|
|
Register To Post |
| jhammons01 | She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
 
|
Here is the earlier thread.
http://www.corvetteguruforum.com/modu ... id=132309#forumpost132309 well, today I finally got around to changing the rears. 255 45 18 is what I put on just now....now, that tire size calculator was way off from what it stated..... The old tires were more like 23" tall..... Stock 1984 16" tires are 26.4" if you measure the overall height of the tire.....So, yeah, there was a huge difference....and not a good one either. I was really put out by the drive and the acceleration of the smaller tire. Unless I romped on it, Cavaliers where beating me from stop light to stop light and I DID NOT LIKE that. This tire I just put on is 26.2 overall height......man!! Huge huge difference in highway ride and acceleration out of the hole. Highway speeds, if felt like....well it was like I was going slow and I look down at the speedo and it was 75ish.... Then off the line....just let the clutch out and the car is gone.....everyone, including Cavaliers, are in the rear view.....and I mean, I am not hammering it off the line...just letting the clutch go and this car just naturally (with the right size tires) takes off. That's the update. Rear tire size can change the gearing.... |
||
Posted on: 2012/3/2 22:22
|
|||
 Transfer
|
 
|
||
| bogus | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Grand Imperial Pooh-Bah
 
|
Yup, it sure can. The equation is called "roll out".
It takes the tire diameter and integrates it with the gear ratio. Given time, I can conjure up the formula. I used to use it ALL the time with RC car racing. The end result is an index number, as to how far the vehicle moves in one rotation of the tire. Or something like that. |
||
Posted on: 2012/3/3 5:06
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| jhammons01 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
Ya know, there is more too it as well. I think the car sitting so low in the back affected the alignment via stance.....I'm not so sure but it sure rides much better and looks much better with the bigger rubber in there.
|
||
Posted on: 2012/3/3 14:46
|
|||
|
Transfer
|
|
||
| bogus | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Grand Imperial Pooh-Bah
|
tire height should not effect geometry... that is a fixed factor based on the car. Change the tire will not change camber or caster.
It's all in the roll out. When I raced RCs, you would ask the question, what is good roll out for this track. They would give a number, either in inches or mm and you can then compare to your current roll out and adjust the ratio from those numbers. TIRE CIRCUMFERENCE / TRANSMISSION RATIO / (SPUR / PINION) Now, we would take the tire circumference with a caliper. Another trick we did, if the car used foam tires (touring or oval), we would put them on a lathe and then turn the foam down. About 1/2 the mass. On an oval car, that meant a circumference drop of about .25" This also made the tire last longer AND improve cornering by getting rid of a bunch of unnecessary sidewall height AND with the extra material removed, it was less prone to getting these chunk of sidewall removed. The lathe allowed us to put a nice angle on the sidewall to better prep it with. The roll out equation can be used to solve for X, too. If you have the roll out, or the ratio, you can calculate back. |
||
Posted on: 2012/3/3 20:44
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| BillH | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
The Stig Moderator
 
|
Quote:
Right. One thing changing tire sizes will do is change the chassis rake. We sometimes play with rake to change the handling characteristics of the car before we do a test day. Rides better - always, even if you put on new tires of the same brand & model. Tires work harden just like metal, the durometer changes abit every time you drive the car (gets harder). That's why we determine when to change race tires by the number of heat cycles no matter what the tread gauge holes measure. Did this on my Silverado last year, took off old Bridgestones, put on the exact same new ones and there was a huge improvement in the ride. |
||
Posted on: 2012/3/3 21:28
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| Churchkey | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Guru
 
|
A taller tire on the front will decrease the scrub radius as compared to stock suspension design & tire size.
A smaller tire will increase the scrub radius. |
||
Posted on: 2012/3/4 3:38
|
|||
|
Transfer
|
|
||
| bogus | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Grand Imperial Pooh-Bah
|
Scrub radius, tho, IIRC, isn't a fixed measure within the geometry of the suspension - meaning - it can't be adjusted.
It is, tho, a ratio within the tire width. So yes, you can change scrub radius, but you haven't changed the actual geometry of the vehicle. |
||
Posted on: 2012/3/4 7:38
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| jhammons01 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
ok, tell me this, back in the 70s when we used to use "air shocks" (installed at Sears) to jack up the back of the car....
.....what would that do to the rake? |
||
Posted on: 2012/3/4 14:44
|
|||
|
Transfer
|
|
||
| BillH | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
The Stig Moderator
|
Quote:
Yea, I remember. But that would be a huge change in rake vs changing tire size. Depending on how much you jack it up, it would throw things off. On alignment, it would affect the castor some. Usually that made it a bit easier to light the tires up.  |
||
Posted on: 2012/3/4 14:49
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| jhammons01 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
OK, so, mine would "at 75mph or better" have a sort of vibration that would oscillate....meaning....it would come and the stop...then start up, vibrate, then stop.....
I "KNOW" I have a front end issue that needs addressing, but the rears wore in a funny way was well. The car no longer oscillates at 75+....it's nice. The front left tire still has a bit of a vibration.....I'm looking into that, most likely a worn ball joint. |
||
Posted on: 2012/3/4 15:40
|
|||
|
Transfer
|
|
||
| BillH | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
The Stig Moderator
|
Quote:
Probably the old tires were a bit out of balance, had a broken cord, etc. Same thing on my Silverado, had a bit of vibration, totally went away with the new tires. |
||
Posted on: 2012/3/4 15:57
|
|||
|
_________________
Every man dies but not every man lives. |
|||
|
Transfer
|
|
||
| jhammons01 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
Trying to resize pics.....PITA Pictures are worth a thousand words... Before with small 18s http://forums.corvetteforum.com/pictu ... 10334&pictureid=47891 After with tires put on just last week http://forums.corvetteforum.com/pictu ... 0334&pictureid=106165 No changes to the ride height via suspension issues....just tire size changed. "I think" it looks much better and it seat of the Pants SOTP feel is much much better..... http://forums.corvetteforum.com/pictu ... 0334&pictureid=106167 Look at the distortion on this pic, makes it look like the front wheel leans in.... http://forums.corvetteforum.com/pictu ... 0334&pictureid=106166 **Edit - click on the links, the IMG tag won't handle a php rendered image. - Bogus |
||
Posted on: 2012/3/12 18:39
Edited by bogus on 2012/3/12 19:01:06 Edited by bogus on 2012/3/12 19:01:15 Edited by bogus on 2012/3/12 19:01:29 Edited by bogus on 2012/3/12 19:03:45 |
|||
|
Transfer
|
|
||
| bogus | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Grand Imperial Pooh-Bah
|
The new tires look much better. They fill the wheel wheel like it should!!!
|
||
Posted on: 2012/3/12 19:05
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| jonszr1 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
Quote:
|
||
Posted on: 2012/3/13 2:59
|
|||
|
Transfer
|
|
||
| jonszr1 | Re: She's Back.....(earlier thread continuation) Tire size issue | ||
|
Senior Guru
|
Quote:
|
||
Posted on: 2012/3/13 3:04
|
|||
|
Transfer
|
|
||
You can view topic.
You cannot start a new topic.
You cannot reply to posts.
You cannot edit your posts.
You cannot delete your posts.
You cannot add new polls.
You cannot vote in polls.
You cannot attach files to posts.
You cannot post without approval.
|
|