Tyre size

[Murf]

Hi my 1975 550 K1 has standard rims and came with a 110 x 19 front and a 120 x 18 rear  tyre, from what I read these tyres are too wide for the rims, they are really old anyway and I need to replace them as part of my rebuild.
I can get a pair of Bridgestone BT 46  100/90 x 19 front and a 110/90 x 18 rear, at what passes as a reasonable price for tyres these days and I really like Bridgestone tyres. Even got them on my car👍

However I want to check if these sizes are ok as I am struggling to find any imperial sized tyres to suit.  Also what tyres have people found tend to suit the 550 as I am open suggestions about tyre make.
Thanks

[Oddjob]

You could consider this. If the rims currently fitted aren’t in the best of condition then fit the rims off the 750, unlike the 500/550 which got 1.85 rims the 750 got 2.15 which will allow you fit wider tyres without sidewall flexing that would occur if using the standard rims.

I fitted Lester alloy wheels for the same reason, 2.15 rims. I ran 4.10 front and 4.25/85 Pirelli Phantoms and they were awesome, which equates to your 110 and 120 sizes.

[Johnwebley]

I previously used Avon

3.25x19 f
4.00x18 r

Now have Bridgestone,

Feel great, run them at 28 f and 33 r,

If you use 90/90x19 f and 100/90x18r,I find it lowers the bike, makes for good handling but scrapes to easily



Sent from my SM-A546E using Tapatalk

[Oddjob]

Could it be the better handling which allows you to get the bike over that causes the scraping though John?

Personally I found the 500 easy to get everything scraping regardless of what size tyres were on, I fitted the footrests off the 550F just to get the hero blobs underneath, that way I could feel the footrest lifting my foot up as it started to slide and I knew where the limit was much easier. My mainstand and footrest blobs were all chamfered in the end.

[Johnny4428]

Toe of my boot seems to be my guide when out on the Pan.🤭

[florence]

I like Avon SM and Speedmaster.  The rear tyre looks square but don't be fooled, can be leaned as far as you like.

[Seabeowner]

I've used Avon 100/90 x 19 and 110/90 x 18 on my main 500 for 5 years. Seem about right. Any smaller metric sizes are too small.

[Murf]

Thanks for the replies.
I think I am going to go with the 100/90 x 19 front and 110/90 x 18 rear Bridgestone BT 46 tyres.   
 They seem to be close to original size,  the dealer seem to have them in stock and they are well priced compared to other premium makes at the moment. I was also struggling to get the size I wanted with other makes. 

Thanks OddJob for the tip about increasing rim size and using slightly wider tyres if the rims need changing, my rims seem to be pretty good on the outside so I am hoping there is no nasty surprises when the tyres are removed. 

[Murf]

Well I thought I would check the rim sizes as stamped on the rims before I ordered any tyres, I have to admit that I had not done that yet.  Well the Sizes are Front 1.85 x 19 and surprisingly the Rear is also 1.85 x 18, it is actually stamped 1.85B x 18, not sure what the B means,  I was expecting the rear to be a wider rim. 
It does seem that the early US 550 was fitted with the 1.85 rear rim.

So does this affect my tyre choice and will I still be able to fit a 110/90 tyre as planned. I really don’t want to go much narrower on the rear.
It really is surprising that someone has put a 120 tyre on this diminutive rear rim.😄

[Oddjob]

I ran a 4.25/85 rear tyre on the rear of my 500, paired with a 4.10 front and it was ok until you really pushed hard. Then the tyre wall would start to flex on corners as the rim size just didn’t give enough support.

Most ran 3.60 and 4.10 rears and that seemed to be almost ideal. So around 100 and 110 is the equivalent.

[Seabeowner]

Both my rims are the original 1.85 on my post above.

[Oddjob]

Both my rims are the original 1.85 on my post above.

I tend to agree but the original tyre sizes that Honda fitted were 3.25 front and 3.50 rear, which is approximately 90 and 100. Oddly some people say it rides better due to the smaller contact area but I much prefer a larger contact area and staying on the bike. Ok it’s quicker with the thinner tyres but we don’t go into corners flat out so just twist the throttle a bit more and go round just as fast but safer.

A lot of riders choose 3.60 front and rear btw, personally I liked the rear tyre fatter than the front. Personal choice and style of riding can dictate which suits you better.

[Johnwebley]

I use 3.25 f


And 4.00R equal to a 100/100

I run 28psi f

33psi rear

The bike handles and feels nimble in the twistes

Used Avon

Now have Bridgestone

Sent from my SM-A546E using Tapatalk

[Murf]

Thanks everyone great help as usual, you have put my mind at rest, though I will probably have a better look for a 3.25  and  4.00 pair.

I do have a 62 Triumph T100 which has the Avon  3.25 and 4.00 tyres which were recommended by a knowledgeable local tyre dealer we used to have ( sadly closed down now) and they look about right, on the bike, I will have a look at the rim sizes on it tomorrow, used to know but forgotten.
A pair of Avons in the sizes I want just seem very hard to find now, I am going to the Newark classic bike show in January so will probably wait and see if there are any tyres dealers there.

[Oddjob]

I can't ever remember seeing a TT100 rear in a 4.00 size John, they all seemed to be 4.10. Unless of course I'm not remembering correctly. In those days the choice was either Avon Roadrunners or Dunlop TT100s. The Bridgestones the bike came with were scary, ok in the dry but lethal in the wet. They scared me so much I vowed never to have Bridgestones on a bike ever again and here we are 50 odd years later and I still haven't.