Forum

[Martin]

I realize that one could not get
away with this in the UK with your
stringent MOT. but out in the colonies
it's more lenient. Anyway, have a new
100/80 Bridgestone BT45 front tyre
which will be OK for the front, and
a new 100/90 Bridgestone Spitfire,
clearly a front tyre too with the
directional arrows, BUT thought I
would fit it to the REAR since both
are 'H' designation, and intend lo-
key riding. Out here no one was too
fazed at this sacrelige. but some said
to reverse the tyre's direction when
installed on the rear for 'traction',
whilst others said keep it the correct
direction for 'rain drainage', Anything
would be better than the rock hard K70s
currently on there. Thank you!

[Les H]

Hi Gordon. About your new tyre sizes. The 100/80 is just under 4" wide but with a diameter of slightly bigger than a 3" tyre. The rear 100/90 size is also just under 4" wide with a rolling diameter of the original 3.5" wide tyre. I think it's likely the front 100/80 tyre might be too wide and rub on the mudgaurd brackets and bolts, so check carefully. If you are fitting a front tyre on the rear (Obviously not recommended) It depends very much on the tread pattern. If the tyre has a central slot then rain drainage won't be to much of a problem, A motorcyle tyre, being half round in profile will mean there is almost certainly somewhere that the rain can flow along the tread gooves to escape and be released, and only at high speed will the water clearing performance be degraded significantly.... For best wear life I would reverse the arrow direction compared to the front, as the tread pattern is designed to resist forces in a particular way and being driven it needs to be reversed, otherwise chunking up or excessive wear will occur on the leading edges of the tread blocks. If you just intend to use the bike for slow riding it might be ok, but should you have an accident an eagle eyed policeman might spot that you have a front tyre on the rear and you might be prosecuted or have your insurance made invalid, so is it really worth that worry just to save 45 quid?

[Jojje]

I once had a Metzeler Lazertec 3.50-19" front tyre fitted on the back of my Enfield. Professionally fitted by a competent mechanic who insisted fitting it the other way around than it would be on the front. This is supposed to be normal practice in these cases - there aren't plenty of tires of this size available. (Expensive and overkill but I was in a bit of a hurry.)
No problems at all.
You may be able to fit a 4" wide (or metric equivalent) tyre on the back. I once did with a Mitas H02 (I accidentally ordered wrong size). But - there are differences with manufacturers. In other words a 4" tyre from a manufacturer A can be several millimeters wider than a product from a manufacturer B. Manufacturers may publish these measurements on their sites. But even these vary depending of the rim on which it is fitted.
When a 4" tyre was on my Enfield there was just a noticeable difference in cornering: a bit more effort was needed but nothing serious. On the plus side was more easily used centre stand.
Have a look what are teutonic friends are wearing: http://www.royal-enfield-forum.de/viewt ... 21&t=68559

[Alan R]

Hi GORDON--- On my 2005 Classic 500 Bullet I'm currently running},FRONT}--- AVON SPEEDMASTE Mkii at 3.25 x 19. and REAR}--- AVON ROADRUNNER at 4.10 H 19 (100/90 H 19). with a nice central groove. Next up on the rear will be a DUNLOP K70.

[Martin]

Thanxs for your constructive responses,ship-
mates. they do help. Was simply ulitizing
tyres one already had from previous orphan
projects. By chance, a set of Pirellis one
ordered for my ancient widow maker Ninja
Z1000R arrived today, and on querying the
shop owner the same question as I presented
here as to the wisdom of swapping tyres about,
he waved to a pix of his sponsored sports
bike racer who used up front tyres on the
rear with impunity. As I knew said shop owner
had some Norton Internationals also, I thought
he would be a diehard purist, aghast at the
suggestion, but he reminded me anything stuck
better than the old days. Les's explanation
of wear patterns to be expected is helpful too
Meanwhile, friends at an earby automotive
tyre shop seem more concerned at the tyre's
age code. Apparently, old stock is viewed as
suspect, car or 'bike. Gordon