Tire Size Question

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Tire Size Question

Post  Zeeman on Mon Aug 25, 2008 7:19 pm

I've noticed that most have gone with the 205/60's, or 50's series tires.
My 1800R speedo is inherently off by 4-5mph on the high side. (reads higher than actual)
These series tires have a smaller over all diameter and would not help the matter. (just my little brain thinking) Why not go the 70 series, which is slightly taller to regain the speedo?

Are there issues with other clearances in this series tire?

Zeeman

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Re: Tire Size Question

Post  horseman8m on Mon Aug 25, 2008 8:48 pm

It's up to you , if you want your speedometer more accurate or if you like to not have to look for sixth gear , then go ahead and go with a bigger tire.
I went with a 26.2 inch tall tire and it brought the speedo close.
Good luck,
Horse
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Re: Tire Size Question

Post  Dan on Tue Aug 26, 2008 8:35 am

Most 70 series CT's these days are for trucks or SUV's with aggressive tread for mud, snow and off roading, or they're too tall for the X without major mods, most 65's are tall enough to bring the speedo in sync., but not so tall as to need any mods, unless you get 215 fever. Cool walk this way :arrow:
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Re: Tire Size Question

Post  studdog on Tue Aug 26, 2008 9:29 am

I never checked my speedo so I have no idea if it's inaccurate. But the 205 60 is at 64.4 mph when the speedo reads 65. The sidewall height is not an absolute figure. It's a ratio. The sidewall height of the 205 60 is 60% of 205 mm or 123mm. So the overall diameter and circumference are functions of both section width and sidewall height. The factory 180 70 sidewall is 126 mm which is why the diameter and circumference of the two are very close and produce very little difference on the speedo. The factory tire circumference is .74" larger than the 205 60 which results in 7.16 fewer rotations per mile.

Compared with the factory tire, when the speedo reads 65 the 205 65 is at 66.43 and the 205 70 is at 68.46.

Talk about way too much information. For an iron worker I can really get to be a dork sometimes. Smile Good luck.
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Re: Tire Size Question

Post  Zeeman on Tue Aug 26, 2008 5:35 pm

Dan wrote:Most 70 series CT's these days are for trucks or SUV's with aggressive tread for mud, snow and off roading, or they're too tall for the X without major mods, most 65's are tall enough to bring the speedo in sync., but not so tall as to need any mods, unless you get 215 fever. Cool walk this way :arrow:

I have to disagree with your summation of the 70 series tires. Looking at the specs and dimensions of this tire...P205/70R-16 Goodyear Eagle LS-2, which is not a LT or a M/S nor an aggressive tread pattern, but a CT with only a slightly taller profile than the factory 180/70/16. If all these 205/60 & 65 series tires are fitting without major mods, the width section is the same for the 205/70. And there is only a 1.38" difference in height, it should work the same! I have checked my speedo on the 03' 18R and it is off, so by my calculations, this should put me close to right on. The circumference of this tire should give me a speedo reduction of 3.5mph and my gps shows that I'm @ 4mph off.

I am no expert, and as a matter of fact know very little about this whole CT on a MC thing...I'm also just being a bit analytical!!!!

Zeeman

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Re: Tire Size Question

Post  Dan on Tue Aug 26, 2008 6:06 pm

1.38" is a very significant difference, my signature tire is only .5" taller than most 205/65 16's and I had some serious mods to do. Also, when I was shopping I didn't look at Goodyear much, except TT, but General, Bridgestone, Toyo, and Michelin didn't have anything in a 70 I could use, and I was going for the tallest I could squeeze in there while keeping the stock parts intact. You like the 70, go for it, Have Fun, and Good Luck!
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Re: Tire Size Question

Post  Zeeman on Tue Aug 26, 2008 8:22 pm

Cool Again, according to the calculations, the 70 should fix my speedo off-set....IF it works!
Like I said, I know nothing and now that I can't see where anyone has used a 70, it may not fit in the fender! Oh well, it's on order and we'll see when it gets in. It'll either work or it won't, right!
I'll either send it back or eat it! Laughing

I will give feedback when I give it a try!

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Re: Tire Size Question

Post  Dan on Tue Aug 26, 2008 9:44 pm

That tire has an O.D. of 27.3" which is going to make your speedo read less than actual, and you're going to need all my mods plus probably more grinding on the swingarm crossbrace and fender brace, I hope you get it done, but you're really pushin it to the outer limits, and maybe one step beyond. My tire's O.D. is 27.0" and is a little wider than yours, but your larger O.D. puts the widest part of the tire more forward in the swingarm which tapers in close, especially on the left side, check mine: http://mcdarksiders.forumotion.com/vtx-1800-tech-f10/general-altimax-hp-215-65r16-install-ride-wildside-t1089.htm Keep us posted Exclamation


Last edited by Dan on Thu Aug 28, 2008 6:54 am; edited 1 time in total
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Re: Tire Size Question

Post  twin1300 on Wed Aug 27, 2008 7:44 am

Zeeman wrote:Cool Again, according to the calculations, the 70 should fix my speedo off-set....IF it works!
Like I said, I know nothing and now that I can't see where anyone has used a 70, it may not fit in the fender! Oh well, it's on order and we'll see when it gets in. It'll either work or it won't, right!
I'll either send it back or eat it! Laughing

I will give feedback when I give it a try!

Zeeman,

Here's what we have found....that in most cases the numbers and the sizes don't mean a thing... Laughing Laughing Laughing Laughing Laughing Some times our tires a larger or smaller than what is shown! It can only be used for a reference!


.

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Re: Tire Size Question

Post  Zeeman on Thu Oct 02, 2008 3:25 pm

Well I finally got around to installing the P205/70R-16 Goodyear Eagle LS-2.
After the discussions around "major mods & too tall for speedo correction", the 70 series tire did require slight grinding of the crimped lip on the inner portion of the swing arm, maybe 3/16! It took a little wiggling but once it went into the final drive, the clearances were fine. As for the speedo, I was 5mph off before and now I'm balls on accurate with my GPS.

First couple rides to work and I found no big issues in turning or handling. On the second trip as I felt comfortable, I rolled the speed on up and found what I'd call a spongy warbble like feeling above 85mph. As I look I see others have had it too. Was running the tire at about 4psi below the max 44 posted on the sidewall. I have increased to the max. and will check it out again.
Have new front tire and have beads in both, so I don't think it is that.
I've got several things to check from this site, so I'm sure I'll find the right one. I do need to fix this, cuz yes I do run at high rates of juice from time to time! Cool

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Re: Tire Size Question

Post  Dan on Thu Oct 02, 2008 4:22 pm

Welcome Aboard Z, glad to hear you got the 70 in there. cheers I hope you were able to leave the spotwelds intact on the swingarm crossbrace seam, the top and bottom sections are not crimped. If the seam starts to open up, you may want to weld a bead across it. You should be able to get it right by adjusting tire pressure, don't be afraid to go lower, that tall tire holds much air volume, which requires less pressure, I prefer mine at 25 psi, solo, no gear. Depends on the tire, and your preference also. Good Luck Exclamation
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Re: Tire Size Question

Post  Zeeman on Sat Oct 04, 2008 6:35 am

Thanks Dan, I'll keep an eye on the seam, but I think I'm good.
Also, interesting that you say a lower psi may be the ticket! I'd think it would allow more sidewall flex, causing a spongy ride. However, I've seen many say that shock bushing can be a cause and low an behold I do have a bad one. I'll order a set of those this weekend.

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Re: Tire Size Question

Post  Dan on Sat Oct 04, 2008 8:12 am

If you're buying OEM bushings, order lower shock bushings for an 05 or later, F, or C, they are poly instead of rubber, longer lasting, and much better for the same price, a little less even, and good for upper and lower on R, N, S, and T's and early C models, Part no. 52489-HNO-671, there's a typo on the fiche I saw that lists rubber bushing as upper, but the upper is a bearing, so you're probably better off just using part no. to avoid confusion, I doublechecked it. The big wide stable contact patch will amplify other problems. And with a 205 made for a 6-7" rim mounted on a 5" it will cause tread to crown more, nevermind the fact it's designed to carry at least twice the weight that's on it, high pressures could cause the tire to ride more on the center tread section and narrow the contact patch for a squirrely feeling, I believe the sidewall needs to flex so the whole tread section can stay firmly planted while cornering, experimenting with your own set of circumstances is the key, especially since a CT doesn't belong there in the first place. Have fun Exclamation


Last edited by Dan on Sat Oct 04, 2008 10:31 am; edited 2 times in total
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Re: Tire Size Question

Post  dirtwarrior on Sat Oct 04, 2008 9:27 am

Comparing a CT with a MT. The sidewall may be the same but on a MC tire the tread is more rounded so the overall height is more. I think???
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