instead of centering. I experienced this numerous times (also, no damage shown in F10 menu) and driving with that is very very weird.

[nikimere]

It happened to me in AS Club ESL testing. It IS due to the inside rear "unloaded" tyre locking up during braking and turning into the last corner.
Eventually after 20 laps or so it blew.
To fix it i move the brake balence slightly more towards the front and i didn't have any problems after that.

[Theafro]

The way i work it is this. for the first stop i woulda had the tyre value at 30 percent. for a third of the race it would change only the tyres which will not last to the end. Assuming as in this case it changes the lot the next one i would adjust it to 50 percent as this applies the same principle but only since the last tyre change. Not fool proof by any means as it assumes consistent driving etc etc but to date hasnt let me down yet.

Hope this is all clear

Unfortunately this dosen't quite work, i'm damn sure that LFS takes an average rather than reading the lowest part :shrug:, what you describe was exactly what i had done, but LFS didn't seem to pick up the flatspots, increasing front bias is problematic too, you'll loose the dynamic balance required for some corners (the ones with awkward/curvy braking zones) and it seems that the only way to go is to change all you're tyres, even if the rears look good for another stint, like i said before, tyre wear (especially on the rear) seems to increase exponentially as they wear/cool, thus making predicting wear a little hit & miss:D

[Gentlefoot]

Grivage - thanks mate - didn't have time to look at the replay last night but I guess that's the answer. So infact the rear right lasted 37 laps and the rear left lasted 48 laps.

Just to make it clear to some other people - it WAS NOT the rear tyres that blew out after 21 laps in testing - that was the front. I NEVER suffered a rear tyre failure during testing even after 28 laps. Even then it was the FRONT tyres that blew in testing.

Next time I will just set the tyre change if wear > setting lower. Reckon that will avoid the problem.

Thanks for all the info everyone.

[Grivage]

Grivage - thanks mate - didn't have time to look at the replay last night but I guess that's the answer. So infact the rear right lasted 37 laps and the rear left lasted 48 laps.
Right rear yes 37 laps, The Left rear was changed at the first stop so it lasted 28 laps. Not as long as you would think but it took a pounding from the 1st blowout spin, the roll on lap 44 and a few excursions to the grass which caused the back end to step out a little more towards the end of its life.

Unfortunately this dosen't quite work, i'm damn sure that LFS takes an average rather than reading the lowest part :shrug:, what you describe was exactly what i had done, but LFS didn't seem to pick up the flatspots, increasing front bias is problematic too, you'll loose the dynamic balance required for some corners (the ones with awkward/curvy braking zones) and it seems that the only way to go is to change all you're tyres, even if the rears look good for another stint, like i said before, tyre wear (especially on the rear) seems to increase exponentially as they wear/cool, thus making predicting wear a little hit & miss:D
Like i said not perfect but how i approach most races, although at dSRC most long races we run are only 1 hour so usually only 1 stop. After thinking a little more on this i prolly would of just set it to always as you rightly say better to lose some time rather than a lap of puncture fun :D