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Old 06-22-2010, 03:17 PM   #1
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Default Compensating for taller tires. How do you do it?

I have been racing nitro sedan for 3 years and still have no clue on the topic . Let me describe my usual race weekend:

1. I start the day with small diameter foams (say 57mm front 58.5mm rear) on the car. I always have a few sets of tires at those diameters so I have no problem practicing and finding setup on them.

2. Now I have a car that handles well on 57mm / 58.5mm tires. I qualify for mid-low pack in the A main.

3. Since our track has 30 min mains, I put taller tires (60mm front / 62mm rear) on the car to last the race.

4. Race starts and the car feels completely different. It has HORRIBLE push, and I am down at least .5 seconds per lap. EVERYONE, including the guys I out-qualified just a few hours ago, passes me easily. After 30 minutes, I finish in the bottom of the A main.

What the heck am I supposed to do? Completely re-do the setup for the mains? Since I am seemingly the only one at my track who slows down noticably in the mains, there must be something I am missing. Help!
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Old 06-22-2010, 03:39 PM   #2
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You have to run the same setup as you do with the smaller tires, as the tires wear in the main, they start to come in, once they are the right size the car allows you to push it more. I've never expirienced a big difference with the bigger tires, the car is not as fast and cant push it as hard, but the feel is the same.
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Old 06-22-2010, 07:08 PM   #3
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You'll need to figure how how much your tires are wearing. In practice try to run as long as you can and measure at regular intervals, you may only need 1 or 2 mm difference for the main. Many guys run the same diameter but a slightly harder compound on the tire that wears the most (left front as an example). Everyone is different though. Setups do change between qualifiers and mains, having a setup for both is a good idea.
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Old 06-22-2010, 07:22 PM   #4
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How about starting the other way? Since smaller tires, lower CG can be faster, why not practice and qualify on bigger tires, to find the best set-up. Then as you run the main, the smaller the tires get, the faster you get?

Just a thought, if you can qualify fast on tall tires, then you can be really fast on smaller tires.

I try to do a little of both, find the best set-up on slow tires (tall) for the main, but true them smaller for qualifying.. This let's me get a good qualifying run, but still feel comfortable about starting the main.
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Old 06-22-2010, 08:29 PM   #5
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Assuming you start final with 60/62, finish with 57/59, this means 3mm wear during final.

This means, the mid-point size is around 58.5/60.5

The complex fix is try to find idea setting with 58.5/60.5, so you are dial-in at mid-point, and tire change across whole final is +/- 1.5.

The easy fix is after you done qualify with 57/59, raise your downstop by 0.75, move spring upward by 0.75. This should give you about the same uptravel/rideheight on 58.5/60.5 tire. Other setting might change a little bit but it's easy fix so live with it....
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Old 06-22-2010, 08:47 PM   #6
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Since you know that you are going to have to run larger tires in the final, try practicing with the larger tires and work on a setup for the final. Another thing to think about is you may have to run harder tires when you go to the larger diameters. Sometimes the softer tires (especially on the front) will fold under a little when the diameter is larger. This can cause the push you are talking about.
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Old 06-22-2010, 10:00 PM   #7
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its seemed to me that if i can find something that works with bigger tires its still good as the tires wear down but a good setup with small tires doesnt seem to work when u put the bigger ones on so i say plus 1 to finding a setup that works with the larger diamiter tires and deal with the minor diffs as they wear i think most imporntant is getting the wear even front to back so u dont loose your spilt that seems to make the biggest difference in handling to me
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Old 06-23-2010, 05:04 AM   #8
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You can setup your car which will work for big tires and as the tires wear down in the final, you can decrease your steering travel when you are pitting if you have too much oversteer.
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Old 06-23-2010, 08:52 AM   #9
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Compensating for taller tires. How do you do it?

1 tooth bigger spur gear, or 1 tooth smaller pinion.

.... use this method for 1st gear only. This way, you still have acceleration power eventhough you are using taller tires.

If your engine is powerful, using taller tires could increase top speed too ( after 2nd gear kicked in ) ..... but not much.

Early this year, I have to use unshaved rear tires too, ... coz my home track become more and more abrassive on tires.

This is how I set up my car before final :

1. I check up my car ( chamber, toe in / toe out, downstop, etc ) with hudy setup system, following my setup sheet.

2. I installed blank rims ( from xray nt1 ) on the car.

3. I set the ride height : 2mm front, 3.5mm rear , with blank rims on the car.

4. That's it ..... I remove the blank rims, and I put new tires on. I dont touch the ride height anymore. >>> this way I am sure my car will not grounded eventhough the foam tires become 2mm thin.
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Old 06-23-2010, 09:08 AM   #10
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thats a good tip ASW im gonna have to give that a try
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Old 07-16-2010, 02:32 PM   #11
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figure out how much tire your wearing in warm ups and 5 min qual. I usally wear 1-1.5 in 2 qual and 2 -3min warm ups. say 15min roughly. Istart 58mm frt 60mm rr (nt1) car runs best at 57.5 rr, 56mm or so frt. generally start my tires for 30 min main 1mm bigger all around so atthe 10-15min mark the car starts really coming in. I do not change my set up from qual. at all.my car does not really handle any diffrent just cant push it as hard up front. hope this helps.
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