got a tire question for nick...........rollout

medic_33

medic_33

Member
To explain we are talkin about street stocks here...... stock metric suspension......My issue has become stagger and rollout..... Without having a pullbar, Zbar and all the other bars and geometry,, to load the corners with engine torque when, where and how you want to......a SS guy has to preload his suspension to work everywhere on the track. me and my team has figured this out....but things like ride height and tire rollout become very important and sensitive areas.....take a car that is unbeatable and (drastic to make my point) change the RF 27.5 89-90 rollout and put on a 26.5 82-83in tire and you have completely changed the car.... it will have no bite and probobly be to loose to drive......that could be said about all 4 tires on a SS...... another issue is stagger....stager effects in my opinion the most important part of the racetrack... the corner exit.....too much stagger and you cannot put the power down and you"ll get beat by a guy who can,,, while your feathering the throttle...trust me thats frustrating...not enough stagger and your pushing to the wall.....that ****s too........

so with that over explained.....

Most SS guys are hitting up mod guys for decent take offs.......which in my opinion is a good practice for the sport.....and can easily keep (at least myself) supplied with tires for the season....throwing on the occasional new "H" a couple times a year ..... I like to call those nights superman nights....

so my problem lays with getting the right size tires in the right places on my car....... I try to rotate my RF and LR as much as possible to keep em fresh and the wear to a minimum.....causes problems with consistancy.....

so my questions are (bare with me some may sound dumb....I'm just trying to put together the whole package)

1. right now my best plan is to stretch a tire,,,,pump about 40 psi in it and lay it in the sun.....hope for the best.......is there a better way and a way to do it with more accurate and consitant results.??......
2. can a tire be shrunk?? I know,, this may be a dumb question.
3. what is the maximum average stretch you can get out of a tire and
4.does it stay that size or does it eventually shrink back to its original size... does it need maint.?
5.is this harmfull to the tires and there composition.....right now I have 2 26.5 tires laying on my black trailer in the sun pumped up to about 45 psi........ need to make them way bigger....

Just thought you wanted to talk about tires for a change......and this is an issue ive been fighting all year......
any ideas????

Kris Blankenship.......
 
Kris, keep in mind stagger is what helps the car turn and probably has lesser effect on corner exit vs. cornering ability through the corner. You should tune your stagger on how well the car rolls through the center of the corner. It sounds like your looking for a way to get better bite off the corner....Weight transfer is what really gives you bite (wheel weight). Lets put it this way....all 4 tires touch the track, but the more weight pushing down on the tire is what traction is. With out the traction devices that late models have you have to rely on springs, shocks, and lead. You can have two matched cars with the same exact tires and set up and have the same lap times, change the shocks to slow down or speed up weight transfer, lets say one car is set up complete opposit of the other and they handle totally different.
Getting the right size tires on the corners is important, but i would only use tire size as a means of tuning the handle of the car through the corner and not exit/entry. JMO
 
thought of another question

what about new tires hows a guy to know what he is buying.......how does the chalk numbers corralate to actual rollout of the finished product??.......all i know about this stuff is how dad did it and what ive seen done....and...there has to be a better way..........
 
champ i think you missed the point......my car handles just fine...... just explaining how tire size effects your setup and when i get used tires i have to adjust the sizes to get what i need to keep my car consistant........but i do agree with you advise and stagger does effect center as well and tires sizes are a great way to fine tune your car through the night ......
 
yea let me rephrase......when i get BJ's old tires.......how do i make em' into big boy tires.....hehehehe....... by the way BJ you let go of that last H way too soon.....i'll get 4 more nights out of that baby...........
 
True, i guess what i has hinting at was it might be easier to figure out if you get a lr tire that is 1/2" smaller in size from your last tire, you would need to tighten up the car just a little and know how or what to change to offset the smaller tire. So let say you put the smaller tire on you may have to stiffen the lf spring to make up for the loss of wedge/bite. Could make it easier and not have to worry about size as much. I know it is hard to get the right size tires. I could not get anything less than 4" on the latemodel for the rear with the size tire I wanted to run. I spent alot of time with string and scales to figure out how much rear steer i would have if i mover this bar or that bar to a different location. I have a big note book on every combination of hole locations and how much rear steer i would have with that combination. It took 2 days to do all of that. Nick will shed alot of light on the tire questions, but the chalk marks are most time bigger by a couple of inches on average. There are some things you can do to change a tire size, but they will not be very big changes. Just a note though, during the race your tires build up pressure and grow in size if you run air, but try using nitrogen in the RR (will not build as much pressure due to lack of expansion) and air in the lr tire, you will loose stagger due to the build up of pressure in the LR and your car will tighten up as long as the tire stays warm. I tested that at highland one night and I found the LR grew 2.5" and 6lbs of pressure and the car tightend up during the long runs, however the heat build up caused loss of grip and a loose condition late in the runs. I ran a soft tire on LR and a hard tire on RR.
 
seems like adjusting your car to tire sizes could be a little inconsistant.....wrenching on jackbolts can be a little sensitive and i imagine you could get pretty far off i about a month of racing...without a weekly scale session and my setup guy dnt work that hard........althought i do like the nitrogen idea good way to tighten your car up as a race goes on.......dont know much about it though
 
i think i missed half of what you were talking about, but the 26.5's seem to be in the 84 1/2 to 85 1/2" area, and the 27.5's seem to be in the 87 1/2 to 88 area, which makes it tought to get 2" of stagger. if you are having trouble with your stock 4 link car getting off the corner, keep putting more LR in it. last year in my gumm car i was up to about 250 pounds LR and i was out running pull bar cars with it
 
oh yeah, and only way i have seen to not 'shrink' a tire, but to keep it on the short side, is to run it 1 or 2 nites and then let it sit for a month or 2 off the wheel, and then when you mount it back up it seems an inch or so shorter than it was. just like after the winter how the tires seem shorter....
 
you guys are hurting my feelings

car handles fine...... bites well.....just wanted to discuss tires a little........although i was wondering if tires shrank......i too have notice after stretching a tire need to keep an eye on it because it seems to go back over time...........hmmmhey jimmy you got any 26.5 D 's layin around.......thats the tire i burn up the most on the LR.......well ive seen you race........your stuff is prolly smoked up racin slicks by now lol......with all that motor i mean..............thanks guys....keep the thoughts coming
 
Jimmy Cummins said:
oh yeah, and only way i have seen to not 'shrink' a tire, but to keep it on the short side, is to run it 1 or 2 nites and then let it sit for a month or 2 off the wheel, and then when you mount it back up it seems an inch or so shorter than it was. just like after the winter how the tires seem shorter....
Click to expand...
I used to do that as well. Run them 2 nites.......dismount and let it set for a month. It does shrink......and i think it actually makes the tire last longer.
 
First off sorry for the delay on the reply, it wasn't letting me into the forum section if I signed in so I couldn't reply to the question.

Naturally a 27.5 has a softer sidewall than a 26.5(spring rate) because it is taller. This can be an adjustment that most never think about. If you were to put a 26.5 where you normally have a 27.5 it will naturally take away sidebite because of the loss of dynamic flex you get to that tire. At the same time though you can gain forward bite because the tire will load quicker and visa versa. Spring rating tires would be a huge advantage to your class, if for anything it would be more predictable what the car would do just by putting a different tire on a certain corner of the car.

Stretching a tire isn't that difficult, the harder part is keeping that tire to stay the same size. The best way to stretch a tire and keep it perdictable is to "shock" the tire. What you want to do is take the valve core out and put it in an oven, hot box, whatever you can design to have a controlled heat source, once you have that get it to 250 degrees for 10 minutes. When you remove the tire put the valve core back into the stem and air the tire up about a half inch bigger than you want it. Then you need to submerge the tire in ice/water for 5 minutes. This will help give the tire memory and it will keep it's size far more consistently.

Shrinking a tire you can do the same thing but just don't put the air back in the tire will cooling the tire. I hope that helps answer some of the questions or problems you are having.
 
thanks nick

so you kinda get my dilema thanks for your help....kinda helped me undrstand the value of a 26.5 over the 27.......still wonderin' though if stretchin tire (my way or our way) hurts the compound, or hinders the bite and while i got your attn.......another debate we have been discussing around the shop is optimum tir pressures for an E-mod roughly lets use say the right front for example.......thats on a 3200 lb car........
 
oh and by the way......my fix to my rollout problem was to ditch the 26.5s and just put shorter 27.5s on the LR.....its just easier to keep my stagger around an 1 1\2.......................seems more consistant....i dont need to stretch them and dont have to worry about em shrinkin back to the original sizes......thanks
 
your still not going to catch your little brother even though you saw what i run now! :) ...With a 27.5 on rr you will not get one ussually smaller than 87 ussually with 14-18psi. The 26.5s will roll out at the tallest 85 1/2 ussually. so if you want less than an 1 1/2 inches of stagger then your best bet would be to run 27.5 on rear on average. you take the same new 27.5 marked 90 and mount them up and with the difference of psi you will get 1/2inch. This is what i have figured out but hoosier is been really incosistant on there tire sizes more this year it seams for some reason. Although you know the stagger guage i use for all my tires and she's tweaked!lol....thank god i'm on 4 3/4 bc i know your on 5o5! life would be so much easier for you if you would of went to 4 3/4 bolt pattern! haha...I would just ask your wife if you can go buy 20 tires and you wouldn't have these issues! She wouldn't care, you don't need electricity to race. Priorities first you know!
 
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