Topic: tyres 400/18 -- 450/18

[neil10]

Hi. I have standard 400/18 on is it ok to go to 450/18 in size   thks

[SteveD CB500F]

On a 550, you might struggle with a 4.50 - we used 4.25/85 back when...

My 500 has a 110 rear = 4.33 inches

[neil10]

thks  I have 750 

[TwoTired]

What is your wheel rim width?  Stock?

[Patrick]

I have a stock rim on my K5 750 and I'm, running a 120/90-18 tire. A 120/90-18 tire is 120/25.4 or 4.724 inches wide. A 4.5 inch tire should fit easily.

Patrick

[333]

You cannot take a ruler and convert tire sizes, to or from, inches and metric.  A 110 even converts to different inch sizes front and back.  Use this chart.  It is from the Tucker/Rocky catalog, but is commonly used by most all manufacturers.

[SteveD CB500F]

You cannot take a ruler and convert tire sizes, to or from, inches and metric.

The engineer in me says "bo****ks"

Tyre dealers are trying to dispute the laws of physics here are they?

Sorry, but 1"=25.4mm, even on a tyre. 

[333]

I'm not saying it's right, I'm just saying how it is.  Even the manufacturers have inconsistencies that pop up.  In any brand, different models will measure out differently.  You just can't use logic and rulers to answer these questions.

Go Figure!

[Bodi]

Sorry, inches = 25.4 x millimetres. Tire makers haven't altered this rule.
The chart shown respects this, but metric sizes don't exactly equal inch sizes. A 4" tire, front or rear, is a 100mm tire as close as can be converted (actually 101.6mm). There's no exact metric size for a 3.75" tire (it's between a 90 and a 100) so they show the 100 as the metric replacement, but that does not mean 100mm equals 3.75 inches for a front tire but equals 4.00 inches for a rear tire.
There are a few oddities, like the 4.10 inch size that Dunlop introduced for the K81. Sometimes the marketing department overrules the engineers (OK, always).
Measured maximum tire width will not be exactly the specified size, depending on rim width particularly.

[333]

And that 4.10 tire is not 4.10 inches wide.  If the size is in 1/4 increments, (.25..50...) it is added to the whole number for width(3.25 =3 and 1/4 inch(sort of)), but if the decimal is an odd one like the 4.10, it is a reference to aspect ratio(height).  Most inch tires in 1/4 inch increments are 90% aspect ratio(height is 90% of the width).

[neil10]

thks everyone

[Tower]

You should find @333, that most Imperial measure tyres have aspect ratios of between 95 and 100.  Remember, these tyre measurements have been around a long time, introduced long before sidewall technology allowed for lower ratios.  There were no standard aspect ratios back then, which gave rise to the confusing assortment of Imperial width x height measurements.  Most Imperial tyres are indeed wider than their sizing would suggest, and taller than their metric counterparts (of equal width).

@Patrick, keep the tyre height in mind when matching front and rear wheels.  Wheel height = rim height + 2 x width x aspect ratio/100.  For Imperial measure tyres, the aspect ratio is about 98 for 3.25" dropping to about 95 on 4.50" For Imperial measure tyres, Add about 1/4" to advertised width size, rising to about 2/5" for 4" or wider tyres.