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Author Topic:   tires sizes and RPM change
ss27
Dirt Full Roller

Total posts: 47
posted May 17, 2005 04:30 PM  
A bigger rear tire will lower the RPM's of the motor. How much tire size change to lower 500 - 700 Rpm's.

Also will timing lower RPM's


Zypher
Dirt Roller

Total posts: 22
posted May 17, 2005 06:12 PM  
Timing is not a good choice in my opinion. You can retard timing slightly and it will kind of act as a limit on how fast it will tach up thus making a cheap way to get traction and if you have traction your rpms will drop. It would be better for you to get the timing set to your specs that are max. performance and not worry about that anymore as a ministock doesn't produce massive power it shouldn't be nessecary to mess with timing after its set. Tire size does make a differance but not 500 or 600 rpm unless again the tires make the car tighter which will reduce rpm. If your car is handling corectly you might want to go ahead and start looking for a gear if you want to turn it less.

b4racing
Dirt Forum Champ
Total posts: 626
posted May 18, 2005 12:09 AM  
what I have figured is for every inch of roll out is 100 rpms.

Zypher
Dirt Roller

Total posts: 22
posted May 18, 2005 01:30 PM  
So looking at 5'' more tire isn't a very good option. Thanks for telling what it is though I never had figured up how much it would take.

bigcityracer
Dirt Freak

Total posts: 431
posted May 18, 2005 07:09 PM  
I have a Celica and drop from 195/70 to 185/70 and went from 5,300 rpm to screaming 6,700 rpm. I was just missing the power curve of the cam and made all the differnets in the world. To say gearing changes by any certain amount I don't think is a true statement, all cars react different to different changes.

Zypher
Dirt Roller

Total posts: 22
posted May 18, 2005 07:22 PM  
195 to 185, I have never saw changing from one size to the other make any major rpm changes. When you went to 185 you probably loosend the car up making it turn more.

bigcityracer
Dirt Freak

Total posts: 431
posted May 18, 2005 08:40 PM  
quote:
Originally posted by Zypher:
195 to 185, I have never saw changing from one size to the other make any major rpm changes. When you went to 185 you probably loosend the car up making it turn more.

That was the only change. I was hitting the center of the straightaway and coming on from there really strong. After the change it comes on strong right out of the corner all the way into the corner. Yes running harder down the straightaway gave excelent cornering with motor braeking the tires for a nice turn keeping RPMS up.

Zypher
Dirt Roller

Total posts: 22
posted May 19, 2005 06:08 PM  
Well I guess that shows how much cars can vary. Maybe that small change put the motor where the peak power was for the cam? I dont know glad that it worked for you though.

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