Confused over tire sizes.. Inches? Metric?

Drumwoulf · Post by **Drumwoulf** » Thu Jul 12, 2007 2:45 pm

Question: 100/90x10, 100/80x10, are they the same as
3.50x10? Slightly bigger? Smaller? Will they fit on the 125 Buddy's rims
which now have 3.50x10's on them?

Also, what is the metric equivilant for 3.50x10?

Moch thanks,

ThisDude · Post by **ThisDude** » Thu Jul 12, 2007 4:42 pm

3.5 x 10 equals 88.9 mm wide and 88.9 mm high you can't find 100% aspect ratio tires in metric sizes the best is 90% which means 100/90-10 are 100 mm wide, a little less than 1/2 inch wider, and darn near the same height, 90 mm, which is important beause you don't want to go any smaller and exacerbate the speedometer inaccuracy. Actually to make the speedometer completely accurate you'd have to go to 4.5 x 10 tires, huge really and they wouldn't fit.

To find out the size of the metric tires the first number is the width of the tire in this case lets take 120/70-10. It is 120 mm or 4.72 inches wide. The second number is the aspect ratio is a percentage of how tall the tire is compared to it's width. So in this case it's 120 times .70 or 84 mm, 3.31 inches tall. The last number is wheel size in this case 10 inch.

KidDynomite · Post by **KidDynomite** » Thu Jul 12, 2007 5:28 pm

ThisDude wrote:3.5 x 10 equals 88.9 mm wide and 88.9 mm high you can't find 100% aspect ratio tires in metric sizes the best is 90% which means 100/90-10 are 100 mm wide, a little less than 1/2 inch wider, and darn near the same height, 90 mm, which is important beause you don't want to go any smaller and exacerbate the speedometer inaccuracy.

So, you're saying we would need 90/90/10 and that doesn't exist.

Also--not to start another thread, but--I'm begining to believe my speedo is off even further than I thought. Are there any adjustments we can make to correct this?

mikalius · Post by **mikalius** » Thu Jul 12, 2007 6:06 pm

I don't think there is anything we can do. As i have posted in a previous thread. I too think the speedos are about 10mph off at least. I have tested with several different gps units as well as had a cop use his radar gun. He stated that i was only going 40mph when my speedo said 50mph. And that seems to be accurate with all the gps units i have tested.

ThisDude · Post by **ThisDude** » Fri Jul 13, 2007 6:06 am

90/90-10 is only 81 mm high, you need a tire thats 88.9 mm high to be exactly 3.5 x 10. The closest is 100/90-10 which is 90 mm high. Unless there is an 88.9/100-10 which would be the exact metric conversion of a 3.5 x 10 tire.

There is one thing I'm thinking of that can fix the speedometer and it shouldn't be too hard. Since the odometer also is affected from what I measured on my 40 mile and now a new subsequent 160 mile planned trip on my gps, there is also about a 15% error on the odometer. So I need to make a gear reduction system that will take a 1 turn input and output .85 turns and bang both the speedometer and odometer will be fixed. All I need to do is get some correct sized gears and make a gear case, cut the speedometer cable and splice in the gearbox. Since I work in a hobby store I can get a small 17 tooth pinion gear, that'll clamp onto the cable, matched to an idler gear and another 20 tooth pinion attached to the other end. When I make them I'll put up plans here.

sparty · Post by **sparty** » Fri Aug 03, 2007 4:57 pm

can a 400 tire (instead of 350) be used in the back wheel? My local motorcycle shop can't find a 350 tire (guess his source had them in back order) so he thinks 400 might work. I am not sure.... help?

krylonics · Post by **krylonics** » Fri Aug 03, 2007 5:34 pm

Couldn't you just order one and have them put it on for you? I guess I'm assuming you were going to have the shop do the work.

sparty · Post by **sparty** » Fri Aug 03, 2007 5:40 pm

I know... I was going to do that, but I thought it's cheaper to buy locally because of shipping, and when I stopped by the shop last week, he said he should be able to order a 350x100 without problem, but a week later he said they're out of stock. today, he said he can order a 400x100 right now, but I don't think that will work. I paid already so I guess I don't have much choice now. just kind of bummed because there's a scooter ride tomorrow.

I think for the next replacement, I will just order a zippy 1 online and have the shop change it...

cowgirl helmet · Post by **cowgirl helmet** » Fri Aug 03, 2007 6:43 pm

ThisDude wrote:All I need to do is get some correct sized gears and make a gear case, cut the speedometer cable and splice in the gearbox.

Oh, is that all?

I am pretty intimidated by the technical expertise on here. But I'm learning a lot from you all.

DarbyWalters · Post by **DarbyWalters** » Fri Aug 03, 2007 7:31 pm

Actually Bridgestone makes the Bridgestone Scooter in a 100/100/10 in tubeless...Front and Rear...both are ~$38.00 each.

http://www.bikebandit.com/product/3391

Unless I am reading the chart wrong...

ThisDude · Post by **ThisDude** » Sat Aug 04, 2007 12:52 am

Those 100/100-10's are just 4 x 10 tires, metric tires never have a 100% aspect ratio and 4 x 10's are too big for the buddy, you'll lose torque and on top of that probably rub the rear fender. If you want a wider metric with the same sidewall height go with 100/80-10 tires you'll corner better with more grip because of it's flatter contact patch. But you'll find you'll need to countersteer more because the scooter will tend to want to straighten itself up instead of just falling into the corners like the buddy normally wants to do. But hell if that page isn't the most confusing I've ever seen. Because they give you metric measurements for the tire and also absolute inch measurements of sidewall height and overall width. I guess if you know what all those numbers mean you'll be well informed of exactly how the tires will fit and behave on your bike. I'm surprised they didn't give shore hardness and tire compound with all those numbers they're throwing around.