OK--What do I do now?
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,470
Likes: 2
From: levittown pa. usa Even a bad day with my `Vette, is better than a good day at work
St. Jude Donor '10
OK--What do I do now?
I just picked up a set of oem CE wheels, with like new Bridgestones for my `87 coupe. The original tire/wheel combo for my car is "16. The CE combo is "17. Now when I go down the road at 40mph, the digital speedo says I`m doing about 65mph. How do I correct this minor problem. Also, everyone I talked to said I would need spacers to run these wheels on my car. Ron at Contemporary Corvette, where I bought the wheels said thats 
, they will work & look ok without spacers. I put them on, & they look fine to me. 
Ken
, they will work & look ok without spacers. I put them on, & they look fine to me. Ken
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
there are some of those wheels designed to work on the earlier cars...
As for the error... with the difference in wheel size, versus, tire profile, it should be a wash... what are the 16" tires again? I can do the math...
As for the error... with the difference in wheel size, versus, tire profile, it should be a wash... what are the 16" tires again? I can do the math...
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,470
Likes: 2
From: levittown pa. usa Even a bad day with my `Vette, is better than a good day at work
St. Jude Donor '10
Thanks: I`m tire math " challenged " myself
old tire size is 255/50/zr16. New tire size 285/40/zr17
Ken
old tire size is 255/50/zr16. New tire size 285/40/zr17
Ken
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
last time I tried to post this, I got a database error!
here goes... the old wheels were 24.75" tall, the new ones, 26" tall!
That's a big difference... you will have to change the speedo gear on the tranny... to what? I donno.
here goes... the old wheels were 24.75" tall, the new ones, 26" tall!
That's a big difference... you will have to change the speedo gear on the tranny... to what? I donno.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
I think the old data base error has hit again. P255-50 R16's are approx 26.1" tall. I haven't done the math, yet, I just know the tires. I think the 285/40/17's are considered a "plus 1" and SHOULD be the same diameter.
RACE ON!!!
RACE ON!!!
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by kenv
Thanks: but if they are, why is the speedo way off?
Ken
Ken
An indicated 65 mph at a true 40 mph, is a whooping 62.5% error. There is a bigger problem here, than a tire size switch.
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,470
Likes: 2
From: levittown pa. usa Even a bad day with my `Vette, is better than a good day at work
St. Jude Donor '10
Hmmm, the only things I replaced were the tires & wheels
Ken
Oh yeah: all the tires & wheels are the same size 9.5 x 17". They are all from a CE, but I don`t know if they are from the "same" CE. They may all be front wheels. I don`t know if this makes a difference.
Ken Oh yeah: all the tires & wheels are the same size 9.5 x 17". They are all from a CE, but I don`t know if they are from the "same" CE. They may all be front wheels. I don`t know if this makes a difference.
Last edited by kenv; Jul 25, 2004 at 10:50 PM.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,470
Likes: 2
From: levittown pa. usa Even a bad day with my `Vette, is better than a good day at work
St. Jude Donor '10
Ummm--- no, I just bought them this weekend. Put them on saturday.
speedo worked ok with the "16 wheels. The car has the Z52 suspension, I don`t know if that makes a difference or not.
Ken
speedo worked ok with the "16 wheels. The car has the Z52 suspension, I don`t know if that makes a difference or not.
Ken
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Your speedo problem was NOT caused by the tire change. The speedo does NOT care if the tires or the wheels came off of the same car or if they are off the front of something. The speedometer reading is based on distance the tire travels per revolution (rolling circumference) and the rear axle ratio. Since you made an insignificant change in tire size, your speedo problem has another cause.
RACE ON!!!
PS. It just dawned on me. You didn't happen to inadvertantly hit the display switch on the dash from standard to metic, did you? Forty mph is 64.36 KPH. I'm betting BIG money on this one!
RACE ON!!!
PS. It just dawned on me. You didn't happen to inadvertantly hit the display switch on the dash from standard to metic, did you? Forty mph is 64.36 KPH. I'm betting BIG money on this one!
Last edited by CFI-EFI; Jul 28, 2004 at 08:44 PM.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,470
Likes: 2
From: levittown pa. usa Even a bad day with my `Vette, is better than a good day at work
St. Jude Donor '10
DOH! :bb :bb Thanks: You guys were right. I was changing an ip bulb the same day I changed the wheels, & must have hit the english/metric switch. If it weren`t for the knowledgeable folks on this forum, I would have gone down the road in the metric mode for the next six months, going 
& 
Thanks again
Ken
& Thanks again
Ken
