Scooterotica

I know I'm old school. I understand 3.50 x 10. It's easy, but I struggle with the new sizing of tyres.

I'm after a couple of 10" tyres for SIP tubeless rims for a SS90 copy I am currently completing. I have found some Contitwist tyres at good price. They are 90/100. I have fitted 90/90 tyres previously as I considered the 90/90 to be the equivalent of the 3.50 x 10 (though I might be wrong)

What is the difference between 90/90 and 90/100 tyres?

Next, I need to understand speed ratings. I think 53J would be suitable for running continuously at 100khp. Correct?

As I understand it 90 is the width of the tyre in mm and the 90 or 100 is the aspect ratio or sidewall height. The 53 is the load rating and J is the speed rating in kilometres per hour which is 100.

Could be completely wrong of course

Thanks Jon. I'm not sure I understand the principle of an aspect ratio, but I am willing to learn.

Perhaps my question should be, how does a 90/100 compare to a 3.00 x 10?

The aspect ratio is the percentage of the tyres width, so 90/100 will be 90mm sidewall height and 100/100 will be 100mm sidewall height.
Glad you chose a 100mm tyre width otherwise I'd have to get my calculator out.

The 100/90 10 would be 100mm wide with a 90mm sidewall height and 10inches inner diameter as opposed to
3.00 10 which is 3inches wide with an inner diameter of 10 inches.

So I think the answer to your question is approx 24mm in width?

Correct the 'j' tyre rating is suitable for up to 100kph,if tyres are inflated to correct pressure and not overloaded.
It is an offence to exceed the speed rating of the tyre(I,m sure you know this)

100/90 is about the same width as a 4.00 but just a bit taller than a 3.50

Knowledge wrote: I have fitted 90/90 tyres previously as I considered the 90/90 to be the equivalent of the 3.50 x 10 (though I might be wrong)

What is the difference between 90/90 and 90/100 tyres?

No Martin, the 90/100 x 10 is almost identical the 3.50 x 10. I've got tyres with both markings on the same tyre.
With metric sizes the first number is the width in mm's. In this case 90mm.
The second number is a percentage of the first number. in this case 100%. So it's 100% of 90mm.
So 90/100 x 10 tyre is 90mm wide with side wall of 90mm.
In the case of the 90/90 x 10 then the second number equates to 90% of 90mm which equals 81mm.
So 90/90 x 10 is 90mm wide and 81mm deep.


With 3.50 x 10 tyres ...The speed rating are generally J = 62mph, L = 75mph, M = 81 mph and P = 93mph. But these figures aren't so Black and White and the weight load ratings need to be applied to them. The weight loads generally range from 51 up to 59. 51 being 195 kg and 59 being 243kg. Grey areas apply and an example is the Dunlop Scootsmart tyre, it comes in two 3.50 x 10 versions, 1 is 59J [243kg & 62mph] and the other is 51P [195kg & 93mph]. My own opinion is that the load rating is more important than the speed rating based on the weight of the average scooterist these days and then throw in a pillion passenger and a ton of rallying gear. A wild guess at say 3,000 scooters on the Isle of Wight would be that 50% of them exceeded the weight load of their tyres and only 5% exceeding the speed rating. I doubt if there's a sliding scale of equivalent weight to speed figures so I'll leave you to draw your own conclusions.
I know that Colin shares my opinion.

In the case of the 3.50 tyre the side ratio is deemed to be 100% of the width, ie, 3.5 inches wide and 3.5 inches deep.

90/90 will have a similar rolling radius as a 3.00 x 10 tyre but the 90/90 has a wider tread. Both more liked to be fitted to a small frame Vespa.

corrado wrote:........................I know that Colin shares my opinion.

Certainly do, stiff side walls as found on the high load rated tyres will give you a better chance of staying on if you get a blow out imho.

Colin