Tyre size comparison question

[VAL. H.]

How does the old school tyre measurement compare with the current/modern sizes.

ie, what is the equivelent to a 400-18? Is it a 120/90? or 90/90?


I'm looking at fitting trail type tyres to my R80 Mono outfit.



Val.

 

[r100gser]

Have a look here…. http://www.bits4motorbikes.co.uk/tiresizeconversion.html

 

[Beemerboff]

Seen a few comparison charts which are markedly different to those!
Depends on brands too, not all brands and the same size, and sizes can vary with two nominally identical tires from the same source.
If possible try details from the manufacturer of the tire you intend using, some even tell you what their targeted width is!

 

[tuftywhite]

4.00 is 4 inches wide x 18" diameter

Your nearest size to that is 101mm. I've tried 110mm rear tyre which worked for my particular case, however, like 'The Boff' says, it depends on the tyre brand and tread pattern as to what they'll fit and clearances and rim width etc. etc.

The old tyre sizes are a lot narrower than the new ones, especially the rear.

90/90 is 90mm wide by 90 mm deep.

 

[scooter paul]

4.00 is 4 inches wide x 18" diameter

Your nearest size to that is 101mm. I've tried 110mm rear tyre which worked for my particular case, however, like 'The Boff' says, it depends on the tyre brand and tread pattern as to what they'll fit and clearances and rim width etc. etc.

The old tyre sizes are a lot narrower than the new ones, especially the rear.

90/90 is 90mm wide by 90 mm deep.

90/90 is 90mm wide but 90% of 90 deep. Not 90mm

My ST has a 120 wide rear and fits with good clearance.

 

[VAL. H.]

Have a look here…. http://www.bits4motorbikes.co.uk/tiresizeconversion.html

Ta, Not quite what I was looking for. But at least I know what size tubes I'll need.

Seen a few comparison charts which are markedly different to those!
Depends on brands too, not all brands and the same size, and sizes can vary with two nominally identical tires from the same source.
If possible try details from the manufacturer of the tire you intend using, some even tell you what their targeted width is!

Cheers Mike, Looks like I'll be asking the suppliers to measure the tyres before I buy them.

4.00 is 4 inches wide x 18" diameter

Your nearest size to that is 101mm. I've tried 110mm rear tyre which worked for my particular case, however, like 'The Boff' says, it depends on the tyre brand and tread pattern as to what they'll fit and clearances and rim width etc. etc.

The old tyre sizes are a lot narrower than the new ones, especially the rear.

90/90 is 90mm wide by 90 mm deep.

Thanks guys, that makes sence. inches and mm's.

90/90 is 90mm wide but 90% of 90 deep. Not 90mm

My ST has a 120 wide rear and fits with good clearance.

Ta.


So, considering I should be able to get a 120/80 in the rear. Does anyone know what tubeless trail tyres are out there?



Val.

 

[tuftywhite]

90/90 is 90mm wide but 90% of 90 deep. Not 90mm

I stand corrected. Thank you Paul.

 

[Beemerboff]

Most tires introduced in the last few years have been tubeless, with the note on the sidewall to use a tube on a tube type rim, so they are not hard to find, in 18" at least! And they can be a pig to fit!
Cuts the dealers stock in half so they might be more likely to have them too!
Tires need at least 6mm carcass thickness to hold a plug, so if you intend using plugs the heavy duty tires offered by Mitas and the latest Dunlops might be the go.
Not hard to measure, the thick ones are around twice the weight!

 

[VAL. H.]

Most tires introduced in the last few years have been tubeless, with the note on the sidewall to use a tube on a tube type rim, so they are not hard to find, in 18" at least! And they can be a pig to fit!
Cuts the dealers stock in half so they might be more likely to have them too!
Tires need at least 6mm carcass thickness to hold a plug, so if you intend using plugs the heavy duty tires offered by Mitas and the latest Dunlops might be the go.
Not hard to measure, the thick ones are around twice the weight!

Didn't know there was a minimum depth for plugs. Fitted quite a few with no probs in bikes or cars. Main reason is they are easier to fit and the R80 wheels being alloys it just makes sence.
I'm still looking at fitting a rear to the front, allowing a spare to fit all three positions, with bosses made up to carry the bearings and the discs. Though I was a bit dissapointed to find the rear wheel nut spacing is different from the brake disc bolt holes.


Val.

 

[Beemerboff]

It is on some manufactures sites, but only those that actually permit plugs. Most nominate max 3 mm hole too, which is bigger than auto style plug kits.
FWIW some higher speed rated hypersports tires don't have 6mm from new and cannot be repaired by any means.
Pop had a 16H Norton and the wheels came as standard interchangeable, then drake drum remained in position and the wheel was held to it by/4 long studs, that is why you see 3/4 holes in Norton hubs. Sidecar also came with the same fitting so the spare wheel was truly universal. He used part worn competition tires, winners don't race on worn tires.
Never has a puncture in the car in 50 years and have done over 200,000 km with Mitas's on the G/S without one either, but best not to temp providence!